Wetlands in northern Salt Lake Valley, Salt Lake County, Utah

22Utah Geological SurveyTable 7. Ground-water budget for model layer 1 and wetland areas after a 10% increase in recharge and pumping.RechargeDischargeWater‐budget componentModel layer 1(Acre‐feet per year)Wetland areas(Acre‐feet per year)Precipitation 91,000 27,000Subsurface inflow(from principal aquifer)93,000 6200Irrigation fields 26,000 -Jordan River 1900 30Storage 600 280TOTAL 212,500 33,500Evapotranspiration 32,000 24,000Jordan River 116,000 630Springs and drains 7200 2400Great Salt Lake 1200 1200Canals 7000 -Subsurface outflow 37,000 460Out storage 700 250TOTAL 201,100 28,940springs, discharge to Great Salt Lake, and discharge throughcanals.If recharge increases by 10% while pumpage increases by thesame margin, the wetland areas (table 7) would receive about4,560 acre-feet per year (6 hm 3 /yr) more recharge than discharge.Obviously, this would be beneficial for maintainingSalt Lake Valley wetlands.Conclusions from Water‐Budget ModelingThe wetlands in Salt Lake Valley are downgradient of most ofthe water users in the basin, so wetland health and functionalitydepend on upgradient activity.Determining the worst-case scenario for wetland degradationis difficult due to ground-water-model limitations (such assimplified ground-water recharge mechanisms) and the complexityof the ground-water flow system in Salt Lake Valley.As with all models, the ground-water flow models of Salt LakeValley are based on a conceptual model of the basin that inturn depends on (1) how well we understand the processes operatingin the aquifer, (2) how well we know and represent thegeometry of the system, and (3) how accurate our underlyingassumptions are in relation to development of the model. Webelieve Lambert (1995a) had a good understanding of aquiferprocesses and system geometry and made relatively accurateassumptions in relation to the development of his models, butrecognize the limitations of ground-water modeling. Modelscan predict an outcome that may not actually occur withinthe real-world ground-water system. However, the modelsoffer the best tools we have for evaluating the complexity ofground-water flow. The modeled results are meant to generatepossible outcomes for the proposed scenarios, which, mostimportantly, will help guide land-use planning and developmentdecisions.Maintaining hydrologic conditions at their historical levels isextremely important for the maintenance of the Salt Lake Valleywetlands. The water-budget analysis we conducted quantifiesthe amount of water flowing into and out of the Salt LakeValley wetlands area, at least according to the ground-waterflow models. Our modeling results suggest that recharge assubsurface inflow to wetland areas would decrease more bycontinuing drought than by increased pumping (at least at thedecreased recharge and increased pumping levels used in ourscenarios), especially in light of the lowering Great Salt Lakelevels that could occur during such a drought. The model suggeststhat a change to wetter-than-normal conditions wouldincrease recharge as subsurface inflow to the wetland areas,causing an increase in spring and seep discharge and evapotranspiration;this represents the most beneficial scenario forthe wetlands. Increased water withdrawals from wells in SaltLake Valley causes a reduction in recharge to the wetland