HomeMy WebLinkAbout19970722 Ver 1_Mitigation Plans_20010721 (2)DETAILED WETLAND MITIGATION PLAN;
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RANDLEMAN RESERVOIR WATER SUPPLY
SOPHIA BRANCH MITIGATION SITE
RANDOLPH COUNTY, NORTH CAROLINA
Prepared for:
PIEDMONT TRIAD REGIONAL WATER AUTHORITY
Prepared by:
EcoScience Corporation
1101 Haynes Street, Suite 101
Raleigh, North Carolina 27604
July 2001
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TABLE OF CONTENTS
Page
LIST OF FIGURES .................. ............................. iii
ILIST OF TABLES .. ............ ............................... ... iv
10 INTRODUCTION ...................... .. . ........ ... ....1
1.1 PURPOSE ................ ...... ............... .... 1
1.2 OBJECTIVES OF WETLAND RESTORATION . ............. .... 1
1.3 PRIMARY METHODS FOR WETLAND RESTORATION . ..... . ..... 3
1.4 MITIGATION SITE SELECTION .. ..... ........... ... . 4
1 2.0 METHODS .................. ............... .. ...... .....8
30 EXIST
31
3.2
3.3
3.4
35
3.6
ING CONDITIONS ........ . ...... ...... 12
PHYSIOGRAPHY, TOPOGRAPHY, AND LAND USE ... ..... 12
SOILS.......... .. ......... .... 15
PLANT COMMUNITIES .............. ............ .. .... 18
HYDROLOGY . ....... .... ........ .................22
WATER QUALITY ........... .......... ............. ..24
JURISDICTIONAL WETLANDS .. ...... ....... ....... .... 25
4.0 WETLAND RESTORATION STUDIES ... 28
4.1 RESTORATION ALTERNATIVES ANALYSES .. ..... ....... 28
4.2 SURFACE WATER ANALYSES ............................... 30
4.3 GROUNDWATER MODELING ........... .......... ........ 37
44 REFERENCE GREENTREE IMPOUNDMENTS ................. .... 40
4.5 REFERENCE PLANT COMMUNITIES ... .. ............ ....... 45
5.0 WETLAND RESTORATION PLAN . ....... ... . ...... . ... .51
5.1 IMPOUNDMENT / WEIR CONSTRUCTION ... .... .... ... 52
5.2 STEP -POOL GRADE CONTROL STRUCTURE .... 55
53 WOODY DEBRIS DEPOSITION .. ..... ... ... ... ..... 55
54 WETLAND COMMUNITY RESTORATION ... ....... 55
6.0 MONITORING PLAN .......................... ....... .. .... 63
6.1 HYDROLOGY ............. ...... ........... .. ... ..63
6 2 HYDROLOGY SUCCESS CRITERIA ... .............. .... .. 63
6.3 SOIL ... ... . ....... ... .............. ... ....66
6.4 SOIL SUCCESS CRITERIA .. ..... ....... 66
6.5 VEGETATION .......... . ... ................ 66
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6.6 VEGETATION SUCCESS CRITERIA
67
67 REPORT SUBMITTAL
. .. .. . . . .
. . . . . . 68
70
IMPLEMENTATION SCHEDULE ........... .. ..
.... . ......... 69
8.0
MANAGEMENT PROGRAM
................ . .
.... ...........70
9.0
DISPENSATION OF PROPERTY
........
72
100
WETLAND FUNCTIONAL EVALUATIONS
... 73
10.1 EXISTING CONDITIONS
.... ..
.... .. ... 73
10 2 PROJECTED, POST- RESTORATION CONDITIONS
................. 73
11.0
REFERENCES
................. ..................
....... ...74
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LIST OF FIGURES
Paqe
Figure 1:
Mitigation Site Locations: Randleman Reservoir ..... ... .. ..... 2
Figure 2.
Site Location: Sophia Branch Mitigation Site ..... ...... ........
6
Figure 3:
Aerial Photograph (1999) .... ... ... ... .. .... ..
9 -10
Figure 4•
Physiography, Topography, and Land Use .. .. ... ...
13 -14
Figure 5.
Soil Map Units
16 -17
Figure 6.
Plant Communities .. . .... .........................
19 -20
Figure 7:
Jurisdictional Wetlands ... ...................... ......
26 -27
Figure 8:
Flood Frequency Analysis .................. ... ........
35 -36
Figure 9.
Site Location- Falls Lake Greentree Impoundment ...........
.41
Figure 10.
Site Location- Country Line Creek Greentree Impoundment ... .......
42
Figure 1 1 •
Site Location: Jordan Lake Greentree Impoundments ........ ....
. 43
Figure 12:
Conceptual Impoundment Design ........................ ...
44
Figure 13
Reference Greentree Impoundment ......... ......... ..
.46
Figure 14•
Reference Plan View and Cross Section ..... .... ....
47
Figure 15:
Hydrology Restoration Plan ..................... ......
53 -54
Figure 16:
Conceptual Design: Step -Pool Grade Control ........... . .
. 56
Figure 17.
Planting Plan ........ ...... .. .. ....
61 -62
Figure 18.
Monitoring Plan / Mitigation Design Units .... ....
64 -65
J
0
LIST OF TABLES
Paqe
Table 1: Estimated Area of Mitigation Design Units Based on Preliminary
Studies for 10 Potential Mitigation Sites Associated with the
Randleman Reservoir ............. ..... .............. .. 5
Table 2: Water Surface Elevation Estimates for Various Flood Frequencies ... 32 -33
Table 3: Modeled Groundwater Discharge Zone of Influence
on Wetland Hydroperiods: Congaree Soils . ... .............. .. 39
Table 4: Reference Forest Ecosystem Plot Summary ..................... 48
Table 5• Reference Forest Ecosystem Plot Summary ...................... 49
Table 6. Planting Plan ............. ........ ..... .... ...... 59 -60
IV
DETAILED WETLAND MITIGATION PLAN
RANDLEMAN RESERVOIR WATER SUPPLY
SOPHIA BRANCH MITIGATION SITE
RANDOLPH COUNTY, NORTH CAROLINA
1.0 INTRODUCTION
1.1 PURPOSE
The Piedmont Triad Regional Water Authority (PTRWA) proposes development of the
IRandleman Reservoir in Randolph and Guilford Counties, North Carolina (Figure 1) The
purpose of this project is to develop a safe and dependable water supply source for North
Carolina's Piedmont Triad region that will satisfy the projected water demand for a period of
50 years. The proposed 3000 -acre reservoir will unavoidably impact approximately 121 acres
of wetlands through impoundment and establishment of an open water system. These
jurisdictional wetlands are subject to regulation under Section 404 of the Clean Water Act
(CWA) (33 U S.C. § 1344)
For unavoidable wetland impacts, compensatory mitigation is required to facilitate no net loss
of wetland functions in the region. Compensatory mitigation is typically performed to replace
similar wetland types and wetland functions as those impacted (for example, forested, stream -
side wetlands). Wetland restoration, creation, enhancement, and preservation are typical
methods designed to offset wetland impacts. The North Carolina Division of Water Quality
(DWQ) has instituted a policy that prefers a minimum of 1 acre of wetland be restored or
created for every acre of wetland impacted. Subsequently, remaining wetland functional
replacement needs may be off -set through wetland enhancement and /or preservation.
The purpose of this study is to evaluate wetland restoration /creation potential at Sophia
Branch, a proposed mitigation site located in two parcels. The project boundary encompasses
approximately 35.6 acres. Wetland mitigation is projected to involve approximately 21.7 acres
of created /restored wetlands and open waters and approximately 2.4 acres of
preserved /enhanced wetlands. Other sites will be evaluated in separate documents to address
the 121 -acre mitigation needs of Randleman Reservoir.
1.2 OBJECTIVES OF WETLAND RESTORATION
The primary objectives for wetland restoration include the following:
1) Restore or create 121 acres of wetlands as required under regulatory guidance.
2) Assist in protecting the drinking water supply from pollutants discharged from
the developing upstream watersheds. Excess nutrients, fecal coliform bacteria,
sediments, and chemical contaminants (metals, etc.) represent the primary
water quality concerns for the reservoir.
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3) Maximize benefits to water quality through establishment of functioning
wetlands above the reservoir pool.
4) Replace habitat for wetland- dependent wildlife displaced by establishment of
open water.
5) Maximize the area of wetland restoration or creation achieved at the Sophia
Branch mitigation site
Goals 1 -4 will be accomplished at multiple sites, including Sophia Branch
Water quality benefits are maximized by reducing the capacity for sediment to reach open
water within the reservoir pool Entrenched streams in the region have abandoned adjacent
floodplains and tend to discharge large quantities of sediment into water supply reservoirs
(Simmons 1976). Within reservoir pools downstream of entrenched streams, sediment from
the watershed is deposited directly into the water supply, in a permanently inundated, reducing
'environment Without periodic oxidation processes, pollutants generally dissolve within the
water column and consequently reduce drinking water quality.
Therefore, wetland restoration for water quality should be designed to reduce entrenchment,
erosion, and sediment transport within streams and to entrap sediment within vegetated
wetland surfaces Sediment would be deposited on floodplain surfaces that periodically dry
out in areas outside of the reservoir pool. Wetland vegetation would be established on the
alluvial deposition to stabilize the sediment and provide for pollutant recycling through
oxidation (drying) and reduction (wetting) processes. Wetland vegetation would serve to
provide nutrient uptake and recycling functions within deposited sediment. Using this
rationale, entrenched stream and terrace systems would be converted into alluvial wetland
fans or greentree impoundments. A highly sinuous (E) to braided (D) stream system would be
developed within the alluvial deposition area (Rosgen 1996).
1.3 PRIMARY METHODS FOR WETLAND RESTORATION
Two primary methods for wetland restoration have been proposed to extend the sediment
wedge into design wetlands above the reservoir pool, restore 121 acres of nvenne wetlands,
and provide suitable habitat for wetland dependent wildlife Primary methods include 1) in-
stream structures designed to reduce sediment transport capacity, and 2) greentree
impoundments designed to allow management of water levels and sediment deposition
patterns
In- Stream Structures
In- stream structures are proposed primarily along dredged or entrenched stream corridors on
relatively low -slope valley floors ( <0.009 rise /run) supporting forest vegetation and broad
floodplains (greater than 500 feet in width). Adjacent floodplains have been abandoned by the
incised stream and converted to elevated terraces not regularly exposed to overbank flooding
or wetland hydrodynamics Properly designed in- stream structures are expected to reduce the
3
degree of channel incision, reduce the rate of groundwater discharge from the floodplain into
the channel, increase overbank flooding from the channel onto the floodplain, reduce sediment
transport capacity, and provide greater sediment deposition within vegetated wetlands.
Greentree Impoundments
Greentree impoundments are typically proposed on more steeply sloped, narrow floodplains
and stream terraces ( >0 008 rise /run) or where relatively severe stream channel degradation
and steepening has occurred above the reservoir pool. Greentree impoundments have also
been considered in instances where water levels may need to be controlled for wetland
development in rapidly urbanizing areas. The greentree impoundment option is the preferred
alternative for wetland restoration /creation at Sophia Branch.
In general, a greentree impoundment consists of a floodplain levee and controllable outlet
structure that is modified periodically to promote the development of forested wetlands.
Functioning greentree impoundments above the lake reservoir are expected to provide for
significant nutrient uptake, recycling, and management benefits, including increased habitat
for wetland- dependent wildlife species.
