Using existing cropland for groundwater recharge could potentially be more cost-effective than dedicated recharge basins
Groundwater overdraft has become a serious problem in many parts of California as water is being extracted at far greater rates than it is being replenished. With above average precipitation forecast for the winter, Sustainable Conservation has been working with farmers, the Kings River Conservation District, UC Davis, and others to explore the feasibility of applying flood water on existing cropland to recharge groundwater. This technique could potentially be a cost-effective way for groundwater sustainability agencies to recharge groundwater basins rather than relying on dedicated recharge basins which are only used in those years when there are rains and heavy runoff.
At the January meeting of the California Water Commission, Stacey Sullivan, Policy Director for Sustainable Conservation, gave a presentation on his organization’s efforts to capture this year’s anticipated rainfall to recharge groundwater basins in the San Joaquin Valley.
“Sustainable Conservation has been working to promote on-farm groundwater recharge opportunities since 2011,” he said. “We believe we have a unique opportunity in 2016 to demonstrate the efficacy of this practice and to position it as an important part of California’s strategies for groundwater storage and replenishment. We think farmers can play a much greater role in ensuring a reliable water supply for agriculture, and after four years of drought, and the passage of SGMA, we feel they are motivated to do so as well.”
Mr. Sullivan noted that Sustainable Conservation is a California non-profit working to unite diverse groups to solve tough land, air, and water problems in ways that also make economic sense. “We work from the ground up,” he said. “We try to be very non-ideological in the way we identify what to work on. We listen to the challenges faced by folks in the field, we try to identify promising solutions, and then we work with farmers and agencies and environmental interests to field test those ideas and to see how possible it is to take them to scale. We’re science based, collaborative, and transparent; we like to see ourselves as an honest broker.”
“The idea of recharging groundwater using active farmland came to us from Don Cameron at Terranova Ranch in western Fresno County, which is an area of serious groundwater overdraft,” he said. “Don’s been experimenting and promoting this concept for 20 years. It’s really basically very simple. You take unused peak flood flows, in Don’s case from the Kings River, apply it to cropland with a suitable soil profile to allow it to percolate into the groundwater aquifer. This mimics the natural floodplain process that creating both the farmland and recharged the aquifers for a millennia.”
“However, we have separated our rivers from the floodplains; the water in the streams is contained by levees and moves downstream, sometimes at very high velocity, creating many opportunities for farming, but also creating flood risks in critical periods,” he said. “So what Don demonstrated is that we can reconnect floodwater to the land in a way that controls where and when the waters flow in order to protect farming and communities from uncontrolled flooding.”
Starting in 2011, Sustainable Conservation started working with Don to help measure the benefits of this practice and to tell the story to a wider community of farmers, water agencies, and researchers. In 2012, the California Water Foundation funded RMC Consultants and UC Davis to conduct a research project to look at the water supply and recharge potential of this practice on a larger scale.
“UC Davis did an analysis of suitable soils for our recharge and recently published a map that shows that there are 3.6 million acres of farmlands that has high potential for recharge based on the top 6 feet of soil,” he said, noting that the areas in green indicate where those areas are.
He pointed out that the study only looked at the top 6 feet of soil. More recently the almond board and land IQ completed an analysis that added depth to groundwater and geologic permeability to the mix, resulting in more of a “in depth” picture of site suitability, he said.
“Meanwhile, RMC did a detailed analysis of the recharge potential in Merced, Madera, and Fresno counties and identified enough appropriate land to potentially reduce average annual groundwater overdraft by 20% just by capturing flood flows between November and March,” he said, noting that those areas are also shown in green. “That could be added to by excess rainfall or late spring snowmelt. This analysis also looked not just at surface soil suitability, but also groundwater geology, the availability of floodwater, and the existing canal infrastructure to deliver the water to the land.”
He pointed out the graph in the upper right of the graph which shows diversions of flood flow. “The orange bars along the bottom indicates the actual historic diversions generally the canals and dedicated recharge basins, and the green bars indicate in those particular flood years, what could be delivered to appropriate recharge land just using existing infrastructure, so you see there’s a significant increase in the amount of water that could be stored,” he explained. “But of particular significance, the purple bar at the top indicates the amount of water that could be captured with an investment in additional canal infrastructure in order to make sure that the maximum amount of water could get to the land that would be suitable for recharge.”
A commissioner asks about the infrastructure changes needed to capture the additional water. “It depends on if the land still has flood irrigation canals on it, or whether you would need to put in a canal or a new delivery system, but it’s really pretty low tech, certainly when you compare it to an injection well or a dam, or something like that,” Mr. Sullivan replied.
He noted that they surveyed a number of growers in the area surrounding where Don Cameron farms, and found that 90% of those farms would be willing to take floodwater on their land, provided they could decide how much they took and when they took it.
