FLOOD03253

• County: Boulder
• Community: Boulder
• Stream Name: South Boulder Creek
• Basin: South Platte
• Title: South Boulder Creek Draft Hydrology Study Phase III
• Date: 2/10/2000
• Prepared For: UDFCD
• Prepared By: Taggart Engineering Associates, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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UDFCD authorized the Phase II Initial Reconnaissance Study to estimate the
distribution of flooding in West Valley downstream of Highway 36 to the area of
the Wellman Ditch. For the purposes of the Phase II study the Corps' hydrology
remained unchanged upstream of Highway 36 other than modifications to better
reflect floodplain routing downstream of the mountains. However, all new basins
and routing elements were inserted into the hydrology model for the Viele Basin and
the area downstream of Highway 36.

Also, since questions regarding hydrology had been raised by the local governments
and our work, requests of the Corps were made to obtain background data, basin
mapping, and verification studies.

OBJECTIVES OF THIS STUDY

The primary objective of this study is to prepare a new hydrologic analysis of the
South Boulder Creek Watershed.

The initial use will be for the evaluation of flood damage mitigation alternatives for
the reach of South Boulder Creek from Highway 93 to Boulder Creek.

Ultimate uses of the study will be for base hydrology for UDFCD flood hazard
delineation studies (FHAD),or FEMA Flood Insurance Rate Maps (FIRM). or planning
of road and bridge improvements, channel modifications, and flood control
structures. The hydrology should meet the requirements of the "Rules and
Regulations for the Designation of Floodplains and of Storm or Flood Water Runoff
Channels in Colorado" by CWCB and FEMA's "Guidelines and Specifications for
Study Contractors."

SIMPLIFIED SCOPE

This effort is focused on:

1 . Determining the design rainfall from NOAA references that is most
appropriate for the South Boulder Creek watershed, particularly on the South
Boulder watercourse below Highway 93 to Boulder Creek.

2. Checking the Corp's SWMM runoff model upstream of Gross Reservoir
especially with respect to runoff area and infiltration characteristics.

3. Reconstructing the model, especially from just upstream of Highway 93 to
Highway 36 downstream, using the City and County database (detailed
topographic mapping) and the previous hydraulic analysis of flow splits and
floodplains by TEA and others. The dual stream character of the floodplain
will be simulated, where the present mode ignores this phenomena.

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