Presentations 2016

The McMullin Project: The Justification and Process to bring On-Farm Flood Capture from Concept to Implementation

Bachand & Associates

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The McMullin Recharge Project, a $7 M project funded through a California Department of Water Resources (DWR) Flood Corridor grant, represents the first large-scale implementation of On-Farm Flood Capture as an approach to recharge aquifers and mitigate downstream flood risks. On-Farm Flood Capture leverages large areas of private farm lands for operation under dual purposes: farming and capture of available river flood flows. This concept was first funded through a USDA Natural Resources Conservation Service (NRCS) Conservation Innovation Grant (CIG) feasibility study (2010 – 2012) that tested technical and logistical questions associated with implementing this new approach: i.e., what farm level infrastructure is required, how to integrate flood capture and farming BMPs, which crops are compatible, what infiltration rates are achievable, what are the water quality challenges, what are the costs? These questions were addressed and answered to varying degrees through the CIG grant which identified infrastructure needs, determined anticipated infiltration rates on farmlands, identified compatible crops, estimated costs, and recommended approaches to managing water quality challenges. The CIG project led to the DWR-funded McMullin Recharge Project. Since awarded to the Kings River Conservation District (KRCD) in 2012, and with matching funds from Terranova Ranch, progress has been made with implementing this large-scale On-Farm Flood Capture project with the completion of Hydraulic and Hydrologic (H&H) analyses showing positive economics strictly from flood mitigation benefits; the development of the 30% design identifying design elements for implementation; development of a California Environmental Quality Act (CEQA) Initial Study to identify environmental impacts and recommended mitigation measures; development of a contractual framework for implementation and further expansion to neighboring farms; and beginning the permitting process. After completion of the McMullin Recharge Project Phase 1, the project will be able to divert up to 150 CFS of excess flood flows from the Kings River across over 5000 acres of farmland for monthly recharge total over 9000 ac-ft/month. Under full buildout in future phases, the project will cover over three times the acreage and be designed to capture about 30,000 ac-ft/month. This project ultimately seeks to provide a cost-effective means for agricultural communities to participate in creating more sustainable water supplies and for GSAs to comply with the SGMA; and to provide a template for future On-Farm Flood Capture projects, identifying and providing solutions to the technical and regulatory challenges associated with implementing this technology.

Historic, Current, and Future Availability of Surface Water for Agricultural Groundwater Banking in the Central Valley, California

University of California, Davis

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Groundwater banking, the intentional recharge of groundwater from surface water for storage and recovery, is an important conjunctive use strategy for water management in California. A largely unexplored approach to groundwater banking, agricultural groundwater banking (ag-GB), utilizes flood flows and agricultural lands for recharging groundwater. Understanding the availability of excess streamflow (e.g., the magnitude, frequency, timing, and duration of winter flood flows) is fundamental to assessing the feasibility of local-scale implementation of ag-GB. In this study, we estimate the current availability flows based on current and historic daily streamflow records for about 100 stream gauges on tributaries to and streams within the Central Valley, California by quantifying the magnitude, frequency, duration, and timing of winter flood flow events. For each gauge, we consider flows above a stationary 90th percentile as ideal (available) for ag-GB because reservoir operations mitigate flood risk by releasing early winter flood flows. Additionally, we investigate the future availability of flood flows by determining the long-term trends in the magnitude, frequency, duration, and timing of winter flood flow events. Results suggest that on average across all year types, there are 5 million acre-feet of flows above the 90th percentile available from rivers in the Sacramento, San Joaquin, and Tulare basins between December and February. Trend analyses indicate that Sierra watersheds show 1) increasing trends in the average flood flow volume, 2) increasing trends in the average number of days, and 3) increasing trends in the average number of flood peaks above the 90th percentile. These positive trends suggest ongoing climate change effects on snowpack and the progressive shift from snow- to rain-dominated runoff generation. In contrast, CV gauges show predominantly negative trends in all metrics. Finally, we compare the quantified available water to the existing water rights (eWRIMS database from the State Water Resources Control Board) for each station to determine the amount of surface water that could potentially be allocated for groundwater recharge through a temporary water permit.

