Sonoma County Winegrape Commission

Drought conditions require everyone to conserve water in 2009.

Growers Can Help Conserve Water by adopting best management practices in their vineyards.

The Sonoma County Water Agency may implement mandatory conservation requirements on its water contractors as early as April. A 30% cutback may be required and that could increase to 50%, depending on the amount of water in Lake Mendocino. Growers and water users not receiving water from the Water Agency are also being asked to conserve. Lake Mendocino currently has 30,000 acre-feet of water, which is less than half of normal Water Agency annual deliveries to its contractors. Both Lake Mendocino and Lake Sonoma are at historical lows for this time of year. Dr. Greg Jones, Southern Oregon University climatologist, reported at Dollars and $ense that water temperatures in the Pacific are not favorable for above normal rainfall this spring. Hopefully spring rains will be sufficient to recharge the soil profile for grape vines.

Grape Grower Proactive Steps to Conserve Water.
A group of growers have been meeting to outline steps growers might take to conserve water and still produce a good grape crop. The first step is to conserve soil moisture in the profile today. Earlier than usual removal of cover crops except near streams is one step. This can be done by disking, repeated mowing to limit cover crop leaf area, herbicide treatment or a combination of these methods. If spring rains do come, it is important to maintain vegetated filter strips (or cover crops) of at least 25 feet to trap sediment before it reaches a stream.

Delaying initial irrigation is a second conservation measure. Soil or vine water status should be monitored in order to determine when irrigation is required. Growers can employ soil moisture measuring tools, such as neutron probes, and plant water status tools, such as pressure chambers or “pressure bombs”, wherever possible. By delaying irrigation and then maintaining a level of deficit water status, vine leaf area will be reduced, which will save water all year. Avoid overwatering at any time. Consider shorter, more frequent irrigations that insure water does not migrate below the root zone where it cannot be used.

Frost protection is critical, but conservation is still possible. Watch dew point as well as air temperature. If dew points are high, you might delay starting frost protection until closer to 32 degrees. Also stop frost sprinkler systems following sunrise as soon as the temperature rises above 32 and no ice remains on the vine. Water used for frost protection will be stored in the soil profile and should delay irrigation initiation later in the season.  Growers will need to minimize sprinkler run times during frost events and still protect the crop. Growers should reevaluate the number of staff needed to more effectively manage the timing of the starting and stopping of their frost sprinkler systems. This is most critical where personnel are managing multiple systems at multiple sites throughout the night.

Growers should also prepare for potential heat spikes later in the season. Canopy management that provides more shade to the clusters may eliminate or reduce the need for sprinklers for heat suppression.

Finally, growers can help the Water Agency manage releases from the reservoirs such that minimum flows are maintained for fish and excess flows are avoided that are wasted when unused water enters the Pacific. Nighttime irrigation can create a more uniform water demand throughout a 24-hour cycle and allow for a more uniform flow regime for the Water Agency. Time of use estimates by growers (and other water users) may help the Water Agency better schedule water releases from Coyote and Warm Springs dams.

Additional emergency measures will be pursued with the CA Water Resources Control Board. If growers were allowed to store riparian water in their reservoirs for more than 30 days, diversions could begin at an earlier date and be diverted at a lower rate over a longer period of time. This could minimize demand peaks for the Water Agency.

Water Storage Projection Reservoir Will Run Dry Given Current Water Use, Dry Weather - SCWA Press Release [pdf]