FLOOD04318

• Designation Number: 495
• County: Arapahoe
• Community: Cherry Hills Village
• Basin: South Platte
• Title: Flood Insurance Study - Arapahoe County, Colorado and Incorporated Areas, Cherry Hills Village - Volume 1
• Date: 3/1/1991
• Designation Date: 5/1/1999
• Floodplain - Doc Type: Floodplain Report/Masterplan

were computed using the USGS regional analysis outlined in Water
Supply Paper 1660 (Reference 36) for Region B, Area 10. The
relationship between flood magnitude and frequency, as portrayed in
the composite frequency curve in Water-Supply Paper 1660, was
extrapolated to give a ratio of lOa-year flood discharge to mean
annual discharge as the basis for the regional curve in Pigures 4,
5, 6, and 7. The streams whose hydrology was derived from this
regional analysis were the upper reaches of Piney Creek and Coal
Creek, Lone Tree Creek, Senac Creek, 1-05-4412 Creek, West Box
Elder creek, Box Elder Creek, Kiowa Creek, Wolf Creek, Comanche
Creek, Little Comanche Creek, West Bijou Creek, Middle Bijou Creek,
and Deer Trail Creek. This curve was used as a comparison for
synthetically generated hydrograph flows for each stream in the
study. Por some streams, the lOa-year flood discharge generated by
hydrograph methods is higher than the curve would indicate due to
the effects of recent urbanization.

The South Platte River peak di scharges for the 100- and SOO-year
floods below the dam were computed to reflect information on the
operation of Chatfield Dam. Por that reason, the South Platte
River does not match the USGS regional data.

Rainfall data for the synthetic hydrologic analyses was taken from
the UDPCD Urban Storm Drainage Criteria Manual (Reference 37).

Synthetic hydrograph procedures used in the study included the
Colorado Urban Hydrograph Procedure (CUHP), outlined in the UDPCD
Manual (Reference 37), and the COE HEC-l Flood Hydrograph Package
(Reference 38).

The SOO-year flood discharges for all detailed-study streams were
checked by straight-line extrapolation of frequencies previously
determined using the procedure of the USGS (References 27 and 36),
and compared to the COE Standard Project P100d data when available.

Hydrologic analyses included in the P100d Insurance Studies for the
incorporated communities of Aurora, Cherry Hills Village,
Littleton, and Sheridan were incorporated into the restudy in their
entirety with the exception of streams or portions of streams which
were superseded by more up-to-date information (References 2, 3,
and 5 through 9). '

In addition, hydrologic data from various engineering reports
(discussed in Section 7.0) were used extensively in the restudy of
Arapahoe County. The methods used in these reports include CUHP,
MITCAT, and Stormwater Management Model (References 10, 11, 12, 13,
14, 15, and 16).

Peak discharge-drainage area relationships for the streams studied
by detailed methods within Arapahoe County, except Spring Creek and
SJCD 6100, are shown in Table land Pigures 4, 5, 6, and 7.

12

~