APPENDX A RANFALL LOSSES (Dat o section o Maicopa County, Aizona, )
H land Rainall ':~':"'::""S ~:.,':.i::!:;i::i:~~~ :: (::: Geneal Rainall excess is tha t potion o the total ainall depth that dains diectly om the suace by oveland low. Bya mass balance, ainall excess plus ainall loss equals pecipitation. When peonning a lood analysis using a ainall-uno model, the detennination o ainall excess is o utmost impotance. Rainall excess integated ove the entie wateshed esults in uno volume, and the tempoal distibution o the ainall excess will, along with the hydaulics o uno, detemine the peak dischage. Theeoe, the estimation o the magnitude and time distibution o ainall losses should be peomed with the best pactical technology, consideing the objective o the analysis, economics o the poject, and consequences o inaccuate estimates. Rainall losses ae geneally consideed to be the esult o evapoa tion o wa te om the land suace, inteception o ainall by vegetal cove, depession stoage on the land suace (paved o unpaved), and iniltation o wate into the soil matix. A schematic epesentation o ainall losses o a uniom intensity ainall is shown in Figue 4.1. As shown in the igue, evapoation can stat at an initially high ate depending on the land suace tempeatue, but the ate deceases vey apidly and would eventually each a low, steady-state ate. Fom a pactical standpoint, the magnitude o ainall loss that can be ealized om evapoation duing a stom o suicient magnitude to cause lood uno is negligible. nteception, also illustated in Figue 4.1, vaies depending upon the type o vegetation, matuity, and extent o canopy cove. Expeimental data on inteception have been collected by numeous investigatos (Linsley and othes, 1982), but little is known o the inteception values o most hydologic poblems. Estimates o inteception o vaious vegetation types (Linsley and othes, 1982) ae: 37
a aoiiauu.. ' Rainall Losses..,.----- NTAL ABSTRACTON (A)= ACCUMULATED LOSS UP TO TME OF PONDNG -- w :2 t- t Z ~ et:: W... t- o... W o CONSTANT NTENSTY RANFALL TOTAL RANFALL LOSS RATE DEPRESSON STORAGE + NTERCEPTON PEROD 1 PEROD 2 Tp= TME TO PONDNG TME EVAPORATON PEROD 3 Figue 4.1 Schematic Repesentation o Rainall Losses o a Uniom ntensity Rainall 38
hadwood tee cotton alala meadow gass Vegetation Type nteception, nches.9.33.11.8 Rainall Losses No inteception estimates ae known o natual vegetation that occus in Maicopa County. Fo most applications in Maicopa County the magnitude o inteception losses is essentially., and o pactical puposes inteception is not consideed o lood hydology in Maicopa County. Depession stoage and iniltation losses compise the majoity o the ainall loss as illustated in Figue 4.1. The estimates o these two losses will be discussed in moe detail in late sections o this manual. Thee peiods o ainall losses ae illustated in Figue 4.1, and these must be undestood and thei implications appeciated beoe applying the pocedues in this manual. Fist, thee is a peiod o initial loss when no ainall excess (uno) is poduced. Duing this initial peiod, the losses ae a unction o the depession stoage, inteception, and evapoation ates plus the initially high iniltation capacity o the soil. The accumulated ainall loss duing this peiod with no uno is called the initial abstaction. The end o this initial peiod is noted by the onset o ponded wate on the suace, and the time om stat o ainall to this time is the time o ponding (Tp). t is impotant to note that losses duing this ist peiod ae a summation o losses due to all mechanisms including iniltation. The second peiod is maked by a declining iniltation ate and geneally vey little losses due to othe actos. The thid, and inal, peiod occus o ainalls o suicient duation o the iniltation ate to each the steady-state, equilibium ate o the soil (c). The only '- /5 -n ;:'J"e 4-,;1.) /.' appeciable loss duing the inal peiod is due to iniltation..y'.,::- 4.5GJl:11t!'pt The actual loss pocess is quite complex and thee is a goo;tdeal o intedependence o the loss mechanisms on each othe and on the ain~)..y(tsel. Theeoe, simpliying assumptions ae usually made in the modeling o ai 'alliosses. Figue 4.2 epesents a simpliied set o assumptions that can be made;'that suace etention loss is the summation o all losses othe than those due to iniltation, and that this loss occus om the stat o ainall and ends when the accumulated ainall equals the magnitude o the capacity o the suace etention loss. t isassuned that iniltation does not occu duing this time. Ate the suace etention is satisied, iniltation begins. the iniltation capacity exceeds the ainall intensity, then no ainall excess is poduced. As the iniltation capacity deceases, it may eventually equal the ainall intensity. This would occu at the time o ponding (Tp) which signals the beginning o suace uno. As illustated in both Figues 4.1 and 4.2, ate the time o ponding the iniltation ate deceases exponentially and may each a steady-state, equilibium ate (c). t is these 'simpliied assumptions and pocesses, as illustated in Figue 4.2, that ae to be modeled by the pocedues in this manual.
