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Home My WebLink AboutAPA1227I I li I I I I I I •• I I; I; I I I I I I () ALASKA POWER AUTHORITY SUSITNA HYDROELECTRIC PROJECT SUBTASK 3.05 (ii)--CLOSEOUT REPORT PROBABLE MAXIMUM FLOOD DETERMI~ATION FIRST DRAFT FEBRUARY 28, 1981 Acres American Incorporated 1000 Liberty Bank Building Main at Court Buffafo, New York 14202 Telephone (716} 853-7525 P5700,.03.05.002 Subtask 3.05 (ii) Flood Studies -'-'Probable Maximum Floocr:·Atc;end~~ ~ March 1981 "· · ------------------------~----~~~~~-- (a) Objectives To re-evaluate probable maximum flood estimates based on a more comprehensive cl imato1ogical study ~nd mpde.l ing procedure. (b) Approach The approach would entail re-assessing precipitation maximums, temperature gradients and tempGrature maximums based on a thorough study of the meteorological characteristics of the Susitna River &asin. ,Applicable storm maxim·ization techniques \'li11 be used to develop a probable maximum rwecipitation storm for both spring and summer seasons. Paralleling the climatological study will be a further calibration of the SSARR model. The intent of this calibration is to develop a reasonable \vatershed model based on procedures that follow generally accepted mathematical modeling technique~ The calibration will start With assuming that the basin's ~et~l~,Co..t. ?.."':! .~~~d~~':'OJ parameters used in the Corps of Fngineers (COE) PMF estimates are the most representative. These parameters may be adjusted as analysis proceeds. When the set of watel"Shed pat"'ameters that give the most reliable estimation of spring and summer floods are deter111ined~ a verification study wfl1 be conducted using this data set. Severa1 floods will be used that at"e indep·~ndent of the floous used in the calibration study. The verif·Xcation of the SSARR model will determine the accuracy that can reasonably be expected from the model. Estimates of the probable maximum flood at critical locations along the Susitna R~ver for both spring and summer will be determilled using climatological data developed and the most reliable set of basin parameters. (c) Discussion The motivation for this addendum stems from thr: results of the assessment of the COE 1975 studies. The assessment determined the sensitivity of the PMF estimates to changes in critical meteorological and basin parameters. The magnitude of the changes are given in Table 1 and are discussed completely in S-ubtask 3.05 {ii) -Probable Maximum Flood Closeout Report. < The meteorological data used in the COE estimates were developed by they National Weather Service (NWS) in a preliminary study \thich gi.ve a general range of criteria within which it was believed values from a more comprehensive study would fall.. In their conclusions to the study~ the NWS noted •.• 11 Time hasn 1 t allowed checks~ evaluation~ and comparison of the several types of data summarized here.n The NWS naturally recommended further study. This is borne out by the increases to the Pr~F peak found in the sensitivity analysis. The operation of Watana Reservoir for power generation will have an effect on storage attenuation of the spring and summer peaks. Consequently~ it is not a clear cut case of developing a maximum .•. : • .' \\. . :·.:= . . . -, . . .. • ·~; ; .. -~~· • . .•.. , .. : •• ~ ·~ ~ ."'"i ~ .1 . . • . . . ' \ f . " .... : .,··.~·:;\ .:· ·•. .• . 'q·. :,.· ~·r·. . . . . . '} '· J\.·. :'' .;·". . . . . . . ~·· .. \.. . '. ". {I·~ \· ~o.· ·"'~ • ;. .f ,1 : r. • ,. ,...: #, ~. • • ... ... " -• • l. storm as a sma'ller flood entering a full rese:rvoir may require 'Jarg'er spillway faciliities than a·1arger flood entering a depleted reservo·ir ... The operation of Watama Resey,·voir will .result in the lowest reservoir 1 eve 1 s occurri n~J in Apri 1 or May each year. Therefore, there is substantial storage available to attenuate the spring flood peak. )~\l:t\.': .J..11.J? On the average~ ·~it would appear that approximately 2.3,. 2.3 and 1.6 ·iv..v\'\A'Y'w.J.y/ltl. ~ ·million acre-feet of storage is. available in April, May and June respectively. Thc~se values are for· Watana \'lith full supply level of 2~200 feet and 800 MW installed capacity. In August, September and October, no signif·.icant storage is available. A preliminary estimate of the spring PMF \rolume is about 4.5 million acre-feet. Consequently, approximately 36 percent of the s.pring flood volume could be stored ...... -·~ - without reservoir surcharging. Jl(]J~ surcharge is allowed, then about 50 percent of the spring flood volume can be stored. The . . effect of the storafJe is to attenuate the flood peak significant1y. For the summer PMF, reservoir lev,el~ '}[.€· .. close to maximum so no 0'<-Arf."A.<' • .. ~t.;;. ·'-~ . significant flood storage is lj.ke:ly: The case for flood storage in spring is strong as the reservoir can only be full~ assuming normal power operation~ after snowmelt runoff. Therefore it may be only applicable to design spillway criteria based on summer floods and full reservoir conditions. TVte a.loo~e g tA.e s h""" s w iII be a.ddJtes::se o i"' ~e pRO pc~ ed shtdt'e.s. . \ _1 • t · ~ r::r .a. L .1 elic~.:t. --rlAe 'T\Ae ~ \Ao"l w-.\ g_e_~t.l\R.E? opptOCtV.}('.~I.C~q uOC v\,tov.-ViCUIC.c;; C'-r If \oJec;.t posr.i"~\e dctto.. 4o s\a-r":.:t me ~\vtcl.:i '' Ap~tt -b 1 t<351 • \tAw drth:: \s \o et.As.\tee a ~·t&tw' e~·hMcltc; cf;_IJ~~~\F k sp\ .. Uwo.!::l des1.90 ~~ ~J.·Ile 8., l'=lVL l::.xfc:-c~ed Cc.t,v.rle'n~t-'* ct \:b\.e ~h-td..:J ,~;u be JtA.\.9 b.,~ ll?~L A P~el~\'tt~·DYtJ sc.l.tedLt\a w !Ctt,.~Lr\ ttl\ h.5lA~e !l. - .. DATE APR 15 13 20 27 MAY4 It WEEK o-2 4 5 DESCRIPTION COLLECT AND PROCESS -~----------KEJ--.:1_._._ .. _... CLIMATOLOGICAL OAuA MAXIMIZE PMP, TEMPERATURE SEQUENCE AND SNOW .. PACK PARAMETERS. CALIBRATE AND VERIFY SSARR MODEL OEVEI..OPE PMF ESTIMATE REVIEW ESTIMATE DRAFT REI)()RT FINAL REPORT NOTES: TOTAL HRS: 20 MAN WEEKS : 800 MAN HOURS COMPUTER * 2000 TRAVEL AND DATA $ 1000 $ 3000 18 25 JUN I 8 6 7 8 9 15 10 ATES ESli3NS 22 29 Jl 12 ~-,~ ~ ( '\'\,.. > w 0: t -' . ·.v:~ .. '~/ .. ~ .. . ) ., ~ . . . . • ~ ~ •• ~ ,. J • • . : . . ·. . . ... ~ \ . ; r.·-· --.. -. ~.·.-~·~· --------------··-------------~----------------------~~J~OB __ N_U~M-B•E·R-.---------------- Calc~l.idation!; FILE NUMBER-. ------~~-om. • . SUBJECT: _________ SHEET --0-F-=--=--_-_--_---Hu~tlo __. .. -BY gt S\61~\.... DATE 5iJ4QQ' -------De . 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SUSITNA HYDROELECTRIC PROJECT TA!~ k ~ 4~ tf]ll;~LPCf\( SUBTASK 3.05 (ii) -CLOSEOUT REPORT PROBABLE MAXIMUM FLOOD DETERMINATION FIRST DRAFT FEBRUARY 28, 1981 I I I 1 .. I I I I I I I I I I I I I I I TABLE Of CCINTENTS List of Tables· List of Figures 1 -INTRODUCTION 2 -SUMMARY 3 -SCOPE OF WORK evQl...ao:.!•an 3.1-Probable Maximum Flood 9etermination 3.2 .. Scope of Work 4 -REVIEW C\F CORPS OF ENGINEERS PMF EVALUATION 4.1-Data Input to SSARR Model 4 .. 2 ... Calibration and Verification Studies 4. 3 -Summary S -~. SENSITIV-ITY ANALYSIS 5.1 -Intrt'lducti on 5. 2 -Base Case 5.3 -Sensi·tivity Studies 5.4 -Summar·y 0 ~• I I I 1- -1. I I I I I I I I I I I I . . . . . 4 • .. • -: • •• • • • ,. •• .,T:.<. -• . . ~ ·: ~ . ·. . .. • ' LIST OF TABLES Table 4.1 COE Calibration Study Results-Susitna River at Gold Creek 4.2 COE Calibration Study Results -Susitna River near Cantwell 4.3 COE Calibration Study Results _, Maclaren River near Paxson 4.4 COE Calibration Study Results -Susitna River near Denali 5.1 Precipitation Values-1:100 Stann 5.2 Pr·ecipitation Values -PMF Storm 5. 3 Snowp·ack· ~iater Equiva 1 ents 5.4 Sunnnary of Sensitivity Runs -Peak Inflow-to Watana Reservoir 5.5 Summary of Sensitivity Runs -Peak Inflow to Devil Canyon Reservoir I I " LIST OF FIGURES I Figure I I' I I I I I I I I I I I I I I 4.1 Schematic Diagram of tbe Susitna River 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 Soil Moisture Index -Runoff Percent Relationships Baseflow Infiltration Index -Percent Runoff to Bas.eflow Relai~ionships Input Rate -Surface Component Input Rate Rtilati onships Math -Evapotranspiration Index Relationships ·Precipitation Rate -Evapotranspiration Rate Relationship " Accumulated Generated Runoff -Snow Covered Area Rel ati·onsh1p Percent Total Seasonal Accumulated Runoff -Snowmelt: Rate Relationship COE Calibration·-Hydrographs Susitna Riv.er at Gold Creek 1972 & 1967 COE Calibration -Hydrographs Susitna River near Cantwell 1971 & 1964 COE Calibration -Susitna River near Cantwell 1967 & 1972 HvdroQr-aohs --. 4.12 COE Calibration -Hydrographs for Susitna River near Denali 1\171 & 1964 4 .. 13 4 .• 14 4 .. 15 COE Calibration -Hydrographs for Susitna River near Denali 1972 COE Calibration -Hydrographs for Maclaren River near Paxson 1971 & 1964 COE Calibration -Hydorgraphs for Maclaren River n1ear Paxson 1972 & 1967 5.1 COE Spring PMF Estimate -Wataria Inflow 5.2 COE Temperature Sequences 5.3 ? C..OE. Assumed Snowpack 5.4 AAI Temperature Sequences 5 .. 