Groundwater Recharge in a Desert Environment: The Southwestern United States

314 Pages·2004·15.179 MB·English

Water Science and Application 9
Groundwater Recharge in a
Desert Environment:
The Southwestern United
Water Science and Application 9
Groundwater Recharge in a
Desert Environment:
The Southwestern United States
James E Hogan
Fred M. Phillips
Bridget R. Scanlon
Editors
AmericanG eophysicUaln ion
Washington,
Publisheudn detrh ea egiso f theA GUB ooksB oard
Jean-LouBios ugerCeth, airG; rayE .B ebouCt,a rTl .F riedricJhasm, eLs. H orwitUz,s aA .L evinW, .B errLy yons,
KennetRh. M inschwanAenrd, yN ybladDe,a rreSllt robealn, dW illiamR. Y oungm, embers.
GroundwatReer chargien a DeserEt nvironmeTnht:e S outhwesteUmn itedS tates
Water Science and Application 9
Library of Congress Cataloging-in-Publication Data
Groundwater recharge in a desert environment: the southwesternU nited States /
James F. Hogan, Fred M. Phillips, Bridget R. Scanlon, editors.
p. cm.
Includes bibliographicalr eferences.
ISBN 0-87590-358-4 (alk. paper)
1. Groundwaterf low--SouthwesternS tates. I. Hogan, James F. (James Francis)
1973-II. Phillips,F red M. (Fred Melville) III. Scanlon, Bridget R.
GB1197.7G766 2004
551.49'0979--dc22
2004050501
ISSN 1526-758X
Front cover: Sierra Bianca, Chihuahuan Desert, Texas (courtesy Bureau of Economic
Geology, Universityo f Texas at Austin).
Back cover: Foreground:C reosote-saltbusha ssociationi s ubiquitousi n the Amargosa
Desert and characteristic of the Mojave Desert ecosystem. The subhorizontal scar
shows abandoned channel of the Amargosa River which has migratedt oward the cam-
era due to relative uplifto f the far (northeast)s ide of the basin. Background:B ig Dune
and Yucca Mountain form the near background,w ith Crater Flat to the left of Yucca
Mountain. High ranges on the Nevada Test Site form the far background( courtesyo f
D.A. Stonestrom).
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CONTENTS
Preface
JamesF . Hogan, Fred M. Phillips, and Bridget R. Scanlon .......................................... vii
Section I: Introduction and Overview
Introduction and Overview
Fred M. Phillips, JamesE Hogan, and Bridget R. Scanlon ........................................... 1
Section II: Recharge Mechanisms and Processes
Hydrologic Processesin Deep VadoseZ ones in Interdrainage Arid Environments
MichelleA . Walvoorda nd BridgetR . Scanlon. .................................................... 15
Tectonic,C limatic, and Land-Use Controls on Groundwater Recharge in an Arid Alluvial Basin:
Amargosa Desert, U.S.A.
David A. Stonestrom,D avid E. Prudic, Randell J. Laczniak, and Katherine C. Akstin ..................... 29
Millimeter- to Kilometer-ScaleV ariationsi n Vadose-ZoneB edrockS olutes: Implicationsf or Estimating
Recharge in Arid Settings
l(cid:127)ctor M. Hellwell and D. Kip Solomon ......................................................... 49
ProcessesC ontrolling Recharge Beneath Ephemeral Streamsi n Southern Arizona
Kyle Blasch,T yP A. FerrY,J ohnH offman,D onaldP ool, MatthewB ailey,a ndJ effreyC ordova ............. 69
Comparisono f Methods to Estimate Ephemeral Channel Recharge,W alnut Gulch, San Pedro River
Basin, Arizona
David C. GoodrichD, avid G WilliamsC, arl L. UnkrichJ, amesE Hogan,R usselLl . Scott,K evinR . Hultine,
Don Pool, Alissa L. Coes, and Scott Miller ....................................................... 77
Modeling Variably Saturated Flow Using Kinematic Waves in MODFLOW
RichardG Niswongera nd David E. Prudic ..................................................... 101
Mountain-BlockH ydrology and Mountain Front Recharge
John L. Wilson and Huade Guan .............................................................. 113
ConstrainingM ountain-BlockR echarget o the EasternS alt Lake Valley,U tah With DissolvedN oble Gas
and Tritium Data
AndrewH . Manninga nd D. Kip Solomon. ...................................................... 139
Section III: Case-Studies at the Basin Scale
FundamentalC onceptso f Rechargei n the DesertS outhwest:A RegionalM odelingP erspective
AlanL . Flint, LorraineE . Flint, JosephA . Hevesi,a ndJ oanB . Blainey. .............................. 159
UsingG eochemicaDl ata and Aquifer Simulationt o CharacterizeR echargea nd GroundwaterF low in
