Experimental Research On The Impacts Of Ground Slope On The Runoff Of Turf

It is should not be ignored that the runoff of urban turf and the green land is a useful water source. In order to understand the hydrological mechanism of rainwater harvesting and make full use of rainwater on the green land, the runoff differences of different slopes and rainfall characteristics were analyzed by observation the rainfall, runoff at three slopes (0%, 10% and 20%), as well as the change of runoff at various slopes and the variations of biomass at different slopes with time were analyzed. The research is also helpful to establish the turf rainwater collection system and explore the potential of water resource on the green land. The runoff-rainfall threshold is an important parameter to understand the rainfall runoff process and the potential of rainwater collection of the turf, and also an important parameter to design rainwater collection system of green grassland. In this paper, an experiment was conducted at the Luyuan Garden in Beijing in 2006 to determine the rainfall-runoff -threshold of turf based on four slope treatments, three reduplicates of land with green grassland. The slopes were 0%, 5%, 10%, and 20% respectively, and rainfall and runoff were observed for every plot. The main results are as followers.1. The runoff efficiencies of grass land and bare land increased with rise of the slope, and there were significant differences between plots; there was significant difference in runoff between bare land and grass land; by comparing the relative contributions to runoff among rainfall variables, it is concluded that the rainfall intensity (I), maximum 30 minutes rainfall intensity (I30) and compound rainfall index (PI30) are major factors which have positive correlation with runoff coefficient. The influence order of turfgrass runoff coefficients reacted by rainfall characteristic is PI30>I30 > I. However, the significant influence factors of bare land are precipitation (P), I30 and PI30, and the influence order is PI30> I30> P. As the precipitation, the rainfall intensity, the maximum 30 minutes rainfall intensity and the compound rainfall index increasing, the larger the slope, the lager the runoff efficiency increase rate and the runoff efficiency increase rate of the bare slope is much higher than that of turfgrass.2. The runoff models of grass land and bare land were gutted. By use of the models, the runoff of grass land and bare land were mainly decided by compound rainfall index and slope, and there was positive correlation between runoff efficiency and compound rainfall index, slope. The influence of compound rainfall index may be greater than that of slope for grass land. It is just on the contrary for bare land.3. The runoff-rainfall threshold was 9.5 mm for the turf green space of four slopes. 4. The biomass aboveground and underground were decreased as the slope increasing. There is no significant difference between root-shoot ratio and slope.Further researches are needed for the runoff characteristics under different conditions of turf coverage, slope length, soil moisture content before rainfall and other greenbelt types, so as to determine the turf runoff-rainfall threshold.