U.S. Geological Survey (“USGS”) has developed a model that will help the Borrego Water District meet requirements under the Sustainable Groundwater Management Act (“SGMA”).
Borrego Water District is the water management agency for the Borrego Valley, which is supplied solely from groundwater resources. Water is used for agricultural and municipal purposes, as well as recreation at Anza Borrego Desert State Park. About 5,600 AF recharges each year, while total use in the basin is four times more than recharge, and groundwater decline exceeds 100 feet in some areas.
The Borrego Valley Hydrologic Model, a 3-D model of the aquifer system developed using data representing 66 years of historical conditions, allows researchers to test different water management scenarios and evaluate the impact. Researchers compared six scenarios representing different levels of pumping reductions.
Scenario 1 is a baseline scenario that keeps pumping levels at the current (2010) rate. Under this scenario, drawdown continues with groundwater depletion reaching 1 million AF by 2060. In addition, the water table will decline to the middle aquifer in some areas, which because of certain properties of the middle aquifer, will lead to larger and more rapid declines in the future.
Scenarios 2-4 examine changes in use under different low, medium and high growth rates—ultimately configuring different reductions in agricultural and recreational use, along with increases in municipal use. The high growth rate scenario comes the closest to bringing pumping in line with recharge, but it cuts off agricultural use completely.
Scenario 5 nearly reaches sustainable pumping levels with 6,051 AF/year pumped in 2060. Under this scenario, agricultural and recreational uses are cut back to 32% of the 2010 levels, and municipal is cut back to 52%. However, the timeline for scenario is 50 years—which exceeds the 20-year requirement under SGMA.
Scenario 6 was designed to bring pumping down to a sustainable level with the SGMA timeline. It would cut agricultural use to 40% of the 2010 rate, while recreational and municipal use would be cut 50%. Researchers argue that under this scenario recharge approximates pumping. The water table would be drawn down nearly 50 feet over most the basin, but long-term groundwater levels would stabilize. They caution, however, that climatic variability would cause changes in storage and recommend also pursuing managed artificial recharge using enhanced infiltration of storm water or imported surface water.
The USGS recommendation presents less dramatic cutbacks than the Borrego Water Coalition suggested in its 2014 policy recommendations. The coalition’s 10-point policy recommendations called for a physical solution that would ramp pumping down 70% over a 20-year period. Additional recommendations cover the necessary policy changes to implement, administer and enforce the physical solution—such as establishing non-compliance and administrative fees, requiring meters to be installed on production wells, creating a JPA to implement the physical solution, and establishing funding mechanisms to acquire or fallow agricultural land, pay to implement the physical solution and administer transfers among the pumpers.
Written by Marta L. Weismann