the Middle Rio Grande Basin, New Mexico
L. Niel PlummegW ardE . SanfordL, auraM . BexfieldS, cotKt . Anderholma,n dE urybiadeBs usenber.g.. ...
CONTENTS
The Origins, Ages and Flow Paths of Groundwater in TusconB asin: Results of a Study of Multiple
Isotope Systems
ChristopheJr . Eastoe,A iliang G(cid:127)t, andA ustinL ong ............................................... 217
Section IV: Synthesis
Evaluation of Methods of Estimating Recharge in Semiarid and Arid Regions in the SouthwesternU .S.
BridgetR . Scanlon ......................................................................... 235
Semi-DiscreteD ynamical Model for Mountain-Front Recharge and Water Balance Estimation,
Rio Grande of Southern Colorado and New Mexico
Christopher(cid:127). D(cid:127)tfj(cid:127) ........................................................................ 255
Effects of Environmental Change on Groundwater Recharge in the Desert Southwest
Fred M. Phillips,M ichelle(cid:127) 4. WalvoordE, ric E. Small .............................................
PREFACE
Groundwaterre charget,h e flux of water acrosst he water storms and limited infiltration capacity of desert soils
table,i s arguablyt he mostd ifficultc omponenot f the hydro- resultsi n overlandf low, surfacer unoff and the possibility
logic cycle to measure.I n arid and semiaridr egionst he for focusede phemeralc hannelr echarge.
problemi s only exacerbatedb y extremelys mall recharge We have structuredth is monographin to four sections(:1 )
fluxes that are highly variable in spacea nd time. Despite Introductiona nd Overview; (2) RechargeM echanismsa nd
these challenges,r esearchersh ave focusedc onsiderable Processes(;3 ) Case Studiesa t the Basin Scale; and (4)
effort on this topic due to its practicali mportancei n the SynthesisT. he introductiona nd overview (chapter 1), by
designo f nuclearw astei solationf acilitiesa nd for the sus- the editorso f this volume,p resentsa conceptuaflr amework
tainablem anagemenot f basing roundwaterre sourcesO. ver for basin-scalere charge,a brief historicalp erspectivea, nd
the past two decadesr, esearchf ocuseda t proposedw aste a discussiono f emergingo pportunitiesa nd futured irections
isolations ites, such as Yucca Mountain, has significantly for improving our understandingo f rechargei n arid and
advancedo ur understandinogf arid regionst hat have limit- semiaridr egions.T he seconds ectiona ddressetsh e individ-
ed rechargea nd deepv adosez ones.A t the samet ime, dra- ual mechanismsa nd processesth at occur within a basin.
matic populationg rowthi n the southwesterUn nited States For each rechargep rocesst here is a review chapterf ol-
and associatedi ncreasesi n groundwaterp umping have lowed by one or more cases tudiesf rom the southwestern
resultedi n significantg roundwaterd epletions,l and subsi- United States.R echarget hrought he basinf loor is covered
dence,a nd loss of riparianh abitat.C onsequentlyth ere is a in chapters2 -4, rechargeb eneathe phemeralc hannelsi n
recognizedn eed for effectivea nd sustainableg roundwater chapters5 -7 and rechargew ithin mountainousre gionsa nd
managemenat nd an improvedu nderstandingo f basin-scale alongt he mountainf ront in chapters8 and 9. The third sec-
groundwaterr echarge.T his monographs eeks to address tion presentsa selectiono f cases tudiesa ddressingre charge
this needb y providinga currents ynthesisa nd the latests ci- at the basin scale.I ntegrativem ethods,s ucha s hydrologic
entific understandingo f the rechargep rocessesth at com- modeling( chapters1 0 and 11) and isotopict racers( chap-
priseb asins caler echargei n arid and semiaridr egions. ters 11 and 12), are usedt o evaluatet he importanceo f dif-
Rechargei n desertb asinsi s often consideredt o be the ferent rechargep rocessesf or basin groundwaterb alance.
