Research on Effective Installation of Subsurface Drain and the Maintenance of its Function

地下排水是改善农田条件、提高农业生产力的重要技术之一。需要一种简单、客观的地下排水效率评价方法。井上和山本从管道安装条件的角度，通过对管道对准的凹凸性进行分析，研究了管道排水管的问题，并提出了将偏离配置对准和管道弯曲率用于管道状态的方法。通过对地下水位和管道流量的连续测量，验证了排水功能的可持续性。试验证明，随着龄期的增加，排水能力逐渐下降。Kashiwagi对乳草产量和地下排水的影响进行了调查。Nakamura还对水田转耕旱田的地下水位和地下排水效率进行了长期调查。他特别对两条地下排水管道之间的土壤渗透情况进行了精确的测量。为了恢复农田的排水功能，北川开发了“截排法”新技术。该方法不仅适用于泥炭土，也适用于安土和灰色旱地土。它是一种鼹鼠排水，但具有更持久的腐烂，造价便宜。他还开发了过滤材料，以避免在多立大山下游的泥石流地区等酸性土壤中排水管堵塞。

Subsurface drainage is one of the important technologies for the improvement of field condition for agricultural productivity. Simple and objective method for evaluation of efficiency of subsurface drain is required. Inoue and Yamamoto investigated the problem of pipe drain from the viewpoint of its condition of installation by analyzing the concavity and convexity of pipe alignment, and proposed the use of deviation from the configured alignment and the flexion rate of pipe for the pipe condition. The sustainability of drainage function was also verified by continuous measurement of groundwater level and pipe discharge. It is proved that the drainage capability gradually declines with the age.Kashiwagi made investigation on dairy grass productivity and the effect of subsurface drain. Nakamura also made long-term survey on groundwater level and the efficiency of subsurface drain in the paddy-converted upland field. He especially made precise survey on soil permeability condition between two underdrain pipes.Kitagawa developed new technology of 'Cutting drain method' for the restoration of drainage function of the field. This method is applicable not only for peat soil but also for Andosol and gray upland soil. It is a kind of mole drain but has more durability on decay, and cheap to construct. He also developed filter material to avoid clogging of the drainage pipe in acid soil such as mudflow region in downstream of Mt.Tokachi-dake.