The vineyard's plumbing system results in less water falling into the soil in winter and therefore less water absorbed into natural groundwater. Less groundwater can hurt surrounding plant life and provide less water downstream in the creeks and streams for spawning fish. Growers sometimes dig wells more than 400 feet deep to gain groundwater and use powerful pumps that some property owners claim have caused their neighboring wells to go dry. But growers point out that the movement of underground water changes for many reasons and that it is difficult to identify the causes, including whether new vineyards are a factor. Some industry representatives also say the groundwater taken by many new vineyards is less than what might be pumped for a home built on the same property.
Erosion is another major issue.
A small patch of forest provides thousands of trees, bushes, grasses and weeds that all act to hold topsoil in place during winter storms. Removal of the vegetation, experts say, results in a tremendous increase in downstream runoff. Higher runoff can result in more sediment in streams and creeks. Too much sediment in the streams can pose problems for spawning fish. Sediment buildup also has been cited as a major contributor to downstream flooding.