Manteca is not taking any chances.
Hours after the San Joaquin County Office of Emergency Services Wednesday raised their “awareness and preparedness” level  to Mode 3 – shorthand that the potential exists for a significant incident regarding San Joaquin River flooding — the city issued its own flood warning to Manteca residents.
The city release makes it clear that “while the city does not anticipate an immediate threat of flooding, we are providing contacts to (allow residents) to remain up to date on conditions and services, to prepare in the event of a flooding event.”
Mayor Steve DeBrum noted the decision to do so is to error on the side of caution. Should the levees south of Manteca fail for the 12th time since 1927, the city has a second line of defense with a dry levee south of Woodward Avenue that became perilously close to failing when flood waters pushed against it in 1997.
The most likely flood victims would be farms and rural residents primarily west of Airport Way as well as property south of Nile Garden Road on the east of Airport Way. Floodwaters 20 years ago came up to the Nile Garden School playground.
Manteca Unified personnel are continually monitoring the situation and should the need arise parents will be notified through existing phone and social media alert systems that are in place.
All of the Manteca Unified campuses in Lathrop and Weston Ranch could experience flooding should the levee fail farther north than it did in 1997. Twenty years ago the 13 levee breaks were south of Manteca along the San Joaquin and Stanislaus rivers. There were several boils — the precursor that could signal an impending failure that consists of water bubbling up on the land side of the levee — but they were successfully contain.
Should a levee failure occur far enough north all of Lathrop except for River Islands and Weston Ranch would be threatened. If a break does occur and the water flow can’t be contained, it would take eight hours to reach the French Camp Slough levees that tower some 30 feet above homes at the northern edge of Weston Ranch that is one of the lowest spots in San Joaquin County.
Wetherbee Lake and Haven Acres — two rural neighborhoods at the end of Woodward Avenue and southwest of Oakwood Lakes — are at risk should a levee failure occur.
Twenty years ago the two areas were under 10 feet of water for more than two months.
If the same 70 square miles minus Stewart Tract’s 4,800 acres that were taken out of the path of flood threats due to 300-foot wide super levees put in place to protect River Islands at Lathrop were to be flooded, upwards of 2,000 people would be forced to flee in both rural Manteca and rural Tracy.
A levee failure father north such as what happened in 1955 when floodwaters did reach the French Camp Slough would involve more than 30,000 residents in Lathrop and Manteca.
Local agencies such as the Lathrop Manteca Fire Department, City of Manteca Fire Department, Reclamation District 17, Department of Water Resources and the SJ County Office of Emergency Services are working together under updated plans to be ready to respond if and when a break occurs.
Whether that involves Manteca’s fallback line of defense as well as a strategy that could save Lathrop east of Interstate 5 from flooding if breaks happen north of where they did in 1997 or should the dry leeve south of Woodward Avenue fail after an initial river levee break is unknown.
Both the 120 Bypass and Interstate 5 were designed as an emergency levee when they were built. It is why freeway lanes are elevated on earth through most of Lathrop. In 1997 crews filled the 120 Bypass underpass of McKinley Avenue in Manteca as well as the Louise Avenue underpass of I-5 in Lathrop with 10 feet of dirt covered with plastic. Dirt had been placed at the Lathrop Road undercrossing of I-5 in case that had to be plugged.
The big difference this time around is Manteca has allowed hundreds of homes to be built along Airport Way south of the 120 Bypass plus the county allowed Oakwood Shores to be built.
Twenty years ago there was no urbanization west of I-5 in Lathrop.
Mayor DeBrum noted Manteca “is ready to help our neighbors” as the city did in 1997 when the unthinkable happened.
 
To contact Dennis Wyatt, email dwyatt@mantecabulletin.com