FLOOD03140

• County: Denver
• Community: Aurora, Denver
• Stream Name: Westerly Creek
• Basin: South Platte
• Title: Flood Hazard Area Delineation
• Date: 1/1/1977
• Prepared For: Aurora, Denver
• Prepared By: UDFCD
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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6

particularly in the area of the East Colfax Avenue crossing

of Westerly Creek, interrupting traffic for periods of up to

3 hours. East Colfax Avenue (Rte. U.S. 40 and 287) is a

heavily travelled, major east-west thoroughfare. Flood flows

in this area (north of Lowry Air Force Base) for these storm

events were in the range of 300 to 600 cfs, well beyond the

capacity of existing drainage structures.

HYDROLOGY

Hydrologic analyses of the study area were carried out to

establish the peak discharge-frequency relationships for

floods of 2-, 10-, and 100-year recurrence intervals and

the Corps of Engineers' Standard Project Flood (SPF).

In the earlier years, from 1942 through the early 1960's,

flooding problems were confined to areas downstream of Lowry

Air Force Base. Since about the year 1965, flood events have

begun to occur in the upper watershed as a direct result of

the increasing density of development. In particular, frequent

flooding has begun to occur in the vicinity of the South Havana

Street-East Alameda Avenue intersection upstream of Lowry Air

Force Base. The flooding problems have been alleviated in the

area upstream of Highline Canal since the construction of

three detention ponds and concrete lined channel in this area.

The Colorado Urban Hydrograph Procedure, as outlined in

the Urban Storm Drainage Criteria Manual, was used to deter-

mine the peak discharges for 2-, 10-, and 100-year storms

for each drainage area. The "Standard Project Flood

Determination" (Corps of Engineers Publication EM 1110-2-1411)

was used to determine the Standard Project Flood.

Rainfall Data

The rainfall intensity was assumed to be the same in the

entire drainage basin. The rainfall depths for floods of

2-, 10-, and 100-year recurrence intervals were obtained

from Rainfall/Runoff Infonnation published by the Denver

Regional Council of Governments and Urban Drainage and Flood

Control District in May, 1972. The rainfall depth for the

SPF was derived from the Corps of Engineers publication

EM 1110-2-1411. Table 2 lists the rainfall depths for each

storm frequency for a 3-hour duration storm.