FLOOD05818

• County: Jefferson
• Community: Golden
• Stream Name: Clear Creek
• Basin: South Platte
• Title: Hydrology Study of Clear Creek Between Wadsworth and Federal Boulevard
• Date: 4/1/1977
• Prepared For: Jefferson County
• Prepared By: Colorado Division of Highways
• Floodplain - Doc Type: Floodplain Report/Masterplan

I 76-1(35) PE

HYDROLOGY

Introduction

The peak flow prediction of Clear Creek is most critica1~ The vast
amount of development within the natural flood plain must not be
endangered by under design. However, the space 1imi~ations for inter-
lacing the proposed highway through the established corridor and the high
construction costs dictate that the luxury of overdesign cannot be tolerated.

This report considers applicable stream flow history and previous hydrologic
studies to obtain the peak design flow along Clear Creek in the reach of
the proposed I 76 highway encroachments.

The Clear Creek study is divided into two reaches as Ralston Creek is
the only major tributary between the project limits. See Figure No.1.
The upper reach is above the Ralston Creek confluence and the lower
reach is below the confluence.

Design Frequency

Federal Administration Federal-Aid Program Manual 1 directs the following:

a. Where encroachment on a flood plain is necessary, an
evaluation, using the basic (100 year) flood, shall be
made of the flood hazard to the highway, and the effect
of the proposed highway on the flood hazard to other
property, stream stability, and the stream and flood
plain environment.

1

b. The design flood selected for each encroachment and the
des i gn for conveyance of the bas i c (1 00 year ) flood shou1 d
be supported by the following, where applicable: an
incremental analysis of estimated construction costs;
probable property damage including damage to the highway;
the cost of traffic delays; the availability .01' alternate
routes, emergency supply and evacuation routes; and with
cons i derati on of the potenti a 1 for loss of 1 ife and of
budgetary cons tra i nts.

f. All highways on the Interstate System that encroach on
flood plains shall be designed to avoid inundation of the
highway from floods at least as great at the 50-year flood.

1.

Federal Highway Administration, Federal-Aid Highway Program Manual,
Vol. 6, Chapter 7, Section 3, Subsectlon 2, May 29, 1974.