20090451 Ver 1_Stormwater Plans_20090309

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STORMWATER MANAGEMENT PLAN
R-240813, WBS No.: 34427.1.1 Date:03/03/09
Macon County
Hydraulics Project Manager: Andrew Nottingham, PE
ROADWAY DESCRIPTION
TIP Project U-2550B proposes to modify the existing interchange at the intersection of I-
40 and NCI 8 in Morganton. The project also proposes to continue the.multi-lane
widening ofNC18 (Sterling Street) completed under Tip project U-2550. NC 18 will be
widened to a four-lane,, concrete median divided facility. To accomplish this, the I-40
bridge over NC 18 will need to be reconstructed in order to provide adequate horizontal
clearance. An on-site detour and temporary structure will be constructed to maintain
traffic along I-40 during construction. The I-40 westbound off-ramp will be realigned in
order to accommodate the temporary onsite detour. The I-40 westbound on-ramp will be
realigned to tie into the current intersection of NC 18 and the I-40 westbound off-ramp.
Acceleration and deceleration lanes along I-40 will also be extended improving safety for
traffic entering and exiting the highway.
ENVIRONMENTAL DESCRIPTION AND IMPACTS
The project is located in the Catawba River Basin (HUC-03050101); Subbasin 03-08-31
and crosses East Prong Hunting Creek. Adjacent to the proposed improvements are two
perennial streams: an unnamed tributary to East Prong Hunting Creek (UT to East Prong
Hunting Creek) and an additional unnamed tributary (UTI). East Prong Hunting Creek
crosses under I-40 and then under NC 18 (Sterling St.) directly north of the interchange
through 10'x I V triple box culverts. UT to E. Prong Hunting Creek runs westwards
paralleling the I-40 eastbound lanes. It then crosses under I-40 through a 78-inch
diameter, 345-foot long steel pipe culvert. UT to E. Prong Hunting Creek then parallels
the I-40 westbound off-ramp and Bush Drive for approximately 835 feet before flowing
into East Prong Hunting Creek. UTl flows from a pond adjacent to Bush Drive and then
through a 350-foot long, 66-inch diameter steel pipe culvert before flowing into UT to E.
Prong Hunting Creek.
Impacts to East Prong Hunting Creek will involve extending the existing triple-barrel
culverts carrying the creek upstream (south) of I-40 and downstream (north) of NC18.
Also the two culverts under I-40 and NC18 will be connected to accommodate the
realigning of the westbound I-40 on-ramp with the westbound I-40 off-ramp. The total
?- --- length of new triple-barrel culvert is 250.9'. Upstream of I-40, the existing stream has
migrated eastwardly and has begun to undermine the eastern wing-wall. Approximately
63' of stream will be relocated to better align the stream to the culvert entrance.
Impacts to UT to E. Prong Creek will involve the relocation of 702' of stream and
extending the 78" pipe under I-40 on the upstream end of the reach, as well as the dual

U-2550BB SMP.
03/03/09
36" pipes on the downstream of the reach. The total length of pipe extensions for UT
East Prong Creek are 101.6'.
Impacts to UTI East Prong Creek include temporary impacts associated with re-lining the
existing 66" metal pipe under I-40 with a welded steel liner. The existing pipe length
will be retained.
Neither High Quality Waters (HQW), Water Supplies (WS-1 or WS-II), nor Outstanding
Resources Waters (ORW) occur within 1.0 mile of the project. The North Carolina
Wildlife Resources Commission (NCWRC) lists Burke County as a trout county. East
Prong Hunting Creek is not listed as a trout stream. There are no 303(d) streams within
one mile of the project.
BEST MANAGEMENT PRACTICES
Best Management Practices (BMPs) and measures used on the project are non-structural
and attempt to reduce storm water impacts to the receiving streams due to erosion and
runoff. NC 18 is a curb and gutter road with associated piped drainage systems. I-40 is
typically a shoulder-section road with a few areas of curbing in high fill locations and
some areas along the ramps at steeper grades. Where possible, the piped outlets will be
discharged into grassed roadside ditches prior to the receiving streams. Where warranted,
ditches will be armored with appropriately sized rip rap to provide erosion resistance.
Culverts were designed to protect stream stability and provide fish passage where
possible. In locations where the proposed alignment will be shifted from the current .
alignment, the existing pavement will be removed. The remaining areas will then be
replanted with vegetation. Natural stream design will be used in the stream relocation.
Stream Relocation
Ramp A station 14+45 to station 22+94 left side. 702 feet of natural stream
design proposed.
Culverts
-_ = --- ->--.:==-L- StationA8+1.4_left.to.21+24 right and -Yl- 46+50 left to 47+99 right: extend
and connect 3@10x1 I reinforced concrete box culverts.
- •-° . =-RPA= 14+45-1eft to =Y1'=36+73 right: extend existing 78" corrugated metal pipe.-