Cooperative Extension San Joaquin County
University of California
Cooperative Extension San Joaquin County

Posts Tagged: Thomas Harter

Replenishing California groundwater

Groundwater must be recharged so the aquifer is available to get through future droughts.
For more than a century, California farmers have extracted water from underground to irrigate crops during droughts or where surface water is not available. However, in recent decades, water reservoirs that accumulated over thousands of years underneath the state's valleys are being tapped with deeper and deeper wells that pull out more water than can be replenished in the winter.

The 2012-14 drought intensified the problem. Greater groundwater usage than recharge has left some rural homeowners' wells completely dry. Land is subsiding as clay layers that are interspersed between sandy and gravelly aquifers beneath the surface compress due to lower pore water pressure, which is responsible for keeping clay pores open.

To ensure California's aquifers are available to meet future generations' water needs, proper management in terms of extraction and replenishment is critical, says Thomas Harter, UC Cooperative Extension groundwater hydrology specialist.

Urbanization and advances in agricultural technology have reduced historic groundwater replenishment. Asphalt, concrete and buildings block water infiltration. Water-saving irrigation devices – like drip and microsprinklers – are more protective of groundwater quality, but have reduced the amount of water applied to crops and are cutting down on recharge into the aquifer.

In urban areas, substituting gravel for concrete and leaving areas undeveloped can boost aquifer levels. There is also more that can be done in the agricultural sector to replenish groundwater with clean recharge.

“This will not happen overnight,” Harter said. “But in the intermediate term, it is important to understand how we can use the agricultural landscape to apply additional clean water to recharge the aquifer.”

Microsprinklers have allowed farmers to use water more efficiently, but compared to flood or furrow irrigation, less water percolates down to replenish groundwater.
In 2014, the UC Division of Agriculture and Natural Resources funded a three-year research project to study the use of agricultural production land for recharging excess surface water.

The project is led by Helen Dahlke, assistant professor in integrated hydrologic sciences at UC Davis and faculty member with the UC Division of Agriculture and Natural Resources Agricultural Experiment Station (AES). The team includes UCCE specialists Harter, Daniele Zaccaria and Samuel Sandoval Solis, AES faculty member Dan Putnam, and UCCE advisors Allan Fulton (Tehama, Colusa, Glenn and Shasta counties) and Steven Orloff (Siskiyou County).

The scientists hypothesize that alfalfa fields and irrigated pastures might be ideal locations for clean aquifer recharge. Both crops demand a relatively low use of fertilizers and pesticides, which means the water soaked down from these fields will be unlikely to carry large amounts of contaminants to the aquifer. The prevalence of flood irrigation in these systems might provide the infrastructure needed to convey surface water, reducing the potential cost of implementing new flood flow capture systems.

The idea is that during storms (or flood control releases) excess surface water could be directed from streams via existing water conveyance systems onto dormant agricultural fields, which would serve as infiltration basins. If successful, tens of thousands acre-feet of water could be recharged annually into California's aquifers during very short periods.

“The banked groundwater would then be available to farmers and municipalities to draw on during dry years,” Harter said.

The project will provide data to address concerns about the costs and risks to crops, the influence these projects may have on groundwater levels and flows, and the possibility of recharging contaminated water or degrading groundwater quality by leaching contaminants such as nitrate into the aquifer.

For more information on groundwater replenishment, see Out of sight but not out of mind: California refocuses on groundwater in the July-September 2014 issue of California Agriculture journal.

An initiative to improve California water quality, quantity and security is part of the UC Division of Agriculture and Natural Resources Strategic Vision 2025.

Posted on Monday, January 5, 2015 at 9:13 AM
Tags: drought (35), groundwater (5), Thomas Harter (3)

Out-of-sight groundwater is not always well understood

Groundwater is a vitally important natural resource in California.
It can be challenging to imagine the stores of water underlying California. But Thomas Harter, UC Cooperative Extension specialist in the Department of Land, Air and Water Resources at UC Davis, shares a vivid vision of the state's vitally important groundwater resources.

In a videotaped presentation, Harter said California's Central Valley is like a giant bathtub; its walls are the Sierra Nevada and coast mountain ranges. Clay, silt, sand and gravel washed into the bathtub over millions of years and fresh water from streams, rivers and rainfall soaked into pores between sand and gravel pieces, between clay and silt particles, and in the fissures and cracks in rocks, where it has accumulated for eons.

Harter outlines the nature of California's groundwater situation in a 30-minute video that is part of the UC California Institute for Water Resources online video series. The series consists of presentations featuring UC and other experts speaking on topics aimed at helping farmers and all Californians better understand and cope with drought.

