Editorial: Houston’s floods are a warning for California to shore up its water systems. The good news: We’re getting started.

Southern Californians have to prepare for earthquakes and drought, but thankfully we will never have to deal with Houston-type flooding.

Or will we? Like Houston, Los Angeles is built on a floodplain. The whole reason the Los Angeles River is encased in concrete is to protect against the kind of terrifying, deadly flooding that raged through the region in 1938, caused by a storm the likes of which is expected only once every 50 years. Hurricane Harvey has been variously called a 500-year and a 1,000-year event, so it’s important to remember that in L.A.’s short history, we haven’t yet seen anything like that kind of a deluge. That doesn’t mean it’s not coming.

L.A.’s focus in recent years has been on drought and water shortages, which look like the polar opposites of flooding. In the 20th century, the different challenges of supplying the city with water and protecting against floods meant two very different engineering solutions: a network of storm drains feeding cement-paved rivers to get all that dirty floodwater out to the ocean as quickly as possible, and simultaneously a network of aqueducts to get clean Sierra and Rocky Mountain snowmelt to the city as quickly as possible. These were accompanied by a third feat of engineering genius to meet a third challenge: a separate sewer system that, unlike the combined sewage-and-storm drain systems once common in Eastern cities, did not cough up human waste whenever a rainstorm hit, but instead directed sewage into treatment plants that cleaned it just enough to allow it to be dumped into the ocean.

Three different goals, three different public works agencies (Department of Water and Power, county Flood Control District, Bureau of Sanitation), three different mind-sets, three different funding sources. But surely it should be possible to plan and build integrated systems that have multiple benefits and meet multiple goals — and don’t work against each other or cost three times as much in taxes or bond funding.

That ought to be, and increasingly is, the 21st century model. In Los Angeles, the three agencies are working on plans to make each of their systems more efficient and effective by planning and building jointly. Some crazy ideas — such as huge cisterns in backyards filled by storm runoff and emptied into the aquifer when it needs to be replenished, or carefully constructed creeks that lead to settling basins where rainwater and runoff can be cleansed for reuse — turn out not to be quite so crazy. A lot is riding on whether those sorts of projects can move Los Angeles to water self-sufficiency in a timely and affordable manner.

Affordable? There was a saying, popular in public works circles in the late 20th century, that still has some currency: The four most expensive words in engineering are, “While we’re at it.” In other words, since we’re already renovating the kitchen, why don’t we add a bathroom? Since we’re already building one new dam, why not two? Costs jump along with ambitions.

But in the 21st century, “while we’re at it” may be the most cost-effective words. We should make sure that our new water delivery system also wards against flooding, restores fisheries, cleans the bay — in short, that it does all the things we’d eventually be required to do anyway because of the demands of nature, law or lawsuit — and does those things in an integrated fashion.

In late August, a Sacramento-based agency called the Central Valley Flood Protection Board adopted a new flood management strategy that departs from the old model of just raising levees to meet the challenge of greater flood risk. In a model of smart, joint planning among interests that too often work against each other, environmentalists and flood engineers collaborated on a plan that restores ecosystem health along the San Joaquin River and replenishes the groundwater, which in turn stabilizes supplies for the State Water Project.

Why should Southern Californians care?

Because we drink that State Water Project water and have a vital interest, to say the least, in making sure it doesn’t run out, and that it is not contaminated or lost by levee failures in the distant (to us) Sacramento-San Joaquin River Delta due to rising sea level. Meanwhile, we have a vital interest in our own locally captured, stored and consumed water, and should take hope and inspiration from the little-discussed but crucially important Central Valley plan. The proper test when considering new water bonds (which we are likely to see on the ballot next year), new taxes and new projects is whether they try to accomplish just one thing, in last century’s mold, or instead to fit into a many-faceted 21st century framework that does many things simultaneously: securing our supplies, sustaining our environment and keeping us safe during Houston-style calamities.

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