FLOOD10391 ‎(2)‎

• County: Boulder
• Community: Boulder
• Stream Name: South Boulder Creek
• Title: Proposal, South Boulder Creek Floodplain Study Hydrology and Hydraulic Analyses, RFP No 17-2003
• Date: 3/14/2003
• Prepared For: Boulder Department of Public Works Utilities Division
• Prepared By: Ayres Associates
• Floodplain - Doc Type: Floodplain Report/Masterplan

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AYRES

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TASK 3: WATERSHED HVDROLOGV

Input to the Watershed Hydrology will be provided by both the Resource Atlas and
Climatology Tasks. The hydrologic analysis itself will consist of the following main
components:

Flood Frequency A definition of the peak discharge associated with floods of
specific frequencies of occurrence based on the statistics
of past recorded floods

Rainfall Runoff A definition of peak discharge and hydrographs associated
with basin meteorology (rainfall and snowmelt runoff)
based on precipitation duration/frequency. This will be the
basis for evaluating transposed meteorologic "scenario"
events and alterations to basin physical characteristics.

Paleohydrology A definition of peak discharge and frequency based on
paleostage indicators (primarily biologic and geomorphic),
both for floods that have a recorded hydrograph as well as
those that have occurred outside of recorded history. This
establishes the relative magnitude of paleo floods. This
information, in combination with the statistics of recorded
flows, defines a discharge-frequency relationship with a
high level of confidence for flows with a frequency of 50 to
500 years in which we are most interested.

Regional A definition of peak discharge associated with events that
have been experienced in geographically similar areas
along the Front Range. This is to provide a perspective on
floods that can occur, but may not yet have occurred at this
specific location.

The Resource Atlas Task will provide the digital platform for hydrologic information.
The basin hydrologic inventory will consist of information obtained from the immediate
preceding hydrologic study (Taggart 7/2000) and our independent reconnaissance.
This inventory will cover both physical/environmental information and relevant historical
changes in basin hydrologic conditions. This will include historical, anthropocentric
land use basin changes (forest logging, roads and railroads, community development,
mining, water storage and delivery systems, and agriculture). It will also include other
basin changes (forest fires, insect timber kill, drought, etc). Climatic changes are not
expected to be evaluated at this time. This information will provide a better
understanding of flood events that have occurred in the basin, will establish a basis for
adjusting recorded data or extending data and adjusting model parameters, and will
provide a normalized basis for comparing floods. This compilation and validation of
information will help us understand the realistic constraints involved with using this data
in the several hydrologic analyses. The amount and apparent accuracy of the data
controls the extent to which hydrologic model calibration and verification can be
accomplished. It also controls the type of calibration that is reasonably possible and
meaningful (for example, to what extent it can be accomplished to recreate virgin flows,
1938 flood peak flow, the 1969 post-Gross dam flood flow, etc.).

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