Simulating the Effects of Policy-Driven Hydrodynamics in the Salton Sea Watershed

Background/Question/Methods

Managing water resources often involves competing stakeholders which makes achieving consensus among management scenarios difficult. Mediated modeling coupled with a system dynamics approach provides a framework for stakeholders to quantitatively explore the system-level effects of multiple scenarios. The aforementioned approach was applied to develop a system-level model of the Salton Sea (SS) watershed. The effects of several policies on SS hydrodynamics were examined, elucidating how each scenario could affect the salinity, elevation, and selected biota. The Salton Sea Stochastic Simulation Model (S⁴M) is a stochastic, simulation model, formulated as a difference-equation compartment model representing water flow, i.e., water volume and quantity of Total Dissolved Solids (TDS) and Phosphorus (P), in the Lower Colorado River Basin and SS watershed. The experimental design included a combination of scenarios representing each of seven water management policies: incorporating the New River wetlands, agriculture and fallowing, lining the All-American Canal, additional power plants, incorporating waste water treatment facilities, SS brine extraction, and North and Main Sea impoundments. The scenarios were compared to baseline conditions (100 replicates), from 1980 through 2024. Sensitivity analyses were conducted to observe cumulative effects on changes to SS elevation and salinity with up to ± 20 % of watershed inflow volume.

Results/Conclusions

The results of the S⁴M simulations, compared to similar studies, yielded similar future downward trends in sea elevation and upward trends in salinity under the premise that no preventative actions are taken. Both of the SS impoundment scenarios significantly (P < 0.05) improved (lowered) the salinity in the North and Main Sea impoundments; compared to the no action alternative (baseline). Further, the elevations of the North and Main Sea impoundments were stabilized at -220 feet above sea level (fasl), but the year 2024 salinity values for the two impoundment scenarios were significantly different (P < 0.05), 7,262 mg/L and 15,083 mg/L, respectively. Should action be taken to stabilize the SS and reduce salinity; the impoundment methods analyzed herein can adequately achieve such a result, whereas the other scenarios do not. The climate sensitivity analysis revealed that the cumulative effects and changes of ± 10 % in SS inflows can have significant effects (P < 0.05) on sea elevation and salinity. Given that the model has been constructed, tested, and validated, future research efforts could use the S⁴M to test many different climate scenarios and associated implications that climate change may hold for policy-making in the region.