Laserfiche WebLink
<br />~ <br /> <br />-::-- <br /> <br />,. <br />. . <br /> <br />Agenda Item 13 <br />November 25.26, 2002 Board Meeting <br />Page 2 of3 <br /> <br />A base flow of 150 cfs should be maintained, and flows lower than 150 cfs should not occur . <br />more often than 1% of the time, based on daily average flows at Watson, Utah. <br /> <br />. <br /> <br />The channel-maintenance flow recommendation of 1413 cfs was determined by evaluating <br />sediment transport in the river channel near Watson. The study found that flows from 1700 to 2900 <br />cfs were responsible for maintaining the form of the channel, while flows of about 1450 cfs were <br />necessary for maintaining an annual cycle of scour and fill in the riverbed. Additionally, the <br />researchers used a rule of thumb from federal investigations into channel maintenance in Idaho, <br />where all flows are claimed that are greater than the flow at which 70% of the annual sediment load <br />is transported; this flow is about 1400 cfs on the White River near Watson, Utah. <br />The base flow recommendation of 150 cfs was identified through analyses of river flows and <br />their effects on Colorado pikeminnow habitat at several locations along the river. Study results <br />indicated that habitat proportions remained constant from 150 to 600 cfs. Also, an analysis <br />comparing wetted perimeter and river flow showed that below 150 cfs the wetted perimeter (and, <br />hence, pikeminnow habitat) decreased more rapidly. <br />The graph below shows the flow duration curve for the White River near Watson, Utah. <br />Daily flow records from 1923 to 2001 were sorted by flow magnitude and graphed to show the <br />probability of exceedance for a certain flow. For example, a flow of 1000 cfs is exceeded during this <br />time period at Watson about 17% of the time. The two flow recommendations are also shown on the <br />graph. The channel-maintenance flow recommendation of 1413 cfs is exceeded about 12% of the <br />time, whereas the base flow recommendation of 150 cfs is exceeded over 99% of the time. <br /> <br />White River near Watson, Utah <br />Flow Duration Curve for April 1923 to September 2001 <br />(gage inactive from Oct. 4, 1979 to Sept. 30, 1985) <br /> <br />. <br /> <br />1000 , <br />~~ <br /> <br /> <br />.II'~. <br />i.~: <br />ii:'l\. <br />tl~ <br /> <br />9000 <br /> <br />8000 <br /> <br />7000 <br /> <br />~ <br />.2- <br />~ 6000 <br />o <br />u:: <br />2:05000 <br />... <br />o <br />(; 4000 <br />!<l <br />o <br />- 3000 <br />~ <br />~ <br /> <br />2QOO <br /> <br />o <br />0% <br /> <br />10% <br /> <br />20% <br /> <br />30% <br /> <br />40% <br /> <br />50% <br /> <br />60% <br /> <br />70% <br /> <br />80% <br /> <br />90% <br /> <br />. <br /> <br />Probability of Exceedance <br /> <br />Flood Protection. Water Project Planning and Financing. Stream and Lake Protection <br />Water Supply Protection. Conservation Planning <br />