Post-fire observations of Little Creek Watershed: Evaluation of change in sediment production and suspended sediment export.
Drew Loganbill, Natural Resources Management Department, Cal Poly State University, San Luis
Obispo/Swanton Pacific Ranch; 125 Swanton Road, Davenport, CA 95017; (805) 503-8462; dloganbill@gmail.com
Brian Dietterick, Ph.D, P.H., Swanton Pacific Ranch, Cal Poly State University
The Little Creek study was initiated to document the watershed’s response to selective timber harvest in the Santa Cruz Mountains by evaluating event-based suspended sediment export, sediment sources, and channel change. A 7-year calibration period was conducted using 3 monitoring stations providing for a paired and nested watershed study. The North Fork of Little Creek was harvested in 2008 and the post-timber harvest evaluation included one year with below average rainfall amounts. The Lockheed
Fire occurred in August 2009, consuming 92% of the 500 hectare watershed, and subsequently changing the focus of the Little Creek study to determining the watershed’s response to wildfire.
In order to assess response to wildfire in the Little Creek Watershed efforts were made to identify changes in event-based suspended sediment export, identify change in sediment production locations, and determine the influencing factors contributing to sediment production. Eight years of pre-fire event-based suspended sediment data from 3 monitoring stations were compared to the first year of post-fire data to identify changes in suspended sediment export. Sediment source surveys were performed to document near-stream sediment contributions dating back to 1998 and these observations along with data from sediment fences and field observations were used to identify change in sediment source areas. Multivariate analysis was used to determine the most influencing factors for sediment production using rainfall data from 6 gauges and streamflow data. Hydrophobicity tests, rainfall simulations, surface erosion plots, and site characteristics were used to further support the objectives of this study.
Watershed response to wildfire is not well documented in coastal redwood forests. Identifying changes in sediment sources and sediment transport provides essential information to landowners and regulatory agencies in understanding the risks of wildfire and for planning management activities in the
Santa Cruz Mountains.