Rainall Losses ~ w 2 - z ::> a::: w.. -.. W o.. w - «a::: 4 \ \ \ NFLTRATON CAPACTY CURVE RANFALL EXCESS TME --~...,...,..--,.---,--,..4- - - -..:.. - - _1_ - - T NFLTRATON SURFACE RETENTON LOSS Figue 4.2 Simpliied Repesentation o Rainall Losses A 6. A Function o Suace Retention Losses Plus niltation.. c -
Suace Retention Loss 1::::::,:,:::::!',:,:j[~11:! Rainall Losses Suace etention loss, as used heein, is the summation o all ainall losses othe '""',,',,',,,,', than iniltation. The majo component o suace etention loss is depession stoage; elatively mino components o suace etention loss ae due to inteception and evapoation, as peviously discussed. Depession stoage is consideed to occu in two oms. Fist, in-place depession stoage occus at, and in the nea vicinity o, the aindop impact. The mechanism o this depession stoage is the micoelie o the soil and soil cove. The second om o depession stoage is the etention o suace uno that occus away om the point o aindop impact in suace depessions such as puddles, oadway guttes and swales, oos, iigation bodeed ields and lawns, and so oth. A elatively mino contibution by inteception is also consideed as a pat o the total suace etention loss. Estimates o suace etention loss ae diicult to obtain and ae a unction o the physiogaphy and land-use o the aea. The suace etention loss on impevious suaces has been estimated to be in the ange.625 inch to.125 inch by Tholin and Keee (196),.11 inch o 1 pecent slope to.6 inch o 2.5 pecent slopes by Viessman (1967), and.4 inch based on ainall-uno data o an uban wateshed in Albuqueque by Sabol (1983). Hicks (1944) povides estimates o suace etention losses duing intense stoms as.2 inch o sand,.15 inch o loam, and.1 inch o clay. Tholin and Keee (196) estimated the suace etention loss o tu to be between.25 to.5 inch. Based on ainall simulato studies on undeveloped alluvial plains in the Albuqueque aea, the suace etention loss was estimated as.1 to.2 inch (Sabol and othes, 1982a). Rainall simulato studies in New Mexico esult in estimates o.39 inch o easten plains angelands and.9 inch o pinon-junipe hillslopes (Sabol and othes, 1982b). Suace etention losses o vaious land-uses and suace cove conditions in Maicopa County have been extapolated om these epoted estimates and these ae shown in Table 4.1. niltation 1::1[,:1,,:;::";;:::1;:;;1 niltation is the movement o wate om the land suace into the soil. Gavity,',...,... and capillay oces dawing wate into and though the poe spaces o the soil matix ae the two oces that dive iniltation. niltation is contolled by soil popeties, by vegetation inluences on the soil stuctue, by suace cove o ock and vegetation, and by tillage pactices. The distinction between iniltation and pecolation is that pecolation is the movement o wate though the soil subsequent to iniltation.!,!, i, 1:1' 1\:, i : ' :1,,!i, ' 41 11, i,!j "! d
Rainall Losses Table 4.1 Suace Retention Loss o Vaious Land Suaces n Maicopa County ---- Suace Retention Land-use and/o Loss Suace Cove la, nches (1 ) (2) -' Natual ---- Deset and angeland, lat slope _..35 Hillslopes, Sonoan Deset.15 Mountain, with vegetated suace -.25 Developed (Residential and CommeciaQ Lawn and tu.2 Deset landscaee.1 Pavement -.5 Āgicultual Tilled ields and iigated pastue.5 ~ i niltation can be contolled by pecolation i the soil does not have a sustained dainage capacity to povide access o moe iniltated wate. Howeve, beoe pecolation can be assumed to estict iniltation o the design ainalls being consideed in Maicopa County, the extent by which pecola tion can estict inilta-. tion o ainall should be caeully evaluated. SCS soil scientists have deined hydologic soil goup D as: "Soils having vey slow iniltation ates when thooughly wetted and consisting chiely o clay soils with a high swelling potential, soils with a pemanent high wate table, soils with a claypan o clay laye at o nea the suace, and shallow soils ove nealy impevious mateial." This deinition indicates that hydologic soil goups A, B, o C could be classiied as D i a nea impevious stata o clay, caliche, o ock is beneath them. When these soils ae consideed in egad to long-duation ainalls (the design events o many pats o the United States) this deinition may be valid. Howeve, when consideed o shot-duation and elatively small design ainall depths in Maicopa County, this deinition could esult in undeestimation o the ainall losses. This is because even a elatively shallo~ hoizon o soil ovelaying an impevious laye still has the ability to stoe a signiicant amount o iniltated ainall. Fo example, conside the situation whee only 4 inches o soil coves an impevious laye. the eective poosity is.3, then 1.2 inches (4 inches x.3) o wate can be iniltated and stoed in the shallow soil hoizon. Fo design ainalls in Maicopa County, this epesents a signiicant stoage volume o iniltated ainall and so when using'. that contain signiicant aeas classiied as hyd ogic soil goup D, the eason o that classiication should be detemined. ' >t:"/~ Y-...!'P"'- '5 cj' :.:.:.:.:.::.::.:.:.:::.:.:.:.:.:.:.::.:.:.::.::.:::::.:.::.::.:.:.::.:::.:::::::::/~t::;::t.~(:':!.:~:::::~1(((~;:::ci~~e:.::::::::::.:::.:.:::.:.:.:.::.::-:.:.:.::::::::::.:.::::.:: 42 - -
Rainall Losses Hydologic soil goup D should be etained only o:» clay soils,» soils with a pemanent high wate table, and» ock outcop. ~ Hydologic soil goup D should pobably not be etained in all situations whee the classiication is based on shallow soils ove nealy impevious layes; site speciic studies and sensitivity analyses should be peomed to estimate the loss ates to be used o such soils. :::::_'".;,a.':: Recommended Methods o Estimating Rainall Losses Many methods have been developed o estimating ainall losses; ive ae listed as options in the HEC-l Flood Hydology Package. They ae: 1. Holtan niltation Equation 2. Exponential Loss Rate 3. SCS Cuve Numbes (CN) Loss Rate 4. Geen and Ampt niltation Equation 5. nitial Loss Plus Uniom Loss Rate (L+ULR) O these ive, howeve, only two-geen and Ampt and L+ULR-ae ecommended o estimating ainall losses in Maicopa County o the easons discussed below. The Holtan niltation Equation is an exponential decay type o equation o which the ainall loss ate asymptotically diminishes to the minimum iniltation ate (c). The Holtan equation is not extensively used and thee is no known application o this method in Aizona. Data and pocedues to estimate the paametes o use in Maicopa County ae not available. Theeoe, the Holtan equation is not ecommended o geneal use in Maicopa County. The Exponential Loss Rate Method is a ou paamete method that is not extensively used, but it is a method peeed by o the U.S. Amy Cops o Enginees. Data and pocedues ae not available to estimate the paametes o this method o all physiogaphic egions in Maicopa County, but Exponential loss ate paametes have bepn developed om the econstitution o lood events o a lood hydology study.i1:~potion o Maicopa County (U.S. Amy Cops o Enginees,. 1982). Howeve, adequate data.i6not available to estimate the necessay paametes ad. 43
