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j~ :'!" ~,,:~.' :~"- United States Department of the Interior GEOLOGICAL SURVEY 3 Novnnber 1994 HI.h DiKhanf' ReIeue from Glen. Canyon Dam. ADrill99S; _............ rr-lhe U.s.G.s. ......rdt t..... This experiment. at its core.. deals with erosion of accumulated sand (from ban. debriJ f.... and the chomel). tranJport (into eddies and to clw1nel marginJ). and depooition (as Janel haB). Much of the respOllJibility for litis _ in the GeES program bas been Ibat of the USGS 81 a sister agency 10 Reclamation. The Sunrey's research team, therefore, bas taken the planning to a point uf pm" detail than what has been provided in the recent mailing to the cooperating agencies from Recl.....ion (Calhoun. 21 October 1994). U.S.G.S. planning bas been done witbin the boundari.. of that pi.... but it bas Jltoccedl.d further in terms of observational requirement&, model development. computatiooal predidi..... mcthodJ, and timing. In short. the experiment is central to our work and we undcntand the burden of responsibility for careful measurement. anllysis. and interpretation of the results. The research team will meet in Flagstaff on Saturday and Sunday (Nov. .5. 6) to finish our contribution to the work plan. RaDOlllH to thl'ft ~ms railed at the last mftdnlr of tOOIM'radn. .l!!'mdes. 1. 42,000 fIJI_ \'I. 51,000 ft"/. - JIod<voond: (l) Optimum beach building fl""" will be the largcol dischlrgel that can occur without causing a net long-term depletion ofsand. So long as the quantity ofsand supplied to the Colorado River by tributaries over several years is in excess of the quantity of Janel expectod to be tranJported by an.xperimentaI flood. we are confident that there will be sufficient sand available for deposition in eddi... (l) Larger di5cbargeJ will depooit Janel in eddi.. much more rapidly tban ....lIer diJcharges (tranJport and depooition rat.. vary between the 3" and 4' power of diJcbarge). Thi. i. why a bigber now for a short duntion uses less water in excess of power plant capacity than . lower flow depositing the same amount of sand. (3) Beacheo formed by I..... diJCbargeo will stand higber above the water surface elevltion of normal dam rclcues. DfriIIon: The spring 1994 estitnal. by Recl.....ion was Ibat more water would be available and that Lake Powell's stage would be high enough to use the spillways. This would allow either inaasing the magnitude or extending the duration ofOte now. The u.s.a.s. .cco.,......1ded the increaaethe magnitude {in this CaJe 52.000 11'/.). This ( I ) increases meuurement precision to test computational predi<:tions becaUJC the depooition rat.. are higber. and (2) provides data on chomel geometry. debriJ fan inundation. and eddy patternJ at ,ignificaotly higher fl""" than could be gatbeml during the 1991 resardt flows. We perceived . "win-win-win" condition for achieving sand bar management. supporting science, and minimizing I..... ofbydropower........ . The ronHqllftlftl of redarine the flow _pl.ade from 52.000 11'/. to 42.000 11'11 .... be amoIIo....... JUIIotantIaUy by ...........lhe dantlon of tho _. TImbI.1a April: There is great latitude u to the seasonal timing of the flow for purpoICI of making flow and...w-n measurements. The impot1aIx:c ofllte datil hu been ~ wi1h lite NIlicnaI Puk --./......;r -- .- - - . Service. U.S. Fish and Wildlife Service. tbe Arizona Game and Flab Dept., and the Bureau of Reclamation to ~IU.~te ICheduIes and lif. history featurCI ofbiological componenta of the system (trout spawning earlier. blUllp-back'" chub spawning later, and..... Jet of exotic tamarisk later) and modem use patterns by raften. There are secondary COlIJiderations JUch as day Ieogtb for work. probability for good weather for comfort, cl.... oki.. for aerial photograpby, and diminiJhed probability oflributary flow. On bal__ witb all of _things COlIJidered, early April was JUggest'" as the optimal time. J. 1995.. ftuther delay: Opposition to the relcuc of water in excelS of power plant capacity bas int....ifi... in the spring and summer 1994. There are legal.... to be decided and prooedural maUen 10 be accomplished if the 1995 schedule is to be met. Some explanation of the value in performing the experiment in 199~ seems to be in order. I. Flows oflhis magnitude (up to 4'.000 ft"s) are included in the ahernalives in the Glen Canyon Dam Envirornnentallmpact Statement (GeDiEIS~ To have examined such flows in detail before the termination of interim flows would seem to be an advantage to early decisions under the adaptive management procell that is also included in the GCDIEIS. 2. FY 199' is said to be the last yearofthcGlcnCanym Environmental Studies (GeES) program. Thua, it may be the last year Ibat Ibis",,", force (U.S.G.S and othen) is supported and working II an efficient and foc:uaed group. It would be unlikely Ibat the...... people could be assembled at some later date. say. two to five yean &om now. Another group would take substadial time to achieve the same level of intellectual intensity with much groater costs. 3. An intense interim monitoring network is in place. including a network of stage gages at mlall spatial interval.. several gages and cableways. There 1ft current data ....Ibat document the recen\ conditions in groater detail Iban is lik.ly at some later dat.. Tbese data will improve interpretation of results. Much of this equipment is JCbeduI... for ........1 at the end of GeES and the post-EIS long-term monitoring proaram is neither plamed in detail nor schoduled for impl..-ation. If, at bas been JUggested. the experimental flow .....Id be conducted in response to a "spin" to avoid legal issues. we doubt seriously that there could be sufficied ... time for computation. prediction. and pluming to achieve the degree of readiness Ibat is """,ible oow. Additionally. under crnaga:q conditions. there would be 1_ control over the flow, or hydrography, characteristics (low flOW! before and after the flood flow, the magnitude of the fIoocI flow itself, .be duration of the rei..... and its ......... timing). 4. 5. The oppoIIitionlo thi..~ crealed delayl a year agolbat pre-empted the work in 1994. That is happening this year as well. The uncatainty impedeJ _ and integrated planning. I( when JUch fl""" an JCbeduIed later by adaptive management, they are to be challenged. Ihcn 1Iteto is vaIuc to havinslClllcd lite ilauclnow n1Iter than later.