Evaluation of Factors Affecting Surface Runoff on Alpine Rangeland in Victoria.

A 'portable' rainfall simulator was used on alpine soils on the Bogong High Plains in Victoria, to determine the relationship of surface runoff to soil moisture, rainfall intensity, slope and the percentage of the area lacking vegetation cover (bare ground). A strong inverse relationship (R' = 0.64) existed between total runoff and antecedent soil moisture conditions. The other factors, within the range evaluated in these experiments (bare ground 0 to 33'70, rainfall intensity 37 to 97 mm/hr and slope 6 to 23%) had no significant influence on runoff. Time to runoff initiation was influenced by antecedent soil moisture, slope and rainfall intensity ( ~ ~ ~ 0 . 7 1 ) . It was found that time to runoff decreased as the soils dried, and the slope and rainfall intensity increased. The percentage of bare ground had little influence on the time to runoff initiation. These results show that differences in grassland condition, including large differences in the percentage of bare ground, had little influence on either surface runoff or on the time to runoff initiation. The single most important factor influencing runoff rates was the antecedent moisture content of the soil. This factor is generally outside management control.