Modeling shows long-term overdraft in Indian Wells Valley; board discusses management scenarios

The Groundwater Authority heard technical modeling results showing large historical groundwater losses and options for stabilizing the basin.

A model developed and run by the Desert Research Institute (DRI) and reviewed by a technical advisory group indicates the basin has been losing tens of thousands of acre‑feet per year historically and would continue to decline under a baseline “no‑action” scenario. Jean Moran, a hydrogeologist with DRI, told the board the model’s historical water‑budget runs show average annual reductions in storage in the range of thousands of acre‑feet; shorter dry periods showed larger annual losses. Moran said the model predicts partial recovery of water levels if pumping were reduced to an estimated natural recharge of about 7,650 acre‑feet per year, then levels would asymptote at a new equilibrium over decades.

The model integrates MODFLOW (flow) and MT3D (solute transport) packages and includes six vertical layers, mountain‑front recharge, subsurface inflows and outflows, evapotranspiration, fault behavior and pumping. Moran emphasized the model captures seasonality and variable hydrology, and that DRI calibrated hydraulic conductivity, storage and other parameters against observed water levels and water‑budget data.

Why it matters: the model provides the technical basis for the Groundwater Sustainability Plan (GSP) the Authority must prepare under the Sustainable Groundwater Management Act (SGMA). Board members, technical advisers and many public commenters said the model will guide decisions on allocations, reductions, and potential augmentation (recycled or imported water).

Key figures and findings - Historical water‑budget runs (multi‑decadal) show median storage losses measured in the low tens of thousands of acre‑feet per year; a recent 5‑year dry period had larger annual losses. - A “no‑action” forward projection to 2070 under current pumping schedules showed continued drawdown and localized large drops in water level, with a modeled average change in storage on the order of 30,000 acre‑feet per year for that scenario. - A test run that reduced pumping across the basin to the modeled recharge (about 7,650 acre‑feet per year) showed partial recovery of water levels and stabilization over decades, indicating the basin can move toward sustainability if pumping is substantially lowered. - Total dissolved solids (TDS) modeling indicates some parts of the basin would experience modest salinity changes under the baseline; the modelers flagged where TDS concentrations are already higher and noted the role of evapotranspiration and clay layers in concentrating salts.

What the board discussed and directed Board members and the public pressed modelers and staff on: (a) how shallow domestic wells will be affected, (b) the breadth and assumptions behind the 37,000‑acre‑feet baseline pumping estimate used in the “no‑action” run, and (c) how management options (proportional ramp‑downs, agricultural reductions, leased allocations, recycled water, imported water) were represented. - Jean Moran and Steve Johnson (Stetson Engineers) said the current flow model's upper layer is represented at roughly 500 feet; because many domestic wells are shallower, the model output must be paired with separate shallow‑well impact analyses. Moran noted the model treats upper layers coarsely and that predicted impacts on shallow wells require an external, well‑level analysis using model water‑level projections. - The “baseline” pumping number (~37,000 acre‑feet/year) was developed by soliciting projected pumping from major pumpers (municipal, agricultural, industrial, Navy). Board members and staff said the figure reflects what parties reported they would pump absent constraints; it does not establish legal entitlements or allocations.

Public comments and concerns Public commenters included domestic well owners, representatives of agricultural interests, and legal counsel for large pumpers. Common themes: concern for shallow domestic wells, requests for clarity about how the model’s assumptions were developed, and calls for more modeling scenarios and outreach to affected residents. Several speakers urged that the Authority prioritize analysis of shallow‑well impacts and expand modeling scenarios to inform measurable objectives in the GSP.

Next steps Modelers and staff said they will finish additional scenario runs, including brackish‑water and imported‑water simulations, and expected to complete the set of scenario results and supportive documentation for April–May drafting of GSP sections. The technical advisory committee and an ad‑hoc modeling subgroup will continue review; the Authority also asked staff to present additional shallow‑well impact analyses derived from the model outputs.

Ending note Board members repeatedly framed the modeling work as a planning tool rather than a definitive forecast: the model identifies trends, data gaps and likely outcomes under different management assumptions, and it will be used to craft the GSP’s sustainability criteria and management actions.