TECHNIQUES FOR ESTIMATING SEDIMENT YIELD OF UNGAGED TRIBUTARIES ON THE SOUTHERN COLORADO PLATEAU

Transcription

1 Procngs of th Svnth Fral Intragncy Smntaton Confrnc, March 2 through 29, 2, Rno, Nvaa TECHNIQUES FOR ESTIMATING SEDIMENT YIELD OF UNGAGED TRIBUTARIES ON THE SOUTHERN COLORADO PLATEAU By RH Wbb, Rsarch Hyrologst, PG Grffths, Hyrologst, an DR Hartly, Hyrologc Tchncan, US Gologcal Survy, Tucson, Arzona Abstract: Numrous rgonal smnt transport ata ar us to valuat thr tchnqus for stmatng stramflow smnt yl from ungag trbutars of th Colorao Rvr n Gran Canyon Ths tchnqus nclu: () a rgrsson quaton rlatng ranag ara to smnt yl for all rlvant smntyl ata from northrn Arzona, (2) an mprcal rlaton vlop by Rnar (972) slct from 8 potntally rlvant mthos, an (3) a nw procur that combns rgonal floofrquncy analyss wth smntratng curvs Rsults bas on tchnqus () an (2) ar not sgnfcantly ffrnt Th thr tchnqu rqurs numrous assumptons, most notably that smnt yl on a caal avrag can b scrb by svral floos of rcurrnc ntrvals of 2 yr, yr, an yr scrb by rgonal floofrquncy rlatons Usng ata collct at gagng statons, w vlop a rlaton btwn pak scharg an totalvnt smnt yl rv from hyrographs an smntratng curvs Ths thr tchnqu proucs smnt yl stmats comparabl to thos of th rgonal ata rgrsson an Rnar (972) rlatons an may b a mor robust tchnqu for stmatng smnt yl whn stramflow ata ar avalabl INTRODUCTION Roughly 768 trbutars of th Colorao Rvr ran th Gran Canyon n northrn Arzona (fg ) Rangng n sz from < to 934 km 2, wth a man basn ara of 6 km 2 (fg 2), ths ungag trbutars hav phmral flow, gnratng sasonal floos n summr an wntr, an cut through brock that s promnantly smntary Smnt ata from ths trbutars ar vrtually nonxstnt, an ata from th canyon n gnral ar lmt to thos collct at gagng statons on th Colorao an ts major trbutars (th Para an Lttl Colorao Rvrs, an Kanab an Havasu Crks; fg ) (Garrtt t al 993; Rot t al 997) Howvr, th southrn Colorao Platau has a walth of smnttransport ata that can b us to stmat smnt yl from ungag trbutars W us thr mthos to stmat stramflow smnt yl: () a rgrsson quaton rlatng ranag ara to smnt yl for all rlvant smntyl ata from northrn Arzona, (2) an mprcal rlaton vlop by Rnar (972), an (3) a nw procur that combns rgonal floofrquncy analyss wth smntratng curvs All thr mthos ar compar aganst rgonal ata to valuat thr appropratnss for stmatng smnt yl n Gran Canyon Fgur Th Colorao Rvr an major trbutars n northrn Arzona I 24

2 Procngs of th Svnth Fral Intragncy Smntaton Confrnc, March 2 through 29, 2, Rno, Nvaa b r T f o g a t n c r P Rang n Dranag Ara (km 2 ) Fgur 2 Hstogram of ranag aras of ungag trbutars n Gran Canyon ESTIMATING SEDIMENT YIELD Rgonal SmntYl Data: Smnt loas at gagng statons on th pram Colorao Rvr, ts major trbutars, an small ranags suggst a rgonal smnt yl of 82 Mg km 2 yr (tabl ) Ths yls assum mnmal longtrm chang n storag (Graf, 987) On th bass of a rang n ranag ara most comparabl wth that