Controls and determination of resistance to overland flow on semiarid hillslopes, Walnut Gulch

Athol D. Abrahams; Anthony J. Parsons; John Wainwright

ABSTRACT:

We performed 136 experiments on small runoff plots on semiarid grassland and shrubland at Walnut Gulch using trickle to generate overlandflow. The values offiiction factor f obtained were an order of magnitude less than those values recorded by Welt. et al. (1992). A second set of experiments on the grassland reveals that the dzfference between the values of f arise from the fact that we used trickle whereas Welt. et al. used simulated rainfall to generate overland flow. The higher values of f under rainfall are due not only to the retarding effect of rain on the flow but also to the overland flow generated by rain being distributed over a larger proportion of the plot than that generated by trickle. Although trickle experiments help to understand the factors controlling f, they do not yield values that can be used in modeling runoff and soil erosion. For such purposes f must be determined using rainfall-generated overland flow.

Footnotes

Athol D. Abrahams is a professor, Department of Geography, State University of New York at Buffalo, Bufalo, NY 14261; Anthony J. Parsons is a senior lecturer, Department of Geography, University of Keele, Keele ST5 5BG, United Kingdom; and John Wainwright is a Lecturer, Department of Geography, King's College London, The Strand, London WC2R 2LS, United Kingdom. The field experiments at Walnut Gulch were conducted with the assistance of the USDA-Agricultural Research Service, Southwest Watershed Research Center, Tucson. We thank Leonard Lane for permission to we the facilities at the Tombstone foeld station and Mark Weltz for providing a copy of the program to calculate the friction factor from the runoff hydrograph. This research was finded by a grant from the Natural Environment Research Council (GR3/7999).
Copyright 1995 by the Soil and Water Conservation Society

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