Implications for post-fire management
In the absence of disturbance, upslope runoff and sediment generation are minimal. When forests are burned as in this study, surface runoff and soil erosion are greatly increased. As shown in Table 3, a large portion of uphill flow paths were stopped by road segments when intercepting the dense inflow than when intercepting the sparse ones. This implies that roads will be relatively more efficient in altering surface flow pattern under the post-fire conditions that generate more flow paths. By intercepting upstream runoff, road segments may prevent sediment transport to downstream channels. Sosa-Pérez and MacDonald (2017) observed that road segments could divert hillslope and road surface runoff to a single drainage point, thus reducing infiltration below the road. From this perspective, a road can act as a hydrologic barrier and reduce sediment yield in a fire disturbed forest (Gucinski et al., 2001). The ability of roads to manage overland flow means that conservation measures can be incorporated into road drainage sites. An example of these measures is the use of sediment basins installed below culverts on Road 2, making it unnecessary to treat the whole area below road 2 to limit erosion (Figures 2 and 5).
On the other hand, roads can intercept the high sediment loads that result from surface erosion from upslope burned areas as observed with Road 1. Sediment and other debris can accumulate and block ditches and culverts, leading to road damage and failures that compound the erosion (Foltz, Robichaud & Rhee, 2009). The detailed WEPP results in Figure 2 showed high sediment yield near channel outlets below the road. In the watershed that included the Road 1 culvert near the junctions of Roads 1 and 2, channel erosion was predicted to be the source of 20 percent of the total sediment delivered from this watershed. Sediment basins, channel energy dissipation structures and in-channel grade control structures (Napper, 2006; Robichaud, Storrar and Wagenbrenner, 2019) may be beneficial to control erosion on such steep channels and to reduce the risk of gully initiation.