sum of several distinct processeso ccurring in different The final sectionp resentsa serieso f synthesisp aperst hat
areas of the basin. Mountainous regions are typically examineb asin-scalere chargein a broaderc ontext.C hapters
viewed as significants ourceso f recharged ue to the large includea n evaluationo f methodsf or estimatingb asin-scale
precipitation input that results from orographic effects. recharge( chapter1 3), an integratedc onceptual-dynamical
Rechargec an either occur through fracturesi n the crys- modelf or rechargea crossth e varied landscapeo f the desert
talline bedrock as mountainb lock rechargeo r as surface southwest( chapter 14) and a discussiono f the effects of
runoff that rechargesth roughs treamc hannelsa t the moun- environmentacl hangeo n recharge( chapter1 5).
tain front, a processk nown as mountainf ront recharge.I n We recognizedt he need for this monographd uring dis-
contrastt, he basin floor receivess ignificantlyl essp recipi- cussionst hat occurred at two meetings. The first was a
tation but makesu p the vast majority of the land surface. workshops ponsoredb y SAHRA (Sustainabilityo f semi-
Even small rates of diffuser echargei n interdrainagea reas Arid Hydrology and Riparian Areas) that focused on
of the basin floor may be significantb ecauseo f their large groundwaterre chargein the southwesterUn nited Statesa nd
area. Similarly, the combination of intense convective was held in SocorroN, ew Mexico duringM arch 2001.
GroundwaterR echargei n a DesertE nvironment:
The Southwestern United States
Water Sciencea ndA pplication9
Copyright2 004 by theA mericanG eophysicaUl nion.
10.1029/009WSA00
vii
secondw as a specials ession", Rechargea nd VadoseZ one We musta lsoa cknowledgeth e supporto f our respective
Processesin Add and SemiaridR egions,"h eld at the 2001 institutionsI.n particularw e appreciateth e supporpt rovid-
Fall Meeting of theA mericanG eophysicaUl nion (AGU) in ed for editors Phillips and Hogan by SAHRA
San Francisco,C alifornia. The interest generatedb y the (Sustainability of semi-Arid Hydrology and Riparian
presentationsp,o stersa ndd iscussioant theset wo meetings, Areas) under the STC Program of the National Science
along with the encouragemenotf AGU Books, led to the FoundationA, greemenNt o. EAR-9876800 andt he support
proposala nd subsequendte velopmenot f this monograph, provided for editor Scanlon by Jackson School of
which includesa number of invited papers from leading Geoscienceast the Universityo f Texas.F inally,w e express
researchers who did not attend either meeting. our gratitudet o Allan Graubard,A GU acquisitionse ditor,
Furthermorew, ith the exceptiono f the overviewc haptera, ll and our AGU productionc oordinatorsfo r their guidance,
papersu nderwenat formal,a nonymourse viewp rocessW. e cooperationa, nd patiencei n publishingt his volume.
gratefullya cknowledgeth e effortso f our many colleagues
who contributedb y reviewing individual chapterst, hereby JamesF . Hogan
ensuringt he scientific integrity of the monographa s a Fred M. Phillips
whole. BridgetR . Scanlon
Water Sci. and Appl.Groundwater Recharge in a Desert Environment: The Southwestern United States Vol. 9
Introduction and Overview
Fred M. Phillips
Departmento f Earth & EnvironmentaSl cienceN, ew MexicoT ech,S ocorroN, ew Mexico
JamesF . Hogan
Departmenot f Hydrologya nd WaterR esourceasn d SAHRA,U niversityo f Arizona,T ucsonA, rizona
Bridget R. Scanlon
Bureauo f EconomicG eologyJ, acksonS choolo f GeosciencesT,h e Universityo f TexasA, ustin,T exas
Rechargei n arid and semiaridr egionsr epresentsa challengingt opic for the
hydrologics ciencesI.m provedq uantificationa nd conceptuaul nderstandinogf
rechargep rocesseasr e criticalf or developingm odelst hatw ill allow stakeholders
to manageg roundwaterr esourcesf or long-terms ustainabilityw hile limiting
impactso n ripariane cosystemsW. hen the last comprehensivsey nthesiso n this
topic was published2 5 yearsa go, a conceptuaml odel of rechargei n the desert
Southweswt asb eginningt o emerge.R echargew as vieweda s the sumo f several
distinctp athwaysi ncludingm ountainb lock rechargem, ountainf ront recharge,
diffuser echargea, nde phemeracl hannerl echargeT. his volumes ynthesizerse cent
advancest hat have occurreda s a result of new measurementte chnologiesa nd
