Geomorphic Connectivity in Recently Burned Watersheds

East Carolina University, Greenville NC

Investigators

Abstract

Wildfires are a growing global problem that directly impact society. Fire also is a disturbance mechanism that alters watersheds dynamics through rainfall interception, runoff, and sediment transport/deposition, thereby promoting secondary hazards like floods and debris flows. Although researchers generally concur that debris flows in recently burned basins initiate from progressive-bulking, a process whereby the flow picks up more and more sediment as it travels through the watershed, an integrated watershed-scale understanding of material fluxes in recently burned catchments has not yet been developed. This research project aims to address this shortcoming by using the conceptual context of connectivity, examining the transfer of energy and matter between individual landscape compartments, such as hillslopes, gullies and stream channels. This one-year study will examine the feasibility of using repeat terrestrial laser-scanning techniques to capture fine-scale topographic changes resulting from matter exchange during sediment transport and deposition at the U.S. Geological Survey (USGS) and National Weather Service (NWS) Intensive Research Area (IRA) in southern California. Sediment dynamics on an event-by-event basis will be assessed using 1-cm resolution digital terrain models (DTM). This will be accomplished analytically by using DTM differencing techniques to capture the volumetric changes in sediment sources and sinks through space and time. The variability of erosion and deposition through space and time will be analyzed with the aid of fine-scale sediment budgets between the various landscape compartments. The budgets and the DTM difference data will be used to assess connectivity between the various landscape compartments. These analyses also will provide insights regarding how to integrate process-oriented data, such as rainfall amount and intensity, soil moisture, and stream discharge, from the IRA into future research. The analyses also will inform basic and applied science whether more field data on process information is required or whether statistical or numerical models from current data sampling are sufficient for studies of process-form relations. Many residents in Southern California are prone to multiple natural hazards. The USGS is dedicated to assist southern California communities in order to educate and reduce their risk from these hazards. Results from this project will provide valuable information for USGS models to predict post-fire debris-flow probability, magnitude, and potential inundation. Project findings will enhance efforts to improve the predictive capability of the USGS/NWS Flash Flood and Debris Flow Early Warning System for communities prone to flooding and debris flows. The strong connections to the USGS will assure the outcomes are disseminated to local communities through implementation of research findings into hazard mitigation programs and public outreach. In addition, this research will integrate active scientific investigation into the educational experiences at East Carolina University. Two undergraduate research assistants will be integrated into all aspects of the project and these students will develop their own research projects to culminate in honors theses. Furthermore, an interactive website will discuss the findings and allow rapid updates of the research progress. The website also will permit private citizens and various local, state, and federal agencies to engage in two-way dialog with the principal investigator.