of Gran Canyon trbutars, th most approprat ata ar smntaton ata from 2 small rsrvors n northastrn Arzona (Fort Dfanc rgon of th Navajo Inan Rsrvaton; Hans t al 92) W combn ths rsrvor smntaton ata wth th annual smnt yls from gagng statons n th rgon, xclung th manstm Colorao Rvr, an ft a powr functon to ths ata (fg 3) to obtan Q s = 93 A 4, R 2 = 86, (), whr Q s = smnt yl (Mg/yr), A = ranag ara (km 2 ), an n = 37 Th hgh R 2 valu suggsts smnt ata from th southrn Colorao Platau ar raly mol by a lnar rlaton to ranagbasn ara Consquntly, w us ths rlaton ntrchangably wth th rgonal ata n valuatng th othr two stmaton tchnqus Emprcal SmntYl Rlatons: W compar svral xtant mprcal rlatons for stmatng stramflow smnt yl (tabl 2) An mplct assumpton n ths approachs s that th prcnt of xpos brock n a ranag basn s not a factor n smnt yl Stran (97) bas hs mtho on rsrvor survys throughout th wstrn Unt Stats Rnar (972) an Rnar an Laursn (97) us both rsrvor smnt ata an a stochastc runoff mol calbrat to southwstrn watrshs to calbrat thr mthos Dny an Bolton (976) rlat both ranag ara an man annual runoff to smnt yl Flaxman (972) vlop a mor complcat mprcal approach that rlats smnt yl to man annual clmat (a proxy for vgtaton), watrsh slop, an sol charactrstcs Th PSIAC mtho (Pacfc Southwst IntrAgncy Commtt, 968) nvolvs ratng a watrsh on th bass of nn factors rlat to roson (surfac gology, sol, clmat, runoff, topography, lan us, uplan roson, an channl roson/smnt transport) to prouc an stmat of smnt yl Ths mtho can b appl to larg aras usng prcalculat PSIAC smntyl ratngs mapp by th Sol Consrvaton Srvc (SCS, 97; Hlun an Curts, 984) Th approachs by Howar an Dolan (98) an Ranl an Pmbrton (987) wr vlop spcfcally for Gran Canyon Howar an Dolan (98) assum that ungag trbutars yl as much smnt pr unt ara as th gag trbutars (tabl 2) Ranl an Pmbrton (987) rv thr stmat rlatng smnt yl to ranag ara from rsrvor smntaton survys of th wstrn Unt Stats an ajust t wth ata from th Para an Lttl Colorao Rvrs, an Kanab an Havasu Crks I 2

3 Procngs of th Svnth Fral Intragncy Smntaton Confrnc, March 2 through 29, 2, Rno, Nvaa Tabl Masur smnt loas at slct gagng statons on th Colorao Platau Gagng staton nam Yars of ata (Watr yars) Dranag ara (km 2 ) Smnt loa ( 6 Mg/yr) Smnt yl (Mg yr km 2 ) * Monkop Wash # * Yllow Watr Wash # * Coal Mn Wash # * R Pak Vally Wash * Coal Mn Wash # * Yllow Watr Wash # * Monkop Wash # * Coal Mn Wash # Kanab Crk nar Frona , Para Rvr at Ls Frry , Monkop Wash nar Tuba Cty ,29 6 Lttl Colorao Rvr nar Camron , Colorao Rvr at L s Frry , 6 22 Colorao Rvr nar Gran Canyon , * Smnt ata ar unpublsh valus from Paboy Coal Company Smnt ata ar annual mans for th watr yars shown from th USGS ADAPS atabas Tabl 2 Estmats of smnt yl by stramflow from 29 ungag trbutars of th Colorao Rvr A Smnt Sourc Orgnal quaton * Unts ( 6 Mg/yr) (Mg yr km 2 ) Flaxman (972) log (Y + ) = log (X + ) + acft/m 2 /yr log (X 2 + ) 644 log (X 3 + ) + 42 log (X 