Rainall Losses 44 o all soil types and land uses in Maicopa County, and this method is not ecommended o geneal use in Maicopa County. The SCS en method is the most extensively used ainall loss ~ethod in Maicopa County and Aizona and it has wide acceptance among many agencies, consulting engineeing inns, and individuals thoughout the community. This method is limited, howeve, by both theoetical and pactical deiciencies, and thus is not ecommended o geneal use in Maicopa County. Deiciencies o the SCS CN method include: 1. Rainall losses ae independent o the duation o ainall. That is, o a given depth o ainall, the same ainall loss esults (egadless o the duation o ainall) and the same ainall excess would be estimated o a given ainall depth occuing in, o example, eithe 1 hou o 24 hous. 2. The estimated ainall loss ate is a unction o ainall intensity. Shot peiods o high intensity ainall would oten esult in lage estimates o ainall losses. This is contay to the geneally accepted iniltation elation as illustated in Figue 4.2. 3. The iniltation ate appoaches zeo athe than a minimum iniltation ate (c). 4. The initial abstaction is equal to.25 whee S = looo/cn -1 This equation is not theoetically justiied no is it based on data o hydologic conditions that ae epesentative o Maicopa County. 5. The selection o CN is too subjective and is oten based moe on taditional acceptance o CN values athe than on scientiically substantiated indings. 6. At low ainalls (less than 4 inches), the estimate oainalllo~s is vey sensitive to the selection o CN. As mentioned peviously, the two ecommended methods o estimating ainall losses in Maicopa County ae the Geen and Ampt iniltation equation and the initial loss and uniom loss ate (ll+ulr) method. Both methods, as pogammed into HEC-1, can be used to simulate the ainall loss model as depicted in Figue 4.2. (Fo a ull discussion o these methods, see Sections 4.4.1 and 4.4.2.) The L+ULR is a simpliied model that has been used extensively o lood hydology and data ae,is-available to estimate the two paametes o this method. The Geen and Ampt iniltation equation is a physically based model that has been in existence since 1911, and has ecently been incopoated as an option in HEC-1. \i o.ced.. Ues have been dev.elo~ tq~imate. th~.~~~~en and AE"pt. iniltclti~~_9...uat!~1},/ The peeed method, and the mos~ theo(:~~_~~v c ate, is the Geen and Ampt ~tation equati~e C+ULR1Seeommended as an altenative i t is not possil5letcesimate the Geen and Ampt equation J
Rainall Losses paametes, o o othe valid easons. t should be ealized, as explained late, that the use o the Geen and Ampt equation and paametes, as deined heein, will pobably esult in lowe peak dischages and uno volumes than the use o the L+ULR. Othe methods should be used only i thee is technical justiication o a vaiance om this ecommendation and i adequate inomation is available to estimate the necessay paametes. Use o ainall loss methods othe than those ecommended should not be undetaken unless peviously appoved by the Flood Contol Distict and the local egulatoy agency. 4.4.1 Geen and Ampt niltation Equation This model, ist developed in 1911 by W.H. Geen and G.A. Ampt, has since the ealy 197s, eceived inceased inteest o estimating ainall iniltation losses. The model has the om: whee :... Ks (1 +~) - F o < i =i o ';? i = inilttation ate (LT), Ks ' e F = ainall intensity (LT), = hydaulic conductivity, wetted zone, steady-state ate (LT) = aveage capillay suction in the wetted zone (L), = soil moistue deicit (dimensionless), equal to eective soil oosity times.- (the eence in inal and initial volumetic soil satuations, and = depth o ainall that has iniltated into the soil since the beginning o ainall (L). A sound and concise explanation o the Geen and Ampt equation is povided by Bedient and Hube (1988). t is impotant to note that as ain continues, F inceases and appoaches Ks, and theeoe, is invesely elated to time. Equation 1 is implicit with espect to which causes computational diiculties. Egget (1976) simpliied Equation 1 byexpanding the equation in a powe seies and tuncating all but the ist two tems o the expansion. The simpliied solution (Li and othes, 1976) is: (1) (2) 45 1 l' i 1
Rainall Losses whee ~t = the computation inteval F = accumulated depth o iniltation at the stat o ~t. The aveage iniltation ate is: (3) Use o the Geen and Ampt equation as coded in HEC-l involves the simulation o ainall loss as a two phase pocess, as illustated in Figue 4.2. The ist phase is the simulation o the suace etention loss as peviously descibed; this loss is called the initial loss (A) in HEC-1. Duing this ist phase, all ainall is lost (zeo ainall excess geneated) duing the peiod om the stat o ainall up to the time that the accumulated ainall equals the value o LA. t is assumed, o modeling puposes, that no iniltation o ainall occus duing this ist phase. nitial loss (A) is pimaily a unction o land-use and suace cove, and ecommended values o A o use with the Geen and Ampt equation ae pesented in Table 4.1. Fo example, about.35 inches o ainall will be lost to uno due to suace etention o deset and angelands on elatively lat slopes in Maicopa County. The second phase o the ainall loss pocess is the inilta tion o ainall into the soil matix. Fo modeling puposes, the iniltation begins immediately ate the suace etention loss (A) is completely satisied, as illustated in Figue 4.2. The thee Geen and Ampt equation iniltation paametes as coded in HEC-l ae:» hydaulic conductivity at natwal satuation (XKSA n equal to Ks in Equation 1;» wetting ont capillay suction (PSF) equal to 'l' in Equation 1; and» volumetic soil moistue deicit at the stat o ainall (DTHET A) equal to e in Equation 1. The thee iniltation paametes ae unctions o soil chaacteistics, gound suace chaacteistics, and land management pactices. The soil chaacteistics o inteest ae paticle size distibution (soil textue), oganic matte, and bulk density. The pimay soil suace chaacteistics ae vegetation canopy cove, gound cove, and soil custing. The land management pactices ae identiied as vaious tillages as they esult in changes to soil poosity. Values o Geen and Ampt equation paametes as a unction o soil chaacteistics alone (bae gound condition) have been obtained om published epots (Rawls and othes, 1983; Rawls and Bakensiek, 1983). Aveage values ox<sat and PSF o each o the soil textue classes om Rawls and Bakensiek (1983) ae shown in Columns (2) and (3) o Table 4.2. Values oxksat and PSF (as a unction o pecent o sand and pecent o clay o soil with.5 pecent oganic matte and base value (unalteed] soil poosity) ae shown in Figues 4.3 and 4.4, espectively (Rawls and Bakensiek, 1983). The values o XKSAT and PSF om Table 4.2 should be used i 46