5 AAI Spring PMF Estimates .... ~latana Inflow 5.6 AAI Spring PMF Estimates .... Watana Outflow ' . : . . ~ ~~... . . . . . . . . ·. , -~· :: R ~~< ~. 1 -INTRODUCTION I I I I I I, . The objective of the work conducted JJ\')der Subtask 3.05 ( i i) "Probable Maximum Flood Determination" wa.s to determine if the probable maximum floc~ (PMF) peaks evaluated by the U.S. Army Cq'ibjs of Engineers (COE) (1) are sufficiently accurate for use in the feasibility study and FERC license application. X 2 -SUMMARY . The: method used by the COE in evaluating the PMF involved the application of a calibr-ated river basin computer model which simulates stream flow in response to specified jJ.l.ptrt" temperature and precipitation inputs.. This study included a detailed review of the model used~ the calibration procedures adopted, the calibration results achieved and a rang•~ of ~'klnal sensitivity runs using the SSARR model and the COE data. The sensitivity runs involved making systematic plausible changes to the· snowpack, temperature and precipitation input data in order to see what e1~~ect ttr~e, have on the flood peak. The results of these studies indicate\ the following: -the ca 1 i bration procedure used by the COE was no1t rigorous and does not allow a realistic assessment of the modelling accuracy to be made; -the timing of the key input. parameters, that is, temr1erature and precipitation used by the COE does not reasonably ensure that the flood peak is a prob~ble maximum; -the magnitude of the· probable maximum precipitation and temperature sequences were based on a preliminary study made by·~. wlho themselves suggest more detailed work (Appendix A). 1P N w S. t1 I I I I I I Indications· are that the peak flow associated with the PMF event could be c.onsid~rably higher than that estimated .b,Y. the CGE. t It i.s tnerefore recommended ,.~;nal--the PMF ·Stuafes:::::5ir""Eeifone-·prfor"'·to-compl eticm of the current feasibi 1 ity studies: T~~ motivati~n for\this recommerydation is reinforced ~~.the fact that the proJect 1s large, 1nvolv1~g large cap1tal out;lays and very 1mportant to the future development of Alaska .. \t~u~~ J J ! ; :t:.l· "\ ,...-.r i . \ "' ' ·I·\\?' s . /*This is of· particular importance to spi11wayj design as the rifk of failure ;' associated with a given design discharge may be substantially higher if the I \ ... design discharge is exceeded. I I I Q ·t·· .• . ~ .. " . • • •, r../' ~-/'"' -.-) · .. >( X I I I I I 3 -SCOPE OF WORK 3.1-Probable Maximum Flood Evaluation The probable maximum flood (PMF) is generally considered as a flood resulting from the worst possible combfnation of a number of maximum credible meteorological parameters and antecedent basin conditions. Although no annual probability of occurrence.can be accurate1~7 attached to this PMF event, it is generally accepted to be Tn the lo-5 to 10 P range. · ...... t~ (,~"~,. ,.p' V""" The ~i~st step in the ~stimation of\the PMF is to detennine cr. itical m~teo.rological cond1t1ons such as max1mum snowpack,\...temperature sequence, and the max1mum I probable precipitation (PMP). The timing of these maximum events are usually assumed to occur so that the resultant peak is nyijfimized. However, in many cases, a judgement is made as to the reasonableness of the occttrrence1. pf such a combination of events. The respon5~ of the watershed to the .-F'r6bable-~Maximum I i"' ~recipjtation (PMP}, with antecedent conditions suitably primed to give severe flooding~ can either be determined using computer mathematical models or by use of unit hydrographs and rainfall-runoff relationships. I Usually, a computer simulation model of the basin is preferred over the unit hydrograph ar rainfall-runoff methods. The advantage of this method over I conventional methods lies in the ability of the computer model to test . r hypoth.ese§~of 1tfnoff whJs;h involve complex interactions of hydrologic elements and in the'~"'tlEiY~:case)in which a non-homogeneous basin can be sub-divided I, ·.· into smaller fiomogeneous,hydrologic units. Consequently, the selection of the ·SSARR (Stream Flow Synthesis and Reservoir Regalation) computer model by the , COE to estimate streamflow is believed appropriate for the Susitna Basin. '~ I 'It: •• L t.~,r. •} ' ~ -~·c. ~ ¥JJ6\'~ ' ,~\.».,:~ v .)':! I I I I I I I I .•.. , . •• I I I I •. ~. I I' I I •• I I I I I I I ' ·• 3. 2 -Scope of tt/o rk The obJective of, the work was to assess the accUracy of the CO£ estimates ~~ spring and sulllner PMF events. In undertaking this ;;'Grk. the following re I steps were performed: (a) Review of Work done by the CO£ (b) ( i) Review of the CO£ input data to the S:iARR Model particularly with resPect to: · · -basin and sub-bas'in PhYsical characteristics; -precipitation (antecedent storm and PMP storm); -temperature sequences; -snowpack accumulation over winter months. ('ii) Review of calibration runs made by CO£ with the SSARR Model to determine i'f the parameters selected to describe the physical characteristics of the basin are acceptable. Sensitivity runs with SSARR Model (i) Additional computer runs to determine the sensitivity of PMF peak estimate to dhanges in either input variables (snowpack. temperature and precipi~ation) or basin cha~ctertst'ics, Detailed discussion of the above review steps are g'iven in the fo11owing "ection I I I 1° I I I I I I I I I I I I I I I 4 -REVIEW iF CtE PMF EVALUATIIN The review of the work conducted by the COE included an assessment o.f the input data used and the SSARR Model calibration procedure and ·results. These two · aspects are d'"iscussed below. 4.1 -Data Input to the SSARR Model (a} Basin Characteristit:s The SSARR computer model obtains the best estimates of streamflow when the basin ·is divided into relatively homogeneous sub-basins.. Flows from these sub-basins are combined and routed downstream to derive the flow at specified :Jllection points.. A schematic showing the sub-basins used by ~he ~OE for the Susitna Basin above Go~d Creek gaging station is give~ . 1n F1gure 4.1 . Cl/~~&· 9 ~Q.~ ' <'. .•• .. ~· . Each sub-ba:in l-5' ascribed phy:ical characteri:tics tha. t a~e{~elievea)~'"' : .. representat1ve of that sub-bas1n.. The sub-bas1n character1st~~ · . defined in the computer model by tab1 es. These tables, converted to · figures to present a clearer pictures are given in Figures 4.2 to 4.8. The majority of the· parameters, describing the physical characteristics are determined by assuming 1 ikely values and relationships for each of .. the sub-basins. The assumed values are a function of the sub-basins ~ hydrological char-acteristics such as soil types, slopes and aspect. to The assumed values are then "fine tuned 11 .e-f obtain~\t strealfiflow estimates , that are within acceptable limits of observed values. This is the usual ,1lr~~t.J~)1J-'k 'Jii1:Y to ~al ibrate t~e ~odel when o~ly sears~ data ~n hydrologi~al r~rameters V are ava1lable. Th1s 1s further d1scussed 1n Sect1on 4.2 (Cal1brat1on. Studies). Generally, the basin parameters detennined for the basin are acceptable at this stage. l ·~ ~ ·-· Several discrepancies, common to both summer and spring Pf~F files1 exist~. These are: .. ,~·"" i (a) (b) For Maclaren Glacier a table, Number 4006 is specified for montqJy evapotranspiration index. No Table 4006 iS/'given~so a zero evapotranspiration index would have been asSnmed. However, it is· unlikely that this erl'"OY' wuld significantly affect peak values, but would probably~~ affect the accuracy of. any long term streamflow simulations or would be important if antecedent soil moisture conditions fluctuate significantly. It is believed that this table should be T~ble 4009 which would make Mac1aren Glacier similar to Susitna Glacier. ~\Hro..'ho:f\ A base flow mtta:trnn index of 0.03 inches/day has been assigned to Maclaren Glacier. We believe this should be 0.30 inches/day .. '" .. """1-9 '" ... ul ~":\""1. • . It J'l. .,..