4 + ) Rnar (972) 846 A 87 acft/ac/yr Sol Consrvaton Srvc (97) PSIAC mtho acft/m2/yr 3 4, Stran (97) 3 A 77 m 3 /yr # Dny an Bolton 28 Q 46 (43 26 log A) tons/m 2 /yr (976) ** Howar an 78 A Mg/km 2 /yr Dolan (98) ** Ranl an 7 A 24 m 3 /km 2 /yr Pmbrton (987) Graf (987) 2 A m 3 /yr 39,9 * A = ranag ara km 2 f unts ar mtrc; othrws n ara unts gvn Smnt nsty s stmat as,2 kg/m 3 Y = smnt yl n acft/m 2 /yr; X = man annual prcptaton (nchs) / man annual tmpratur ( F), stmat as 9; X 2 = watrsh slop, stmat as prcnt grant of man channl; X 3 = prcnt of partcls > mm n amtr n th frst 2 nchs of sol, stmat as 6%; X 4 = sol ph factor, assum to b (ph of 7) # Q = annual runoff n nchs assum to b 4 A 449 (A n m 2 ) ** Drv from aly suspn smnt loas W rjct othr smntyl approachs, such as th Unvrsal Sol Loss Equaton (USLE) (Wschmr an Smth, 978; Ptrson an Swan, 979) an th CREAMS an WEPP mols of th Agrcultural Rsarch Srvc (Knsl, 98; Glly t al988) Th USLE was vlop strctly for lowslop agrcultural lan an s not approprat for th stp trran of Gran Canyon Lkws, th CREAMs an WEPP mols wr vlop for rlatvly lowslop agrcultural an ranglan an rqur consrabl watrsh ata for propr applcaton In orr to lmt th ata collcton ncssary to valuat th mor complcat rlatons, w calculat smnt yl for a subst of Gran Canyon trbutars (n = 29) an compar th rsults Estmats rang through two orrs of magntu, from 43 to 4, Mg km 2 yr (tabl 2) an most ar sgnfcantly largr than masurmnts at gagng statons (tabl ) Flaxman's (972) approach prouc th lowst smnt yl (43 Mg km 2 yr ) I 26

4 Procngs of th Svnth Fral Intragncy Smntaton Confrnc, March 2 through 29, 2, Rno, Nvaa M ( 8 l Y 7 6 Small Rsrvors (Hans t al, 92) Gagng Statons Q s = 93 A 4, R 2 =86 t n m S Dranag Ara (km 2 ) Fgur 3 Smntyl ata from small rsrvors (Hans an othrs, 92) an gagng statons on th Colorao Platau (n = 37) M ( 8 l Y t n m S Rgonal ata (Q s = 93 A 4 ) Rnar (972) Stran (97) Dny & Bolton (976) Flaxman (972) Dranag Ara (km 2 ) Fgur 4 Estmats of stramflow smnt yl from mprcal quatons an th rgonalata rgrsson rlaton unrprctng substantally for largr ranags n comparson to rgonal ata (fg 4) whl th PSIAC mtho prouc th hghst smnt yl (4, Mg km 2 yr ) Rlatons that prouc stmats outs th rang of rgonal gag ata (Flaxman 972, th PSIAC mtho, Howar an Dolan 98, Ranl an Pmbrton 987, an Graf 987) wr lmnat from furthr consraton Smnt yl was calculat for all ungag Gran Canyon trbutars wth ach of th thr rmanng tchnqus an compar to rgonal gag ata (fg 4) Th Stran (972) quaton consstntly ovrprct smnt yl I 27

