A study of infiltration trenches in unsaturated soil

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Virginia Polytechnic Institute and State University

Interest in infiltration structures to control peak runoff in urban areas has increased in recent years. The work reported here is a study of infiltration trenches in unsaturated soil. The infiltration rates and the water content distributions in soil calculated by Fok's model and a finite-difference model are compared for both the Ida silt loam soil and the Webster clay loam soil considering the capillary zone effect due to groundwater table. A computer program for hydrologic routing in infiltration trenches has been developed with the infiltration rate calculated based on a 3-dimensional cumulative infiltration equation. The 3-D cumulative infiltration equation developed in this study is recommended for the analysis and practical design of infiltration trenches, since it is easy to use and inexpensive in computation. An infiltration trench with overflow has been examined allowing the overflow not to exceed an allowable discharge to downstream. It has been found that the surface infiltration due to overland flow does not significantly alter the infiltration rate from a trench. It has also been found that a long narrow trench is more effective for water to infiltrate into soil than a short wide trench for the same trench area( length x width ). The hydraulic conductivity of a soil is an important factor in the design of an infiltration trench, whereas the porosity and the effective capillary potential have minor effects.