Groundwater and surface water, which exist and behave differently each other in contrast, are very important water resources for social and economic activities. The sound interaction between groundwater and surface water is a main factor to maintain the sound hydrological cycle in a river basin. However it has been damaged by the recent water use and urbanization. The artificial recharge by well, which directly converts surface water into groundwater and compensates the decrease of natural recharge, has a great possibility to restore efficiently the sound interaction between groundwater and surface water. However clogging occurs inevitably and decrease the efficiency of the artificial recharge. This study reveals the general characteristics of the clogging by suspended solid and biological clogging by the basic laboratory tests. The relation between the permeability decrease and the clogging by suspended solid is formulated. The decrease of the permeability is also formulated when the clogging combined by suspended solid and biological clogging takes place. The formulations are found to be reasonably explain the results of the laboratory sand column tests.

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 A procedure for estimating flood damage to buildings, roads, and railways located in mountainous flood-plains due to probable maximum precipitation events is proposed. Probable maximum precipitation and consequent flood are estimated using the method proposed by Kadoya and Nagamori, 1979. For case study simulations, two areas, both located in the Chugoku District and damaged by recent large flood events, are selected. The characteristics of inundation flow in two areas under flood conditions caused by probable maximum precipitation are estimated using a two-dimensional flow model with fine-resolution calculation grids. Damage to humans and structures caused by probable maximum flood events is estimated based on the relationship between recorded damage due to recent large floods and inundation flow characteristics estimated using our numerical model. Effective measures to increase resilience in communities in mountainous regions are also discussed.

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 In flood risk curve estimation under various scenarios, inundation simulations with various spatio-temporal rainfall distributions are required since a rainfall pattern has a large impact on estimating economic flood damage; however, inundation simulation takes longer time than rainfall-runoff simulations due to its high computational costs. If a hydraulic variable calculated by a rainfall-runoff model has a single-valued relation with economic damage for any rainfall pattern, we can estimate an economic damage by only rainfall-runoff simulations without inundation simulations by applying the obtained relation for one rainfall pattern to others. This study analyzed the relations of several hydraulic variables with economic damage in the Yura-gawa River basin. It clarified that a uniform relation between flood peak discharge and economic damage is obtained in an area where inundation occurs along river channels. Finally, using the obtained relation, a flood risk curve in the area was estimated with sufficient accuracy.

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 This paper proposes a fitting method for discharge rating curves using Bayes spline regression. At present, these curve-fittings are conducted empirically. Operators usually employ piece-wise least-squares method for estimating these curves with linearizing height-quantity relationship via taking the square root of flow quantity. However, this method has a serious fault; difference in the form of curves among operators. In our method, arbitrariness of operators is excluded with determination of the number of knots via the generalized model selection that minimizes ABIC and EIC. Furthermore, spline curves that sustain continuity evacuate conflict of lines near boundaries and guarantee continuity of discharge rating curve. To verify validity of our model, we adapt our method to the cross-sections of the Toyohira and the Tama rivers. As a result of the analysis, we can obtain favorable fitting curves in the both rivers.

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