FLOOD09594

• Designation Number: 63
• County: Adams
• County: Arapahoe
• County: Douglas
• Community: Denver Metro Region
• Stream Name: SJCD Basins 6200 North and South, 6100.5
• Basin: South Platte
• Title: Major Drainageway Planning - Volume I
• Date: 7/1/1976
• Designation Date: 11/17/1976
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Chapter 4
HYDROLOGY AND HYDRAULICS

Local flood hydrographs were developed for selected hydrologic
or pick-up points in each of the four basins. A flood hydro graph
measures total runoff, peak flow, and runoff distribution with
respect to time, the three most important parameters for
describing a flood event for a specific drainage basin. The
peak flow rate and runoff volume were determined for 2-year,
10-year, and 100-year storm frequencies.

As explained below in the "f1ydrology" section, each local
flood hydrograph was combined with the upstream flood hydrograph
and routed through upstream waterway crossings to allow for
flow backing up or impoundiAg at the crossings. The resulting
peak flow rate was used in ~he hydraulics analysis to determine
flood oepths and flood plaiA boundaries. This procedure is
discUS!iied in the "Hydraulic!>" section below.

The hyorographs are based oA each basin's existing level of
development and its total development as projected from the
planning maps of Arapahoe apd Jefferson Counties. Thus, the
flood bydrographs provide comparative data on existing land
use versus projected land u!iie ur.der the three flood frequencies.
Also, the results of the hyoraulics analysis, such as flood
water surface profiles and flood boundaries, are given for
both ezisting channel conditions and proposed channel improvements
based on a 100-year flood for a totally developeo basin.

HYDROLOGY

Each drainage basin was divided into subareas for study. The
subareas were determined from a field survey of tributary
collection points. The hydrologic or pick-up points associated
with each subarea are shown on Figure 3-2. Basin 6100 has
seven pick-up points (1-7 on Figure 3-2) and the North Tributary
to Basin 6200 has five pick-UP points (A-E on Fi~ure 3-2).

A single hydrograph was used for Direct Flow Basin 6100.5.
The pick-up point was at Platte Canyon Road and the culvert
250 feet north of Ken Caryl Road. A single hydrograph was
also set at the Platte Canyon Road crossing for the Downstream
Reach (Kiewit Area) of the Main Branch of Basin 6200. The
drainage area above this point is about 1,984 acres. The
hydrologic analyses for these two basins are discussed in
Chapters 7 and 8.

The local inflow flood hydrographs were developed from the
Colorado Urban Hydrograph Procedure (CUHP) as explained in
urban Storm Drainage Criteria Manual, March 1969, by Wright-
McLaughlin Engineers, distributed by the Urban Drainage and

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