* .... }'. Vi \ l ; ·~~· -l; .1,~" v :# -~. "· q. t " '"""' h ' (!:"'!.: fy"~ " ; ~I.P.,t,v. -. , . , :.Jv I I I I •• I I I I I I 1: I I' I . I I I .. • J I I I I I I I I I I I I I I I I I 4.2 -Calibration and Verification Studies The results of calibration and verification studies are provided to indicate in an objective fashion as possible, the level of accuracy that can be expected {:rom the use of the Model. It should. be em~sized that the degre.e of acceptance of any model is ultimate1y judgemental in nature, and should be continuously reviewed and updated as new information and data are obtained. Before proceeding further, it will be instructive to ··review the objectives of model calibration and verification. Model calibration and verification are separate buf related activities, both of which should be performed in the process of the models' development and application. In the process of model calibration a data set is selected _which is assumed to be representative of the type of problems to which the model will be applied. The model is then run with this data set and its coefficients are adjusted to provide the best agreement between estimates and observed values.. Often several data sets ·are. applied and a compromise set of coefficients obtained. When the model coeffi'cients are determined from the calibration exercise, the model should be run with one: or more data sets which are independent of the one.susedfor calibration. 1n no circumstance should the model 1 s coefficients , be adjusted when using the subsequent data set and the accuracy achieved by the model constitutes the measure of the model's verification or accuracy. ~~-(c-··~ ~-~ .c:. . In the review of the COE studies, i-t ha.s .... hee~ne.d...-t~ no verification of the model was undertaken; only calibration runs were made. Consequently~ the accuracy of the modelling app~ch adopted has not been tested. The COE selected spring floods in_ '964 and 1972, and summer floods in 1967 and 1971 as representative of floods on the Susitna River and its tributaries upstream of the GoltJCreek gage. Calibration was performed at four gaging stations;· X' three ~on the Susitna River and the fourth on the Maclaren River·. The results of these calibration runs are given in Tables 4.1 to 4.4. Flow values for the Gold Cr,~ek gage sho~,>}in the table on page A-31 of the COE, Inte~rim Feasibility Report!app~ar to be in error as they do not agree· with the computer output values. Tables 4o2 to 4.4 also show; the return period for the X observed floods at the four gaging stations. The observed and modeled hydrographs are given in Figures 4.8 to 4.14 .. The results of the calibration study indicate that snowmelt flood peaks are consistently underestimated for floods at the Gold Creek gage; 6.3% and 14% for 1964 and 1972 floods respectively. However, snowmelt floods peaks at the next upstream gage (C~ntwell) are consistently over-estimated by 4.1% and 0 .. 5% for 1964 and 1972 respectively~ No conclusive pattern exists for Denali and Maclaren Gages. Rainfall flood peak estimation for 1971 is 4.6% less than the observed value at Gold Creek gage and is 22J~% greater than the observed value at the Cantwell gage.. All estimates and observed values are given in Tables 4.2 to 4.5 for the four locations. \=.xtt . 0 ••• I .--;»' ,. .. ... -" ...... • .. t, ,.,.~ ~ .·\ ~p \\. ~ !< .!>3' v pJV:·•' "~.~ I. 1 _ The coe4'fc~ent~ used in each calibration ru!l are in many ~espe<:ts different. \.,7>''\J' For PMF est1mat1on the data sets developed tnrough the cal1brat1on of the • t,.<Y'. 1972 flood has been used for both . th~ spring and summer f1 oods. Consequent 1 Y, I -&.J.~.~" .. "'"' \ ·. lv\the data sets develop«;d for floods ~n 19~4, 1967 and 1971 can ~t:lY be assumed • <>.,.i> \.<> ,,~c '. J.·· to be not representat we of the bas 1 n . 1\5 the data sets are d1 fferent for e'J.~ .J \.>•· -te. two spr~ng and sUillller. calibration· runs no verification of the data used for I \~1 ~ \J .. ~ . t·""IV" PMF estimates has been made and the accuracy of the model has not been assess . "' ... ~\ t~~t; . '!; J. tL<qt f'('.;J1 ~ I I I •• I I 4.3 -Summary The COE followed the usual procedure for calibrating a computer model of physical processes. However. no verification runs using independent data were made to determine the acceptabilitY of the coefficients determined from the calibration actj.\dtiY. Consequently, no degree of accuracy in modelling the basin can be ~based on the available calibration study. ' ft ' . ?~,.,~t ~· (JJ:; li ~,,/'$ I I I I I I I I I I I. I I I I . . ~ ... ( ( \. S:S.! :'<A l. A! \\<."0 t.:.D: wt~J:m REFERENCE: US ARMf CORPS OP ENGH~EERS INTER?,1 FEASiBILITY REPORT, 1975 APPENDIX ! Ph~T [ SGHEf\1ATIC s.::;n\!. l. ~. ~-~:.I s:..~w..t. Z::! ~. 1'1. 0 \ !;::.;•); R, "'._-tA~ ~'~t 1-r-::,J.',i~ '! ;-.1'\,~i':t /7\ t 20 l"J£ ;!ji:,.t !!;!, "'P' ,_ t'.. lit! ....... ~-· . ;.. DIAGRAM OF SSI.'-.RR COFv1PUTER ~JlODEL 0 0 D FIGURE 4 1 ~ • !'"-'---·' ,, .. f."' ... "' larr i ~· ·~-· "- ---·---______ EL __ _ - .,., , . . ... -. :~..~ I •] . . l ~~ 100 90 ~A£102~·-") j I r ---·--!· ---1-•• ·-· ~ .. : . 1 •• ~IOJ5 ' If ~ ~~,.,..,.· ' i 1· ' ' 80 / ,1020 l l .. ; I ~ 0.. (J) i 10 en • I> J-z £-() .~ l&.l :0 lf. It 50 s: tt 0 o· 0 z 40 ::) 1'11 a: r (R 30 s: """""' ~ 20 .. :a iO 0 "'0 .. ' , ../ ,101~ f , i v l· ~ !I If ~ 11 ~ ~ ~ -lf ""' .............. ....- ~ __,.,.,.. ' ' ---~ v I ~ V' . ~ ~ l;..-.== cL21 ~-.,_,._ .... 1---1--·-1--;.. - - 1---· 4p.-. - 2 3 5 6 7 8 9 10 II l2 13 14 15 SOIL MOISTURE INDEX SMI (INS) ·---------~-~---~ lOO 90 ltso m • ~ g 70 l&.. I&J Cl) <t m60 g 1&.. 50 LL 0 z ~ 40 LL. 0 ~ ffi 30 0 0: w 11. 20 10 r"'"' ........... ......... ~ ~. XZ009 ~~ ··~ \011 ~ . . ,__ --------~----· ! . ~, "' ........ . ,,. ' ....... "' ' r--....... ~2012·"'; ---..... -.... - " ~-.... ...._, __ ~'.-....... ___ -,._ _____ " I-----~ ~---z-1-----::"" - -. 1'4"-~ 2orr ··~l r~~{~·*· ..... H f If ' .. •i .. / .· . .-" !;,, . ' .. 1\ -1 \ .. .. ······ \ \;-.~·- ,<"' ~ ~ l' ~ ., ; ( .. .. en'"""'"" ......... fl<, \'. I .. ~ \J2009 " ~ ---.... -~-=-J:5:..J ---,.._ __ ·-~ .....,_,, ~------· ~-------. l 2 3 4 5 6 7 8 10 BII-BASEFLOW INFiLTRATION INDEX (INS/CLAY) •• ,of •• • •• : ~ ... ~: ! ~-• .,: :. • .. • ~· : ,• •• • •• ·:~ ... h"' .;~ ~ • 4' i' • • ~ .. ' • : tf. .. • • • • . • • • • . '. ~: •• -.4 • • • • • : •• : •••• '* I -- I (I) (I) ):> A). :u i: 0 0 f!l :0 G) CJ) < en ::0 (/) ill.· . ' ~ ---------- J2 .ll .10 -!f' ...... (/) D9 ~ -(/) a: .08 ~ 5 .(Jf a.. ~ f-.06 ffi z ~ .05 :E 0 u I.IJ .04 u ~ a: :l .03 (/) .02 .01 ....-~ L ~3003 / "Ni-"'tl<>! .. ~"" J• ./ ,~ .. ~~""";,· ' , ' 30081 \} ,~·· , .. ·" ~/ ·f.:' / J,. ~ "'""'J,(· ~·•"'"" / tl''"' _..,_~.;.. " ', ', / ,., ' ., ~ t' 3009· v~ _...A... -+-v ~ ·~~---r--· '.· . -~---~-·-·--~ . . ._ 0 .01 .02 . .03 .04 .05 .06 .01 .08 .0~ ..10 INPUT RATE RGS 1 (INS/HR) LO ,· ------ ' ·""' / v • ~,.: It 1 j l!IJ A .. ~vt,..-v . . - ~ ""'- l5 v ~ 1.2 /; v ' 'r!''. ·' \. ~. 300'5? 1.1 ' ,' t.O -··· ; ; ·~ rt; ... 17-. 3oo9 ~+-~· 0.0 2.0 I I· I '· I .5 r--~-~~~----. I ( 4010 j I I I I ~,.,~.; . j I \ I -' ~·~· ~ . 4008 :! 8 ~' 1 ¥; .; ',> ··~..._..;-.:P'-4-f;-.· I I .4 I ~ I.IJ • X liJ I Q ~ .3 z Q I !i a: ~ (IJ z <t 1 ' I ~ .z 0 ~- ~ I . ' ~ I ~ ·• tr.l I .I '\oo: \ : ---"~ I : ---. "·~">---~-- I " -?" ,r.J.::..· .. ~ ....... •• 4 5 6 7 8 9 I MONTH I I I I I SSARR MODEL MONTH VS. ETI I I I I •• 100 I I ~ 80 0 ' I uJ ~ I C/) UJ 3 I ~ ~ 60 .... , . () \ ~ • (.) ~ I ·fii 0: l.tJ ti a:· I z 40 0 fi a: a: I (/) z <t a: 5 0-20 I ~ w ~ ·J ~ ~ ~ !,.,""....;.-.. ) l/ "'-j;5001 ·~ I-__......... - I 0 .I .2 .4 .s .a tq. · . tz 1.4 ?RECIPlTATIOW RATE -IN~S/ HR t.S 1.8 2.0 I I I I SSARR MODEL PPT \IS. KE. I' ,. I .• I I I I I ~ 0. I I 8 (/) I i.3 •• a: <t Q LU a: IAJ I {5 (.) 3:: 0 z I fh- I I I I I I I I 100 K''4 ~ ~oo¥ ' ... \ --., ~, '~ ' -"' 90 80 ~ ' ' \ " ~, ~"-' -'""'' I· .,-.- r·"'*'-· ' THEORETICAL SNOW 70 60 50 40 30 20 10 0 o _ ro ""' '4 ~ DEPLETION CURVE (SNOW HYDROLOGY) \. ~l ,. ~ 1 ,, \, l ' " ~ ', " ~ • '" "'' i''-' ' .4J flJ .:,--, • ~~ r", . ("" -. ' .. ' .. _:. 6006~ ~ ", £ ~" ....___ ~ ,.-, z.o . '30 40 50 60 10 ACCUMULATED GENERATED RUNOFF 0/0 OF SEASONAL 'TOTAL -QGEN. 80 SSARR MODEL QGEN VS SCA so roo I .. I I I I .5 -· .4 I cr <: I fJ) z ' t; .3 :.J I l.&J :E tLl ~ I ..J ...J ~ 2 ~· z. I en I .I // k:~ // f v // / r v I ~· j r.L1ao~ f 7 \ I'--·--·-------~-,__ 1---·· ~~~ ..... ~· v . 1 / v v I ~~-') 100A ~ \ ... ·--------/ ' .~~u } ~II" l . )( ----. .... v I I ' !. J 0 so 90 100 10 20 30 40 50 60 70 0/o· TOTAL SEASONAl... ACCUMULATED RUNOFF I I I FlGUR.E 4.8 tiJ . --~--~~----~-----------------~--------~----~~--~~· I -I SSARR MODEL QGEN VS MELTR I I t' '\. I I I I I I I I I I I I I I I ! ' I .I _____ .,._.., ___ ~.----------~-------~-----~-----,~--·---~.,.,......,----- FtC>Nm CFS ' ·-----~------.... -........ --~-----~ .... -~-----~----~...-.olf~-~-... ...,. _______ ~,.,-~.,,.,~.,._--....__,,,, __ ~ so IO::J.OOO 70 60 80,000 50 !::: w :I: ~0 CO.fJ~>Q z w c:: ~ 30 5!>,CCO (I) w w c:: C> ..: ,)f,JC':IO w 20 0 I w c:: 10 ::o.o·;o ::> .... < cr w. a. 0 20,000 ::E w .... -10 :;J,O;)O -20 0 REFt~E~ ~C_E ~ U.S : .. :::.:~.~y c::~PS Gf' ENGn~C:EfiS !NTE:=i.'t~ FE,:.S!BIL;Tt REPORT, 191~ APF-ENDiX 1 PART I . . . I ,.. ....... ..._ .. "' 00 10 . . "?d:·~-':l::;-:::-: .......... -: .... -. -........... " ~ .... ·: ......... ,.. .... " - I i . I . eo o~c · ..... ~ ... -~---... -.... • 1 " ............... -...... ~ ' ~j .. ~:'~. ~!0 0 • • • • • • • •••••••. " ..... - . ' ... ~ ...... ..