20030909 Ver 1_Fax_20030929

SEP-29-2003 08 36
NCDOT
NATURAL STREAM DESIGN
NARRATIVE
June 5, 2000
919 250 4108 P.01%0
PROJECT: S.U492101 U-2524AB
COUNTY: Guilford County
LOCATION: Greensboro Westem Outer Loop from North of I-85 near
Groometown Road to North of High Pofnt Road.
PREPARED BY: McKim & Creed, P.A
5625 Dillard Drive
Cary, NC 27511
CHANNEL -L- 3a+00 to -L-37+00 Left
LOCATION:
PROJECT DESCRIPTION
The Greensboro Westem Outer Loop U-2524AB section is located in an urbanized
section of Greensboro. From station 34+00 to 37+00 the roadway is located petween
two neighborhoods and subsequently over an existing stream, which was classified as
jurisdictional by the NCOOT Planning and Environmental piviaion. This stream is being
relocated as much as possible to the south side of the roadway.
EKISTING STREAM
The Headwater of the stream is a storm sewer system that conveys stormwater runoff
from an apartment complex and roadway. At station 24+OD the existing stream has a
drainage aroa of 10.5 Ha (26 Acres), of which one hell is fully urbanized. At station
34+70 a 1200mm (48-inch) RCP discharges into the stream. This storm sewer conveys
stormwater runoff from 1D.9 Ma (27 Acres) of asingle-family residential subdivision.
The stream was looked at in two different sections, above and below the 1200 mm RCP.
The stream above the 1200mm RcP was entrenched. This stream has eroded to
accommodate the Increase in runoff due to development. This is evident by the vertioal
stream banks and undercut trees. The stream bed consisted of cobbles end the
meanders were relatively sharp. The stream was classified as C34 according to the
Rosgen stream olassifcation procedure.
The stream below the 1200mm RCP varied from entrenched to slightly entrenched. A
section of this stream between station 35+60 and 36+00 was stable. Below this stable
section the stream was similar to the stream upstream of the 1200mm RCP. The stream
was entrenched and the banks were eroding. The meanders end valley length were
larger in this section and the slope greater. This section of stream was classiled as G3
according to the Rosgen stream classification procedure.
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SEP-29-2003 08 37 NCDOT 919 250 4108 P.02i0c.
U-25~4A6
Natural Stream Design
Page 2 of 2
REFERENCE REACH
The section of stream between 35+60 and 38+QO was utlllzed as the reference reach for
the stream relocation. This section was slightly entrenched with a stable bed of cables
and stable banks. This section had a shallower maximum depth, and wider fl©odplain
width. This contribut®d to the stability of the stream because higher flows are not
constricted to a narrow section, thus reducing erosive velocities in the stream. This
section was classified as a E3 stream, according to the Rosgen classification procedure.
The stream was utlllzed as a reference reach because the other streams In the area with
similar drainage areas were all experiencing the same eroding conditions. This section
of stream was stable and similar to the downstream largor stream thstt was stable due to
shallawe,r stream banks and wider floadplain.
PRQPC?$E© STREAM
The stream relacatlQn had to be pertarmed an the south side of the roadway because of
the existing neighbafiaad on the north side. A 130 meter long 1350mm RCP wes
designed between station 35+00 end 38*20 because the natural topography of the area.
The natural ridge fn this area along with the existing neighborhood #o the south restricted
how much area could bB excavated to create the relocated floodplain.
Two different sections were designed, one upstream of the 1350 mm RCP and one
dt~wnstream. Both sections incorporated the same general principals to establlsn a
stable stream as reflected in the reference reach. Each section has a shallow bank full
channel (.3m and .46m) and flat overbanks 15 meters wide to allow the larger flows to
flood the averbanks and reduce the erosive velocities.
The stream was meandered to be consistent with the meander's measured in the field.
The upstream section had shorter valley lengths (15m) than the downstream section
(28m). The stream slopes generally matched the existing slopes and were controlled by
the existing elevations at the beginning and end of the relocated stream.
The outside stream bank of the meandering channel was protected with riprap tp prevent
erasion 0'f the channel bank. Willow stakes will be installed throughout the rip rap to
produce a vegetative cover. All other disturbed areas will be covered with local
vegetativn. ~

