HOW DO WATERSHED CHARACTERISTICS INFLUENCE POST-FIRE SEDIMENT STORAGE AND DELIVERY OVER TIME? (Invited Presentation)

Considerable advances have been made in understanding post-fire runoff, erosion, and mass wasting at the hillslope and small watershed scale, but the larger-scale effects on flooding, water quality, and sedimentation are often the most significant impacts. The problem is that we have virtually no watershed-specific tools to quantify the proportion of eroded sediment that is stored or delivered from watersheds larger than about 2-5 km². In this study we are quantifying how channel and valley bottom characteristics affect post-fire sediment storage and delivery. Our research is based on intensive monitoring of sediment storage over time in two 15 km² watersheds (Skin Gulch and Hill Gulch) burned in the 2012 High Park Fire using five airborne laser scanning (ALS) datasets from fall 2012 through summer 2015, repeated cross-section and longitudinal surveys, and both radar and ground-based precipitation measurements. We have computed spatially explicit changes in sediment storage and erosion by registering consecutive ALS point clouds, differencing the point clouds with the multiscale model to model cloud comparison (M3C2) algorithm, and calculating the total volume of positive and negative elevation changes in 50-m segments along the channel network. These changes are being related to key morphometric indices such as valley width, valley slope, confinement, contributing area, valley expansion or contraction, and estimated sediment inputs. We hypothesize that maximum rainfall intensity and lateral confinement will be the primary independent variables that describe observed patterns of erosion and deposition, and that the results can be used to predict post-fire sediment delivery and restoration priorities.