It was a heavy snowfall – much like the Sierra experienced before Christmas – that set the stage 12 years ago this week.
It was followed by unseasonably warm temperatures for several weeks triggering a premature snowmelt that threatened to overwhelm New Melones Reservoir. That forced heavy releases that met up at Veritas southwest of Manteca with heavy releases as well Friant Dam up on the San Joaquin Valley watershed.
The rising water was too much for the levees protecting rural Manteca and Tracy to handle the volume. It started with one boil on the Stanislaus River levee. Before it was over, there were nine breaks that ended up flooding 70 square miles, damaging more than 800 structures, forcing 4,000 people to flee, and ultimately caused $80 million worth of damages.
By contrast, the biggest recorded flood in modern South County history started in 1950 with unusually severe rain storms over a three-week period. It caused flooding west of present-day Interstate 5 in Lathrop. Flood waters threatened San Joaquin County Hospital and came within four miles of downtown Manteca. There were 2,000 people evacuated. Today, if the same flooding occurred, it would force 20,000 people to flee.
The odds of either scenarios happening – at least to Lathrop, Weston Ranch and a small portion of area to the southwest of Manteca – will diminish significantly in 2010. That is when Reclamation District 17 is expected to complete over $11 million in upgrades to the levee running from Mossdale Crossing to French Camp Slough.
A majority of nearly 4,000 home owners in Lathrop, Weston Ranch and the extreme southwest edge of Manteca approved a $37 tax assessment to strengthen levees.
The assessment will raise $1 million over five years.
The money 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.
Flood fears closed August Knodt School for several days in 1997. It also prompted Caltrans to “plug” the Highway 120 overcrossing of McKinley Avenue and the Interstate 5 overcrossing of Louise Avenue to turn elevated freeways into secondary levees in the event of a levee failure. Dirt and other material were also dumped at the Lathrop Road undercrossing of Interstate 5 with Caltrans tractors parked nearby if the word was given to create an emergency water wall.
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.
The additional $11 million is being used to build a series of berms next to 21 crucial spots in the levees. The 50-foot long by 4-foot high berms will serve to strengthen the levees if water manages to seep through.
The typical homeowner previously paid $1.75 currently to fund the Reclamation District. Passage of the ballot measure increased the tax by $5.60 to $7.35 for five years. The average assessment over five years would be just under $37.
Farmers previously paid 58 cents an acre. The five-year special assessment added $1.86 to that tax to push the cost to $2.44 per acre for five consecutive years.
River Islands at Lathrop resolved their flood concerns by creating 300-foot wide levees.
southwest of Manteca
The large area southwest of Manteca that flooded in 1997 is not protected by Reclamation District 17 work. Instead, a separate district is moving forward with plans to upgrade levees along the Stanislaus and San Joaquin rivers in that area.
The City of Manteca is exploring the possibility of pursuing levee improvements as far south as Nile Garden School or extending the current levee that parallels Woodward Avenue west of Airport Way and extending it to a point about midway between Union Road and Tinnin Road.
The levee would be 80 feet wide and six feet high to the west of Airport Way, 50 feet wide and four feet high east of Airport Way, and 40 feet wide and four feet high east of Union Road.
Funding would come from property assessment plus development fees and possibly state funds.