The elevation of the outlet is typically raised during winter months to promote ponding,
sediment deposition, and waterfowl habitat. The elevation of the outlet is lowered in early
spring to allow for vegetation growth, nutrient uptake, and seedling establishment Regular
monitoring and maintenance of the wetland system is considered critical, including periodic
vegetation sampling, periodic replanting, structural repair, and precise hydrologic control on
a semi- annual basis.
1.4 MITIGATION SITE SELECTION
During the environmental impact assessment, project planners identified and evaluated a total
of 25 potential mitigation sites within stream corridors extending above the reservoir pool. A
description of mitigation potential for each of these sites was prepared in previous documents
(ESC 1998a, ESC 1998b, ESC 1999)
Of these 25 sites, 10 sites were determined to support wetland restoration / creation potential
on up to 121 acres of floodplain. Table 1 and Figure 1 depict the location of each site and
projected areas potentially available for wetland restoration use.
This document details restoration and enhancement procedures for riverine wetland restoration
and creation along Sophia Branch, one of the 10 mitigation sites (Figure 2) The stream
referred to in this document as Sophia Branch is an unnamed tributary of the Deep River,
originating near the community of Sophia, North Carolina. The Sophia Branch mitigation site
(Site) consists of two parcels separated by an approximately 3000 foot reach of the branch
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(Glenola /Randleman, N.C.)
Dwn. by:
EcoScience RANDLEMAN RESERVOIR MITIGATION PROJECT Ckd by: MAF FIGURE
PHASE II ES
Corporation SOPHIA SITE Rafe JUL 2001 2
Raleigh, North Carolina Randolph County, North Carolina Project:
01 -075
The upstream section of the Site will herein be referred to as the Upper Sophia Branch site,
and the downstream section will be referred to as the Lower Sophia Branch site The Site
contains approximately 35 acres that encompass the stream and adjacent floodplain. Sophia
Branch drains a watershed of approximately 1.57 square miles (1005 acres). A series of
greentree impoundments is proposed within the stream channel and adjacent floodplain to
reduce the rate of groundwater discharge from the floodplain into the channel, increase
overbank flooding from the channel onto the floodplain, and increase deposition of sediment
on vegetated wetland surfaces above the Randleman Reservoir
This document includes the following. 1) descriptions of existing conditions, 2) surface and
groundwater hydraulic analyses, 3) reference greentree impoundment studies, and 4) reference
soil and forest ecosystem investigations. Detailed plans are provided for wetland
restoration /creation, vegetation planting, site monitoring, and success criteria.
7
20 METHODS
Natural resource information for the Site was obtained from available sources, including U.S
Geological Survey (USGS) topographic mapping (USGS Randleman and Glenola 7.5 minute
quadrangles), U.S. Fish and Wildlife Service (USFWS) National Wetlands Inventory (NWI)
mapping, and Natural Resource Conservation Service (NRCS) soil surveys for Randolph County
(USDA, unpublished) These resources were utilized for base mapping and evaluation of
existing landscape and soil information prior to on -site inspection. Current (1999) aerial
photography was obtained and utilized to map relevant environmental features (Figures 3A and
313)
Characteristic and target natural community patterns were classified according to constructs
outlined in Schafale and Weakley's Classification of the Natural Communities of North Carolina
(1990). North Carolina Natural Heritage Program (NCNHP) databases were evaluated for the
presence of protected species and designated natural areas which may serve as reference
(relatively undisturbed) wetlands for restoration design.
Regional reference (relatively undisturbed) stream and wetland sites were selected to orient
restoration design and to provide baseline information on target (post - restoration) wetland
conditions. A regional vegetation reference database and on -site inventory were used to
characterize target, post- restoration species composition. Topographic maps of the basin floor
were also prepared to determine valley slope characteristics and to establish target (post -
project) water surface elevations within wetland restoration /creation areas. A reference flood
and sedimentation study provided information on sedimentation and wetland development
associated with existing greentree impoundments in the region. Topographic data were
overlaid on wetland restoration areas to establish methods for construction and restoration of
wetland communities within each Site.
Detailed topographic mapping to 1 -foot contour intervals was developed by ground survey
19 paneling and aerial photogrammetnc methods. Additional land surveys were performed to
establish channel cross - sections and measure reference wetland surface topography.
Field investigations were performed in the Spring of 2001 including soil surveys, on -site
resource mapping, land surveys, and landscape ecosystem classifications. Existing plant
communities and jurisdictional wetlands were described and mapped according to landscape
position, structure, composition, and groundwater analyses.
Wetland boundaries were obtained from a delineation performed in 2001 by ECS, Ltd. NRCS
soil map units were ground truthed by licenced soil scientists to verify units and to map
inclusions and taxadjunct areas The revised soils maps were used as additional evidence for
predicting natural community patterns and wetland limits prior to human disturbances
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Groundwater conditions were modeled using DRAINMOD, a computer model for simulating
withdrawal rates for shallow soils with high water tables The model was utilized to predict
historic hydropenods, the extent of wetland degradation due to channel entrenchment, and the
potential for wetland restoration through stream modification.
Surface water analyses for the Site were completed using standard study methods of the U.S.
Army Corps of Engineers (USACE) and NRCS Flood events of a magnitude which are
expected to be equaled or exceeded once on average every 5 -, 10 -, 25 -, 50 -, or 100 -year
period were selected for use. These analyses reflect either existing or proposed conditions at
the Site The projected frequency and extent of overbank flooding were used to determine
potential for rivenne wetland restoration in floodplain portions of the Site. In addition, potential
for impacts to adjacent roads and bridges was evaluated for pre - project and projected, post -
project conditions '
This Site has been selected for wetland restoration use to promote a reduction in sediment,
nutrients, and pollutants flowing into Randleman Reservoir. Mitigation activities are intended
to provide sediment deposition, and pollutant recycling from surface waters within created and
restored wetland areas Recycling functions are designed to reduce elevated nitrogen and
phosphorus loads from the watershed towards background (forest) levels, prior to discharge
into the reservoir
11
3.0 EXISTING CONDITIONS
3 1 PHYSIOGRAPHY, TOPOGRAPHY, AND LAND USE
The Site is located in the Piedmont Physiographic Province of North Carolina. Physiography
is characterized by moderately hilly terrain with interstream divides intermixed with steeper
slopes along well - defined drainage ways. The Site is situated in the Deep River floodplain
within the Cape Fear River Basin (Hydrologic Unit #03030003 [USGS 19741, DWQ Sub -Basin
03- 06 -08). The Site is located approximately 14 miles southeast of High Point and
approximately 17 miles south of Greensboro. Annual precipitation in the region averages 42
inches per year (USDA 1977).
Project boundaries f - -
� t bou da es or each site are derived from the 5 year, post project flood elevations. The
stream terrace (abandoned floodplain) at the Upper Sophia site occupies approximately 23
acres located along both sides of the stream channel, while the stream terrace at the Lower
Sophia site contains approximately 9 acres (Figures 4A and 4B) This terrace historically
supported frequent overbank flooding and was periodically re- worked by alluvial processes and
periodic, long term inundation /saturation. Dredging along the stream has reduced the
frequency of overbank flooding within the primary floodplain from an estimated 1 -year return
interval to a 5- to 10 -year return interval (Section 4.2). Therefore, associated nvenne wetland
functions (sediment retention, nutrient cycling, energy dissipation, etc ) have been effectively
eliminated from the physiographic area by stream alterations. Accelerated drainage is evident
throughout the stream terrace physiographic area due to dredging activities and secondary
stream diversions.
Following dredging operations along Sophia Branch, portions of the stream terrace appear to
have been converted for agricultural or pastoral use. However, these agricultural tracts have
been abandoned over the last several decades, allowing re- development of disturbance
adapted, successional communities Under historic conditions, natural communities are
expected to include Piedmont bottomland hardwood forest and oval to linear pockets of
nvenne swamp forest in low -lying areas (Schafale and Weakley 1990).
Land areas immediately adjacent to the Sophia site contain large agricultural fields and
pastures, woodlots, and sparse residential development (Figures 4A and 413).
Upper Sophia Site: This portion of the Site contains an approximately 1935 -foot reach of
Sophia Branch, as well as a tributary reach approximately 1875 feet in length (Figure 4A).
Dredging and straightening of the main channel is apparent The elevated stream terrace
(abandoned floodplain) as well as the second, much older, terrace formation farther away from
the stream is easily observed at this open, grassy site. This section of Sophia Branch supports
a primary watershed of approximately 0.65 square miles. After construction of the Randleman
Reservoir, the downstream terminus of the Upper Sophia site will reside approximately 5100
feet upstream
12
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of the Reservoir's conservation pool. On -site elevations range from71 1 feet to 745 feet above
mean sea level. The Reservoir's conservation pool will average 682 feet.
The Upper Sophia site consists of pasturelands in active use along the main channel of Sophia
Branch, and mixed hardwood forest corridors in large patches along the tributary reach. A
farm pond is situated approximately 8 -10 feet above the floodplain. Outfall from the pond
flows into Sophia Branch at the downstream end of the Site. Other buildings in the vicinity
include a residence on SR 1941 (Wall Brothers Road), situated 15 -20 feet above the floodplain
SR 1941 crosses Sophia Branch Just downstream of the Upper Sophia site. Streamflow is
maintained by a 6 foot metal culvert. The SR 1941 roadbed lies at 718 feet, 2 -3 feet above
Ithe adjacent floodplain.
Lower Sophia Branch- The lower portion of the Site contains an approximately 1590 -foot
reach of Sophia Branch (Figure 4B) This reach maintains a relatively natural meander pattern
and riffle and pool sequence The lower section of Sophia Branch supports a primary
watershed of approximately 1.57 square miles and flows into the Deep River 1.1 miles
downstream. After construction of the Randleman Reservoir, the downstream portion of the
Site will reside immediately adjacent to the reservoir's conservation pool, at 682 feet above
mean sea level. On -site floodplain elevations range from 680 feet to approximately 700 feet.
The Lower Sophia site consists of large patches of mesic hardwoods along the stream terrace,
as well as smaller patches of shrub habitat. Evidence of recreational use is seen in off -road
vehicle trails parallel to the stream channel. An existing pond is located downstream of the
Lower Sophia site. This pond will be inundated with the filling of Randleman Reservoir. A
residence with outbuildings is situated on a rise above the floodplain near SR 1990
(Commonwealth Drive) Sophia Branch flows through two 8 foot culverts as it passes under
SR 1990 into the Lower Sophia site.
3.2 SOILS
Surficial soils have been mapped by NRCS (USDA, unpublished). Soils were verified in the
spring of 2001 by licensed soil scientists to refine soil map units and locate inclusions and
taxadjunct areas Systematic transects were established and sampled to ensure proper
1 coverage. Refined soil mapping is depicted in Figure 5A and 5B. Primary soil types include
the Chewacla series, Wehadkee series, and Georgeville series.
Chewacla soils are somewhat poorly drained, nonhydnc soils which have been formed on
floodplains primarily by fluvial activity. Chewacla soils generally exhibit broad, inter- layered
variability in texture and permeability dependent upon energy dissipation and sediment
Jdeposition patterns associated with each stream overbank flood event. Soil texture generally
ranges from coarse sandy loam to silt loam of moderate to moderately rapid infiltration.
