WSP05499

• File Number: 8200.766
• Description: Gunnison River General
• State: CO
• Basin: Gunnison
• Water Division: 4
• Date: 4/1/1997
• Author: Mueller and Hiebert
• Title: Assessment of Kokanee Salmon Transport through Blue Mesa Powerplant - Colorado - During the Spring and Summer of 1994-1996
• Water Supply Pro - Doc Type: Report/Study

I
I
I
I.
I
I
I
I
I
I
I
I
I
I
I
I
I

I
I

D!J239~

A scientific echosounder allows for an evaluation of fish size.
Unlike commercial or recreational echosounders, a scientific
echosounder has a time varied gain (TVG) function which corrects
the effects of sound attenuation (scattering) on return signal
strength. In short, a target at a 1 meter depth will produce the
same signal strength as the same target at 30 meters. Target
Return strength is closely proportionate to fish size, the larger
the target the stronger the signal. The HADAS program analyzes
these signals and shorts them into 10 bins according to signal
strength (Figure 3). These ten bens were grouped into small
-56-44 dB), medium (-45-37 dB), large (>37 dB) sized groups which
represent fish >10 cm, 10 to 20 cm, and fish >20 cm.

Population estimates of the kokanee and the pelagic fishery were
developed through data collected by hydroacoustic surveys and
vertical gill netting. An average pelagic fish density for the
reservoir was calculated by taking the average fish density
(fish/hectare) of each transect. Average pelagic fish density
was multiplied by reservoir surface area to determine population
size. Population estimates of specific species were based on
species composition of vertical gill net samples.

Flow Profiles

An acoustic doppler current profiler (ADCP) instrument was used
to perform a three-dimensional profile of the intake flows in
July 1996. These profiles were taken at various increments from
the intake tower when the powerplant was operating at maximum
generation (89 megawatts, 3,285 CFS).

ADCPs use the Doppler effect to determine the current velocity by
measuring the velocity of sound reflectors (sediment or plankton)
moving with the current. ADCPs use the Doppler effect by
transmitting sound at a fixed frequency and listening to echoes
returning from the sound scatterers in the water column. The
echoes are referred to as backscattered signals. The amount of
frequency shift in the backscattered signal is proportional to
the relative velocity between the ADCP and scatterer. In
addition, the ADCP can only measure the velocity component in the
direction of a line between the scatterer and the acoustic

10