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- land restoration
- Japan
- Land subsidence and ground water management, Japan
Problems
Starting from 1910, the ground in Tokyo has been subsiding, especially in Koto-ku. This is due to factories and other facilities extracting large amounts of groundwater. The problem became more severe after World War II, during economic recovery and rapid growth. This has increased subsidence in areas at or below sea level, commonly known as the "zero-meter zone." As a result, the risk of flooding has increased, and the floating structures have damaged underground pipes.
Solutions
Conservation of Ground Environment
Author: Ministry of the Environment, Government of Japan
The progressive damage caused by ground subsidence made the public realize that controlling groundwater pumping was necessary to solve the problem. Two laws, the "Industrial Water Law" and the "Law Concerning the Regulation of Pumping-up of Underground Water for Use in Buildings," enacted in 1956 and 1962, respectively, have been enacted and enforced to reduce groundwater yields. At present, parts of ten prefectures are regulated under the former law, and parts of four are regulated under the latter. In addition to these laws, local governments formulate ordinances to control groundwater pumping. Industries also carry out voluntary measures to reduce and rationalize groundwater use. Construction projects have been carried out to supply additional surface water to reduce groundwater demand. In the greatly subsided areas, buildings damaged by ground subsidence have been repaired, and structures have been erected to prevent damage from floods and high tides. Additionally, pumping regulations were introduced to counter ground subsidence, and restrictions on groundwater pumping are primarily aimed at the structural design of pumping facilities. These restrictions are implemented by the Industrial Water Law, the Law Concerning the Regulation of Pumping-Up of Groundwater for Use in Buildings (Building Water Law), and the Tokyo Metropolitan Ordinance Concerning the Environment for Ensuring People’s Health and Safety (Environmental Preservation Ordinance). The laws ban new and existing wells that fail to meet certain requirements in the outlet's cross-section area and the strainer depth in the zone where the regulations apply. In contrast, the ordinance only forbids the installation of any such well. Existing wells subject to regulatory controls have all been replaced by industrial water supply services or other facilities. As pump performance improved in recent years, many small pumping facilities became exempt from the laws or ordinances on pumping groundwater.
Gallery
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Timelines
2004
Pump performance was improved, and many small pumping facilities have become exempt from the laws or ordinances on pumping groundwater. The TMG tightened the new Environmental Preservation Ordinance regulations to address this growing gap.
2003
TMG’s waterworks system operated up to 290 wells, treating groundwater at 50 water purification plants. Guidelines were issued for rainwater infiltration facilities to increase groundwater recharge.
2002
There was still no provision on 1,4-dioxane in Japan’s drinking water quality standards, but three wells with a 1,4-dioxane concentration exceeding 0.03 mg/L were closed to prevent any possible hazard. Earlier, the U.S. Environmental Protection Agency (EPA) confirmed that this substance was carcinogenic and set the potable water concentration associated with a cancer risk of 1/100,000 at 0.03 mg/L.
1994
When almost the nation suffered drought, ground subsidence intensified in areas such as the northern part of Kanto Plain, Chikugo, and Saga Plains. To monitor the rapid drop in the groundwater level during drought and evaluate the need for installing a telemeter system to upgrade the real-time monitoring of groundwater level, the Environment Agency established observation stations at several monitoring wells on Chikugo and Saga Plains (Saga Prefecture) and the northern part of Kanto Plain (Saitama Prefecture).