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glen N M c go u rt y Grounded Grapegrowing A Tale of Two Watersheds F arming in California is becoming increasingly complicated as growers in our populous state are held responsible for the wellbeing of public trust resources that are on their property: air, water, fish and wildlife. Agriculture is estimated to use 80%-85% of the available water in our state to irrigate about 10 million acres of farmland. The most common conveyances of water in our state are naturally flowing rivers. Rivers serve many purposes including water for towns and cities, farms and wildlife. Managing to satisfy all of these needs is a challenge. There are few rivers left that flow naturally unimpeded, the result of many dams that have been constructed during the past 100plus years. Since much of California exists under drought conditions for many months of the year, storing water when it rains makes great sense. Problems arise when these impoundments impact the natural hydrology of a region (movement of water and sediment through the rivers) and prevent fish or other wildlife from their former habitat. How water is apportioned for different uses creates much controversy, and balancing the needs of natural systems, agriculture and urban use is a never-ending task. What is a watershed? John Wesley Powell, famous for exploring the Colorado River Basin and serving as the head of the U.S. Geological Survey in the 1890s, defined a watershed as "that area of land, a bounded hydrologic system, within which all living things are inextricably linked by their common water course and where, as humans settled, simple logic demanded that they become part of a community." This thoughtful definition still works well today. 42 W in es & V i ne s January 20 14 It is important for our industry to understand how much water we use, when we use it and what the constraints are due to competing interests (or "stakeholders"). These competing uses include urban and industrial water use, fish and wildlife, recreational use, aesthetics and replenishing aquifers that would naturally be filled by seasonal flows of water. With the listing of Coho and Chinook salmon as endangered species—and the steelhead trout as threatened—agriculture can expect water use to be looked at very closely, if for no other reason than that we are very visible to the community. I have worked on two projects in Mendocino County that have assessed agricul- tural water use, particularly for irrigating and frost protecting vineyards, orchards, pastures and other water uses. We focused on agricultural water use in both the Upper Russian River Watershed and the Navarro River Watershed. Both projects were commissioned by the Mendocino County Water Agency and involved a host of scientists and our assistants to complete. We used a variety of tools including GIS data to show spatially where the farmland is located and how much of it is under cultivation, where irrigation ponds are located, evaluation of irriga- The Russian River is dropping in elevation, and the banks have been destabilized, causing considerable erosion. tion systems for uniformity, measuring canopy shading to estimate crop coefficients, focus groups and surveys to determine how growers schedule irrigations and the volume of water that they use. Wild river vs. managed river Highlights • t is important for our industry to I understand how much water we use, when we use it and what the constraints are due to competing interests (or "stakeholders"). • his column shares results of detailed T water-use studies by grapegrowers in the Russian River and Navarro River valleys of California's Mendocino County. • ractical limits on water use are P becoming essential. All water users are going to have to show that they are using the resource efficiently and for a good purpose. The Navarro River is actually rather small (26 miles long) and drains from coastal mountains into the Pacific Ocean. It drains a watershed formed by the Mendocino Mountains and flows from southeast to northwest. Much of the watershed is covered in deep ravines and forests of redwoods and Douglas fir on north slopes, whereas many of the south-facing slopes are oak woodland and grasslands, making the watershed very much a cross between Mediterranean California and conifer forests more typical of the Pacific Northwest. Rainfall is hugely variable in both watersheds. The Navarro River flow, as measured at the USGS gauge near Philo, Calif., varies from a high of 950,000 acre-feet (1983) to a low of about 25,000 acre-feet (1977). There is very little water storage in the watershed, with only about 160 reservoirs holding less than an average of 10 acre-feet of water each. Disappointingly, there is very limited groundwater, as the subsurface is mostly fractured Franciscan rock with lim-