Efforts to complete the widening of Paradise Cut that would significantly improve flood protection for urbanized areas of Manteca, Lathrop, and Stockton may finally move forward.

The San Joaquin Area Flood Control Area (SJAFCA) is positioning itself to be the lead agency to shepherd the project involving widening the seven-mile long Paradise Cut where it branches off the San Joaquin River and passes beneath Interstate 5 just north of the Interstate 205 interchange to where it connects with the Old River.

Engineers have 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 and caused property losses in excess of $80 million.

It would also lower water levels at Stockton, French Camp, and Lathrop by two feet to enhance 200-year flood protection by directing some water to the south Delta and away from downstream levees.

It is an idea that has been floating around the state Department of Water Resources since the 1980s.

The seven-member Central Valley Flood Protection Board along with personnel for Reclamation District 2062 that protects Stewart Tract that is where the 15,000-home planned of River Islands at Lathrop is located, and SJAFCA staff toured Paradise Cut last week.

SJAFCA was formed by Manteca, Lathrop, Stockton, and San Joaquin County to work toward upgrading levees along the east side of the San Joaquin River as well as putting in place a  dry levee also known as a cross level south of Manteca in order to secure state-mandated 200-year flood protection.

A 200-year flood is hydrology vernacular for a flood event that has a 1 in 200 year chance of happening in any given year. Increased development that has added impermeable services such as roof tops, parking lots, streets, driveways, and sidewalks has increased runoff over the years that in turn increases flood risks both in intensity and frequency.

The Paradise Cut project by itself won’t provide the level of flood protection the state has mandated to be implemented. It will, however, significantly increase the effectiveness of levees after they are upgraded to withstand flooding.

Part of the project — the north side — has already been started by Cambay Group. That involved building a new levee set back further to the north from the existing Paradise Cut levee and removing trees.

Cambay intends to level the existing levee to create a shelf between channel and the new levee. The shelf will be planted in shrubs conducive to wildlife and reducing erosion. That work can’t take place until regulatory approvals have been secured.

The Paradise Cut project has languished for a number of years due to an agency not moving it forward through the regulatory process. SJFCA will solve that dilemma.

The work Cambay Group has done to date did not need regulatory approval due to it being behind the existing levee and not within the channel or altering existing levees.

Once regulatory approval is secured Cambay Group will do the work on the north side in its own dime.

There are state and federal grants being lined up for the work on the south side. While Cambay Group will not do that work or pay for it, they are collecting a fee on each home built on River Islands that will raise $10 million to help with the purchase of land to push back the channel on the south side of the cut.

The River Islands project is based on a specific proposal made years ago that resurfaced 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.

The 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.

The Paradise Cut endeavor has been embraced by environmental groups as it would allow the restoration of habitat.

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.”

Government gave RD-17

levees split decision in 2010

Reclamation District 17 oversees the levees from a point midway between Mossdale and the San Joaquin River’s confluence with the Stanislaus River to French Camp Slough on the northern edge of Weston Ranch. That is the key reclamation district that protects Lathrop, Weston Ranch, and parts of southwest Manteca. It also involves where the river bends at Mossdale where water pressure pounds the levees.

The federal government in 2010 gave a split decision to the effectiveness of the Reclamation District levees. The Federal Emergency Management Agency granted the levees 100-year flood accreditation a week after the Army Corps of Engineers said RD-17 was among seven of the 10 Central Valley levees they inspected did not meet federal safety criteria and could be threatened in a flood or storm. The Corps conducts Central Valley levee system inspections every five years with engineers literally walking them.

It was the same year RD-17 was awarded $62.4 million in state bond money to strengthen levees.

The work funded was designed to maintain protection against a 100-year flood event and go a long way towards 200-year protection.  The 100-year and 200-year monikers are a bit misleading as they are described as flooding that has a chance of happening in any given year based on natural conditions. As more valley soil has been paved or built on run-off has increased significantly reducing the times between major flooding.

Parcel tax allowed RD-17

to secure $10M for levee work

The money was wedded with $1 million raised from a $37 parcel tax assessment over eight years that a majority of 4,000 home owners in Lathrop, Weston Ranch, and the extreme southwest edge of Manteca voted to put in place. The parcel tax made it possible to secure the state bond money.

The parcel tax also allowed the district to secure a $10 million U.S. Army Corps of Engineers grant to improve flood protection for a large swath of land generally west of Interstate 5 from Mossdale north to Weston Ranch and a large chunk of the developed portion of the City of Lathrop.

The work involved building a series of berms next to 21 crucial spots in the levees. The 50-foot long by 4-foot high berms serve to strengthen the levees if water manages to seep through.

River Islands at Lathrop resolved their flood concerns by creating 300-foot wide levees at a cost of $70 million to take 900 acres on Stewart Tract out of the floodplain.

In addition River Islands spent $2 million on studies to prove to the state that the levees created in 2006 provide 200-year flood projection as mandated by Senate Bill 5.

The last floods were in 1997 when roughly a dozen breaks along the San Joaquin and Stanislaus rivers ended up flooding 70 square miles, damaging more than 800 structures, forcing 2,000 people to flee, and ultimately caused $80 million worth of damages.

The Army Corps of Engineers spent $2 million to patch the existing levees after the 1997 flooding to restore them to the same condition they were in prior to the failure.

To contact Dennis Wyatt, email dwyatt@mantecabulletin.com