WSP10633

• File Number: 8240.200.30.E
• Description: Guru I And II
• Basin: Colorado Mainstem
• Date: 1/1/1993
• Author: Jack Stafford
• Title: Instream Flows to Assist the Recovery of Endangered Fishes of the Upper Colorado River Basin: Review and Synthesis of Ecological Information, Issues, Methods and Rationale
• Water Supply Pro - Doc Type: Publication

Table of Contents

Abstract............................................................................................................................................i

I. Introduction........................... .... ................ .............. .......... .............................. .................... .......1
Endangered Fishes of the Upper Colorado River Basin......................................................l
Figure 1. The Upper Colorado River Basin ecosystem upstream
from Lake Powell...........................................................................................2
Pwpose and Objectives of the Study ..................................................................................3

n. Methods and Approach.............................................................................................................4
Review of Information ........................................................................................................4
Peer Review and Schedule ..................................................................................................5
Ecological Context for Instream Flow Analysis ..................................................................6

m. River Ecology and The Effects of Regulation on the Endangered Fishes of the Upper
Colorado River Basin: Review and Synthesis.........................................................................7
Ecology of the Endangered Fishes......................................................................................7
Figure 2. Schematic representation of geomorphic processes.....................l1
Figure 3. Relationships of Colorado squawfish spawning dates

to Yampa River flows ...................................................................................13
Figure 4. Catch per effort of post larval squawfish .....................................15
Figure 5. Distribution of squawfish by size and number caught

in the Colorado River...................................................................................16
Dynamic Relationships Between Flow, Channel Geomorphology and Food Webs.......... 17
Figure 6. Generalized relationship between average daily flows
in the Green River ........................................................................................18
Influences of Stream Regulation.......................................................................................22
Figure 7. Regulation offlow in the Green River system .............................23
Figure 8. Regulation of flow in the Colorado River system ........................24
Figure 9. Regulation of flow in the Gunnison River system. ......................25
Alteration of Flow, Temperature and Sediment Regimes.......................................26
Figure 10. Daily flows on the Green and Yampa Rivers during

winter 1991-92.......... ................ .................... .......................... ........... ....... ...27
Figure 11. Variability of flows on the Gunnison River ...............................28
Figure 12. Hourly discharge measured on the Green River
at the Jensen gauge during August, 1992.....................................................29
Figure 13. Hourly discharge measured on the Green River
at the Jensen gauge during September, 1992................................................30
Figure 14. Summer and fall baseflows on the Green River
at Flaming Gorge Dam and at Jensen ..........................................................3 I
Channel EncroacIunent by Riparian Plants ...........................................................32
Loss of Food Web Function in the Varial Zone....................................................34
Stream Regulation Mediates Invasions of Nonnative Predators and
Complicates Provision of Instream Flows to Protect Endangered Fishes..............36
Figure 15. Graphic models of the dynamic relationship between native
and nonnative fishes in regulated and unregulated arid-land streams ...........37
S~ ~e~ation in an Ecosystem Context: Occurrence of Ecological
DISCOntinUIties.... ...... .......... .................................. .............................. ...... ...... ...... 38 .
Figure 16. A. Altitudinal profIle of the Gunnison River. B. Biomass
and density of total zoobenthos in the Gunnison River................................40
Conclusions Based Upon Review of the Ecological Literature Pertaining to the
Endangered Fishes and the Regulation of Flow .....:..........................................................41

GI 0008