Study On The Mechanism Of Rainwater Interception By The Pebble And Sand Mulches

Pebble and sand mulching technology has some effects on soil water evaporation and soil erosion. The sandy field was used in the arid and semiarid region of northwest China for a long time. This method is used to alter environmental conditions at the micro-scale to increase crop yields. Therefore, the research on the pebble and sand mulching technology is of considerable theoretical significance and practical value.During a rainfall event, raindrops fell on the surface of the mulch. The rainwater flowed down to the surface of the soil through the gaps between particles in the mulch, and infiltrated into the soil. In this process, some of the rainwater was intercepted by the mulch. It is one of the objectives of this work to analyze the effects of the mulch quantitatively. The models to determine rainfall interception by homogeneous and inhomogeneous particle mulches were established based on the physical and mechanical properties of particulate matter, materials science and statistics theory. The effectiveness of these models was verified by the experiment of measuring the rainwater interception by the mulch under simulated rainfall conditions.The main results of this study are as follows:(1) For homogeneous particle mulch, the particles were characterized by the mean equivalent diameter of particles. A fragmented material composed of particles with different shapes and sizes may be appropriately represented as a fractal. For instance, the fractal dimension has been used to quantify texture changes of soils. The value of mass may be 0 in the fragment range with smaller pebble and sand particles sizes. Because log 0 does not exist, fractal dimensions of the particle samples can not be determined. The fractal dimension is thus not suitable to characterize the pebble and sand samples.(2) For inheterogeneous particles, the overall equivalent average particle size of the inheterogeneous particle sample can be obtained according to the experimental results of sieve analysis method. So the overall equivalent mean diameter was chosen as the index to characterize the inheterogeneous particle samples.(3) The rainfall retention in the mulch can be divided into static and dynamic parts. The dynamic rainfall retention represents the rain water held in the pebble mulch during the rain event and drained to soil surface under the pebble mulch after the rain event. The dynamic rainfall retention is too difficult to be determined in the complex rainfall process. The static rainfall retention is defined as the rainwater held in the pebble mulch when the rain stopped and did not drain to the soil surface under the pebble and sand mulch. The static water held in the mulch can be considered as the actual amount of rainfall interception by the mulch after one rainfall event.(4) According to the analysis of the physical characteristics of the homogeneous particles in the mulch, the calculation method of the maximum static water retention in the mulch using homogeneous particles was determined. A paired samples two-tailed t test was used for the comparisons between the results of experiments and those calculated. The values calculated using the calculation method were not significantly different from measured values.(5) According to the analysis of the grading characteristics of the inhomogeneous particles of the mulch, the calculation method of the maximum static water retention of the mulch using inhomogeneous particles was determined. A paired samples two-tailed t test was used for the comparisons between the results of experiments and those calculated. The values calculated using the calculation method were not significantly different from measured values.(6) The method to determine the maximum rainfall interception by mulch was given in this work. The calculation method was not only based on the size characteristics of the pebble mulch, but also simulated the interaction between the water and pebbles. This calculation model may work with a wider range of adaptability and flexibility in engineering than the regression model based on the specific test data. It is a semi-theoretical model and can be used to quantitatively predict the rainfall interception by pebble and sand mulches.