Potential for managed aquifer recharge on alfalfa crop land in California.

University of California, Davis

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Agricultural groundwater banking (ag-GB) seeks to opportunistically use winter storm flows from surface water sources for the artificial recharge of groundwater by spreading water onto crop land. Among the over 400 crops grown in California alfalfa represents an attractive cropping system to implement ag-GB practices on. Alfalfa is attractive for ag-GB for several reasons: 1) it comprises greater than one million acres in CA (high probability of finding suitable soil types and infrastructure); 2) it requires relatively low N fertilizer and agrochemical inputs compared to other crops (limited environmental impact of flooding); and 3) it is often flood irrigated using surface water (high capacity conveyance system). In addition, utilizing mature alfalfa fields at or near the end of a rotation (e.g. after 4 years) poses little risk for economically significant crop loss or negative environmental impacts. Preliminary studies of the tolerance of alfalfa to large winter irrigation events conducted during the 2014/2015 recharge season suggest alfalfa is capable of withstanding cumulative applications of water in the order of 4 to 6 feet during the months of January, February and March. Where water was delivered to fields as several pulsed applications, no complications due to excess water were observed. In a treatment where water was continuously applied to dormant alfalfa over a 6 week period, with a cumulative application of 29 feet of water, a statistically significant decline of biomass was observed in the second cutting. Since site specific characteristics influence the subsurface storage capacity, travel times and the recoverability of “banked” water at these preliminary experimental sites more research is necessary to identify the bounds on crop tolerance for different site conditions.

Integrated Modeling of In-Lieu Groundwater Recharge Using Recycled Water for Agriculture-Maximizing Benefits to Groundwater Dependent Ecosystems and Sustainable Groundwater Management

Sacramento Regional County Sanitation District (Regional San)

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The Sacramento Regional County Sanitation District (Regional San) is planning to distribute tertiary treated recycled water to south Sacramento County, which overlies the South American Subbasin, a high-priority basin under the Sustainable Groundwater Management Act. Recycled water will be used by farms in lieu of pumping existing groundwater supplies. The project will result in multiple benefits such as increasing groundwater levels, and improving conditions for adjacent Groundwater Dependent Ecosystems (GDEs) within the Cosumnes River Preserve, increasing in-stream flows for fisheries and improving water supply sustainability. The South Sacramento County Agriculture and Habitat Lands Recycled Water Program proposes reuse of up to 50,000 AFY of recycled water on approximately 16,000 acres. Title 22 recycled water will be produced by the Sacramento Regional Wastewater Treatment Plant through the EchoWater project, a $2 billion dollar wastewater treatment plant upgrade. The SacIWRM model shared by all users in the basin evaluated the water budget for multiple scenarios, all involving delivery of recycled water for agricultural uses in-lieu of groundwater pumping. Regional San partnered with The Nature Conservancy (Conservancy), modeling multiple potential scenarios for recycled water distribution and banking, prioritizing benefits for adjacent habitats, under certain groundwater use conditions. Results project groundwater levels increasing as much as 30’, with elevation increases extending outside the project limits to support valley oak riparian forest health. Raised levels would also benefit wetlands with listed species and increase in-stream flows for anadromous fisheries. Inclusion of ecosystem benefits in the design of the project provides a model for multi-benefit water supply projects. It also informs how groundwater basins can best identify, protect and even improve Groundwater Dependent Ecosystems with Sustainable Groundwater Management Act implementation. Some supplied water goes to Stone Lakes National Wildlife refuge, a wetland area in the Pacific flyway, benefitting migratory waterfowl and other birds. In another area, a recharge component is being evaluated. It would use winter over-irrigation to create flooded habitat for migratory bird roosting and foraging, while allowing continued farming during the primary growing season. Siting of the recharge farm on looser soils increases project benefits for the water table and instream flows in the Cosumnes River. 293,000 AF of new groundwater storage is projected over 30 years of project operation, with twice that amount returning to area rivers. The presentation will include maps showing groundwater elevation and in-stream flow benefits, some arriving less than ten years after project implementation. One scenario modeled includes hypothetical extraction of groundwater by municipal users in the driest 30% of years. Modeling of this scenario still shows an overall increase in the water table while allowing for improved regional and statewide water storage options and operational flexibility. Assurances for agricultural and environmental users will need to be developed over the next several years to ensure projected benefits occur when implemented, with resulting sustainable groundwater management benefiting both people and nature.

