Date of Award

6-2012

Degree Name

MS in Agriculture - Soil Science

Department

Earth and Soil Sciences

Advisor

Lynn Moody

Abstract

The Lockheed Fire occurred in August 2009, burning 7,819 acres of the coastal mountains north of Santa Cruz, California. The fire burned a large portion of the Scotts Creek watershed, including over 90 % of the Little Creek watershed, much of which is on Cal Poly’s Swanton Pacific Ranch (SPR). After intense winter rains in 2010 there was a significant amount of hillslope-derived sediment deposited on the roads and in the creek. A large portion of this material was derived from two chaparral hillslopes. These hillslopes were identified as the only two hillslopes within the Little Creek subwatershed where an extensive network of rill erosion had occurred. The purpose of this study was to determine what factors were related to the erosion process on two burned hillslopes. Water repellency, infiltration, saturated hydraulic conductivity, and particle size class were assessed to determine how the impacts of the fire affect the soil physical properties where rill erosion occurred. In order to address this goal, the soil physical properties were characterized on two hillslopes influenced by three different types of parent material: Santa Cruz mudstone, Santa Margarita sandstone and colluvium derived mainly from the Santa Cruz mudstone. The study, consisted of 10 transects and three sampling points at 3, 18 and 27 m, on 45-80% southeastern facing slopes. The vegetation consisted of knobcone pine chaparral mix, transitioning down slope to a chaparral mix. The results showed slope length, clay content and infiltration, were statistically significant. Hydraulic conductivity (Ksat) and slope steepness were not significant, but were included as associated variables with the occurrence of rilling. The study has provided information about post fire soil properties to determine what factors contribute to rill erosion causing the sedimentation into the streams. The observation from the study site can be used in similar conditions within the coastal mountain range setting, thus helping to create models for future planning of the overall watershed management.

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