FLOOD10234

• Designation Number: 148
• County: Adams
• County: Arapahoe
• County: Douglas
• Community: Denver Metro Region
• Stream Name: Harvard Gulch, West Harvard Gulch & Dry Gulch
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Harvard Gulch, West Harvard Gulch and Dry Gulch
• Date: 12/1/1979
• Designation Date: 1/30/1980
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Above Logan Park, from Ogden Street to Downing Street, improvements
included a second box culvert. This culvert connects with a high
velocity concrete channel from Downing Street upstream to Race Street.
Above Race Street, improvements were made to the existing grass-
lined channels.

at a stream gaging station near Logan Street.
was approximately 1,600 cfs, and this flow was
within the drainageway improvements.

The hydrograph peak
completely confined

- FLOOD RELATED STUDIES -

In addition, since 1964 several storm sewer systems have been con-
structed in this basin. The most extensive system is along the
Dry Gulch tributary to Harvard Gulch where the storm sewer serves
to intercept nuisance flows that would otherwise flow through resi-
dential lots where this channel has been obliterated.

A detailed hydrologic investigation was completed for Harvard Gulch
as a part of the "Harvard Gulch Flood Control Project." This analy-
sis included a determination of frequency disCharges for the 2~-, 5-,
10-, 25-, 50-, and lOa-year recurrence interval flood events (Refer-
ence 3). The hydrology was recomputed for this study, however, using
the Colorado Urban Hydrograph Procedure (CUHP) (Reference 4) which
was developed for the Denver area subsequent to the "Harvard Gulch
Flood Control Project." The results of this analysis indicate fre-
quency discharges well in excess of those computed for the design
project.

In the West Harvard Gulch basin, the main drainageway improvement
is an underground conduit that extends from just above the Colorado and
Southern Railroad to Zuni Street. The conduit handles West Harvard
Gulch low flows, and an improved grasslined channel above these
culverts carries overflows during flood events.

- FLOOD HISTORY -

The CUHP method reflects the latest data gathered by the Urban Drain-
age and Flood Control District for predicting frequency discharges
in the Denver area. The District has reviewed and approved the hy-
drology presentEd herein.

Prior to 1965, Harvard Gulch experienced regular flooding due to
summer thunderstorms. Considerable encroachment of the floodplain
and channel occurred because of the lack of city zoning designed
to prevent such encroachment. The infringement on the channel
was so complete that the defined channel ended approximately one-
half mile from the South Platte River. Flood waters, searching
out a route to the river, flowed down South Broadway, an important
neighborhood business street (Reference 3).

- HYDROLOGIC AND HYDRAULIC DETERMINATIONS -

Hydrologic Analysis

A hydrologic analysis was completed to establish the peak discharge-
frequency relationships for floods or the la-year, 50-year and 100-
year recurrence intervals for Harvard Gulch, West Harvard Gulch and
Dry Gulch. The Colorado Urban Eydrograph Procedure (CUHP), as out-
lined in the Urban Storm Drainage Criteria Manual (Reference 4) was
the hydrologic mOdel used in analysis.

The Harvard Gulch Flood Control Project completed in 1966 was designed
for the la-year flood and has alleviated these nuisance problems.

The largest flood event since the completion of this project
occurred on June 8, 1969. Three gauges in this basin recorded
between 1.2 inches and 2.6 inches of rainfall in a one-hour
period. The runoff hydrograph for this event was recorded

The primary source of flood producing runoff in the Denver area
is the summer thunderstorm. The la-year and laO-year, I-hour, 6-
hour and 24-hour precipitation values were taken from the Rainfall

-3-