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<br />LETTER OF TRANSMITTAL
<br />
<br />the west. TIle Sun ~lnTcinl UTea is becoming a silt-detention basin.
<br />It is freqllp,nUy overflowed and is densely co,'ered with water-Io\'ing
<br />vegetation slIch as silt grass and snIt cednl.
<br />The present, irrigated arca t,hat will benefit by thc proposed middle
<br />Rio Grande project is ubol1t. 85,000 acres. It IS understood t.hat, after
<br />the men is rehabilitat.ed in nCCOrdl1IlCe with the plans of the Bureau of
<br />Redu,ma.tian, tlw irl'ignted lu'cn of the midJle Ylllley will be inCI'l'f1SCU to
<br />about 85,000 f\(..~i'e5. Therefore, tho totol future irrigllt,('d area nbove
<br />Ekplll1nt Butte area t.hltt will be benefitcd by the proposed project
<br />will be 90,000 acres,
<br />
<br />Degrad'ing ~f river bed by flood releases
<br />The proposed plan, Itmong other things, contemplates the degmdin!,;
<br />of the river channel bv relellses of floodwater st.ored in Uw flood-control
<br />resen'oirs. The maximum permissible flow through the middle Rio
<br />Grande valley is fixed at 5,000 c, f, s, It is belie\"ed that a fairly stnble
<br />channel can be created find maintained if flood flows arc regulated to
<br />proper fates, providing the scdilnent is withheld from the floodwaters
<br />in the reservoirs. It is believed, however, that the degrading of the
<br />channel cannot be accomplished by meltns of flows ItS small as 5,000
<br />e, f. s, A study of thc eliselmrge mCltsuremcnts of the United Stntes
<br />Geologiclll Survl~Y for various river stHtion~ between Otowi Rl'id~c
<br />g,nd San Acacia indicates that scour docs not begin to take placo with
<br />flows less thltn 5,000 e, f. s, at Otowi Bridge, and less thltn 7,000 c, f. s,
<br />and 9,000 e, f. s, Itt Bernilillo Ituel San Felipe, respectively, It is
<br />believed, thereCore, to accomplish the desired results, flows t.hrough
<br />the mirldle valley, which arc subj"et to control by proposed flood-
<br />control reservoirs, should be ag sustained as the flood. volume will per-
<br />mit und should not he limitcd to rates less thaIl 7,000 to 8,000 cubic
<br />feet per second.
<br />The two agencies estimate tbat tbe degradation of the rh"er channel
<br />by mcans of the release of controlled floodwater nft,er t.he sediments
<br />have becn rcmoved \\~ll require from 10 to 20 years, If the process is
<br />accelemted by increasing tbe amounts of the floodwa.ter that are
<br />released, it is recognized that, until the channel co.pncity increases by
<br />tbe degradation process, the larger relenses will callSe. some excess
<br />maintenaIlce of the levees. Since t.he degradatioll of Lhe chunnel is
<br />an essential part of t.he program of construction of the project., the
<br />same as the excavntioll of the. channel ahove Elp.phant Butte Reservoir,
<br />and the sarne as the construct.ion 01 tile reservoirs, it .would appeRl' that
<br />during the time when the deg:Ndlttion is taking pl..ee tbe cost of
<br />inereltscd maint,enanee of the levee system should be borne by the
<br />Fedeml Government,
<br />An itcm, which ~pJlltrently is lost sigbt of, is the fact that after the
<br />degra.ding process COffinlenccs the capncit.y of the river channeJ will
<br />grn.dulllly increase and will nccommo(hte grea tel' rates of tlischn.rge.
<br />without damn!';e to the levee system, Whil" this gradual degrading
<br />process is being aecompl1shed there will be avniln.ble for flood-control
<br />capnci!.y as such much of the 'capacity of the proposed reservoirs that
<br />h~s been allootcd to sedimentat.ion control. The capacities so allo-
<br />cl1ted are estimated to ue sufficient to impound 0. 50-year accumulation
<br />of sediment. During the 10 to 20 years of the degrading process,
<br />there will bc av.,iIltble for flood-control purposes at the beginning of
<br />the period the cIltire capacity allocated to sediment detention, and at
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