雨水地下浸透モデル実験とその問題点

―世田谷区成城における場合―

抄録

Experiments of rainfall infiltration were carried out using water from storage tank. Water was sluiced into the infiltration measuring box (2 m × 3 m × 2 m) at the rate of 80l/min without interruption on the supposition that rainfall was received at the intensity of about 50 mm/hr on the roof with the area of 96.6 m². On finishing the artificial supply, ponding depth was measured every 5 minutes until the water table came down to the bottom level of the infiltration measuring box.
Using the experimental data of total infiltration depth and the time required, the average velocity of infiltration was calculated to be about 80 cm /m² (1,920l/hr). Furthermore, the terminal infiltration capacity was determined to be 79.1 cm/hr/m²(1,898l/hr) for the first attempt and 72.6 cm/hr/m² (1,742l/hr) for the sec ond.
When the average velocity of infiltration is assumed to be constant, rainfall d uration needed to fill the infiltration measuring box with water is estimated to be ∞,∞,5.348,2.574 and 1.696 (hours) at the rainfall intensity of 10,20,30,40 and 50 (mm/hr)respectively and it takes 0-1.415 hours for the water to be fully drained. On the other hand, when the average velocity of infiltration is assumed to be variable, the computa tion gives such values for rainfall duration as 5.764,3.390,2.488,1.998 and 1.685 (hours)at each intensity and 1.5-6.0 hours are needed for draining the water. Comparison of these two cases reveals that infiltration effect becomes larger as rainfall intensity grows down.
We can see the groundwater recharge effect in terms of groundwater rise in the observation well. There are some peaks of groundwater rise between 3 and 5 hours after starting the artificial rainfall supply. This, however, is based' on calculations using too large permeabilities (10⁰-10^-1 cm/sec) that further study is required.