FLOOD06025

• County: Boulder
• Community: Louisville
• Stream Name: Coal Creek, Rock Creek
• Basin: South Platte
• Title: Major Drainageway Planning
• Date: 11/1/1982
• Prepared For: Boulder County
• Prepared By: WRC Engineering, Inc.
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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SYNOPSIS

prepared showing the proposed Outfall System Plan. A detailed cost estimate was

developed for each of the alternatives along with a suggested construction priority

for implementation of the plan.

This report represents the results of a detailed hydrologic analysis and
master planning of the drainageways in the City of Louisville/Boulder County area.
The report was prepared by Water Resources Consultants, Inc. (WRC) under contract
with the Urban Drainage and Flood Control District (UD&FCD), City of Louisville,
and Boulder County. The purpose of the study was to define an economical and
technically feasible storm drainage outfall system for the existing and future
developed areas of the basin. Copies of this report are available for reference
and purchase at the office of UD&FCD.

The Outfall System Plan consists of 45,940 lineal feet of channel, 55,71D

lineal feet storm sewer, 20 culvert improvements, and onsite detention for all new

development, The total cost of the improvements is estimated at $21,044,5DD.

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The planning area consists of portions of the Coal Creek and Rock Creek

basins. The area contains 10.6 square miles and includes 20.3 stream miles of

outfall drainageways. The Roek Creek basin area contains 5.8 square miles with

10.7 stream miles of outfall drainageways. The remainder of tlle planning area

lies within the Coal Creek basin. The storm drainage problems in the planning

area are mainly caused by developments in the basin encroaching on the existing

drainageways without providing adequate drainage facilities. Various culverts

and storm sewers in the area are incapable of carrying the minor storm flows

without inundation of local streets and adjacent properties.

The Outfall System Plan presented herein was developed for the purpose of

providing a guideline for the orderly planning and construction of drainage

facilities. The plan is conceptual in nature and other alternatives can be consid-

ered. Methods of funding the construction was not in the scope-of-work since

development is required to provide adequate drainage facilities, in accordance

with the Outfall System Plan. In addition, the facilities will most likely be

constructed in segments as development progresses and local, interim problems may

result.

The methodology utilized in the analysis consisted of first defining the

storm runoff peak flows and volumes from the various drainageways in the planning

area. This information was used to assess the capabilities of the existing faci-

lities and to size the proposed facilities. Next, storm drainage design and

technical criteria was developed (Reference-I) and used to evaluate a series of

alternative solutions for the outfall drainageways. These alternative plans were

selected from a matrix of drainage improvements that included status quo (requiring

floodplain regulation and recommending flood insurance), selected structural, grass

channels, riprap or concrete channels, storm sewers, regional detention, and re-

location or diversion from existing drainageways. A recommended alternative plan

was selected by the consultant on the basis of economics and local requirements

for each drainageway and presented to the City of Louisville and Boulder County

for reVlew. After acceptance of the recon~ended alternative plans, the preliminary

design of the outfall drainage systenl was initiated. Plan and profile sheets were

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