This study aims to find out care points of greening plan in re use plan of Marine Corps Air Station Futenma. Research methods were observed daily spring water flows, multiple regression analysis, analyzed out and in flow characters of each spring waters, and then assuming the subsurface structure.
At first, by using observed daily value of each spring waters (total 489 times), we developed estimation formulas, which described as form of multiple regression analysis formulas, of daily spring waters and cumulative total value of short & long term precipitation. The results were that these adjusted R2 of estimation formulas are from 0.51 to 0.77, these mean that formulas could give explanations of existing circumstances. These estimation formulas are called response models in hydrology which explains interconnection of amounts precipitation and spring waters.
On Second, we analyzed out and in flow characters of each spring waters by response models. The results of this step, we got 3 types (subdivided in 4types) of out and in flow characters of each spring waters. Type I is spring waters which explain by constant term mainly. It means that these spring waters gush out stably and constantly, and so, it assumed these spring waters flow out from one depthless and broad tank. (Fig. 6, spring water(3)(6)(9)) Type II is spring waters which explain by influence of long term precipitation mainly. It means that these spring waters flow around from 1to 3 months behind precipitation, like very long and slow pace rivers. So we assumed these spring waters come from small surface area tank or the come from thick Ryukyu lime stones layer(Fig. 8, spring water:(11)(13)). Mixture type I and IIis spring water (8). This spring water has both character of I and II. Type III is spring water influenced by short term precipitation. It means that the spring water flows out comparatively soon after rainfall, within few days. So we assumed the spring water is connected with cave and it works like a underground river.(Fig. 9, spring water:(7))
Considering our all results, we proposed and discussed to local government and land owners about the point of greening plan in reuse plan of Futenma. 1) Greening plan which located type I, Mixture Type I and II, and watershed C and D should be care for quantitative approach. Because these springs are assumed to be shared a depthless and broad underground tank, every precipitation will be penetrating and finally reach same water basin. So, the point of greening area is not a location but the enough quantity for recharging amounts of spring waters. (Fig. 14 enough quantity greening in the same water basin, watershed C and D, type I) 2) Greening plan which located above the underground water vein, like type II and watershed D and E should be care for on-site approach. Because these springs are assumed be pooling precipitation in the gryke of Ryukyu lime stone layer, if the surface of this site be covered by buildings or be paved, it will be directory influenced to recharge spring water. (Fig. 14 on-site greening above the underground water vain, watershed D and E, type II)
Conclusion of our proposal-based research is that our proposals were adopted in the official reuse planning as a policy in March 2017.
This work was supported by JSPS KAKENHI Grant Number JP17K06714.
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