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Important factors in the formation and maintenance of wetland systems as hydnc inclusions
in the Chewacla map units include 1) microtopography and variability in fluvial deposition
across the landscape, 2) groundwater and surface water movement from adjacent uplands
along the outer edge of the floodplain, and 3) groundwater discharge rates from the interior
floodplain into the stream channel. These soils are subject to frequent flooding. The seasonal
high water table is within 0.5 to 1 5 feet. Stream dredging, straightening, and conversion to
agricultural lands has likely increased the extent of Chewacla (nonhydric) soils and
concurrently decreased the extent of Wehadkee (hydric) map units in the Site
Hydric soils are defined as "soils that are saturated, flooded, or ponded long enough during the
growing season to develop anaerobic conditions in the upper soil layer" (USDA 1987) Hydnc
soils comprise the Wehadkee series (F/uvaquentic Endoaquepts), located primarily within relict
backwater sloughs, depressions, ephemeral channels, and swales which remain within the
secondary floodplain. These soils are very deep and poorly to very poorly drained.
Georgeville silty clay loamy (Typic Kanhap /udu /ts) are strongly sloping, very deep, well drained,
eroded soils on uplands They formed in residuum from Carolina slates and other fine grained
rocks They have a loamy surface layer and a clayey subsoil. Permeability is moderate and
shrink -swill potential is low Seasonal high water table is below 6.0 feet.
Upper Sophia Site. Chewacla (F/uvaquentic Dystrochrepts) loam encompasses 22.5 acres of
the 23.7 -acre site. Under existing conditions, the Wehadkee series comprises approximately
0.1 acres of the site. Georgeville soils comprise approximately 1.1 acres on drier, steep
slopes. The very small percentage of Wehadkee series on stream terraces is likely due to
conversion of the former floodplain into a stream terrace through dredging and incision of the
stream channel.
Lower Sophia Site. At the lower site, hydnc soils comprise a greater percentage of the land
1 area. The downstream site is located at lower elevations and contains a less disturbed stream
channel. Chewacla soils comprise approximately 9.3 acres of the 11.9 acre site, while
Wehadkee soils encompass approximately 2.3 acres. No Georgeville soils are included at this
site.
H 3.3 PLANT COMMUNITIES
Plant communities are influenced by logging, grazing, and past conversion to agricultural lands.
Four primary communities have been identified for descriptive purposes: 1) basic mesic forest,
2) shrub /scrub assemblage, 3) dry oak - hickory forest, and 4) pasture / open field (Figures 6A
and 6B).
Basic Mesic Forest
The basic mesic forest assemblage has experienced some degradation from past logging and
high - grading, and exists in a somewhat disturbed second - growth state Forested areas are
fragmented, and consequently are composed of a substantial percentage of edge habitat.
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Invasive and opportunistic species are common at forest edges and in gaps farther inside forest
boundaries At the Sophia Branch Site, the basic mesic forest canopy includes sweet gum
(Liquidambar styraciflua), red maple (Acer rubrum), sycamore (Platanus occidentalis),loblolly
pine (Pinus taeda), Virginia pine (P. virginiana), white ash (Fraxrnus americana), hackberry
(Celtis laevigata), eastern red cedar (Juniperus virginiana), and black cherry (Prunus serotina).
Subcanopy and shrub layer species distribution is variable along hydrologic gradients and
sunlight regimes, and includes ironwood (Carpinus carohniana), elderberry (Sambucus
canadensis), flowering dogwood (Corpus flonda), black willow (Salix nigra), winged elm (Ulmus
alata), blackberry (Rubus sp.), multiflora rose (Rosa multiflora), and Chinese privet (Ligustrum
sinense) Vines include muscadine grape (Vitis rotundifoba) and Japanese honeysuckle
(Loniceralaponica), which becomes invasive in sunnier areas. The herb layer includes common
blue violet (Viola papilionacea), henbit (Lamium amplexicaule), chickweed (Stellana media),
dock (Rumex sp.), Indian strawberry (Duchesnea indica), ebony spleenwort (Asplenium
platyneuron), and jewelweed (Impatiens capensis)
Upper Sophia site: This plant community occurs along the tributary stream of Sophia Branch,
comprising approximately 9.5 acres It grades into dry oak - hickory forest at higher elevations.
Lower Sophia site: Basic mesic forest comprises the majority of area at this site, occupying
approximately 9.8 of the 1 1.9 acres.
Shrub /Scrub Assemblage
This community type is diagnostic of disturbed habitats. Recently - cleared and maintained open
areas support limited growth of persistent woody species, including Chinese privet, black
willow, blackberry, multiflora rose, eastern red cedar, and white ash saplings or young trees.
The herb layer is typically composed of species from adjoining community types
Upper Sophia site: Shrub /scrub assemblage occurs along the banks of Sophia Branch within
open pasturelands It forms a narrow buffer along the stream, and is a minor component of
the site (approximately 1.4 acres).
Lower Sophia site: A maintained open area near SR 1990 supports approximately 0.9 acres
of shrub /scrub assemblage. This area was possibly a former pasture Young white ash trees
are rapidly overtaking the grassy areas.
Dry Oak - Hickory Forest
Dry oak - hickory forest occupies drier ridges at the Upper Sophia site (approximately 1.1 acres).
It shares some canopy species with basic mesic forest, such as eastern red cedar and
sweetgum, but also contains a large component of more xeric species such as southern red
oak (Quercus falcata), white oak (Q. alba), post oak (Q. stellata), and white hickory (Carya
alba). Shrub layer species include flowering dogwood, winged elm, and black cherry. The
21
I herb layer is sparse At forest edges, Ptendium a u/lln m I
y p ( q u ), goldenrods (So %dago
Ispp ), and vetch (Vicaa sp.) occur, along with species characteristic of fields and pastures
Pasture / Open Field
This community designation is composed of active pastureland and agricultural fields. Pasture
land is dominated by a variety of grasses and herbs The predominant species is fescue
(Festuca spp.). Agricultural fields lack a continuous grassy cover, but support many of the
volunteer species found in open pastures Characteristic volunteer species occurring in fields
and pastures include asters (Aster spp.), goldenrods, dock, buttercup (Ranunculus sp.), wild
radish (Raphanus raphanistrum), wild onion (A//ium canadense), cocklebur (Xanthium
strumanum), clovers (Trifohum spp.), and crabgrass (Digitaria spp )
Upper Sophia site: Pastureland comprises the majority of this site, occupying approximately
11 7 acres. The entire main stem of Sophia Branch and the lower tributary stream are
surrounded by pasture.
Lower Sophia site: The open community type at the Lower Sophia site is confined to
approximately 0.9 acre of an agricultural field at the downstream end of the site.
3.4 HYDROLOGY
The Site is located within the Piedmont hydrophysiographic province, which encompasses the
entire drainage basin for the East and West Forks of the Deep River. The region is
characterized by moderately hilly terrain with interstream divides exhibiting dendntic drainage
patterns and moderately steep slopes along valley floors (0.005 -0.015 rise /run).
The region is characterized by moderate rainfall. In Randolph County, precipitation averages
42 inches per year with precipitation evenly distributed throughout the year (USDA 1977).
Large floods (20 -100 year return interval) typically correspond to large thunderstorms and
tropical events in the region.
Bed -load material supplied by the region consists primarily of silts, sands, and weathered
bedrock (very coarse sand and small gravel). Bedrock outcrops are common within incised
streams in more steeply sloped valleys. Suspended load consists primarily of easily eroded
clays and silts, which transport attached nutrients into downstream waters. Sediment forms
a thick layer over coarser materials in heavily disturbed sites. Erosion and suspended sediment
loads have been linked to nutnfication problems within the Piedmont hydrophysiographic
province, including the Randleman Reservoir region (DWQ 2000).
Surface Water
Upper Sophia Site: The Site encompasses a 1950 -foot reach of Sophia Branch and a 210 -foot
tributary supporting a drainage area of 0 65 square miles. The valley slope measures
22
approximately 0 007 to 0 008 rise /run, suggesting the presence of a slightly flat valley floor
relative to typical conditions in the Piedmont Province. The floodplain ranges from 100 feet
to 400 feet in width along the length of the Site
Incision and straightening of the stream channel is apparent along the main stem of Sophia
Branch. This reach is also heavily impacted by livestock. The average existing bankfull depth
of the channel is 3.4 feet, compared with 1.1 feet calculated form the regional curves based
on drainage area. In addition, the average existing cross - sectional area of the Sophia Branch
channel measures approximately 53.2 square feet. According to regional curves, a stable
Sophia Branch channel is projected to support cross - sections of approximately 1 1.8 square
feet (assumes rural conditions) (Harman et a/. 1999, Rosgen 1996). The incised and
straightened main channel supports a sinuosity (channel length /valley length) of 1 0, while the
tributary stream has a sinuosity of 1.17. Substrate within the main channel is composed of
a thick layer of silt and mud atop unconsolidated sand, small gravel, and bedrock, while the
tributary exhibits a bed of sand, gravel, and rock outcrops exposed by incision and localized
bank erosion. The main channel is classified as E6 (silt /clay dominated channel), while the
tributary is classified as E4 (sand dominated channel) based on fluvial geomorphic features
(Rosgen 1996).
Lower Sophia Site: The Lower Sophia site contains a 1650 -foot reach of Sophia Branch
supporting a drainage area of 1 46 square miles The valley slope measures approximately
0 011 rise /run, suggesting the presence of a valley floor typical for conditions in the Piedmont
Province. The floodplain ranges from 100 feet to 350 feet in width along the length of the
Site
This section of Sophia Branch exhibits a relatively undisturbed meander, although the channel
is somewhat incised The average existing bankfull depth of the channel is 4 8 feet, compared
with 1.5 feet calculated form the regional curves based on drainage area In addition, the
average existing cross - sectional area of the Sophia Branch channel measures approximately
31.7 square feet According to regional curves, a stable Sophia Branch channel is projected
to support cross - sections of approximately 22.7 square feet (assumes rural conditions)
(Harman et a/. 1999, Rosgen 1996). The channel supports a sinuosity (channel length /valley
length) of 1.05. Substrate within the main channel is composed of sand, gravel, and rock
outcrops exposed by incision. The channel is classified as E4 (gravel dominated channel),
based on fluvial geomorphic features (Rosgen 1996).
Stream discharge and flood elevations under existing conditions have been predicted based on
hydraulic models. Section 4 2 provides model predictions for the 5- and 100 -year storm under
current conditions. The study suggests that overbank flooding occurs on an interval as short
as five years. However, entrenchment has likely confined the 1- to 2 -year flows within the
eroding channel banks, effectively bypassing floodplain functions associated with pollutant
23
1
1
removal and maintenance of wildlife habitat for overbank flood dependent species No
evidence of overbank flooding has been noted during field studies.
Surface water runoff within the stream terrace would be relatively sluggish in wooded areas.
Surface detention and ponding on the rough soil surface, and interception by dense forest
vegetation, would occur in this area immediately after significant rainfall events with delayed
return flow into the main -stem channel. Cross - valley and down - valley flow would be more
rapid from steep side slopes planted in pasture grasses or crops.
The hydraulic models suggest that structures and roadways remain unaffected by floodwaters
during the 100 -year storm under current conditions. No evidence of flooding was noted during
field studies.
1 Groundwater
Surface water hydrodynamics, such as periodic overbank floods, fluvial sediment deposition,
and hydraulic energy dissipation, represent important attributes of floodplains and bottomland
hardwood forest in the region However, streams in the region typically function as
groundwater withdrawal features throughout most of the year Therefore, groundwater inputs
from auxiliary watersheds and upland slopes abutting the floodplain represent the primary
hydrologic input resulting in the development and maintenance of riverine wetlands at this Site.
Groundwater gradients in May 2000, and after rainfall events in August 2000, indicate that
the groundwater table typically resides from 1 foot to 6 feet below the land surface. The
groundwater gradient typically remained more than 2 feet below the surface throughout the
stream terrace with a relatively steep gradient induced by the dredged stream channel.