i,... 'i!l - z -< () (~ AV1~ Figue 4.3 Geen and Ampt Loss Rate Hydaulic Conductivity at natual satuation n nches/hou XKSAT (.5% oganic matte) Rainall Losses ~.:.:.;.:,:,;,:,:,:,:,:,.:::.:.: ;.: ; ;.x :-): ::: ;.}: :': : : ; ': : :.:::-:.:.;..;,;..:,~~;.;.;.:.:.~:.:,;.:::...:.:.:.;.::;.:-:.;.: :.::;.:::::,:.:.:.;,:,::~,:,:,:,:,:,:,:,:,:,:,;,:.: ::.;.: :.; :.: ;.; : :.:.:.:.;.; ;.;.; :.:.: :.:.:.:.: :. ;..:. :.:.:,:.:.:.;.:.; ;.:.:.;,;.:.:.:::.:. :.:.:.:.:.;.:. ;::;:.:::::,:.:.:.;.:.:.:.:,:.:.:.:.:;~:::.:-:.:.:.:.:.:': : ;.: z.;.:.;..:.; ::~:.:.:::.:.:.:,;::,:::. ~.:.;. ;.:.;.:.:::,:::,:::.:.:.:.::~. 47
Rainall Losses,... ~ - a z < en (...--." "> N.,..-... v~ 'X:) t<) ~ 'v~ ~~ /""'\ " Figue 4.4 Geen and Ampt Loss Rate Wetting Font Suction n nches (cm) PSF
- - - - - Rainall Losses geneal soil textue classiication o the dainage aea is available. The values o XKSAT and PSF om Figues 4.3 and 4.4 can be used i moe speciic soil textue classiication is available om a detailed soil suvey o which the pecentages o sand and clay have been detemined by an appopiate ield soil suvey. The use o the inomation in Figues 4.3 and 4.4 will equie an extensive study o the soil o the dainage aea, and o most dainage studies only geneal soil textue classiication will be known so the values om Table 4.2 should be used. The soil moistue deicit (OTHET A) is a volumetic measue o the soil moistue stoage capacity that is available at the stat o the ainall. DHETA is a unction o the eective poosity o the soil. The ange o DTHETA is. to the eective poosity. the soil is eectively satuated at the stat o ainall then DTHETA equals.; i the soil is devoid o moistue at the stat o ainall th~thet A equals the eective poosity o the soil. The poosity o soil as a unction o soil textue (pecent o sand and pecent o clay) is shown in Figue 4.5 (Bakensiek and othes, 1984). Unde natual conditions, soil seldom eaches a state o soil moistue less than the wilting point o vegetation. Figue 4.6 is a gaph o volumetic soil moistue at wilting point as a unction o soil textue. Due to the apid dainage capacity o most soils in Maicopa County, at the stat o a design stom the soil would not be expected to be in a state o soil moistue geate than the ield capacity. Figue 4.7 is a gaph o volumetic soil moistue at ield capacity as a unction o soil textue. Table 4.2 Geen and Ampt Loss Rate Paamete Values o Bae Gound Soli Textue XKSAT PSF DTHETAl Classiication nches/hou nches Dy Nomal (1 ) (2) (3) (4) (5) - sand 4.6 1.9.35.3 loamy sand 1.2 2.4.35.3 sandy loam.4 3.5._- ---.35.25 loam.25 4.3.35.25 silty loam.15 6.6.4.25 silt.1 7.5.35.15 sandy clay loam.6 8.6.25.15 clay loam.4 8.2.25.15 silty clay loam.4.- 1.8.3.15 sandy clay.2 9.4.2.1 silty clay.2 11.5.2.1 clay.1 12.4.15.5 1 Selection o DTHETA: Dy = Noniigated lands, such as deset and angeland; Nomal = igated lawn, tu, and pemanent pastue; Satuated = igated agicultual land. Satuated (6) '--.-'-- 49
Rainall Losses "'T. a: w - - < :2: () Z < '" c:!?- 1 w CJ Z «:c u >- - en a:.. ;S?...?. - «- ()..J U en () () \ "<t -J' to C'? -' () -' o () U en 1i--~~~~~~--~~-~---~~--~--~--~--~~~~--~--~--~ ~ ~ o C'? "<t \ "" <Xl o en o Figue 4.5 Poosity
-- <:Pa z < en (%) A.V'~ Figue 4.6 Geen and Ampt Loss Rate 15-Ba Soli Moistue by Volume (assumed wilting point) Rainall Losses
Rainall Losses o.-.. - o <.J (J) en..- ~ ('./ (').J U en (.) en " 1 co (%) "Vl::> o,... o Cl) Figue 4.7 Geen and Ampt Loss Rate 1/3 Ba Soli Moistue by Volume (assumed ield capacity) o ) o
-. - Rainall Losses Howeve, Maicopa County also has a lage segment o its land aea unde iigated agicultue, and it is easonable to assume that the design equency stonn could occu duing o shotly ate cetain lands have been iigated. Theeoe, it would be easonable to assume that soil moistue o iigated lands could be at o nea eective satuation duing the stat o the design ainall. Thee conditions o DTHET A have been deined o use in Maicopa County based on the antecedent soil moistue condition that could be expected to exist at the stat o the design ainall. These thee conditions ae:» "Dy" o antecedent soil moistue nea the vegetation wilting point;» "Nomal" o antecedent soil moistue condition nea ield capacity due to pevious ainall o iigation applications tmnonagicultuallands; and oj», "Sahated" o antecedent soil moistue nea eective satuation due to ecent iigation o agicultual lands. Values o DTHETA have been estimated by subtacting the initial volumetic soil moistue o each o the thee conditions om the soil poosity. The value o DTHETA "Dy" as a unction o soil textue is shown in Figue 4.8. This igue was pepaed by subtacting the wilting point soil moistue in Figue 4.6 om the soil poosity in Figue 4.5. The value o DTHETA "Nomal" as a unction o soil textue is shown in Figue 4.9. This igue was pepaed by subtacting the ield capacity soil moistue in Figue 4.7 om the soil poosity in Figue 4.5. The value o DTHETA "Satuated" is always equal to. because o this condition thee is no available poe space in the soil matix at the stat o ainall. Values o DTHETA o the thee antecedent soil moistue conditions ae shown in Table 4.2. DTHETA "Dy" should be used o soil that is usually in a state o low soil moistue such as would occu in the deset and angelands o Maicopa County. DTHETA "Nomal" should be used o soil that is usually in a state o modeate soil moistue such as would occu in iigated lawns, gol couses, paks, and iigated pastues. DTHETA "Satuated" should be used o soil that can be expected to be in a state o high soil moistue such as iigated agicultual land. The hydaulic conductivity (XK5AT) can be aected by seveal actos besides soil textue. Fo example, hydaulic conductivity is educed by soil custing, inceased by tillage, and inceased by the inluence o gound cove and canopy cove. The values o X<SAT that have been pesented o bae gound as a unction o soil textue alone should be adjusted unde cetain soil cove conditions. Gound cove, such as gass, litte, and ock will geneally incease the iniltation ate ove that o bae gound conditions. Similaly, canopy cove-such as om tees, bush, and tall gasses-can also incease the bae gound iniltation ate. The pocedues and data that have been pesented ae o estimating the Geen and. Ampt paametes based solely on soil textue and would be applicable o bae gound conditions. Past eseach has shown that the wetting ont capillay suction 53
Rainall Losses ~ ~ ~..,... -(J..J,, \ t) \ \ \ \ \.\ ~ ~ t"')... Figue 4.8 DTHETA "Dy" o nitially Dy Soil Moistue Condition (wilting point) : :.:.~:.:,:.;.:,:.:.:.:.:.:.~:.:::.:.:,:.:.:.;.:;:;:.:.:.:::,:,:,:,:,:,:,:,~,:::,~,:,:,;,:,:,:::,~: :.;.;,:.:::'.:.~:':.::::~,:::::.:.~.:::.:.:. :::.:.:-:-;:.:.:.:.::~:.:.: :.:.:.:.:.:.:.:.:.:.:.:.:::.: ;.:.:. :.:.:.:.:.:.:.:.:. :.:.:.: :.: :.:.:.:.:.: :::':":':'~:":':':':'i' :.: : ; :,: : : : : : : : ::: z : :.::::: : : ; : : : ::: :.:.:::.:':.: :.: ~.:.~ ~.% : : :.:.:.:.:.:.:.: : : : : ~: :.~,;.: ;.:,:,:::::.~.:::.:.:.:.:,:,:.:.:::.:.:.:. 54
j -' ~ j -~ "<t \ / \ ~ \, i \ ' i...j ' ~,., \ \ " 1 '., i...j \ ' ; ~ / V)!, ', ;,,! i :, Figue 4.9 DTHETA "Nomal" o nitially Wet Soli Moistue Condition (ield capacity) u, ~ C co en,...
