20160110 Ver 2_Drainage Revision Narrative (2016-06-20)_20160622

Division 5B — Year 2
WBS:I7BP.5.R.47
Bridge 910132 (Rogers Road)
Description of Original Drainage Design and Revised Drainage Design
Be�in Brid�e
June 20, 2016
Ori�inal Hydraulic Desi�n
Original design called to outfall road drainage to the left side ofthe road at structure 0405 into a ditch
that ran down to Smith Creek. During design it was discussed with NCDOT to try to discharge the system
on the right side of the roadway. However, there were multiple conflicts and working around these
conflicts would have required an atypical design. Conflicts included:
- Existing stormwater pond and spillway that treats water from Heritage Middle School from Station
19+56 to 20+46 -L-. Spillway for pond ends right at Buffer Zone 2. In addition, slope stakes were
revised to 1.5:1 and armored with rock plating to avoid filling into pond.
- Due to location of pond and spillway, the road storm drain system would have to be discharged
directly into the buffer.
- Conflict with sanitary sewer manhole and system at Station 20+20 -L-.
- Outfall on left side of the road allowed for water to outfall outside of Buffer Zone 2. No treatment
was able to be provided because the ditch required a rip rap lining due to the steepness of the
existing ground.
- Offset for ditch was pushed further out to avoid a high powered underground Wake EMC power
line.
Revised Hydraulic Desi�n
Revised design discharges water through a pipe into Buffer Zone 1 on the right side ofthe road. Pipe
has been designed flat (Structure 0403 has been designed as a 16.6' deep drop box). Pipe outfall is
located at the low point of an existing swale that serves as the connection ofthe stormwater pond to
Smith Creek. Rip rap embankment protection was added at the stream banks due to adding this outfall
and additional water. The existing swale was lined with rip rap from the pipe outfall up to the top of the
embankment protection to help protect the existing swale from erosion.
End Brid�e
Ori�inal Hydraulic Desi�n
- Took all road storm drainage to the right side of Rogers Road to outfall at structure 0501. Only
water that was discharged through the buffer on the left side of the road was from existing offsite
areas, which matched the existing drainage pattern. The water on the left side of the road consisted
of the re-established roadside ditch that runs in front of the Hope Lutheran Church from Station
22+50 to 25+50 -L-, water from the Hope Lutheran Church storm drain system (24" outfal I pipe
flowing through a detention pond and level spreader), and any overland flow that falls between the
tops of bank of Smith Creek and the level spreader (from Station 20+92 to 21+82 -L-). No additional
water from the project was taken to the left side of the road.

- Required capturing all water flowing towards the stream in a system in order to pipe under the
greenway alignments (G1 and G2).
- Utility conflicts had a major influence on the design. Utilities in the area include two underground
power lines, a water line, fiber optic line, telephone lines and pedestals; and a sanitary sewer line.
- The original design had to pick up the water from the 24" outfall pipe from Hope Lutheran Church
because the existi ng level spreader was to be impacted by the portion of the greenway to be
constructed by others. This system was tied to the system capturing the roadside ditch. They
converged i n a junction box that was placed offset to the north from the high voltage power I ine.
The outfall to the stream could not go to the south of the high voltage power line due to an
additional water line and power line conflict. The combined storm system was piped underthe G1
greenway and the outfall was stopped prior to the stream bank to flow into a ditch to help dissipate
the water prior to entering the stream.
Revised Hydraulic Desi�n
The revised design called to pi pe the 24" system from the Hope Lutheran Church al I the way to the
stream in order to reduce impacts to the mitigation site and reduce ROW. To stop the pipe prior to the
stream in a ditch section to allow for dissipation would require the ROW to remain as it currently was in
the original design due to impact from laying back the ditch slopes. The pipe outfall was kept at the
same stream location as the center of the original ditch. This was recommended by NCDOT as to place
the outfall point above the peak of the existing in stream rock vane. The pipe alignment was revised to
parallel the high voltage power line. This revised design eliminates crossing the high voltage power line
and provides enough offset to construct the proposed pipe without conflict.
Revised Sketch at Bridge

Revised Notes at Bridge
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