Ad. Ziegler et Tw. Giambelluca, IMPORTANCE OF RURAL ROADS AS SOURCE AREAS FOR RUNOFF IN MOUNTAINOUS AREAS OF NORTHERN THAILAND, Journal of hydrology, 196(1-4), 1997, pp. 204-229
Unpaved road surfaces have extremely low infiltration rates compared w
ith other watershed land surfaces and, therefore, are significant sour
ce areas for erosion-producing Horton overland flow. The hydrologic ro
le of roads is an important issue in mountainous areas of the tropics
where erosion control efforts are predominately focused on deforestati
on and agricultural practices. We report on an investigation of soil p
hysical properties that control excess rainfall (rainfall intensity in
excess of infiltration capacity) on rural roads and surrounding lands
in a mountainous watershed in northern Thailand. The results of our d
isk permeameter measurements indicate that saturated hydraulic conduct
ivity on unpaved roads is about one order of magnitude lower than on a
ny other land-surface type. Median saturated hydraulic conductivities
were not exceeded by measured rainfall intensity on any land use excep
t road surfaces and roadside margins. By simulating excess rainfall, w
e found that in contrast with other areas of the watershed, the road s
urface tends to generate excess rainfall early in a rain event, and on
nearly all of its area. Despite the relatively small areal extent of
road-related surfaces ( < 0.5% of basin area), they contribute a large
portion of basin-wide total excess rainfall during frequently occurri
ng, small rainfall events. However, during larger events, agricultural
, secondary vegetation, and forested areas assume greater importance b
ecause of their larger areal extent. (C) 1997 Elsevier Science B.V.