FLOOD03288

• County: Morgan
• Community: Wiggins
• Stream Name: Kiowa Creek
• Basin: South Platte
• Title: Kiowa Creek at Wiggins Flood Warning System
• Date: 9/1/1990
• Prepared For: Wiggins
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Floodplain Report/Masterplan

A-1 Hydrology Discussion

A-1.1 The Basin Model
The Beta Tes.t Version of HEC-1 (February 1990) for MS-DOS
compatible class microcomputers .ms u~;ed to develop a
rainfall-runoff and channel routing model for the Kiowa Creek
Basin. The unit hydrograph method, with Snyder's coeffi-
cients, was used in this application. The parameters Cp and
ct were obtained from the corps publication "Water and Land
Resources Management Study Vol. V Appendix H, 1977". The pa-
rameters, developed for that:: study, were based upon previous
Corps studies of the adjacent Cher:ry Cree!k Basin. Tp, for
each subbasin, was compute!d from ct and basin geometry.
Rainfall values were taken from Page 4 of Appendix F of the
"Wiggins 0 &M manual, 1989". Those values were checked
against the data listed in "NOAA Atlas 2 Vol. III, 1973".
Infiltration rates were based on the soil infiltration map;
"Missouri Basin Interagency Committee Gene!ralized Soil Infil-
tration Map, 1966". Subbasin infil1:raticm rates used ranged
from 0.7 to 2.5 inches per hour. According to the map, the
greatest infiltration rates occur in the lower portion of the
watershed, including Rock Cre!ek. Infiltration rates, in this
area, range from 2.0 to over 6.3 inches per hour. Infiltra-
tion rates of from 1.9 to 2..5 inches per hour were selected
for subbasins in, and bordering, this area and were used in
the model. The lowest infilt.ra.tion rates were given for the
portion of the basin upstream of Hiqhway 52. According to
the map, infiltration rat:E!S in this arE!a ranged from as
little as 0.05 inches per hour, Easi: of 1:he town of Kiowa up
to 6.3 inches per hour South of Kiowa. Average subbasin in-
fil tration rates sele!cted for this r'~gion ranged from 0.68 to
0.91 inches per hour.

A-1.2 Calibration
Since the peak discharges (It: Wiggins were set by the CWCB,
the HEC-1 model was calibrated to those quantities.
Calibration was accomplished by varying infiltration rates
within limits set by the infiltration map. The discharge
values provided by t:he CWCB were developed by FEMA and were
published on Page 5 of the "wiggins I) & M Manual, 1989".
It was not possible to match both 'the discharges given for
Wiggins and .those given for Highway 52. In the report pro-
vided by the CWCB, peak discharges at Wiggins were always
higher than those at Highway :;2, Using the HEC-l model, at-
tenuation in the lower basin resulted in peak discharges that
were actually lower at Wiggins than at Hiqhway 52. The at-
tenuation in flood peaks, est:imated with the HEC-1 model are
listed in Table A-l as follmvs:

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