Journal of Rainwater Catchment Systems
Online ISSN : 2186-6228
Print ISSN : 1343-8646
ISSN-L : 1343-8646
Volume 24 , Issue 2
Showing 1-7 articles out of 7 articles from the selected issue
  • Eiji Ichion, Mitsunori Nakano, Kenji Tanaka, Shunsuke Chono, Yoichi Fu ...
    2019 Volume 24 Issue 2 Pages 1-7
    Published: 2019
    Released: October 28, 2020
    JOURNALS FREE ACCESS

    ??Sloped-weir fishways have been proposed to improve aquatic connectivity and restore fish migrations in agricultural ditches. However, the most suitable design for such fishways has not been identified. The goals of this study were to identify the most suitable sloped-weir fishway design for ascending fish and to determine suitable flow rates when fish ascend the fishway. Nine types of weirs were made by changing the angle of the weir slope (α) and that of the V-shaped notch on the upper surface of the weir (β). Several volumetric flow rates (1.58-1.98 L/s, 5.09-5.37 L/s, 9.24-9.54 L/s, and 14.35-14.43 L/s) were used in the experiments for each weir type. The ascent rates for three fish species (Oryzias sakaizumii, Misgurnus anguillicaudatus, and Carassius sp.) were determined for each type weir in the experimental flume. Hydraulic conditions were measured, including velocity and depth of water flowing over the weir, and flow velocity and depth in the area downstream of the weir. We identified two types of suitable weirs for O. sakaizumii: one with α = 60°, β = 5°, and the other: α = 45°, β = 30°; O. sakaizumii was not affected by flow velocity while ascending the fishway. The three weir types with β = 30° were suitable for the ascent of M. anguillicaudatus, which ascended well when the flow rate was above 5 L/s. For Carassius sp., all weir types were well, especially with flow rates over 9 L/s. In addition, our results suggest that the weir with α = 45°, β = 30° was suitable for all three species.

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  • Emal Wali, Masahiro Tasumi, Yoshinori Shinohara, Shinichi Takeshita
    2019 Volume 24 Issue 2 Pages 9-15
    Published: 2019
    Released: October 28, 2020
    JOURNALS FREE ACCESS

    ??Khost province of Afghanistan faces scarcity of water because of immature agricultural water management. Neither detailed information on agricultural land cover for specific crop types are available, nor are crop water demands estimated. Satellite remote sensing is a powerful tool for monitoring cropping areas and estimating crop water requirements. However, small fields in the Khost province makes a field-level analysis from satellite challenging. In this study, a crop-type classification was conducted by NDVI time-series provided by Sentinel-2 satellite images with 10-m resolution. The accuracy assessment using 1,804 ground-truth data indicated the crop classification was successful, with 90% overall accuracy. The accurate crop information enables us to estimate the crop water requirements of the agricultural region, with the spatial distribution. Crop water requirements, which is identical to the field evapotranspiration requirements, were estimated for each crop type, by referencing evapotranspiration computed by ground-measured weather data and by determining crop coefficients, which were determined by interviewing the local farmers and literature. The resultant map of crop water requirements is the spatial information of field evapotranspiration requirement, and it is expected to contribute towards advanced irrigation and water resources planning and management in the Khost province in future.

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  • Hideto Fujii, Takashi Nakamura, Sarann Ly, Sambo Lun, Sokchhay Heng, Y ...
    2019 Volume 24 Issue 2 Pages 17-25
    Published: 2019
    Released: October 28, 2020
    JOURNALS FREE ACCESS

    ??This paper analyzes the results of observation of the flow in the Tonle Sap River in Cambodia from March 2017 to March 2018, which were obtained using an acoustic Doppler current profiler (ADCP) with the goal of gaining a better understanding of the complicated flow characteristics of the river's seasonally repeating normal and reverse flows and obtaining reliable calibration and validation data for a hydraulic model. The objective of this study is accuracy evaluation of ADCP and clarify the factors to reduce accuracy of moving boat technique based on the obtained data equipped with a real-time kinetic (RTK) -GPS. The data were gathered at the Prek Kdam water level observation station, at which the river width is approximately 600 m. ADCP observation was carried out using the moving boat technique, which involved the towing of a HydroBoard-II equipped with a Xylem M-9 ADCP system and RTK-GPS module. The findings obtained were as follows: 1) It was possible to observe the seasonally repeated normal and reverse flow rates of the Tonle Sap River accurately by using ADCP. In 17 out of 22 times observation sessions, the CV of the flow discharge during round-trip observation was less than 5%. 2) Low data accuracy could arise from several factors if an inappropriate observational method was applied. To avoid this, care must be taken to understand the particulars of ADCP observation using moving boat technology. 3) When the transducer depth was shallow and the boat speed and pitch angle were large, Signal Noise Ratio (SNR) attenuation occurred as a result of air entrapment. To reduce this factor, the depth of transducer is very important.

