普天間飛行場基地跡地計画における緑地計画に関する提案型研究

Abstract

After the Special Action Committee on Okinawa (SACO) agreement in 1996, Okinawa Prefecture and multiparty have been developing fundamental reuse plan with landowners and citizen. It was changed several times through expert investigations and discussions among them. 2013 plan has come to the halfway point of it. In the plan, some points, especially preservation policy of green, under ground water, and historical heritage in the base were reached consensus among parties. Despite some preservation policy of green and underground water, it has been missing throughout the water balance model study of this area. When people want to save the under ground water to reply the water demand, generally it needs an investigation of current water balance model and water use. So we started a proposal-based study about this research issues. This study aimed to clarify two study objectives. The 1st goal is to calculate exact a water balance model about approx. 1617ha of the 5 watershed areas, A, B, C, D and E, in Ginowan City where the Futenma Air Station is located in. At first, we calculate each land use ratio by GIS to simulate the amount of underground seepage of the rainfall in these 5 watershed areas. It is as for theoretical value. And the other hands, we also researched the amount of several water springs to calculate the amount of underground seepage of the rainfall in these areas as an observation value. The field surveys were held 60 times at each spring waters by flow speed measurement and positive displacement flowmeter. The observation value is in agreement with the theoretical value that we simulate. The finding and the fixed water balance model will contribute to the huge area planning like Futenma. The 2nd goal is to review the open space plan in Futenma reuse plan to fit water demands in these areas by using our water balance model. Because the today's 70% of Futenma Air Station is covered green, it functions as like watershed protection forest. But according to contemporary Reuse plan, after the developing, the green area will decrease than today's area. According to our data gathered by interviewing to farmers and industrial officers who use under ground water and spring water, today's water demand reaches almost 5-62% per supply from the natural condition. We analyzed the demand-supply water balance after the development, it will show over demand at some springs. And the worse more, there are some struggles between farmers in the dry season by the lack of water supply. This result is very important. Before our research, there is no report of the amount of water demand. It means that the demand-supply balance had not been paying little attention. Thus, we proposed to Prefecture Office and City Office to review the open space plan with considering water demands. We explained our analysis in detail at the closed meeting of them. Then almost of our concepts was accepted in the public plan. This study's consequences and contribution are three points. 1) The water balance model of this area is established. 2) The under ground water and spring water demand of this area are calculated. 3) Through continuing discussion with parties, our proposal-based study is accepted in the public reuse plan of Futenma. This work was supported by JSPS KAKENHI Grant Number JP24710168.