Journal of Natural Disaster Science

PERFORMANCE OF WATER INFILTRATED WITHIN INFILTRATION STRATA AND KANTO LOAM TAKING INTO ACCOUNT HYSTERESIS

Shigeki HARADA
and
Arata ICHIKAWA
Department of Urban Engineering, University of Tokyo

(Received 21 May 1990 and in revised form 17 January 1991)

Abstract

Infiltration strata is an artificially devised soil structure comprised of artificial turf permeable pavement, a layer of crushed gravel and a layer of sand. This strata is meant to reduce stormwater surface runoff in urban areas by passing stormwater from its surface to the natural base soil laid below the strata. The natural base soil is ordinary Kanto loam in Tokyo. To simulate the performance of water infiltrated within infiltration strata and Kanto loam, we used two columns. Both columns were set outdoors, and data of rainfall, evaporation and drainage were obtained. We have made a model to predict the performance of water infiltrated within two columns, based on the numerical solution of Richards' equation together with Campbell's equations that are used to express soil property functions. The drainage profiles of two actual rainfalls from the two columns were predicted using the data of rainfall and evaporation, and these profiles were compared with the observed profiles of drainage. The predicted drainage volume was similar to that of observed one, but the rapid changes in the drainage rate produced by the rapid changes in the rainfall rate were not adequately predicted. Hysteresis which makes the soil property functions irreversible and many valued was introduced to Campbell's equations using Mualem's model, and the rapid changes were well predicted.

Key words

Richards' equation, Campbell's equations, Mualem's model, hysteresis, infiltration strata, Kanto loam