SEP-29-2003 08 37 NCDOT
919 250 4108 P.03•'0
ITEM Units EXISTING REFERENCE PROPOSED
STREAM STREAAA RELOCATION
Stream Narne Trib. To Reddidcs Trib. 7b RBddicks Cr. Tnb. To Reddicks Cr .
Drainage Araa DA Ha 10.53 21.4 10.53
Channel Slope {S m/m 0.012 0.012 0.012
Bankfull Width m 2.1 2.1 2.1
Channel Bottom Width m 1.2 1.2 0.9
t3ankfUll X-section Area (Ab m2 0.495 0.759 0.450
Mean Depth (c1bKt) m 0.296 0.881 0.214
Width/Depth Ratio 6.9 5.8 9.8
Moximum I]Qpth m 0.3 0.46 0.3
Wfth Flood-Prone Area rn S 1 b 15
Entrenchment Ratio 1.4 7.1 7.1
Channel Material: D50 mrn 100 100 100
Stream Len th m 15.2 15.2 15.2
Valle Len th m 14.9 14.9 14.9
Sinuosity (K) 1.02 1.D2 1.02
Moandors:
Avg. Length m 15 15 15
Avg Amplitude m 5 5 6
Avg. Radius m 4 4 4
Discha es:
QbankTull
cros
O.ZS
1
0.5
Q2 cros 0.5 1 0.5
Q10 cros 1 2 1
Velocity
Vbankfull rn/s 0.61 1.32 1.37
V2 rn/s 0.75 1.32 1.37
V10 m/s 0.91 1.62 1.44
Clesaificatioa D4 E3 E3
N.C. DEPT. OF TRANSPORTATION
QIVISION OF htIGWWAYS
-L- 34+20 to -L- 35+00
PROJECT: 8.U492101 (U-2524AB)
C3REENSBORO WESTERN OUTER LOOP
SHEET 1 OF 2

5EP-29-2003 08 37 NCDOT 919 250 4108 P.04i0c•

ITEM Units FaCISTING REFERENCE PROPOSED
STREAM STRF~IM1A RELOCaTIt]N
Stream Name Trib. To Reddicks Cr Trib. To Redddcs Cr. Trib. To Reddicks Cr.
DreinsAe Ares (DA) Ha 21.4 21.4 21.4
Channel Slo (~ m/m 0.0214 0.012 0.0178
Bankfull Wldth Icf) m 3 2.1 3.p4
Channel Bottom t m 1.5 1.2 1.2
Benkfull X-section Area Abkf) m2 2.025 0.759 0.975
Moon Do th db m 0.810 0.361 0.321
WidthlD th Ratio 3.3 S.8 9.6
M ximu , De th m 0.9 0.48 0.46
With Flood- Prone Area m 3 15 15
Entrenchment Ratio 1.p 7.1 4.9
Channel Material: D50 mm 100 100 100
Stream Len m 29 15.2 29
Valle Len th m 28 14.9 28
Sinuos (K) 1.p4 1.02 1.04
MQanders~
Av .Len th m 28 15 28
Av Am Iitude m 7 5 7
Av .Radius m 6 4 B
Discha as:
Obankfufl cros 1 1 1
Q2 cros 1 1 1
Q10 cros 2 2 2
Velo
Vbankfull m/s 1.p3 1.32 1.58
V2 mis 1.03 1.32 1.58
V10 mis 1.42 1.62 1.85
Claeslflcation G3 E3 E3
N.C. DEPT. OF TRANSPORTATION
-L- 36+20 to -L- 37+10 DIVISION OF HIGHWAYS
~~ 1
PROJECT: 8.U492101 (U-2524A8)
GREENSBORO WESTERN OUTER LOOP
SHEE'T' 2 OF 2

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