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  • Asep Denih, Masahiro Tasumi, Yoshinori Shinohara, Shinichi Takeshita
    2019 Volume 24 Issue 2 Pages 27-32
    Published: 2019
    Released: October 28, 2020
    JOURNALS FREE ACCESS

    ??In this study, the accuracy of evapotranspiration estimated by the Global Change Observation Mission-Climate (GCOM-C) evapotranspiration index (ETindex) estimation model was evaluated using a scintillometer flux measurement dataset provided by the Idaho EPSCoR program, which was collected at an open lodgepole pine tree forest in eastern Idaho, United States. The scintillometer-measured sensible heat flux was quality-controlled, and evapotranspiration was computed using radiation data. The results of this analysis indicate that evapotranspiration was overestimated by the estimation model during summer. Owing to the overestimation in summer, the overall mean absolute error for the entire study period was 33 mm month-1, or 47% of the actual evapotranspiration. However, by conducting simple linear adjustment, the overall mean absolute error was improved to 14 mm month-1, or 19% of the actual ET. As the simple linear adjustment attempted in this study does not consider the seasonal trend in error, there is room to further improve the evapotranspiration estimation in the forest area by considering the seasonal effect during adjustment.

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  • Noriaki Takeda, Hitone Inagaki
    2019 Volume 24 Issue 2 Pages 33-44
    Published: 2019
    Released: October 28, 2020
    JOURNALS FREE ACCESS

    ??In this study, we investigated the water supply function of the primary open channel, which is 31 km, extending from upstream to end of the lower Aichi irrigation project. The target channel has been used only for agricultural purposes. Based on numerical computations, we examined the potential problems that could occur when the secondary channels are converted from an open channel type to a pipe flow type, while still using the existing amyl-type upstream water level control gate by the phase-I project.

    ??Consequently, problems in water distribution such as supply shortage or unused water were predicted as unavoidable owing to the diurnal variations in open channel type waterway systems, even if supply was managed using upstream water level control gates connected in series.

    ??The case where the length of the waterway is extended to 60 km, i.e., nearly twice the length of the target channel, it was predicted that the scarcity of incoming water volume tends to increase. Extension of the open channel length derives the delay in arrival time of water, because it requires considerable time for forming the surface slope.

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  • Siqinbilige Wang, Keigo Noda, Masateru Senge, Weilisi
    2019 Volume 24 Issue 2 Pages 45-51
    Published: 2019
    Released: October 28, 2020
    JOURNALS FREE ACCESS

    ??Due to excessive water usage in the middle and upper basin, the discharge in Ejina River Basin, Heihe River, China, has been decreasing and the lakes in the downstream have dried up recently. The purpose of this study was to evaluate the change of vegetation area in Eajina River Basin, interpreting two periods (1990 and 2009) of Landsat images using maximum likelihood method. The result showed that the vegetation area decreased in the two decades from 23.1% to 18.4% by 223.4km2, of which the decrease ratio was about 20%. The decreased parts changed into gobi, desert or arable land. Water area decreased from 1.6% to 0.8% by 39.9 km2, of which the decrease ratio was 52%. On the other hand, non-vegetation area increased from 75.3% to 80.8% by 263.3 km2. Remarkable changes of land cover are mostly accountable by the change of water availability because of agriculture promotion and/or environment conservation policies.

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  • ―Evaluation and Estimation based on Predictive Equations for Life-span of Pipes―
    Hitone Inagaki
    2019 Volume 24 Issue 2 Pages 53-59
    Published: 2019
    Released: October 28, 2020
    JOURNALS FREE ACCESS

    ??Establishment of planning and design method to appropriately predict degradation of performance of irrigation system and to ensure proper function preservation is required to maintain functions with high superiority of pipeline in the future. Based on yearly and cumulative number of unexpected accidents, predictive equations for Life-span were established. The accident ratio of the accident curve in the pipeline temporarily declines due to partial function preservation, the rise becomes gradual but the overall curve gradient is maintained.

    ??Therefore, with the passage of time, functional deterioration in most unrepaired sections becomes obvious, and when returning to the previous accident curve, accidents increase rapidly after 2010. Based on the accident estimation after 2014, it can be predicted that there is a possibility of an explosive accident in the aged pipeline.

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