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Fisheries Section Research Reports and Abstracts

A Recommended Method to Protect Instream Flows in Georgia

Project number: F-24
Final Report Date: December 1995
Author: James W. Evans and Russell H. England

Study Objectives

This report reviews instream flow requirements for fisheries and the available assessment methodologies. The objective of this review was to recommend an instream flow policy for Georgia that would meet the following criteria:

  1. provide significantly better protection for native stream fishes than is currently provided,
  2. be simple to understand and apply,
  3. be scientifically defensible, and
  4. could be readily incorporated into state water quality regulations so that it would have the force of law.
Report Summary

The increasing demand for water to support Georgia's growing human population creates significant challenges for natural resource managers responsible for protecting the state's fish and wildlife. Heavy dependence on surface water supplies for municipalities, industry, and agriculture has severely depleted and/or altered natural stream flows, adversely impacting aquatic habitat. Georgia's present policy protects stream flow from being depleted below the 7Q10 flow (a ten-year frequency drought event), but there is an overwhelming consensus among aquatic resource managers that higher flows are necessary to support the fish and wildlife, recreation, and aesthetics that Georgia's citizens expect from their natural environment. The 7Q10 flow was not intended to define adequate base flows for aquatic habitat requirements or other instream uses; its purpose was to protect aquatic life downstream from point source discharges during expected low flow conditions by providing a basis for calculating instream concentrations of specific pollutants in such discharges.

Instream flow requirements for fisheries and methods to protect stream flows have been the subject of extensive study. This report provides a thorough literature review of these efforts, which range from simple "office" methods that establish general statewide guidelines to more time-consuming and expensive field methods that may be necessary to develop site-specific recommendations for controversial projects. Many states have developed comprehensive instream flow policies that require considerably greater flows than 7Q10, and several of these are summarized. Finally, a revised policy based on broadly applicable office methods is proposed for Georgia. The proposed standard provides significantly better protection for native stream fishes than the current policy, is simple to understand and apply, and is scientifically defensible.

Recommended protective flows for Georgia's streams are summarized below. Flow recommendations should be based on at least ten years of continuous flow records where possible. In all cases these are recommended instantaneous flows rather than average flows over various time periods.



Recommended Protective Flow 

Unregulated Streams
- Warmwater streams


30% average annual discharge 

Unregulated Streams
- Trout streams


 September median flow

Regulated Streams

  July through November 

 30% average annual discharge


January through April

 60 % average annual discharge


 May, June, December

 40% annual discharge

 Special Case Streams


 Approved field studies to determine flow requirements

Peaking Hydropower Projects: Site-specific IFIM studies to determine flow requirements.


Full Report

 Download the full PDF version of this document (188 Kb) (Adobe Acrobat Viewer Required)

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