HomeMy WebLinkAbout19970722 Ver 1_Report_20010712DETAILED WETLAND MITIGATION PLAN_, /�
RANDLEMAN RESERVOIR WATER SUPPLY
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EDGAR 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
Jul. 12 2001
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TABLE OF CONTENTS
Page
LIST OF FIGURES iii
LIST OF TABLES ................... ............................... IV
1.0 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
2.0 METHODS ................... ..............................8
3.0 EXISTING CONDITIONS 11
3.1 PHYSIOGRAPHY, TOPOGRAPHY, AND LAND USE ................ 11
® 3.2 SOILS ................... .............................14
3.3 PLANT COMMUNITIES ..... ............................... 17
3.4 HYDROLOGY ............. .............................20
3.5 WATER QUALITY .......... .............................22
3.6 JURISDICTIONAL AREAS ... ............................... 23
4.0 WETLAND RESTORATION STUDIES ............................... 26
4.1 RESTORATION ALTERNATIVES ANALYSES ..................... 26
4.2 SURFACE WATER ANALYSES .. .............................28
4.3 GROUNDWATER MODELING . ............................... 33
4.4 REFERENCE GREENTREE IMPOUNDMENTS ...................... 36
4.5 REFERENCE PLANT COMMUNITIES ........................... 41
5.0 WETLAND RESTORATION PLAN ... ............................... 47
5.1 IMPOUNDMENT / WEIR CONSTRUCTION ....................... 50
5.2 WOODY DEBRIS DEPOSITION ............................... 50
5.3 WETLAND COMMUNITY RESTORATION ....................... 50
6.0 MONITORING PLAN ............ ............................... 56
6.1 HYDROLOGY ............. .............................56
6.2 HYDROLOGY SUCCESS CRITERIA ............................ 56
6.3 SOIL .................... .............................56
6.4 SOIL SUCCESS CRITERIA ... ............................... 59
6.5 VEGETATION ............. .............................59
6.6 VEGETATION SUCCESS CRITERIA ........................... 60
6.7 REPORT SUBMITTAL ........ .............................61
7.0 IMPLEMENTATION SCHEDULE .... ............................... 62
8.0 MANAGEMENT PROGRAM ......... .............................63
9.0 DISPENSATION OF PROPERTY ...... .............................65
10.0 WETLAND FUNCTIONAL EVALUATIONS ............................ 66
10.1 EXISTING CONDITIONS .... ............................... 66
10.2 PROJECTED, POST - RESTORATION CONDITIONS ................. 66
11.0 REFERENCES ................... .............................67
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LIST OF FIGURES
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Figure 1 :
Mitigation Site Locations: Randleman Reservoir ....................
2
Figure 2:
Site Location: Edgar Branch Mitigation Site .......................
6
Figure 3:
Aerial Photograph (1999) .... ...............................
9
Figure 4:
Physiography, Topography, and Land Use ....................
12 -13
Figure 5:
Soil Map Units ........ ...............................
15 -16
Figure 6:
Plant Communities ..... ...............................
18 -19
Figure 7:
Jurisdictional Wetlands .. ...............................
24 -25
Figure 8:
Flood Frequency Analysis ...............................
31 -32
Figure 9:
Site Location: Falls Lake Greentree Impoundment ................. 37
Figure 10:
Site Location: Country Line Creek Greentree Impoundment ........... 38
Figure 11:
Site Location: Jordan Lake Greentree Impoundments ...............
39
Figure 12:
Conceptual Impoundment Design .............................
40
Figure 13:
Reference Greentree Impoundment ...........................
42
Figure 14:
Reference Plan View and Cross - Section ........................
43
Figure 15:
Hydrology Restoration Plan ..............................
48 -49
Figure 16:
Planting Plan ......... ...............................
54 -55
Figure 17:
Monitoring Plan / Mitigation Design Units ....................
