California flooding : a water principles perspective
Coupling groundwater, surface water, and atmospheric water via land cover
I was working on finding, and writing about, a set of water principles that could unify our knowledge of the water system, a continuation of a collective project I initiated a year and a bit ago, when California, which was still reeling from previous years of drought and fire, was hit by atmospheric river after atmospheric river. Levees broke, mud slid, towns flooded, and many people, including some of my friends, were left scrambling.
I decided to instead switch to writing about the floods this week. I would use, to explain the situation, a subset of the water principles I had been working on. These principles illustrate how a properly functioning eco-water system would dampen the extreme water behavior, i.e. floods and droughts, and explain how places like Australia, South Africa, Brazil, British Colombia, Greece who have all been experiencing the drought-fire-flood feedback loop, can get out of this disaster cycle.
Here are some of the relevant water principles to the drought-fire-flood situation:
Increasing the ability of land to slow, spread and sink water, dampens surface water variability
Groundwater, surface water, and atmospheric water are coupled via land cover
When the coupling works well it dampens surface water extremes (like floods and dryed out landscapes) and atmospheric water extremes (like too much rain or too little rain)
When the carbon cycle couples well with the water cycle, the eco-climate system evolves to dampen water extremes via increasing soil absorbency and biodiversity.
The drought-fire-flood feedback loop is conditional.
1. Ability of land to slow, spread, sink and store water dampens surface water variability.
The more water that can be slowed, spread, sunk, and stored higher in the landscape, the less flooding happens below. Forests, grasslands, wetlands, floodplains slow and absorb stormwaters. Soil can slow and absorb water; the more organic content in the soil, the more air pockets it has, and the more it can absorb water. Rivers can overflow banks, and slow in the adjacent floodplains and wetlands.
Levees, roads, concrete on the other hand, lessen the ability of the land to slow and absorb water. Levees increase river velocity, and increase downstream flood probability during extreme rain events. Roads channelize the water to accumulate in lower areas. Concrete repels water.
A key switch California can make in regards to the flood prevention, is to decrease the paving over of nature, decrease levees and dams, and increase the restoration of the ecosystem.
If surface water is spread out over more of the landscape, surface water has less variability spatially.
If water is sunk away from the surface during times of much surface water, and returned to the surface (via springs and rivers) during times of lack of surface water, then the surface water has less variability temporally.
In the Mississipi engineers have removed levees and restored floodplains so the river can overflow sideways, spreading the spatial variability laterally so that less of it builds up downriver.
In China’s sponge city concept now underway in 30 Chinese cities, they have implemented multiple nature based solutions of slowing, sinking, and spreading the rains with bioswales next to roads, turning roads and developed land back into floodplains, digging wetlands.
California used to have many more wetlands which were able to slow and absorb floodwaters, bring back some of these will help with lessening flooding.
2. Groundwater, surface water, and atmospheric water are coupled via land cover
Land cover is the physical material at the surface of the earth - vegetation, soil, bare ground, earthworks, concrete. And it is the connective tissue that couples the different domains of water - groundwater, surface water, and atmospheric water, together.
Land cover affects how surface water becomes groundwater via soil infiltration and tree roots pushing the water down (hydraulic redistribution). Land cover affects how groundwater becomes surface water by tree roots and mycelia pulling up the water (also part of hydraulic redistribution). Land cover affects how surface water becomes atmospheric water by vegetation and soil evapotranspiring it. Land cover affects how atmospheric water becomes surface water by seeding rain nucleation with airborne bacteria and fungi spores, and by changing the air temperature through evapotranspirational cooling. Land cover couples with the three altitudes of water, weaving it into a self-organizing system.
In working on various sets of water principles I have been considering different formulations of each principle. Another formulation of this principle could be “Small water cycle and hi-lo cycle are coupled”, or “Large water cycle, small water cycle, and hi-lo cycle are coupled”. The large water cycle is where water vapor blows in from the ocean, turns into rain, and then flows out back to the ocean via rivers. The hi-lo cycle is the name I gave (I considered the name deep water cycle, but that sounds too much like an ocean water cycle) to the groundwater-atmospheric water cycle (see the 52 min mark of my interview with hydroclimatologist Francina Dominguez on this)
3. When the coupling works well it dampens surface water extremes and atmospheric water extremes
The system works best to lessen water during times of large surface water (floods) if the soil can absorb more water, and if there are more tree roots to push down the water. The system works best to increase water during times of little surface water (droughts) if there are enough deep tree roots and mycelia to pull the groundwater up, and if there is enough groundwater that the tree roots can reach it. The system also works best in this situation, if some of the rain that infiltrates underground in wet season comes out as springs and rivers during times of drought.
If during floods, rivers are allowed to overflow into floodplains, then there is much more area over which the water can descend from being surface water to becoming aquifer water. Lateral lessening of surface water spatial variability (spreading) helps with the coupling between surface water and groundwater.
The system works best to lessen rain during times of large rain events, if the soil can absorb water to take it out of the small water cycle. The system works best to increase rain during times of little rain, if there is enough soil moisture and groundwater, and enough vegetation to evapotranspire that water into the atmosphere.
I believe large rain events can be lessened in size. The reasoning has to do with the idea that during large rain events, secondary rain is created by the rains falling to the ground, evapotranspiring, and then creating more rain. If you can get rid of some of this secondary rain, then the amount of rain decreases.
Imagine two scenarios, one where you are pouring water into a bowl, and another where you are pouring the same amount of water onto a sponge which soaks it up. Which do you think would emit less water vapor initally? ……….. The answer is that the sponge will emit less water vapor. By analogy, an absorbent soil sponge, will evapotranspire less and create less secondary rain.
