This rainy season, people who know that I’m a hydrologist increasingly press me: “So, have you had enough of this rain yet?” At the risk of seeming callous, my answer is no.
“But our reservoirs are full and our rivers are nearly flooding!”
It’s true that our surface supplies have been temporarily restored by this rainy season, but we need more than an average rainfall year to make up the deficits that have accumulated underground in soils and aquifers as a result of the extended drought. Our below-ground water is invisible, and yet that is the supply that we use during drought emergencies.
Data from the U.S. Geological Survey show that within the drought window from 2012 to 2015, our soils never got fully recharged with water to what might be considered “normal” conditions. Instead, like a bank account, they remained overdrawn, in the red relative to soil moisture. So while in our human memories the drought may be fading away, in our landscape its presence remains felt. The combination of extremes is part of why we see trees falling all over the county — trees weakened by drought and then knocked out by storms.
One of the real flood protection challenges facing Sonoma County is that much of our infrastructure was originally designed to support homes for summer use, when the creeks barely dribble and even the main stem of the Russian River just whispers by. In the hills, it was easier to put the roads in flood plains, the flat zones carved by peak flows next to streams. The cool-shaded stream zones also attracted people to build their homes there. By building in floodplains, we forced the water into smaller and smaller areas. In turn, the deeper and narrower flows increase the force of erosion, creating a destructive feedback that further erodes river and stream channels and accelerates flood peaks downstream.
So, to some extent, we are feeling the bite of unintended consequences associated with “drain and reclaim” land and water practices that started with the early American settlers.
The paradox is that climate projections suggest our water may arrive in bigger and bigger storms. In order to get the water we need to survive — given our unique combination of climate, geology and the modifications we have made as humans — more flash flooding in the future seems pretty inevitable to me. Now science confirms the interconnectedness of our surface and groundwater supplies and that it is imperative that we protect and restore our floodplains to slow down floodwaters and facilitate groundwater recharge (the process by which water infiltrates into the ground).
Many local jurisdictions are in the process of exploring and advancing innovative ways to manage storm water. We have to support our local government leaders in investing in maintenance and upgrades to meet this challenge and to protect those at risk. If there’s a lesson from our neighbors impacted by the near failure of the Oroville Dam, it’s that our mid-20th century feats of engineering now need to be updated based on advances in our scientific understanding of the hydrologic cycle. Beyond maintenance, we need to move to the next stage of refining and modernizing our water infrastructure to work with nature instead of against it — and, in the process, waste as few drops as possible.