20190910 Ver 1_Const Notes for Stream Crossings_20190722

JOHNSTON COUNTY
SWIFT CREEK INTERCEPTOR & PUMP STATION
SWIFT CREEK & SIDE CHANNEL
CONSTRUCTION NOTES FOR THE SEWER CROSSINGS
FORD VEHICLE CROSSING AT LOW FLOWS
I 100 -year Flood Elevation b 1
A. Map Number 3720163700J
B. Flood Elevation = 189.8 ?
11. Channel Dimensions at Proposed Sewer Outfall Crossing 7
A. Dimensions based on survey dated April 2019
B. East Channel - Interceptor Station 52+00 ID
1. Side, natural by-pass, of the main Swift Creek +'o+eeeoaoi'j4•
2. Bottom Elev. = 175.2, Top of Bank Elev. = 183 to 184
3. Depth to top of Bank = 8 feet
4. Width at Top Bank to Bank = 48 feet
5. Width at Toe to Toe = 10 feet /28 feet @ 2.5 ft depth
6. Cross Section Area = 246 sq ft
7. Length from upstream fork in stream to crossing = 850 feet
8. Length from crossing to downstream West Channel = 150 feet
C. West Channel - Interceptor Station 60+60
1. The main channel for Swift Creek
2. Bottom Elev. = 176.8, Top of Bank Elev. = 184
3. Depth to top of Bank = 7 feet
4. Width at Top Bank to Bank = 56 feet
5. Width at Toe to Toe = 28 feet @ 2 ft depth
6. Cross Section Area = 260 sq ft
7. Length from upstream fork in stream to crossing = 640 feet
8. Length from crossing to downstream East Channel = 1,850 feet
D. Sanitary Sewer Interceptor
1. Length of sewer main between crossings = 850 feet
III Stream Crossings Required
A. East Channel
1. Open Cut - Gravity Sanitary Sewer in Casing
2. Vehicle Access
a. Low flow condition access
b. Temporary construction vehicle access - converted after construction to:
c. Permanent maintenance vehicle access
B. West Channel
1. Open Cut - Gravity Sanitary Sewer in Casing
IV. Means of Installation - East Channel
A. Protection of Aquatic Life
1. Two days prior to start of construction the crossing sight will be surveyed for aquatic life
and specifically mussels. The area will be surveyed 50 feet up and down stream of the
40 foot construction corridor.
2. Mussels located in the area will be relocated in accordance with the requirements of the
US Fish & Wildlife.
3. Two hours prior to the start of construction a final mussel survey will be made of the
crossing area. Mussels will be relocated as necessary immediately prior to the start of
construction.
B. Stream Dam for Flow Control
1. The construction crossing will be made at a low flow condition of the stream.
2. The bottom width channel is approximately 28 feet.
3. Coffer Dams: Large construction sand bags (3 ft x 3 ft x 3 ft) will be used to reduce the
center channel width to 10 feet at both the upstream and downstream easement lines.
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4. A minimum of two steel plates or sheet piles will be used to close the 10 foot opening
between the sand bags. In the event of a significant storm event the steel plates can be
pulled to allow the flow of water through the channel.
5. The upstream closure shall be installed first. This will allow a portion of the stream water
to drain naturally from the work area. A sump pit will be dug within the work area to allow
the pump out of the remaining stream water and to continue to dewater the work area as
necessary during construction. The dewatering pump will discharge through a silt / water
separation device, filter bag or settling tank, before discharge downstream of the work
area. Discharge shall be on an energy dissipater gravel pad.
C. Stream Water Pump Around
1. Channel Stream Closure
a. Since a natural by-pass channel is available, by-pass pumping of the stream flow
should not be necessary.
b. During a low stream flow condition the water in the east channel will back up to the
fork with Swift Creek.
c. Due to the close proximity of the work area to the West Channel water is expected to
back flow to the coffer dam.
d. A by-pass pump will be available at the site if it is necessary with a minimum capacity
of cfs.
e. The channel will be closed for approximately four (4) weeks for construction of the
sewer main across the east channel and to the east bank of the west channel.