Stormwater Runoff Analysis for Placement of Managed Aquifer Recharge Projects in Santa Cruz and Northern Monterey Counties, California

UC Santa Cruz

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We apply a USGS surface hydrology model, Precipitation-Runoff Modeling System (PRMS), to analyze stormwater runoff in Santa Cruz and northern Monterey Counties, CA with the goal of identifying catchments (generally 100-1000 acres) from which hillslope runoff can be collected and infiltrated for managed aquifer recharge (MAR). Under the combined threats of multi-year drought and excess withdrawals, this region's aquifers face numerous sustainability challenges, including seawater intrusion and degradation of water quality. Four of the region's eight groundwater basins are classified as medium or high priority by the CA Department of Water Resources, and two of these are critically overdrafted. We address the supply side of this resource challenge by investigating the spatial and temporal dynamics of stormwater runoff, which could be used to replenish aquifers via MAR projects that use infiltration basins, drywells, and flooding of agricultural fields or flood plains.Ensuring the effectiveness of MAR using stormwater requires a thorough understanding of runoff distribution at the subwatershed scale, as well as site-specific surface and subsurface aquifer conditions. In this study we use a geographic information system (GIS) and a high-resolution digital elevation model (DEM) to divide the region's four primary watersheds into Hydrologic Response Units (HRUs), or topographic sub-basins, that serve as discretized input cells for PRMS. To facilitate evaluation of hillslope runoff at a fine scale, we create a high-resolution HRU grid (using 0.1-1.0 km2 cells) and spatial and density-weighted averaging schemes to assign topographic, vegetation, and soil characteristics. Additionally, we couple high-temporal-resolution with high-spatial-resolution climate data to generate input precipitation catalogs that drive the model, allowing analyses of a variety of climate regimes. To gain an understanding of how surface hydrology has responded to agricultural and urban development, we develop input datasets to represent both pre- and post-development conditions. Combined with a concurrent surface and subsurface analysis, our model results help screen for suitable locations of future MAR projects. Additionally, our results improve our understanding of how changes in climate and land use impact runoff and recharge.

Soil water repellency - a concern for groundwater recharge and quality?

Plant & Food Research

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Water repellency has been shown to occur in many soil orders under different types of vegetation and climate. It is now understood that the transient development of water repellent soil conditions is the rule rather than the exception. While it is easy to measure how repellency impedes the infiltration of single water droplets into soil, the effect of repellency on water dynamics at larger scales and over longer time periods has hardly been quantified. When water infiltrates into repellent topsoils, preferential flow can develop and bypass large parts of the soil matrix. Repellency could thus also accelerate contaminant transport to aquifers and could negatively affect groundwater recharge rates. Lack of mechanistic process understanding limits prediction of how soil water repellency affects infiltration, runoff generation, contaminant transport and groundwater recharge at larger spatial scales in different seasons. Our research aims to isolate the effects of repellency on soil water dynamics by directly quantifying how repellent soil conditions affect water sorptivity, infiltration and runoff at the mesoscale. We developed a fully automated tension disc infiltrometer and a runoff measurement apparatus. Using these in laboratory infiltration and runoff experiments with intact soil cores and slabs we studied water fluxes in a water repellent pastoral soil from New Zealand. In all our experiments, we compared the behaviour of water to that of an aqueous ethanol solution to directly quantify the effects of repellency. New insight into the transitory character of water repellency was inferred from early- and late- time infiltration and runoff patterns as well as analysing the behaviour of soil collected at different times of the year. In addition, in the infiltration experiments we compared flux dynamics at different effective tensions. Results highlighted the fractional wettability of soil. We showed that pore size classes differ in wettability. We also measured the soil’s repellency dynamics over a range of volumetric water contents using the sessile drop method. Our novel measurement technologies were combined with models based on the resulting soil water repellency characteristic curve. Our research highlights the opportunity to develop new approaches for gaining insight into these complex transitory processes, particularly over time scales of infiltration and groundwater recharge. Our preliminary results emphasize that soil water repellency should be included in hydrological and solute transport modelling. It also highlights that research is required to assess the effects of repellency at field and catchment scales.

