FLOOD06450

• Designation Number: 92
• County: Jefferson
• Community: Arvada
• Stream Name: Ralston, Leyden Creeks
• Basin: South Platte
• Title: Major Drainageway Planning - Ralston/Leyden Creek, Arvada, Jefferson County, CO
• Date: 8/1/1977
• Designation Date: 1/1/1978
• Floodplain - Doc Type: Floodplain Report/Masterplan

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SECTION I

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EXECUTIVE SUMMARY

URBAN DRAINAGE AND FLOOD CONTROL DISTRICT

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Ralston Creek and Leyden Creek are the drainage outfalls for a 91.5 square
mile basin. They have a tributary area which extends into a wide variety
of topographic and land use features. The area varies from extremely steep
rugged mountainous terrain west of State Highway 93 to gentle flat terrain
at its confluence with Clear Creek just west of Sheridan Boulevard,

The Urban Drainage and Flood Control District has identified Ralston Creek
and Leyden Creek as being high-priority items in the continuing program of
preparing master plans for major drainages. It has been concluded that
corrective measures and master planning for these creeks are needed now,
before additional costly mistakes are made. It is a well-established fact
that through early-action-projects, corrective costs can be substantially
reduced. As a result, the benefits to society and the various governmental
entities are increased. At the same time, the public will be able to enjoy
recreation and other auxiliary benefits which would not otherwise accrue,

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In Jefferson County there is little development within this basin since
most of this area still has a rural agricultural nature, As such, there
has been 1 ittle encroachment into the flood plains of Ralston and Leyden
creeks,

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. field and office hydrological studies;
. field examinations of the channels and structures;
. coordination with the study of Van Bibber Creek by the
Urban Drainage and Flood Control District;
. examination of existing and future basin development;
. correlation to previous studies on Ralston and Leyden
creeks;
. determination of flood plains;
. analysis of flood damage potentials;
. analyses of various alternatives to reduce flood damage;
. operation and maintenance;
. secondary benefits,

Federal and State Laws. The Flood Disaster Protection Act of 1973 (PL 93-
234), The Water Resources Development Act of 1974 (Pl 93-251) and HB 1041
of the State of Colorado, under which the Colorado Water Conservation
Board promulgated a Colorado Model Flood Plain Regulation, provide signif-
icant new constraints to flood plain development and opportunities for
flood plain management. Full implementation of these laws and related
regulations wi 11 tend, over the years, to improve the cost-effectiveness
of those alternatives which are based on nonstructural solutions, or for
the improved flood plain.

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The City of Arvada is almost entirely urbanized and some portions of Ralston
Creek and most of Leyden Creek have been treated with respect and have been
utilized as an asset. However, there are certain reaches of Ralston Creek
where urbanization has restricted the channel, The Phase A report involved:

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RECOMMENDED SOLUTION

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The optimized and recommended plan for Ralston Creek and Leyden Creek
flood management is based upon minimizing the hazard to life and property
along the full reach of the creeks, in harmony with providing reasonable
and useful amenities consistent with accepted urban and rural planning
principles.

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The legal analysis was conducted by Mr. Joseph Shoemaker of Denver.

The recommended plan represents a flood plain zoning approach with grass-
1 ined channels in areas of major urbanization and encroachment upon the
stream. In a few reaches concrete side-walled European type channels
would be used.

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Computer models were utilized for the flood plain determination and hydro-
logical analyses. The former utilized approximately 330 cross sections and
was developed by the U,S. Army Corps of Engineers. The latter model (MITCAT)
is a fairly recent innovation and was particularly suited to this complicated
hydrologic study, (For a more complete discussion on contract items, see
Appendix to Section I,)

Some 60 residential structures will be relocated from the Ralston Creek
floodway and channel right-of-way, Table 1-1 lists, by reach, the houses
to be removed. It is anticipated that most of these houses will be pur-
chased as they come on the market. These residential buildings are
situated such that they represent a hazard to their occupants as well as
to the adjacent buildings.

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This report (Phase B) has investigated the flood potential of Ralston Creek
and Leyden Creek and has evaluated several alternatives that can minimize
damages with the best trade-off of costs for improvements. The selected
flood control plan for these creeks is a "soft approach," utilizing natural
features and characteristics where reasonable.

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Van Bibber Creek, being a major tributary of Ralston Creek, contributes
significant flows to the Ralston Creek drainage basin, A master plan re-
port On Van Bibber Creek was completed in March 1977, and is available from
the Urban Drainage and Flood Control District,

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