-... .. . ' · ff:t:>:. Fi:'A"~'!ON 1 P; i'~;::HE: S 3 HYDROGR.APH SUSITNA RtV·ER AT GOLD CREEV: ~~---------------------------~--------·~--------------------------------------~~-------------- ~t:Ct?:.fAT;O~t IN I'{':HES 0 2 3 • F:GuRE 4.9 j I t I I l t I I / ~ ... I I I I I I I ,I I I ·I I I I I C.. • I I FLc;:.v IN CFS eo e:);:;:.oo 70 !~.Q:)Q 50 ~,?00 ~ 42,000 t-w ·.::: 40 3~,:l0~ z w 5 ~ "'-3;) :3-0,:JOO (;'). Ll ;;J c: ~ 20 24,000 w 0 1 w 0: 10 18,~00 :> ~ c:: . w 0. 0 I~,COO ;:;; w ._ -10 6,000 -20 0 s~:~ ~:-~ '~ § !t;, ).;~ ~ ... "' ............ " . .. .............. "'" l . .......... -.. -. . . . . . . . I -.............. -·=-. --. ... /. ······-······-·· ........._J 197! . ---'·------·--~-P..-fi-€:-CI~?I-i-t.-T-IC-.4·----·------l. • .. • fN U.CHES Hi:n~"-'%:-:"t~ ~ t. :'l ~--~1 ., fl}t t• ~:c~ t.: ~ Ct·,'! s t' .. •• !~~o ... -~ c 2 ...... ,.. -.. . .. .. .. '"' . .,. ~ ......... -~ . .._ .. ·~ .......... " .......... -... , ........ . . ': ............ ~ .................... : .. ~ .... ~ ~. . "' ... .. . ,.' " .............. ' . . •• J ..... . . ---~--..... ~_._.., ... ,. .. _-.. -~~ ... -........ --~-..... ~ t: ~ ;;.- t.. a: -~ c.') w ltJ c:: \:1 w 0 .I w 0:: :;) ti tr w n. ::: w ... REFERENCE~ . • r .. ~":..: ... -~~ ,. .... · --...... ;.. . . ~ ... "" . " ........... "". 70 60 5~ .;o !.'0 4;) 1~ v -·i .. "' . . ~ . : . ·-... FLOlf ~ CFS ~<;,:::-::<:. .;._q;.;:.a .;::._c<).) :;£•.).)':) ~..,;.r:o 2~.~J0 tE,~"'C J?.p:o 0 l r I . ·' ..... :. t;' .• -} ..., :: • : ,!. • ~ .... ! .... ••.• t~-.,., t A t , ! , ; . ............. ,X'\--~r ·l\·-···i· :f:" • rr•~ ,..,...,..._ I ~ . . , A ~"'t. -'-''-'7"-':;1 \ \~-,.:.. x.::-t;:!\VED I \. • ····· ·.i· •r • ..;._ .V • '../ / f 1 1J~·.. . . . . ' •'- ..... :-":':' .. -._,t J . ~ ' \. / ; ·. {\ .. •· ',_( l \;\· •• • 'j' • \I ".\· J_ ,, . ; \ v. : J, J , \ . r ·t .... J. . \. ;r ~\\fJ f ! 1, X, •• •••••·•·1· •,••·' 1i_ • •'• I I • ... "' ~ • "' .. " ~ II! I . . ······ ·--1 . J ' " ' ~ .. • . t . I . ..... j -........ . .. "' ., .. . . .. . . ........... ' ... ' . .. ' .. ~ ~ .. J H~lP:T.-..T:O~ IN ~~,;: ... ;;:s . . . . ~ .. . ,.._ . ~ . ' .. .. ~ ~ • " ~ ;1. ~ ' • ·--.. ---~ -~-.. _. __ "--.. -~ ..... _ ... ........... # -··-- ~ .. -.,. .. 'f" . ~ ;,;' ": ~ ., ........... i1 .. .. .,.. -... .... -~.... . .. .. ... a. .. ~ • 'f .. . .. H S t.Ft.MY CGR?S Cf E~.StLE:t:?~S ;~JTER;~.~ ?E.:.S o li1Y REPCRT, i975 hPrEI~JIX l Phr~T I HYDROGRAPHIC SUSITNA ~--~--------------------------------~~--~--~-----------------------~---------RIVER NEAR CANT\1\'ELL I ( I I I I I I I I ( I I I I I ·I I ( I 1- ~ z. w c::: ::c < \i. t.') w u: c::: 0 Uo 0 I w eo ?o 60 .s:> .;o 30 <:0 :::: tO ;::, .1-< c::: w ..._ 0 :::;: w l- -10 f'~cwm CFS M.c~:> !j4 .o~o 4a,c.oo ~ 2,CC'O .. 3-6:,000 ! 3o,o::w i 24,000 . . 18,000 6,000 .. "'"\.../"'" ..,"··~ ! ... \ .. ..-'-; l ' . ' I '\..j t.i " ' •or,; ........ ~ .................. ~ .. 1 -;vu~:.:.£ T..,.l .,. -• _..oor. ,_, .• . r,. •• }.-_~t. ~.-..... J'?\!'_._ :-.,-. .....;r"'"""" !~ ' .. "" \ .... _.; .. -... 'j I ../ .. -~ ~ . ' . -" ~ * "' -• .. • • • 1 • "': " .... t -"' ..... t ~ 1 : . ............ "' "\ .. "' . ·" ~ ; ' . .,. I : ~ • , JJ r . /' I'. r' . . Vv-. \{ 'j· ...... .. /\. : . . : : . --. . : : . : : : -.. .. .r \ . ,. . ,, /'-...._J ~ i V\ / ~~-·/ .... . .. ··! . l./·······~\ ·-······· .:"':\,.>.·, .. : f '"···,.··.··~·'""' ...... : v· "-" \ I • \., .... • \ I ' \ c• ..... ~~o .. ·. . • . • • . • . . . -••.•••. {(· • :-_~'-:'"7 t. • . ' \ ' ' ·\n~~·-'\·······.·'···· . . .J' ; \_ ~j ,.,. .. _. ___ ..... _ ................ ! .......... ,. . : ·./ ~ ~-,., . ··-.v .......•.. . . .. .. ~ .,. • ' ... .,. .. " .... '"' ....... ~ •'\,,,_,;.- ... ~ .. _ ......... ~..,. ...... ~ ........... • i • • • > •• '* • ... .. . • ..... ~ --"-.. ""I ... -.. -.., ": -"' • ... .. • .. -~ ....... ,., ...... ! ·• -..-..... -....... -.... ·20 0 ••.•.•.. .. ' 4 .. ( ' ~·!.·•"·4'•\ .. , ..... ~ ..... -..... , .... ~ .......... ~ ............ ~··~ -;··~, ! .... -... ! ........... . .. .. .. ~ "' ,;_ t ~ • .. ~ .... , ...... ,. ··~~~:.- . : : ~ .: . : ; ~-;<' · : : L _ ; : E . : ;: :·; H:: ; ?i;! i ~; 13H. Hi :, . .-~ .. -• "-""':'"' .. '! .. - -............ .. . _. . . ~ .. -~ -~ . " ..... ~ ... ' ,. .. . -~ -· .. --~ .. . . ... REFEt,~C:r~CE: .. -· ........... -.. . u S. t..~MY C0R?S CF E'~Git;Ee.RS r~.;;:::R,~.1 FE:t:.S'5.LTY RE;:.>CRTt 1975 f...F ::~ 5:~\DIX I ;:;..rrf l cr.. w w .0: eo 70 8 20 Cl I u. § lO 1-< c::: u c. 0 ~ w t- -to -20 -' .• ..... ~-= ,, ~ . i ~.... r. !-~ ~ .. ~:·· "'::.;'-: ....... ~ .. ~~ .:-=.:::.;.:_:·::.-r,:; :-..... ~;~~ .:..::;-;:-"-·.t·~-.:.::-:- FLC"HIN CFS 60,0'JO w ;s~ .. ~~-~ 1.1 P!=:Ec:;;t:t..-;4~ 1:1 ;~;CH:: S (I S4 ,Co::> 3€. .ono · · . . .. .. .... . . ;.. . ~{ ... ! \ I .\. . CAtc:.:,.;m:.D -C!I~!:?.-EO / \ ····· !.. ..... {\······· ··f \ .A. . I \ ·...,.,-.{. .\~ --_) .. (! -. '~· ... r;:j .... -.. · \J -..._ ._· \J1rr-....: ~ J l · "'-"-" ~(',000 IS,OOv 12 ,000 --.••. -. • • • . • • • . . • •••••. € .oc.o 0 _,.o, • •. ' . ~ . .. ' .. . .. ,. ...... .: -...... t: .. ,. " y ~ " ...... HYDROGRAPH SUSITNA RIVER NcAR CAN1"\~ELL f''1!C.f!>i'tt.r:cN 'lN: I',CHES 0 2. I I I ' --'.!;-~-·--· , r ~ FIGL!RE 4.!! ~ ~~~ .. I fLCW l~.c CF$ eo 40,0JO I ¥"' •· \ TO :5 s.ocn 60 32,CCO I 50 26,.COO I ,_ w 40 2 4,00.1 2: w c:: :r it 30 2~,;::;oo I '-"1 u w c:: 20 I €,CC3 0 w 0 I I w c:: 10 12,000 :> ,_ < a: w n.. 0 s,oco ~ I LJ ,_ -1.0 4,000 I -20 0 I I ~ I I I I I I I I ( I ~ ....... -.... "'''*" ....... -~--.......... ...,,,, t u ~ w -C::: :r <; .... (.") bJ w c:: a w 0 1 w (':" ::> ~ n: L... r. ~ w r- eo 10 eo ~C) 40 20 to 0 ~!O -~0 FLWI.'i CFS 40JOO 36~CO 32:0:::0 28000 24-)00 20000 !60C'O l2Ci.Jl c~:. ':>::> t;:j:::O G. • .. ,. ""~ -~· t ~ .. 0 ~ ..... ~-\.~ ... ~-"' ·······-~\ ··-·· · ....... ;.· . : I ~\ . 2: ....•... -. -·I· . . . ... .... ·W\ .. :·· .. -.. ·· .. : .. ' -o=:.E?r.."D \ \ }) ··--·~----·· --:~j . ~ I ( . ' ~ ••• 4 . 1· • : ~'E:~~·7~T :« ~~ ~\CJ-t~S 400 HYDROGRAPH SUSITNA RIVER NEAR DENALI FRE'::•?tTATIQN IN t::.::11;;:s 0 J I I ( I I I I I I I I I I I I I I I I I eo fl!'..".'l lH CFS 60 ~2 ,000 • . . ~0 2S ,C·OO • · "? LJ w a 20 w 0 I w 10 § !< {;::: w ~ 0 ~ w t- -10 -20 H'i,QOG 12,000 •• ,.. ...... w ....... s.o:m · 4,000 0 .. + ...... -.......... --..... -·.., • ... ...... _ .. --• .I • ~ ' ' . . •. --....... -' . ., ~ . . . .,. . . . •. . . .. ~ ; ; ! :-... ~ .. : ~ . ~ ... ,. : . ~ :-. ~ .. :: . ' ... : ~: 4. .. -· ~~FEns·l ... -:;E-. U 5 •• R'.1Y CORPS 'OF ENG~'.E£RS ~~ ... TE!1:i:,1 r"Et.srSI:...iT'f RE.P;:;.rr, i37 5 c.;:;?EN:;·iX ~ P;.RT .... -j ; .. .......... 3 ...................... "' ' ............. .. .... ~-.. ~ .. , ...... 1)72 } I ·' HYDROGRAPH SUStTNA F~IVER NEAR DENALI I I ( I I I I I I I ( I I I I I I I flvWIN CF$ 80 lO,QOO jj 70 9,000 ~.ooo 7,000 l,ooo I,COO 0 .. ~ c PEFE=tENCE; -. .. .. ... .. .. ,. • .. ' • j . . . . lJ S. AR:.w CORPS OF Er;G'NEERS H~TER.~.~ FE.:.SH3!UTY RE:?ORT, 1975 APPENt'iX I P:.RT f ' 70 60 50 "'~~.'1..:0 ;; t;!'{ st.: ~ .................. _.,. ........ . Ft.C'h !•l CFS 10000 9000 0 . .. . -., .... ~ .. .. -...... . . . ' . ' " . . . .. . ~ ... .. ' .. -' ......... • : ~~·:.~·~ ... .. ! ~:, ~:.!. :· !: .. --.;: " .. " .t· " ....... • ; ~:.;:}'"';_,;.;.:7' .. -~ ~=r~!.¥==-~--· ,': "~'""i;:"'a,"''~"• •• ,.. ~..::-.." ., ' r~t :,:~;~~-: 'Y; f't t\. ;~.;-4) 0 ~ ... ,. ...... ,. -. . " /" t .i • i I . ··:· -,-. _: -t, -~·t ~---... --\..-... v I ;' , _ ....... ,.. -'Jl ······ .r·· " ... ·.r ·-.•• \. j ' ... ~ ~ .... .. .. -.......... _,.,.._· ......... ~··-...... : -·..-.. .... ~.-.. _ --_..-.............. ~. .. " " ~ .. '"' .. ... ~ ,. .. ... . -. .. -.. M • ...... -........ --· HYDROGRAPH ~liACLAREN RIVER NEAR PAXSON. . ~· ! j. . . rJ .. ~ ~ot•._., • ·~ I f -~ t ' I . . ' . • . I - z 3 . • j , i " I. =~ I ( -... '- 60 I !V l- I w .... 40 z w c: -<:: :~; ... L.. _...., I I I -10 I ·20 I I I I I I I I I ' I (_ I I FLvW1~ CFS 10poo 9 .0:}0 ?,000 ?.OOC 6,000 r-_.r·.., • .J I 5,000 / . . . .; ,000 3,000 2,000 -~ ....... -~ . .._..,-.~---'---·!~~~-~-----..-----------~ ~ ,, ~ ............ _ ... ~ ........ ,., :..~.,_~£.qA~E~.., Tt. •l·; r:-R~-;l,.~t \ , '. I ~ • • • • ! •• • \: ,. . • / . . . -. . /; . . . . . . ~--·_ -1~ .-~f\f\ .; : .'-. \___ rv · I r •r '/ IM/'/ 1 \; ' ·J·~··. V·----. r :_J· \ ! ... \ ~.. \. . . . .,, " I . . . . .1 ~-. I ... \~ ............... J\ ... : .... \.. . ~""":~~. . . . . . 7 .. \.. . l . . . . . . .. . . . . . . . . . . . ..... . I ~J ~ -·. . . . . . . • . . -....• -. -•.•...•....... -. . . . . .. -. . • . . . . • J972 '-_/ {\ )i ~ f\~\;;J?·. ''V \ 1 . ... J. . .. . "' ,. . .. . . . .. ,, • ... • -~ -'! .. ' ~ ........ ~ ..... ~ ..... .. ..... , " ........ -.. .. 0 .................... ~ ............ _ . .., ....... ~., ................................... _ ... .., .• ---............ .._ ....... 