FLOOD02072

• County: Logan
• Community: Logan County
• Stream Name: Pawnee Creek
• Title: Floodplain Management Study
• Date: 4/1/1992
• Prepared For: Logan County
• Prepared By: USDA Soil Conservation Service
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Hydraulic analyses conducted in this study were done using u.s.
Army Corp of Engineers computer model HEe2. The general land
slope in the study reach is less than 1 percent, therefore
backwater effects from roads, bridges, ete are very significant.
In some cases HEe2 was used to develop discharge-elevation rating
tables for use in TR20. Water surface profiles were computed for
three general reaches.

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Reach number one includes a profile of Pawnee Creek from the
South Platte River upstream through the Burlington Northern
Railroad and U.S. Highway 6 bridges, then continuing on through
County Road 33 and 31.

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A considerable out of bank division of flow occurs between County
Road 31 and the Pawnee DitCh crossing. The Pawnee Creek channel
at this location has a very limited carrying capacity. A portion
of the out-of-bank flow moves toward the southeast to the
vicinity of Atwood. water surface profiles were not computed for
this out-of-bank segment of flow, except along U.S. Highway 6
between Atwood and the main channel, because of the lack of
topographic data.
A significant out-of-bank division of flow also occurs just below
County Road 33. The out-ot-bank flow at this location moves
overland away from the main channel towards the northeast and
eventually to the vicinity of the Riverside Cemetery. Water
surface profiles were not computed for this segment of flow
because of the unpredictable meandering flow pattern through
farmland; however, a probable flow path was sketched on the flood
plain Il'.aps.

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Alluvial fan type topography exists along Pawnee Creek
immediately below U.S. Highway 6 and the railroad. The flow
here divides three ways: the main channel, left overbank, and
right OVerbank. Only a profile along the main channel is shown
in the included flood profiles. Backwater computations were
~ade, however, for the overbank tlow segments for purposes of
defining the flood boundaries on included flood plain maps. '

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A ~cco~d rcac~ includc~ ~ ~~ort cc~c~t of flew ~long thc
railroad and U.S. Highway 6 between the main Pawnee Creek channel
and the town of Atwood. The source of this flow is from out-of-
bank conditions at the upper end of reach one, discussed
previously. A major part of this segment of flow will overflow
the highway and railroad near AtWOOd with the residual moving on
to the main Channel at U.S. Highway 6.
the third reach is a profile along U.S. Highway 6 and the
railroad from the Riverside Cc~etery upstream to the bridges or.
Pa\lll1ee Creek.

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