20051748 Ver 1_Erosion Evaluation 1_20070803

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' EcoScience Corporation
1101 Haynes Street, Suite 101
Raleigh, North Carolina 919-828-3433
EcoScience
MEMORANDUM
TO: George Howard,
Restoration Systems, LLC RS tag
FROM: Jens Geratz AU6 3 2001
' DATE: June 30, 2006 pERH - WATER QUALITY
WETLANDS AND s70R! U7ER BRANCH
RE: Erosion Evaluation No. 1 (6-20-2006) 06-276
INTRODUCTION
' The North Carolina Division of Water Quality (NCDW
Q) Section 401 permit condition #8 associated with the
' Lowell Mill Dam - Little River Watershed Restoration Site requires that a "survey [of] the present lake bed
and its flooded tributaries [shall occur] at least every two weeks (bi-weekly) or within three days of a rain
more than or equal to one inch at Princeton, NC." Modifications to the permit condition described above are
' proposed. The text below describes the reason behind the modification and proposed methodology to satisfy,
in spirit, the permit condition set forth in the permit.
' The permit condition requested by NCDWQ presents several logistical difficulties. First, only a USGS river
gauge is present near Princeton. No publicly available or trustworthy real-time weather data are available in or
around Princeton, NC. The nearest weather station to Princeton is located in Smithfield, NC. Second, ESC
believes that using rainfall from one weather station from within the 215-square mile watershed is not properly
indicative of increased river stage conditions within the former impoundment. Thus, ESC has investigated and
developed a new method for determining when a field evaluation should be performed.
In preparation of the erosion evaluation, EcoScience Corporation (ESC) collected three years of continuous
daily precipitation and river stage data from 1990 through 1993. The data showed that a one inch rainfall
' event is a relatively commonplace weather occurrence. If the permit condition #8 remains as stated, then more
than 33 field evaluations (>10 per year) would have been required during the period for which ESC collected
the correlated rain/river stage data. It is important to note that one inch rain events do not appear to have a
' corresponding rise in river stage. Since the perceived purpose of the NCDWQ permit condition is to evaluate
the former impoundment after increased river stage to monitor for erosion, then a one inch rainfall event is not
the best indicator for the initiation of a site evaluation. Isolated thunderstorms can produce large amounts of
' precipitation in a localized area, without contributing significant rain to the overall watershed. To monitor
multiple weather stations in real-time throughout the watershed to identify a regional precipitation event is
' time consuming and not practicable. Alternatively, ESC proposes to use the correlation between large,
regional rain events that cause more than a 750 cubic feet per second (cfs) reading at the Princeton gauging
station (USGS 02088500) to be the "initiation threshold" for a field evaluation. ESC estimates that this
' initiation threshold will occur after a river stage rise equal to approximately 30 percent of bankfull.

EcoScience Corporation
Mr. George Howard, Restoration Systems, LLC
June 29, 2006
Page 2 of 5
Once the initiation threshold for evaluation has been exceeded, ESC proposes that we monitor the river stage
until the river falls below 500 cfs, which is proposed as an "evaluation threshold" river stage. Once the river
stage falls below the evaluation threshold, ESC personnel will perform an erosion evaluation within a 72 hour
period. Using the initiation and evaluation thresholds for the field effort will facilitate ESC personnel in
t reviewing the former impoundment under the safest and most data productive periods after a substantial rise in
river stage.
In order to satisfy the modified permit condition #8, RS has authorized EcoScience Corporation (ESC) to
conduct weather related erosion evaluation within the former Lowell Mill Dam Impoundment (ESC Proposal
P06-004 January 19, 2006). The purpose of the evaluation is to document any evidence of erosion within the
' former dam impoundment including but not limited to bank failure, loss of stream bank trees, severe head-
cuts, and the loss or gain of large depositional features.
' The remnants of Alberto, the season's first tropical storm unleashed heavy rain over a large area of central
North Carolina on June 13, 2006 (Figure 1). The National Weather Service recorded 7.6 inches of rain at its
' Raleigh office with as much as 8 inches of rain recorded along the storm's path (Figure 2). Included in the
storms path was the upper watershed of the Little River including Wake, Franklin, and Johnston counties. The
resulting event caused the USGS gauge at Princeton to register a peak discharge on June 18, 2006 of
' 2370 cubic feet per second (cfs) (Figure 3). The initiation threshold occurred on June 14`h and the evaluation
threshold occurred on June 20`h. An erosion evaluation was conducted within the former impounded reaches
of the Little River on June 20, 2006.
