Editorial: How to make the most of rainfall
How much rain has fallen in Ventura County over the last week? More than enough to meet the needs of every person, business, strawberry field, avocado grove and irrigated urban landscape in the county for an entire year.
One can arrive at that conclusion by multiplying the number of acres in the county (1.4 million) by a countywide average of 4 inches of rainfall. The amount of water dropped from the sky, then, would be 471,000 acre-feet. Average annual water use in the county, agricultural and urban combined, is about 445,000 acre-feet.
Other than as a parlor game, there isn’t much value to be found in such a calculation — but it does highlight the significant potential of capturing the runoff from the storms California has experienced over the last few weeks.
The potential is especially significant in places such as Ventura County that are highly dependent on groundwater, which supplies nearly two-thirds of the county’s agricultural and urban water demands. Nearly everywhere in the county, rain that falls and collects on soil contributes to replenishing precious groundwater supplies. That which falls on rooftops, roadways, parking lots and other impervious surfaces does not.
An analysis by the Pacific Institute and the Natural Resources Defense Council estimates that in urban areas of Southern California and the San Francisco Bay Area that overlay groundwater basins, up to 440,000 acre-feet of runoff could be captured and stored for use each year.
Much of that could be accomplished through relatively simple public and private actions — retrofitting parking lots and streets to direct runoff to landscaped medians, parks or other open spaces, for instance, or redirecting downspouts to flow into landscaped areas. Simply harvesting rooftop rainwater from residential housing through devices as simple as rain barrels, the analysis finds, could yield up to 145,000 acre-feet per year for irrigation, toilet-flushing or other non-potable uses.
There is also the potential for projects on a larger scale, as is evidenced by the project completed in 2020 by the County of Ventura and the United Water Conservation District in Piru.
That project captures and treats stormwater runoff from all 36 urban acres in the Piru community. Trash and other pollutants are removed by a separation unit and then piped to the water district’s spreading ground to recharge the Piru Groundwater Basin. The scale of capture is modest — just an estimated 17 acre-feet per year, but the supply is a sustainable addition to the local water supply and in addition the project substantially improves the water quality of Piru Creek, a major tributary of the Santa Clara River.
Water in the Santa Clara River downstream from Piru does not meet federal bacterial objectives, and discharges from urban areas are a major source of that contamination.
The best time to think and act on such projects, of course, is not when the rain is falling and water is flowing into storm drains. It is when the skies are clear, the days are hot, and we’re all wondering whether there will be enough water to get us through.
It remains to be seen how long this series of winter storms will continue and, thus, whether they will significantly ease this state’s severe and prolonged drought. There is, after all, a very substantial deficit to make up — as of Thursday afternoon, Lake Casitas was still at less than 40% of capacity.
These storms are welcome, however, and they provide a reminder that some may have forgotten during this long drought: When rain comes in Southern California, it typically comes in bunches. And when that happens, we should be prepared to make the most of it.
This article originally appeared on Ventura County Star: Editorial: How to make the most of rainfall
