By allowing ads to appear on this site, you support the local businesses who, in turn, support great journalism.
RIVER ISLANDS : WHAT 200-YEAR FLOOD PROTECTION LOOKS LIKE
Where other nearby levees on San Joaquin River are 20 feet or so wide at the top, River islands’ are between 100 and 300 feet
super levees
At the bottom of the photo looking to the northeast from above River Islands toward Lathrop are the “super levees” that are 300 feet across the top that protect the planned community from the San Joaquin River.

High water. High winds. High tide. Heavy rain.

Combine those four factors with significant releases from massive reservoirs in the Sierra foothills.

Toss in the constant need  for money for upkeep and you have what used to set the stage for high anxiety for Reclamation District 2062 located where the San Joaquin River drains 12,250 square miles into the Delta.

That’s because Stewart Tract that Reclamation District 2062 protects — the most southeastern of 55 islands in the Sacramento-San Joaquin Delta created with more than 1,000 miles of levees —a history of levee failures.

They failed in 1997. They failed in 1951.

Those were the big breaks among failures in the past 75 years.

Each time the San Joaquin River reclaimed a large swatch of the 4,800 acres with an elevation of 13 feet above sea level. In some places the water was as high as 6 feet.

 Today, the river that is shoving the equivalent volume of water that 32,000 basketballs could hold at any given second past a point beneath the iconic Mossdale railroad bridge is at monitoring stage. That 32,000 cubic feet per second of water flowing by is roughly six times the amount that flows on an average first day of spring.

Susan Dell’Osso, one of the three RD 2062 board members, can see nature’s fury unfolding on the San Joaquín River literally a dozen or  so yards away from her office window in the old Mossdale Marina that was remodeled as the offices of River Islands at Lathrop.

Some might argue that RD 2062 has a reason to be a tad smug these days.

After all, they have the newest levees on the San Joaquín River as well as the Delta.

They’ve been called “super levees.by some as

The levees were not just simply built to the 200-year level of flood protection before that became the mantra to protect urbanized areas along the river after the California Legislature adopted stringent mandates in the wake of the Katrina disaster in 2005 in New Orleans.

Instead of being the minimum 20-foot width at the top, the 18 or so miles of levees protecting the planned River Islands community of 15,001 housing units are 100 to 300 feet wide.

Unlike most levees in the Delta built 70 to 100 years ago, they are not simply comprised of what dirt was handy. Instead. they have a robust clay formulated to be resilient and — fairly effective — at keeping water at bay.

 

River Islands levees in process

of being certified as effective

for 200-year flood protection

 

The levees are in the middle of a long laborious process requiring piles of paperwork to gain coveted certification as 200-year levees.

Such certification, by the way, doesn’t mean guarding against a flood event on such a scale that happens only once every 200 years.

It reduces the frequency of such an event possibly happening in any given year — a 1 in 200 chance.

And given increased runoff over the years from upstream urbanization that is creating more impermeable surfaces such as rooftops, sidewalks, roads, parking lots, and such along with climate shifts, 200-year events are expected to become more common.

Although the district protecting part of Manteca, Lathrop east of the San Joaquín River, French Camp, and Stockton’s Weston Ranch neighborhood is working toward a $270 million solution to upgrade to 200-year protection level as early as 2030, it has roughly the same level of protection as most  urbanized areas along flood-prone California rivers which is a 100-year event.

Even though Stewart Tract reincarnated as River Islands at Lathrop has gone from the bottom of the heap in terms of levee resilience to being the  gold-plated platinum standard, RD 2062 is taking no chances.

Although the river is only at monitoring stage as it passes the district’s levees, the RD 2062 is conducting levee patrols as if it were at flood stage.

That means frequent repetitive patrols 24/7. It involves both driving and walking the levees day and night that currently protect roughly 7,000 residents.

They are looking for puddling water. Boils. Any issues with the levee’s integrity.

Dell’Osso stresses regardless of how new or strong levees are it requires constant vigilance specially during current conditions.

River Islands’ has set aside 300

acres for Paradise Cut widening

as region waits for state action

 

Taking nothing for granted is what drives reclamation districts.

The built-in advantage that RD 2062 has is the fact Cambay Group — the developer of River islands — was initially the only property owner when new levees were put in place.

The cost of such work is ultimately is collapsed into the price of new homes.

But equally important Cambay Group put in place the tax mechanism to assure more than  adequate funding to maintain the levees.

That means River Islands has urban-level levees in the middle of what is still farmland on arguably part of the most problematic stretch of the San Joaquin River.

The levees are stronger than what are protecting nearby areas. And they are more robust than what is protecting Stockton.

At the same time, River Islands has stepped up to be part of a regional solution to reduce flooding potential.

They gave up 300 acres plus that could easily have allowed 2,000 more housing units to be built so Paradise Cut can be widen when state officials get around to putting that plan in place to make the area a bypass of the main channel for flood control.

They also invested upwards of $2 million In strengthening levees across Interstate 5 where there is a sand pit operation.

The levees at Stewart Tract are the direct result of two things:

*They were done with a clean slate in terms of no existing development of consequence allowing the master planning of the  4,800 acres from scratch.

*A developer who had the long-range commitment and the means to do so.

“River Islands homeowners pay more,” Dell Osso said, while noting they are getting the level of basics and amenities they need/want.

 

To contact Dennis Wyatt, email dwyatt@mantecabulletin.com

 

.