D. Construction at the Crossings
1. Channel
a. Construction and maintenance vehicle access will be required across the channel.
b. The stream side banks will be graded back to 4HA V slope with a 10 ft width.
c. Construction Traffic Access
i. The entrance and exit slopes to the stream channel and the channel bottom will
be excavated down to allow for the below stone bedding.
ii. Stock pile the top 6 - 8 -inches of channel bottom material beyond the stream
bank for later replacement.
iii. Geotextile fabric shall be placed below the stone.
iv. 6 -inches of Class #57 Stone and 12 -inches of type Class B rip -rap shall be
placed down the slopes and across the channel. The top of the stone shall be
placed 12 -inches below the proposed finish grade of the slopes. Place stone to
within 6 -inches of the existing stream channel bottom.
V. During construction Class B rip rap will be added as necessary.
d. Install Sanitary Sewer Pipe
i. Install sewer pipe across East Channel and proceed to the West Channel in
accordance with plans.
ii. The work area between the channels shall be graded to original elevation and
seeded.
iii. After construction is completed to the West Channel, equipment and excess
material will be removed from the area between the channels.
e. Maintenance Traffic Access
i. Convert construction traffic crossing to permanent maintenance traffic crossing
ii. Channel Bottom: if necessary use Class B rip rap to bring material within 6 -
inches plus or minus of original channel bottom. Use the previously stock piled
channel bottom material to bring the crossing to the original channel bottom
grade.
iii. Entrance / Exit Slopes: Add #57 stone to bring slopes to within 8 -inches of the
design grades. Install 8 -inch articulated concrete block on top of the stone.
iv. Areas outside of the 10 foot vehicle access shall be seeded and covered with
erosion control matting.
2. Stream Dam Removal
a. Remove downstream dam.
i. Remove steel plates.
ii. Remove sand bags
iii. Grade stream banks to a consistent slope with upstream and downstream
conditions. Seed banks and cover with erosion control matting.
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b. Remove upstream dam in the same manner as downstream.
V Means of Installation - West Channel
A. Protection of Aquatic Life
1. Two days prior to start of construction the crossing sight will be surveyed for aquatic life
and specifically mussels. The area will be surveyed 50 feet up and down stream of the
40 foot construction corridor.
2. Mussels located in the area will be relocated in accordance with the requirements of the
US Fish & Wildlife.
3. Two hours prior to the start of construction a final mussel survey will be made of the
crossing area. Mussels will be relocated as necessary immediately prior to the start of
construction.
B. Stream Dam for Flow Control
1. The construction crossing will be made at a low flow condition of the stream.
2. The bottom width channel is approximately 28 feet.
3. Coffer Dams: Large construction sand bags (3 ft x 3 ft x 3 ft) will be used to reduce the
center channel width to 10 feet at both the upstream and downstream easement lines.
4. A minimum of two steel plates or sheet piles will be used to close the 10 foot opening
between the sand bags. In the event of a significant storm event the steel plates can be
pulled to allow the flow of water through the channel.
5. The upstream closure shall be installed first. This will allow a portion of the stream water
to drain naturally from the work area. A sump pit will be dug within the work area to allow
the pump out of the remaining stream water and to continue to dewater the work area as
necessary during construction. The dewatering pump will discharge through a silt / water
separation device; filter bag or settling tank, before discharge downstream of the work
area. Discharge shall be on an energy dissipater gravel pad.
C. Stream Water Pump Around
1. Channel Stream Closure
a. Since a natural by-pass channel is available, by-pass pumping of the total stream
flow should not be necessary.
b. Since there is approximately 1,850 feet of stream channel below the construction
area, a minimum flow release past construction dams will be necessary to maintain
the aquatic life during the construction.
c. One (1) 12 -inch DI pipe shall be installed from the upstream dam to the downstream
dam to maintain a minimum downstream flow.
d. A by-pass pump will be available at the site if it is necessary with a minimum capacity
of cfs.
e. The channel will be closed for approximately two (2) weeks for construction of the
sewer main across the west channel
D. Construction at the Crossings
1. Channel
a. Install Sanitary Sewer Pipe
i. Install sewer pipe across East Channel and proceed to the West Channel in
accordance with plans.
ii. The work area between the channels shall be graded to original elevation and
seeded.
iii. After construction is completed to the West Channel, equipment and excess
material will be removed from the area between the channels.
2. Stream Dam Removal
a. Remove downstream dam.
i. Remove steel plates.
ii. Remove sand bags
iii. Grade stream banks to a consistent slope with upstream and downstream
conditions. Seed banks and cover with erosion control matting.
b. Remove upstream dam in the same manner as downstream.
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