FLOOD10164

• County: Arapahoe
• Community: Littleton
• Stream Name: Slaughterhouse Gulch
• Basin: South Platte
• Title: Major Drainageway Planning
• Date: 4/1/1974
• Prepared For: Littleton, DRCG, DHUD
• Prepared By: Frasier & Gingery, Inc.
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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D. HYDROGRAPHS

As mentioned above, design storm hydro graphs were computed at
each of the design points for the four storm frequencies under
consideration, and for a projected, total basin development
condition. Prior to calculating the storm hydrographs at
each of the design points, storm hydrographs were calculated
for each of the design points, storm hydrographs were calculated
for each of the subbasins. Next, each reach was evaluated
for the approximate flow times through the reach. This was
done utilizing the 1" = 50' scale mapping prepared specifically
for the project. To compute the peak flows at the design
points, it was necessary to compute the storm hydrograph for
each of the basins and then lag the hydrograph from the upper
basin through the basin under consideration and add it to the
storm hydrograph at the design point. At Powers Park, the storm
hydrograph was routed through the pond and lagged downstream
to the next design point. The hydrograph is then added to the
storm hydro graph at that point. Because of the complexity of
this procedure and due to the number of hydro graphs which have
to be considered in an analysis of this type, the total process
of computing the storm hydrograph, routing, lagging and adding
to the downstream design point has been computerized to operate
on an IBM 1130 computer using disc storage.

In the upper part of the basin, upstream of the study reach,
where the Highline Canal crosses the gulch, the assumption was
made that the canal intercepts the tributary runoff for storm
events up to the 2-year frequency. Storm frequencies greater
than the 2-year were assumed to pass through the canal crossing
without any hydrologic affect. These assumptions are logical
and appropriate. Normal canal flows are much below ditch
capacity. Even though other areas are tributary to the canal
ditch spill structures presently exist on Big Dry Creek to the
north and Lee Gulch to the south, relieving the canal of unde-
sired flood waters.

At present, it is possible that storm water runoff generated by
storms of a frequency less than the 2-year (3, 5 and possibly
the 10-year) event will be intercepted by the canal. It is also
possible that the canal may overtop at some point within the basin,
other than the collection point, or within the adjoining basins.
In light of this possibility, the Urban Drainage and Flood Con-
trol District has financed a study to evaluate the effect of the
Highline Canal on major drainage. It is quite probable that this
study will culminate with the recommendation that the canal be
provided ,controlled overflow points at each major drainageway
crossing to eliminate the chance for indiscriminate canal over-
topping. Thus, for the purposes of this study, major flows on
Slaughterhouse Gulch were considered to be unaffected by the
canal.

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