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.