Effectiveness of road ripping in restoring infiltration capacity of forest roads
Luce, C.H. 1997.
Effectiveness of road ripping in restoring infiltration capacity of forest roads.
Restoration Ecology 5(3) 265-270.
Keywords: Road ripping, infiltration
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Abstract:
Many forest roads are being closed as a step in watershed restoration.
Ripping roads with subsoilers or rock rippers is a common practice to increase
the infiltration capacity of roads before closure. When considering the effectiveness
of ripping for reducing runoff and erosion and the potential reduction in slope
stability by saturating road fills, it is important to know how ripping changes
the infiltration capacity of forest roads. Hydrographs from simulated rainfall
on 1 X 1 m plots were analyzed to find the saturated hydraulic conductivity, an
indicator of infiltration capacity. I examined saturated hydraulic conductivity
for three treatments on two different soils. One road was built in a soil derived
from the metamorphic belt series geology of northern Idaho, a soil noted for
its high rock fragment content. The second road was built in a sandy soil
derived from decomposed granitics of the Idaho batholith. On each soil, five
plots were installed on a road before ripping, and nine plots were installed on
the same road segment following ripping, four covered with a heavy straw mulch
and five without. Three half-hour rainfall events with intensities near 90 mm/hr
were simulated on each plot. Results show that ripping increases hydraulic
conductivities enough to reduce risk of runoff but does not restore the natural
hydraulic conductivity of a forested slope. The unripped road surfaces had
hydraulic conductivities in the range of 0-4 mm/hr, whereas ripped roads
were in the range of 20-40 mm/hr after the second event. Surface sealing
and tilled soil subsidence processes are important in reducing the hydraulic
conductivity of the soils with repeated wetting. Subsidence appears to be
important on the granitic soil, whereas surface sealing was more important
on the belt series soil.
Moscow FSL publication no. 1997c
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