California is currently experiencing severe drought, with the water years 2012–14 being the driest three-year period in history. The state’s response to multi-year droughts, on a municipal level, is based on water conservation. This reactive approach is responsible, yet it does not produce more water.
The collection of rainwater on a square-mile scale may be a solution to ease severe droughts. Billions of gallons of water could be collected this way.
Let’s look at the city of Sacramento as an example. Sacramento acquires 84 percent of its drinking water from the American and Sacramento rivers and 16 percent from groundwater. Both resources are dependent upon precipitation. In times of drought, demand exceeds precipitation.
Areas of high precipitation in the coastal regions of Washington, Oregon and California are potential resources for potable water. Some of these regions receive more than 100 inches of rain per year. Volumetrically, 100 inches of rain over one square mile accounts for 1.74 billion gallons of water.
Specifically, areas of Del Norte County, California, can receive in excess of 100 inches of rainfall per year. In 2012, the Gasquet Ranger Station outside of Crescent City, California, recorded 124.13 inches of rain. This rainfall over a single square mile equals 2.16 billion gallons of water.
In 2008, average daily water consumption by the city of Sacramento was 118 million gallons per day (MGD), with an estimated 70 percent (82.6 MGD) used by private homes. Of the 82.6 MGD accounted for by residential use, about 40 MGD was used indoors. Thus, indoor residential water use in the city of Sacramento was 14.6 billion gallons for 2008.
Therefore, rainfall around Crescent City in 2012 over one square mile would have met almost 15 percent of Sacramento’s indoor residential water demands.
As a long-term investment to ease drought, the city of Sacramento should consider purchasing large tracts of land in areas of California that receive high rainfall, specifically Del Norte County. A “rain farm” on a square-mile scale is possible. It is important to note that a square mile is only 640 acres, or a few golf courses, or less than half of Chico Municipal Airport.
Contouring the land surface with a food-grade plastic of a few millimeters thickness would suffice as the main component of a catchment system. Grading the land and piping the water out would be a matter of creative engineering.
The collected rainfall could be pumped to Trinity Lake, which is connected via a U.S. Bureau of Reclamation pipeline and tunnel system to the Sacramento River.
Though it is feasible, there are certainly barriers to this idea.
One probable concern is the water stolen from streams and rivers. In response, it is important to note the majority of Del Norte County loses 46.3 inches of rain per year to evapotranspiration. Therefore, assuming rainfall is collected over a square mile in Del Norte County, 800 million gallons of water would be gained that would otherwise be lost to evapotranspiration.
Further, collecting rainfall from a small area would be much less taxing on the ecosystem and basin of the Smith River than a dam. The Smith River is not currently dammed and there is no reason in the world why it should be. However, I think collecting rain is a fantastic environmental compromise.
There also are legal issues. State law allows residential collection of rainwater if it does not need an engineering permit or affect agriculture. The state hasn’t planned for rainwater collection on this scale, and it would be considered a special case. My proposal will definitely require an engineering permit.
Another concern is the environmental cost of diverting rain from an entire square mile of habitat. Desertification of the collection area should be minimized as much as possible. Initial ideas include: using a rocky valley as the collection area; designing the catchment system to have permeable sections every few hundred feet; or alternating collection areas seasonally or annually.
Large tracts of land are utilized for agriculture, livestock and solar energy, and rain collection should be no different. Occupying one or two square miles to collect rainfall from an area that is 1,230 square miles (the approximate area of Del Norte County) is using only 0.08–0.16 percent of available land to provide water for the nearly 500,000 people in Sacramento.
Of course, compromise is crucial. We already have large areas of land throughout California that are effectively desertified by pavement, such as Pelican Bay State Prison (located in Del Norte County), not to mention thousands of shopping centers.
There are no examples of this kind of water system anywhere in the world from which to draw lessons. There are risks and challenges involved. But large-scale rainwater collection could become another technology that California pioneers for the world.