Key to having the coupled water system work is get enough groundwater into the aquifers, so that the tree roots can reach them. In California groundwater has been vastly overdrawn. If California removed many of its levees, and deconstructed some of its 1500 dams, then the rivers would be able to overflow into the floodplains, form wetlands, and allow a lot more water to then be able to sink down into the aquifers.
Hydrology professor Helen Dahlke has been working with Californian farmers to flood their farmers in wet times to have the water move downwards, so they can bring the water up from the aquifers in dry times. (See my podcast interview with her here). We can also funnel water into ‘paleo’ valleys in California to recharge aquifers below. (See Erica Gies article on this in the New York Times). If we can refill the groundwater enough in California during wet years, then nature is able to use that groundwater to increase surface water during the dry years.
The resiliency of a system is defined by its ability to absorb impacts. Extreme rain and extreme drought are impacts. When the various parts of the water system are coupled properly by the biology, then an ecosystem’s resiliency increases.
Measurements in the Amazon show that about 10% of the rains can be pushed down by tree roots, and 10% brought up. This leads to about a lessening of 10% variation of water extremes.
4. When the carbon cycle couples well with the water cycle, the eco-climate system evolves to dampen water extremes via increasing soil absorbency and biodiversity.
When the carbon cycle is coupled well with the water cycle, the carbon cycle evolves to create more soil and vegetation, which in turn, then helps regulate the water cycle to create even more soil and vegetation.
As the carbon cycle diversifies, more biodiversity develops, more seed propagation pathways emerge, via birds and squirrels and butterflies, and more nutrient pathways grow, via animals eating plants and other animals and their poop fertilizing the landscape. As the landscape is filled with an ever richer array of carbon-based matter and organisms, the ability of the landscape to slow, sink, spread, store, and lift water around to where it is needed, increases.
In California, the Ventura River flooded. The Ventura River is usually bare, wide and dry, with listless dirt, and only a smattering of vegetation. If the Ventura River had more vegetation and trees, the stormwaters could have slowed and been absorbed further uphill, leading to less flooding downhill.
The carbon-water cycle to restore Ventura’s water health, can be jump started by revegetating the river basin higher up, where the vegetation can slow smaller rains when they happen, and then use that water to help further grow the riparian ecosystem. In addition with enough revegetating and repairing of the soil in the mountains, rain water will seep into the ground during the wet season, and then come out lower in the landscape in the dry season to help keep the riparian vegetation hydrated. As more riparian vegetation grows it will help guide more water into the aquifers below. At some point, groundwater may increase high enough that the tree roots and mycelia can tap into it to bring up water to hydrate the landscape. Some of this water will then evapotranspire into the air, which will increase the probability of rain in the usually dry Ventura area. The hydrologist Michal Kravcik, has done calculations that show its possible to increase rain in Ventura when eco-hydro-restoration happens. This rain can further help grow the vegetation in the area, which then further helps rainwater get guided into the aquifers. Its an ever increasing cycle. New habitats may appear, like vernal pools, which increase biodiversity. This biodiversity may then help with generating better soil, creating new seed pathways, and establishing new nutrient pathways; all of which then further increase vegetation with its ability to slow floodwaters in wet times, and increase rain in dry times.
5. The drought-fire-flood feedback loop is conditional.
Droughts dry up the vegetation and soil which makes fires more likely. Fires destroy vegetation and soil, making floods and landslides more likely when big rains come. Floods wash away the topsoil, so that it cannot absorb and store the rain in wet season to hydrate the landscape and increase rain when droughts come.
Its key after fires in recent years, to help regenerate land cover more quickly with techniques from the likes of permaculture and agroecology, mulching, cover cropping, composting, mycelia inoculation etc, so that floods and landslides are less likely. It would save the government a lot of money to work in a timely manner with these ecological friendly flood protection measures.
Montecito, a township in Santa Barbara, California was hit by floods and had to be evacuated. The floods were due in part to the fires a few years back that had burnt down trees, and weakened the soil. A concerted effort then to restore the ecology could have lessened the floods and landslides.
After floods its also important to regenerate the lands ecologically, so they are better able to store rains in the soil and the aquifers for when dry season hits.
The keys to extracting ourselves out of the drought-fire-flood cycle is growing land cover to slow the rain, and increasing the groundwater-surface water-atmospheric water coupling, the carbon-water coupling, and the ecological succession-water evolution coupling.
Much of what Alpha describes in the benefits of beaver dams, plant and tree root/soil interaction, revegetated river beds, and the spreading of flood waters onto plains for groundwater recharge is essentially the physics of energy dissipation. Slowing the water dissipates the energy. This is the same principle behind the benefits of mangroves to dissipate coastal storm surge flooding.
The topography of California unfortunately includes mountain ranges with deep river canyons depositing flow onto coastal plains and valleys which are overdeveloped by industrial scale agriculture and urban areas. Energy is channelized until banks are topped and levees breached.
Portions of Southern California’s coastal mountain ranges and hills are shale which can have unfavorable bedding planes from faulting and uplift over the last 10 to 15 million years. Picture this as a layer cake or lasagna tilted at 45 degrees or steeper. When angled in the downhill direction, this geologic structure is subject to slope instability. This condition is worsened by heavy saturation top soils and slopes left barren by wildfire. It is also caused by poor grading and land development practices. Much of the property damage to structures and roads from mudslides and landslides shown in the news after storms can be attributed to this. The unfavorable bedding planes are most predominant in western Los Angeles, Ventura, and Santa Barbara Counties.