WSP05674

• File Number: 8200.760
• Description: Yampa River General
• State: CO
• Basin: Yampa/White
• Water Division: 6
• Date: 3/1/1978
• Author: USGS
• Title: Analysis of Waste-Load Assimilative Capacity of the Yampa River - Steamboat Springs to Hayden - Routt County - Colorado - March 1978
• Water Supply Pro - Doc Type: Report/Study

OG2559

Calibration results indicated nonmixed conditions in the stream cross
sections at site YM-3. Visual inspection of this location in October 1975
also indicated nonmixed conditions. Site YM-3 is located approximately 500 ft
(150 m) downstream from the discharge outlet of the main wastewater-treatment
plant at Steamboat Springs. The stream at site YM-3 divides into two channels
with approximately 75 percent of the flow in the left (southern) channel and
25 percent of the flow in the right (northern) channel. The right channel,
where the samples were collected, receives the largest proportion of the
treated-wastewater effluent. Because of this nonmixed condition, all observed
data at site YM-3 were adjusted by the approximate flow ratio so that the data
could be used in the model-calibration analysis.

Computed versus observed concentrations of CBODU for the study reach are
shown on figure 14. The decay-rate coefficient for CBODU used was 0.1 per day
for the entire study reach and corresponds to the average-bottle decay-rate
coefficient previously computed. Even with using the O.l-per-day decay-rate
coefficient, the computed profile was low compared with the means of the
observed data. One explanation could be that some additional BOD loading,
such as irrigation return flows, could have affected concentrations of CBODU
in the' upstream subreaches. The values of CBODU computed by the two,models
were almost identical for the entire study reach.

The reaeration formula of Bennett and Rathbun (1972) was used in the DO
computations. The reaeration formula has the following form:

K2 =8.76 VO.607/V1.689,
20

where

K2 =reaeration-rate coefficient at 20oC, in 1 per day;
20

V=mean velocity in the river, in feet per second; and

D=mean depth in the reach, in feet.

This reaeration formula expressed the reaeration-rate coefficient of the
stream as a function of mean depth and velocity. The temperature-corrected
reaeration-rate coefficients ranged from 3.8 to 13.1 per day with the larger
coefficients occurring in the upstream subreaches between sites YM-01 and YM-
4. The temperature correction of the reaeration-rate coefficient is of the
following form:

K2 =K2 (a)T-20,
T 20

where

K2T=reaeration-rate coefficient at temperature, T, in 1 per day;

T=temperature, in degrees Celsius; and

(a)=empirical constant, set equal to 1.024 for the U.S. Geological
Survey and Pioneer-I models.

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