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Manteca races to reduce odds of street floods
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Manteca street crews were scrambling Thursday to clear as many storm drains as possible of leaves in preparation for five days of rain that could drop between two to three inches on the city.

The National Weather Service also said it expects south winds 20 to 35 mph to accompany the rain.

The precursor to a series of three storms expected at least through Tuesday dusted Manteca  with a hundredth of an inch of rain late Thursday night. It brought the season total to 5.18 inches.

Manteca’s Deputy Director of Public Works Jim Stone said the expected heavy rains may cause localized street flooding primarily from leaves clogging storm drain inlets.

“Residents can help minimize the risk of flooding on their streets by removing any leaves from the areas of the street where water will flow,” Stone indicated. “If a resident only has a small quantity of leaves, they can place them in their green Toter for collection.  Larger piles should be arranged so that they are clear of the concrete gutter along the street curb.  If a small quantity of leaves is blocking a storm inlet, residents may be able to rake the leaves away from the inlet to restore flow.”

 To report street flooding that is impeding the flow of traffic or threatening to flood homes during business hours, residents should call 456-8400.  Outside normal business hours or on alternating Fridays such as today that are furlough days for most city employees, residents should call the Police Department non-emergency line at 456-8100.

The possibility of the series of storm overpowering the city’s storm drain system isn’t as great as it was just a few years ago thanks to improvements that have increased capacity at key locations. The biggest problem today is leaves blocking the flow of water into the storm drainage system.

Manteca is dotted with numerous parks that encompass storm retention  basins that double as open play area in more conducive weather situations.

How 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.

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.