Subsurface Water Movement and Groundwater Recharge of Terraced Paddy Fields in a Watershed-Experimental and Simulation studies

• Main Authors: Kung-Wei Kuo, 郭功偉
• Other Authors: 陳世楷
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/7qr9n5

碩士 === 國立臺北科技大學 === 土木工程系土木與防災碩士班 === 105 === The purpose of this research is to study the infiltration characteristic, the subsurface flow pattern, and the related preferential flow mechanisms of terrace paddy fields in the mountain areas. The experimental terrace paddy field is located in Gongliao District, New Taipei City. The in-situ tests including water requirement rate, double ring experiment, and soil water distribution. The soil textures and hydraulic conductivity is analysed in the laboratory. Based on the field and laboratory data obtained from experimental paddy field, a three-dimensional groundwater model FEMWATER was adopted to simulate subsurface water movement in the terraced paddy field subjected to various soil/water conditions for two adjacent upper and lower terraced blocks. The simulation scenarios including 1) with constant ponding water in both upper and lower blocks, 2) with constant ponding water only in upper block but remained dry condition in lower block, 3) with constant ponding water in both upper and lower blocks, and setting all soil layers to be saturated condition, and 4) with varied ponding water from rainfall were used to simulate the 3D subsurface water flow conditions. Simulation results showed that lateral seepage play an important role in subsurface water flow, which occupied 62%, 66%, 65%, and 60% of total field infiltration water in upper block for scenarios 1~4, respectively. For deep percolation, which can be regarded as groundwater recharge, scenario 1 achieved the highest amount, followed by scenario 4, 2, and 3. Simulation results also indicated that when water seepage into the slop embankment from upper block, downward movement will develop to the slop bottom and flow pattern will change in this area for different scenarios. For scenarios 1 and 4, the flow will converge the lateral seepage from lower block and continuously move downward, however, a portion of water from upper slop embankment will laterally flow into the lower block due to the tension force in scenario 2, and piezometric head difference in scenario 3, which will reduce the groundwater recharge amount compared to scenario 1. In addition, after the more long-term simulation, the scenario 3 will turn out to be unsaturated flow condition, which means the setting for all soil layers to be saturated condition was not suitable for real paddy environment in study site. It’s worth noting that groundwater recharge amount in scenario 4 was approximately 93% of scenario 1, which may due to the extremely high annual rainfall (>5,000mm) in the research area. The result of this research can be taken as reference for formulating future policies on the conservation of terraced paddy fields and the management of water resource.