Rainall Losses Hydolo~lc Design Manual paamete (PSF) is elatively insensitive in compaison with the hydaulic conductivity paamete (X<SAT); theeoe only the hydaulic conductivity paamete is adjusted o the inluences o cove ove bae gound. Pocedues have been developed (Rawls and othes, 1988) o incopoating the eects o soil custing, gound cove, and canopy cove into the estimation o hydaulic conductivity o the Geen and Ampt equation; howeve, those pocedues ae not ecommended o use in Maicopa County at this time. A simpliied pocedue to adjust the bae gound hydaulic conductivity o vegetation cove is shown in Figue 4.1. This igue is based on the documented incease in hydaulic conductivity due to vaious soil coves as epoted by investigatos using ainall simulatos on native westen angelands (Kincaid and othes, 1964; Sabol and othes, 1982a; Sabol and othes, 1982b; Bach, 1984; Wad, 1986; Lane and othes, 1987; Wad and Bolin, 1989). This coection acto can be used based on an estima te o vegetation cove as used by the Soil Consevation Sevice in soil suveys; that is, vegetation cove is evaluated on basal aea o gasses and obs, and is evaluated on canopy cove o tees and shubs. Note that this coection can be applied only to soils othe than sand and.{hlrdy "~am. J CKH'lj ~d#a, The inluence o tillage esults in a change in total poosity and theeoe a need to modiy the thee Geen and Ampt equation iniltation paametes. The eect o tillage systems on soil poosity and the coesponding changes to hydaulic conductivity, wetting ont capillay suction, and wate etention is available (Rawls and Bakensiek, 1983). Although this inomation is available, it is not pesented in this manual, no is it ecommended that these adjustments be made to the iniltation paametes o design pupose use in Maicopa County, because o mos t lood pedietier puposes it cannot be assumed that the soil will be in any paticula state o tillage at the time o stom occuence and theeoe the base c9ndition iniltation PSi'il"?4':Z; l?/' paametes, as pesented, should be used o lood peeuenon puposes. Howeve, appopiate adjustments to the iniltation paametes can be made, as necessay, o special lood studies such as econstitution o stom events. The necessay soils inomation may not be available o all aeas o Maicopa County o the pupose o estimating the Geen and Ampt equation paametes based on soil textue, but the SCS CN method has been used extensively in Maicopa County to estimate ainall losses. Estimates o CN can be obtained by compaison o watesheds o which no geneal soils epots ae available to watesheds o which soils data ae available. Bakensiek and Rawls (1983) have gouped soil accoding to textue into the ou hydologic soil goups as shown below: 56 -
- - o~ 1-5 l- >- 1-:::> 5 FZ.:::) z_ O...J..:::{. :::) o o~...j~ ~:: a:: Oz >-:::) :Co lla:: o(!) 2. 1.5 ~~ 1.1 <{<{ a::cn 1. Rainall Losses 2 4 6 8 1 VEGETATON COVER, N % Figue 4.1 Eect o Vegetation Cove on Hydaulic Conductivity Fo Hydaulic Soli Goups B, C, and, and Fo all Soli Textues othe than Sand and Sandy-Loam. ioqm/ 5ql?L i i.! 57
Rainall Losses Hydologic Design Maiual Hydologic Soli Goup, Soli Textue A sand... ''''''-..."ndll loami 5"'/1 B slit loam loam C sandy loam silt clay loam silty clay loam sandy clay silty clay clay 58 This gouping o soils is based on the ou hydologic soil goups as deined by SCS soil scientists, with limits o each goup established by the minimum iniltation ate as deined by Musgave (1955). This classiication system assumes that the hydaulic conductivity (XKSA T) o the Geen and Ampt equation coesponds to the minimum iniltation ate (c). Classiication o soil accoding to hydologic soil goup involves some lage scale lumping o soils. Fo example, silt loam is placed in hydologic soil goup B based on soil textue classiication, wheeas using paticle size pecentages (and pecent oganic matte) can place silt in any o the ou goups. The A and D soil goups ae most nealy invaiant with espect to soil textue classiication, and the Band C soils ae less deinitive in egad to soil textue. This classiication indicates that the SCS hydologic soil goups ae not uniquely elated to soil hydaulics and hydologic popeties; but it does indicate that Geen and Ampt equation paametes can be estimated with some degee o conidence and epoducibility om eadily available soil popeties and om an estimate o en. Bakensiek, Rawls, and Stephenson (1984) extended this geneal classiication o soils into a pocedue o estimating hydologic soil goups and en bas~ on soils data. Thei analysis esulted in a pocedue to elate en to satuated hydaulic conductivity o the soil. This pocedue has been modiied so that hydaulic conductivity o the Geen and Ampt equation can be estimated om the en o the soil-cove complex and pecentage o vegetation cove. This is shown in Figue 4.11,and this igue can be used to estimate hydaulic conductivity om an estimate o en. Capillay suction (PSF) is usually invesely elated to the value o hydaulic conductivity (XKSAT), as illustated in Figue 4.12. Figue 4.12 can be used in conjunction with Figue 4.11 to estimate the Geen and Ampt equation paametes. DTHETA should be selected om Table 4.2 based on the assumption o initial soil moistue and estimated XKSAT and PSF. --- - -
Rainall Losses 15 () w :: (,) z.. --- ll.. ().e:. 1 Z F= (,) ::J () >- ~ ~..J..J a.. ~ (,) 5..- z :.J.. (!) z..- l- ~ 5.8 ""': N.5 1. 1.5 BARE GOUND HYDRAULC CONDUCTVTY (XKSAT), N/HR Figue 4.12 Relation o Capillay Suction (PSF) as a Function at Bae Soli Hydaulic Conductivity (XKSA n 6