improvedc omputerm odeling.K ey advancesin clude:1 ) recognitiono f the criti-
cal role of vegetation( "hydroecologicapl rocesses"i)n mediatingg roundwater
recharge,w ith desertv egetatione ffectively eliminatinga ny rechargei n many
areaso f the basinf loor; 2) recognitionth at in basin-floore nvironmentsr,e charge
throughc hannelsis vastlym orei mportantt hant hroughi nterchannedl esertf loor;
3) developmenot f environmentatlr acerst o the point that they can fingerprint
sourcesa nd amountso f groundwaterre chargea t the basins cale,i ncludingc han-
nel rechargea t low elevationsa nd mountain-blockre chargea t high elevations;
and 4) applicationo f highly resolvedG eographicaIln formation System( GIS)
basedm odelst o simulatep rocessesc ontrollingg roundwaterre chargea t the land
surface.S ignificantc hallengesr emain. Mountainousr egionsr emain a virtual
frontier;i mprovingo ur understandingo f all mountainoush ydrologicp rocesses,
notj ust recharger, equiress ignificantr esearchfo cus.A notherc hallengeis to com-
bine the emergingp rocess-baseudn derstandinogf rechargew ith highly resolved
land-surfacem odelst o assessh ow futurec hangesin vegetationa nd climatem ay
impact basin-scaler echargeo ver a decadal timescale.W hile this volume is
focusede xclusivelyo n the southwesterUn nited States,f indingsf rom this region
shouldb e relevantt o otherd esertr egionsa roundt he world.
GroundwaterR echargei n a DesertE nvironment:
The Southwestern United States
Water Sciencea ndA pplication9
Copyright2 004 by the AmericanG eophysicaUl nion.
10.1029/009WSA01
Water Sci. and Appl. Groundwater Recharge in a Desert Environment: The Southwestern United States Vol. 9
2 INTRODUCTION AND OVERVIEW
STATEMENT OF PROBLEM Over the past several decades,d ramatic population
growth in the southwesternU nited Statesa nd associated
Significanceo f GroundwaterR echarge increasesin groundwatepr umpingh aver esultedin signifi-
cant groundwaterd epletions,l and subsidencea, nd loss of
Accurate representationo f groundwaterr echarger ates riparianh abitat.C onsequentlyw,a terr esourcem anagersa re
andm echanismsin arid and semiaridr egionsi s a significant increasinglyfa ced with developing" sustainableg" round-
challengew ithin the hydrologics ciencesf or three primary water planst hat allow for economicg rowthw hile limiting
reasonsF. irst, therei s the difficultyo f measuringe xtremely the adversee ffectso f over-pumpingC. entralt o this is the
small rechargef luxes that are highly variable in time and idea of "safe yield," which can be broadly defineda s the
space. Secondly,r echargee stimateso ften have legal and amounto f water that canb e pumpeda nnuallyw ithoutp ro-
policy implicationsb ecauset hey are tied to the ill-defined ducing an undesired result [Alley and Leake, 2004].
concepto f "safe yield," limiting groundwaterp umpingt o Groundwatepr umpingi s oftenm istakenlyv ieweda s "safe"
the sumo f naturala nd artificial rechargeF. inally, an under- if it is less than or equal to the rate of natural recharge
standingo f both recharger ates and mechanismsis critical [Bredehoefi1, 997]. Rather,t he magnitudeo f development
for developmento f groundwaterm anagementm odelst hat primarilyd ependso n how mucho f then aturald ischargec an
go beyondt he concepto f safey ield and attemptt o balance be captureda ndt he magnitudeo f the hydrologice ffectst hat
the demandsf or groundwaterp umping while sustaining can be tolerated[ Bredehoefei t al., 1982]. Hence, the "sus-
ripariane cosystems. tainabley ield" of a groundwaters ystemw ill be consider-
Recharge is arguably the most difficult hydrologic ably lesst hanr echargein ordert o sustains treamsa ndo ther
parameter to quantify with confidence [NRC, 2004]. In groundwater-dependeenct osystems[S ophocleous2,0 00a].
arid and semiaridr egions,t he difficulties are exacerbated Still, the linkage of safey ield to naturalr echarger atesh as
by recharger atest hat are highly variable in time, recharge persistedin the hydrologics ciences[B redehoefei t al., 1982;
mechanismst hat vary throughoutt he basin, and a multi- Bredehoefi1, 997;B redehoefi2, 002] to the pointw heret he
tude of approachesf or measuring recharge. In humid concepth asb een incorporatedin to legal and policy frame-
regions, rechargei s commonly estimatedu sing a water workst hat governg roundwaterm anagement.
