Approaches for Assessing Ground-Water Availability Under Competing Demands and Climate Change Matt Bachmann, Matt Ely, John Vaccaro— U.S. Geological Survey, Washington Water Science Center

Introduction: Yakima River Basin: Gold Creek

Area of 6,200 square miles covering alpine mountains to arid lowlands Many areas of the American West struggle with the allocation of diminishing water supplies · EXPLANATION between growing municipal and agricultural demands. In the Pacific Northwest, surface- · Precipitation between 6 and 120 inches per year Saddle Mountains Basalt water supplies are additionally stressed by in-stream flow requirements mandated for the · Snowpack-derived streamflow dominates in spring and summer head decline, in feet Five major reservoirs with more than 1 million acre-feet of storage 21 - 75 stable protection of endangered salmonid species. In the Yakima River Basin in Washington State, C · 76 - 150 rise le Three counties and the Yakama Nation Reservation where river and stream flows primarily are derived from winter snowpack in the mountains, · >150 E ApproximatelyTe 300,000 people and 600,000 irrigated acres surface-water supplies are fully allocated in wet years and over-allocated in dry years. lu · ana m wa In areas of heavy pumping, head declines Tribal water rights from the1800s supersede irrigation or municipal rights in the basin, and R y R · Location of Yakima River basin iv iv k of greater than 150 feet have been measured ongoing litigation to discern the influence of ground-water pumping on surface-water flows e er e in Washington state r st Predicted Effects of Climatee ChangeFir on Streamflow Ground-water users must pay for additional led to U.S. Geological Survey involvement in a comprehensive assessment of ground water. r · C power to pump from greater depths Big Creek k 6,000 u Lowered water tables likely increase capture a Water-Table Declines · · Winter accumulation of mountain snowpack w of water from streams S Ya supplies streams and rivers in spring 5,000 kim Cle Elum Ta D a and summer ne r River um y 4,000 C A billion-dollar agricultural economy in the ree C · k r e basin lowlands uses both surface and e k EXPLANATION 3,000 k e e ground water for irrigation r Depth-to-WaterEXPLANATION Contour, in feet

C in feet 2,000 k DepthToWater Contour n Minimum instream flows are legally protected e · a < 20 0 0 e m r for endangered salmonid species Currier Creek 1,000 e < 80 1 - 100100 l C N Nor o e a < 200 101 - 200 Ground-water pumping for irrigation and th k Ellensburg 200 C o c