Based on observed groundwater gradients, the Site is expected to support limited groundwater
storage potential typically associated with maintenance of wetland surfaces. Although
adjacent escarpments supply riparian inflow of groundwater, this flow appears steeply inclined
with relatively rapid discharge towards the stream channel. Entrenchment of Sophia Branch
has accelerated groundwater discharge to depths of 4 -5 feet below the surface near the
stream channel Restoration of a shallower (less incised) stream network will generate a flatter
groundwater gradient. However, groundwater models (Section 4.3) suggest that groundwater
tables will continue to remain more than 1 foot below the surface. Therefore, restoration of
wetlands within this Site may require establishment of backwater (surface water induced)
wetlands behind a greentree impoundment.
3.5 WATER QUALITY
Sophia Branch, from its source the Deep River, maintains a State best usage classification of
WS -IV CA* (Stream Index No. 17- 9.6 -(1) (DWQ 2000). Class WS -IV waters are protected as
water supplies which are in moderately to highly developed watersheds. Point source
discharges are generally required to meet stringent pre- treatment standards, to maintain pre-
treatment failure (spill prevention) plans, and to perform point source monitoring for toxic
24
substances. Local programs to control nonpoint source and stormwater discharge of pollution
are also required. The designation "CA" denotes a Critical Area The symbol * signifies
waters that are within a designated Critical Supply watershed and are subject to a special
management strategy specified in 15A NCAC 2B .0248. In this case, the watershed areas is
within 0 5 mile of a water supply intake for the reservoir
Upper Sophia site: The Upper Sophia site consists primarily of active pastureland and second -
growth forest adjacent to the tributary stream channel. Fertilizers, pesticides, and nutrients
associated with land uses may influence water quality in the vicinity. Restoration of wetland
hydrology and diversion of area runoff onto restored wetland surfaces will provide local water
quality benefits, including important functions such as particulate retention, removal of
elements and compounds, and nutrient cycling.
Historically, the floodplain provided water quality benefits to the entire watershed associated
with Sophia Branch. However, runoff from cleared land area effectively bypasses wetland
floodplains and flows directly to the channel and through the Site. Restoration of wetland
hydrology and diversion of watersheds onto restored wetland surfaces will provide for
restoration of overbank flooding and associated water quality benefits above the Randleman
Reservoir.
Lower Sophia site: The Lower Sophia site is largely wooded, and maintains a functional
forested buffer within the project boundary. However, agricultural lands on upper slopes and
upstream may be supplying Sophia Branch with additional nutrients and sediments. Wetland
hydrology on a restored floodplain will provide enhanced nutrient and sediment removal, and
additional water treatment opportunities for waters entering Randleman Reservoir.
3.6 JURISDICTIONAL WETLANDS
Jurisdictional areas are defined using the criteria set forth in the U.S. Army Corps of Engineers
Wetlands Delineation Manual (DOA 1987). Approximately 0.1 acre of Jurisdictional wetlands
were delineated on -site at the Upper Sophia site The Lower Sophia site contains 2.3 acres
of Jurisdictional wetlands and 0 3 acre of open waters Jurisdictional areas were delineated
on June 18, 2001 and confirmed by the USACE. Figures 7A and 713 depict the boundary
locations of existing Jurisdictional areas. Wetland extent was most likely more extensive prior
to Site stream dredging.
25
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4.0 WETLAND RESTORATION STUDIES
This section summarizes studies performed to orient restoration design. Studies include the
following
1) Restoration Alternatives Analyses- Alternatives for wetland restoration relative
to stream, floodplain, and reservoir functions were assessed
2) Surface Water Analyses: Overbank flooding frequency and extent was evaluated
for wetland restoration alternatives to assess potential for impacts to adjacent
roads and structures.
3) Groundwater Modeling: The effect of drainage features on groundwater wetland
hydropenods was modeled.
4) Reference Plant Communities: Reference wetland communities were sampled
to predict the target distribution of vegetation to be established in restoration
areas.
5) Reference Physiography and Surface Topography: Reference wetland surfaces
were measured within an existing greentree impoundment to characterize long
term, projected Site conditions.
4.1 RESTORATION ALTERNATIVES ANALYSES
The objectives of this project include the following.
1) Assist in protecting the drinking water supply from pollutants discharged from
the developing watersheds. Pollutants attached to sediment represent the
primary water quality concern for this project.
2) Maximize benefits to water quality through establishment of functioning
wetlands above the reservoir pool.
3) Replace habitat for wetland- dependent wildlife displaced by establishment of
open water.
4) Maximize the area of wetland restoration achieved by the project.
Restoration alternatives suggested by project participants are briefly described below.
Stable Channel Construction
Reconstruction of a potentially stable stream system was assessed as a replacement for the
existing dredged and incised channel. The new channel would be designed to mimic
referenced, stable attributes including the geomorphic dimension, pattern, and profile needed
to transport water and sediment produced by the watershed. The restored channel would
reduce the rate of groundwater withdrawal from adjacent floodplains, potentially resulting in
wetland hydrology restoration in certain areas.
28
Stream restoration through natural channel design represents a viable option for portions of
this Site. In particular, the dredged and straightened pastureland section of the branch in the
Upper Sophia site would be appropriate for stream restoration. If applied, approximately 2200
linear feet of channel could be relocated into a sinuous channel that reduces bank erosion and
increases in- stream aquatic habitat. Based on groundwater models, this option is expected to
provide for less than 1 acre of wetland restoration on the relatively narrow floodplain floor.
Because the wetland restoration area is inadequate, the stable channel construction option was
discarded.
Alluvial Wetland Fan Development
This option is designed to elevate water tables and reduce sediment transport within the
floodplain and stream corridor Alluvial fan development entails placement of fixed, in- stream
weirs within the dredged channel. The in- stream modifications are expected to reduce the
degree of channel incision, increase overbank flooding, reduce stream sediment transport
capacity, and provide greater sediment deposition within vegetated wetlands. The system
would progress toward an alluvial wetland fan where the channel actively migrates across
fluvial material. During the interim period, in- stream structures will sustain significant energy
during flood events; therefore, the potential exists for development of channel by- passes
(shoot cut -offs) around the structures. As such, risk of wetland restoration failure exists. The
structures must be designed to avoid short- circuiting and provide for sediment deposition in
the incised channel.
Over a relatively long period of time, the shallower channel would inevitably abandon the
structures and begin to actively migrate across the restored floodplain. At this point, the
system would need to be monitored for evidence of head - cutting from the downstream reach.
A step -pool channel would need to be established due to the significant change in elevation
immediately above and below the alluvial wetland fan. Because the potential for future head-
_ cutting is considered significant, this option was discarded for the Upper Sophia site. Sites
located immediately above the Randleman Reservoir conservation pool elevation (682 feet
above mean sea level) will not be threatened by future head -cuts because the conservation
pool is expected to serve as a grade control structure. However, this site is located 0.9 miles
upstream of the conservation pool.
Alluvial wetland fan development was also considered as an option for the Lower Sophia site
Narrowness of the stream floodplain at this reach reduces the wetland area achievable by
alluvial fan development. Shoot cut -offs have the capacity to erode the surrounding terrace
slopes, causing sloughing of soil and introducing a large component of new sediment into the
Randleman Reservoir water supply. Due to the restricted nature of the floodplain in this reach,
alluvial wetland fan development was discarded as a wetland development option.
29
Greentree Impoundments
This alternative is similar to alluvial fan development described above. However, greentree
impoundments include a floodplain levee and controllable outlet structure that is modified
periodically throughout the year to induce backwater flooding and promote the development
of forested, shrub - scrub, and emergent wetlands. Greentree impoundments have been
constructed above other water supply reservoirs in the region for wetland, wildlife, and
sediment retention functions These structures can be controlled to regulate the depth and
frequency of inundation based upon objectives of the system In this case, the structures
would be used to establish vegetated wetlands and limit transport of pollutants into the
reservoir.
In general, the levee system is constructed to provide for less than 2 to 3 feet of inundation
during winter months, to prevent over - topping, and to allow for survival of tree seedlings. The
winter depth is generally dependent upon the height of seedlings. The raising and lowering of
outlet structures requires regular monitoring and maintenance by qualified personnel to
facilitate the growth of tree species. The actual date that the outlet is modified may vary
annually and is dependent upon localized conditions within the watershed Seedling mortality
is tracked on an annual basis and the date of spring lowering is modified to maximize the rate
of forest regeneration. Tree species selected for planting may also be modified based upon
collected data. Greentree impoundments designed for forested wetland restoration have failed
in the past, due primarily to lack of resources for long -term monitoring, management, and
manipulation
Based on alternatives analyses, construction of a greentree impoundment across the Sophia
Branch floodplain represents the preferred option for this Site. The capacity to manage,
regulate flows, and regulate sediment transport/deposition rates at the Site outfalls will reduce
potential for head -cut migration into an alluvial wetland fan as described above In addition,
the structures would allow pro - active control of wetland development and function behind
each impoundment.
4.2 SURFACE WATER ANALYSES
Surface drainage on the Site and surrounding area was analyzed to predict the effects of
diverting existing surface drainage into wetland restoration areas along the primary and
secondary floodplains Several alternatives were evaluated to determine surface water
modifications that minimize potential for impacts to adjacent properties and maximize wetland
area.
Hydrologic and hydraulic analyses were completed using standard study methods of USACE
and NRCS Flood events of a magnitude which are expected to be equaled or exceeded once
on average every 5 -, 10 -, 25 -, 50 -, or 100 -year period were selected to characterize existing
and proposed conditions at the Site
30
Hydrologic Analyses
Hydrologic analyses were carried out using the USACE HEC -1 model to establish the peak
stream discharge for the 5 -, 10 -, 25 -, 50 -, or 100 -year flood events at the Site.
Input forthe HEC -1 model consisted of synthetic storm precipitation data, drainage area, NRCS
curve numbers, and drainage basin lag time. Tables 2A and 2B list the total, 24 -hour
precipitation event for each storm that was analyzed Precipitation data was obtained from
U S National Weather Service documents (NOAA TP -40 and Hydro -35). The drainage area
was delineated on 7.5- minute USGS topographic maps and then subdivided into sub - basins
based on land use or location of tributaries. The drainage area for each sub -basin was
estimated using a planimeter. The NRCS curve numbers were estimated using methods
described in NRCS TR -55. Sub -basin lag times were estimated using Snyder's method.
qBecause there were no on -site gage data, the HEC -1 computer models could not be calibrated.
The models were validated by comparing the 100 -year peak discharges estimated from the
HEC -1 models with peak discharges estimated by regional formulas for the Piedmont region
of North Carolina in the USGS Water- Resources Investigations Report 87 -4096. NRCS curve
numbers for the HEC -1 models were adjusted until the HEC -1 peak discharges were within 25
30 percent of the regional formula values. Tables 2A and 2B summarize peak discharges
estimated by the validated HEC -1 model and the regional equations.
Hydraulic Analyses
Water- surface elevations of the 5 -, 10 -, 25 -, 50 -, or 100 -year floods of Sophia Branch were
estimated using the USACE HEC -2 computer program. Channel cross sections for the hydraulic
analyses were obtained from digital orthophoto maps prepared by Geodata Corporation with
a contour interval of 1 foot. Photography was taken on April 8, 1999.
Roughness coefficients (Manning's "n ") in the channels and on the overbank areas were
obtained from FEMA studies previously conducted in the area Roughness data were verified
with field inspections of the sites. Roughness coefficients were 0.06 in the main channel and
0 12 for overbank areas
Starting water surface elevations and energy slope for existing conditions were estimated
using data from the HEC -1 analysis and digital orthophoto maps. A water surface elevation
computed by the HEC -1 model was used to estimate the true value of the water surface
elevation at the beginning cross - section for Sophia Branch. This initial water surface elevation
corresponds to the water level in the existing ponds on these sites during the specified flood
events. It was assumed that the existing ponds shall remain in place.
