Explore the hydrological dynamics of the Great Salt Lake, including factors influencing its water levels, precipitation, evaporation, and salinity. Discover the lake's water budget, sensitivity to climate variations, and historical level fluctuations. Gain insights into how a closed basin system works, impacting the lake's water balance over time.
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Presentation Transcript
Modeling the Hydrology of the Great Salt Lake: What makes the Great Salt Lake go up and down David Tarboton Utah State University dtarb@usu.edu 435-797-3172
Outline Lake level fluctuations Water Budget Precipitation Streamflow Evaporation Sensitivity Salinity Modeling integrated water and total salt (not individual minerals)
How a closed basin (e.g. GSL works) If I > E x A level rises If I < E x A level falls Level adjusts to fluctuating inputs so that on average I = E x A Evaporation depth E Evaporation volume E x A Inflows I E x A I includes inflows from streams and precipitation on the lake I = Q + P x A Subject to climate variability. Level Area, A I E x A Level Area, A E is less variable, but also depends on climate and salinity, C. Volume, V Salt Load L Salt Concentration C=L/V As C increases E decreases
GSL Level Record Max 4211.6 on 1872-06-27 1986-06-23 South Arm USGS 10010000 Great Salt Lake at Saltair boat harbour, UT North Arm USGS 10010100 Great Salt Lake near Saline, UT South Arm water year mean 4210 84% 4205.5 4205 84% 4202.2 Level (ft) 50% 4200.8 4200 50% 4198.8 16% 4195.7 4195 16% 4194.9 2014-05-03 N 4194.4 S 4195.1 Min 4191.4 on 1963-10-15 1850 1900 1950 2000 10/1/1949 - 09/30/2013 period with complete climate and streamflow data
Water Budget A P Q + = V E A Wnet Q, Streamflow+Groundwater 3 major rivers. Multiple USGS gauges Groundwater 75000 acre ft/yr (Waddell and Barton, 1980) A, V Area and Volume From bathymetry and level P, Precipitation From PRISM (Oregon State University) E, Evaporation Withdrawals (West desert pumping, Evaporation ponds) 69% 2% 29% -96% -4%
Bathymetry North Arm South Arm Baskin 2006 Loving 2000 Baskin 2005 Loving 2000 Baskin 2005 + Farmington Bay +MagCorp ponds 4210 4210 4200 4200 Level (ft) Level (ft) 4190 4190 4180 4180 4170 4170 0e+00 2e+05 4e+05 6e+05 8e+05 1e+06 0 200000 600000 1000000 Area (acre) Area (acre) the lake bed topography that relates area to level and volume
Great Salt Lake Precipitation and Streamflow Mean Annual Values 1949-2013 Area (km2) 4713 19262 6413 9963 14604 - 54953 Precipitation (mm) 326.7 536.4 657.4 563.9 347.7 - 565.6 Streamflow (acre-ft) - 1328023 (57%) 338634 (15%) 509638 (22%) - 135240 (6%) 2311434 (100%) Basin Great Salt Lake Bear Weber Jordan/Provo West Desert Other (Davis etc) Total Precipitation from aggregation of PRISM data over each area Streamflow from multiple USGS gauges
Great Salt Lake Inputs (1949-2013) Total Natural Input Streamflow Precipitation Groundwater W Desert Pumping W Desert Return Mineral Pond Withdrawal 8e+06 acre ft 4e+06 0e+00 1950 1960 1970 1980 1990 2000 2010 Water Year Precipitation 991,992 acre-ft (29%) Adjustments to GSL inputs West Desert pumping. 2.5 MAF removed 4/87 to 6/89. 27 months 200000 AF return from West Desert. 1/90 to 6/92. 30 months Pond operations 5 months per year May Sept with withdrawals based on reported water use and water rights. Streamflow 2,311,435 acre-ft (69%) Groundwater 75,000 acre-ft (2%) Total Inflows 3,378,427 acre-ft Net pumping and withdrawals -132,060 acre ft (4%)
Salinity dependent evaporation (Penman evaporation equation modified for salinity based on ion activity coefficients, Mohammed and Tarboton, 2008) 1.0 0.9 0.8 Ebrine/Efresh 0.7 0.6 0.5 0 100 200 300 400 TDS (g/L)
Annual GSL Evaporation 60 1.4 50 1.2 40 1.0 meters inches 0.8 30 0.6 20 Mass balance Mean = 1.06 m North Mean = 1.05 m South Mean = 1.21 m 0.4 10 1950 Evaporation in each arm calculated from Penman Equation with activity coefficient adjusted for salinity 1960 1970 1980 1990 2000 2010
What input is the lake level most sensitive to? ? = ?? + ? + ? ?? ???? ????=???? 0.3 0.55 0.83 Sensitivity ? ? Variability dominated by Q, but stabilized by Ev But how does Ev depend on area and salinity? Mohammed, I. N. and D. G. Tarboton, (2012), "An examination of the sensitivity of the Great Salt Lake to changes in inputs," Water Resour. Res., 48(11): W11511, http://dx.doi.org/10.1029/2012WR011908.
