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。地下排水效率的评价需要一种简单、客观的方法。Inoue和Yamamoto从管道安装条件的角度研究了管道排水问题，通过分析管道对中的凹凸性，提出了在管道条件下使用与配置对中的偏差和管道的弯曲率。通过对地下水位和管涌流量的连续测量，验证了排水功能的可持续性。研究结果表明，随着牧草年龄的增长，牧草的排水能力逐渐下降。柏木对牧草生产力和地下排水效果进行了调查。中村还对退耕还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之间的土壤渗透状况进行了精确的调查。北川开发了一项新技术--“割漏法”，以恢复油田的排水功能。该方法不仅适用于泥炭土，也适用于红壤和灰色旱地土。它是一种摩尔排水沟，但具有更好的耐腐蚀性，而且建造成本低。他还开发了过滤材料，以避免在酸性土壤中的排水管道堵塞，如高知山下游的泥石流地区。

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.