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REDUCING SJ FLOODING

Will consultant miss solution again in city’s general plan?

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REDUCING SJ FLOODING

State and federal studies show widening Paradise Cut enhances flood protection for Manteca and Lathrop.

HIME ROMERO/The Bulletin/


POSTED August 28, 2017 12:32 a.m.

The San Joaquin River flowing between its confluence with the Stanislaus River south of Manteca to where the Old River channels splits off just beyond the new river overcrossing in Lathrop is essentially a tourniquet.

The State Department of Water Resources’ Regional Flood Atlas pegs the San Joaquin Rover capacity between those two points at 37,000 cubic feet per second. That compares with 52,000 cubic feet per second flow capacity on either side of those points.

The inability of the river to carry 15,000 cubic feet per second (cfs) past Manteca and the higher points in Lathrop on the north side of the San Joaquin is one of the primary contributors to 100-year floods that is a short hand for major flooding that has a one in 100 chance of happening in any given year.

Whether the hired gun that is fashioning the general plan update that will serve as Manteca’s growth blueprint through 2040 will identify a 30-year-old plus state study that identifies a way of diverting flows above 37,000 cfs that imperil Manteca will be answered Oct. 2. That’s when the firm that’s being paid in excess of $200,000 to fashion the general plan update conducts the citizens’ advisory committee meeting regarding safety and noise. Flood concerns are part of the safety and noise element of the general plan. The meeting is Monday, Oct. 2, at 6 p.m. at the Manteca Transit Center.

DeNovo Planning Group — the same firm that was paid to cobble together the May 2016 update to the safety element to address the realities of Senate Bill 5 regarding 200-year floodplains — has never referenced the Paradise Cut bypass and focused exclusively on levee issues.

Paradise Cut has little water in it much of the year. It runs under Interstate 5 just north of the Interstate 205 interchange and serves as a bypass of the main river channel between a point midway between the Stanislaus River and the Mossdale Crossing to the Old River. The proposal to widen Paradise Cut was first advanced by a state agency concerned with flooding in the early 1990s. It re-surfaced in 2001 in an Army Corps of Engineers report to create a river bypass to reduce the potential for flooding in Manteca, Lathrop, and Stockton.

 

Engineers: Widening

Paradise Cut would drop

water levels in river

during floods by 1.8 feet

Engineers determined expanding the Paradise Cut would reduce flood stages significantly at Mossdale Crossing — 1.8 feet under a 50-year event as well as under a 100-year event such as the 1997 flood that inundated 70 square miles between Manteca and Tracy. 

At the same time it would offer habitat and migration territories for juvenile steelhead, salmon and spawning split tail that are driving some water use debates

That’s a significant way to reduce the threat of Manteca flooding that appears nowhere in the city’s general plan documents.

Widening Paradise Cut would also allow upstream reservoirs to be managed more conservatively to reduce water releases during the rainy season and spring runoff to conserve water for summer use.

David Kennedy, the longest serving director of the Department of Water Recourses, in 1998 wrote the following about the Paradise Cut bypass proposal in the forward of the second edition of “Battling the Inland Sea”: “Recognizing the futility of simply raising the levees, flood control experts will now evaluate the feasibility of removing levees in some locations and simply letting future flood flows pond onto adjacent lands. Further, consideration is being given to opening up some form of bypass through the south Delta to relive pressure on the levees as the San Joaquin River flows into the Delta. It is hoped these issues will be resolved and changes will be made before the next flood.”

 

Flood control board for

Central Valley embraced

Bypass approach last week

The idea: “Spread it out, slow it down, sink it in, give the river more room” was how Kris Tjernell, special assistant for water policy at California’s Natural Resources Agency. described the recommendation last week by the Central Valley Flood Protection Board that oversees flood control for a 500-mile stretch of the valley where the Sacramento and San Joaquin rivers flow.

In essence, the board advocates creating bypasses such s the Yolo Bypass of Sacramento that takes pressure off the Sacramento River before it reaches the confluence with the American River in times of high water flows. The wetlands and flood plains within the Yolo Bypass also allow rice farmers, migratory birds and baby salmon to thrive there.

The state doesn’t have the funding for the nearly $20 billion in projects envisioned by the plan that is meant as a broad outline to resolve long-term flood concerns.

The Paradise Cut widening — known officially as thee Lower San Joaquin River Flood Bypass Proposal — was formally submitted to the California Department of Water Resources in March 2011 by the South Delta Levee Protection and Channel Maintenance Authority and other partners. It was an effort to secure $5 million to create the new flood bypass in the last corridor of undeveloped land between Tracy and Lathrop.

Currently the cut does take pressure off the main channel but it isn’t large enough where it connects back to the Old River to be effective after a certain point. 

 

River Islands offered to

pay for needed work

but after 14 years are

still waiting to get OK

Ironically, nine years earlier Cambay Group — the developers of the 11,000-home planned community known as River Islands at Lathrop — applied for permits through the Army Corps of Engineers to widen Paradise Cut as the state and the Army Corps advocated as well as pay for it.

Cambay Group was told it would take 18 months to get federal and state approval when they applied for the permits to do the work. That was in 2002. Now 14 years later officials are hopeful that River Islands’ permits will be approved by 2018.

During that time only two comments have been made on the Cambay Group request by government agencies. Meanwhile, the regulations governing such work keep changing.

As soon as the permits are obtained, Dell’Osso said Cambay Group intends to start work to add the 200 acres and construct improved levees to protect an additional 6,716 home sites in the 11,000-home planned community being developed in Stewart Tract.

 

Lack of inclusion of

flood solution meant

council never asked

lobbyist to help clear

approval for project

Had DeNovo highlighted the well-documented solution to ease Manteca flooding in the safety and noise element of the general plan, it could have provided the City Council the impetus to call upon the Washington, D.C., Van Scoyoc Associates lobbying firm they have on retainer for $89,000 a year to help cut through red tape so the privately funded work for the government generated solution could move forward.

Residents south of Manteca as well as farmers at various times over the past four years have asked the city to work toward moving the Paradise Cut project. While it is out of Manteca’s jurisdiction, the city would benefit significantly by the enhanced ability of the stretch of the San Joaquin River to carry water as state and federal engineers have ascertained would happen if the work was done

The real advantage — if it can be called that — of Paradise Cut in previous 100-year flood events in 1955 and 1997 were levee failures. In the previous two flood events the levee failures along Paradise Cut flooded the 4,900 acres on Stewart Tract with between one and five feet of water. That won’t happen with the 300-foot wide levees River Islands has put in place. 

Manteca and Lathrop are working on upgrading levees protecting the two cities as well as the Weston Ranch part of Stockton and French Camp to 200-year status  with a $180 million plus project.

While the Paradise Cut widening isn’t likely to address a 200-year flood threat, it builds in additional assurance of safety that the city commits itself to in the summary language of the general plan without costing the city, its residents, or the state and federal governments a dime.

 

To contact Dennis Wyatt, email dwyatt@mantecabulletin.com

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