LITTLE RIVER EROSION EVALUATION
' A two-person team performed a 7-mile canoe transit of the Little River. The point of ingress was the bridge
crossing at Old Beulah Road (SRI 934) and the point of egress was the former Lowell Mill Dam location
' (Figure 4). The team stopped at the mouth of all credited tributaries as well as at points along the river where
notable conditions occurred. At each observation point, GPS data was collected for the location, photographs
' were taken, and notes where recorded to describe the condition.
River Observation Point 1
River Observation Point 1 is located on the Little River within Horsehead Bend (Figure 4). At this point on
the Little River, the sediment deposition on vegetation is clearly observed at or near bankfull height following
the rise in storm flow. Numerous other areas along the canoe transit were observed to have sediment
deposition at a similar height (Photo 1).
River Observation Point 2
River Observation Point 2 is located on the Little River at the Wildlife Resource Commission boat ramp
(Figure 4). At this location sediment was observed to have been deposited approximately 5 feet up the ramp
signifying the high water mark following the rise in storm flow (Photo 2).
EcoScience Corporation
Mr. George Howard, Restoration Systems, LLC
June 29, 2006
Page 3 of 5
River Observation Point 3
River Observation Point 3 is located on the Little River approximately 1,000 feet downstream of the Wildlife
Resource Commission boat ramp (Figure 4). At this location a newly formed logjam caused by a recent tree
fall created an obstruction across the entire length of the Little River. The tree was most likely uprooted due to
instability as a result of it's location on the river bank. Additional woody debris and floating particulate has
begun to collect behind the fallen tree (Photos 3-4).
' River Observation Point 4
River Observation Point 4 is located on the Little River approximately 600 feet below the US 301 bridge
crossing (Figure 4). Battery Bar, named for the presence of discarded batteries, was formerly a large
depositional area constricting flow at this location. Following the rise in storm flow the sand bar was observed
to have been downsized significantly due to an increase in sediment transport capacity. The channel is
currently reestablishing bankfull dimensions at this location (Photos 5-8).
River Observation Point 5
River Observation Point 5 is located on the Little River approximately 1,100 feet below the CSX Seaboard
Rail crossing (Figure 4). At this location well established herbaceous vegetation was observed along both
banks of the river below the elevation of the former dam crest pool. The establishment of herbaceous
vegetation aids in stabilizing the banks and preventing loss of bank material following the rise in storm flow
(Photo 9).
River Observation Point 6
River Observation Point 6 is located on the Little River approximately half way between the CSX Seaboard
Rail crossing and the I-95 overpass (Figure 4). At this location well established herbaceous vegetation was
observed along both banks of the river below the elevation of the former dam crest pool. The establishment of
herbaceous vegetation aids in stabilizing the banks and preventing loss of bank material following the rise in
storm flow (Photo 10).
River Observation Point 7
' River Observation Point 7 is located on the Little River at the I-95 overpass (Figure 4). At this location well
established herbaceous vegetation was observed along both banks of the river below the elevation of the
former dam crest pool. Within the NCDOT right-of-way the vegetation has been mowed. The establishment
' of herbaceous vegetation aids in stabilizing the banks and preventing loss of bank material following the rise
in storm flow. The bridge piers located within the Little River contained only a small amount of debris and no
evidence of scouring was observed (Photos 11-12).
' River Observation Point 8
River Observation Point 8 is located approximately 300 feet upstream of the former dam site (Figure 4). At
this location a change in river dynamic was observed as a result of a logjam break directly upstream of the
former dam. Several feet of sediment and organic debris was scoured from the river bank and transported
downstream. Additional scouring of the river bank may occur until herbaceous vegetation is able to
' reestablish (Photos 13-14).
EcoScience Corporation
Mr. George Howard, Restoration Systems, LLC
June 29, 2006
Page 4of5
River Observation Point 9
River Observation Point 9 is located along the inside bend (north bank) of the Little River at the former dam
site (Figure 4). At this location fluvial deposition has accumulated on the point bar constructed at the time of
dam demolition. Herbaceous vegetation in addition to the planted vegetation has begun to establish along the
' bar. Swift moving water was observed flowing only in the center of the channel, with slack water present at
the over widened reach along the north bank. Additional sediment is expected to continue to deposit along the
point bar as the Little River narrows to a width and depth consistent with bankfull dimensions. Toe of slope
' protection and vegetation along the south embankment of the former dam site was intact following the rise in
storm flow (Photos 15-18).
