Water Resources Collections and Archives

In 1991 Napa County adopted an erosion control ordinance that regulates alterations of landscapes with slopes greater than 5%. The objectives of the Hillside Ordinance are to reduce erosion from hillsides into streams and improve water quality. Vineyard development and management are regulated by this ordinance.

Little research has directly addressed the effectiveness of erosion control strategies as recommended by the Hillside Ordinance. The Napa Conservation District (RCD) initiated the first monitoring that will compare management techniques for erosion control. They are recording suspended sediment concentrations (SSC) flowing from two vineyard plots under different management. The RCD will conduct further data analysis in May of 2004.

Another study conducted by Lutrick (2000), a student in landscape Architecture 222, focused on the impacts of vineyard development to a stream in Napa. After the plots were cleared Lutrick (2000) conducted basic stream surveys and pebble counts pre and post rains. She chose an adjacent watershed as an analogous control. Her findings indicate that the grain size of the stream changed similarly to the control. In both streams, grain size decreased after one winter (Lutrick 2000). Lutrick (2000) concluded that the development had no significant measured effects on the test stream.

In spring 2004 I resurveyed the streams. My objective was to analyze more longterm changes that might have occurred to Lutrick’s (2000) study sites. My findings indicate that the pebble size D50 for cumulative percent finer in both streams seems to be decreasing. Increased sedimentation in both streams may be due to upstream human activity or natural phenomena.