5 Procngs of th Svnth Fral Intragncy Smntaton Confrnc, March 2 through 29, 2, Rno, Nvaa Tabl 3 Estmat annual stramflow smnt yl from ungag trbutars n Gran Canyon, Arzona Dranag Smnt yl (Mg/yr) Smntyl rach ara Data rgrsson Rnar (972) Floofrquncy (km 2 ) quaton * quaton mtho * Lak Powll Para Rvr 32 64,8 76,4 4,2 Para Rvr Lttl Colorao Rvr 2,93 6, 93, 47, L Colorao R Brght Angl Crk ,7 27, 82,3 Brght Angl Kanab Crk,64 332, 37, 24, Kanab Crk Havasu Crk 276 7, 63,7 4, Havasu Crk Damon Crk 3,98 82, 779, 488, Damon Crk Lak Ma 3, , 633, 397, Total 2,878 2,6, 2,6,,7, * Smnt yl s calculat usng an quaton or mtho vlop urng ths stuy Smnt yl s calculat usng th Rnar (972) quaton convrt to mtrc unts wth a smnt nsty of 2 Mg/m 3 rlatv to rgonal ata, th gr of ovrprcton ncrasng sgnfcantly wth ranag ara Th Dny an Bolton (976) quaton ovrprct smnt yl as wll, though to a lssr gr an bttr wth largr ranags than Stran (972) Howvr, th rlaton that bst approxmats th rgonal ata s th Rnar (972) powr functon rlatng smnt yl to ranag ara (fg 4) Th Rnar (972) quaton, convrt to SI unts an assumng a smnt nsty of 2 Mg/m 3, s Q s = 3 A 88, (2) whr Q s = stramflow smnt yl (Mg/yr) an A = ranag ara (km 2 ) Smnt yl calculatons bas on ths quaton ar n clos agrmnt wth thos from th rgonalata rgrsson, always wthn th sam orr of magntu an ffrng by no mor than 3% (Tabl 3) Th FlooFrquncy, RatngCurv Tchnqu: W vlop a thr mtho for stmatng stramflow smnt yl bas loosly on th work of Stran (97) an Stran an Pmbrton (982) Ths tchnqu uss local floo hyrographs as th lnk btwn rgonal floofrquncy rlatons an smnt ratng curvs Ths mtho rqurs numrous assumptons, on of th most mportant of whch s that th caal stramflow smnt yl n a trbutary can b scrb by svral floos of rcurrnc ntrvals scrb by rgonal floofrquncy rlatons Consrng th ntrmttntflow rgm of ths trbutars, whch probably hav flow lss than on prcnt of th tm, ths s lkly not to b an unrasonabl assumpton for most of th trbutars Floo volums an smntratng curvs: Hyrographs for floos on Brght Angl Crk (fg ) collct btwn 924 an 972 ar th only avalabl ata concrnng th form of stramflow floos n small Gran Canyon trbutars Although smnt ata wr collct at Brght Angl Crk btwn 99 an 993, thy ar of lmt xtnt an possbly sasonally bas (Wbb t al 2) Insta, w us smnt ata collct at 8 gagng statons oprat by th Paboy Coal Company on Black Msa to calculat smnt ratng curvs (tabl 4) Ths gagng statons (tabl ) ar on Coal Mn Wash (3 gagng statons), Yllow Watr Wash (2 gagng statons), Monkop Wash (2 gagng statons), an R Pak Vally Wash ( gagng staton) Although Black Msa s about klomtrs ast of Gran Canyon (fg ) an s unrlan by ffrnt gologc formatons, th clmat at Black Msa s smlar to that of Gran Canyon an th brock n both aras s mostly smntary In gnral, th Crtacous strata of Black Msa ar notably lss comptnt than th Palozoc strata of Gran Canyon an nclu non of th wllnurat carbonats typcal of Gran Canyon (g, th Rwall Lmston) Consquntly, th ranags on Black Msa lkly yl a hghr proporton of smnt pr unt ara than most of th ungag trbutars of Gran Canyon Smntyl stmats bas on ths ata may ovrstmat Gran Canyon smnt yl Th ranag aras of th Black Msa trbutars ar also mor comparabl to thos of ungag Gran Canyon trbutars than thos of th largr gag trbutars (fg an tabl ) Usng hyrographs for 42 floo vnts n Brght Angl Crk, w appl ach of th ratng curvs from Black Msa to calculat fv stmats of total smnt yl for ach vnt Aftr sparatng bas flow (4 to m 3 /s) from th runoff to calculat pak scharg for ach vnt, w us lnar rgrsson to trmn th rlaton btwn pak scharg an total smnt yl for ach ratng curv (tabl ) Th rlaton of smnt yl to pak I 28

