Tuesday, Aug. 26, 2008

Water atlas provides county with a starting point

Data put all parties on same page in state's most argued problem

In any contentious issue, the core facts are key to making progress: If opposing sides don't start with the same information, it's tough to reach consensus.

Water has a long history of contentiousness, but at least in Stanislaus County, there now is a starting point.

The county's Department of Public Works has developed a water atlas, which collects studies, reports and compiles general information about water in the county and puts it in one place. It's full of interesting facts about the county's water use.

For instance, do you know how much water is used each year in Stanislaus County? The water atlas says 1,944,400 acre-feet. That's enough water to cover the county with 2 feet of water, give or take a gallon or two.

Farm irrigation uses most of that water, 1.7 million acre-feet. Urban uses, such as taking showers, watering lawns and flushing toilets, account for 210,100 acre-feet. Cities and farmlands use about the same amount of water per acre, said county Public Works Director Matt Machado, so residential growth doesn't change the water demand.

Most of the county's water use, about 1.4 million acre-feet, comes from surface water -- the system of rivers, canals and reservoirs that supplies irrigated farmland and, increasingly, urban residents.

The rest is pumped from the ground, which leads to another interesting part of the water atlas: groundwater contour maps that show what's happening to the water underground over time.

The maps date back 50 years and show groundwater overdrafts under Modesto and east of Turlock developing over several decades.

The Modesto overdraft, Machado said, was from city wells pumping more water than nature could percolate back into the ground. The overdraft had begun to correct itself by 2005, after the city shifted to a combination of wells and surface water supplied by the Modesto Irrigation District.

The overdraft east of Turlock, however, is caused by agricultural pumping, Machado said, and it continues to get worse. The water atlas recommends that localized groundwater quality and elevation be watched and addressed.

While surface water is closely monitored and managed by irrigation districts in the county, groundwater in the north portion of the county and the West Side lacks organized oversight, the atlas concludes.

The idea for the water atlas sprang from the countywide water summits that began a few years ago, Machado said.

"It's a tool to bring people together to talk about water," he said. "It shows we all have similar issues. Communities can see what others have done, and it saves time looking for information."

Bill Harrison, general manager of Del Puerto Water District, said the atlas is a valuable resource.

"Water has become very critical to the planning process," he said, noting that new development is required to identify a long-term water source. "There's been difficulty in getting information together in a consistent way, an interpretable way," Harrison said.

His West Side district is far more vulnerable to water shortages than irrigation districts such as those in Modesto and Turlock. The MID and TID have reservoirs to draw from in droughts. Del Puerto Water District, serving a long, narrow agricultural area from Vernalis to Santa Nella, gets its water from the Delta-Mendota Canal. That supply is curtailed quickly in a dry year.

The water atlas maps the territory of all the water providers in the county, and all the rivers, canals and reservoirs.

Walter Ward, MID's assistant general manager of water operations, said he has been pushing for a central repository of water information for a long time. "I'm glad to see it happen," he said. "It's an information-gathering effort that gets everyone on the same page."

Planning efforts sometimes get sidetracked when, for instance, people use different population projections, Ward said. Population projections, and their impact on land use and water supply, are included in the water atlas.

The water atlas isn't meant to be a static document, Machado said. As more information and studies come out, they will be added.

"It's not an end product," Ward said. "It's just the beginning."

The water atlas can be seen on the Stanislaus County Public Works Web site, at www.stanco-pworks.org/wateratlas.

Bee staff writer Tim Moran can be reached at tmoran@modbee.com or 578-2349.