SUMMARY
' The remnants of tropical storm Alberto which triggered this erosion evaluation caused the USGS gauge at
Princeton to register a peak discharge on June 18, 2006 of 2370 cubic feet per second (cfs). This is the largest
discharge event recorded at the Princeton gauge since August 14, 2003. The formerly exposed banks of the
Little River below the elevation of the former dam crest pool have established rapidly with herbaceous
vegetation. Bare sediment along the banks was rarely observed, suggesting limited occurrences of sediment
erosion. Sediment erosion is restricted to channel bank and bed associated with channel adjustments in
' locations where sediments have accumulated due to woody debris jams, low water slope, or high sediment
input locations near confluences with larger tributaries. Woody debris was less evident throughout the former
impoundment. Most of the large debris jams, so prevalent prior to dam removal, have been dislodged. As
' should be expected several new log jams have developed resulting from floating debris and downed trees from
adjacent banks. Tree fall from adjacent banks over normal occurrences may be expected in the near term as
trees and soils adjacent to the channel experience increased stress. The bridge piers and abutments of the
' various bridge locations crossing the Little River contained only a small amount of debris and exhibited no
visible evidence of scouring.
LITTLE RIVER EROSION EVALUATION FIGURES
0 - 25 50 mi.
Little River Watershed
Dwn. by:

EcoScience
ALBERTO PRECIPITATION EVENT JWG
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Lowell Mill Dam Restoration Site JWG
Date:
JUN 2006
I? Raleigh, North Carolina Johnston County, North Carolina Project
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Source: National Weather Service
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Erosion Evaluation (6-20-2006) Date: Jun 2006 3
Raleigh, North Carolina Johnston County, North Carolina Project:
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LITTLE RIVER EROSION EVALUATION PHOTOS
Photo 1. River Observation Point 1. Sediment deposition on vegetation
indicating discharge at or near bankfull in Horsehead Bend.
Little River, Johnston County.
Photo 2. River Observation Point 2. Sediment deposition and high water
mark at the Wildlife Resource Commission boat ramp.
Little River, Johnston County.
Photo 3. River Observation Point 3. Newly formed logjam caused by recent
tree fall. Little River, Johnston County.
Photo 4. River Observation Point 3. Newly formed logjam looking
upstream. Little River, Johnston County.
Photo 6. River Observation Point 4. The remains of Battery Bar located
approximately 600 feet below US 301 crossing, looking downstream.
Little River, Johnston County.
Photo 5. River Observation Point 4. Change in sediment transport capacity
has caused the removal of a large section of Battery Bar, formerly
a large depositional area constricting flow. Little River, Johnston
County.
Photo 7. River Observation Point 4. Establishing GPS coordinates at Battery
Bar, named for the discarded batteries found at this location.
Batteries visible in foreground. Little River, Johnston County.
Photo 8. River Observation Point 4. Reestablishment of channel dimensions
at Battery Bar, looking upstream toward CSX Seaboard bridge
viewed in background. Little River, Johnston County.
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Photo 9. River Observation Point 5. Well established herbaceous vegetation
along the banks of the river below the elevation of the former dam
crest pool. Note the elevation of adventitious roots at former water line.
Little River, Johnston County.
Photo 10. River Observation Point 6. Herbaceous vegetation establishment
along both banks of the river, within the former Site Impoundment.
Little River, Johnston County.
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Photo 12. River Observation Point 7. Photo looking upstream at the I-95 overpass.
Note: No evidence of scouring and only a small amount of debris among
the bridge piers. Little River, Johnston County.
Photo 11. River Observation Point 7. Well established herbaceous vegetation
along the north banks of the river at the I-95 overpass. Note the
vegetation in the NCDOT right-of-way has been mowed.
Little River, Johnston County.
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Photo 13. River Observation Point 8. Change in river dynamics as evidenced
by log jam break directly upstream of the former dam. Little River,
Johnston County.
Photo 14. River Observation Point 8. Removal and transport of several feet
of sediment and organic debris from logjam. Little River, Johnston
County.

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Photo 16. River Observation Point 9. Sediment deposition and elongation
of the constructed point bar located at the inside bend of the river
at the former dam site. Note the slack water at the over widened
reach of river at the toe of the remnant dam structure (center).
Little River, Johnston County.
Photo 15. River Observation Point 9. Sediment deposition and vegetation
establishment within the constructed point bar along the inside bend
of the river at the former dam site. Note swift moving water in center
of channel. Little River, Johnston County.
Photo 17. River Observation Point 9. Toe of slope protection along the south
embankment, former location of the dam's south abutment and mill
works. Little River, Johnston County.
Photo 18. River Observation Point 9. Photo taken from the remnant dam
structure (north bank) looking south at the toe protection placed at the
former location of the dam's south abutment and mill works.
Little River, Johnston County.