By using a self-designed lysimeter to measure surface runoff on a slope in Taihang Mountains

we analyze the impacts of the factors influencing runoff in the Granitic Gneiss Region (GGR) of the mountainous area. The analysis shows that (1) rainfall intensity is a key factor for initiating runoff. Surface runoff occurs when rainfall intensity is above a critical value. The gentler the slope

the higher is the critical value of rainfall intensity needed to initiate runoff. When rainfall intensity reaches a critical value

runoff becomes positively correlated with rainfall significantly. However

the correlation between runoff and rainfall intensity is insignificant. (2) Runoff does not increase with the increase in the catchment area. A strong slope infiltration capacity enhances convergent runoff infiltration into soil. Surface slope is also a key factor influencing the process of runoff in the GGR area. With increased slope

surface runoff increases significantly. Since different slope aspects have different soil textures

runoff on sun-ward slope is higher than that on shade-ward slope. The averaged runoff coefficient for sun-ward slope is higher than that for shade-ward slope as well. Generally

however

runoff coefficient is low in the study area. For instance

it has the maximum of 7.3% for a 2 meter-length slope. An important finding from the study is that there exists a very strong infiltration capacity on the GGR slope in the study area. This has a significant implication for understanding the mechanisms of surface runoff

infiltration

and groundwater recharge in the region.