How do changes in area and salinity affect evaporation volume ??= ?.???.??? 0.07 0.49 0.09 Variability in evaporation volume is dominated by changes in area with only small effects due to changes in salinity and changes due to potential evaporation
What about salinity? Causeway Closure 300 C L/V North 200 C (g/L) Causeway closure South 100 LVG4 NML RD2 RT3 ECN FB2 AS2 RT2 RT4 NLN AC3 SS AC1 AC2 IS1 IS2 RT1 50 0 1950 1960 1970 1980 1990 2000 2010 Data from Utah Geological Survey (Andrew Rupke 10/10/2012).
Calculation of Salt Load Lake Level h (?1+ ?2)/2 z1, C1 z2, C2 (?2+ ?3)/2 z3, C3 ?1= ?( ) ?( (?1+ ?2)/2) ?2= ?( (?1+ ?2)/2) ?( (?2+ ?3)/2) ? = ?1?1+ ?2?2+ ?3?3+
Salt Loads 4.807 Billion Tons 4.793 Billion Tons 5 3.844 Billion Tons 4 Total Load Total Dissolved Load Precipitated Load Billion tons North Arm Load 3 2 West Desert Return Flow South Arm Load West Desert Pumping 1 0 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 LVG4 NML RD2 RT3 ECN FB2 AS2 RT2 RT4 NLN AC3 SS AC1 AC2 IS1 IS2 RT1 Inferred decline in total dissolved salt in GSL Data from Utah Geological Survey (Andrew Rupke 10/10/2012). Loads here are reported in US or short tons. 1 US ton = 0.9072 metric tons = 907.2 kg.
Evaluating the impact of Mineral Evaporation Ponds on Lake Level 500000 Current Modified Input balanced by less evaporation -> Smaller Area Bathymetry altered due to Pond occupation of part of Lake Net effect is a difference in lake level Time series modeling to account for variability 400000 Smaller Area Area (acre) 300000 Change in level 200000 4194 4196 4198 4200 4202 4204 4206 Level (ft)
Predictive Mass Balance Model Inputs Precipitation (N and S) Evaporation (Historic or Calculated) Streamflow Initial Level A P Q V + = Evaluated separately for N and S arm with Causeway flow by USGS model E A W Q net C Output Levels and volumes
Validation Observed and Modeled Lake Level South North South Modeled North Modeled Validation case driven by Mass Balance Evaporation 4210 4205 level 4200 4195 4190 1970 1980 1990 2000 2010 Note: West desert pumping salt loss reduced to 40% of reported to reconcile with load observations
Validation Observed and Modeled Concentration 350 300 250 200 g/L 150 100 50 South North Validation case driven by Mass Balance Evaporation 0 1970 1980 1990 2000 2010 Note: West desert pumping salt loss reduced to 40% of reported to reconcile with load observations
Validation Observed and Modeled Salt Loads Validation case driven by Mass Balance Evaporation South North Precipitate Total Dissolved Total Observed 5 4 billion tons 3 2 1 0 1970 1980 1990 2000 2010
Future simulations Annual Total Inflow autocorrelation from knn Water budget model with inputs P, Q, E/T resampled from historic years retaining each year as a block Resampling used k-nearest neighbors (based on total streamflow) to group similar years together and maintain statistical dependence Evaporation used either the historic value from mass balance, or was calculated from salinity Pumping limits level to 4208 ft Pond withdrawal and altered bathymetry scenario 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 0 1 2 3 4 5 6 7 8 9 11 13 15 17 Lag years
100 resampled input simulations 10 year simulations Distribution of 10 year ahead Levels 4205 20 4200 15 Frequency 4195 10 4190 5 4185 0 4190 4195 4200 4205 2010 2012 2014 2016 2018 2020 Level (ft)
Evaluation of Expansion Pond Alternatives 100 simulated traces of South Arm Level for the no action scenario. 10th year quantiles. South Arm Level - NA South Arm Level 16% 4190.4 4194.1 4188.1 4192.4 4210 Quantile NA PA 50% 84% 4199.8 4199.0 4200 Level (ft) North Arm Level 16% 4189.4 4187.0 Quantile NA PA 50% 84% 4190 4192.8 4190.9 4199.4 4198.7 South Arm Concentration (g/L) 16% 50% 86.9 118.4 80.8 119.5 4180 Quantile NA PA 84% 153.6 151.5 2012 2014 2016 2018 2020 100 simulated traces of South Arm Level for the proposed action scenario South Arm Level - PA 4210 North Arm Concentration (g/L) 16% 50% 263.8 337.6 239.8 332.1 4200 Quantile NA PA 84% 343.8 341.7 Level (ft) 4190 Note: These simulations are from the permit request as of 2010. The permit request has since evolved Net additional withdrawal 280,000 acre-ft/yr 4180 2012 2014 2016 2018 2020
Great Salt Lake level predictions time series under different streamflow input change scenarios Shaded colored areas give the 25th and 75th percentiles for lake level predictions under streamflow changes. Lines give the median (50th percentile) lake level predictions. Mohammed, I. N. and D. G. Tarboton, (2012), "An examination of the sensitivity of the Great Salt Lake to changes in inputs," Water Resour. Res., 48(11): W11511, http://dx.doi.org/10.1029/2012WR011908.
Conclusions Multi-year dynamic variability with 5-10 year adjustment time scale Streamflow is most sensitive input Lake area is most sensitive evaporation determinant Total dissolved salt load is declining Integrated water and salt simulation effective for addressing questions about future management scenarios Questions? dtarb@usu.edu