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Model Results: Existing Conditions
Tables 2A and 2B summarize the water surface elevations for existing and proposed
conditions Figures 8A and 8B depict modeled flood elevations for the 5 -, and 100 -year, 24-
hour storm event for existing conditions, and for the 5 -year event under post - project
conditions. The model suggests that overbank flood events occur during the 5 -year storm at
both sites. However, frequent inundations (1 -year return interval) have likely been effectively
eliminated along the entrenched channel under existing conditions. Evidence of overbank
flooding has not been observed at the Site from May 1998 through June 2001 (3 years).
The hydraulic model suggests little danger of flooding along either SR 1941 downstream of
the Upper Sophia site, or at SR 1990 upstream of the Lower Sophia site (Figures 8A and 813).
Local sources have indicated that SR 1941 was last inundated over ten years ago. Table 2A
L indicates that the 100 -year water surface near this road resides at 715.8 feet above mean sea
level, while the roadbed lies at approximately 718 feet.
At the Lower Sophia site, the 100 -year storm under present conditions is projected to reach
693 feet above sea level, while the adjacent surface of SR 1990 lies at approximately 711 feet
(Table 26).
Model Results: Proiected Post Restoration Conditions
Several restoration alternatives were evaluated to determine the change in flood elevations for
various storm events and the associated impacts on surrounding structures. Alternatives
included in- stream weirs located at systematic intervals within the entrenched channel. Ten
structural arrangements were investigated, including cross -vane weirs spaced at up to 150 -
foot intervals within the channel. The structural arrangement was also modified to establish
a pool to pool spacing characteristic of natural channel design.
The selected alternative minimizes potential for impact and maximizes wetland
restoration /creation area associated with the design. In summary, a series of nine greentree
impoundments is proposed for the Upper Sophia site beginning approximately 300 feet
upstream from SR 1941 The impoundment weirs will be designed to allow unrestricted
channel flows during periods of increased probability for large (tropical) storms. The weirs
were modeled with a top elevation of 714 feet at the downstream end to 729 feet at the
upstream end of the main channel. For the Lower Sophia site, a series of two greentree
impoundments is proposed The uppermost weir would be placed approximately 900 feet
downstream of SR 1990, at an elevation of 686 feet
The model suggests that floodwaters arising from the 100 -year storm will continue to avoid
roadways and structures. With levee construction, the 100 -year storm level adjacent to SR
1941 at the Upper Sophia site is expected to increase less than 0.2 feet (Table 2A) Post -
construction flood levels for the 100 -year storm adjacent to SR 1990 (Lower Sophia site) are
34
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expected to increase by approximately 0.5 feet (Table 2B). Residences and other structures
at both the Upper Sophia and Lower Sophia sites area expected to remain well above
floodwaters for the 100 -year storm
Restoration methods are designed to reduce the channel from 4 -5 feet in ,depth below the
floodplain to saturated / inundated conditions at the floodplain sureface during the winter and
early portions of the growing season. The weirs and associated water levels would be lowered
during the remaining portions of the year. The model assumes that the weirs will remain in
place during a 50- to 100 -year storm during the winter (flooded) season. Ideally, weirs would
be lowered prior to such storms to avoid damage to impoundment structures.
r4.3 GROUNDWATER MODELING
Groundwater modeling was performed to characterize water table elevations under historic
(reference), existing, and post - restoration conditions. The groundwater modeling software
selected for simulating shallow subsurface conditions and groundwater behavior at the Site
is DRAINMOD. This model was developed by R.W. Skaggs, Ph.D., P.E., of North Carolina
State University (NCSU) to simulate the performance of water table management systems.
Model Description
DRAINMOD was originally developed to simulate the performance of agricultural drainage
networks on sites with shallow water table conditions. DRAINMOD predicts water balances
in the soil -water regime at the midpoint between two drains of equal elevation. The model is
capable of calculating hourly values for water table depth, surface runoff, subsurface drainage,
infiltration, and actual evapotranspiration over long periods referenced to climatological data.
The reliability of DRAINMOD has been tested for a wide range of soil, crop, and climatological
conditions. Results of tests in North Carolina (Skaggs, 1982), Ohio (Skaggs et a/ 1981),
Louisiana (Gayle et a/. 1985, Fouss et a/. 1987), Florida (Rogers 1985), Michigan (Belcher and
Merva 1987), and Belgium (Susanto et a/. 1987) indicate that the model can be used to
reliably predict water table elevations and drain flow rates DRAINMOD has also been used
to evaluate wetland hydrology by Skaggs et a/. (1993). Methods for evaluating water balance
equations and equation variables are discussed in detail in Skaggs et a/. (1993)
DRAINMOD has been modified for application to wetland studies by adding a counter that
accumulates the number of events wherein the water table rises above a specified depth and
remains above that threshold depth for a given duration during the growing season. Wetland
hydrology is defined as groundwater within 12 inches of the surface for 28 consecutive days
(12 5 percent of the growing season), and 11 consecutive days (5 percent of the growing
season) Wetland hydrology is achieved in the model if target hydropenods are met for more
than one -half of the number of years modeled (i.e., 16 out of 31). Groundwater drainage
contours are established on available mapping for various durations of saturation within 1 foot
of the soil surface (i e. saturation contour for 0 -5 percent, 5 -12.5 percent, and 12.5 -20
percent of the growing season).
37
Model inputs for DRAINMOD simulations were obtained as follows: the United States
Department of Agriculture (USDA) soil texture classification, number of days in the growing
season (defined as March 26 - November 6), and hydraulic conductivity data were obtained
from the NRCS soil survey for Randolph County and Guilford County (USDA unpublished,
USDA 1977). Inputs for soil parameters such as the water table depth /volume, drained /upflux
relationship, Green -Ampt parameters, and water content /matric suction relationship were
obtained utilizing the MUUF computer software developed by NRCS Precipitation and
temperature files were obtained for the years 1930 through 1980 for Charlotte, North Carolina.
DRAINMOD simulations were designed to predict the transition zone from Chewacla soils to
Wehadkee soils based on groundwater drainage conditions within a relatively flat floodplain
surface Chewacla soils represent a non -hydnc (non - wetland), somewhat poorly drained soil
that is common on primary floodplains immediately adjacent to streams. The Wehadkee series
comprises hydnc (typically wetland), poorly drained soils that are typical in backwater
floodplain areas situated further from drainageways
Forested conditions (evapotranspiration rates) and published hydraulic conductivity values were
assumed for Chewacla soils. The simulations were run for six channel inverts (0, 1, 2, 4, 6,
and 8 feet) and at various target hydroperiods during the growing season. Table 3 provides
a depiction of the groundwater discharge zone of influence by invert depth (elevation below
floodplain). For example, a stream channel invert 6 feet below the floodplain elevation is
modeled as reducing surface hydroperiods below 5 percent of the growing season at a
distance of 215 feet from the channel. A former floodplain surface 6 feet in elevation above
the channel invert and greater than 215 feet from the channel is projected to support
wetlands.
The preliminary groundwater drainage model was interpreted based upon field verification of
NRCS soil map units, channel depth (based on measured cross - sections), and floodplain
elevation (based on topographic maps). Model parameters were set to predict the average
annual duration in which groundwater remains within 1 foot of the soil surface at assigned
elevations above a channel invert or in- stream structure. The floodplain elevations outside of
the groundwater drainage contour and at the modeled channel depth were fudged to have a
hydropenod greater than 5 percent.
Post - Restoration Model Applications and Results
For groundwater wetland restoration, the primary objectives of this project include 1) a
reduction of channel incision along Sophia Branch and associated tributaries, 2) elevation of
the groundwater gradient into the rooting zone for developing vegetation, and 3) establishment
of minimum wetland hydroperiods encompassing 5 percent of the growing season, which are
typical for rivenne wetlands in the Piedmont hydrophysiographic province. Therefore, the
effective post - project depths of the Sophia Branch channel will be reduced from an average
of 4 -5 feet under existing conditions to gradients between 1 to 3 feet below the floodplain.
38
Table 3
Modeled Groundwater Discharge Zone of Influence on Wetland Hydroperiod
Chewacla / Wehadkee Soil
Floodplain
Groundwater
Number of
Groundwater
Number of
Surface
Discharge Zone
Years
Discharge Zone
Years
Elevation Above
of Influence 2,1
Wetland
of Influence
Wetland
Channel Invert /
Ifeet)
Criteria
(feet)
Criteria
Weir Height'
(Surface
Met
(Surface
Met
16/31
Hydropenods <5%
16/31
Hydropenods <
215
(feet)
of the growing
16/31
12.5% of the
245
16/31
season)
16/31
growing season)'
Forested Conditions
1 "Weir Height" is assumed to represent the effective depth (invert) of the drainage feature
2 Soil hydraulic conductivities and drainage rates have been generalized based upon NRCS data and
regional averages.
3 Discharge Zone of Influence is equal to %z of the modeled ditch spacing
4• Based on field observations, sod types projected to support wetland hydropenods for greater than
5 percent to 12 5 percent of the growing season are expected to exhibit characteristics more
indicative of the Wehadkee series, a poorly drained sod Based on the model, these areas may
occur on floodplains within 25 feet to 200 feet of streams potentially lacking significant effluent
(groundwater withdrawal) character, such as very shallow channels Conversely, the model
suggests that the transition from Chewacla sods (somewhat poorly drained) to Wehadkee sods
(poorly drained) may be achieved adjacent to larger (dredged) effluent channels at distances
ranging from 300 feet to 400 feet from the drainage structure (assuming a relatively flat
floodplain surface)
39
(relatively high surface water storage and rooting functions)
0
- - - --
29/31
- - - --
27/31
1
253
20/31
145
16/31
2
85
16/31
225
16/31
3
125
16/32
275
17/31
4
160
16/31
315
16/31
6
215
16/31
380
16/31
8
245
16/31
405
16/31
1 "Weir Height" is assumed to represent the effective depth (invert) of the drainage feature
2 Soil hydraulic conductivities and drainage rates have been generalized based upon NRCS data and
regional averages.
3 Discharge Zone of Influence is equal to %z of the modeled ditch spacing
4• Based on field observations, sod types projected to support wetland hydropenods for greater than
5 percent to 12 5 percent of the growing season are expected to exhibit characteristics more
indicative of the Wehadkee series, a poorly drained sod Based on the model, these areas may
occur on floodplains within 25 feet to 200 feet of streams potentially lacking significant effluent
(groundwater withdrawal) character, such as very shallow channels Conversely, the model
suggests that the transition from Chewacla sods (somewhat poorly drained) to Wehadkee sods
(poorly drained) may be achieved adjacent to larger (dredged) effluent channels at distances
ranging from 300 feet to 400 feet from the drainage structure (assuming a relatively flat
floodplain surface)
39
DRAINMOD simulations modeled the zone of influence of the post project channel on wetland
hydroperiods within the primary floodplain. The maximum zone of influence may be used to
predict the area of groundwater wetland hydrological influence that may result due the
elevation of stream flow within the channel. In addition, the model provides an estimate of
the area that may continue to be affected in perpetuity by the stream channel at a depth of
1 to 3 feet below the floodplain elevation.
