| Summary: | 碩士 === 國立宜蘭大學 === 土木工程學系碩士班 === 94 === As for traditional flood control point of view, rainfall and runoff were treated as the source for flood and should be constrained and expelled as soon as possible. Efforts were thus spent in flood control and in the mean time fresh water resource were wasted. On the other hand, for water conservation in concern, water retention efficiency is now an important aspect in building design and land development. Most of the time, unpaved ground surface or permeable pavements were adopted for increasing infiltration rate and consequently improving water retention efficiency. However, as soil becomes saturated along with continuous rainfall, the amount of infiltrated water reduces to nil and rainfall turned to flown-away surface runoff. Very few research have been done on the water retention efficiency when surface runoff were collected to a underground flood retention pond. In this research site, surface runoff was collected by a system of underflow to a boulder packed underground pond for water retention and the water retention efficiency for such an arrangement were evaluated.
Piezometers and a rain gauge were installed to collect data for a period of one year. Correlation among precipitation, storage pond water level and groundwater table were analyzed and the water retention efficiency of the site was found to be satisfactory as the water source for ecology pond in the area. In addition, from digital elevation model (DEM) of the site and rainfall data collected, HEC-GEOHMS was used to simulate the correlation between rainfall and storage pond water table. Hydrological parameters and the porosity of the packed boulder were then back analyzed comparing the simulated results and the data collected in-situ. Furthermore, efforts were made on changing the location and surface condition of the collecting ditch and underflow during the simulation to find the optimal conditions as for water retention efficiency in concern. The quantity of water retained was also estimated through correlating with rainfall intensity and duration for use in evaluating the efficiency for water retention.
Methodology and Results introduced in the research are believed to be helpful in evaluating the water retention efficiency of underground boulder packed storage pond. These could also be applied to future design of water retention pond for community, park and other public facilities.
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