Modesto to gradually replace rock wells to fight flooding problems

kvaline@modbee.comMay 8, 2013 

    alternate text Kevin Valine
    Title: Reporter
    Coverage areas: City of Modesto and nonprofits
    Bio: Kevin Valine has been a copy editor and reporter at The Bee since January 2006. He's worked at the Reno Gazette-Journal, Sarasota (Fla.) Herald-Tribune and Paradise Post as a reporter and copy editor. He's a graduate of San Jose State.
    Recent stories written by Kevin

— Modesto officials believe they have a solution to a problem that has vexed them and outraged residents for decades — streets that flood after just an inch of heavy rain.

Public works crews have started replacing antiquated rock wells with dry wells (See graphic on differences between dry wells and rock wells), a type of storm-water drainage system used in the rainy Pacific Northwest.

Work started in February. Robert Englent, the city's waste-water collections manager, said the city should replace about a dozen rock wells by June 30, the end of the fiscal year. He said the city has the funding to do 20 to 30 of these projects each fiscal year. He said it costs about $30,000 to replace one rock well with a dry well.

It could take years to replace the rock wells, which provide storm-water drainage for about a third of the city. Modesto has about 11,000 rock wells, and a quarter to half of them clog with leaves and other debris during heavy rain, causing localized flooding.

"We recognize that a lot of the city has flooding problems," Englent said. "We've developed a strategy to significantly reduce localized flooding and maintenance costs. We do understand that a lot of people suffer from occasional flooding."

Englent said some of Modesto's rock wells were built in the 1920s and '30s, but most of them were built in the 1940s and '50s. He said the wells were an inexpensive way to provide storm-water drainage for a city that does not get a lot of rain. Modesto averages about 12 inches annually.

"It's an outdated system," he said. "But it has worked reasonably well, but it's prone to failure, and it's labor and maintenance intensive."

Modesto spends about $1 million a year cleaning and maintaining its rock wells. Englent said the dry wells need far less maintenance.

Public works crews are focused first on heavily traveled roads that flood, and then will replace rock wells in flood-prone neighborhoods. The city also is replacing 50 rock wells that are connected to the city's sewer system. That kind of connection no longer is allowed by the state.

Englent said about a third of Modesto floods during heavy rain. Newer parts of Modesto, such as the Village I neighborhood, don't flood because they have better storm-water drainage systems.

Englent said replacing rock wells with the web of pipes and storm basins found in Village I would cost hundreds of millions of dollars, which is too expensive for the city.

He said he came across dry wells while researching how to reduce the flooding associated with rock wells and found they are common in Oregon and Washington. He said he spent about a year working out the details and modifying the rock wells for use in Modesto.

Residents who want to learn more about this project can call the city at (209) 577-6300.

Bee staff writer Kevin Valine can be reached at or (209) 578-2316.

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