57 -58
LIST OF TABLES
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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 ...... 29
Table 3: Modeled Groundwater Discharge Zone of Influence
on Wetland Hydroperiods: Congaree Soils ....................... 35
Table 4: Reference Forest Ecosystem Plot Summary ..................... 45
Table 5: Reference Forest Ecosystem Plot Summary ...................... 46
Table 6: Planting Plan ............ ............................... 53
I
DETAILED WETLAND MITIGATION PLAN
RANDLEMAN RESERVOIR WATER SUPPLY
EDGAR BRANCH MITIGATION SITE
RANDOLPH COUNTY, NORTH CAROLINA
1.0 INTRODUCTION
1.1 PURPOSE
The Piedmont Triad Regional Water Authority (PTRWA) proposes development of the
Randleman 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 Edgar Branch,
a proposed mitigation site located immediately contiguous with proposed reservoir pool
elevations. The project boundary encompasses approximately 45.5 acres. Wetland mitigation
is projected to involve approximately 36.1 acres of created /restored wetlands and open waters
and approximately 0.9 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 Edgar
' Branch mitigation site.
IGoals 1 -4 will be accomplished at multiple sites, including Edgar 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
1 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 nverine wetlands,
Iand 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
I development in rapidly urbanizing areas. The greentree impoundment option is the preferred
alternative for wetland restoration /creation at Edgar 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
I 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 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 nverine wetland restoration
and creation along Edgar Branch, one of the 10 mitigation sites (Figure 2). The Edgar Branch
mitigation site (Site) consists of approximately 46 acres that encompass the stream and
adjacent floodplain. The stream drains a watershed of approximately 2.06 square miles (1320
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
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Reservoir
Mitigation
Site Location
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Source USGS 7 5 Minute Topo Maps
(Glenola / Randleman, N C
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EcoScience
Corporation
O Raleigh, North Carolina
RANDLEMAN RESERVOIR MITIGATION PROJECT
PHASE 11
EDGAR SITE
Randolph County, North Carolina
Dwn by
MAF
FIGURE
Ckd by
ES
Date JUL 2001
Pro)ect 01-075
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
2.0 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 (Figure 3).
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. A reference flood and sedimentation
study provided information on sedimentation and wetland development associated with
existing greentree impoundments in the region. 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. Topographic data were overlaid
on wetland restoration areas to establish methods for construction and restoration of wetland
communities within the Site.
Detailed topographic mapping to 1 -foot contour intervals was developed by ground survey
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 May 2001. 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.
9
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Groundwater conditions were modeled using DRAINMOD, a computer model for simulating
r withdrawal rates for shallow soils with high water tables. The model was utilized to predict
historic hydroperiods, 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-
rproject 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.
10
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 Edgar Branch floodplain
within the Cape Fear River Basin (Hydrologic Unit #03030003 [USGS 19741, DWQ Sub -Basin
03- 06 -08). The Site is located approximately 11 miles southeast of High Point and
approximately 16 miles south of Greensboro. Annual precipitation in the region averages 42
inches per year with June and August representing the months that support the highest
average rainfall (4.21 inches and 4.36 inches, respectively) (USDA 1977).
The project boundary has been defined as the limit of the 5 -year, post - project flood elevation.
The Site contains an approximately 8550 -foot reach of Edgar Branch (Figure 4). The on -site
section of Edgar Branch supports a primary watershed of approximately 1.95 square miles and
flows into Muddy Creek 0.7 miles downstream. Muddy Creek empties into the Deep River 3.0
miles downstream of its confluence with Edgar Branch. After construction of the Randleman
Reservoir, the downstream portion of the Site will reside immediately upstream of the
reservoir's conservation pool, at 682 feet above mean sea level. On -site floodplain elevations
range from 683 feet to approximately 730 feet.
The Site consists of agricultural and pasture land, as well as bottomland hardwood forest
corridors along the stream channel and in a few larger patches. A few scattered residential
'and farm buildings are also present (Figure 3). Near the downstream end of the Site, an
' outbuilding on a residential property on Spencer Road is located approximately 9 -10 feet above
the floodplain (701 -702 feet above sea level). A group of three buildings on a cul -de -sac off
Banner Whitehead Road is situated approximately 10 -15 feet above the floodplain (705 to 710
feet above sea level). Another residence and two outbuildings at the same cul -de -sac are 15-
20 feet above the floodplain. At the western (upstream) end of the study corridor, a building
to the north is situated approximately 12 -15 feet above the Edgar Branch floodplain.
