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Transboundary groundwater resources
management implemented in the
Kumamoto region of Japan
Tadashi Tanaka, Department of International Affairs, University of Tsukuba, Japan
T
he Transboundary Groundwater Resources Management
system is a typical groundwater management system
implemented in the Kumamoto region of Japan. The
system was introduced in 2004 and, in cooperation with neigh-
bouring municipalities, the Kumamoto City government has
created a unique funding system to encourage artificial ground-
water recharge projects through abandoned rice paddy fields
in neighbouring towns outside the city boundary. These will
enable sustainable use and management of regional groundwa-
ter resources and the passing down of this precious resource
to future generations. The groundwater management system is
regulated by the Kumamoto City, local governments and the city
people. It provides a good example for assessing and manag-
ing aquifer systems crossing regional administrative boundaries
within a given country, as well as of a typical self-governance
system for managing regional groundwater resources.
In addition to aquifers that continental countries share with other
countries, there are aquifers crossing regional administrative bounda-
ries within a given country. These aquifers are distributed in different
parts of Japan which have diverse regulations and social conditions.
The monitoring and management of such aquifers need
at least the same amount attention as those of trans-
boundary aquifers between national boundaries.
There is currently no unified national law in Japan to
manage groundwater resources except for preservation
of the land against subsidence. Therefore, the right of
groundwater resources belongs to the landowners.
Two groundwater laws, the Industrial Water Law
introduced in 1956 and the Law on Regulating the
Extraction of Groundwater for Use in Buildings intro-
duced in 1962, are effective across Japan, but practical
application of these laws to a specific area has been
decided by local government. For example, the Tokyo
Metropolitan Government has succeeded in reduc-
ing the rate of land subsidence by converting water
resources for industrial use from groundwater to
surface water, and by providing legislative guidance
to save groundwater resources in factories and build-
ings depending on these two laws. However, bordering
prefectures are still suffering from land subsidence.
Besides preservation of the land against subsid-
ence, however, a new concept is now growing
among Japanese municipalities, communities and
citizens. They see groundwater as a shared natural
resource that needs to be managed on that basis.
One typical groundwater management system is the
Transboundary Groundwater Resources Management
system implemented in the Kumamoto region of
Japan. The artificial groundwater recharge project
proposed by this system, using abandoned rice paddy
fields, is considered an excellent example of ground-
water management in Japan.
The vast groundwater reservoir and regional
groundwater flow system cover 13 local governments
including Kumamoto City, with an area of around
1,040 km
2
and 1 million residents. All the water for
the city’s residents is supplied from these abundant,
pure and crystal-clean groundwater resources. Most of
the region is covered by pyroclastic deposits created by
the four major eruptions of Mount Aso between 0.26
Ma and 0.09 Ma. There are two main aquifer systems,
namely the unconfined aquifer (No. 1 aquifer) and the
confined aquifer (No. 2 aquifer). The No. 2 aquifer
T
ransboundary
W
ater
M
anagement
Transboundary aquifer crossing 13 local governments in
the Kumamoto region
Source: T. Tanaka