20060310 Ver 1_Meeting Minutes_20020224

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SUBJECT: Draft Minutes of Interagency hydraulic design review meeting on Jan 24, 02
For U-3613 B &C, Pitt County j)
TEAM MEMBERS: Andrew Nottingham, NCDOT Hydraulics
Mike Bell, USACE-Washington
John Hennessy, NCDWQ
Tom McCartney, USFWS
David Cox, NCWRC
Alice Gordon, NCDOT - PD&EA
Marc Shown, NCDOT Hydraulics
To open the meeting Andrew gave a general overview of the project and distributed copies of the
Stormwater Management Plan. He stated that there are three (maybe four) crossings. The team decided to
look at the crossings and not go through the red line plans sheet by sheet.
The first crossing discussed was the western tributary to Fork Swamp. On the west side of the
crossing the stormwater is being treated with a grassed swale that is long enough to treat the entire drainage
area. Mike, John and David agreed with this design. On the eastern side of this crossing there was not
enough area to get a length of grassed swale to treat the entire drainage area. Andrew displayed two
hydrographs showing that the urbanized area and roadway runoff would peak before the off-site runoff
from the undeveloped area and therefore the grassed swale could treat the entire area. There was some
concern with this approach as to what would happen when the undeveloped area is developed. John
indicated that this approach had been discussed and that he needed to look at it and come up with a
formalized process for using the hydrographs. Andrew also presented the option of piping the urbanized
off-site runoff straight to the creek and treating the roadway and undeveloped off-site runoff with the
grassed swale. With this option the grassed swale is long enough to treat the entire area coming to it.
Mike, John and David indicated that it would be preferable to put all of the runoff through the swale.
The second crossing is at Fork Swamp. Andrew showed the original design that used two wet
detention ponds to treat the runoff. It was decided not to use this plan due to development of the area
where the ponds were proposed. On the east side of this crossing a grassed swale with enough length to
treat the runoff is proposed on both sides of the roadway. On the west side of this crossing the roadway
drainage will be treated with a grassed swale on the north side of the roadway. Off-site drainage on the
south side will be piped to the floodplain and dispersed using a preformed scour hole. Mike, David and
John agreed with this design.
The third crossing is questionable as to whether it is actually a stream. It is shown on the soils
map and John indicated that if it was on the map DWQ would need to look at it and make a determination.
If it is a stream additional measures will need to be taken. Hydraulics will investigate and report in the
next meeting.
The fourth crossing is at an eastern tributary to Fork Swamp. Andrew indicated that at this site it
is proposed to extend two pipe arches with the low flow directed through a single arch. He also explained
that the original plan had used level spreaders as BMW's but there was a problem with backing water up in
the systems and into adjacent yards. The revised design uses a grassed swale on the north side of the west
approach to treat all of the runoff and a preformed scour hole to treat the runoff from the east. John, David
and Mike agreed with this design. John brought up the possibility of doing some stream mitigation
upstream of this crossing.
In general it was questioned as to why use curb and gutter on this project when swales were
needed to treat the runoff. Curb and gutter is being used because it is typical of an urban thoroughfare and
it is needed with the presence of sidewalks.