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close this bookFreshwater Resources in Arid Lands (UNU, 1997, 94 p.)
close this folder5: The development of groundwater resources on the Miyakojima Islands
View the document(introduction...)
View the documentIntroduction
View the documentOutline of the Miyakojima Islands
View the documentGeology and the hydrological cycle
View the documentOutline of the irrigation project on Miyakojima
View the documentThe construction and concept of the underground dam
View the documentThe Construction of the Cut-off Walls
View the documentThe construction of the intake facilities
View the documentThe storage situation of the Sunagawa underground dam
View the documentConclusion
View the documentBibliography

Outline of the irrigation project on Miyakojima

In order to reduce the burden of drought and to modernize agricultural management, an irrigation project has been implemented since 1987. The area benefiting from the project is 8,400 ha, which occupies half of the total surface area of the islands and about 90 per cent of the arable land. The total project cost was estimated at ¥89 billion in 1986.

The irrigation project is divided into the following three parts (table 1):

1. The construction of two underground dams, named Sunagawa and Fukuzato, and intake facilities (a number of wells with submergible motor pumps) installed in the storage area of those dams, which will be implemented by the JALDA Project;
2. The construction of farm ponds and the main pipelines, which will be implemented by the Japanese National Irrigation Project;
3. The construction of irrigation facilities on the farm and the field consolidation, which will be implemented by the Prefectural and Local Government Project.

The water sources for the project depend on two underground dams, one experimental underground dam (Minafuku) and one natural groundwater basin (Nakahara). The total amount of developed groundwater resources in this project will be 24 million cubic metres (mcm), which constitutes 40 per cent of the total unused groundwater returning to the ocean per annum, an estimated 60 mcm (table 2).

Table 1 Planned Infrastructure Facilities of Irrigation Project

Administrative organization

Planned infrastructure facilities

Quantity

Costa (million $)

JALDA

Underground dam (incl intakes)

2

181

Government of Japan

Irrigation canal (km)

135.1



Water compressing facility

8



Farm pond

7



Water management facility

1

145

Local government

On-farm irrigation facility (ha)

8,394



Land consolidation (ha)

3,140

267

Total



593

a. Estimated costs based on 1986 prices ($1 = ¥150).

Table 2 Water Resources Development Plan

Underground basina

Sunagawa

Nakahara

Fukuzato

Minafuku

Underground dam

Sunagawa: main dam

(Natural basin)

Fukuzato: main dam, 2 sub-dams

Minafuku Dam

Basin area (km²)

7.2


12.4

1.2

Reservoir area (km²)

4.89


7.0

0.9

Total capacity (mcm)

9.5


10.5

0.7

Effective capacity (mcm)

6.8


7.6

0.4

Water utilization capacity (mcm)

8.8

3.6

11.0

0.6

a. mcm = million cubic metres.