balance approach,w here recharger epresentst he differ- While mostg roundwatepr olicy focuseso n the amounto f
enceb etweeni nputs( precipitation)a nd outputs( evapora- water that can be extracted,w ise managemenst houlda lso
tion, transpiration, and runoff). In arid and semiarid consider the impact on the natural environment
regionst his approachi s not often practicalb ecausei nputs [Sophocleous2,0 00a]. Groundwatemr odelsa re the primary
equal outputs within measuremente rror. Furthermore, tool for thoroughlya ssessingm anagemenpt lans and pre-
over most of the basin and throughoutm ost of the year, dicting the dynamic responseo f aquifers to pumping
potentiale vapotranspiratiofna r exceedsp recipitationa, nd [Sophocleous2,0 00a; Bredehoefi,2 002]. The reliability of
no rechargeo ccurs.B ut during some extreme eventst hat thesem odels is limited by the uncertaintyo f their input
may last a fraction of a day to a few days, precipitation parametersi,n cludingr echarge.I n most groundwaterm od-
inputs may be sufficient for recharget o occur.T his high els, the locationo f rechargeis typicallyb asedo n a concep-
degreeo f temporalv ariability at any one site has resulted tual understandingo f the system.I t is worth notingt hatj ust
in the developmento f a numbero f time-integrativem eth- as groundwater models are sensitive to well location
odst hat typically rely on geochemicatlr acers,e achw ith a [Bredehoefei t al., 1982], they are alsoa ffectedb y the loca-
uniques patiala nd temporals cale.M any of thesem ethods tion and amount of recharge.F or example, recharget hat
were developedt o estimater echargeo ver the very long occursp eripherallya long the mountainf ront impactst he
temporal scales( >10 kys) requiredt o evaluatep roposed aquifer's response to pumping differently than does
waste isolation facilities in low-rechargee nvironments recharget hat occursw ithin a basina longe phemerals tream
(e.g., Flint et al., [2002]). In contrastw, hile the pathways channels.
of recharge (e.g., diffuse, ephemeral channel, etc.) are The recharge amount used in groundwaterm odels is
understoodt,h erei s little understandinogf the factors( e.g. eitherb asedo n an estimatef rom field data,c alculatedu sing
vegetation, climate variability, soil characteristicse, tc.) an empiricalr elationship,o r estimatedd uring model cali-
that control the spatialv ariability of recharge.H owever, bration. Recent advances in computing power have
this knowledgei s necessaryt o improve the conceptual increasedt he popularityo f model calibrationu sing inver-
understandingo f rechargea t the basin scalea nd aid in the sion techniques. Model calibration methods based on
effectivem anagemento f groundwaterr esources. hydraulich ead data are limited to estimatingt he ratio of
Water Sci. and Appl. Groundwater Recharge in a Desert Environment: The Southwestern United States Vol. 9
PHILLIPS ET AL. 3
recharget o hydraulic conductivityA. dditional information 15% of the water supply[ TAMA, 1998]. Presentlyg round-
from groundwatear ge datingo r flux information( e.g. base- waterd emandi s -390 million m3yr- 1, with naturalr echarge
flow discharges, pringf low) is requiredt o betterc onstrain (bothm ountainf ront and streambede) stimateda t 95 million
rechargee stimatesu sing inversem odeling[ Sanford,2 002; m3yr-1. In addition, an estimated 110 million m3yr-lof
Scanlone t al., 2002]. All of thesem ethodsp roducer echarge incidentalr echargeo ccursd uringa griculturali,n dustrial,o r
estimatesf or one moment in time, but, just as rechargei s municipal water use, resultingi n an overdraft of roughly
not constanti n space,t here is little reasont o believe that 185 million m3yr- 1 [TAMA, 1998; Gelt et al., 1999]. In
recharge will be constanto ver time. Understandingt he order to reduce the overdraft and achieve safe yield by
impact of environmentacl hange,i ncludingn aturalv egeta- 2025, the TucsonA MA hasd evelopedf acilitiesf or the arti-
tion change,h uman land-use,a nd climate variability, on ficial rechargeo f treatede ffluenta nd surfacew ater from the
groundwaterr echargew ill be essentialt o understanding Colorado River, which began delivery via the Central
how recharger atesm ay changew ith time. Thus, an under- Arizona in the early 1990s. Presentlyt he amount of this
standingo f recharger ates, locations,a nd mechanismsis rechargei s relativelys mallb ut is expectedt o grow signifi-
critical for the developmento f modelst hat allow optimal cantly,r educingt he amounto f overdraft[ TAMA, 1998; Gelt
managemenot f groundwaterr esources. et al., 1999].