41 ...... -... -..... .. ·. ; ...... FlO"' I~ CFS 80 J.J.C·OO ,,~ 10 EiO zo 1- G4c ::r % w c:: X < ?Xl 1... ~, u tu 9,'.)00 &,OCO 1,000 6,000 5,000 g 20 4,000 w 0 I w c:: 10 3,000 ;:J ~ a: w c.. 0 2,{;100 :::!' "-~ 1- ~ro 1,ooo .. . .. \' .... ~~~ .. -. ' \ \ \ \ \ ·\ .. ~~.: W£C~PtT~1:0J4 !"t 1N:e-:£5 0 2 HYDROGRAPH tvi.b.f:LAREf~ RIVER NEAR PAXSON .. .. .. . .. .. . . . .. ... . ' .. ~ ...... . . -.......... , .. -... , .. ~.. ... . ~ .; ·-==~-.:~.: ... . .. 0 2 3 . ! JOB NO Mae R Psl oo • o:; .o"\ .oo l... -. FILE NUMBER _____ _ SHEET_. ----OF __ _ BY t/C-0ATEZ?\-e~8l APP DATE I. ....... . ·/ . \.! ! • Ct .J .• -\J. K: € C C'!l S. ,-._. ,L,t~~~ ..;. iV' :.:.1 q *..... CS ~ t4 I <;"UJ.l~a. e Je.~ cit 9dcl c ~ee.k.... .,, USGS Ctorjc J,b. IS2.q~ooo :_,:1.:~3,.'1Q ~~-:_e.C\. t;,H:cwft,. y ~ ~ I I ------·---------·--·---. - l A -•I ·.''n v tl/v.'l.. _ D sc ~,..,a £::8-e "~R.ved dar~ Colc~l~~d ra d\::=e-ev ed ~R..ILO fl.... t -eQ M ~II'\ f.e te.tc I I 'tt.b4- !Cl Mo.~..1 to t~,liA~ \ ~<»M1 e.t *-8 'S ~eo g ... , ' t ~ • \C(b, ~~~( -b ?I J\.tg Ro.t~teJl l b 000 ~' • \q1' I bM£(1b3o5ep Svt~et+ <ob'3oo ~tt-t·\~( \)/ 00 -1o.\ - 14-100 I tC£12 '2. ~1o.'1 io ~? SIAo,WAeH lo"loo \1 ~U}\ l.oo~eo t 1 ~\.{ 1'\. ...;-\4-.0 I R.al~~ti=J.l 'Lb 4oo 14-Ser -;z. ';oo lS'Sep + 't'l.·4 I - I I I I -:> w a; 1-N I 1.0 -ci z I :a• a: ~f I ·I I I I I I I I I I I I I I I s- 1 I -> w a: Calculations SUBJECT: -.' l a.~te 4--z.. ~ C·t-!.·F) ...... J . \ elf(\od 'flcad l 4 -Jl Ct ¥ to'./. lA Y.t BJe<~-1 d.o=:e tz.ved -·· \qbq.. .. I l q w1tt"i -b zrJl{l\1! s~o.-rM.e.lt:-4-Ci ,\00 lqb1 ' \~lA\ k,~l~ ~t \t Rctt~+a: . ~b,4oo I ,q,, . fa Ma.tt ~ 3o $e~ . .6l1~\.t Z.4oco l i?_o\~~ll '3booo lt\12. I ;,'.• . 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Z fJ.tA._,-b3o)ep SftcvJMe.!+ fu.\(1{~( SHEET OF ·-·------- BY -~ DATE --APP DATE CeE' C,o .. h ~t'C\.hc\tl Keect~t '5: 1-c: t,r !,cX-1 Shtd t.f ~ csvt tt, JJ1ac.la.r£e\A etc.Je/t Vlea:e-';>c:t'X..~OV\ USGs go.9Q i-.b. I S'2. q I zoo l>o:>.~rf fJ1 c-t '! n•i tA ~ oto.::eRued ~4-oo 1Z.Bo '[), sc~ a e..o. -e dot-~ f j""' I J4-Au;1 ! I I l{ ~ lb ~UV\ '~ S~p CalctAlab:c:l b'<..~o I -=70f&o.. (l~ ~ zq"S""o ------.----------~ to \ ...!.. ~JUl.. E.fl~fL 4 ~\.ttJ\ -'2..1 loi\uq - l{ \b ~un ~ ~ {1 ~ \b•'7J ~ . " \'2.. 'Sep ., I I I 1 .. I I I I I I I ,. I I I •• ... . > UJ a: d z :;: a: 0 u. "' Calculations . A~~m SUBJECT: _c ' -!' io.k e 44 .-----~----...---·--------------···- 1 ' -l='loo 6 rJic.t y. t#V.l\t 1) sC:~ a e.._y.e BJevr\ d.oseeved da-l-e.. CoJcv.lab:td lqb~ 51\owMe.\r Itt ~~q.le.Ju~e~ lbooo I -i~AII\ li .. Zoo ~ _lqti1 l..k\ \o '3\ ~9 R ct ;II\ 'foo..U ~ I lbooo t - J . t l q, \ btL-ttl., 4o 3.o~p 1 Sv\o..vMe.lt 1 llboe '"2..., ~\.{" \i~o 1 g_;\1A{~U ~~0 \0 Atq 31500 I \ct1Z ZJAD.tf Jo ~ ~ Sv\.~tAe..lt .. l4 tOO lb :Sl.t II\ 2.o3oo Rot\~forll 56cto ~~Ser-)~"'3oo i l t no Re.ca~ d· 1 ..!OS NUMBER FILE NUMBER SHEET OF BY \:"C DATE APP DATE ---.,. ----------+- . 4-.l....r'\ &4 ri.S lb~~ -- Z.4 oll!f~ -h"1 - f ll Av.a.. -5:1 -. ri S~An. +~~., \~~p 4-\\,<; t I - I .. :: ·.I I I I I I I I I 01 I ·I .. ' S ~ {~l!l,~ALl SENSITllft'tY ANALYSES 5,. 1 -!n~duct1 Otl The objective of this part of the study was to obtain an indication of the ~tflsitivity of the .ood~l to ehan;es in critical pcrrametersi, The sensitivity \'),f the SSMR mod•1 U wariatfgns. 'in soi1 moi~ture index or any of the other ~ny~1ca1 par!lnteters is small when compared to the model~s sensitivity to ~~anges tt:i §nowpa.ck · vo 1 umes,. temperature sequences·~ and the vo 1 ume a~d iltstributiovl .of the mP stonn. Cons~quently 1 no changes to the phys1ca 1 ~ramet~ ~~re mad~ ~t this stage and sensitivity studies were only made to $tudy vat""'iations in flood peaks ttue to snowpack~ temperature and ,_;rre.ci pitati~n changes. At:cepting that no. verification oftbe model has been undertaken, it has been assurn~d ti'at tile lilQde11 wilr reasonabl~ reflect the basin • s response to '.Mr 1 nt;Q-t c;Q.~i tiof\~.. _ . I I I •• I I I I ·I I I I I 5~Z.-Base Case The data files for t~~Lspring and summer PMF estimate~ obtained from the COE and loaded· onto ,1;he computer system. As a f1rst check~ the spring PMF -was. run again to obtain the same hydrograph as that obtained by the COE in 1975,. This indicated that the SSARR program and that data JJ~e"oWer-e,~·"'~ ~"~-~ unchanged. The COE estimate was used as the base caseAWhich.each sensitivity run was compared.. The base run hydrograph· for peak flow periods is given in Figure 5.1 ~t-J,.~~ .., The spring. PMF b~se run jis dis~i~gui~Qhkt by two dist~nct peaks, one due t_o snowmelt on June ll andJa prec1p1tat1o'fi .... snowmelt max1mum on June 16. The decline in discharge between the two peaks is due primariiy to a temoerature drop during th~ PMP storm.. The temperature sequence used by the COE is given in Figure 5.2. The temperature sequencf!during the PMP and for the four preceeding days was obtained by the COE from the National Weather Service (now NOAA). The temperature and PMP s&tirm are .gi"len in a memo from the NWS to COE and is attached in Appendix 'e. ihe temp.erature sequence used by the COE was divided into the following four periods: J.,j.,, t~~· ;1<:1/' ~-L~-- X X -May 1 to May 28 -This period was given by actual 1971 records at Summit e;,{t .. ., ... ~ Station -May 29 to June 10 -This perioti' was synthesized by the COE to obtain the maximum flood peak. For this period, the COE tried three temperature sequences as shown on Figure 5.2. The peak discharge was obtai.ned •nith the third and lowest temperature used . -June 11 to June 16 -This period follows the reconmended temperaturs as computed from values given by the NWS, Appendix A • ... June 17 to July 30 -Records for Sunmit in 1971 applied. Precipitation in the base run consists of two storms, o~centered on May 31 and represents the 1:100 year storm and the other the PMP storm centered on June 15. The intensity of the two storms are given in Tables 5.1 and 5.2. Snowpack was obtained by estimating maximum water equivalents and gross smoothing to obtain a ~ontour map of water equivalents throughout the basin, Figure 5.3. Basin parameters used during the base run have been given in Section 4.1 and are duplicated for the sensitivity runs described below. ~ ~ ••• I I I I ; ~I I I I I I I :I I I -o sh.rd·es So.R' -Sensitivity ~ Three main groups o.f sensitivity runs were performed to determine the effect on the flood peak due to like changes in temperatures snowpack and precioitation input data. These are disc~ssed below. {a) Temperature Sensitivity The COE may have over-estimated the temperatures in May resulting in too much runoff prior to the critical snowmelt period in June. In some cases, notably in the lower reaches of the basin, snow cover has been depleted to as much as 60% of the available area. In the base run, approximately 1270 sq. miles or 20% of the basin is snow free before the critical snowmelt period. Although it is recommended.that some melting should occur prior to PMP storms, to ripen the. snowpack and saturate soil moistures it is believed that a coo~ler t-1ay could result in a higher flood peak. Temperature records at Summit indicate a normal monthly temperature for May of 37 .. 4~.F. Consequently, a temperature of 320F has been assumed as representative of a cool May~ Coldtest mean May temperature on record at Summit station is 29.1°F. The sharp rise in temperature necessary to pr,oduce substantial snowmelt has beten further d~ed in June to attempt {}v a. juxt,position of maximum runoff f1rom snowmelt and precipitation. The temperature sequence as.sumed is givt~n in Figure 5.4. The assumed temperature sequence produced a peak inflow to Watana reservoir of 243s000 cfs as compared. to 233,000 cfs for the base ruu. This represents a 4.3% increase in peak inflow. The hydrograph· is given in Figure 5.5 •. The above result~ indicates that spring PMF estimates are relatively insensitive to temperatu1res during May. The sensitivity of peak discharge to temperature gradients inmediately before severe storms is believed to ba~ important. The results of the COE runs in obtaining the critical temperature sequence inmediately before the PMP storm did not-take into account the temperature gradient; only the timing of the temperature rise. The three temperature sequences assumed are essentially garallel as shown in F·igure 5.2.. The effect~ of a sharp temperature rise~ mainly in producing very large amounts of snowmelt in short periods of time. This effectively saturates soil moisture capacity very quickly resulting in quick runoff and large streamflow rises. The temperature gradient is consequently of the more influencial parameters in the estimation of peak spring floods. The temperature gradient is also o~.~ .of ~h.~_ maw _paramet~~s that should bt:~ maximized~.~.