Category: Recharge and Extraction Methods and Measurement

Tulare Irrigation District Winter Irrigation

In 2022 the Mid-Kaweah GSA implemented an Emergency Ordinance to allocate groundwater extractions, measured as evapotranspiration (ET), and to limit the amount of ET used per acre. This Emergency Ordinance was put into place to address the ongoing drought. The MKGSA also implemented a remote ET tracking system and developed an online tool called the Water Dashboard, which allows growers to see their allocations and ET usage in real-time.

In January 2023, after several atmospheric rivers hit the Central Valley, the District began a winter flood and irrigation release. Immediately upon making water available for irrigation, 80+ landowners began taking water. During the winter months, very little ET is taking place, so much of the water applied to the field during irrigation is actually returned to the groundwater system. This is tracked and reported on the Water Dashboard as a groundwater credit. The program was very successful. Prior to SGMA, the District winter diversions rate was approximately 350 cubic feet per second (CFS). Upon our early release of irrigation supplies our diversion rate was approximately 750 CFS, essentially doubling our winter recharge activities. For the month of January 2023, the District imported approximately 36,000 acre-feet into our District, which is 65,000 acres. This was a record for the District.

Replenishing Groundwater in the San Joaquin Valley

The San Joaquin Valley—which has the biggest imbalance between groundwater pumping and replenishment in the state—is ground zero for implementing the 2014 Sustainable Groundwater Management Act (SGMA). Expanding groundwater recharge could help local water users bring their basins into balance and make a dent in the long-term deficit of nearly 2 million acre-feet per year.

The experience with recharge in 2017―the first wet year since the enactment of SGMA―offers valuable insights in how to expand recharge. A survey of valley water districts’ current recharge efforts revealed strong interest in the practice, and a number of constraints.

On the risk of pesticide residue leaching under agricultural managed aquifer recharge

In collaboration with the California Department of Pesticide Regulation this project is assessing pesticide residue leaching in response to agricultural groundwater recharge. To evaluate the risk of pesticide residue leaching we conducted 1) a towed Transient ElectroMagnetic (towTEM) geophysical survey to characterize sediment types in the deep vadose zone underlying the recharge site; 2) we flooded an 8 acre section of a fallow field for 8 days and monitored pesticide residue concentrations in soil cores, groundwater, and soil pore water before, during, and after the recharge experiment; 3) we performed a potassium bromide tracer test during the recharge experiment to measure solute travel time and breakthrough in nearby monitoring wells; and 4) we are in the process of developing a pesticide fate and transport model for the soil root and deep vadose zones underlying the recharge site using data collected from the study. The experiment was conducted at Terranova Ranch near Helm, CA. The soil at the site is characterized by sandy loams and loamy sands with a cemented duripan at around 1 m depth in some areas (Bachand et al., 2014). The experimental site was flooded in February 2021 using pumped groundwater. In total 38,774 m3 recharge water was applied at a flow rate of ~885 gallon/min; the total infiltration was 1.2 m. Sensors were installed at 0.2, 0.6, 1, 1.75 and 2.5 m at three locations within the flooded area and two locations in the non-flooded (i.e., control). At each sensor profile soil moisture, EC, temperature, gaseous O2, and redox potential were measured and pore water samples were taken from suction cups. CO2 and N2O emissions, ponding levels, pore water, and sediments were sampled too.

In the flooded area, sensor data showed a fast increase to near-saturated conditions within about one day. During the recharge, the shallow vadose zone at the three profiles remained in oxic conditions, except at the shallowest depths of 0.2 and 0.6 m. Pore water results showed that legacy nitrate concentrations were above MCL before flooding, reaching up to 600 mg/L in profile #3 at 0.2 m. During flooding, a large fraction of the initial soil nitrate was leached below 2.5 m, but nitrate was not fully flushed from the first 2.5 m of the vadose zone since nitrate concentrations during- and post- flooding were still above zero in most locations in Terranova. Ammonium concentrations were generally very low and showed no significant changes pre- and post-flooding. Prior, during and after flooding detectable concentrations of several pesticide residues could be measured in soil and pore water samples including imidacloprid, Metolachlor, thiamethoxam, methoxyfenozide and azoxystrobin. Some of these residues showed a clear leaching trend over the course of the experiment, indicating mobilization and dilution. Analysis of the field-collected pesticide residue data is still ongoing.

Flood-MAR Research and Data Development Plan

This Flood-MAR Research and Data Development Plan (R&DD Plan) presents the work of the Flood-MAR Research Advisory Committee (RAC), a multidisciplinary group of subject matter experts across 13 research themes. The RAC was tasked to identify the research, data, guidance, and tools necessary to support and expand the implementation of Flood-MAR projects. Well-formulated Flood-MAR projects can benefit Californians and the environment through improved water supply reliability, flood-risk reduction, drought preparedness, aquifer replenishment, ecosystem enhancement, subsidence mitigation, water quality improvement, working landscape preservation and stewardship, climate change adaptation, recreation, and aesthetics

Flood-MAR White Paper

The California Department of Water Resources (DWR) prepared this white paper to explore opportunities to use flood water for managed aquifer recharge (Flood-MAR) because DWR recognizes the need to rehabilitate and modernize water and flood infrastructure in California. Large-scale implementation of Flood-MAR can fundamentally change how flood and groundwater management are integrated by using flood water resulting from, or in anticipation of, rainfall or snowmelt for groundwater recharge on agricultural lands and working landscapes, including but not limited to refuges, floodplains, and flood bypasses.