Approximately 925 feet upstream of the Site, US 311 crosses Edgar Branch. The road
elevation at this crossing is 738, while the adjacent floodplain reaches 732 feet. The
projected inundation level during the 100 -year storm after construction of greentree
impoundments is 730 feet, with the normal winter pool level at 726 feet. A soil road at the
upstream end of the Site crosses Edgar Branch by means of a ford. This road would be
inundated by approximately 4 -6 feet of water during winter impoundment periods.
Lower and upper stream terraces form two primary physiographic landscape areas for
restoration planning purposes. Upper stream terraces will experience saturation due to the
proximity of open water and elevated water tables. Lower stream terraces will be actively
inundated. Stream levees, a feature often found in floodplains of dredged streams as well as
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in undisturbed drainages, are virtually absent at the Site. The primary variables utilized to
segregate landscape units include land slope, overbank flood frequencies (Section 4.2), and
the rate and direction of groundwater flow (Section 4.3).
The lower stream terrace physiographic area encompasses approximately 40 acres located
along both sides of the stream channel and open waters of Edgar Branch (Figure 4). This
terrace historically supported frequent overbank flooding (estimated at an approximate, 1 -year
return interval for hydraulic models) and was periodically re- worked by alluvial processes and
periodic, long term inundation /saturation. Dredging and incision along the stream has reduced
the frequency of overbank flooding within the primary floodplain from an estimated 1 -year
return interval to a 5 -year or more return interval, with some sections of the reach never
overtopping their banks (Section 4.3). Therefore, associated riverine 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.
During dredging programs along Edgar Branch, portions of the stream terraces appear to have
been converted for agricultural 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 riverine swamp forest in low -lying
areas (Schafale and Weakley 1990).
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
coverage. Refined soil mapping is depicted in Figure 5. Primary soil types include the
Chewacla series, Wehadkee series, Mecklenburg series, and Wynott -Enon complex.
Two nonhydric soil series occur on the steep, drier slopes of upper terraces, along the edges
of the project boundary. Mecklenburg clay loam (U /tic Hpa/uda/fs) consists of very deep, well
drained, eroded soils that have developed in residuum from mafic rock. The soils have a loamy
surface layer and a clayey subsoil with low permeability and high shrink -swell potential. The
seasonal high water table is below 6 feet. Wynott -Enon complex map units consist of an
intergrade of strongly sloping soils on uplands. Both Wynott (Typic Hapiudaifs) and Enon
(U /tic Hapiudaifs) soils are deep and well - drained. They formed on residuum from mafic rock,
have slow permeability and a high shrink -swell potential. Depth to the seasonal high water
table is greater than six feet. Mecklenburg and Wynott -Enon map units are not expected to
have supported wetlands historically.
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Chewacla (Fluva uentic D strochre P is ) loams encompass 41.9 acres of the 45.5-acre Site.
These soils occur on the flat historic floodplain of Edgar Branch. Chewacla soils are somewhat
poorly drained, nonhydric 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 deposition 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.
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 (Fluvaquentic 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. Under
existing conditions, the Wehadkee series comprises approximately 1.1 acres of the Site.
Important factors in the formation and maintenance of wetland systems as hydric 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, incision, 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.
3.3 PLANT COMMUNITIES
Plant communities are influenced by logging, grazing, and past conversion to agricultural lands.
Three primary communities have been identified for descriptive purposes, including 1) mesic
mixed hardwood forest, 2) shrub /scrub assemblage, and 3) crop land / pasture (Figure 6).
