Journal of Rainwater Catchment Systems
Online ISSN : 2186-6228
Print ISSN : 1343-8646
ISSN-L : 1343-8646
最新号
選択された号の論文の5件中1~5を表示しています
  • Yuta Yaegashi, Hidekazu Yoshioka, Koichi Unami, Masayuki Fujihara
    2018 年 24 巻 1 号 p. 1-8
    発行日: 2018年
    公開日: 2019/08/06
    ジャーナル フリー

      Release of artificially hatched juveniles of P. altivelis into river systems has been a common solution strategy to maintain their population. In addition, each inland fishery cooperatives in Japan is required to release fishes into the block in rivers that they manage; a block is a set of several fishing sites with the same river environment. The release should be carried out considering characteristics of blocks in a river system, so that a performance index is maximized, which consists of the utilities of blocks that increases as the total number of the allocated fish increases and the penalty that restrains difference in the allocated fish between the blocks. However, such an approach has not been addressed so far. In this paper, to tackle this problem, an optimal allocation model to determine the allocation of the released fish into several blocks in a river system is proposed. The decision-makers in the model is a fishery cooperatives which manage blocks in the river system. Here, an optimal allocation policy can be obtained by solving a constrained nonlinear and static optimization problem and is numerically computed with a logarithmic barrier function method focusing on the particular case of Hii River, Japan.

  • Asep Denih, Akira Maeda, Masahiro Tasumi, Yoshinori Shinohara, Shinich ...
    2018 年 24 巻 1 号 p. 9-14
    発行日: 2018年
    公開日: 2019/08/06
    ジャーナル フリー

      This study attempted to evaluate the performance of the GCOM-C ETindex estimation algorithm at a lodgepole pine tree open forest in eastern Idaho, United States using a dataset provided by the Idaho EPSCoR program. As a limitation of the study, the energy balance closure problem in flux measurement, which is a typical problem in flux measurements by eddy covariance systems, prevented a robust, quantitative evaluation of the ET estimation accuracy. Under this limitation, the results indicated that the estimation algorithm overestimated ET in the conditions of the study area, especially during summer time. One possible reason for the overestimation was that the algorithm overestimated surface wetness over most of the year, except in winter. The results of this evaluation provide valuable information for future improvement of the estimation algorithm. Further investigation of the weather and flux conditions, including the use of additional data such as scintillometer-measured flux data, might reduce uncertainty in the measured flux data.

  • -Case Study of the Majuro Atoll in the Republic of the Marshall Islands-
    Kazuhisa Koda
    2018 年 24 巻 1 号 p. 15-21
    発行日: 2018年
    公開日: 2019/08/06
    ジャーナル フリー

      Laura Island is located about 50 km away from downtown in Majuro atoll, which is the capital of the Republic of the Marshall Islands. It has been very important for Majuro atoll to ensure the conservation of its water resources because low and flat Majuro atoll in fact has neither river nor lake. Nevertheless, up-coning, which is the process of partial rising of the freshwater-saltwater interface in the freshwater lens near the water-supply well, was caused by the excess pumping from it during the severe drought in 1998. The up-coning will make the water usage of the freshwater lens difficult. Thus, sustainable water usage, as demonstrated in this present study, is immediately required to prevent the up-coning in the freshwater lens because there is no other water source during drought. SEAWAT model simulation of the groundwater usage was conducted at the central part of Laura Island, including the water-supply well, which was affected by the up-coning. The sustainable pumping discharge from the water-supply well was calculated under the conditions that variable daily pumping discharge without monthly rainfall was assumed. Consequently, due to the increased daily pumping discharge the total amount of pumping discharge was increased. This indicates that it needs more time to recover from the up-coning in the freshwater lens. Therefore, a pumping standard and the appropriate water usage to reduce the pumping intensity is being proposed, which is based on the numerical simulation concerning the occurrence of the up-coning phenomenon in Laura Island during the drought.

  • Tran Tuan Thach, Masayoshi Harada, Kazuaki Hiramatsu, Toshinori Tabata
    2018 年 24 巻 1 号 p. 23-31
    発行日: 2018年
    公開日: 2019/08/06
    ジャーナル フリー

      This study involved regular observations for four years in the reservoir, in which overabundant organic matter was prominent due to humic acid, to evaluate the water quality dynamic near the bottom during long-term anoxic periods. Based on the temporal changes of dissolved oxygen, nitrate-nitrogen, ammonia-nitrogen, phosphate-phosphorus, sulfide, total iron ions and sulfate, this study focused specifically on the influence of the redox state of the sediment surface during the early stage of thermal stratification on the anaerobic biochemical reactions. As a result, nitrate-nitrogen started to decrease to zero due to denitrification as soon as the anoxic sate occurred, and then both ammonia-nitrogen and phosphate-phosphorus increased linearly with time due to iron reduction after nitrate-nitrogen had decreased to zero. Sulfide began to increase linearly due to sulfate reduction as soon as nitrate-nitrogen disappeared. Also, the initial redox state of sediment impacted on the change characteristics of phosphate-phosphorus, ammonia-nitrogen and sulfide in the points of increasing timings, duration and rates. It was concluded that our results would provide important finding about the mechanisms of aqueous environmental deterioration due to organic pollution as well as beneficial information for the modification of water quality prediction model.

  • Elizaphan Otieno Ndede, Koichi Unami, Masayuki Fujihara
    2018 年 24 巻 1 号 p. 33-36
    発行日: 2018年
    公開日: 2019/08/06
    ジャーナル フリー

      Fish is one of the most important primary sources of animal protein for human consumption globally. Fish harvesting strategy in artificial fish ponds is important to fish-farmers who practice commercial aquaculture under uncertainties of market prices. Robust optimization was developed to solve uncertain optimization problems by considering the uncertain data to be existing in an uncertainty set. In this study, we consider that growth models for market price of fish with volatility are given and then analyze harvesting policy for fish in the framework of discrete robust optimization. Demonstrative optimization is performed using a robust counterpart optimization technique, which involves numerical solution of nonlinear algebraic equations systems, with hypothetical model parameters. With discrete harvesting stages in the time domain, the robust optimal harvesting policy under presence of volatility is prescribed as a partial harvesting strategy.

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