FLOOD10854 ‎(2)‎

• Designation Number: 590
• County: Denver
• Community: Denver
• Title: FIS - Denver - Volume 1
• Date: 11/17/2005
• Prepared For: Denver
• Prepared By: FEMA
• Floodplain - Doc Type: Current FEMA Regulatory Floodplain Information

Split flows were calculated along Harvard Gulch between South Downing Street and
South Logan Street. Due to the limited capacity of the box culvert between
South Downing and South Ogden Streets to carry the 1-percent-annual-chance flood,
flooding occurs overland to an old channel, through a detention pond, and rejoins
Harvard Gulch. These flows through Logan Park are referred to in this study as
Harvard Gulch Overflow.

Dry Gulch (Harvard Gulch Tributary) consists of two 43- by 68-inch."
reinforced-concrete pipe culverts along the entire study reach. l'hese culverts carry
only 250 cfs of the 1,330 cfs I-percent-annual-chance flood event. The remaining
floodwaters flow overland through a park area and continue down Pearl Street to the
confluence with Harvard Gulch.

Peak discharges for Goldsmith Gulch and Southmoor Park Tributary were
determined as part of the 1976 UDFCD Flood Hazard Area Delineation report
(Reference 15). The 10- and 1-percent-annual-chance discharges were computed
using the Colorado Urban Hydrograph Procedure (Reference 40). The 2- and
O.2-percent-annual-chance discharges were obtained by interpolation and
extrapolation of the frequency-discharge curve.

Southmoor Park serves as a detention pond to reduce flows along Southmoor Park
Tributary. Reduced flows are released through an intake pipe to a culvert located
under the detention pond and Hampden Avenue (State Highway 30).

Peak discharges for Sanderson Gulch and Weir Gulch were determined as part of the
1972 UDFCD Major Drainageway Planning report (Reference 41). The 10-, 2-, and
1-percent-annual-chance discharges were calculated using the Colorado Urban
Hydrograph Procedure (Reference 40) for fully developed basin conditions. The
O.2-percent-annual-chance discharge was extrapolated from the data.
Peak discharges on Weir Gulch downstream of Barnum Lake were revised to reflect
channel improvements at Barnum Lake and increased culvert capacity at
West 6th Avenue (U.S. I-lighway 6).

Peak discharges for First Avenue Tributary and Dakota Avenue Tributary were
determined as part of the 1977 UDFCD Flood Hazard Area Delineation report
(Reference 20). Those discharges were calculated in accordance with the Colorado
Urban Hydrograph Procedure (Reference 40) assuming fully developed basin
conditions. The subbasin hydro graphs were routed downstream. The PuIs Method
was used to calculate discharges at locations where storage had a significant effect.

Peak discharges for Sand Creek were determined as part of the 1977 UDFCD Flood
Hazard Area Delineation report (Reference 42). The hydrologic analysis was based
on the development of a surface runoff model of the Sand Creek basin using the
runoff block of the EPA Storm Water Management Model (Reference 37).
Discharge hydro graphs developed from the model were then routed along the main
stem of Sand Creek by use of an unsteady flow-routing procedure developed by
James A. Harder and modified by the Missouri River Division of the USACE.
Discharge probability relationships were developed by inserting

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