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

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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.