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Impacts of Wine Grape Frost and Summer Stream Diversions

At the presentation to the Board of Supervisors on Frost Protection, County staffer Peter Rumple said that “streams go dry naturally”. This was reiterated by Peter Opatz, vineyard manager. Peter Rumple also indicated to Board of Supervisors that the Eyler Report was the latest and best of studies done on frost protection.

They have “studied this to death” and I will add a few more observations.

Drs. Merelender, Deitch and Kondolf:

“HYDROLOGIC IMPACTS OF SMALL-SCALE INSTREAM DIVERSIONS FOR FROST AND HEAT PROTECTION IN THE CALIFORNIA WINE COUNTY”

“Though many river studies have documented the impacts of large water projects on stream hydrology, few have described the effects of dispersed, small-scale water projects on streamflow or aquatic ecosystems. We used streamflow and air temperature data collected in the northern California wine country to characterize the influence of small instream diversions on streamflow. On cold spring mornings, when air temperatures approach 0˚C, flow in streams draining catchments with upstream vineyards receded abruptly, by as much as 95% over hours, corresponding to times when water is used to protect grape buds from freezing; flow rose to near previous levels following periods of water need. Streams with no upstream vineyards showed no such changes in flow. Flow was also depressed in reaches below vineyards on hot summer days, when grape growers commonly use water for heat protection. Our results demonstrate that the changes in flow caused by dispersed small instream diversions may be brief in duration, requiring continuous short-interval monitoring to adequately describe how such diversions affect the flow regime. Depending on the timing and abundance of such diversions in a drainage network, the changes in streamflow they cause may be an important limiting factor to valued biotic resources throughout the region.”

“The methods through which humans acquire water supply can fundamentally alter stream ecosystems. Aquatic scientists across many disciplines have demonstrated that centralized water projects operating on or near major rivers, including dams and large instream and groundwater diversions, can change the flow regime (describing the magnitudes, durations, timing, rate of change and other characteristics of runoff patterns, Poff et al., 1977) of that river system as well as those in adjacent riparian zones.”

Their data shows flow reduction up to 97% in Franz Creek during frost events. As a side note, their study and others, also indicates:

“Kondolf et al. (1987) and Zariello and Reis (2000) both describe groundwater pumping as causing long-term reductions to streamflow during base flow periods by lowering groundwater tables.” “These changes in base flows may alter macroinvertebrate and fish community composition (McIntosh et al., 2002; McKay and King, 2006; Willis et al., 2006).” “Because of their potential impacts on low flows and ubiquity throughout the northern California wine country, small instream diversions may threaten the survival of salmonids throughout the region.”

Earlier, Merelender and Deitch reported:

“In 2000 we reported in California Agriculture on the expansion of vineyards into upland coastal watersheds. With this expansion came changes in where, how, and to what extent water is extracted from these watersheds for irrigation, frost and heat protection. Like most wine-grape growing regions around the world, coastal California has a mediterranean-climate with most of the rainfall occurring int he winter months, followed by a dry period that can last six months. Not surprisingly, in many parts of the Russian River Basin for example, water rights records predict that demand for water during the spring and summer growing season exceeds supply; while streamflow during the wet season exceeds winter water removal estimates. Our monitoring of flow in tributaries of the Russian River reveals dramatic drops in streamflow during spring frost protection periods as well as decreases in flow during extreme hot temperatures. Comparisons between historical and present streamflow data also demonstrate that vineyard development has decreased spring streamflow.”

I have seven (7) research papers by this group and others. They all say the same but recent research shows that heat protection is even more damaging than frost protection. If you wish to read or download the documents, please go to the Friends of Mark West Watershed’s document directory on their website.

JIM