~~ . ~ ~JJ;lts b&jlJllg;e.ap.p.lJ~ based on what ~ reasonable for the bas1n. ,. ,,~~~f1:'~1N':ff.,..,l . .do The COE ~J; temperature rise of approximately 4 .. 3°F/day over a six day period. Records at Talkeetna Airport and Summit Station indicate that temperature gradients of this order ar .. e typical for May and June and therefore cannot be assumed to be representative of extreme events. • - X X .I I The determination of the maximum observed temperature rise i~. '1ay or June is beyond the scope of work under this· task. However, it appe..,· "S from' a {A,; very cur~ory appraisp*1 of avai1able data that a temperatu~e grachent of about tw1ce that assumed by the COE may be close to a max1mum .. Consequently, a sensitivity run~with a temperature gradient of 8.5°F/day has been 1 4_ . • v• • }performed. In addition, the temperatures during the PMP storm have been J 1<.~···t .. /} ,. I J\..fo .... ~"/ · 1 increased by 9°F to produce a maximum temperature of 660F instead of 57°F. I .~ t-~8 (~,, ~ . •. ~\'" lt>! This_is beli_~~~? to b~ not unreasonable based on records available at ~h:l~t.f~~>t~"i:r-A"'" .. r: rtl'.,....,. ~ Summ1t and{a~~stat1ons.. ··· \ \ ~ •. C) I . ~:·· . _,.,.· The above changes to temperatures prc.1duced an inflow peak of 302,000 cfs /"' an increase of 29.6~, Figure 5.5. Obviously, the temperature gradient X prior to the PMP storm and temperatures during the stfun are very · I . important parameters in determining PMF discharges. The temperatures selected, a.lthough higher than assumed by the COE, are not unreasonable. I I I I I I I I I I I I I However, it should be noted that the temperatures were only selected to determine the sensitivity of peak discharges to such changes and do not necessarily represent the sequence that should be used . .. (b) Initial Snowpack Sensitivity The derivation of snowpack quantities for each sub-basin of the study area has been based on records from stations outside the area and on judgement. The ~jJabl.e data was only available for lower elevations. The method used to obtain snowpack ·amounts was to accumulate the maximum recorded snowfall for the months of November through April. This produced snowpack amounts at various points surrounding the basin. Using available regional mean precipitation distributions, the COE developed a minimum water equivalent contour map for the basin, Figure 5.3. This was further averaged to give]f snowpack water equivalents for each sub-basin as shown in Table 5.3. The additional years of records obtained from the snow course stations, subsequent to the COE studies and the data obtained from the additional stations established during 1980 do not indicate that any significant heavy snow accumulations have occurred. Consequently~ no conclusive . statements as to the accuracy of the assumed snowpackwater equivalents used by the COE can be made. In ~l the spring PMF estimates, the COE has not assumed any precipitation during May. Therefore, it ca-R only be ~i'· assumed that May precipitation is also included in initial snowpack amounts. The sensitivity of the peak discharge to initial snowpack water equivalents \:>s~-P¥ha-s--been determined by increasing the initial snowpack by 50%. This analysis was in fact performed by the COE in 1975 and was not repeated~ by AAI. The peak inflow to ·Watana was found to increase to 2'54,000 cfs, a 9.0% increase, Figure 5.1. The result indicates that the PMF peaks are fairly insen$itive to changes in initial snowpack water equivalents. I I (c) Precipitation Sensitivi-ty iv~--t!L.<-i£, The PMP estimates c.o.Rdttct""ed for the COE by the NWS involved only a I sullltler rainfall event. The NWS ~eco~ended. that 70% of tilt; sullltler ~MP \. . : . be used as. the PMP stonn for spr1ng PMF est1mates.. No basls for th1 s ,..,"":''t"'vd\":~<:., -,.c decis.ion. to use 70% PMP is given in either NWS or COE documents and I ~ i_t...woutd-be · di ff-i-ettlt to defend this number. A separate study of spring ·storms would have been more appropriate. /' u;;tJ/ -· I I I I I I I I •• j~ To determ. i~e s~nsitl."vity. to changes in quantity ofLPrecipitation ~alling on the bas1n, 1t was dec1ded to assume that the .fulDPMP occured 1n June, but remains centered on June 15. To observe ·anTY-the effect of the precipitation change it was decided to assume antecedent conditions equal to these in the base run except for 50% more initial snowpack water equivalent. Temperature sequences were unchanged. The result of this run is a substantial increase in peak inflow to Watana to 342,000 cfs, a 46.8% increase Figure 5.5. Obviously, it may not be correct that the recommende.d-.P~1P-storm occurs in June, but the result of thris run clearly indicates that precipitation amounts are by far the most important parameters in PMF estimation. -It is therefore essential to ensure that a well defined PMP ~tonn be used for flood 1t~_urposes. ~sh~-:> a." AS a ¥concluding run, it, was decided to obtainAestimate with the case of f1iti PMP storm with the 8.5°F/day temperatu~ rise to a maximum of 660F. This run clearly indicates that the PMPf'estimate carr change substantially when what can be regarded as plausible changes to a range of input parameters are made. The peak inflow to Watana obtained from this combination was 430,000 cfs, an increase of 85%. Outflow from Watana Reservoir obtained from the above sensitivity runs are shown on Figure 5.6. 5.4 -Summary The sensitivity runs indicate that the estimates of peak inflow to Watana Reservoir and discharges at qr&( otherwlocation~are particularly sensitive to variations in s~Ettri-wrre-nts, temperature gradient and temperature maximums, and precipitation volumes and intensity. Sensitivity to changes in sub-basin parameters are small relative to the sensitivity of the basin to the three main input parameters given above. Table 5.4 sunmarizes each sensitivity run and gives the percent change· from the COE estimate for inflow into Wata.na Reservoir. Percent changes to inflow for Devil Canyon Reservoit are summarized in Table 5.5 I I I ~"' ,·" w~·~·-•~'-" \ \ } / ff I I I I I I I - I I -I I I I I I I I I I I PRECIPITATION ---ORIGINAL ( 70°/o PMP )/ ··:·:·:·:· _INFLOW TO WATANA 300~--------------~----------------------------------·------------------------------------------------------------------------- SPRING PMF by U.S. CORPS OF ENGINEERS 280 260 240 ff: 200t----~--------~~---------~-~-·~~- (.) 0 0 0 !80 3: 0 ~ 160 140 120 (HR.) 02 f DATE) JUN 8 14 5 LEGEND I I I I 20 2 8 14 20 2 6 50°/u INCREASE IN SNOW I I I I . I I l I I l 8 14 20 2 8 14 20 2 8 f4 20 2 8 14 7 8 9 10 ~ I l I l I l l I I 20 2 8. 14 20 2. a 14 20 2 8 II 12. 13 TIME 1 l I 1 ] 14 20 2 8 14 20 14 l _ _L._L_I 2 a .14 20 15 I I [ I } ? 8 !4 20 2 16 - 4 1 I I JJ a f4 20 ·2 a 14 17 18 INFLOW TO WATANA FIGURE 5J ·I I I I •• I I I I .I I I I I I I I I I I 0 5 JO 15 MAY ' . ; MAY 1•28, 1971 DAILY AVG. TEMP. I 1--.. 20 25 30 ;~ H') 15 JU.._,E I 3 DAY SERIES n I l - - I 20 25 5 10 15 20 JUlY SPRIN.G PMF TEMPEP..ATURE REGiME ( COE) 25 REFERENCE·~ [iJ U.S. ARM'r C-QRPS OF ENGINEERS. INTERIM . FEASIBILITY REPORT, . .._......,..t9 ... 7!5...,.A..._Pf!!fmJ't~·' PART!i-·~· ...,. .. -. ......_.~---......._, .. ......,....,-....,. ·-··--..... · -....._,OIIIii!iiMilj~~·~ " FIGURE 5.2 ' _,! ,-;-~.:.:..:--.~ . . . ~ . •• < • . ... . .. ' . . • ' ' • · • -1'f: • ~ "~ , "' ,._ ~CI o~~o ' '" 'f , • ' • '"". ' tf. '' • ,. • .., • • "1.... ~· ~ ~ • " • • 0 .. f.' 4, Jtll . • .. "' • ,, ' ' •• J1 : .. ' • '-. • • . • " • • ,.... " • • • • • .. • • • ., • • .I # ~ '•. ~-• • • -'!> • I I I I I I I I I I I I, I . ! ,, ' .. , . :•l"'.;".-.::.~-... .. . .... \' ;::::: ASSUMED SNOW P.llCK -~---;-------------····- LEGEND .,_.._ --. ORIGINAL TEMPERATURE + -....... TEMPERATURE $fNSITIVITY f!UN (RUN NQ I ) • t MELT RATE INCREASED BEFORE STORM 70~----~--------~--------~--------~----------~--------~----------~--~~----~--------~--------~ w·~-----+--------~---------r--------~~--------~-----~--+-----------~~~-------r---------+--------~ 5 .10 15 20 .25 30 5 10 15 20 ~---------------------------MAY ------------------.......,t4------------.--JUNE-----------.,....,..~Ml· flGIJ~E 5.\.lil .;_.' J\ SPRING PMF TE,\1PERATURE SEQUENCE 2 MAY .. 20 JUNE I I I I I I I I I I I I I I I I I I I I PRECIPITATION: : : .-., ORIGINAL (70% P~ 1.( \ -----PPT. RUN ( 100 o/o} \ INFLOW TO WATANA \ .. ,.--,., \ • SPRING PMF by ACRES 3oor-------------~--------------------------------------------------------------·-----------I . I .. I .. I .. 1 LEGEND· . 240 BASE RUN I ~ I ---TEMPERAWRE SENSITIVITY RUN {RUN NO.I) ·-·-·-INCREASED PRECIP./SNOWPACK (RUN N0.2) 220 PRECIPITATION (70 °/o} OCCUR 12 HRS. EARLIER THAN BASE (RUN NO.3) I 200r----------~-=·=-~-~-==·~~s~T~EEP~~T~E~M~P~ER~A~T~U~R~E~R~I~SE~--------------------------------------------------------·--------------------r--T----~ -.ISO Cf) lL. (.) 