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r..!/{ ~"'''j -I'kG//H() (If- cd, ~SPI'/ -f?-.:J"'~ . MEMORANDUM COLORADO WATER CONSERVATION BOARD j. William Me-Donald DireClor TO: Bill McDonald Gene Jencsok FROM: Randy Seaholm ~ DATE: July l7, 1989 SUBJECT: McElmo Creek Hydrology As requested, I in greater detail. follows: have evaluated the McElmo Creek hydrology The results of this evaluation are as Stream Gaqes . The USGS records list ten stream gaging stations in the McElmo Creek Basin. Gage records for McElmo Creek were first started in 1951 with the establishment of the stateline station. In-depth gaging of the basin began in 1971. Attachment 1 shows the ten gaging stations in downstream order along with the corresponding periOd of record and the annual discharge values in acre feet for water years 1975, 77, 79, 80, 8l, 82 and 1983. The relatively dry years were 1977 and 1981. The average water years 1975 and 1982. The relatively wet years were 1980, 1982 and 1983. The stream gaging which has occurred in the basin is all downstream of heavily irrigated areas and is therefore reflective of significant amounts of irrigation and municipal return flows. You will note when reviewing the gage record that the stream continually gains as you proceed downstream. This gaining trend here is somewhat unusual in that it occurs despite the decreasing significance of the tributaries coming into the mainstem of McElmo Creek, a generally decreasing precipitation pattern and additional depletions. In light of these factors the stream accretions which do occur then must be attributable primarily to the irrigation return flows. . Attachments 2 through l4 show the average daily and monthly flows for water years 1981 and 1982. Please note the relatively uniform nature of the flows from month to month in the different years reviewed, This is a further indicat~RnA that the hydrograph is significantly influenced by @qJ~~~n return flows. 0456E'"