Based on these simulations, the post - restoration channel is expected to continue to effectively
drain groundwater from the Chewacla soils within the map unit. Model simulations indicate
that a series of in- stream weirs placed to within 1 foot of the adjacent floodplain elevation may
not restore significant areas of wetlands in Chewacla soils. A channel invert 2 feet below the
adjacent stream terrace continues to effectively drain an area 85 feet adjacent to the drainage
feature Gradual slopes in remaining portions of the outer floodplain are projected to continue
draining towards the modified stream channel. Therefore, in- stream weirs do not provide a
viable option for wetland restoration based on the groundwater model. To create wetlands,
greentree impoundments will be required to elevate the groundwater surface above the
floodplain elevation (immediately adjacent to the channel) periodically throughout the year.
4.4 REFERENCE GREENTREE IMPOUNDMENTS
Established greentree impoundments within the Piedmont of North Carolina were visited to
measure wetland attributes, review various structural designs, and to discern management
strategies employed. Reference systems include the Rocky Branch impoundment above Falls
Lake in Wake County, the Country Line Creek impoundments in Caswell County, the Beaver
Creek greentree impoundment above Jordan Lake in Wake County, and the Little Creek
impoundment above Jordan Lake in Durham County (Figures 9-11). These impoundments have
typically been located above water supply reservoirs in the region to replace wetland habitat
inundated by the reservoir, provide waterfowl habitat, and control sedimentation.
Controllable weirs range from concrete dams and electronic sluice gates on larger tributaries
to corrugated metal pipe using flash -board risers on smaller systems The associated dams
typically consist of an earthen causeway with rip- rapped emergency spillways and erosion
control areas. Dams likely to be overtopped within watersheds greater than 10 square miles
have often been reinforced with concrete materials placed on the earthen dam.
Figure 12 provides a conceptual depiction of a typical weir and dam for greentree
impoundments within watersheds ranging in size from 2 to 7 square miles. The weir consists
of two 4 -foot wide slots with wooden flash -board risers used to control the water surface
elevation For this application, the flash boards could be completely removed to provide for
existing channel flows during summer months, planting periods, or for other management
purposes Subsequently, the boards may be installed during the winter and /or early part of the
growing season to establish wetland hydrology behind the impoundment. The type or size of
the weir used at the Sophia Branch Site may be modified during the engineering design phase
to reduce flood potential, increase potential for stability, and /or other management concerns.
40
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A profile of the Country Line Creek impoundment in Caswell County was measured to evaluate
wetland development relative to the dam height, typical winter weir height, summer weir
height, and valley slope. Figure 13 provides a depiction of the reference greentree
impoundment characteristics, including vegetation development patterns relative to water
surface elevations Within the reference greentree impoundments, stream channels have been
obscured due to alluvial sediment deposition and vegetation development patterns. The stream
channel has been altered to the extent that wetland characteristics typically occupy the entire
impoundment land area, up to the water surface elevation established during winter months.
Figure 14 depicts the plan view and cross - section of a typical altered stream channel.
4.5 REFERENCE PLANT COMMUNITIES
In order to establish a forested wetland system for mitigation purposes, a reference community
must be established. According to Mitigation Site Classification (MIST) guidelines (EPA 1990),
the area of proposed restoration should attempt to emulate a Reference Forest Ecosystem
(RFE) in terms of soils, hydrology, and vegetation In this case, the target RFEs were
composed of steady -state woodlands in the region that have sustained loading of fluvial
sediments on floodplains in the past. Forest canopies have developed on these reference sites
which support soil, landform, and hydrological characteristics that restoration will attempt to
emulate
All of the RFEs have been impacted by sediment deposition, selective cutting or high - grading,
channel migration /disturbances, and relatively high energy flood events. Therefore, the species
composition of these plots should be considered as a guide only. Reference forest data used
in restoration was modified to emulate steady state community structure as described in the
Classification of the Natural Communities of North Carolina (Schafale and Weakley 1990).
Two RFEs were selected within floodplains along the Rocky River in Cabarrus County, North
Carolina. Floodplains associated with this river system have aggraded over the past century,
inducing braided channel configurations and accelerated sediment deposition within reference
feeder tributaries (Figure 14). Sixteen plots have been placed within relatively mature
bottomland hardwood /swamp forests that have developed on accreted sediment.
The reference vegetation samples are designed to characterize the plant communities proposed
for restoration Circular, 0 1 -acre plot sampling was utilized to establish base -line vegetation
composition and structure in reference areas Species were recorded along with individual tree
diameters, canopy class, and dominance From collected field data, importance values (Brower
et al. 1990) of dominant canopy and mid -story trees were calculated (Table 4 and Table 5).
The composition of shrub /sapling and herb strata were recorded and identified to species.
At Site 1 (Table 4), the forest canopy is dominated by green ash, (Importance value [IV] 28
percent), sweetgum (IV 19 percent), American elm (Ulmus americana) (IV 11 percent), box
elder (IV 8 percent) and red maple (IV 7 percent). Canopy species with lesser importance
include black willow, slippery elm (Ulmus alata), river birch, tulip poplar, and water oak
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(Quercus nigra). Understory trees include flowering dogwood, ironwood, and sugarberry
(Celtis laevigata) A developed shrub layer is not generally present Herbs include Nepal
microstegium, violets ( Viola spp ), asters (Aster sp ), and river oats (Chasmanthium latifo /rum).
At Site 2 (Table 5), the forest canopy is dominated by green ash, (IV 39 percent), box elder
(IV 22 percent), American elm (IV 12 percent), and swamp chestnut oak (IV 6 percent).
Portions of the canopy at RFE locations were also dominated by ironwood, overcup oak
(Quercus lyrata), sugarberry, sweet gum, red maple, black willow, slippery elm, water oak, and
river birch. The shrub /sapling layer is characterized by the non - native Chinese privet
(Ligustrum chinensis), paw -paw (Asimina tr1loba), and shade tolerant canopy species
Herbaceous species include Japanese honeysuckle (Loniceralaponica), blackberry, muscadine,
common greenbriar, sedges (Carex spp.), and poison ivy.
Piedmont swamp forests are communities located in depressional areas, along toe slopes, and
at the confluence of alluvial valleys, where lateral flow is restricted. These sites are
hydrologically influenced by upland seeps and drainages, and by occasional riverine flooding
Overstory species are dominated by flood - tolerant bottomland elements such as sweetgum,
American elm, willow oak (Quercus phe/ %s), swamp chestnut oak, green ash, overcup oak,
and swamp cottonwood (Populus heterophylla). Wetter sites may provide a broken to open
canopy providing enough light for development of a dense herbaceous /shrub layer. Species
found on these sites may include button -bush (Cephalanthus occidentalis), elderberry
(Sambucus canadensis), silky dogwood, false nettle (Boehmeria cylindnca), sedges (Carex
spp), rushes (Juncus spp ), and lizard's tail (Saururus cernuus). Giant cane (Arundinaria
gigantea) is prevalent in places.
50
50 WETLAND RESTORATION PLAN
This restoration plan has been designed to establish wetlands within watersheds situated
immediately upstream of the Randleman Reservoir. A series of greentree impoundments is
proposed to establish contiguous wetland presence within 15.6 acres of the upper Sophia
Branch floodplain at elevations ranging from 715 feet to 730 feet above mean sea level. At
the Lower Sophia Branch site, two greentree impoundments is proposed to establish 6.1 acres
of wetlands at 683 to 690 feet above mean sea level. Wetland acreage to be created /restored
is a subset of the total project area, which has been defined as the limit of the 5 -year post-
project flood.
Wetland restoration or creation comprises approximately 19.1 acres of the total wetland
presence. This area is composed of actively inundated land surfaces, and passively formed,
saturated wetlands within 1.0 foot in elevation above the impounded water surface. Based
on reference studies, the one foot delineation of passively formed wetlands constitutes a
conservative estimate of the extent of wetland formation expected. (See ESC 2000a and ESC
2000b for a description of the passive formation of wetlands).
An additional 2.6 acres of the mitigation total is composed of open waters. The shorelines of
these areas are expected to accrete as sediment deposition within the impoundments
progresses. Submerged, emergent, and shrub /scrub aquatic vegetation is projected to colonize
these areas.
Finally, approximately 2.4 acres of the mitigation area is comprised of pre - existing wetlands.
These areas will be preserved or enhanced during impoundment construction. Enhancement
activities will include hydroperiod regulation and improvements in buffer vegetation.
The green tree impoundment comprises an embankment (floodplain levee) and weir
(controllable outlet structure). The elevation of the outlet is typically raised during the winter
months, while trees are dormant, to promote ponding, sediment deposition, and wetland
habitat. The elevation of the outlet is lowered in early spring to allow for vegetation growth,
nutrient uptake, and seedling establishment For this project, the outlet may only be raised
during a brief portion (5 percent to 12.5 percent) of the growing season until wetland
communities and associated habitat are successfully restored. Subsequently, the period that
the outlet is raised may be incrementally increased during the winter months each year to
increase inundated wetland habitat for water fowl and other species adapted to use of
greentree impoundments during the winter season The long term objective of wetland
restoration /creation by greentree impoundments is to maintain forested wetland communities
to the maximum extent feasible Therefore, long -term management will be required.
A management plan has been prepared (Section 8.0) for long term maintenance of the
impoundment over the life of the Randleman Reservoir. Management techniques for greentree
� 5,
ti
impoundments surrounding the reservoir will be managed according to constructs outlined in
the Greentree Reservoir Management Handbook (Fredrickson and Batema 1996).
Components of this plan have been established based on reference wetland studies described
in Section 4.0. This effort will be performed by 1) installing a controllable weir and dam, 2)
installing a step -pool grade control structure, and 3) planting of target wetland tree species in
the area Monitoring of wetland development will be performed to track successional
characteristics of the Site and to verify wetland restoration success.
5.1 IMPOUNDMENT / WEIR CONSTRUCTION
Upper Sophia site: A series of greentree impoundment structures consisting of nine
embankments will be constructed within the Site, as depicted in Figures 15A and 15B The
impoundment series begins approximately 300 feet south of SR 1941, at a channel elevation
of 714 feet.
Lower Sophia site: Two greentree impoundments will be constructed, beginning approximately
900 feet north of SR 1990. The channel elevations at the impoundments will be 680 and 686
feet.
Construction of impoundment and weir structures may be subject to restrictions under the
North Carolina Dam Safety Law of 1967 (GS 143 -215 23) Detailed construction plans will
be described in the design engineering phase of the project.
Embankments
The embankments will be constructed to elevations ranging from approximately 722 -733 feet
above mean sea level at the Upper Sophia site, and at 690 and 694 feet at the Lower Sophia
site. The embankment elevation may be modified during the engineering design phase to
provide increased capacity for transporting floodplain flows across or around the structure.
As proposed, the embankment surface will reside up to eight feet in elevation above the
existing floodplain surface.
Weirs
The weirs (outlet structures) will be designed to allow for open channel flow at base levels of
723 -714 feet (Upper Sophia site) and at 690 and 694 feet (Lower Sophia site) The weir
design will allow raising of the water surface to 718 -729 feet during impoundment periods at
the Upper Sophia site, and to 680 and 686 feet at the Lower Sophia site. Figure 12 provides
a conceptual depiction of the proposed impoundment structure. Target elevations for the
winter water surface and embankment height are listed in Figures 15A and 15B. The design
or placement of these impoundments may be modified during the engineering design phase
based on potential stability, constructability, cost, or other constraints.