0 0160 0 120 {HR.} (DATE) 80 60 I I 8 14 9 10 u J I I I I I I 20 2 8 (4 20 2 8 12 I I ,J I I I [ l_ ... l I I4 20 2 8 14 20 2 8 !4 20 2. 8 i4 20 ~~ .14 15 lG 2 s 14 20 2 a t4 rr 1a TfME INFLOW ro WATANA FIGURE 5.5 Alnm · ~--------------~----------------------------------------------------------------------··-----·---------~------~----------------~---l~~~:-~~~~~~!:~~~~~~~~====~1 ' I I ~I I I I I I I I I I I I I I I I I I OUTFLOW FROM WATANA SPRING PMF ~OO~-----------=by~· ~A~C=R=ES=-------------~ ---~------------------------------------------------=-----------------------~--------------------------- 280 260 . /.~ .. ------. .. ~ 240 LEGEND /. ·"· BASE RUN ;· '· 220 TEMPERATURE SENSITIVITY RUN (RUN NO. 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L.., \«~~:I ~2-,ooo ~~.<.. 2.-C)~ooo -::; ltN ..... 4-. ;.,d y I -... ~ I Z4.~ 2Q.S;Ql)0 Lc.eeAc:.z'~ \,~~ · u<l'f-Z5'2: ·>co g~ t''ll>..i~ 9c:rN~ ,.h·v;~y f - ~M.b-·~J. ~ ~Q.N.:=: tl~ ~ t·l'"J Co£. c:;&Jo"-1 ~ . z?2,ooCc . 2o,4-Zb'4 ()OL:I ~~~.\.iv~ly I I I I . i I I I I • I f JO!J NUMSER ·-------.FILE NUMSI;R _____ _ SHEeT OF -------------- SY -~·S:tobb DATE.a~_ !.' J I APP. . ;: • . . DATE:~ == ~ 1!1N~~ ~M ~c::;e. O,o :,fz... o.<) ~\!.:. ' 1~?:,. C) o.o I ' .'1· I I I ·C; I I I I I I I I I I I I 6 -CONCLUSIONS AND RECOMMENDATIONS 6.1 -ConclPsions . . ..... ,_ i ,<~.,.,," r ,,. ·-::: The bo.s·is of any model of physical processes is_ the ability t!(i.c;~yr~~Jy_..,.) ~ ... ~ .. ,.._.~~'"~,~,_,rr simulate the processes with different· input conditions. The model must therefo~·e be calibrated to within acceptable limits by the selection of the M b. est .comb.ination c?. pa·r .• ame.t~rs, c.oeffic.ients ~.-nd .re.l:itionships.· tha. t. m. a.k. e \\llfA"~.~ ! up the mcdel. The cal1brat10f' of the SSARR model by the COE has produced . t ~· e inconclusive and indefensible recsults. The acceptance of the parameters in tfies-sftRR model' is therefQr~.,noi;_fu11l .. jlJ,~tifi .. agle. The .acceptance of • the model is further~tg_mpounded ey the lack· of any verificatiotr ·runs •. _Therefore, we eo.ncl ude tha.t the procedurss. of. calibration should be reoeated and several verification runs be made to prove the acceptability {)f model parameters and the accuracy limits that can be applied to PMF estimates. The estimate of flood flows is particular·ly sensitive to precipitation.. The estimate of the PMP storm was derived by analyses performed by the National r Weather Se~v~ce ~n early 1Stt7~·tt;r~~~comment can· be m~de on the v~lidity of,u_. .. ~ll 1 these prec1p1tat1on analyses fM. oo back-up computat1ons a~ or .9llBJl wl:ric~fom. ~ ~~Jn maximiz~t~on ~roce@te ~· us~d. Due to the sensitivity. K of the Pr-1F est1rtia'te to prec1p1tat1on, rurther analyses to develop both a spr1ng .,. PMP an~ a summ~r P~P is requ~red. rhese analYses should be performe~ .undE7r-,. ... Jt.J~ ;'t-~~,Q.i establ1shed gu1del1nes and w1th~ procedures. . .·· . , / rtt.· .. ,~p~~ ... ,.~~-1;~ c-• '' '' " ' ~:·c~,, I' 't>lioij~ ,>;JJ:},~ c'l4~(.jf1 In; conjunction Vlith precipitation maxil_!ljzation\1 studies should be conducted to determine reasonable temperature sequences. The sequences determined shov~'ii! define antecedent temperatures (cool per·iod fo11owed by a sharp temperature rise) _and tef!lperature rl~ring stonn periods. It is particularly important to ., 1 " redef1ne max1mum dew P9-Jnt temperatures. -'~,.~,v, ~ rt: r.;,;o{_.., dttv<J r~~~ ~::~ ?-'~~'""'··~· · ,.:;.,;f! .. ,~...: ·.·-A Jl .. _ ... ~ -. ( ~<"-(' "'-?' •\ /.. t ~';::~'!\ Tjjr...c:;;..~·~ • ~""""' ... .. ••. The ~ snow course data should be utilized in determining areal distribut·ions of snowfall, particularly the distribution with;,.respect to elev(.ltion. Unfortunately, the first yeCJ.r records (1980-1981) ~ indicatl.M a below nonnal snowfall, so it is unlikely that a better definition C'~ maximum snowpack water equivalents can be determin~d. ( <~~ '-J"l~,~-? Records· collected within the basin should now be utilized to reconstitute discharges fo~ The reconstitution with more· representative temoerature and precipitation data may lead to a more accurate model. of the physical . .·· ~· ~· , characteristics of th~ basin and ~ill p~o~ably ;.efk:tee.~r"'i~~c-esflma1:itf(f"'\ 1. ""f". '""',. peak flows at the var1ous collect1on po1n\..s. l!fi}"C.::lv<{A. &.t : "":·<~-~ ~,~~ •.,.,,'' . '~ ·I I I I I I I I I ~ I I I I 'I - I I I I ·:I 6.2 -Recorrmendations It is recommended that a more comprehensive PMF study be undertaken as soon as possible so that the results can be incorporated in the ongoing engineering feasibility studies. This more comprehensive study should include the following: ... recalibration of the SSARR computer model using the data collected within the basin since the COE study; -verify the acceptability of the model and define limits of accuracy by applying independent input d~ta not used in ca1ibration ·studies; J9 .?t/" ~~ !J,.;~ (,?~:.,;if'' -redefinition of the)taximum precipitation during spring and summer periods; -the maximum likely dew point temperatures and temperature gradients plus temperatures during severe storm events should be redefined; -the appropriate timing of the precjpitation and temperature events should be reassessed and used in conjuction to re-evaluate the PMF. .i j ;;ttlf\., ~~· . '~. ,."t • JJ • • ....... ~ .... <ot • • .;:I ' • ,._, ~ >'J I I I I I I I I I I I I I I I I I I I '~ Referent:es {1) u.s. Army Corps of Engineers "Interim Feasioility Report, Southcentral l~rilbe1t Area, Alaska, u Appendix 1, Part ·1, Section A, 1975 fl. ,., , .• I .I I I I· I I I I I I I I I I I I I 0 I I I I ·- 1 -· I . 1-.!r. Ver.aon K. liagen . _ -Office of Chief of Engineers Co4Ps of Engineers Forrestal Bldg., h. 5-F-039 · Yasld.ngtons-D. C. 20314 .John T. Riedel _ C".nief -~ Rydrome;teorological. ~ranch ,- ' Tentative l~tdtimates of Probable Maximum Precipit:ation (PMP) and SnoWiTlelt - -Crit~rl.a fo1: Four Susitna Rive!: Drainages In.~oduction l The Office of Chief of Engineers, Corps.of ~gineers.requssted PMP a~d sno~elt criteria for the subject drainages in a memorandum to the · liydrometeorological l3raneh, dated December 12~ l$'74. The Alaska District: request:ed the study be completed by February l, 1975; however, a more I • tit • .. -realistic. date for completing a study in "W'ni~"1 'We have confidence is ,June 1, 1975. Because of the need to soot:. begin hydrologic stndi.es ~ ba&-ad on meteorological criteria:t the Branch has conce;1trated on the. problem and has determined the general. level of criteria. A range. of PMP co v.2J.ues are given in this memorandum w.ithin ,..hic:lt we believe val.ues £~om- I a more :onrpre~ns:tve. 3tudy will fall. !he sequences of sno-w-melt td.nds ~ 1- I I I I I temperatu1:esl' and dew pohtt-s should be checked with add:ttional stud'ies. In addition~ if we knew in detail how sno~--=elt Yill ·be computed, T..te could~ give emphasis to t.he more itnportant elerr~-c.ts. P~~ !sti~tes for four drainages A rttnge of estimates ·of P].!P for 6, 24, cu:.d 72 ltours for four -drainages outlined on the TDap aceompanpng· the D~cember 12, 1974 memorandum a-re listed itt. taole 1. T"nesa are numbered f-ror:t 1 to 4 {smallest to largest). • , I ,,, ,('" . 1 . • » "'" > -I I I I •• I ,, I I I I I I I I •• I .I ::c:':> , -.. 'l:he estilnates are fo-.e the months of :August co: Sapte.mber -the. season of greatest rainfall potential. Fo-r the sne"'o~·lt s~ason., mult:iply th~ estimates by 70 percent. Tlie estimates take into account numerous ccresi::.a~a.t:iGns i:nclud:i.ng' several -.. methods of mQdifying PMP estimates made pre-ric----sly for other Alaska drainages, and PMP estimateS from the V.este:n ':-:r.it~i States for area$ 'With s1.mila1: tel:'ra.in. . -. • . . I A. ·I -· " I . I I I I I s. I I I I I •• I· I .\ I .-:;-:..'·, Temperatures and De-w Poi'o.ts for Snowmelt Dur,ing PMP Storm .. ' 1. Dew point far PMP centered on .June !.3 • 56°F {assume maximum l.-day P~!P in middle of 3-day stol:m) & ~er.lod prior to lune l5 (e.g.., the ~ dew point: for June 12 will be · 1-da.y dew point during the Pl-iP back ~o as early as May lS. ' . 3. ·Fox first day of PMP storm~ subtract 1°F from criteria of~ for 3rd day of Pl~ storm subtt"act 2°F. .4. Add Z°F to each of the three dai~y c~w points to get daily temperatures for the 3-day PMP period. .I Temperatures and Dew Points Prior to 3-Day ~MF .Storm (High dew point case) Day prior to PMP 1st 2d 3rd 4th. Adjustment to terrperatur!! and dew point on. ~ day of ma::d:rr::a P'MP " . . ~ Te..:nperatu:~ C''F) -2 -1 0 +l 7' ... Dew point C''F) -2 -4. -4 -s .. .. .. ,. 1t ~. ~I I. ,_ I I I I Day prior to PHP lst:· · .. 2d 3rd. 4th Ce Temperatures, Dew Points Prior to 3-day PMP · (High temperatu:::"e case) . Adjustment of temperatura· and deTN" point on day of ~ P'MP · +1. +2 +7 . Dew uoint, r'F) -12 - 9 -7 -6 -~~ ~levation Adjustment c.