6 Procngs of th Svnth Fral Intragncy Smntaton Confrnc, March 2 through 29, 2, Rno, Nvaa Tabl 4 Smnt ratng at fv gagng statons on Black Msa, Arzona Trbutary Yars of ata (Watr yars) Dranag ara (km 2 ) Coffcnt a Exponnt b R 2 Maxmum scharg (m3/s) Monkop Wash # , Yllow Watr Wash # , Coal Mn Wash # , Yllow Watr Wash # , Coal Mn Wash # , Th coffcnt an xponnt ar for th quaton S y = a Q b, whr S y = smnt yl (Mg/ay) an Q = nstantanous scharg (m 3 /s) Mnmum scharg for th ratng curvs s m 3 /s Ratngs ar rv from unpublsh ata, Paboy Coal Company Tabl Lnar rgrsson btwn pak scharg an smnt yl for 42 floos n Brght Angl Crk Smnt ratng curv us Yllow Watr # Yllow Watr #2 Coal Mn # Coal Mn #2 Monkop # Coffcnt (a) Exponnt (b) R Th coffcnt an xponnt ar for th quaton Q s = a Q b p whr Q s = smnt yl (Mg/vnt) an Q p = nstantanous pak scharg (m 3 /s) Th Brght Angl Crk gag rcor runs from 924 to 973 scharg took th form: Tabl 6 Rgonal rgrsson quatons from Rosk (978) for stramflow floo Floo frquncy rgon * Rcurrnc ntrval(yrs) Floofrquncy rlaton Q = 9 A 66 Q = 663 A 6 Q = 27 A 66 Q = 3 A 49 (E/,) 22 Q = 39 A 446 (E/,) 36 Q = 43 A 423 (E/,) 43 Q = pak scharg (ft 3 /s); A = ranag ara (m 2 ); E = man basn lvaton (ft) * Rgon 4 s ast of th Colorao Rvr an north of th Lttl Colorao Rvr; th rmanr of Gran Canyon falls wthn Rgon Q = a Q p b, (3) whr Q = smnt yl n Mg/vnt, Q p = pak floo scharg n m 3 /s, an a an b ar rgrsson coffcnts Th R 2 valus rang from 76 to 82, ncatng a hgh gr of rlaton btwn pak scharg an smnt yl pr vnt (tabl ) Of th ght rlatons, w lct to us that rv from Monkop Wash # bcaus: ) t ha th hghst R 2 (82), 2) t ha th lowst coffcnt an woul prouc th lowst smnt yl stmat as a countrbalanc to potntal ovrstmaton of Gran Canyon smnt yl, an 3) th ranag ara of Monkop Wash # (292 km 2 ) s closst to th man ara of ungag trbutars n Gran Canyon (6 km 2 ) Rgonal floo frquncy: W valuat th rgonal rgrsson rlatons for floo frquncy gvn by Thomas t al (997) for th southwstrn Unt Stats, but foun sgnfcant problms whn applyng thm to th Gran Canyon rgon (Wbb t al 997, 2) Fw small ranags n Gran Canyon hav gagng rcors, an thrfor ths trbutars ar poorly rprsnt n th Thomas rlatons Atonally, most of th ata for ths quatons com from aras outs northrn Arzona In contrast, th floofrquncy rgrssons of Rosk (978), although calculat wth shortr gag rcors an fwr ntal basn varabls, us Arzona ata xclusvly an contan th sam npnnt varabls of ranag ara an man basn lvaton us by Thomas t al (997) W thrfor lct to us th rgonalrgrsson quatons publsh by Rosk (978) for calculatng smnt yl n Gran Canyon (tabl 6) Calculatons of smnt yl: W lnk floofrquncy scharg stmats to smnt ylpak scharg rlatons usng I 29

