Water

Greening can be central to increasing water supplies, reducing water use, improving water quality, and even supporting flood management.

All life depends on water. For the millions of residents of our great metropolitan area, protected mountains, unpaved land, monumental dams, vast basins, and intricate canals and conveyance systemsallow water to be delivered to our taps from both local sources and vast distances.

Approximately 2.26 million acre-feet (football fields one foot deep in water)—735 billion gallons—flow across the Los Angeles Basin in an average year. About 1/10th of this quantity is in the form of urban irrigation. 66% of the total is evaporated or breathed out of plants, 8% is absorbed into the ground, and 26% is channeled out to the ocean [1].

Into the early 1960s, more than 80% of the region’s rainfall is estimated to have been absorbed into the ground or evaporated [2]. Now, the amount of water absorbed is less than 50% of this figure, and evaporation may be even greater with prolonged exposure as runoff over impermeable surfaces.

Effectively, the rainwater that falls on the region flows quickly out to sea. However, even with systems designed to drain water away as quickly as possible, about 40–45% of water is still supplied from local sources [3], in some cities more and in others less. In the words of Dorothy Green, “We have enough to live on, but not enough to waste” [4]. At the same time, almost all waterways in Los Angeles County are considered impaired due to contamination and pollution from runoff. Across the region less than 5% of our original wetlands remain [5].

Given climate challenges—challenges for drought and water security, water quality, flooding, and biodiversity—there are growing imperatives to manage water resources better and differently.During the last century, when concrete flood control channels took the place of naturally flowing rivers, our relationship with local rivers as natural and living resources was broken. Buildings, streets, and parking lots now populate the floodplains that once supported scented scrubland and clusters of oak, sycamore, and willow woodlands, tidal lagoons, and coastal wetlands teeming with life [6]. Roofs, driveways, parking lots, and streets have dramatically reduced the amount of open land capable of naturally cleansing, capturing and infiltrating the rainwater. 

Yet nature is still at work in even in the middle of our cities. Our yards, parks, and open spaces quietly continue to do the work of a porous river floodplain, whose job is collecting, cleansing, and infiltrating water. We can help the floodplain by looking for more opportunities to allow it to cleanse and infiltrate water. Our city streets, which convey floodwaters to our rivers, can be adapted to help cleanse polluted water. We can pave less and grade earth not to drain but instead to capture water to irrigate landscapes, reduce runoff, passively irrigate landscapes, and even support groundwater supplies where water can infiltrate into groundwater aquifers. Working with nature is a relatively inexpensive way to increase our water supply and water quality, but nature needs our help. 

By incorporating nature-based systems back into our homes, neighborhoods, and cities, we can better cleanse, infiltrate, and use water locally, restore balance to our water system, increase access to the benefits of nature, and reconnect once again with our rivers. Each of us has a role to play in this transformation. Slowing and absorbing stormwater can also impact flooding. There is a point in every storm where there is a greatest amount of water flowing—this is known as peak flow. This is the point at which the most damage may be expected at any given location. Across an entire watershed when water is slowed down and absorbed, rather than drained and channelized, time to peak and volume of peaks may be reduced. Healthy soil alone can increase water infiltration and hold up to 20 times its weight in water [7].

The USGS projects an ARkStorm (atmospheric river 1,000-year storm) scenario like that of 1861 could generate losses three times greater than the largest possible earthquake, and has an equal opportunity of occuring [8]. Disasters exceeding $1 billion dollars have nearly doubled across the US in recent years including droughts and floods, and impacts have steadily grown. Between 1980 and 1989 the average cost was $17.8 billion. Between 2017 and 2019 the average cost was $153.6 billion [9]. However, according to the National Institute of Building Sciences every $1 spent on proactive measures can save $6 in reactive disaster costs [10].

A first step for all of these potential benefits is to see that even in the middle of the city, we are all connected to our rivers and part of a shared watershed.

[1] Hevesi and Johnson. 2016. Estimating spatially and temporally varying recharge and runoff from precipitation and urban irrigation in the Los Angeles Basin, California. Scientific Investigations Report 2016–5068. U.S. Geological Survey. 

[2] Dallman, S. and T. Piechota . 2010. Stormwater: Asset, Not Liability. Los Angeles, CA: Council for Watershed Health.

[3] Porse, Mika, Litvak et. al.. 2018. The economic value of local water supplies in Los Angeles. Nature Sustainability.

[4] Green, Dorothy. 2008. A heartfelt plea for a sensible water policy. Los Angeles Times. Accessed from: https://www.latimes.com/la-oe-green8-2008oct08-story.html

[5] Faber et. al. 1989. The ecology of riparian habitats of the southern California coastal region: A community profile. Biological Report 85 (7.27). US Department of the Interior Fish and Wildlife Service.

[6] Grossinger, Sutula, Stein et. al.. 2007. Historical Ecology and Landscape Change of the San Gabriel River and Floodplain. 

[7] California Department of Food and Agriculture. 2018. Healthy Soils Initiative. 

[8] Porter, K. et al. 2011. Overview of the ARkStorm Scenario. U.S. Geological Survey Open-File Report 2010-1312. 

[9] US National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information (NCEI). 2020. U.S. Billion-Dollar Weather and Climate Disasters. 

[10] Multihazard Mitigation Council. 2017. National Hazard Mitigation Saves: 2017 Interim Report: An Independent Study. Washington, DC: National Institute of Building Sciences.