Functional analysis and estimate of irrigation and drainage system as social common foundation for the coexistence of rural and urban areas

最近，随着日本社会的转型，农业政策也发生了转变。到目前为止，农业政策的主要目标一直是粮食生产，但近年来，除了粮食生产外，农业作为农业的副产品，其多功能的实现也得到了重视。此外，除了农业政策作为产业政策外，从农业和城市共存的角度来看，国家土地管理也非常重要。因此，农业的多功能性作为国家土地政策和区域政策在农业政策中具有重要意义。在这项研究中，我们侧重于农业的具体功能，即通过农田、灌溉池塘和水道来控制洪水、缓解气候变化(防止气温上升)和防止土壤流失。调查的田间地块位于大阪府仙南地区，有农业池塘灌溉系统，农业用水在一个地区的公共社会平台中发挥着重要作用。我们进行了各种水文和气象观测，并利用测量数据进行了分析，结果发现，灌溉设施，如灌溉池塘和水道，不仅发挥了农业生产粮食的平台的作用，而且还发挥了区域社交平台的作用，为整个社区提供区域安全和舒适等广泛的服务。特别是在农民和非农民共同占有的城市化地区，灌溉设施作为共同的社会平台发挥着重要的作用。此外，由于社会资本对于发挥农业和灌溉设施的多功能非常重要，因此社会资本的建立在每个地区都是必要的。土地改良区是农民管理灌溉设施的组织，是潜在的社会资本。

Agricultural policy has veered recently in parallel with the transformation of Japanese society. The main objective of agricultural policy had been the food production until now, but the realization of multifunctionalities of agriculture, which are by-products of agriculture, has been paid attention in late years in addition to food production. Furthermore, aside from agricultural policy as industrial policy, national land management has been very important from a standpoint of the coexistence of agricultural and urban areas. Thus, multifunctionalities of agriculture have an important meaning in agricultural policy as national land and regional policies. In this research, we focused on specific functions of agriculture, which were flood control, climate mitigation (prevention of air temperature rising), and prevention of soil loss by agricultural lands, irrigation ponds, and water channels. The investigated field site had irrigation system using agricultural ponds and was located in Sennan region in Osaka Prefecture, in which agricultural water utilization played important roles in common social platform in a region. We conducted various hydrological and meteorological observations and analyzed using measured data.As a result, it was found that irrigation facilities, such as irrigation ponds and water channels, played a role not only as agricultural platform to produce food, but also as regional social platform to supply wide-ranging services such as regional security and amenity to overall community. Especially, in urbanized area, in which both farmers and non-farmers occupy, irrigation facilities fulfill an important role as common social platform. In addition, because the social capital is very important to exert multi-functions of agriculture and irrigation facilities, the establishment of the social capital is requisite in each region. Land improvement districts, which are organizations to manage irrigation facilities by farmers, are potential social capital.