FLOOD07296

• Designation Number: 569
• County: Mesa
• Community: Grand Junction
• Stream Name: Bosley Wash
• Basin: Colorado Mainstem
• Title: Bosley Wash Drainage Master Plan - Phase 1: Watershed Floodplain Delineation
• Date: 11/1/2002
• Prepared For: Bosley Wash Watershed
• Prepared By: GMS
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Bosley Wash Drainage Master Plan
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Phase I: Watershed

above, However, both represented high intensity events with a recurrence interval in the range
of the lOO-year event.

4. HYDROLOGIC MODELING PROCESS

Due to the lack of stream gage records, a rainfall/runoff model was used to generate design flow
estimates within the Bosley Wash Basin, HEC-HMS (HMS) was used to model the hydrologic
response of the entire watershed, HMS is a Windows-based program, which incorporates a
synthetic SCS unit hydro graph to compute hydrographs for individual subbasins within the
watershed, The program then routes these hydrographs through a stream network, HMS was
developed by the D,S. Army Corps of Engineers Hydrologic Engineering Center and is
commonly used when developing and routing hydrographs for a large number of sub-watersheds,

4.1 Hydrologic Data Requirements

A number of model inputs are necessary for each HMS subbasin to produce the desired
hydro graphs , These include, but are not necessarily limited to:

. Contributing drainage area

. Basin shape

. Time of concentration

. 24-hour rainfall depth

· Rainfall distribution

. Subbasin curve number (primarily derived from soil type and land use)

· Antecedent moisture condition (AMC II assumed throughout)

. Length and geometry of drainage path to be used for routing

. Stage-storage-discharge rating curve for storage nodes

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