Economic Analysis of Groundwater Banking on Agricultural Lands in California

University of California, Davis

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Since 1865 California has practiced underground water storage through artificial recharge; however, in many parts of the state, these efforts have been insufficient to meet growing water demands, particularly for irrigated agriculture. During dry periods, vast agricultural areas depend upon groundwater for irrigation. In these areas, groundwater banking (GB) can be an essential strategy for water management operations. GB is the practice of diverting surface water to percolation or injection sites for aquifer storage and later recovery. One variation of GB is agricultural GB -- the use of agricultural lands for GB (Ag-GB). The economic implications of Ag-GB are an unknown component of GB necessary to inform water agencies and farmers interested in implementing the practice. Therefore, this study proposes a conceptual model for determining the economic feasibility of Ag-GB at the irrigation district level. The Orland-Artois Water District (OAWD) in Glenn County is considered as the case study, and alfalfa as the test crop due to its tolerance to flooding and low use of pesticides and fertilizers (potential sources of aquifer contamination). The proposed model consists of four components: (1) an agricultural water demand calculator, which calculates agricultural water demands based on historic land use, monthly precipitation, and crop coefficient values, (2) a one-bucket aquifer mass balance model that quantifies inflows and outflows to the simplified aquifer, (3) an agronomic model, which estimates costs and benefits of Ag-GB in terms of energy savings from pumping and crop production, and (4) an economic feasibility output, in which costs and benefits are evaluated to determine economic feasibility.

Aquifer Studies and Recharge Assessment of the Northern California Lower Tuscan Aquifer System

Kleinfelder

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The Sacramento Valley Groundwater Basin and the Redding Groundwater Basin represent the principal groundwater basins of the broader Sacramento River Hydrologic Region. The Sacramento Valley Groundwater Basin is bound by the Coast Ranges to the west, the Cascade Range to the northeast, and the Sierra Nevada to the east, extending from the City of Red Bluff in the north to the Delta in the south. As described by California Department of Water Resources (DWR), the Sacramento Valley groundwater basin underlies approximately 4,900 square miles of the Sacramento Valley.The Tuscan Aquifer system, a regional aquifer of the Sacramento Valley Groundwater Basin, is among the principal water bearing units in Butte County. The Lower Tuscan is a critical resource to the region. However, there is incomplete data pertaining to aquifer system functions in terms of source, recharge and recovery. Butte County was awarded grant funds from DWR through Proposition 50 (Water Security, Clean Drinking Water, Coastal and Beach Protection Act of 2002) for implementation of the proposed Lower Tuscan Aquifer (LTA) Project.The primary objective of the LTA project was to collect and analyze technical data through development of innovative analytical investigative tools to further the scientific understanding of the LTA system and assess potential recharge sources. Key components of the overall project included development of cost effective methods to conduct and analyze aquifer parameters during the agricultural pumping season using newly installed and existing groundwater monitoring systems; evaluation of LTA recharge from upper reaches of creeks and, analysis of stable isotopes of hydrogen and oxygen from groundwater and surface water samples to assess the source of the recharge water.Aquifer tests were conducted during various agricultural pumping schemes including heavy continous pumping used for flood irrigation and intermittment pumping used for drip and spray irrigation of orchards. Qualitative analysis of drawdown curves from aquifer tests provided significant insights into the interactions between stratigraphically adjacent aquifer systems as well as aquifer stresses to the LTA resulting from various agricultural pumping schemes. The results of this analysis indicated that the LTA is a complex interconnected aquifer system and that a major recharge source to the LTA is through the overlying aquitard and overlying aquifers.Overall, isotopic data for samples collected from groundwater wells throughout the area was indicative of precipitation from elevations that are not far above the valley floor. Moving out along the valley floor isotopic data suggested recharged water may be due to a mixture of lower-elevation precipitation along the basin perimeter and interaction with the Sacramento River and other local streams. The study also found that the upper reach of the creeks contributed little to LTA recharge. Results of water level studies compared to flows recorded from the Sacramento River also suggested a potential connection during high storm events.

