7848

• UCREFRP Catalog Number: 7848
• Author: Burdick, B. D.
• Title: Minimum Flow Recommendation For Passage Of Colorado Squawfish And Razorback Sucker In The 2.3-Mile Reach Of The Lower Gunnison River
• USFW Year: 1997.
• USFW - Doc Type: Redlands Diversion Dam To The Colorado River Confluence.
• Copyright Material: NO

CRITICALLY LOW WATER DEPTHS OCCURRED AT THREE LOCATIONS IN THE
2.3 -MILE REACH DURING LOW FLOWS IN 1994
Transects 9, 19, and 20 (river miles 2.7 and 1.4, respectively), had
empirical maximum water depths of 0.8, 1.1, and 1 feet, respectively, at flows
ranging from 245-276 cfs during late-July and early August 1994. Predicted
maximum water depths were 1.1 feet at transects 9 and 19 at 300 cfs. Although
there were two thalwegs across transect 9, only 7% of the channel width exceeded
1 foot at 300 cfs. A maximum water depth of 1 foot was exceeded at only one
location at transect 9 at 300 and 400 cfs. A water depth of at least 1 foot
would be maintained across 10% of the channel width at 500 cfs. A flow of 850
cfs was estimated to maintain a mean water depth of 1 foot through the.entire
transect.
At transect 19, the predicted mean and maximum water depth was 0.7 and 1
foot, respectively, at 300 cfs; only 5% (one predicted observation) of the
channel width exceeded 1 foot. Seventy percent of the channel width had a mean
water depth of 1 foot at 600 cfs. A flow of 1,400 cfs would be required to
maintain a mean water depth of 2 feet. At transect 20, the empirical measured
mean water depth was 0.6 at 266 cfs; none of the water depths exceeded 1 foot at
266 cfs.
CATCH RATE VERSUS FLOW WAS NOT PRACTICAL FOR IDENTIFYING MINIMUM FLOWS
A minimum "threshold flow" for fish passage could not be determined using
catch rate and flows because a strong positive relationship between the two
variables did not exist. Although flows were known on capture dates, this method
did not provide the resolution to identify the flow endangered and native fishes
might leave the reach and move downstream where more suitable habitat conditions
existed. Instead, the relationships were a reflection of catch efficiency:
higher catch rates occurred during low flows because fish were more vulnerable
and easier to capture than during high flows.
A 300 CFS INSTANTANEOUS FLOW IS RECOMMENDED FOR THE
2.3-MILE REACH OF THE LOWER GUNNISON RIVER
Predicted and empirical water depths were used to recommend a 300 cfs
minimum flow to provide passage in the 2.3-mile reach of the Lower Gunnison River
using water releases from upstream Federal Reservoirs. A 300 cfs flow will