Mr. Sullivan then compared the costs of on-farm recharge to the costs of dedicated recharge basins. “For on farm recharge, we found the costs running between $40 and $107 per acre-foot, and the range on that is very much on whether or not there’s existing flood irrigation capacity on the land, or whether you’d need to put something in,” he said. “But even with adding additional canals, it’s still cheaper than building a dedicated recharge basin at $124 an acre-foot and obviously, if we’re going to start talking about significant surface storage, those numbers go up by a factor of 10 or more.”
Mr. Sullivan said they are very involved with the issue of nitrate contamination in the Central Valley. “One of the concerns we have is the idea that if you deliver additional floodwater to lands where there are residual nitrate in the soil, will the percolation will result in driving those nitrates down into the groundwater and increasing contamination? We’re working with UC Davis to determine how much of that water would be need to put on the land not only to avoid that problem but to actually dilute the contaminants in such a way that it could lead to an improvement in groundwater quality.” He reminded that this is clean floodwater coming off the river, not tailwater or agricultural water.
So with the information compiled and the coming of El Nino rains, Mr. Sullivan pointed out that it’s a great opportunity to demonstrate and monitor on farm recharge in a variety of locations. They mobilized their network of agricultural organizations and others to get out the word that they were looking for demonstration sites with different types of both row and permanent crops on them to monitor how much water can be captured and recharged as well as to learn from the growers when it’s acceptable to apply the water to avoid impacts for crop management, crop health, and crop productivity. They are focusing on the San Joaquin Valley because that’s where groundwater depletion has been the biggest problem.
The response to the solicitation was very encouraging. “We have over 20 farmers and companies who are willing to accept water and measure the water applied,” he said. “That translates to 140 sites throughout the Central Valley from Modesto down to Bakersfield; 10 different crop types, 6500 acres including 2000 acres of almonds, so it was very encouraging. We actually continue to get solicitations.”
Mr. Sullivan said they are establishing some screening procedures, such as looking at the water rights as this doesn’t really work with riparian rights because you can’t store riparian water. They are also checking with the irrigation district and the growers to make sure they have the water rights that are necessary to do this, and also that the irrigation districts are willing to deliver the water if its available.
Sustainable Conservation has entered into a partnership with the Almond Board in which they are sharing in the cost of monitoring sites on almond orchards, as well as recruiting growers and promoting the concept to its members. They are also working with a group of multinational food and beverage companies on how they can help inform and encourage sustainable groundwater management throughout their supply chains, and several of these companies, such as General Mills, Coca Cola, and Miller Coors, have also invested financial resources to advance the demonstration and monitoring of recharge.
“All of our current work developing decision support tools, getting the demo projects and field assessments going and doing outreach and promotion is being planned so that by the end of 2016, we’ll be in a position to provide guidance to farmers on the practice of recharging groundwater on their lands, and also to provide guidance to the Groundwater Sustainability Agencies that are being created about how on-farm recharge might serve as a valuable tool for their groundwater sustainability plans so that they can then identify infrastructure and other investment needs that they may need in order to be able to take advantage of this and take it to scale.”
He said they hope to have data in place to move from demonstration projects to broader implementation by the beginning of 2017. “At which point, irrigation districts and GSAs will need to design and plan infrastructure expansion projects after identifying potential benefits, even though some of them are doing this now, and they’d hit the shovel ready funding ready point probably in late 2017 through 2019.”
Mr. Sullivan said that although they’ve accomplished a lot, they are still faced with some challenges. “We are looking to complete the nitrate leaching study and we’re also looking for more research on suitability of different crop types,” he said. “We’ve been having very useful conversations with the water board and with irrigation districts about water rights issues in terms of both the diversion of the flood water and its ultimate use.”
“We are looking to identify incentives to compensate growers that are willing to take action that benefit all water users in the basin,” he said. “This is not a water bank that we’re talking about here, so you can get into that situation of a kind of free rider situation where one grower is taking the incentive to do this and provide groundwater benefits to all his neighbors, and while we’ve been able to find farmers who have been willing to do this because they think it’s a good idea, I think we could find a lot more of them if we were able to identify incentives to compensate them for this.”
There are also infrastructure investments that need to be made. “New canal infrastructure won’t be as cheap as using current canal capacity, but it will be necessary to move water to new dedicated basins and on-farm recharge. It’s still cheaper than new reservoirs and utilizes existing groundwater storage capacity to capture these infrequent but significant flood flows.”
“Finally, it’s really kind of almost a cultural issue working with water managers to consider how this approach can be part of their portfolio,” he said. “We’re not considering this a magic bullet; it’s a tool in the toolbox but we think it could be a very valuable tool in the toolbox. But there is sort of a default preference for larger, centralized projects, whether that’s a recharge basin or something larger, and so we’re hoping to bring people along, and one of the reasons we hope these demonstration projects go forward the way we hope they will is that this will be something we can use to demonstrate to these managers that this is a good way to go.”
“So in a nutshell, what we’re doing is we’re trying to leverage a current practice, this is not new stuff,” he said. “Don is not the only person who has been doing this, but we’re trying to work with new partners to demonstrate solutions that can help the entire state. We feel this is an exciting time in California for creating new solutions to meet future water needs.”