Mesic Mixed Hardwood Forest
Mesic mixed hardwood forest accounts for approximately 16.4 acres of the Site. This forest
assemblage occurs in a relatively continuous swath along the project corridor. The forest
canopy includes sweet gum (Liriodendron tulipifera), red maple (Acer rubrum), sycamore
(Platanus occidentalis), black walnut (Juglans nigra), green ash (Fraxinus pennsylvanica), tulip
poplar (Liriodendron tulipifera), redbud (Celtis laevigata), American elm (Ulmus americana),
black willow (Salix nigra), and hackberry (Celtis laevigata), and, in drier areas, eastern red
cedar (Juniperus virginiana) and hickory (Carya sp.). Under -story and shrub layer species
distribution is variable along hydrologic gradients and sunlight regimes, and includes horse
sugar (Symplocos tinctoria), ironwood (Carpinus caroliniana), hop- hornbeam virginiana),
elderberry (Sambucus canadensis), multiflora rose (Rosa multiflora), and Chinese privet
(Ligustrum sinense). Vines include muscadine grape (Vitis rotundifolia) and Japanese
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honeysuckle (Lonicera capon /ca), which becomes invasive in sunnier areas. The herb layer
includes speedwell (Veronica persica), common blue violet (Viola papi/ionacea) and jewelweed
(Impatiens capensis). Other herbs are bedstraw (Galium sp.), chickweed (Stellaria media),
dock (Rumex sp.), Indian strawberry (Duchesnea indica), bitter cress (Cardamine parviflora),
and Christmas fern (Polystichum acrostichoides). This community intergrades into dry -mesic
oak - hickory forest at higher elevations, outside of the project boundary.
Shrub /Scrub Assemblage
This plant community occurs as a distinct type only at the western end of the Site. In this
1.5 -acre area, shrub /scrub assemblage lines the banks of Edgar Branch as it winds through a
pasture. The thin, linear strips of this community contain both relict bottomland species and
early - successional, opportunistic species. The canopy layer consists of a few isolated
individuals of shagbark hickory (Carya ovata) and eastern red cedar. Among the shrub layer
are winged elm (Ulmus alata), black willow, sassafras (Sassafras albidum), Chinese privet, tag
alder (Alnus serrulata), and blackhaw (Viburnum prunifolium). The herb layer consists of
grasses and other species common to the surrounding pasture community, such as white
clover (Trifolium repens), buttercup (Ranunculus sp.) and common blue violet.
Crop Land / Pasture Land
Approximately 16.3 acres of the Site remains as active crop land and maintained pasture land.
Pasture land is dominated by a variety of grasses and herbs, including fescue (Festuca spp.).
Other characteristic volunteer species occurring in fields and pastures include buttercup,
goldenrod (Solidago sp.), dock (Rumex crispus), horse nettle (Solanum carolinense), wingstem
(Verbesina occidentalis), common blue violet, milkweed (Asclepias sp.), burdock (Arctium
minus), wild onion (Allium canadense), clovers (Trifolium spp.), thistles (Carduus spp.), and
henbit (Lamium purpureum).
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 dendritic 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. Erosion and
20
suspended sediment loads have been linked to nutrification problems within the Piedmont
hydrophysiographic province, including the Randleman Reservoir region (DWQ 2000).
Surface Water
The Site encompasses a 3930 -foot reach of Edgar Branch supporting a drainage area of 1.93
square miles. The valley slope measures approximately 0.007 rise /run, suggesting the
presence of a relatively flat valley floor relative to typical conditions in the Piedmont Province.
The lower valley slope may be due to the presence of geologic controls and a change in valley
orientation downstream from the Site. The floodplain ranges from 100 feet to 350 feet in
width along the length of the Site.
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.
Numerous upstream ponds may be partly responsible for incision of the stream channel. The
average existing bankfull depth of the channel is 3.6 feet, compared with 1.7 feet calculated
from the regional curves based on drainage area. In addition, the average, existing cross -
sectional area of the Edgar Branch channel measures approximately 89 square feet. According
to regional curves, a stable Edgar Branch channel is projected to support cross - sections of
approximately 27 square feet (assumes rural conditions) (Harman et a/. 1999, Rosgen 1996).
The incised channel supports a sinuosity (channel length /valley length) of 1.14. Substrate
within the channel is composed of unconsolidated sand, small gravel, and bedrock outcrops
exposed by incision and localized bank erosion. The channel is classified as an E4c (gravel
dominated channel) based on fluvial geomorphic features ( Rosgen 1996).
