20051748 Ver 1_Erosion Evaluation 2_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)
FROM: Jens Geratz AU G 3 ZU07
DATE: December 21, 2006
bENk - VYiiTER :1i1.4LX'f
RE: Erosion Evaluation No. 2 (11-28-2006) wEnAND3 AND STOR!?ATER BRANCH 06-276
INTRODUCTION
The North Carolina Division of Water Quality (NCDWQ) 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, because the Smithfield weather station is outside the Little River
watershed, ESC believes using data from this source is not indicative of accurate 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 ofprecipitation
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
EcoScience Corporation
' Mr. George Howard, Restoration Systems, LLC
December 21, 2006
Page 2 of 5
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. 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 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 initiation threshold occurred on November 16th and the evaluation threshold occurred on
November 27th (Figure 1). An erosion evaluation was conducted within the former impounded
reaches of the Little River on November 28, 2006.
A nor'easter produced heavy rainfall over a large portion of eastern North Carolina on November
' 17th. As a result of the storm, the State Climate Office of NC Station 317994 (Smithfield, NC)
recorded almost an inch of rainfall (Figure 1). An additional 12.35 inches of rain were recorded at
the same station between November 8th and 23rd. The initiation threshold of 750 cfs occurred twice
' within the span of a week on November 16th and November 22nd (Figure 1). Two corresponding
evaluation thresholds of 500 cfs occurred on November 21St and November 27th (Figure 1). The
resulting events caused the USGS gauge at Princeton to register a peak discharge on November 17th
' and November 23rd of 1740 and 1930 cfs, respectively.
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 (SR1934) and the point of egress was the former Lowell Mill
Dam location (Figure 2). The team stopped at the mouth of the two credited tributaries as well as at
previously established observation points along the river. At each observation point photographs
were taken if significant changes had occurred since the first transit or to note continued stability of
certain stream features.

EcoScience Corporation
' Mr. George Howard, Restoration Systems, LLC
December 21, 2006
Page 3 of 5
River Observation Point 1
' River Observation Point 1 is located on the Little River within Horsehead Bend (Figure 2). At this
point on the Little River, the sediment deposition on vegetation was clearly observed at or above
bankfull height following the rise in storm flow. Numerous other areas along the canoe transit were
observed to have sediment deposition at a similar stage (Photo 1).
' River Observation Point 2
River Observation Point 2 is located on the Little River at the Wildlife Resource Commission boat
ramp (Figure 2). At this location sediment was observed to have been deposited approximately
' 15 feet up the ramp signifying the high water mark following the rise in storm flow (Photo 2).
River Observation Point 3
River Observation Point 3 is located on the Little River approximately 1000 feet downstream of the
Wildlife Resource Commission boat ramp (Figure 2). At this location during the last transit, a newly
formed logjam caused by a recent tree fall was creating an obstruction across the entire width of the
' Little River. Since the last transit, the log jam has been dislodged with minor woody debris
remaining near the banks (Photo 3).
River Observation Point 4
River Observation Point 4 is located approximately 600 feet below the US 301 bridge crossing
' (Figure 2). Battery Bar, named for the presence of discarded batteries, was formerly a large
depositional area constricting flow at this location. During the first transit, the sand bar was
observed to have been downsized significantly due to an increase in sediment transport capacity.
' The sand bar is continuing to erode as the channel is still in the process of reestablishing bankfull
dimensions at this location.
' River Observation Point 5
River Observation Point 5 is located on the Little River approximately 1100 feet below the CSX
Seaboard Rail crossing (Figure 2). At this location well established herbaceous vegetation was
' observed during the first transit 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. The vegetation is currently dormant but is still
visible and will continue to help stabilize the banks as it continues to grow next spring.
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 2). Formerly inundated banks remain stable
with dormant herbaceous vegetation. Conditions remain the same since the first transit.
EcoScience Corporation
Mr. George Howard, Restoration Systems, LLC
December 21, 2006
Page 4 of 5
River Observation Point 7
River Observation Point 7 is located on the Little River at the I-95 overpass (Figure 2). 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. The
vegetation is currently dormant but is still visible and will continue to help stabilize the banks as it
continues to grow next spring. The bridge piers located within the Little River contained only a
small amount of debris and no evidence of scouring was observed (Photo 4).
' River Observation Point 8
River Observation Point 8 is located approximately 300 feet upstream of the former dam site
(Figure 2). At this location a change in river dynamics was observed during the first transit as a
' result of a log jam break directly upstream of the former dam. In addition to the removal of large
woody debris, several feet of sediment and organic debris had been scoured from the river bank and
transported downstream. Some woody debris remains along the banks, however flow is no longer
impeded (Photo 5). Water levels were high during the current transit making it difficult to determine
if any additional scouring had occurred.
' 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 2). At this location, fluvial deposition continues to accumulate on the point
' bar that was constructed at the time of dam demolition. Volunteer herbaceous vegetation in addition
to the planted vegetation has established along the bar. Swift moving water was observed flowing in
' the center of the channel, with slack water present along the north bank, where the channel remains
over-widened. 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 6-7).
' SUMMARY
Conditions observed during the current transit are similar to conditions observed during the first
' transit. The formerly exposed banks of the Little River below the elevation of the former dam crest
pool are covered with dormant herbaceous vegetation and continue to appear stable. Exposed banks
along the channel were rarely observed, suggesting limited occurrences of bank failure or erosion.
' Erosion is restricted to channel bed and bank associated with channel adjustments in locations where
sediments have accumulated due to woody debris jams, low water slope, and high sediment input
locations near confluences with larger tributaries. After the occurrence of this second large storm
' event since the dam was removed, woody debris was less evident throughout the former
impoundment. Most of the large debris jams that were prevalent prior to dam removal have been
EcoScience Corporation
' Mr. George Howard, Restoration Systems, LLC
December 21, 2006
Page 5 of 5
dislodged. The bridge piers and abutments at the various bridge locations crossing the Little River
' held only a small amount of woody debris and continue to exhibit no visible evidence of scouring.

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LITTLE RIVER EROSION EVALUATION FIGURES

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LITTLE RIVER EROSION EVALUATION PHOTOS
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Photo 1. River Observation Point 1. Wrack and sediment on vegetation indicating
discharge at or above bankfull in Horsehead Bend. Little River, Johnston County.
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Photo 2. River Observation Point 2. Sediment deposition and high water mark (red
dashed line) at the Wildlife Resource Commission boat ramp. Little River, Johnston
County.
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Photo 3. River Observation Point 3. Previous logjam caused by recent tree fall has
been dislodged. Little River, Johnston County.
Photo 4. River Observation Point 7. The bridge pilings (I-95) located within the
Little River contained only a small amount of woody debris and no evidence of
scouring was observed. Little River, Johnston County.
Photo 5. River Observation Point 8. Since the first transit, there has been no
significant change. Water levels were higher then during the first transit making it
difficult to determine if any additional scouring had occurred. Little River, Johnston
County.
Photo 6. River Observation Point 9. Sediment deposition and elongation of the
constructed point bar continues along the inside bend of the river, site of the former
dam. Note the slack water along the north bank within this over-widened reach of
channel. Little River, Johnston County.
Photo 7. River Observation Point 9. Photo taken from the north bank, looking
south with slack water in the foreground. Note the swift moving water within the
outer bend of channel. Little River, Johnston County.