52
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5.2 STEP -POOL GRADE CONTROL STRUCTURE
The outfall from the downstream weir will discharge over a relatively steep incline into the
existing channel immediately below the Site. At the Upper Sophia site, the transition will
extend from a maximum of 718 feet at the structure to 714 feet within the existing channel
bed. At the Lower Sophia site, the water surface elevation at the structure will be 686 feet,
with the elevation of the adjacent channel at 680 feet. This transition will be extended over
an adequate distance (60 -80 feet) to reduce the water surface slope towards stable conditions
characteristic for a step -pool (A -type) stream channel underlain by a boulder substrate The
structure will attenuate flow velocities so that down - cutting into the channel bed will be
avoided immediately below the greentree impoundment. Figure 16 provides a conceptual
depiction of a step -pool grade control channel
The step -pool channel will be constructed over a distance of 60 to 80 feet within the Site
boundary. This distance will provide a bankfull water surface slope of approximately 0.05
rise /run (5 percent slope). In -fill and available boulder material will be arranged in the channel
to provide a step -pool geometry conducive to in- stream habitat, as depicted in Figure 16. The
series of steps and pools will promote capacity for continued fish migration above and below
the greentree impoundment structure
5 3 WOODY DEBRIS DEPOSITION
Woody debris, including downed trees, tip mounds, snags, and decomposing material
represents important habitat elements for wetland dependent wildlife. Therefore, woody
material generated from embankment construction or other Site activities will be distributed
across future wetland surfaces to the extent feasible The material may be lifted or pushed
from adjacent windrows or forest areas as well.
5.4 WETLAND COMMUNITY RESTORATION
Restoration of wetland forested communities provides habitat for area wildlife and allows for
development and expansion of characteristic wetland- dependent species across the landscape.
1 Ecotonal changes between communities contribute to diversity and provide secondary benefits
such as enhanced feeding and nesting opportunities for mammals, birds, amphibians, and other
wildlife.
RFE data, on -site observations, and ecosystem classification has been used to develop the
1 species associations promoted during community restoration activities. Target plant
community associations include 1) bottomland hardwood / swamp forest and 2) scrub -shrub
/ swamp forest Scrub -shrub elements will be targeted towards areas immediately behind the
1 impoundment within the construction limits and along the stream channel banks.
1
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Planting Plan
The planting plan consists of 1) acquisition of available wetland species, 2) implementation of
proposed surface topography improvements, and 3) planting of selected species on -site
Wetland areas of the Site to be created or enhanced (excluding open water areas) will be
planted in a random distribution, including the species listed below. At the Upper Sophia site,
the planted area will total 15 7 acres, while at the Lower Sophia site, a total of 6 3 acres will
be planted.
Bottomland Hardwood / Swamp Forest
1.
Cherrybark Oak (Quercus pagoda)
2.
Overcup Oak (Quercus lyrata)
3.
Willow Oak (Quercus phellos)
4
Swamp Chestnut Oak (Quercus michauxu)
5
Swamp Cottonwood (Populus heterophylla)
6.
Shagbark Hickory (Carya ovata)
7.
Bitternut Hickory (Carya cordiformis)
8.
Green Ash (Fraxinus pennsylvanica)
9
American Elm (Ulmus amencana)
10
Winged Elm (Ulmus alata)
11.
Tulip Poplar (Linodendron tulipifera)
Scrub -Shrub / Swamp Forest
1.
Possum -haw (flex decidua)
2
Carolina holly (flex ambigua)
3
River Birch (Betula nigra)
4
American Sycamore (Platanus occidentalis)
5.
Green Ash (Fraxinus pennsylvanica)
6.
American Elm (Ulmus amencana)
7
Swamp Cottonwood (Populus heterophylla)
8.
Overcup Oak (Quercus lyrata)
9.
Swamp Chestnut Oak (Quercus michauxii)
10.
Silky Dogwood (Corpus amomum)
11.
Button -bush (Cephalanthus occidentaks)
12.
Elderberry (Sambucus canadensis)
Species selected for planting will be dependent upon availability of local seedling sources.
Advanced notification to nurseries (1 year) may facilitate availability of various non - commercial
species In full planting areas (existing agricultural land), the soil surface will be scarified.
Disking or ripping may be employed to create a rough surface for the detention of runoff and
sediment, and to provide a more hospitable planting bed for tree seedlings. Then, bare -root
seedlings of selected species will be planted within specified areas at a density of 680 trees
per acre (8 foot centers). In existing forested areas, a supplemental planting will consist of
57
170 stems per acre (16 -foot centers). Supplemental plantings will retain existing Site canopy
trees, while introducing a greater component of wetland- dependent species. The total number
of stems and species distribution are depicted in Tables 6A and 6B.
Planting will be performed between December 1 and March 15 to allow plants to stabilize
during the dormant period and set root during the following spring season Opportunistic
species, which typically dominate early- to mid - successional forests have been excluded from
initial plantings on interior floodplains. Opportunistic species such as sweetgum, red maple,
and loblolly pine may become established naturally. However, to the degree that long -term
species diversity is not jeopardized, these species should be considered important components
of steady -state forest communities. Planting of opportunistic species such as black willow will
be targeted as stabilization elements in erosion control areas immediately adjacent to the
creek.
The planting plan is the blueprint for community restoration (Figures 17A and 17B) The
anticipated results stated in the regulatory success criteria (Section 6 0) may reflect vegetative
conditions achieved after steady -state forests are established over many years. However, the
natural progression through early successional stages of floodplain forest development will
prevail regardless of human interventions over a 5 -year monitoring period. In total,
approximately 10000 seedlings will be planted during wetland community restoration efforts
(8100 seedlings at the Upper Sophia site, and 1900 at the Lower Sophia site).
58
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TABLE 6A (Upper Sophia Site)
Planting Plan
Vegetation
Association
(Planting area)
Shrub - Scrub/
Swamp Forest
Bottomland
Hardwood/
Swamp Forest
(full planting)
Bottomland
Hardwood/
Swamp Forest
(supplemental
planting)
TOTAL
STEMS
PLANTED
Stem Target (trees /ac)
680
680
170
- - - --
Area (acres)
1 9
7 8
60
157
SPECIES
# planted
(% total)
# planted
(% total)
# planted
(% total)
# planted
(% total)
River Birch
150 (10)
150
Silky Dogwood
150 (10)
150
Button -bush
150 (10)
150
Elderberry
150 (10)
150
Tag Alder
150 (10)
150
Black Willow
75 (5)
75
Possum -haw
75 (5)
75
Carolina Holly
75 (5)
75
American Sycamore
75 (5)
75
Swamp Cottonwood
150 (10)
550 (10)
110 (10)
810
American Elm
75 (5)
275 (5)
55 (5)
405
Green Ash
150 (10)
275 (5)
55 (5)
480
Swamp Chestnut Oak
75 (5)
550 (10)
110 00)
735
Overcup Oak
150 (10)
550 (10)
110 00)
810
Cherrybark Oak
550 (10)
110 (10)
660
Willow Oak
550 (10)
110 (10)
660
Shagbark Hickory
550 (10)
110 (10)
660
Bitternut Hickory
550 (10)
110 (10)
660
Winged Elm
550 (10)
110 00)
660
Tulip Poplar
550 (10)
110 (10)
660
TOTAL
1650
5500
1100
8100
59
TABLE 613 (Lower Sophia Site)
Planting Plan
Vegetation
Association
(Planting area)
Shrub - Scrub/
Swamp Forest
Bottomland
Hardwood/
Swamp Forest
(full planting)
Bottomland
Hardwood/
Swamp Forest
(supplemental
planting)
TOTAL
STEMS
PLANTED
Stem Target (trees /ac)
680
680
170
- - - --
Area (acres)
0.4
09
5.0
63
SPECIES
# planted
(% total)
# planted
(% total)
# planted
(% total)
# planted
(% total)
River Birch
30 (10)
30
Silky Dogwood
30 (10)
30
Button -bush
30 (10)
30
Elderberry
30 0 0)
30
Black Willow
15 (5)
15
Possum -haw
15 (5)
15
Carolina Holly
15 (5)
15
American Sycamore
15 (5)
15
Swamp Cottonwood
30 (10)
70 (10)
90 (10)
190
American Elm
15 (5)
35 (5)
45 (5)
95
Green Ash
30 (10)
35 (5)
45 (5)
110
Swamp Chestnut Oak
15 (5)
70 (10)
90 (10)
175
Overcup Oak
30 00)
70 (10)
90 (10)
190
Cherrybark Oak
70 (10)
90 (10)
160
Willow Oak
70 (10)
90 00)
160
Shagbark Hickory
70 (10)
90 (10)
160
Bitternut Hickory
70 (10)
90 (10)
160
Winged Elm
70 (10)
90 00)
160
Tulip Poplar
70 (10)
9000).
160
TOTAL
300
700
900
1900
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6.0 MONITORING PLAN
The Monitoring Plan will entail analysis of the restoration area according to jurisdictional
wetland criteria (DOA 1987). Monitoring will include the observation and evaluation of three
primary parameters including hydrology, soil, and vegetation. Monitoring of restoration efforts
will be performed for 5 years or until success criteria are fulfilled.
6.1 HYDROLOGY
After hydrological modifications are performed, surficial groundwater monitoring gauges will
be designed and placed in accordance with specifications in USACE's Installing Monitoring
Wells /Piezometers in Wetlands (WRP Technical Note HY- IA -3.1, August 1993). Monitoring
gauges will be set to a depth of up to 24 inches below the soil surface to track water surface
elevations in the impoundment relative to the weir height. All screened portions of the gauge
will be buried in a sand screen, filter fabric, and /or a bentonite cap to prevent siltation during
floods. Recording devices (if used) will be placed 5 feet above the ground elevation.
Placement of recording devices at this height should guard against over topping for a projected
50 -year flood elevation. The gauge will be stabilized from flood shear by reinforcing steel bar
(re -bar).
Four (Upper Sophia site) or two (Lower Sophia site) groundwater monitoring gauges will be
installed in restoration areas to provide representative coverage throughout the Site
Approximate gauge locations are depicted in Figures 18A and 18B. Hydrological sampling will
be performed during the growing season (March 26 to November 6) at intervals necessary to
satisfy the hydrologic success criteria. In general, the gauges will be sampled weekly through
the spring and early summer and intermittently through the remainder of the growing season,
if needed to verify success.
6.2 HYDROLOGY SUCCESS CRITERIA
Target hydrological characteristics have been evaluated using regulatory wetland hydrology
criteria. The regulatory wetland hydrology criterion requires saturation (free water) within one
foot of the soil surface for 5 percent of the growing season under normal climatic conditions
Success Criteria
Under normal climatic conditions, hydrology success criteria comprises saturation (free water)
within 1 foot of the soil surface for a minimum of 5 percent of the growing season. This
hydroperiod translates to saturation for a minimum, 11 -day (5 percent) consecutive period
during the growing season, which extends from March 26 through November 6 (USDA 1977).
If wetland parameters are marginal as indicated by vegetation and hydrology monitoring, a
jurisdictional determination will be performed in the questionable areas.
63
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6.3 SOIL
Mitigation activities are expected to increase the deposition and transport of stream sediments
during overbank flood events. As a result, soils (F/uvaquents) are continuously reworked by
fluvial processes. Because iron reduction rates (gleying) are not spatially or temporally uniform
on recent alluvial deposits, soil color or other visual, hydnc soil properties are not considered
suitable for quantitative wetland soil monitoring /success criteria on active floodplains
Soil monitoring will entail measurement of sediment accretion /reduction ( aggradation/
degradation) at the location of each monitoring gauge and other hydraulically active areas as
identified by Site managers. Mitigation activities are designed to provide for flood and
sediment storage from the watershed. Therefore, hydraulic and energy dissipation patterns
should be distributed throughout as much of the Site as possible. However, an area of
particularly accelerated sediment deposition may raise land surfaces above the elevation of the
primary wetland floodplain over a relatively short period of time. Conversely, deep scour holes
or head -cuts may form in locations where flow velocity or sediment deficits exceed a "normal
distribution." Soil monitoring is designed to provide a cursory review to predict the need for
additional site modifications if accelerated deposition or scour potentially jeopardizes wetland
restoration efforts.
