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Wet & wild? Storm system works
Cotta Park on Mission Ridge Drive is doing double duty this week as a storm retention basin. - photo by HIME ROMERO

A series of storms such as are now moving through Manteca would have sent business and home owners alike scurrying for sand bags in some parts of the city just 30 years ago.

Flooded streets weren’t unusual as downpours or steady rain could easily overwhelm Manteca’s storm drain system and back water up onto surface streets thanks to the community’s essentially flat terrain.

Even just five years ago, there were still isolated streets that would flood including South Main Street near Moffat and North Powers Avenue to name a few.

Although the city can never say flooding won’t occur again, flooding due to inadequate capacity in the storm drain system is now hopefully a thing of the past thanks to the finishing touches put on the city’s storm system. That system relies heavily on parks doubling as storm retention basins to handle run-off that pipes can’t. In addition replacement of severely undersized lines has improved the ability of the system to handle run-off.

“We only had minor problems,” Public Works Director Mark Houghton said Friday of last week’s storms. “Things seem to be working well.”

The city is looking at strategies to provide efficient and effective storm drain removal in the developing area south of the Highway 120 Bypass. At the same time, they are acutely aware that some of the storm system components are aging and may need to be replaced in the near future.

In addition, Manteca is employing new strategies to minimize the impact on infill development on the older segments of the storm retention system. The new senior housing complex being built behind Burger King on North Main Street has underground storage put in place for storm run-off. It is the same type of system that was put in just east of Manteca Bowl & Family Fun Center that ultimately will allow the development of the parcel where the old bowling alley once stood and land behind it without impacting the storm system serving that area.

The city also has allowed French drains – buried gravel – to be used in infill projects such as the Lincoln Estates subdivision. The gravel serves as a holding area for water as it percolates to reduce the potential for flooding.

How the
system works

How the city’s storm system works is part high-tech and part low-tech.

It starts as a light rain.

And then before you know it, the skies open up.

Rainwater runs off your roof, your driveway, your patio and other impervious surfaces.

It trickles into the gutter in a steady stream joining the run-off from nearby homes as well as the streets and sidewalks.

A running stream of water punctuated with a steady downpour flows into the storm drain and disappears beneath the streets of Manteca.

It’s below the surface in storm drains ranging from 12 inches to 48 inches or more that your rain run-off joins that from hundreds of other homes and commercial ventures.

But the trip ultimately to the San Joaquin River and into the San Francisco Bay is interrupted.

The city’s storm system is becoming overloaded. Pumps kick on and the water is taken out of the system into a nearby park that has been designed to provide double duty as a storm retention basin. It is here the water will pool with other run-off waiting for the system to clear up room so it can continue its journey.

The goal is to take pressure off trouble spots to avoid street flooding and backing water up on to private property by controlling flow with a telemetry system that has been programmed to respond automatically when workers detect problems in the city as the torrential cloud burst continues.

The water level in the storm retention basin rises providing an effective safety valve against flooding. Then capacity is freed up in the system and a second pump starts removing the water from the basin and putting it back into underground drains that make their way to the west near the Union Pacific Railroad tracks. It is here that the water comes gushing out through large screens covering culverts and into a San Joaquin Irrigation District drain.

The water will then make its way north to the French Camp Slough about eight miles away before turning west and heading past the northern levees on the northern edge of Weston Ranch in Stockton and into the San Joaquin River to continue its journey to the Bay Area and ultimately into the San Francisco Bay and beyond.

There are more than 2,800 storm drains citywide. All of the storm drains are cleaned before and after storms to prepare for the next rain. Even so Houghton has said it is a big help when citizens keep leaves and other debris away and off grates to the storm system.

System wouldn’t work
without SSJID canals

The system wouldn’t work without access to SSJID canals and drains that are between Manteca and the river. The city works closely with the district and shares in the cost to improvements along the drain that heads to French Camp Slough where all of the city’s storm drain water that enters pipes currently goes.

The city is dealing with a fact it can’t escape -any improvement to land increases the water run-off.

An acre of farmland that used to grow crops typical has a one-tenth of a rating for run-off.

 It increases when you put grass on it, build homes, or put in streets.

It is the same reason why California’s rivers are flooding more often. There is more run-off because more land is being made impervious to percolation during heavy storms.

The city doesn’t have a separate storm system crew but instead relies primarily on sewer system workers. Whenever they work on storm system matters, their time is billed internally to that account since state law requires enterprise fund accounts that serve specific users such as those who access sanitary services can’t legally pay for service other than what the fee is collected to pay for.