Head into the countryside outside of Manteca and Ripon and you will come across a sight that you might view as insanity given the severe drought.
There are literally hundreds if not thousands of acres of almond orchards and other cropland being flood irrigated.
What looks like a waste of water is actually helping keep water flowing to your home to wash clothes, drink, flush toilets, shower or bathe, and wash dishes and such if you live in Manteca, Ripon, Stockton, Lathrop, Escalon and Lodi.
That’s because in typical year water diverted from the Stanislaus River by the South San Joaquin Irrigation District is credited for recharging the Eastern San Joaquin Groundwater Basin with 135,000 acre feet of water. Some of that is seepage from SSJID canals, laterals and reservoirs.
Woodward Reservoir, as an example, was a great place 105 years ago to build an in-district storage facility to allow for the gravity delivery of water. But the soil is less than ideal to minimize percolation, making it a gigantic sieve to replenish groundwater.
That said an equally important — if not more so — source of water to replenish groundwater is deep percolation from flood irrigating.
There is 134,000 acre feet of water that SSJID — not by deliberate design — annually rechargers the aquifer based on a 2018-2019 study. In the same year the district, as well as farmers within the SSJID boundaries plus rural homeowners, pumped 65,000 acre feet of water from the basin.
That leaves 69,000 acre feet of water SSJID recharges the ground with to head north and west to help replenish what cities and out-of-district farmers that rely in well pump out of the ground.
Manteca relies on 15
wells as well as surface
water from SSJID
Manteca and Lathrop — unlike Stockton, Escalon, and Ripon — rely on both SSJID water and well water to meet municipal needs and therefore aren’t 100 percent at the mercy of groundwater as the other three cities are.
Even so, Manteca’s 15 municipal wells, depending upon how the system is operated in a given year, can draw between 5,000 and 7,000 acre feet of water from the ground.
Storm runoff in Manteca has a minimal impact on recharging the water basin the city relies on. That’s because it is collected in basins, released into SSJID canals and drained into the San Joaquin River.
Manteca, once surface water became available in 2005, has operated its system to keep costs down and to try and minimize impacts to groundwater. The city tries to operate 100 percent on surface water in the winter and brings all wells on line in the summer.
Agricultural and municipal wells in the basin go down 80 to 800 feet with the typical well dropping down to 350 feet.
Environmentalists for years would take one look at an almond orchard being flood irrigated and condemn it as a wanton waste of water.
Such irrigation techniques have become a whipping boy of sorts for those dedicated to securing more water for fish.
It is also a convenient target for urban interests that paint agriculture that feeds everybody as needing to be more frugal before cities being required to cut back on water use during droughts. It is also a bone of contention even in normal years when the issue is the fact more water has been committed on paper to be delivered to California’s cities and farms than the state’s hydrology can provide.
Need to stabilize groundwater
prompts a different look at
benefits of flood irrigation
The advent of the state mandate to stabilize groundwater has prompted scientists and researchers to look at the impacts of flood irrigation differently.
The Sustainable Groundwater Management Act that requires a plan in place by 2025 to work toward taking no more water out of a basin than is recharged in a given year. The SGMA mandate must be fully implemented by 2040.
The Eastern San Joaquin Groundwater Basin that the SGMA mandate applies to extends to the San Joaquin River in the west, the Stanislaus River in the south, the base of the Sierra foothills in the east and the Mokelumne River in the north.
In 2016 at the height of the last drought, University of California at Davis scientists started an experiment to see if deliberately flooding almond orchards during the winter when they are dormant and excess storm runoff can be diverted onto them would be an effective way to re-charge groundwater.
One test site was a Modesto orchard owned by almond grower Nick Blom. It was selected due to the soil type that is conducive to percolation and the fact the aquifer is 45 feet below. In times of drought when delivery cutbacks are imposed for surface water from Modesto Irrigation District Blom turns on his wells.
Whether almond orchards can help California make major headway into its chronic groundwater overdrafting hinges on the outcome of research.
That includes whether the roots sustain damage or disease from flooding orchards when the trees or dormant. There is also the question of modifying fertilizing so nitrates don’t becoming a big issue in groundwater.
If using winter storm runoff in almond orchards is found to be an effective and a safe way to recharge groundwater, researchers estimate there are 3.6 to 5.6 million acres of almonds with conducive soil that could be used for recharging purposes in California.
It could be a fast and effective way at getting excess winter water flows that end up in the Pacific Ocean to recharge aquifers.
It is also less expensive that creating recharge basins that are being explored in San Joaquin County and throughout California.
Other UC Davis tests on grapes, alfalfa, and pistachios showed flood irrigation did not harm those crops or impact drinking water.
Depending upon how effective flood irrigation and potential winter flooding of dormant orchards can be recharging aquifers it could bring into question whether it is wise to pursue pressured irrigation systems such as the cutting edge SSJID Division 9 system south of Manteca and west of Ripon.
Such pressurized systems allows for drip irrigation allowing water to be applied directly to the tree roots. It has been found to reduce water use while helping to increase crop yields.
Converting orchards to pressurized drip that are now being flooded would reduce ground water recharging and in turn make less water available via wells for cities, farmers that don’t irrigate with surface water, and domestic wells of rural residents.
To contact Dennis Wyatt, email dwyatt@mantecabulletin.com
