The Power of the Watershed Approach for floodplain management

The Power of the Watershed Approach for floodplain management

by John Cobourn, Extension Water Specialist, University of Nevada Cooperative Extension

One truism often repeated is that droughts end with major floods.  Although every major flood may not be the end of a drought, some of Nevada's river systems have had significant flooding, leading to extensive and long lasting damage (http://pubs.usgs.gov/fs/1997/0182/report.pdf).

I have said that community water issues can be best understood in the context of the whole watershed. I also stated that on the Carson River in Nevada, the Carson Water Subconservancy District (CWSD) sponsors a community watershed group called the Carson River Coalition (CRC). It views all issues in the watershed in terms of integrated watershed management (IWM). This approach says problems with water quality, water supply, fish and wildlife habitat and floodplain management should be addressed in an integrated fashion.

Through a consensus process, the CRC has designated its most important single issue, the Main Message of the Coalition, to be protecting natural floodplains from urban development. (www.unce.unr.edu/publications/files/nr/2004/fs0471.pdf) This is a good example of the power of the watershed approach. Urban development on low-lying river floodplains puts the infrastructure built there at risk of damage from the very large floods that occur every fifteen years or so.  It also converts valuable agricultural land to pavement and rooftops, and it destroys wildlife habitat.

After large floods cause damage to homes or businesses, communities generally build levees along the river channel to protect infrastructure. After a few cycles of larger floods, higher levees and more development, the river could be put in an extremely expensive concrete-lined ditch, like the Los Angeles River.  The wildlife habitat will be lost, and recharge of groundwater aquifers will be reduced. The water quality will often be that of urban stormwater runoff, which tends to be poor.

Since everything in a watershed is interconnected, the CRC does not want to solve a flooding problem in ways that would create water quality or wildlife habitat problems. To preserve the natural functions and values of the river and its floodplain, they recommend using floodplains for agriculture, parks and other open space uses. Keep residences and businesses out of the floodplain, and there will be fewer flooding problems. The CRC’s recommendations for floodplain management can be viewed in the Carson River Watershed Regional Floodplain Management Plan (http://www.cwsd.org/wp-content/uploads/2014/07/FinalDraftfloodplainplan7-08.pdf)

Walker River flooding in 1997 devastated this section of
Route 395 in California, leading to years of road repair and

reconstruction. Photo from
http://monosheriff.org/sheriff/page/emergency-services
 

Learn more about Nevada’s flood hazards at www.Nevadafloods.org. Nevada’s Flood Awareness Week runs from November 1-7, 2015.

Watersheds and why they are important

Contributed by John Cobourn,
Area Water Specialist,
University of Nevada Cooperative Extension





Tau-Gu,Chief of the Paiutes and John Wesley
Powell overlooking the Virgin River, 1873



John Wesley Powell, the first director of the US Geological Survey and the first man to lead a boat expedition down the Grand Canyon, proposed that all political boundaries in the American West should be established along watershed divides. Powell believed that watersheds—also known as basins--are natural units of political and economic community. Powell’s proposal was not adopted.

In the American Southwest, the major watersheds are the Colorado River Basin, the Great Basin (with no outlet to the ocean), the Sacramento and San Joaquin watersheds feeding the Central Valley of California, and the watersheds along the Pacific coastline of California. Within the Great Basin in Nevada, there are four major sub-watersheds, the basins of the Truckee, Carson, Walker and Humboldt River systems.

To explain the importance of the watershed concept, let’s 

The Carson River watershed, shown in light green, flowing
northeast from the Sierra Mountains in California to

the Carson sink in Nevada

look at the Carson River Watershed, which originates at the crest of the Sierra Nevada and flows in two principal forks (East and West Forks) eastward into the Carson Valley, past Minden and Gardnerville, then through Carson City, Nevada’s state capital, and then down through Lyon County and past Dayton to the Lahontan Reservoir. The water is stored in the reservoir for use each summer in the rich alfalfa farming area of Fallon in Churchill County. The reservoir and its water distribution system, known as the Newlands Project, were built by the Federal Bureau of Reclamation in the early twentieth century to “make the desert bloom.”

The State of Nevada created a water resources management agency for the Carson River known as the Carson Water Subconservancy District (CWSD) in 1959. The story of the Carson River Watershed is told by the CWSD Website (www.cwsd.org) and by many publications such as the Carson River Watershed Map (www.unce.unr.edu/publications/files/ag/2003/sp0302.pdf). In 1998, a citizens and interagency watershed management group was formed—called the Carson River Coalition (CRC). Abiding by the principles of Integrated Watershed Management, the CRC attempts to consider and evaluate all issues of water quality, water supply, floodplain management and fish and wildlife habitat in an integrated fashion. Each of these key values within a watershed is connected to each of the others. 

In times of drought, the residents of major watersheds in Nevada are affected differently. The geography, groundwater quality, water rights and Court Decrees are different in each watershed. People suffer in different ways. More about these water supply issues will appear in the next blog. For more information about our drought see www.livingwithdrought.com and www.unce.unr.edu.