7 Procngs of th Svnth Fral Intragncy Smntaton Confrnc, March 2 through 29, 2, Rno, Nvaa / g M 8 ( 7 l 6 Y t n 4 m 3 S 2 Rgonal ata (Q s = 93 A 4 ) Rnar (972) Equaton Monkop Wash # Dranag Ara (km 2 ) Fgur Stramflow smntyl stmats for 768 Gran Canyon trbutars calculat usng th rgonal floofrquncy stmats of Rosk (978) an smntratng ata from Monkop Wash # compar to th rgonalata rgrsson an Rnar (972) quatons Q s = [ f(q ) + 2 f(q ) + f(q 2 )] /, (4) whr Q s s smnt yl n Mg/yar, Q t s th pak scharg of th t yar floo n m 3 /s (from Rosk 978), an f(q t ) s th rgrsson rlatng pak scharg to smnt yl n Mg/vnt (Q calculat for Monkop Wash #) W assum an xpct valu for th numbr of floos to occur n a ca whch calls for fv 2yr floos, two yr floos, an on yr floo to lvr most of th smnt to th Colorao Rvr Rgonal floofrquncy rlatons o not prouc annual floos, so w hav no mans of trmnng th ffct of nglctng th smallst vnts, an w chos not to nclu th nflunc of long rcurrncntrval floos n th analyss Smnt yl calculatons bas on th floo frquncyratng curv tchnqu ar n rasonabl agrmnt wth thos from th rgonalata rgrsson (fg ) an wth no mor scattr than th orgnal rgonal ata (fg 3) Estmats calculat by rach ar lowr than thos from th rgonalata rgrsson an Rnar rlatons (tabl 3), but stll of th sam orr of magntu an nvr vary by mor than 4% CONCLUSIONS All thr tchnqus us to stmat smnt yl from small ranag basns n Gran Canyon agr wll wth ach othr an rgonal ata, suggstng thy may all b usful n stmatng smnt yl lswhr on th southrn Colorao Platau In valuatng ght mprcal smntyl rlatons, complx multvarat mthos, such as that of th PSIAC (968) an Dny an Bolton (976), not prform as wll as smpl powr functons rlatng smnt yl to ranag basn ara Ths suggsts that complx rlatons may not ncssarly b mor accurat n stmatng smnt yl, at last on a rgonal scal Th nw floofrquncy tchnqu was ajust to ft th ata rgrsson rlaton an s not strctly an npnnt approach Nvrthlss, clos agrmnt wth th othr two mthos suggsts that th tchnqu has strong potntal as a nw mtho for stmatng stramflowsmnt yl It may b mor robust than th othrs for stmatng smnt yl whr local stramflow ata ar avalabl Futur tstng of ths tchnqu n sttngs whr smnt yls ar known may bar ths out Th floofrquncy tchnqu pns on numrous untst assumptons, such as quatng caal smnt yl wth th sum of smnt yl from on tnyar, two fvyar, an fv twoyar floos I 3

8 Procngs of th Svnth Fral Intragncy Smntaton Confrnc, March 2 through 29, 2, Rno, Nvaa REFERENCES Dny, FE, an Bolton, GC, 976, Smnt ylrunoff ranag ara rlatonshps n th Unt Stats Journal of Sol an Watr Consrvaton 3, Flaxman, EM, 972, Prctng smnt yl n Wstrn Unt Stats, Journal of th Hyraulcs Dvson, Procngs of th Amrcan Socty of Cvl Engnrs HY 2, Garrtt, WB, Van D Vantr, EK, an Graf, JB, 993, Stramflow an smnttransport ata, Colorao Rvr an thr trbutars n Gran Canyon, Arzona, 983 an 9886 US Gologcal Survy Opnfl Rport 9374, 624 Glly, JE, Lan, LJ, Lafln, JM, Ncks, HD, an Rawls, WJ, 988, USDAwatr roson