HYDRO21737

• Permit No: M1977306
• IBM Index Class Name: Hydrology
• Doc Date: 6/23/2005
• Doc Name: water sampling reports
• From: cotter
• To: dmg
• Media Type: D
• Archive: No

Cotter Corporation Water Quality Assessment CO-0036251
expected to have similar characteristics. During times of rainfall, flow in East Paradox Creek and
Bull Canyon upstream of the Cotter Corporation may cant' as much as 400-600 cfs of flow.
Although there is periodic flow in East Paradox Creek and Bull Canyon and their unnamed
tributaries, the 1 E3 and 30E3 monthly low flows are set at zero based on information provided bythe
local Water Commissioner. For this analysis, low flows are summarized in Table A-7.
Table A-7
Low Flows for the Unnamed Tributaries of East Paradox Creek and Bull Canyon
at the Cotter Cor oration Outfalls

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lE3 0 0 0 0 0 0 0 0 0 0 0 0 0
Acute
30E3
0 0 0 0 0 0 0 0 0 0 0 0 0
Chronic
Because downstream standazds are evaluated in this WQA, the flow of the Dolores River
immediately unstream of the confluence with East Paradox Creek as well as the flow of the Dolores
River upstream of the confluence with Bull Canyon must also be evaluated. To determine the low
flows of the Dolores River upstream of East Paradox Creek, data from USGS gage station 09169500
(Dolores River at Bedrock, CO) were used. This flow gage is located less than three miles upstream
of the confluence of East Paradox Creek with the Dolores River and provides a representative
measurement of the upstream flow because there are no diversions or confluence of significance
between the flow gage and the confluence of East Paradox Creek with the Dolores River.
To determine the low flows of the Dolores River upstream ofBull Canyon, the same flow data were
used. Although the USGS gage station 09169500 is located approximately 17 miles downstream of
the confluence ofBull Canyon with the Dolores River, the local Water Commissioner indicated that
the Dolores River would not gain flow of any significance between the two locations. The local
Water Commissioner confirmed that flow data from USGS gage station 09169500 would be
representative of flow at the confluence ofBull Canyon with the Dolores River.
Daily flows from the USGS Gage Station 09169500 (Dolores River at Bedrock, CO) were obtained
and the annual lE3 and 30E3 low flows were calculated using U.S. Environmental Protection
Agency (EPA) DFLOW softwaze. The output from DFLOW provides calculated acute and chronic
low flows for each month.
Flow data from October 1, 1989 through December 31, 1999 were available from the gage station.
The gage station and time frames were deemed the most accurate and representative of current flows
and were therefore used in this analysis.
Based on the low flow analysis described previously, the upstream low flows available to the Cotter
Corporation were calculated and are presented in Table A-8.
Appendix A Page 9 of 13 Final