Studies on Utilization of Water Resources and Irrigation Facilities for Sustaining the soundness of Hydrologic System in a river basin with an Urban Sprawl Area

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Irrigation water has not only a role of feeding water for crops but also a function as "regional water" associated with the local residents' life and environment. Nowadays it is feared that such the function is being lost due to advancing of urbanization. The objective of this study is to try to investigate the role which agricultural infrastructure (especially irrigation pond) plays for aquatic environment, including artificial water management aspect, at a region or basin level in Kishiwada area where urban sprawl is advancing. In this study, hydrological observations such as river flow, inflow and outflow in an irrigation pond, precipitation, water quality, and so on were continuously carried out, and based on these data, the following aspects were discussed.1.Investigation of the characteristic of climate and water resources in Kishiwada area : Using the AMEDAS data at 7 stations within Osaka prefecture, a potentially available water resource, which is calculated by precipitation m … More inus potential evapotranspiration, were estimated at each station. The result indicated that the study area is categorized into relatively dry climate in Japan. And based on the irrigation pond ledger, the geographical distribution of irrigation pond was investigated, and water resources deposit was estimated.2.Evaluation of flood mitigation function of irrigation pond : For Hoji-ike pond which is one of the irrigation ponds, located in the study area, flood mitigation function of the pond was evaluated through both analysis with observed data and model simulation. As a result, it was indicated that this pond mitigated floods enough though its surface area is relatively small for its catchment area.3.Evaluation of nutrient load reduction functions of irrigation pond : It is sustained that nutrient load in river water which was in hydrodynamic state was reduced by going through the pond in which the water was in hydrostatic state.4.Estimation of nutrient load reduction in the river associated with expanding sewerage infrastructure : The improvement of river water pollution level (decrease of nutrient load) according to increasing of the sewerage connecting ratio in the Haruki River watershed was estimated. The results indicated that increasing the sewerage connecting ratio in the down stream area, where the population density is higher, was more effective than expanding the sewerage system to the upper stream area, where is rural area, for decreasing of nutrient load level in river water.Integrated the above results, it was discussed what the irrigation system should be for sustaining the soundness of hydrologic system from the point of view of "storage" and "purification" of water. Less