An Evaluation Method for Stormwater Infiltration

Abstract

Urbanization of a river basin increases the peak discharge and total depth of a single storm. Any increase in the discharge of a combined sewer requires greater stormwater drainage capacity, which can be costly. By installing stormwater infiltration facilities to control runoff, it is possible to reduce the required capacity and the frequency with which untreated sewage is released into public waters. In this paper, a functional evaluation of stormwater infiltration has been conducted. In Japan, hourly rainfall records are available nationwide. The 60-minute rainfall maximum, the peak rainfall in any 60-minute period, is normally larger than the hourly rainfall on the hour. For a given rainfall, the peak discharge depends on the concentration time. This paper describes how hourly rainfall records should be handled. An equation for a standard equi-risk line has been suggested when evaluating urban river basin control systems utilizing storage. In a combined sewer system, the sewer facility provides the storage, so the catchment for the system is the urban river basin itself, and the standard equi-risk line can be applied to the sewer facility without modification when the treatment capacity is assumed to be constant. Some examples of the use of standard equi-risk lines are introduced. This paper shows that the effects of a stormwater infiltration system can be evaluated by these lines.