Freshwater storage in brackish-saline aquifers for irrigation water supply: a bottomless pit or a fountain of gold?

KWR Watercycle Research Institute

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Aquifer storage and recovery (ASR) can be successful in storing and recovering freshwater via wells for irrigation water supply. It is attractive thanks to the limited space requirements above ground and the generally successful conservation during storage. However, the ASR recovery efficiency (‘RE’, the fraction of the injected water that can be recovered with a satisfying quality) can be limited in brackish–saline aquifers. This is due to the lower density of the injected freshwater with respect to the ambient brackish or saline groundwater, which causes early contamination with ambient groundwater at lower parts of the ASR well. Successful recovery remains unattainable and temporal freshwater surpluses are then injected in a ‘bottomless pit’. However, recent advances in hydrological engineering allow mitigation of buoyancy effects and an increase of RE. In this way, ASR can offer a fountain of gold in water-stressed coastal areas, which typically have shallow brackish-saline groundwater and therefore a lack of suitable ASR target aquifers. To test the ability of the hydrological engineering solutions to improve RE, two dedicated ASR set-ups were recently implemented in coastal areas of The Netherlands. The first used low-cost, independently operated multiple partially penetrating wells (MPPW) in a single borehole. An extra 20-40% of the injected water could be recovered at MPPW-ASR systems storing greenhouse roofwater in confined, brackish aquifers, thanks to preferential deep injection in the target aquifer and recovery at the aquifer’s top. Interception of brackish water via the deepest well screen further increased the RE (10-20%). Detailed hydrochemical monitoring also highlighted relevant water quality changes occurring during MPPW-ASR, mainly a Na-enrichment due to cation exchange. Also, the deeper aquifer had a dominant impact on the final water quality due to the preferential deep injection and the geochemical composition of this interval. In the second set-up, horizontal directional drilled wells (HDDWs) were implemented in an ASR-system for the first time. Two 70m long, superimposed, low-cost HDDWs were assembled in a ‘Freshmaker’ system to enlarge a shallow freshwater lens by simultaneous infiltration (shallow HDDW) in the lens, and deep abstraction of underlying saltwater (deep HDDW). In dry periods, the shallow HDDW was used for abstraction of freshwater from the lens, while the deep HDDW prevented upconing of deep saltwater by continuation of the abstraction. A maximum yearly volume of around 6,000 m3 of surface water could be successfully injected, followed by successful abstraction of an equal freshwater volume for irrigation at a fruit orchard. The presented innovative ASR set-ups were successfully tested in the horticultural sector to provide irrigation water. The estimated costs per m3 are 0.3 to 1.5 US $/m3, and can compete with the local (yet less sustainable) alternatives (piped water, brackish water desalination). In the freshwater management strategy of the National Deltaprogramme, the innovative ASR solutions were therefore embraced to attain local ‘self-reliance’.