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

20Utah Geological SurveyTable 4. Ground-water budget for model layer 1and wetland areas after a 10% drop in recharge for 10 stress periods.Water‐budget componentModel layer 1(Acre‐feet per year)Wetland areas(Acre‐feet per year)RechargePrecipitation 75,000 24,100Subsurface inflow(from principal aquifer)93,000 14,500Irrigation fields 21,200 -Jordan River 1900 30DischargeStorage 77,700 280TOTAL 268,800 38,910Evapotranspiration 32,400 24,940Jordan River 116,200 10,150Springs and drains 7200 2420Great Salt Lake 1200 1180Canals 6400 -Subsurface outflow 36,600 650Out storage 77,800 270TOTAL 277,800 39,610The wetland areas (table 5) would receive a total of 42,410acre-feet per year (50 hm 3 /yr) in recharge, and discharge atotal of 42,420 acre-feet per year (50 hm 3 /yr). A 10% increasein pumping at historical recharge rates will reduce evapotranspiration.Scenario 3 – Increased Pumping and DecreasedRechargeA decrease in recharge by 10% with an increase in pumpagefrom the principal aquifer by 10% would result in a deficitof about 19,000 acre-feet per year (23 hm 3 /yr) in the groundwaterbudget for model layer 1. Both recharge and dischargeare lower than the scenario under which there is a 10% decreasein recharge but pumping remains the same (table 4),and the deficit in the ground-water budget is about doubled.The ground-water budget components under this scenario aresummarized in table 6.For the wetlands areas under this scenario (table 6), theground-water budget is expected to be in deficit by about1.5%. Evapotranspiration would decrease from its historicaltransient level of 27,900 acre-feet per year (34 hm 3 /yr) toabout 17,000 acre-feet per year (21 hm 3 /yr). About 3500 acrefeetper year (4 hm 3 /yr) of ground water would be dischargedthrough springs and drains. This figure is lower comparedto the 3800 acre-feet per year (5 hm 3 /yr) discharged throughsprings and drains during the last stress period of the historicaltransient simulation. Ground-water outflow to Great SaltLake would remain the same at 1200 acre-feet per year (1.5hm 3 /yr), while subsurface outflow would drastically fall from80 acre-feet per year (0.1 hm 3 /yr) at the end the historicaltransient simulation to about 10 acre-feet per year (0.01 hm 3 /yr). The combined effect of increased pumping and reducedrecharge would thus pose the most damaging effect on theconditions of the wetlands in the area.Scenario 4 – Increased Recharge with IncreasingPumpageWith both pumpage and recharge increased by 10%, theground-water budget for model layer 1 indicates a surplus ofabout 11,000 acre-feet per year (14 hm 3 /yr) (table 7). In termsof wetlands hydrology, this is the best (most beneficial to wetlandshealth) of the scenarios we chose to model as part of thisstudy. Recharge from precipitation and subsurface rechargeboth increase with respect to the historical and steady-statevalues. Model layer 1 has no pumping wells completed withinit, and the principal sources of discharge are evapotranspiration,subsurface discharge, discharge through drains and