,, 4.4.2 nitial Loss Plus Uniom Loss Rate (L+ ULR) Rainall Losses This is a simpliied ainall loss method that is oten used, and geneally accepted, o lood hydology. n using this simpliied method it is assumed that the ainall loss pocess can be simulated as a two-step pocedue, as illustated in Figue 4.13. Fist, all ainall is lost to uno until the accumulated ainall is equal to the initial loss; and second, ate the initial loss is satisied, a potion o all utue ainall is lost at a uniom ate. Accoding to HEC-1 nomenclatue, two paametes ae needed to use this method; the initial loss (STRTL) and the uniom loss ate (CNSTL). The initial loss (STRTL) is the sum o all losses pio to the onset o uno and is made up o suace etention loss (A) and an initial amount o iniltation (1L); theeoe, STRTL = la + L. Values o the iniltation component (L) ostrtl o bae gound accoding to soil textue classiication ae shown in Columns (3) though (5) in Table 4.3. These values have been deived om the Geen and Ampt inilttation equation and paamete values that ae shown in Table 4.2. The value o L "Dy" should be used o soil that is usually in a state o low soil moistue at o nea the wilting point o vegetation. This is a easonable assumption o most noniigated lands in Maicopa County because o the inequency o ainall and because o the apid dainage o these soils ate ainall. The value o L "Nomal" should be used o soil that is usually in a state o modeate soil moistue such as occus o iigated lawns, tu, and pennanent pastues. The value o L "Satuated" is used o a soil maintained in a state o high soil moistue, such as in iigated agicultual lands. Values o L o bae gound that have been classiied accoding to hydologic soil goup ae shown in Table 4.4. These values within each hydologic soil goup have been deived om the data in Table 4.3 o the vaious soil textue classiications. The uniom loss ate (CNSTL) epesents the long-tem, equilibium iniltation, -d capacity o the soil. The values o CNSTL shown in Column (2) o Table 4.3 o soils C/(1'~/'j accoding to soil textue.c;ia&&mcabotl ae equivalent to the hydaulic conductivity at natual satuation (XKSAT) as detemined o the Geen and Ampt equation (Table 4.2). The values o CNSTL o soils classiied accoding to hydologic soil goups ae shown in Table 4.;!hhese values within each hydologic soil goup have been selected om inspection o XKSAT values in Table 4.2 o the vaious soil textue classiications. Values o CNSTL shown in Table 4.4 ae consistent with geneal inomation available o estimating CNSTL as shown in Table 4.5. Figue 4.11 can be used to estimate CNSTL based on an estimate o CN i adequate soils data is not available. 61
Rainall Losses w :2 -- - Z :::J ::: W.. --.. W o. W - «::: NTAL LOSS (STRTL) - SURFACE RETENTON LOSS + NTAL NFL TRA lion LOSS UNFORM LOSS RATE (CNSTL) = c RANFALL EXCESS '\-.,.-~--,--.,-.."...-.,.--,--.,...-,.-...,--.y-~-- - - - - - - _1_ - - c NFLTRATON NTAL NFLTRATON LOSS SURFACE RETENTON LOSS Figue 4.13 Repesentation o Rainall Loss Accoding to the nitial Loss Plus Uniom Loss Rate (L+ULR) 62
Rainall Losses Table 4.3 nitial Loss Plus Uniom Loss Rate Paamete Values o Bae Gound accoding to Soli Textue Classiication Soli Textue Uniom Loss Rate nitial LO~, nches L Classiication CNSTL Dy Nomal (1 ) (2) (,)3 )4-- Satuated sand 4.6 1.3 1.3 loamy sand_ 1.2.8.8 sandy loam.4.7 --.6 loam.25.8.7 silty loam.15.6.5 sandy clay loam.6.6.5 clay loam.4.5.4 silty clay loam.4.6.5 sandy clay.2.4.3 silty cla~.2.4.3 clay.1.3.2 --" - '--" - 1 Selection o L: Dy = Noniigated lands such as deset and angeland; Nomal = igated lawn, tu, and pemanent pastue; Satuated = igated agicultual land. Table 4.4 nitial Loss Plus Uniom Loss Rate Paamete Values o Bae Gound accoding to Hydologic Soli Goup (S} nitial LOS" nches Hydologic Soli Uniom Loss Rate L Goup CNSTL ~------~-------.-----'--' Dy Nomal Satuated (1) (2) (~.3 (J)<1- ~p A.4.6 B.25.5 c.15.5 D.5.4 1 Selection o L: Dy == Noniigated lands such as deset and angeland; Nomal = igated lawn, tu, and pemanent pastue; Satuated = igated agicultual land..5.3.3.2 --, ',,,! '., ' \1' i : it " ' : ; 63
Rainall Losses Hydologic Soli Goup (1) Table 4.5 Published Values o Uniom Loss Rates Uniom Loss Rate, nches/hou Musgave (1955) USBR (1975) 1 USBR (1988)' (2) (3) (4) - - A.3-45 4.3 -.5 B.15 -.3.24.15 -.3 -" C t:),tj5' ~.15.12 d,os-- G G.9S- (),/5 ~ jj Cl -,3 (," B ~ Design o Small Dams, Second Edition, 1975, Appendix A Design o Small Dams, Thid Edition, 1988 Pocedue o Estimating Loss Rates.. ;'='(:!: Geen and Ampt Method A. When soils data ae available: 1. Detemine the soil textue classiication. Soils epots such as those o the Soil Consevation Sevice can be used i available, o laboatoy analysis o appopiate soil samples om the dainage aea can be used i adequate documentation on the sampling and laboatoy pocedue is povided and appoved. 2. Estimate the hydaulic conductivity (XKSAT) o bae gound om Table 4.2 i geneal soil textue classiication is available o om Figue 4.3 i adequate soil textue data is available om an appoved sampling pogam. 3. desied, adjust the value o XKSAT o the inluences o vegeta tion cove using Figue 4.1. 4. Estimate the wetting ont capillay suction paamete (PSF) om Table 4.2 i geneal soil textue classiication is available o om Figue 4.4 i adequate soil textue data is available om an appoved sampling pogam. 5. Estimate the value o DTHETA om Table 4.2 i geneal soil textue classiication is available o om eithe Figue 4.8 o 4.9 i adequate soil textue data is available om an appoved sampling pogam. The value o DTHETA must be selected based on the appopiate antecedent soil moistue condition: "Dy" o noniigated lands such as deset and angeland; "Nomal" o soil that would be expected to be nea soil moistue ield capacity such as iigated lawn, tu, and pemanent pas-. tue; and, "Satuated" o iigated agicultual land. :.:.:.:::::::::::.:::.:.:.:::.:.:.:::.:.:::.:;:.:::.:.:.:.:.:::.;.:.:.:::.:.:.:.:.:::.:.:.;.:-:.:.:.:.::-::-:::.:::.:.:.:.:.:.:::.:.:.:.:.:::.:::.:.:.:.:.:.::::.:.::::.:.::::::::.:.::.:':::.::.:.::.:::::.;,>::':-»:.:::.:::::::::.:<.:.:.;.:.:.::::.:':.:.:.:.::,:::.:.:.;.:.:.:.:.:.:.:::.::.:.::.:.:.:.:.:.:.:.:.:.:.:.:.:.:.:.:.:.:':'::::':::::.:.:':::.:.:.:.:.;.:.:.:.:.:.:.:.:.:.:.:.:. 64