Stream discharge and flood elevations under existing and post - project conditions have been
predicted based on hydraulic models. Section 4.2 provides model predictions for the 5- and
100 -year storms, under existing conditions, and for the 5 -year storm after construction of
impoundments. Table 2 (Section 4.2) details flood elevations for the 5 -, 10 -, 25 -, 50, and
100 -year storm. The study suggests that overtopping of the streambanks occurs during the
5 -year storm in most areas of the Site. However, entrenchment of the stream channel likely
confines the 1- and 2 -year flows within the eroding banks, effectively bypassing floodplain
functions associated with pollutant removal and maintenance of wildlife habitat for overbank
flood dependent species. Evidence of recent flooding outside of the stream banks was
observed only in rare, isolated pockets during field surveys.
The hydraulic model further suggests that the existing soil road at the western end of the Site
is overtopped during the 5 -year storm with the roadway inundated along a 125 -foot to 150 -
foot reach. Post - construction flood elevations would extend the inundated roadway segment
21
to approximately 250 feet (Section 4.2). The existing crossing of Edgar Branch on this soil
road simply consists of a ford, with no culvert or bridge construction in place. Stream flow
across the road is shallow and braided. The crossing is undoubtedly a continuing source of
sedimentation in Edgar Branch downstream.
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 incised 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 Edgar Branch has
accelerated groundwater discharge to depths of greater than 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
Edgar Branch maintains a State best usage classification of WS -IV* (Stream Index No. 17 -9 -(1)
(DWQ 2000). Class WS -IV waters are protected as water supplies which are in moderate 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 substances. Local programs to control nonpoint
source and stormwater discharge of pollution are also required. 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 Randleman Reservoir.
The Site consists primarily of existing and former agricultural land, second - growth forest, and
scattered residential development. Fertilizers, pesticides, and nutrients associated with land
22
uses, including the golf course upstream of the Site, may currently influence water quality in
the vicinity.
Historically, the floodplain provided water quality benefits to the watershed associated with
Edgar 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. Particulate retention, removal of elements and compounds, and nutrient cycling
would be among these benefits.
3.6 JURISDICTIONAL AREAS
Jurisdictional areas are defined using the criteria set forth in the U.S. Army Corps of Engineers
Wetlands Delineation Manual (DOA 1987). Approximately 1.1 acres of jurisdictional wetlands
and 1.3 acres of open waters (in- stream habitat) were delineated on the Site on May 3 by ECS,
Ltd., and verified by the USACE. Figure 7 depicts the boundary locations of existing
jurisdictional systems. Wetland extent was most likely more extensive prior to stream
dredging and channel incision on the Site.
23
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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
hydroperiods 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
P 9
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.
'� 26
Stream restoration through natural channel design represents a viable option for this Site. If
applied, approximately 4500 linear feet of channel may 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.
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
27
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 o f a g r eentree impoundment across the Edgar
Branch floodplain represents the preferred option for this Site. The capacity to manage,
regulate flows, and regulate sediment transport/deposition rates at the Site outfall 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
a 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.
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.
Input for the HEC -1 model consisted of synthetic storm precipitation data, drainage area, NRCS
%
curve numbers, and drainage basin lag time. Table 2 summarizes 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
1' estimated using a planimeter. The NRCS curve numbers were estimated using methods
described in NRCS TR -55. The sub -basin lag times were estimated using Snyder's method.
28
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Because 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. Table 2 summarizes peak discharges estimated
by the validated HEC -1 model and the regional equations.
Hvdraulic Analvses
Water- surface elevations of the 5 -, 10 -, 25 -, 50 -, or 100 -year floods of Bob 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. Aerial photography was taken in April 1999. Roughness
coefficients (Manning's "n ") in the channels and on the overbank areas were taken from FEMA
studies previously conducted in the area and 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. The slope -area option
provided by the HEC -2 model was used to estimate the water surface elevation at the
beginning cross - section.
Model Results: Existing Conditions
Table 2 summarizes the water surface elevations for existing conditions. Figure 8 depicts
modeled flood elevations for the 5- and 100 -year, 24 -hour storm event. The model suggests
that Bob Branch overtops its banks on an interval as small as five years. Frequent overbank
flood events (1 -year return interval) have likely been effectively eliminated along the
entrenched channel under existing conditions.