The re -bar used to support monitoring gauges will be marked upon installation and in each
monitoring year at the elevation of the existing ground surface. In addition, the height of silt
lines will be recorded to predict the depth of inundation during the flood period Additional re-
bar will be placed and measured in high energy areas identified by Site managers, as needed
The change in elevation of the alluvial surface and deposition /scour patterns relative to flood
elevations will be recorded and compared to previous years.
6.4 SOIL SUCCESS CRITERIA
Success criteria require that the deposition /scour rate not exceed over 1 foot change in surface
elevations in any given year. Any areas affected by this excessive deposition /scour will be
mapped in the field. The area will be reviewed to determine modifications to drainage patterns
that should be implemented, if any. Changes in surface elevations of less than 1 foot per year
will meet regulatory success criteria, however, modifications to deposition / scour patterns
may also be considered in certain circumstances
6.5 VEGETATION
Restoration monitoring procedures for vegetation are designed in accordance with EPA
guidelines presented in MIST documentation (EPA 1990) and Compensatory Hardwood
Mitigation Guidelines (DOA 1993). The following presents a general discussion of the
monitoring program.
Vegetation will receive cursory, visual evaluation during periodic reading of monitoring wells
to ascertain the general conditions and degree of competition or overtopping of planted
66
elements Subsequently, quantitative sampling of vegetation will be performed once annually
during the fall (September /November) for 5 years or until vegetation success criteria are
achieved. Sampling dates may be modified to accommodate flood events and plot inundation,
as needed.
During the first sample event, a visual survey will be performed in the reference wetlands to
identify all canopy tree species represented within target communities. These reference tree
species will be utilized to define "character tree species" as termed in the success criteria.
Permanent (on each gauge head) or nonpermanent, randomly placed plots will be established
at representative locations in the restoration areas. Each plot will consist of two, 300 -foot
transects extending at a randomly selected compass bearing from a central origin. The plot
width along the transect will extend 4 feet on each side of the tape, providing a 0.1 1 -acre plot
sample at the location (600 feet x 8 feet / 43,560 square feet /acre). Eight plots will be
established to provide an 8 percent sample and a depiction of tree species available for current
and future seed sources within the restoration area. In each plot, tree species and number of
stems will be recorded and seedling /sapling /tree height measured. Tree data from all plots will
be combined into one database to calculate an average density, by species, represented in
restoration areas of the Site.
In each plot, presence /absence of shrub and herbaceous species will be recorded. A wetland
data form (DOA 1987) will be completed to document the classification and description of
vegetation, soil, and hydrology.
6.6 VEGETATION SUCCESS CRITERIA
Success criteria include the verification, per the wetland data form, that each plot supports a
species composition sufficient for a jurisdictional determination. Additional success criteria
are dependent upon density and growth of "Character Tree Species " "Character Tree
Species" are identified through visual inventory of reference wetland communities used to
orient the restoration project design. All canopy tree species identified in the reference
wetland will be utilized to define "Character Tree Species" as termed in the success criteria
(Character Tree Species are generally listed in Section 4 5 and Section 5.6)
An average density of 320 stems per acre of Character Tree Species must be surviving in the
first three monitoring years. Subsequently, 290 stems per acre of character tree species must
be surviving in year 4, and 260 stems per acre of Character Tree Species in year 5. Each
individual species is limited to representing up to 20 percent of the 320 stem per acre total.
Additional stems of a particular species above the 20 percent threshold are discarded from the
statistical analysis. In essence, a minimum of five different character tree species must be
present with each species representing up to 20 percent of the 320 stem per acre total.
67
If vegetation success criteria are not achieved based on average density calculations from
combined plots over the entire restoration area, those individual plots that do not support the
stem per acre requirement and the representative area will be identified. Supplemental planting
will be performed in the identified area as needed until vegetation success criteria are
achieved.
No quantitative sampling requirements are proposed for herb assemblages. Development of
a forest canopy over several decades and restoration of wetland hydrology will dictate success
in migration and establishment of desired wetland understory and groundcover populations.
6.7 REPORT SUBMITTAL
An Annual Wetland Monitoring Report (AWMR) will be prepared at the end of each monitoring
year (growing season). The AWMR will depict the sample plot and quadrant locations and
include photographs which illustrate site conditions. Data compilations and analyses will be
presented as described in Sections 6.1 through 6.6 including graphic and tabular format, where
practicable. Raw data in paper or computer (EXCEL) file format will be prepared and submitted
as an appendix or attachment to the AWMR
7.0 IMPLEMENTATION SCHEDULE
Project implementation will include performance of restoration work in four primary stages
including 1) impoundment / weir construction, 2) tree and shrub planting, 3) monitoring plan
implementation, and 4) management program implementation. This mitigation plan or
implementation schedule may be modified based upon civil design specifications, permit
conditions, or contractor limitations.
Stage 1: Impoundment / Weir Construction
Stage 2 will be performed concurrent with or subsequent to filling of the reservoir. The
greentree impoundment will be installed at the designated location This work will be
performed during late spring and /or early summer months to reduce erosion hazards associated
with saturated soil or large August storms Site preparation, including debris removal, woody
debris deposition, and scarification (if needed) will be performed during the same summer
period, prior to tree planting.
Stage 2: Tree Planting
Tree and shrub planting will be performed the first winter after Stage 2 is complete. The
seedlings will be planted during the winter dormant period, prior to March 1.
Stage 3: Monitoring Plan Implementation
Groundwater monitoring gauges and permanent vegetation plots will be established
immediately after construction and planting activities are completed (prior to March 26, the
start of the growing season). The Site will be visited regularly to read monitoring gauges and
to evaluate wetland development during the first growing season. Vegetation sampling and
hydrology monitoring will be completed by November 6 (the end of the growing season) The
first year of monitoring would be completed upon submittal of the Annual Wetland Monitoring
Report and fulfillment of success criteria. The monitoring sequence will be repeated as
described for four additional years or until success criteria are achieved.
Stage 4: Management Program Implementation
Green tree impoundments require active management throughout the life of the wetland facility
and water supply reservoir. Therefore, long -term management programs will be required to
ensure that wetland development is established and maintained. The management program
will be implemented concurrent with the monitoring plan as described above. Constructs of
the management program are described in the next Section.
.•
8.0 MANAGEMENT PROGRAM
Greentree impoundments require modification of water surface elevations on a regular basis.
Typically, the elevation of outlets is raised and lowered at variable times each year to provide
for development of target wetland vegetation. Wetland vegetation is typically harvested
and /or planted periodically to establish target vegetation patterns for waterfowl or other
wetland dependent wildlife. Invasive species such as kudzu (Pueraria iobata) may require
systematic removal as well. For this project, outlet controls and vegetation maintenance must
also be manipulated to promote forested wetland development within the Site. Target
hydrological goals include soil saturation or inundation for a minimum of 5 percent of the
growing season (March 26 to November 6). The 5 percent criterion must be achieved in 50
percent of the years over the life of the Randleman Reservoir.
The Piedmont Triad Regional Water Authority (PTRWA) will provide the fiscal and
administrative resources necessary to maintain and manage the greentree impoundments over
the life of the water supply reservoir. PTRWA will make provisions for establishment of an
Environmental Compliance Officer (Officer) to serve as the primary administrator and authority
over the greentree impoundments. The Officer will be under control of PTRWA while PTRWA
continues to manage the property. If the property is deeded to a resource agency as described
in Section 9.0, the resource agency will provide resources necessary for establishment and
maintenance of the Officer.
The Officer will be tasked to supervise, coordinate, monitor, and manipulate the greentree
impoundments throughout the life of the water supply reservoir. The Officer will coordinate
and implement, in consultation with qualified wildlife biologists, the following greentree
impoundment management components as described in the Greentree Reservoir Management
Handbook (Fredrickson, L.H. and D.L. Batema 1996, Mitchell and Newling 1986).
1) The Officer will be responsible for raising and lowering the controllable weirs at
a frequency and duration needed to establish wetland hydrology and maximize
development of wetland vegetation. Target vegetation patterns include
establishment of tree species to the maximum extent feasible
2) The Officer will periodically visit the Site to visually assess waste debris
dumping, erosion problems, debris dams on structures, vegetation patterns, and
other aspects of wetland development. The Officer will repair identified
problems to ensure continued functioning of the wetland.
3) The Officer will provide for periodic quantitative sampling of vegetation to
ensure that target vegetation species are developing and being replaced within
the impoundments. The results of vegetation samples will be used by the
1
4
Officer to adjust the frequency and /or duration that the controllable weirs are
raised or lowered and to order and plant vegetation elements as needed.
4) The Officer will submit an annual report to the responsible resource agency
summarizing the dates of weir modification, the current vegetation sample,
trends in vegetation patterns, and recommendations for weir modifications over
the next monitoring weir. The report will also include recommendations for
structural modifications or additional plantings, as needed. These reports will
be prepared and submitted on annual basis over the life of the Randleman
Reservoir Water Supply.
71
9.0 DISPENSATION OF PROPERTY
PTRWA will maintain ownership of the property until all mitigation activities are completed and
the site is determined to be successful. Although no plan for dispensation of the Site has been
developed, PTRWA may continue to manage the property or may deed the property to a
resource agency (public or private) capable of managing the greentree impoundments over the
life of the reservoir. The resource agency will be approved by the appropriate regulatory
agencies. Covenants and /or restrictions on the deed will be included along with adequate
fiscal resources to ensure adequate management and protection of the Site throughout the life
of the reservoir.
72
10 0 WETLAND FUNCTIONAL EVALUATIONS
Mitigation activities at the Sophia Branch Mitigation Site should be determined based on
wetland functions generated and a comparison of restored functions to potentially impacted
wetland resources. Therefore, an evaluation of mitigation wetlands by physiographic area is
provided to evaluate site utility for mitigation in the region.
10.1 EXISTING CONDITIONS
Under existing conditions, hydrodynamic functions have been degraded or effectively
eliminated due to stream entrenchment, bed /bank erosion and removal of characteristic
vegetation. Features which depict performance of hydrodynamic wetland functions such as
surface microtopography, seasonal ponding, meandering stream channels, and characteristic
wetland vegetation have been effectively eliminated on the abandoned floodplains Reduction
or elimination of wetland hydrology has also negated nutrient cycling and biological functions
within the complex. These former wetlands do not support natural communities adapted to
wetlands or the wetland dependent wildlife characteristic in the region.
10.2 PROJECTED, POST - RESTORATION CONDITIONS
The Site will be used to establish wetland communities capable of providing wildlife habitat
and water quality benefits. The greentree impoundment is projected to provide for restoration
of regular overbank flood events and filling of the entrenched channel with sediment over time
As a result, the floodplain areas are expected to support an array of emergent, shrub - scrub,
and forested wetland communities, providing replacement of habitat for wetland dependent
species displaced by the reservoir. Water quality benefits are projected to include sediment
retention and pollutant processing of waters generated by the 1.5- square mile watershed.
Pro - active mitigation within the greentree impoundments is projected to provide approximately
15.7 acres of wetland restoration /creation or preservation at the Upper Sophia site, and 6 3
acres at the Lower Sophia site (Figures 18A and 18B).
73
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