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<br />. OCT-30-90 WED 13:59 <br /> <br />BRR BLD 53 DFC <br /> <br />FAX NO. 2305034 <br /> <br />P.02 <br /> <br />, <br /> <br />PALEOFLOOD STUDY FOR THE 1151 MORGAN, UTAH, 1180 OPAL, WYOMING, AND <br />FOR PORCUPINt! RESERVOIR NEAR AVON, UTAH <br /> <br />Robert D. JarreU <br />U.S. CcolOlllcol Survey <br />Oennr, CO <br /> <br />October 30, 18118 <br /> <br />/4~f'D~ <br /> <br />Introducllon <br /> <br />Tho lICl:uracy 01 numerous extrllmll rainstorm lUIlOUnll and lIood e8tim.lI~ in the Rocky <br />Mountain region has been questloned for more man I decadA. This is dua In part to UmRed data <br />for oxtrome lItoRM in rcmots lIreae. Soma of these storms only havlI onll rainfall 8sllmate, <br />typically ralnrall~ucket data, or nne peak dilCharge estimate. Othllr storms may have no dsta <br />.nd only n.wspaper accounta of rainrllll or flooding. Recently, onslle paleohydrologic <br />Investigations have bun shown to be of villus in providinll supplemental data on hi~lurlcal <br />slorms. These clara also Ir. used to lInllM short precipitation or streamflow records that <br />IIvGrlllle .bout 20 yaara with a few racorda up \0 IIbout 100 years. Information on extreme <br />preclpitatinn and flooding Is critically needed for mo.t waler.resource. Investlg.tIons, <br />parlicualrly for dam ..rely. Paleohydrologic technlqulI recently have bAAn used to assell <br />notable Colorado rainatorms and /Icoding includlnllthe 1938 Bear Creek, 1952 Cimmaron, <br />19611 Big Elk Meadow. lA7S Sweetwater Creek, 11178 Big Thompson, 1994 Cllttcr Crsek, and <br />1998 Duffalo Crlek. On September 23 to 25, 1990. II the request 01 Or. Don Jensen, Utah <br />Stata Climatologist, I visited Utah and Wyominllto conduct rcconnalsaance paleoflood <br />Invesligallons tor the AUgusll11. 1958 Morgan, UtAh, and August 16, 1990 Opal, Wyominll, <br />which ere two benchmark ltorms uslld to define ulrame precipitation In the Rocky Mountains <br />west oIthll Continental Dividll. The PUrp088 01 !he vlait WQll to look for flood evidence preselVed <br />ror many years aller I flood, The data then can be uslld In eslimata peak discharlles for stream. <br />In the IIrllO. of the elorm Ind mallnllude 01 flood runoff. Findy, paleoflood data can be used to <br />help 8S111R.R the reliabillly of maximum point rainfall and relino tho loohyatal map for a <br />rainatonn, which un-n Is based on limited rainfall data. Similarly. thAIIA techniques can be used <br />Immediately after a /Icod. A vlolllo the Eest Fork Little Dear Creek Basin upsl'''iun rrom <br />Porcupine R8IelVo/r near Avon. Utah. which wu the nearllst high priority rll8ervolr of intere.t <br />to tha Morg~an area, also WlllI made, This basin wa. suggested by Mall Lindon to ascertain <br />tha viabilily 01 using paleoflood InvCltigOltiona to provide axtreme-f100d .slimatell Iilat can be <br />wed to complement engineering IIood estimatN to help a5lllll8 hydrologic dam safely issues in <br /> <br />1 <br />