Model Results: Projected Post Restoration Conditions
Several restoration alternatives were evaluated in the hydraulic model to determine the change
in flood elevations for various storm events. Modeled alternatives include in- stream weirs
located at systematic intervals within the entrenched channel. Twelve structural arrangements
were modeled, including cross -vane weirs spaced at up to 150 -foot intervals within the
channel. Channel cross - sectional areas were subsequently reduced along with profiles above
and below each structure. The structural arrangement was also modified to establish a pool
to pool spacing characteristic of natural channel design.
The selected alternative maximizes wetland restoration /creation area associated with the
design. In summary, a series of greentree impoundments is proposed beginning at a channel
elevation of 681 feet. The impoundment weirs will be designed to allow unrestricted channel
flows during periods of increased probability for large (tropical) storms. The series of weirs
30
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were modeled with top elevations of 684 to 726 feet. The results of the projected post -
restoration model are depicted in Table 2 and Figure 8.
Restoration methods are designed to reduce the channel from 5.5 feet in depth below the
floodplain to saturated / inundated conditions at the floodplain surface during the winter and
early portions of the growing season. The weir and associated water levels would be lowered
during the remaining portions of the year. The model assumes that the weirs will be left in
place during large storm events in the winter months. However, maintenance planning
recommends that weirs be lowered prior to large storms, if possible, to prevent damage to the
structures.
4.3 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
1 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 eta/. 1985; Fouss eta /. 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 al. (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 hydroperiods 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).
33
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 hydric (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 judged to have a
hydroperiod greater than 5 percent.
Post - Restoration Model Applications and Results
For groundwater wetland restoration, the primary objectives of this project include 1) reduce
channel incision along Edgar Branch and associated tributaries, 2) elevate the groundwater
gradient into the rooting zone for developing vegetation, and 3) establish 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 Edgar Branch channel will be reduced from an average of 5.5 feet under existing
conditions to gradients between 1 to 3 feet below the floodplain.
34
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 1,3
Wetland
of Influence
Wetland
Channel Invert /
(feet)
Criteria
(feet)
Criteria
Weir Height'
(Surface
Met
(Surface
Met
6
Hydropenods <5%
16/31
Hydropenods <
16/31
(feet)
of the growing
16/31
12 5% of the
16/31
season)
growing season)"
Forested Conditions
(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 % 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).
35
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 to 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
36
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the weir used at the Edgar Branch Site may be modified during the engineering design phase
to reduce flood potential, increase potential for stability, and /or other management concerns.
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).
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. 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.
41
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At Site 1 (Table 4), the forest canopy is dominated by green ash, (Importance value [IV] 28
percent), sweetgum (Liquidambarstyraciflua) (IV 19 percent), American elm (Ulmusamericana)
(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 (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
latifobum).
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 triloba), and shade tolerant canopy species.
Herbaceous species include Japanese honeysuckle (Lonicera japonica), 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 phellos), 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 cylindrical, sedges (Carex
spp), rushes (Juncus spp.), and lizard's tail (Saururus cernuus). Giant cane (Arundinaria
gigantea) is prevalent in scattered locations.
b
44
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TABLE 4
Reference Forest Ecosystem Plot Summary
Bottomland Forest (Canopy Species)
Tree Species
Number of
Individuals'
Relative
Density ( %)
Frequency ,
Relative Frequency
1 %)
Basal Area
(ft2/ acre)
Rely
Basa
1'
Fraxinus pennsylvanica
41
31
6
17
38.8
Liquidambar styraciflua
32
24
5
14
20.7
Ulmus americana
18
14
4
11
9.0
Acer negundo
8
6
3
9
8.7
Acer rubrum
11
8
2
6
8.5
Salix mgra
6
5
2
6
7.3
Ulmus alata
4
3
3
9
1.3
Betula mgra
2
2
2
6
0.7
Liriodendron tulipifera
3
2
2
6
2 2
Quercus michauxii
1
1
1
3
2.6
Quercus nigra
1
1
1
3
1.5
Celtis laevigata
3
2
1
3
1.8
Cornus florida
1
1
1
3
0.2
Platanus occidentalis
1
1
1
3
0.4
Prunus serotina
1
1
1
3
0.4
TOTALS
133
100
35
100
104
1
Summary of six - 0.1 -acre plots
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5.0 WETLAND RESTORATION PLAN
This restoration plan has been designed to establish wetlands within watersheds situated
immediately upstream of the Randleman Reservoir. A greentree impoundment is proposed to
establish contiguous wetland presence within 37.0 acres of Edgar Branch floodplain at
elevations ranging from 676 feet to 719 feet above mean sea level (Figure 15). The area of
wetland restoration is a subset of the area within the project boundary, which is defined as
the limits of the 5 -year, post - project flood elevation.
