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<br />I <br />I <br />I <br />I <br />I <br />I <br />'I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />'I <br />I <br />I <br />I <br />.' <br /> <br />: <br /> <br />: <br /> <br />Or.~~ cg <br />Uv.v <br /> <br />period the native streamflow is typically insufficient to meet irrigation <br /> <br />demands and transbasin water (CBT) constitutes a significant portion of the <br /> <br />water in the river. The storage season typically runs from November <br /> <br />through April. Discharge from the Loveland Wastewater Treatment Plant and <br /> <br />transbasin diversion of CBT water for storage may provide the only source <br /> <br />of streamflow in some reaches. <br /> <br />4.3 AUGMENTATION OF HISTORIC STREAMFLOW RECORD FOR BIG THOMPSON RIVER <br /> <br />The USGS streamflow gauge at the mouth of the canyon (6.0 miles east of <br /> <br /> <br />Drake, Colorado) has been in operation since January of 1927 through the <br /> <br />present time. This historic record is not continuous, the following gaps <br /> <br />are present: <br /> <br />o October 1928 - May 1929 <br /> <br />o 1929 - 1932 <br /> <br />(November through March values are missing) <br /> <br />o October 1933 - April 1938 (Station discontinued; no records) <br /> <br />o October 1950 - March 1951 <br /> <br />o August 1979 - April 1980 <br /> <br />The first step in this study task involved correction of the gauge record <br /> <br />to account for diversions through the Dille Tunnel for hydroelectric <br /> <br />operations of the USBR Big Thompson Hydroelectric Plant at the mouth of the <br /> <br /> <br />canyon. Big Thompson streamflow is diverted above the gauge and <br /> <br />consequently not recorded at the gauge. Outflov from the Hydroelectric <br /> <br />Plant is returned to the river belov the gauge. These Dille Tunnel <br /> <br />diversions must be added to the gauge reading each month to accurately <br /> <br />represent the quantity of "native" water in the river and available to <br /> <br /> <br />dovnstream users. Monthly diversion records were obtained by the City from <br /> <br />the USBR and provided to COM; this data vas used to correct the gauge <br /> <br /> <br />record. Average streamf10vs for native Big Thompson streamf10v vere <br /> <br />computed from this corrected gauge record; these values are given in Table <br /> <br />4-1 and illustrate the seasonal changes described in Section 4.1. <br /> <br />4-4 <br />