9593

• UCREFRP Catalog Number: 9593
• Author: Tetra Tech Inc.
• Title: Concept Development Report Hartland Diversion Dam Fish Passage Structure Delta, Colorado.
• USFW Year: 2000.
• USFW - Doc Type: Grand Junction, CO.
• Copyright Material: NO

IV. HYDROLOGY
The purpose of the hydrologic analysis is to determine low flows, typical flows and high
flows for which the fish passage will operate during the appropriate times of the year. As part
of the design criteria stated in Section III, the operation and flow requirements for the fish
passage structure cannot interfere with the operation of the Hartland diversion dam. This is of
primary concern during low flow conditions. The hydrologic analysis provides the information
necessary to determine the flow conditions for which passage is possible from both a physical
and operational standpoint. Typical flows are used to evaluate the hydraulics of the ladder
design while peak high flows (flood events) are evaluated in order to design a stable structure.
An analysis of historical flows is conducted to assess conditions throughout the course
of an average year. Data used in the analysis came from the United States Geological Survey
(USGS) stream gaging station "Gunnison River at Delta, CO" (number 09144250), which is
approximately 2 % miles downstream from the diversion dam. The gage is located on the left
bank of the Gunnison River near the upstream side of the bridge at U.S. Highway 50 north of
Delta. Records are available from June 1, 1976 through 1999. Since water year 2000 is
considered "provisional data" it is not used in this analysis.

4.1 Flood Events
Major flood events utilized in this report are based on the flows developed and
presented in the Flood Insurance Study (FIS) for Delta County, Colorado, conducted by the
Federal Emergency Management Agency (FEMA 1991). These flows are summarized in Table
4.1.

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