Wetland restoration or creation comprises approximately 30.7 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 5.4 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 0.9 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 winter months. 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
impoundments surrounding the reservoir will be managed according to constructs outlined in
the Greentree Reservoir Management Handbook (Fredrickson and Batema 1996).
47
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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 series of sixteen controllable
weirs and dams, 2) woody debris deposition, 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
A series of greentree impoundment structures consisting of 16 embankments will be
constructed within the Site, as depicted in Figure 15. The impoundment series begins just
within the conservation pool of Randleman Reservoir (682 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.
Embankment
The embankment series will be constructed with crest elevations ranging from 688 to 730 feet
above mean sea level. 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 four feet in elevation
above the existing floodplain surface.
Weir
The weir (outlet structure) will be designed to allow for open channel flow at base levels of
710 feet or below. The weir design will allow raising of the water surface to 714 feet during
impoundment periods. Figure 12 provides a conceptual depiction of the proposed
impoundment structure including target elevations for the winter water surface and
embankment height. The design or placement of these impoundments may be modified during
the engineering design phase based on potential stability, constructability, cost, or other
constraints.
5.2 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.
5.3 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.
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
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 toward areas immediately behind the
impoundment within the construction limits and along the stream channel banks (Figure 17).
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. A
total of 36.4 acres of the Site will be planted in a random distribution, including the species
listed below. Planted areas consist of restored /created wetlands and preserved /enhanced
wetlands, and do not include open waters.
Bottomland Hardwood / Swamp Forest
1.
Cherrybark Oak (Quercus pagoda)
2.
Overcup Oak (Quercus lyrata)
3.
Willow Oak (Quercus phellos)
4.
Swamp Chestnut Oak (Quercus michauxii)
5.
Swamp Cottonwood (Populus heterophylla)
6.
Shagbark Hickory (Carya ovata)
7.
Bitternut Hickory (Carya cordiformis)
8.
Green Ash (Fraxinus pennsylvanica)
9
American Elm (Ulmus americana)
10
Winged Elm (Ulmus alata)
11.
Tulip Poplar (Liriodendron tulipifera)
Scrub -Shrub / Swamp Forest
1.
Possum -haw (ilex 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 americana)
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 occidentalis)
12.
Elderberry (Sambucus canadensis)
51
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
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 Table 6.
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 (Figure 16). 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
20000 seedlings will be planted during wetland community restoration efforts.
1 52
TABLE 6
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)
5.4
19.4
11.6
36.4
SPECIES
# planted
(% total)
# planted
(% total)
# planted
(% total)
# planted
(% total)
River Birch
400 00)
400
Silky Dogwood
400 (10)
400
Button -bush
400 (10)
400
Elderberry
400 (10)
400
Black Willow
200 (5)
200
Possum -haw
200 (5)
200
Carolina Holly
200 (5)
200
American Sycamore
200 (5)
200
Swamp Cottonwood
400 (10)
1400 (10)
200 (10)
2000
American Elm
200 (5)
700 (5)
100 (5)
1000
Green Ash
400 (10)
700 (5)
100 (5)
1200
Swamp Chestnut Oak
200 (5)
1400 (10)
200 (10)
1800
Overcup Oak
400 (10)
1400 (10)
200 (10)
2000
Cherrybark Oak
1400 (10)
200 (10)
1600
Willow Oak
1400 (10)
200 (10)
1600
Shagbark Hickory
1400 (10)
200 (10)
1600
Bitternut Hickory
1400 (10)
200 (10)
1600
Winged Elm
1400 (10)
200 (10)
1600
Tulip Poplar
1400 (10)
200 (10)
1600
TOTAL
4000
14000
2000
20000
53
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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).