In the 1920s and 30s, farmers began pumping groundwater in vast quantities to grow summer crops on the flat dry surface. It wasn't long before the land began to sink, especially on the west side of the San Joaquin Valley and in the Tulare Lake Basin.

“Land surface levels declined as much as 30 feet during the 20th century,” Harter said.

In the 1970s, the state water project made surface water supplies available to farmers, allowing underground water to recover. However, in the last 10 years, as surface supplies have declined, farmers are drilling deeper wells to irrigate crops. Once again the land surface has begun to subside, Harter said.

For the most part, farmers have free reign when it comes to pumping groundwater.

“Landowners are not owners of the groundwater below them,” Harter said. “But they have the right to use the groundwater.” There is a constitutional mandate that all groundwater goes for beneficial use.

In the video, Harter reviews the tangle of regulations and agencies involved in managing the state's groundwater.

“About 42 percent of groundwater basins in California have some form of groundwater management plan,” Harter said. The plans contain some basic elements, but are lacking in terms of enforcement mandate, integration with surface water management and the power for agencies to manage demand.

“One of the biggest political questions is what are the roles of the state, local and regional agencies?” Harter said. “The State Water Control Board recently emphasized that it is pursuing a primarily local, regional management approach to groundwater management. But still it has an oversight role and defining that oversight role is something we will be looking at over the next few months and years.”

View the video here:

Posted on Monday, April 7, 2014 at 9:01 AM
Tags: drought (35), groundwater (5), Thomas Harter (3)

Reinventing agriculture at Russell Ranch

The size, scope and intensity of research at Russell Ranch Sustainable Agriculture Facility at UC Davis make the 300-acre experiment like no other in the world. The ranch’s unique focus on sustainability research is what draws producers, researchers and students to its annual Russell Ranch Sustainable Agriculture Field Day.

Located just west of the main UC Davis campus, Russell Ranch is a testing ground for the long-term sustainability of various farming methods. Research at the ranch focuses on fundamental components of agricultural production – energy, water and land resources – to help address the big questions of the future.

“The human population on the planet is going to increase from about 7 billion people to 9 billion people in 2050, which raises questions about food supply,” said Tom Tomich, director of the Agricultural Sustainability Institute at UC Davis, which houses Russell Ranch. “There is a great success story with agriculture and food production in the last 40 or 50 years – roughly doubling food supply. What that took, though, was doubling of nitrogen, tripling of phosphorus, a lot of advanced research. Now, are we going to be able to do this next doubling to feed the next two billion with business as usual? Or are we are going to have to discover new ways of combining sustainability with intensification to increase productivity?”

A majority of the ranch is comprised of a century-long research project devoted to better understanding the relationships between inputs like fertilizers and cover crops, and various indicators of sustainability. The rest of the ranch hosts a variety of other experiments conducted by researchers not involved in The Century Experiment.

Russell Ranch Field Day
Just as spring gives way to the heat of summer every year Russell Ranch hosts a field day to highlight the research in sustainable farming that is being conducted at UC Davis and primarily at the ranch. This year’s field day focused on issues involving nitrogen, water and climate change.

More than 160 growers, scientists and students learned about greenhouse gas emissions from agriculture, California’s new carbon market and soil microbial communities. Researchers from UC Davis and the company PureSense presented the results of research on a novel method for determining local, crop-specific water demand levels in real time to improve irrigation scheduling.

Thomas Harter, UC Cooperative Extension specialist in the UC Davis Department of Land, Air, and Water Resources, shared the results of a new report, “Addressing Nitrate in California’s Drinking Water,” which is the first comprehensive scientific investigation of nitrate contamination in two of the most agriculturally rich areas of California – the Tulare Lake Basin and the Salinas Valley. Harter and his team found that more than 90 percent of human-generated nitrate contamination of groundwater in these basins is from agricultural activity.

“First and foremost, this is about getting safe drinking water to people,” Harter said.

Problems like these inspire researchers at Russell Ranch to help agriculture develop in a way that will feed the planet’s growing population without creating health and environmental problems, Tomich said.

“California agriculture has always had this spirit of innovation. It has basically reinvented itself every generation. So, a lot of what we’re about here and throughout the Agricultural Sustainability Institute at UC Davis is asking: What’s going to be the scientific foundation for the next generation of California agriculture?”

Field day at Russell Ranch.
Field day at Russell Ranch.

Posted on Wednesday, June 6, 2012 at 8:27 AM
  • Author: Eve Hightower
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