Stanislaus County’s groundwater flows being mapped by new computer program

jnsbranti@modbee.comSeptember 17, 2013 

— Groundwater and geographic data garnered from thousands of Stanislaus County wells are being used to create a computerized 3-D mapping program that may help predict the impact of future pumping on the region’s water supply.

The $1.25million U.S. Geologic Survey study won’t be finished for another year, but it’s expected to provide a high-tech tool for simulating and analyzing groundwater flows.

It will provide water planners a kind of “crystal ball” to determine how pumping – or flood irrigating – in one part of the county could affect water levels elsewhere, explained Walter Ward, Modesto Irrigation District’s assistant general manager for water operations.

“It will help in making water resource decisions,” Ward said. “We want to offer this to the public as a tool.”

Six agencies – the MID, the Oakdale Irrigation District, Stanislaus County, Modesto, Riverbank and Oakdale – contributed $126,000 each toward the project, and the USGS kicked in an additional $500,000.

The “simulation/optimization model for evaluating water management strategies” covers the aquifer from just south of the Merced River to just north of the Stanislaus River, and from the San Joaquin River on the west to the Sierra Nevada foothills on the east.

That includes all of the Turlock Irrigation District, which contributed groundwater data to the USGS project.

Ward said the new computer program will enable people to pose “what if” questions, such as “What would the aquifer’s water level response be in this location if we increased pumping levels in that location?” It also could be used to predict how much the aquifer could be recharged by flood irrigating a certain field.

To accurately calculate such water flows, Ward said soil types and groundwater levels throughout the region had to be mapped. That was done by using data from more than 3,500 drillers’ logs and calibrating water levels measured from 1960 through 2004.

USGS hydrologist Steven Phillips has been the project’s chief since it began nearly 10 years ago.

“It’s been exciting,” said Phillips, who is based in Sacramento. He said the computer program will be available for free to anyone who wants to “compare alternatives and look at the cost and benefit of each option.”

“It can help you understand what might occur in the future with continued development,” Phillips said. The program will provide 3-D simulation of groundwater and surface water flows and how variations in irrigation and pumping would affect them.

But that doesn’t mean the program will be simple to use or pretty to look at. It will produce “numerical models” rather than images, and Phillips said it will “take someone who knows what they’re doing” to use it.

It could produce the kind of data, however, that decision-makers might need for future regulations governing groundwater.

Right now, Stanislaus has virtually no rules about how much water landowners can pump out of the ground, no matter how they affect their neighbors.

As more and more industrial-size water wells get drilled in Stanislaus, such as those tapped for the millions of new almond trees that are being planted, community concerns about groundwater are growing. That’s been especially true this year, as the two-year drought has triggered increased pumping.

The MID’s Ward said he thinks groundwater regulations “are long past overdue.” He fears state lawmakers will step in if local officials do not.

“It’s a can of worms, and it’s going to be hugely controversial,” Ward warned about proposals to limit pumping. He said the new USGS water flow model could be useful in crafting new rules, but “it’s just a tool. It is not the answer.”

Bee staff writer J.N. Sbranti can be reached at jnsbranti@modbee.com or (209)578-2196.

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