Laserfiche WebLink
<br />-30- <br /> <br />less than 10% of AAD into McPhee Reservoir. The pool of water currently <br />available for "fishery and aesthetic purposes" (25,400 AF) is 7% of AAD, <br />assuming 350,000 AF is the AAD. <br /> <br />USBOR-DPO documents indicate that drought year conditions will prevail in this <br />drainage approximately 22% of the time (according to historical records). <br />Serious planning should begin now to avoid the need to manage for an <br />"ecological catastrophe" every 4-5 years. The "bio1ogical evidence" gathered <br />over the past 12-18 months indicates that is what is in store unless <br />corrective action is embarked upon soon. Given the !:ecent controversy over <br />the Dolores River trout fishery, it seems prudent to try to provide a larger <br />pool of water to the downstream system. <br /> <br />The biological data collected during the spring to fall period in 1991 <br />indicates a continuing decline in the fishery. It cannot be determined if the <br />decline (between October 1990 and 1991) was due to continuing low flows in <br />1991, lingering after effects of the severe flow reductions in 1990, effects <br />of sedimentation, or a combination of all these factors. However, it appears <br />that the amount and manner of the 50,800 AF release of water into the <br />downstream system during 1991 did not allow recovery of the trout population. <br /> <br />After more than a year of intensive study, a few conclusions can be made. <br />First, the 20 cfs flow regime is below the amount of water necessary to <br />maintain a viable trout fishery in the Dolores River. Such a flow equates to <br />4% of the AAD into McPhee Reservoir, which is significantly less than other <br />USBOR projects in Colorado. Another facet of the operation of McPhee <br />Reservoir is that it is about the only major USBOR impoundment in Colorado <br />that consistently gains in stored water during the winter months. It has <br />gained an average of about 10,000 AF annually during the October-March period <br />since 1984. Only in 1988 and 1990 was water storage lower on March 31 than on <br />the preceding October 1st. <br /> <br />The USBOR Curecanti Project suffered through the same 3-year drought as the <br />Dolores Project, yet minimum daily flows never dropped below 257 cfs, which <br />was a single day in 35 consecutive months. Mean monthly flows never dropped <br />below 294 cfs during that 35 month (May 1988 - March 1991) period. This flow <br />equates to 21.3% of the AAD of the Gunnison River at the Gunnison Tunnel. The <br />flow in the Gunnison River below the Gunnison Tunnel would have to have been <br />reduced to 55 cfs (4% of AAD) for 100 days for this river to have been <br />subjected to the same scale flow depletion as that which occurred on the <br />Dolores River in 1990. Only once in the last 25 years has the flow in the <br />Gunnison Gorge dropped below 100 cfs for a 24 hour period. <br /> <br />Dolores River Water Temperatures - Water temperatures in the Dolores River <br />downstream from the dam to Bradfield Bridge were measurably cooler during the <br />summer of 1991 in comparison to 1990. Instantaneous daily high water <br />temperatures at the Bradfield Bridge never reached 720 F during the summer and <br />average daily water temperatures never exceeded 650 F. Thermal stress on the <br />trout population during 1991 was certainly much less of a factor than it was <br />in 1990. <br />