FLOOD07727

• County: Jefferson
• Community: Arvada
• Stream Name: Ralston/Leyden Creek
• Basin: South Platte
• Title: Major Drainageway Planning
• Date: 8/1/1977
• Prepared For: Arvada
• Prepared By: UDFCD
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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time of the design storm, resulting in only that storage which would take
place above the spillway crests. Land use patterns were based upon the
latest plans approved by the City of Arvada and Jefferson County. These
land use plans forecast medium to high development densities within the
Arvada city 1 imits, with lower densities and agricultural land in Jefferson
County. In addition to these overall densities, drainage flow paths from
individual areas are also important in predicting future flood flows. For
example, the hydrological response of an area with curbs and gutters is sig-
nificantly different than that of the same area with grass-lined swales.
According to city and county officials, future residential development in
the City of Arvada will be constructed with curbs and gutters, while similar
types of development in Jefferson County will include roadside ditches for
carrying storm runoff,

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12000

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Future land use development patterns assumed for this study are:

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1, A typical continuation of urban development within the City of Arvada
similar to existing development with curbs and gutters, No specific
flow reductions have been incorporated as a result of the Arvada up-
stream ponding ordinance enforcement which would be applied to new
deve I opmen t .

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2. County development in Ralston, Leyden, and Van Bibber Creeks of low
density without curbs and gutters. Roadside ditches would convey
storm runoff at the neighborhood level.

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3. Detention storage on Van Bibber Creek as called for in the 1977 Van
Bibber Master Plan. This results in some future flows being less
than those under present conditions.

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It is not possible to estimate a time period for full development of the basin.
However, for planning purposes it should be assumed that development will
occur by 1995.

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Figure 111-1 shows the discharge profiles for Ralston Creek and Leyden Creek for
the channel and basin. Figure I I 1-2 shows the discharge profiles for the 1DO-
year storm for future basin conditions with the Master Plan Channel.

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Comparison of Table 111-1 and Table 111-2 indicates a sl ight increase in the
future condition flood peaks on Ralston Creek below Ralston Reservoir to the
confluence with Van Bibber Creek. This is due to increased urbanization anti-
cipated to occur below the site of Blunn Reservoir, Downstream of Van Bibber
Creek to Clear Creek, the future flood peaks are anticipated to be less than
the present levels, due to detention facilities to be built on Van Bibber Creek.

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Future Develo ment wi Impro ed Channel
(w/o detenti on Van Bibber Creek)

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Future Develop ent wi Improv d Channel
(detention on an Bibber Cr )

100

200 300
Time in Minutes

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100 Year Storm Hydrographs
Ralston Creek at Mouth

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\NRIGHT- MCLAUGHLIN ENGINEERS
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Figure Ill-I