How California can capture water from atmospheric river

California has seen so much rain in the last few weeks that farm fields are inundated and normally dry creeks and drainage ditches have become torrents of water racing toward the ocean. At the same time, most of the state is still in severe drought.

Why can't more rainwater be collected and stored for the long, dry spring and summer when it's needed?

As a hydrogeologist, I'm interested in what can be done to collect runoff from storms. There are two primary sources for largescale water storage that could help make a dent in the drought: Storing it behind dams and in the ground.

When California gets storms like this, water managers are probably shaking their head and asking, “Why can't we hold on to more of that water?” The reality is, it's a complicated issue.

California has big dams and reservoirs that can store large volumes of water, but they tend to be in the mountains. And once they're near capacity, water has to be released. A lot of that water is going to the ocean.

In more populated areas, one of the reasons stormwater runoff isn't automatically collected is because the first runoff from roads is often contaminated. Flooding also can cause septic system overflows.

You might say, well, the captured water doesn't have to be drinking water, we could just use it in parks, golf courses and strips along highways. But then you would need a place to store the water and you would need a way to distribute it.

There's another option, and that's to put it in the ground where it could help to replenish groundwater supplies.

The process is called

managed recharge and it has been used for decades. The techniques have been gaining more attention lately as wells run dry amid the long-running drought. More than 340 local recharge projects in California have been proposed and the state estimates they could store an additional 500,000 acrefeet of water.

One method being discussed by the state Department of Water Resources is Flood-mar, or floodmanaged aquifer recharge. When there are big flows in rivers, managers could divert some of that flow onto large parts of the landscape and inundate thousands of acres to recharge the aquifers. The concept is to flood the land in winter and farm in summer.

Flood-mar is promising, provided we can find people who are willing to inundate their land

and secure water rights. You could inundate 1,000 acres on a ranch and a lot of it might stay flooded for days or weeks. Depending on how quickly that water soaks in, some crops will be OK, but other crops could be harmed. There are also concerns about creating habitat that encourages pests or risks food safety.

Another challenge is that most of the big river flows are in the northern part of the state and many of the areas experiencing the worst groundwater

deficits are in Central and Southern California. To get that excess water to the places that need it requires transport and distribution, which can be complex and expensive.

In the Pajaro Valley, regional colleagues and I are trying a different type of groundwater recharge project where there is a lot of runoff from hill slopes during big storms.

One program in the Pajaro Valley encourages landowners to participate in recharge projects

by giving them a rebate on the fee they pay for water use through a “recharge net metering” mechanism. We did a cost-benefit analysis of this approach and found that even when you add in all the capital costs for construction and hauling away some soil, the costs are competitive with finding alternative supplies of water and cheaper than desalination or water recycling.

In any case, it's going to take many methods and several wet years to make

up for a long period of low rainfall. One storm certainly doesn't do it and even one wet year doesn't do it.

For basins that are dependent on groundwater, the recharge process takes years. If this is the last rainstorm of this season, a month from now we could in trouble again.