· BASIN MEAN STREAMFLOW CUBIC FEET PER SECOND F o o h > 200 municipal supplies likely diminishes JANrk FEB MAR APRILManastash MAY JUNE JULY Creek AUG SEPT OCT NOV DEC C e W s surface-water supplies e NACHES RIVER BASIN, WASHINGTON R n i Gold Creek RANGE IN MEANa MONTHLY VALUES FOR: 2030 (red), 2060 (green), AND 2090 (yellow) v Simulated heads and measured Water-cycle model showing s e · snowpack-derived streamflow C r heads correspond in both r and role of ground-water e e magnitude and location · Climate Models indicatek warming temperatures, which will reduce recharge over the next 20, 50, and 80 years Dry Creek Simulated Heads A. Basin-Management Tools · More precipitation will be in the form of rain rather that snow ek resulting in increased winter runoff and reduced late-spring and Columbia River Monthly Planning Model (Bureau of Reclamation) Cre W · ake summerN runoff e sn ac n Watershed Models and Riverware Watershed and Ecohydraulic models (USGS) tle h a · at e s · R s River System Management Program Bioenergetic models (USGS) R C · i r ve e (WARSMP) (Bureau of Reclamation, USGS) Stream Network Temperature Model (SNTEMP) for r e · k Yakima · Ecosystem Diagnostic and Treatment Model (EDT) Yakima River Miles 36 to 116 (USGS) EXPLANATION (Bureau of Reclamation) Sediment transport model (Bureau of Reclamation) SummerStream Steelhead with Summer Steelhead Union Gap · r Yakima River Basin · Hec-Ras 1-D Hydraulic Model · Yakima River Decision Support System (YRDSS) (USGS) Rive (Bureau of Reclamation) Teiton ek 2-D Hydraulic Model for 3 reaches Cre Wapato · e Co (Bureau of Reclamation, USGS) ich wi Explanation w che 81,367 Recharge HRUs Co Cre rk ek h Fo Toppenish B. Recharge Sout Wide Hollow Creek Water Supply Wells Water Supply Wells Sunnyside Creek Aquifer recharge was estimated using process- N htanum Yakima River Basin orth Fork A reek Y based watershed models by calculating water Yakima River Basin um C aki Richland Steelheadk DistributionAhtan ma Kiona balances for 81,367 Hydrologic Response Units ree Ri er 1914 - 1960 1914 - 2000m C Prosserv (HRU). For each HRU, the models simulated anu Aht snow accumulation and ablation interception of Fork Endangered Species Act mandates protection uth · precipitaion and some irrigation of vegetation, So of three listed salmonid species S evapotranspiration, surface runoff, infiltration, 2 speciesi already extirpated from the basin · m water storage in the root or soil zone, and recharge. · Minimum cflowo requirements during spawning Precipitation-Runoff Modeling System flowchart Map with 81,367 Hydrologic Response Units season conflicte with irrigation season. in the Yakima River Basin · Precipitation-Runoff Modeling System (PRMS) T · Deep Percolation Model (DPM) o p EXPLANATION pen Water-RightsWater Rights AllocationAllocation is Y h C a reek k Well Cells are 1,000 feet im Senior Surface Water by 1,000 feet C. Pumpage a R Stream 20000 feet iv Junior Surface Water e Between 1960 and 2001, 19,728 new wells were r reek Junior Ground Water GHB drilled in the Yakima River Basin, primarily for Dry C ork Senior Ground Water No Flow agricultural and domestic use. th F or N ek 1960 well locations and abundance 2001 well locations and abundance e Ground-Water Model Discretization D. Ground-Water Model r C Senior surface-water rights (assigned prior to 1906) take Cross-Section along Row 291 s · u Construction t precedence over Junior surface-water rights EXPLANATION 17x Vertical Exaggeration a S Junior surface-water users are typically curtailed during drought years Subbasins Discretization of subsurface hydrogeologic units · · Ground-water pumpers are predominantly Junior users, but are ROSLYN SELAH TOPPENISH was implemented using the Hydrologic Unit Flow not curtailed like surface-water users 0 10 20 Miles (HUF) package of MODFLOW-2000, in which · The Yakama Nation is exercising its Senior Surface-water Treaty rights KITTITAS YAKIMA BENTON three-dimensional geologic structure is defined for the protection of endangered species independently from model-layer geometry. Multi- flow basalt members were idealized as consisting of repeating sequences of hydraulically-conductive flow tops and low-conductivity columnar flow interiors. Contacts: Modular three-dimensional finite-difference A hydrogeologic cross-sectional view through the Toppenish River basin demonstrates how Matt Bachmann USGS Washington Water Science Center Matt Ely USGS Washington Water Science Center John Vaccaro USGS Washington Water Science Center · the HUF package allows discretization of geologic structure into discontinuous units distinct ground-water flow model (MODFLOW-2000) and separate from the uniform model-grid. 934 Broadway, Suite 300, Tacoma, WA 98402 934 Broadway, Suite 300, Tacoma, WA 98402 934 Broadway, Suite 300, Tacoma, WA 98402 · Constructed with HUF and Stream Flow Telephone (253) 552-1672 Fax (253) 552-1582 Telephone (253) 552-1622 Fax (253) 552-1582 Telephone (253) 552-1620 Fax (253) 552-1582 Routing (SFR) packages [email protected] http://wa.water.usgs.gov/ [email protected] http://wa.water.usgs.gov/ [email protected] http://wa.water.usgs.gov/ · 45 hydrogeolocic units represented by U.S. Geological 600 Survey x 600 x 24 cells