Effects of Forest Management and Roads on Runoff, Erosion, and Water Quality: the Judd Creek Experiment

The effects of forest management have long been a concern for land managers, and California has instituted particularly strict best management practices (BMPs) to minimize the potential adverse impacts of timber harvest on water quality and fisheries. This paper presents the results of the long-term study of Judd Creek, a 17.6 km2 watershed in the volcanic terrane of northeastern California. Runoff and turbidity monitoring began in late 2001 at five stations spaced along the main stem. In 2007 extensive road work was conducted in preparation for timber harvest, and this included abandoning 2.4 km of existing roads and constructing 4.23 km of new roads. In summer 2009 16% of the watershed was clearcut in 34 units that were 8-12 ha each. In 2011 detailed assessments were conducted on selected harvest units, 43 landings, streamside protection zones below clearcut units, and 23 km of roads; 30 sediment fences were installed to measure road sediment production. Elevations range from 970 to 1680 m, and mean annual precipitation is about 1200 mm. The clearcut units had little or no evidence of surface erosion, and this was attributed to the ripping and high surface cover from logging slash, rocks, and regrowth. Landings generated only eight rills or sediment plumes; none of these were longer than 24 m long and none were connected to a stream. Mean road sediment production in the relatively dry winter of 2011-12 was less than 10 Mg ha-1. Twenty-eight percent of the abandoned roads were connected to the streams, while only 7% of the new roads were connected. Mean daily turbidity values exceeded 25 NTU only 1.2% of the time, and single highest mean daily value was only slightly greater than 200 NTU. Runoff and turbidity levels are controlled primarily by the interannual variations in precipitation, and there was no evidence of a management impact on either runoff, turbidities, or suspended sediment concentrations. The combination of high infiltration rates, relatively permeable geology, and improved management practices all indicate that intensive forest management in the Judd Creek watershed has not had any adverse effects on runoff or water quality. Future work should focus on the effects of forest management in the more erodible areas, such as highly weathered granitics.