~..::!- I I I I For the 3 days of PMP and for the high de".~ point,..\apply a -3~F per 1000 ft- to the t:elllpe:atures and dew point~~. The basic criteria are considered appli.c:able to 1000mb or zero elevation. · For the lrl.gh temperature criteria app~:y a -4~F per 1000 ft increase in elevation. ~f-dax; Values If half-day values are desired for ter.tl]')eratures and dew points,. the following rules should be followed: 1. For the high-temperature sequence,. apply an l8°F spread for tt..'mpera:tures and a 6°F spread for dew point. For e):ample, for a mean . . da:ily dew point of 50°F ~ 'the half-day values woul~ be 47°F and 53 °F ~ 2. For the high dew point case~ appl:: a l.2°F spread for temper~ture and· a 4°F spread· for de!g point. -s- 3.. Iu no case" howe'\l·er, should a 12-b:r de"'~~ p~int: be used that exceeds the 1-day value for thcit: date. For exalnpla,-the value not to be exceeded· I for June lS is 56°F ~ for June 3 (four 3-day period .. s before June 15) is I S2.8°F. I I I •• •• I •• I •• I I I I I I ;. 4• .• -·. ~ ~ .• .. I 'Wind Criteria for Snowmelt -6- . I Since two sets of criteria (on~ emphasizing high temperature and the I •• I I I I I I I I I I I I .I I . ~ other high dew point sequences) are given for snowmelt p;:ior to PMP, t'Q'c; sets of wind criteria. a.re also necessary since the pre-PMP synoptic situati.on favoring high temperatures differs from the c:rir,-eria favoring l\igh dew points & The recommended winds., tables 2 and 3, are given by ~ elevation bands. In the h~gh dew-point case, table 2., (where synoptic exist . conditious,,favorlng maritime influences P,l."io:;: J:E_ PMP), the same wind. for 4-days prior to PMP is appropriate~ All of the winds presented in tables 2 and 3 have been adjusted for applicability over a snow surface. Although a s.eas.onal variation in the high de'tv point wind criteria is realistic for the present tentative cr:Lteria, they are considered applicable to May and June .. Sno"Wtelt tiinds During the PMP t.Jind criteria for the 3-day PMP are the same for both the high temperature and high dew poi1h. sequences. They are shown in table 4. ··a I I I I ·a I I ,. I I I a· I I, I I. I I Sncw Pack Available. for Melt . Some ~ork was done in determ:Lning the mm and m.aximum. October-April precipitation of record for the avaiJable·preci~itatiott stations • . These stations and ·other data are tabulated in table 5. The drainages and avai.lable stations are shown in figure l • . . . . Tab1e S also shows the years o£ r~cord ava4 Jahle for October-Apr£1 precipitation, as_ veU as a eolU1'DD. 1at,eled "synthetic October-April . precipita:i.on." This gives the sum of the ~eat: est October, gr.ea~est: November, etc., to the greatest April. pred.?itation total from the available record.~ These syn~het:f..c Oc.tober-.!pril precipitation values and the means are plotted on figure l. Approximately 9 years of sntl'G1 course data a:a available for 14 locations, iu. and sur.~ounding the Susitna. drainage. ?:o::! 1:hese records, the greatest ---~·-w.-atar equivalents were plotted on a map. T':ese varied .from. et. low of 6 inches at Oshe&a Lake (elevat:ttJn 2950 £t) 1:0 an extreme of 94.5 inches at Gulkaua. Glacier, station C (elevation 6:;-6~ £t) • A smocth plot of an· . maxima agunst elevati.on gave a. method of det:enining depths at: othe~ elevations. Figure 2 shows resulting smoot:Zt va1:er equivalents based on smoothed eJ.evati.on eont~urs ·. and this rel..at:icn. • Some additional guidance could be obtained f:C'£'1 mean at:t.nual precipitat:lon maps. One such map availabl.e to us is i~ ~A.A. Technical Memorandum ].Tt-15 AR-lO, nMean Monthly and Annual Precipitat!..on~ Alaska. cr The m.e~;n annual.. of this ret:tort covering the Susit:na. draina;e is show."'D. in figur'~ 3. ... ·I I I •• I I I -. I I I . .lila I .; I I I I I I I " . --8-· Also on: this figure is shown the mean runoff for t:hree portions of the Susi_tna River drainage based on· the ye.ars of record shown. No adjustment. has·been made for evapotranspiration 01:' any other losses. 'this indicates that the actual mean annu.al·prec:~pitatian is probablY, greater thcin that: gi.ve~ by 'NV1S AR-lO. Conclusion. Time hasn't: allowed checks, ~uat:i.c:rn~ and comparison of the several t;:rpes of data summarized here. It appears the nsynthetic October-April. ~red.pitation" generally is. less th.m. the m.a:dmwit dapths over the drainages based em snogo course 1!1ea.SU:reme:::ts •. '!here depths, or figure 2, would. be considered the least that could be available for melt in the spring. Further Studies The variaticu of precipitz:J:ion wi.th terrai::. f eatu=as in }..laska 'is import:int but yet mostly unkncwn and unstudied.. 1-!or~ effon: should be placed on attempts to develop mean annual or mean ~e~ ~recipitation ~s; at least for the region of the S.usitna River. Sooe 10 years of data at: about a dozen or so snow courses could be used il:l this a1:tempe, as well. as stream runoff values. Some work has been done toward estimating ~ depth-area-durati~n values in the AuguSt 1967 stom.; an import-C"!"'t in?-t to the present estimates. Attempts should be made to ca%'%Y out a complete Part: ! and Part II for this storm, aJ.though data are sp~se a:!!d emphasizing the use of stre.e.mflow as a data source. -·· I I I I -I I I I I I I I ~l. I I I I I The objective of these two studies w.i.th ragard to the Susit~a drainages is to attempt:. a better evaluation of tcpo~aphic effects, aud to cake · a bett$r eva.lua~ion of snow pack avai 1;:bla for t:1elt. Study of additional .storms could give.some important conclusions and gtdd3llc.e on !low moisture is brought: t1'? t:C.e Cook Inlet to the Talkeetna . Snowm.el.t crl..teria .in this quie.k. study is J imi ted to 7 days. Considerably more· work needs to be dona to extend t;.i s to a longer period. T.a.en we would need to emphas'ize. compata.bility of a large snow cover and high temperatu~ese More known periods of hi~ ~ow~~lt runoff need to be . studi~d to determine ehe synoptic val~es of the meteorological l)a-ram.eters. •• I I I I I .• _.· I I I I I I I I I I -10- Table ~ General level of PMP.es:-t~ate..s for 4 Susitna River d:a.; -ag~s Drainage Azea 72-hr PMP Number (SQ mi) J. 1260 2 4~40 3 5180 4 5810 For 24..,hr PMP, multiply 72-hr value by 0 .. 60. For 6-hr PMP, w.ultiply 72-hr value by 0 .. 30. (in.) .. 9-12 7.5-l.O.S 7.:;.9 ·7-9 PMP, for intermediate durations may be obt.a:.i.:led f:om a plotted smooth curve through the origin and the 3 val.t:.es sp-ecified. Table 2 Snowmelt \7inds pzoeeeding ·PMP for Susitna Basins for high detr1 point: seq"C.~ee Elevation Dai!.y "iii:d speed.* (ft) (11m h) sfc: s 1000 9 2000 l2 3000 13 4000 25 5000 34 6000 36 7000 37 8000 39 54000 '0 ..; 10,000 42 I *For each of the 4 days preceding : t:1:.a 3-l.a.y ~·!? • .. 1 . . . ~. ~ ~ .. I .I I· I •• I I I I I I I I }. I I I I '• -ll- Tab~e 3 Snot~lt winds preceding P~ for Susitna Easins for high temperature sequence Elevat2on (ft) . sfc . 1000 2000 3000 4000 5000 6000 7000 8000 9000 10~000 Dall7 rind speed (mph) Dav -orior to 3-dav Pl-fP -.,. , lsc 2nd 3rd 4th ---- 10 l3 4 4 10 l.3 . 4 4 ll-1.4 5 5 12 16 5 5 13 ~6 6 6 13 17 6 6 14 13 6 6 15 20 6 6 16 20 1 7 16 20 1 7 l1 21 1 7 Table 4 lvindts during 3-day PMP liind speed (mph) Elevation (ft) Day of Day of 2nd maximum P!i? his_hest PMP sfc: 1000 2000 3000 4000 5000 6000 7000 8000 9000 10,000 12 14 19 29 42 56 58 62 64 68 70 9 10 14 21 31 42 44 46 48 51 52 Day of 3ra hi~hest PMP· ---.... 8 9 12 18 27 .36 38 40 4l 44 45 . ---~--------------- Station Susitna Neadovs Gulkana Pa:cson Trims Camp Sunuuit Tel]<eetna Sheep Mountain Table 5 Stations with Precipitation Records in and surrounding the Susitna Drainage Elevation (ft.) ' ' 750 . 1572 2697 2408 2401 2316 .. I Yrs of record for complete Oct.-Apr. pr~cipitation • I 16 2 3 19 35 13 Maximum obs. Oct- ~~r. Erec. (in.) 17.18 6.77 8.42 23o26 14.09 2l.l7 11.91 I Mean Number of montbs.for Yr .. . of synthetic Oct.- 1-iaximum ftp,r. season 70-71 4 56-57 18 43-44 6 59-60 5 51-52 20 29-30 37 59-60 12 Synthetic , ... lf~an Oct.-Apr. O~t.-Apr. _Ereci~ •. ~ec.iJ! ... (ine) (in.) 23.18 13.77 12.68 4.19 14.25 7.64 3~.82 15.3 26.59 7.93 tao. 59· 12.26 . 18.1a2 4.78 r •· .. Figure 1~--Drainagc outlines and Oatoher-April precipitation in inches, (Upper values = synthetic October-April precipi~ation; Lower = mean October-Allril precipitation.) · " . . . • -·'", • --·----.. -------- ,. _,...- .. , .. \ • ' ,. .. Finurc 2,--J-tinitnum lrnter equivalen.ta of snow pnck in inches (bnoed on srona amootbing uf lttUxlu~um onuw eouraQ Jl\tHlUUrementa.) ... - --· - --- - - . . . . ~ 3 --Z.leat'l annual .. . "' ... ~ --·--·~· ·,!: ..... !t r •.•· 111e~t ~~~1\~CJ.-l 4D¥VL Afl~--IP • . • ,,