Rainall Losses 6. Detemine the land-use and/ o soil cove o the dainage aea and use Table 4.1 to estimate the suace etention loss (A). B. When soils data ae not available: 1. Estimate the en based on data o simila watesheds o egional expeience. Estimate the pecent vegetation cove. 2. Use Figue 4.11 to estimate XKSAT based on CN and hydologic condition. 3. Use Figue 4.11 to estimate XKSAT o bae gound. 4. Use the bae gound XKSAT and Figue 4.12 to estimate PSF. 5. Use the bae gound XKSAT and PSF with Table 4.2 to estimate DTHET A. C. Altenative methods: As an altenative to the above pocedues, Geen and Ampt loss ate paametes can be estimated by econstitution o ecoded ainall-uno events on the dainage aea o hydologically simila watesheds, o paametes can be estimated by use o ainall simulatos in ield expeiments. Plans and pocedues o estimating Geen and Ampt loss ate paametes by eithe o these pocedues should be appoved by the Flood Contol Distict and the local agency beoe initiating these pocedues. 4.5.2 nitial Loss Plus Uniom Loss Rate Method A. When soils data ae available: 1. Detemine the soil textue classiication and/ o the hydologic soil goup. Soils epots such as those o the Soil Consevation Sevice can be used i available, o laboatoy analysis o appopiate soil samples om the dainage aea can be used to classiy the soil i adequate documentation on the sampling and laboatoy pocedue is povided and appoved. 2. Use values o CNSTL and L om Table 4.3 i the losses ae to be based on soil textue classiication. 3. Use values o CNSTL and L om Table 4.4 i the losses ae to be based on hydologic soil goup. 4. Detemine the land-use and/ o soil cove and use Table 4.1 to estimate the suace etention loss (A). 5. STRTL = A + L. 65
Rainall Losses B. When soils data ae not available: 1. Estimate the CN based on data o simila watesheds o egional expeience. 2.. Estimate the pecent vegetation cove. 3. Use Figue4.11 to estimatecnst. based on CN and hydologic condition. 4. Use Table 4.3 to estimate L based on the value o CNSTL. 5. Use Table 4.1 to estimate the suace etention loss CA). 6. STRTL = A + L : :.:.:,:-:.;.:.:.:.;.:.:.:, :.:::.:.:.:.:.; :.:.:.:.: :.:.:.:::.:.:::::.:.:.:.:.:-:.:.:::.:.'.:.:.:.: :.: :.:.:-:.:,:.:.:;:.:~:.:::.::;.:::::-::: :. :.:::.:::.:.:::.:.:::::::.:'.:::.:.:.:.:,:-:.: ':-:-:,:.;.:.:::.:.:.:.:.:.:.:.;.:.:,:.' ':.;.: :.: :.: : :.;.:::.:.:.:.:.:.:.:=:.:.:.:.:.; :.:':.:::.:.: ':,:::.:::.:.:.:.;,:.:.:.:.;.:.:.:<.;.:.:.:.:.:.:.;.:.:.:.:.:.:.:-:":::.:.:.: : :. : :"':':':':':':':-:':':':::':':':':': ':.:.:::.:.: :.:.:.:.:.: :. 66 i
,~.. ~ Ree Akell, R.E., and F. Richad, 1986, "Shot Duation Rainall Relations o the Westen United States," Coneence on Climate and Wate Management-A Citical Ea and Coneence on the Human Consequences o 1985's Climate, August 4-7, Ameican Meteoologica 1 Society, pp. 136-141. Bach, L.B., 1984, "Detemination o iniltation, uno, and eosional chaacteistics o a small wateshed using ainall simulato data" unpublished maste's thesis, Depatment o Civil Engineeing, New Mexico State Univesity, Las Cuces, New Mexico, 69p. Bedient, P.B., and Hube, W.e., 1988, Hydology and Floodplain Analysis, Addison-Wesley Publishing Company, 65 p. Bakensiek, D.L., and Rawls, W.J., 1983, "Hydologic classiication o soils," Poceedings o the Natual Resouces Modeling Symposium, Pingee Pak, Coloado, U.S. Depatment o Agicultue, Agicultue Reseach Sevice, ARS-3, pp. 19-114. Bakensiek, D.L., Rawls, W.J., and Stephenson, G.R., 1984, "Modiying SCS hydologic soil goups and cuve numbes o angeland soils," Ameican Society o Agicultual Enginees, 1984 Annual Meeting, Kennewick, Washington. Clak, e.o., 1945, "Stoage and the unit hydogaph," Tans. Ameican Society o Civil Enginees, Vol. 11, pp. 1419-1488. s Cudwoth, A. G., 1989, Flood Hydology Manual, U.s. Bueau o Reclamation, Denve, Coloado, 243 p. Egget, K.G., 1976, "Modeling the unsteady iniltation pocess," unpublished maste's thesis, Coloado State Univesity, Ft. Collins, Coloado. Ucks, W.., 1944, A method o computing uban uno," Ameican Society o Civil Enginees, Tans., Vol. 19. () ' Hydol~gic Engineeing Ce~te, HEC-1..(l9~ Flood Hydogaph Package: Uses Manual, U.S. Amy Cops o Engmees, y. 3~ 'p/ //j A'p'pt ~p//('t"$.. :::::::::::.;: ;:::::::.:.::::::: ::::;::::.:-:::: ;.:.:::;:::: ;.: :.:.::. :::::;:::::.,:: ;.::::.:.:.;.:.:,:::: :.::::::::: :.;: :.::: ;.: ;.;.::.>: :':: :.:: ;.::.;': :.:;::: :.:.~:: 15
