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，还开始关注农业副产品农业多功能的实现。此外，除了作为工业政策的农业政策之外，从农业和城市地区共存的角度来看，国家土地管理也非常重要。因此，农业的多功能性在农业政策中具有国家土地政策和区域政策的重要意义。在本研究中，我们重点研究了农业的具体功能，即防洪、减缓气候变化（防止气温上升）和防止农田、灌溉池塘和水道的土壤流失。调查场地位于大阪府森南地区，农田灌溉系统采用农业池塘灌溉，农业用水在该地区的共同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，并利用实测数据进行了分析。研究发现，灌溉池、水渠等灌溉设施不仅具有生产粮食的农业平台作用，还具有为整个社区提供区域安全、舒适性等广泛服务的区域社会平台作用。特别是在农民和非农民共同居住的城市化地区，灌溉设施作为共同的社会平台发挥着重要作用。此外，由于社会资本对发挥农业和灌溉设施的多种功能非常重要，因此在各个地区建立社会资本是必要的。土地改良区是由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.