FLOOD00853

• Designation Number: 95
• County: Adams
• County: Arapahoe
• County: Douglas
• Community: Denver Metro Region
• Stream Name: Dry Gulch and Tributaries
• Title: FHAD - Dry Gulch and Tributaries, Lakewood, Denver, Denver County, CO
• Date: 11/1/1977
• Designation Date: 1/19/1978
• Floodplain - Doc Type: Floodplain Report/Masterplan

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7

of hydrologic computation" were selected for use in t,he Colorado

Urban Hydrograph Procedure (CUHP) as developed in Reference 1.

The CUHP was then used to compute hydrographs of the predicted

5-, 10-, 50-, and 100-year floods at each point. Table 2 pre-

sents the basin parameters and the computed peak flood flows.

The parameters in Table 2 represent each sub-basin or combination

of sub-basins, as indicated by the notes. Where two peak flood

flows are tabulated, the first is the flow computed from the

tabulated parameters; the second is the peak flow in the channel

determined by COmbining the computed flow with flows from other

sub-basins.

Samples of the computed hydrographs are shown in Figures 1 and

2. Figure 1 illustrates hydrographs computed along Dry Gulch

at various locations, showing the increase in time to the peak

flow as the flood moves downstream. Figure 2 shows the hydro-

graphs on Dry and North Dry Gulches at their confluence at Harlan

Street The hydro graphs are combined to form the composite hydro-

graph of flow downstream from the confluence. Also shown is

a single computed hydrograph at point D-16, which results .1::

a peak flow almost identical to that of the combined hydrographs.

This is justification for computing flows east of Harlan Street

by representing the entire tributary basin by a single set of

parameters.

verges again. Because of these characteristics, the hydrology

and hydraulics of the study are inter-related. Preliminary

hydrologic computations were performed, and then flood profiles
were determined as described in the following section. The water
surface data revealed the locations at which flow splits occurred,
and it then became necessary to estimate the flow rates of the
separated flow so that the hydrology could be revised. The new
flow rates were then used in the backwater computations, and
the new water surface elevations in some cases indicated a need

for further revision of the hydrology. The completion of this

iterative process is presented in Figures 3 and 4, which illus-

trate the inter-relationShip between the flows in the three channels

involved in the study. Presented in the following paragraphs are

generAl descriptions of the flow splits and routes.

The main channel of Dry Gulch begins near Simms Street and

Colfax, with flow reaching that intersection from the west and

north. A planned storm sewer running southerly on Simms to

Lakewood Gulch will divert a significant portion of the Dry

Gulch flow out of its basin. Since the storm sewer is under

contract at the writing of this report, it is regarded as an

existing facility and the flow in Dry Gulch is reduced by the

amount of this diversion. The resulting Dry Gulch flow is con-

sequently quite small at the upstream end of the basin.

The study area 1S characterized by several points at which flow

diverges, traverses distinctly different routes, and then con-