Nine groundwater monitoring gauges will be installed in restoration areas to provide
representative coverage throughout the Site. Approximate gauge locations are depicted in
Figure 17. 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, 1 1 -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.
6.3 SOIL
Mitigation activities are expected to increase the deposition and transport of stream sediments
during overbank flood events. As a result, soils (Fluvaquents) are continuously reworked by
fluvial processes. Because iron reduction rates (gleying) are not spatially or temporally uniform
56
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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
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.
59
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 stems 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 stems per acre total.
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.
61
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 impoundments will be installed at the designated locations. 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.
62
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 /obata) 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
Ipercent 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 jams 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
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.
63
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.
64
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.
65
10.0 WETLAND FUNCTIONAL EVALUATIONS
Mitigation activities at the Edgar 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 2.1- square mile, urbanizing
watershed.
Pro - active mitigation within the greentree impoundments is projected to provide approximately
30.7 acres of wetland restoration / creation and 5.4 acres of open waters with accreting
shoreline. An additional 0.9 acres of wetland and upland buffer preservation will be included
in the Site (37.0 -acre total) (Figure 17).
..,
11.0 REFERENCES
Baumer, 0. and J. Rice. 1988. Methods to predict soil input data for DRAINMOD ASAE Paper
No. 88 -2564. ASAE, St. Joseph, MI 49085.
Beets, C.P. 1992. The relation between the area of open water in bog remnants and storage
capacity with resulting guidelines for bog restoration. (in) Peatland Ecosystems and Man: An
Impact Assessment. (ed.) 0. M. Bragg, P. D. Hulme, H. A. P. Ingram, and R.A. Robertson.
International Peat Society. University of Dundee, Dundee, Scotland.
Belcher, H.W. and G.E. Merva. 1987. Results of DRAINMOD verification study for Zeigenfuss
soil and Michigan climate. ASAE Paper No. 87 -2554. ASAE, St. Joseph, MI 49085.
Brinson M.M., F.R. Hauer, L.C. Lee, W.L. Nutter, R.D. Smith, D. Whigham. 1995. Guidebook
for Application of Hydrogeomorphic Assessments to Riverine Wetlands. U.S. Army Corps of
Engineers Waterways Experiment Station. Vicksburg, MS.
Brinson, M.M. 1993a. Changes in the functioning of wetlands along environmental gradients.
Wetlands 13121: 65 -74, Special Issue, June 1993. The Society of Wetland Scientists.
Brinson M.M. 1993b. A Hydrogeomorphic Classification for Wetlands. Wetlands Research
Program Technical Report WRP -DE -4. U.S. Army Corps of Engineers Waterways Experiment
Station. Vicksburg, MS.
Brinson M., B. Swift, R. Plantico, J. Barclay. 1981. Riparian Ecosystems: Their ecology and
status. U.S. Fish and Wildlife Service FWS /OBS 81/17.
Brower, J.E., J.H. Zar, and C.N. von Ende. 1990. Field and Laboratory Methods for General
Ecology. William C. Brown Publishers, Debuque, IA.
Brown, Philip M., et a/. 1985. Geologic Map of North Carolina, North Carolina Department
of Natural Resources and Community Development, 1- .500,000 scale.
Chang, Howard H. 1988. Fluvial Processes in River Engineering. John Wiley & Sons.
Department of the Army (DOA). 1993. Corps of Engineers Wilmington District.
Compensatory Hardwood Mitigation Guidelines (12/8/93).
Department of the Army (DOA). 1987. Corps of Engineers Wetlands Delineation Manual.
Tech. Rpt. Y -87 -1. U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.
ti
y s,
ti
Division of Water Quality (DWQ). 1998. Classifications and Water Quality Standards
Assigned to the Waters of the Cape Fear River Basin, N.C. Department of Environment and
Natural Resources, Raleigh, N.C.
Division of Water Quality (DWQ). 2000 (draft). Cape Fear River Basinwide Water Quality
Plan. North Carolina Department of Environment and Natural Resources. Raleigh, N.C.
Division of Water Quality (DWQ). 1996. Water Quality Certification Administrative Code
Section: 15A NCAC 2H.0500 as amended October 1, 1996. North Carolina Department of
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