Reeences nyuuuy.\o L~;:"Y" v.allua. Kincaid, D.R, Gadne, J.L., and Scheibe, H.A., 1964, "Soil and vegetation paametes aecting iniltation unde semiaid conditions," lash Bulletin, Vol. 65, pp. 44-453. Lane, L.J., Simanton, J.R, Hakonson, T.E., and Romney, E.M., 1987, "Lage-plot iniltation studies in deset and semiaid angeland aeas o the southwesten U.S.A," Poceedings o the ntenational Coneence on niltation Development and Application, Wate Resouces Reseach Cente, Univesity o Hawaii at Manoa, Honolulu, Hawaii, pp. 365-376. Li, RM., Stevens, M.A., and Simons, D.B., 1976, "Solutions to Geen-Ampt iniltation equation," Ameican Society o Civil Enginees, Jounal o the igation and Dainage Division, Vol. 12, No. R2, pp. 239-248. Linsley,RK.,Kohle,M.A.,and Paulhus,J.L.H., 1982, Hydologyo Enginees, Thid Edition, McGaw-Hill Book Company, 58 p. Mille, J.F., RH. Fedeick and RJ. Tacey, 1973, ''Pecipitation-Fequency Atlas o the Westen United States" V: New Mexico,andVi: Aizona; NOAA Atlas 2. National Weathe Sevice, NOAA. Silve Spings, Mayland. Mitchell, W.O., 1962, "Eect o esevoi stoage on peak dischage," U.S. Geological Suvey, Wate Supply Pape 158-C Mitchell, W.O., 1972, Model Hydogaphs: U.S. Geological Suvey, Wate Supply Pape 25. Musgave, G.W., 1955, ''How much o the ain entes the soil," Wate, the Yeabook o Agicultue, p. 151-159. Papadakis, CN., and Kazan, M.N., 1987, ''Time o Concentation in Small, Rual Watesheds," Poceedings o the Engineeing Hydology Symposium, ASCE, Williamsbug, Viginia, pp. 633-638. i,, ' i:! ' 1 Pedesen, J.T., Petes, J.e., and Helweg, O.J., 198, "Hydogaphs by single linea esevoi model," Ameican Society o Civil Enginees, Jounal o the Hydology Division, Vol. 16, No. HY5, pp. 837-852. t~('j t'/pjl'p/ PREFRE, National Weathe Seviee. i~~, (/t,('y';t.i./.. d- J:!~Mm.#6;;.//. Rawls, W.J., and Bakensiek, D.L., 1983, "A pocedue to pedict Geen and Ampt iniltation paametes," Ameican Society o Agicultual Enginees, Coneence on Advances in niltation, Chicago, llinois, pp. 12-112.[PB] Rawls, W.J., Bakensiek, D.L., and Mille, N., 1983, "Geen-Ampt iniltation paametes om soils data," Ameican Society o Civil Enginees, Jounal o Hydaulic Engineeing, Vol. 19, No.1, pp. 62-71. Rawls, W.J., Bakensiek, D.L., and Sa vabi, M.R., 1989, "niltation paametes o angeland soils," Jounal o Range Management, Vol. 42, No.2, pp. 139-142. 16
nyaologlc uesign Manual neteences Resolution FCD 87-7, 1987, Uniom Dainage Policies And Standads, Aizona, Maicopa County Flood Contol Distict, pp. 1-16. Sabol, G.V., 1983, Analysis o the uban hydology pogam and data o Academy Aces o the Albuqueque Metopolitan Aoyo Flood Contol Authoity," Hydo Science Enginees, nc., Las Cuces, New Mexico, pp. 5-7. Sabol, G.v., Wad, T.J., Coons, L., Seige, A.D., Wood, M.K., and Wood, J., 1982b, "Evaluation o angeland best management pactices to contol non-point pollution," Civil Engineeing Depatment, New Mexico State Univesity, Las Cuces, New Mexico, 12p. Sabol, G.V., Wad, T.J., and Seige, A.D., 1982a, ''Rainall iniltation o selected SQils in the Albuqueque dainage aea o the Albuqueque Metopolitan Aoyo Flood Contol Authoity," Civil Engineeing Depatment, New Mexico State Univesity, Las Cuces, New Mexico, 11 p. Sabol, G.V., and Wad, T.J., 1985, Santa Babaa hydogaph with Geen-Ampt iniltation," Poceedings o the Wateshed Management in the Eighties Symposium, Ameican Sodety o Civil Enginees, Denve, Coloado, pp. 84-91. Sabol, G.V., 1987, S-gaph Study (epot o the Flood Contol Distict o Maicopa County), Phoenix, Aizona, 29 pp. plus appendices. Sabol, G.V., 1988, Clak unit-hydogaph and R-paamete estimation," Ameican Sodety o Civil Enginees, Jounal o the Hydology Division, Vol. 114, No., pp. 13-111. Sheman, L.K., 1932, "Steamlow om ainall by unit-gaph method," Engineeing News Recod, Vol. 18. Shen, J., 1962, A method o detemining the stoage-outlow chaacteistics o nonlinea esevois," U.S. Geological Suvey, Poessional Pape 45-E. Stubchae, J.M., 1975, "The Santa Babaa uban hydogaph method," National Symposium on Uban Hydology and Sediment Contol, Univesity o Kentucky, Lexington, Kentucky, pp. 131-141. Technical Release-55, 1986, Uban Hydology o Small Watesheds, Soil Consevation Sevice. Tholin, A.L., and Keee,G.J., 196,"Hydology o uban uno," AmeicanSodety o Civil Enginees, Tans., Vol. 125, pp. 138-1379. U.S. Amy Cops o Enginees, 1974, Gila Rive Basin, Aizona, New Mexico, and Phoenix City Steams, Design Memoandum No., Hydology Pat, Los Angeles Distict, 51 p. U.S. Amy Cops o Enginees, 1982, Gila Rive Basin, Phoenix, Aizona and Vicinity, Hydology Pat 2, Design Memoandum No.2: Los Angeles Distict, 59 p. 17
Reeences U.S. Amy Cops o Enginees, 1974, Gila Rive Basin, New Rive and Phoenix city steams, Aizona, Design Memoandum No.2, Hydology Pat 1. U.S. Amy Cops o Enginees, 1982a, Gila Rive Basin, Phoenix, Aizona and vicinity (including New Rive), Design Memoandum No.2, Hydology Pat 2. U.S. Amy Cops o Enginees, 1982b, "Hydologic analysis oungaged watesheds using HEC-l," Hydologic Engineeing Cente, Taining Document No. 15, 122 p. plus appendices. U.S. Bueau o Reclamation, 1987, Design o Small Dams, Thid Edition, Denve, Coloado, 86p. Viessman, W., J., 1967, "A linea model o synthesizing hydogaphs o small dainage aeas," Foty-eighth Meeting, Ameican Geophysical Union, Washington, D.C. Wad, T.J., 1986, A study o uno and eosion pocesses using lage and small aea ainall simulatos," Wate Resouces Reseach nstitute, Repot No. 215, New Mexico State Univesity, las Cuces, New Mexico, 71 p. Wad, T.]., and Bolin, S.B., 1989, ''Detemination o hydologic paametes o selected soils in Aizona and New Mexico using ainall simulatos," Wate Resouces Reseach nstitute, Repot No. 243, New Mexico State Univesity, las Cuces, New Mexico, 84 p., 18