Part of Manteca’s future water supply may be heaven sent.
No surprise there given the water that seeps into aquifers and flows into reservoirs falls to earth in the form of water and snow.
But there’s an untapped water source — providing Mother Mature cooperates.
That water source is rainfall in Manteca.
In an average year Manteca receives 14.06 inches of rain. Given the city has 17.76 square miles that translates into 11,316.4 acres. It means the skies soak Manteca with the equivalent of 79 percent of its current water use.
While large sums of that rain is absorbed by vegetation and in the soil — especially large fields and farmland within the city limits — rainfall when it is significant enough to flow into storm drains represents a way to not only recharge groundwater to meet new state requirements but it could be harnessed for domestic use.
The rain water that flows into storm drains and is temporarily held in storm retention basins now ultimately is sent to the San Joaquin River.
The just adopted update of Manteca’s urban water management plan doesn’t contain a strategy for capturing storm runoff. The plan does note that the city has infrastructure in place that could turn storm water into a source for domestic uses. It includes 170 miles of pipeline, 36 pump stations, and 35 detention basins.
A growing number of cities in the Los Angeles Basin are encouraging homeowners to harvest rainwater via the use of rain barrels and cisterns — Stone Age solutions in an Internet Age of water shortages.
That is in addition to cities becoming more aggressive as well. In the unincorporated community of Sun Valley, Los Angeles County is working to capture nearly all the rainfall that falls on the neighborhood to supply the domestic needs of 4,000 residents in a total year. They are doing putting infrastructure in place beneath a proposed 4- acre park that will be created where there is an existing gravel pit and concrete plant.
Keeping water from rain
out of storm runoff system
In Manteca there have been modest efforts at recharging the groundwater primarily to solve issues related to storm water runoff and capacity concerns of existing pipes or to avoid costly projects to increase the size of pipes.
The largest is a series of large perforated massive culvert-style pipe buried behind where Panera Bread is located today on East Yosemite Avenue.
It was put in place to address what to do with runoff that would be created when the overall parcel that was connected to the original project to build the Manteca Strike Zone bowling alley is developed. The late Antone Raymus at one point envisioned a convention center and hotel on the land. That level of development, though, would have created runoff that would have taxed the existing storm lines that served an area that had already been built out for the most part. An above ground storm retention basin would have made the project unfeasible by chewing up too much land.
There are modest French drains — primarily rock either at the surface as the city did at the Moffat Community Center/Manteca Veterans Center or just below the surface as they did on an infill residential project on Edison Street at Lincoln Avenue. A larger French drain is being incorporated into the design of a small affordable neighborhood Raymus Homes is building along Airport Way, north of East Yosemite Avenue and adjacent to Camellia Gardens.
More French drains would help recharge the groundwater and help meet a state mandate that municipalities and others that use well water in any given year not to withdraw more water than flows into groundwater basins.
It also addresses federal mandate that requires most — if not all — runoff from new development not to run-off.
has been stable since 2006
The decision by the City of Manteca to opt for surface water in 2006 from the Nick DeGroot South County Surface Water Treatment Plant took Manteca from relying 100 percent on groundwater to just 52 percent today.
That has allowed the groundwater basin serving Manteca to remain stable including during the drought while basins others are drawing from are dropping. Ripon, for an example, has its groundwater source dropping by about a foot a year.
Manteca has 15 potable wells and 31 irrigation wells.
The advent of the city strategy to put in place shallow wells that tap into higher groundwater that generally isn’t suitable for drinking is accomplishing two goals. It has reduced the use of expensive drinking water to irrigate parks and such by 1,610 acre feet of water a year. It also has helped improve pressure throughout the city especially in mornings when people are getting up to get ready to go to work while parks are still be irrigated.
Manteca, overall in 2014, used 12,844 acre feet of water. Single family homes accounted for 7,468 acre feet with about half of that going to residential landscaping. Municipal landscaping — primarily parks — consumed 2,210 acre feet including 1,610 acre feet of non-potable water. Commercial was the next biggest user at 1,043 acre feet followed by multi-family units at 964 acre feet, other uses at 800 acre feet, industria, at 235 acre feet, government/institutional at 66 acre feet and losses through pipe leaks and such at 55 acre feet.
An acre foot is the amount of water that would cover a standard football field in a foot of water.
To contact Dennis Wyatt, email firstname.lastname@example.org