The city of Sierra Vista, located in the San Pedro River
SocietalN eedf or Basin-ScaleR echargeE stimates Basin,p rovidesa sharpc ontrastt o Tucson.S ierraV ista is a
small but rapidly growing city of 68,000. The nearby San
Two examplesf rom southernA rizona presentc ontrasting PedroR iver is consideredo ne of the mosts ignificanpt eren-
views on how to manageb asin groundwaterr esourcesa nd nial desertr ivers in the United States.I n 1988, Congress
consequentldy ifferingn eedsf or understandinagn d quanti- actedt o protectt his resourceb y establishingth e San Pedro
fying recharger ates.T he city of Tucsont akest he approach RiparianN atural ConservationA rea (SPRNCA). While the
of state-legislatesda fey ield whereast he smallc ity of Sierra SPRNA protectst he landsn ear the river, it doesn ot protect
Vista is trying to maintain economic growth, meeting the river from the possiblee ffectso f groundwaterm ining
increasedw ater demandsw hile sustainingth e local riparian and streamc apture.
ecosystem. Groundwaterm anagemenitn the SanP edroR iver basini s
Tucsoni s a city of-870,000 residentsl,o catedi n a large not organizeda s anA MA, rathera partnershipo f publica nd
alluvial basin in southernA rizona. The primary water private interestsis taskedw ith developinga water plan for
sourcef or early inhabitantsw as the perennial Santa Cruz the basin.T he Upper SanP edroP artnership(U SPP) hast he
River. As the city grew, groundwatepr umpingw as increas- overall goal of meetingl ong-termw ater needso f area resi-
ingly used to meet rising water demands.B y the 1940s, dentsw hile protectingt he San PedroR iver and building a
groundwatepr umpinge xceededn atural replenishmentA. t model for the future [USPP, 2003]. Recent congressional
this time, pumpingw as focusedn ear the SantaC ruz River, legislation( H.R. 1588 sec.3 21) recognizedt he USPP as the
resultingi n lowered water tablesa nd the loss of perennial entity responsiblef or developinga cooperativew ater use
flow. Tucsonc ontinuedt o rely exclusivelyo n groundwater managementp lan for the basin. As a result, USPP must
for the next-50 years.B y 1995, usagew as twice the natu- report yearly on the quantity of water withdrawn and
ral recharge rate. This overdraft resulted in a nearly rechargedto the regionala quifer,a s well as overdraftp ro-
60-meterd rop in the water table in centralT ucson[ Gelt et jections through 2011 when sustainabley ield is to be
al, 1999]. achieved. Presently the basin is estimated to receive
In recognitiono f the unsustainablrea teso f pumpinga nd between1 9 and 22 million m3yr- (cid:127) of yearly rechargem ain-
dramaticl oweringo f groundwatetra bles,t he Arizona State ly as mountainf ront rechargei n additiont o some ground-
Legislaturep assedt he GroundwaterM anagementA ct of water inflow. This is balancedb y 15 million m3yr- 1 of dis-
1980. This act establishedA ctive Management Areas charget o the riparianc orridor( split betweenb aseflowa nd
(AMAs) in regionsw ith the greatesto verdraftp roblems. riparian evapotranspirationa) nd 13.5 million m3yr- 1 of
EachA MA is to achieves afe yield by 2025 by creatinga groundwatepr umpingp er year [Pool and Coes, 1999].
long-term balance between groundwaterw ithdrawalsa nd Becauset he USPP is tasked with achieving sustainable
the annuala mounto f naturala nd artificial rechargeE. ach yield andp rotectingt he SPRNCA, its approachd iffersf rom
AMA allowsf or a certainp ercentageo f the water supplyt o that of an AMA. Critical to the USPP effort has been
be from "groundwatemr ining"[ Jacobsa ndH olway, 2004]. improvedu nderstandingo f the hydrologics ystemsi,n clud-
In theT ucsonA MA, minedg roundwatecra nc ompriseu p to ing the water needs of the riparian area, the sourcesa nd