INFILTRATION AND CONNECTIVITY AT MULTIPLE SCALES IN BURNED WATERSHEDS

The spatial distribution of patches with variable infiltration rates, the connectivity of these patches, and rainfall rates control the routing of infiltration excess overland flow on burned hillslopes. We examined the runoff response at both plot (1-m²) and macro-plot (100-<1000 m²) scales in burned areas in Colorado and Southern California. This multi-scale perspective indicates how observed processes at the plot or point scale may translate to the hillslope/macro-plot scale.

Runoff began when simulated rainfall rates exceeded a threshold value of ~ 20 mm hr^-1 on experimental plots burned by the 2002 Overland Fire in Colorado. At rainfall rates greater than this value, runoff rates increased linearly. Such threshold rainfall/runoff behavior is consistent with observations at both plot and watershed (1-10 km²) scales for similar systems that indicate a change in the rainfall-runoff relation at an approximate rainfall rate threshold of 10 mm hr^-1.

Surface runoff was measured in macro-watersheds burned by the Harvard Fire in California. These plots were subjected to low intensity, long duration natural rainfall inputs (<10 mm h^-1). Monitoring of individual hillslope flow-paths indicated a decrease in flow in the downslope direction. This suggests that water infiltrates downslope along these micro-channels approaching the macro-watershed channel. Permeability increases with increasing flow-path length, so assessing the connectivity of these runoff systems is critical.