prcton projct: Nw gnraton roson prcton tchnology, n Molng, agrcultural, forst, an ranglan hyrology Symposum procngs, pub 788 Graf, WL, 987, Lat Holocn smnt storag n canyons of th Colorao Platau Gologcal Socty of Amrca Bulltn 99, 2627 Hans, CF, Van Sckl, DM, an Ptrson, HV, 92, Smntaton rats n small rsrvors n th Lttl Colorao Rvr basn US Gologcal Survy Watrsupply Papr D, 27 Hlun, JD, an Curts, NM, Jr, 984, A quck an asy approach to stmatng roson on all lan n th wst, abstract Procngs of 39th Annual Mtng of th Sol Consrvaton Socty of Amrca Howar, A, an Dolan, R, 98, Gomorphology of th Colorao Rvr n Gran Canyon Journal of Gology 89, Knsl, WG, (tor), 98, CREAMS A flscal mol for chmcals, runoff, an roson from agrcultural managmnt systms US Dpartmnt of Agrcultur, Consrvaton Rsarch Rport No 26, 64 Pacfc Southwst IntrAgncy Commtt, 968, Rport on factors affctng smnt yl n th Pacfc Southwst ara Watr Managmnt Subcommtt, Smntaton Task Forc, Ptrson, AE, an Swan, JB (tors), 979, Unvrsal sol loss quaton past, prsnt an futur Sol Scnc Socty of Amrca Spcal Publcaton 8, 3 Ranl, TJ, an Pmbrton, EL, 987, Rsults an analyss of STARS molng fforts of th Colorao Rvr n Gran Canyon Flagstaff, Gln Canyon Envronmntal Stus Rport, 4 Rnar, KG, 972, Smnt problms n th ar an smar southwst, n Procngs, 27th Annual Mtng, Sol Consrvaton Socty of Amrca Portlan, Orgon, Rnar, KG, an Laursn, EM, 97, A ynamc bhavor mol of an phmral stram Journal of th Hyraulcs Dvson, Procngs of th Amrcan Socty of Cvl Engnrs HY, 28 Rosk, RH, 978, Mthos for stmatng th magntu an frquncy of floos n Arzona Phonx, Arzona Dpartmnt of Transportaton Rport for Rsarch Projct Arzona HPR(2), 82 Rot, JJ, Flynn, ME, an Blls, DJ, 997, Hyrologc ata, Colorao Rvr an major trbutars, Gln Canyon Dam to Damon Crk, Arzona, watr yars 999 US Gologcal Survy Opnfl Rport 972, 474 Sol Consrvaton Srvc, 97, Eroson, smnt an rlat salt problms an tratmnt opportunts US Dpartmnt of Agrcultur, 2 Stran, RI, 97, Burau of Rclamaton procurs for prctng smnt yl US Dpartmnt of Agrcultur Rport ARSS4, Prsnt an prospctv tchnology for prctng smnt yls an sourcs, Stran, RI, an Pmbrton, EL, 982, Rsrvor smntaton tchncal gulns for Burau of Rclamaton Dnvr, Colorao, Burau of Rclamaton Thomas, BE, Hjalmarson, HW, an Waltmyr, SD, 997, Mthos of stmatng magntu an frquncy of floos n th southwstrn Unt Stats US Gologcal Survy WatrSupply Papr 2433, 9 Wbb, RH, Grffths, PG, Mls, TS, an Hartly, DR, 2, Smnt lvry by ungag trbutars of th Colorao Rvr n Gran Canyon, Arzona US Gologcal Survy WatrRsourcs Invstgatons Rport 4, 67 Wbb, RH, Mls, TS, Grffths, PG, Ellott, JG, Crlng, TE, Pora, RJ, Ws, TW, an Pzzuto, JE, 999b, Lava Falls Rap n Gran Canyon, ffcts of lat Holocn brs flows on th Colorao Rvr: US Gologcal Survy Profssonal Papr 9, 9 Wschmr, WH, an Smth, DD, 978, Prctng ranfall roson losss a gu to consrvaton plannng, Agrcultur Hanbook 37, USDASEA US Gologcal Survy, 67 W Anklam R, Tucson, AZ, 874; rhwbb@usgsgov; xt 238 I 3