20150209 Ver 1_More Info Received_20150409

MEMO
To: Landon Davidson, PG
Zan Price, PE
MFLUENU
ENGINEERING
16 Broad Street
Asheville, NC 28801
828.255.5530
From: Andrew Bick, PE
Subject: Additional Information Date: April 9, 2015
Britton Creek Stabilization
DWR Project # 15 -0209
Hendersonville, NC
This memo responds to your request for additional information for the subject project.
After further investigation, we discovered that the City does not have a formal easement
along the sewer line. Per follow up discussions with DWR staff, it was determined that
the City as a public entity can apply for a NWP 13 on behalf of private property owners
because of their power of eminent domain. The attached plans have been modified to
include a note indicating that the contractor shall not disturb land beyond the currently
cleared path along the sewer line.
2. The attached stone toe detail has been updated to reflect the proposed height and slope of
the stone. The bank slope above the stone toe will be unchanged from the existing
conditions because there is not sufficient space to flatten the slope of the existing bank
without risking exposing the pipe.
3. The stone toe will be comprised of Class 1 riprap. The gradation for this riprap is as
follows:
We created a hydraulic model of the project reach and analyzed channel shear stresses for
discharges ranging from bankfull (1 to 2 year return interval) to the 100 -year return
interval storms. Our analyses are summarized below.
HECRAS Plan Plan 02 River: Briton Creek Reach. Reach-1 F--]
Minimum
Midrange
Maximum
Inches
5
10
17
mm
127
254
432
We created a hydraulic model of the project reach and analyzed channel shear stresses for
discharges ranging from bankfull (1 to 2 year return interval) to the 100 -year return
interval storms. Our analyses are summarized below.
HECRAS Plan Plan 02 River: Briton Creek Reach. Reach-1 F--]

Our model indicates that shear stress values in the downstream half of the project reach
where the stone toe is proposed range from 0.13 to 1.42 pounds per square foot. Since
the stone toe is planned in a straight reach, we do not believe an upward adjustment in
shear stress based on bend radius is necessary. With reference to Shields curve for
incipient motion (shown below), the grain diameter corresponding to the greatest
estimated shear stress ranges from 142 mm to 198 mm for the Shields data and Rosgen
data, respectively. This means that particles larger than this threshold size would be
stable according to this analysis method. Some of the smallest fraction of the Class 1
gradation might be mobile if exposed as single particles under the worst case discharge,
but the interlocking nature of the large and small particles would likely prevent these
smaller particles from being exposed as single stones. Based on our analyses, we believe
the stone toe will be stable through a range of discharges than can reasonably be expected
in the project reach.
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Critical Shear Stress (Ibslscl ft)
Closure
We trust that these responses and the attached revised plan sheets adequately address your
request, but please feel free to contact me if you have questions or if you need more information.
Page 2 of 2

EXISTING
ACTIVE SAN. SEWER
ABANDONED SAN. SEWER
TOP OF BANK
EDGE OF WATER
RAILROAD
TOPOGRAPHY (2' CONTOURS)
TREE LINE
TREE (> 18" DBH)
LEGEND
PROPOSED
SS SS 55 55 GEOLIFTS
BRUSH MATTRESS
— — — — — BANK SLOPING
- — — — — — — — — — STONE TOE
1 1 1 1 1 1
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LOG VANE
TEMP. STREAM CROSSING
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1.
DESIGN PROFILE FOLLOWS EXISTING STREAM THALWEG, WITH MINOR ALIGNMENT SHIFTS AS INDICATED ON PLANS.
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2.
ALL TREES, UTILITIES AND OTHER SITE FEATURES SHALL BE PROTECTED UNLESS MARKED FOR REMOVAL.
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3.
CONTRACTOR SHALL HAVE UTILITIES MARKED IN THE FIELD PRIOR TO STARTING CONSTRUCTION.
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4.
WORK MUST PROCEED IN ACCORDANCE WITH 401,404 AND FLOODPLAIN PERMIT CONDITIONS.
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5.
WORK SHALL BE STAGED SUCH THAT NO MORE CREEK BANK IS DISTURBED THAN CAN BE STABILIZED AT THE END OF
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6. EXCESS EXCAVATED MATERIAL MUST BE DISPOSED IN APPROVED UPLAND AREAS OR OFF -SITE.
7.
ALL EQUIPMENT SHALL BE CLEANED PRIOR TO MOBILIZATION AND SHALL BE MAINTAINED TO BE FREE OF LEAKS.
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8.
FUELING SHALL BE PERFORMED IN A CONTAINED AREA AT LEAST 200 FEET FROM FLOWING WATER.
9.
TREES AND LOGS REMOVED DURING GRADING SHALL BE SALVAGED FOR ON -SITE USE AS IN THE PROJECT UNLESS
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DIRECTED OTHERWISE. LOGS AND CLEARING DEBRIS NOT USEFUL TO THE PROJECT SHALL BE DISPOSED OFF - SITE.;
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10.
BRUSH MATERIALS SHALL BE INSTALLED DURING THE DORMANT SEASON, TYPICALLY DECEMBER THROUGH APRIL.
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11.
CONTRACTOR SHALL NOT BE PERMITTED TO CLEAR OR DISTURB LAND BEYOND THE EXISTING CLEARED LANE ALONG
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THE SEWER LINE.
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EXISTING
ACTIVE SAN. SEWER
ABANDONED SAN. SEWER
TOP OF BANK
EDGE OF WATER
RAILROAD
TOPOGRAPHY (2' CONTOURS)
TREE LINE
TREE (> 18" DBH)
LEGEND
PROPOSED
SS SS 55 55 GEOLIFTS
BRUSH MATTRESS
— — — — — BANK SLOPING
- — — — — — — — — — STONE TOE
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DATE: APRIL 2015
SCALE: AS SHOWN
NOTES
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SHEET 2 OF 7
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SHEET 2 OF 7

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NOTES:
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STREAM SIDE OF ALL STOCKPILES.
2. SILT FENCE SHALL BE REMOVED UPON
COMPLETION OF EARTHWORK.
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3. WHEN WORK IS COMPLETE, CLEAN MATS OF SOIL AND
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LIFT AND REMOVE MATS IN REVERSE ORDER FROM
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DATE:
APRIL 2015
SCALE:
AS SHOWN
DETAILS
SHEET 7 OF 7