??This paper presents a comprehensive analysis of climate change impacts on the discharge in the small mountainous Mizoguthi Catchment, Japan, using a large ensemble of climate simulations from the Database for Policy Decision Making for Future Climate Change (d4PDF) through the TOPMODEL hydrological model. Two sets of experiments for a 60-year period were conducted using d4PDF data: historical and 4-K-warmer climate simulation experiments. The precipitation and discharge analyses were based on cumulative frequency, box–whisker plots, flow duration curves, and return periods under historical and 4-K-warmer climate conditions. Results showed that irrigation periods with low precipitation occurred more frequently, and the catchment was more likely to become more seriously dry than it is at present. Finally, the return period results showed that droughts are likely to have major impacts due to the expected decrease in discharge. These results suggest severe challenges to water resources in the catchment under 4-K-warmer climate conditions and should be used to mitigate the adverse effects of drought in the study area by adopting appropriate adaption strategies.
??The influence of water abstraction for hydroelectric power generation on instream fish habitat was evaluated using a two-dimensional hydrodynamic simulation, the Habitat Suitability Index (HSI), Weighted UsableArea (WUA), and Weighted Suitable Area (WSA) in a midstream reach of the Anegawa River, Japan. The study reach is affected by upstream dam flow regulation and water withdrawal for hydropower generation. The unsteady two-dimensional hydrodynamic model was calibrated and validated with observed data from 2015 and 2016. The reach’s habitat quality was assessed for the adult goby (Rhinogobius flumineus) and dark chub (Nipponocypris temminckii) by combining computed hydraulic variables and suitability indices for the given species. Analysis of the spatial HSI distribution and the WUA and WSA variations under discharges ranging from 0.1 – 40 m3/s revealed that both WUA and WSA for goby tended to be larger than those of dark chub. Water abstraction had opposite effects on goby and dark chub during their spawning months. These results, including the flow curves developed here, could inform improved future management of the flow regime in this and other Japanese rivers.
??We conducted laboratory experiments to clarify the weir designs suitable for Arctic lamprey (Lethenteron japonicum) ascent. Ascent experiments were conducted using three weir types (sharp-crested, inclined sharp-crested and broad-crested). The difference in water depth upstream and downstream of the weir and time period (daytime and night) were changed to determine their effects on ascent behavior. Our results indicated that the difference in water depth negatively and strongly affected ascent behavior and the weir type did not affect ascent behavior. No lamprey ascended the all types of fishway-weir when Δh was 24 cm. The inclined sharp-crested weir had a 45° incline upstream. However, it did not contribute to their ascent and gentler slope than 45° may be better for suitable weir design. The broad-crested weir served the attachment place for lamprey to suck by their mouth and was expected to be suitable for inherent ability of lamprey ascent. However, the ascent rate on the broad-crested weir was not better than the other two types. Additionally, video camera analysis revealed that lampreys attempted ascentsmore during the night than daytime. Our experiment result revealed unknown Arctic lamprey ascent behavior and can contribute to the conservation and modification in freshwater ecosystem.
??The Tonle Sap Lake in Cambodia is the largest fresh water lake in Southeast Asia. Hydrological and hydraulic models are powerful tools to understand water flow in the lake basin. However, due to poor measuring density of gauge-based precipitation in Cambodia, it is difficult to develop accurate models. In this study, Global Precipitation Climatology Project (GPCP) was used as satellite-based precipitation, and as a result of examining its characteristics, we found that GPCP tends to be larger values than gauge-based precipitation in the lake basin. Therefore, the hydrological and hydraulic model used GPCP after adjustment to improve model accuracy. The accuracy of the simulation of the hydrological and hydraulic model was evaluated by NSE. As a result, by using the adjusted GPCP for the hydrological and hydraulic model instead of gauge-based precipitation, the average NSE of the runoff discharge from seven watersheds, which is the simulation result of the hydrological model, was improved from 0.39 to 0.49, the NSE of the water level at Kg. Luong, which is the simulation result of the hydrological and hydraulic model, was improved from 0.93 to 0.97.
??The number of unexpected accidents in agricultural pipelines is increasing in Japan. Appropriate repair and reinforced construction of pipeline methods is critical to extend a pipeline’s life. An internal-leaking preventive joint band method is one measure that can extend pipeline life. The internal-leaking preventive joint method repairs with a band the place where such problems as water leakage occurs. When the band is installed in a pipeline, local loss occurs because the pipe’s inner diameter is locally reduced. But the band’s shapes vary, no magnitude of the band’s local loss has been established yet. We investigated the influence of different band shapes on the loss factor measurements of a single band by both hydraulic model and numerical experiments. Our results found that the loss factor was about 0.8 times that of the non-rounded band edge when the band edge was rounded, and changing the bandwidth from 19 to 50 mm had no effect on the loss factor.