綠建築基地保水指標中滲透及時間因子影響探討

Impact Analysis of Infiltration and Time Parameters to Water Retention Indicator in Green Building

基地保水指標計算是以土壤之飽和滲透係數為計算依據，然實際入滲時土壤多呈未飽和情形，故指標值在土壤滲透性較小時有偏高之趨勢，導致在保水評定時較易通過；且對於時間因子較敏感，故在相同土壤滲透條件下，指標值不一致之情形明顯；另在設計降雨延時則採用44hrs ，則有過大之跡象。因此，本研究考慮實際之降雨逕流機制，以地下水文學理論為依據，對於保水指標中之土壤滲透性及時間因子等計算參數進行探討。藉由Green-Ampt 入滲模式評估土壤之最終入滲率，並以其取代飽和滲透係數為計算參數，進行不同土壤及降雨延時下之保水指標值探討。結果顯示本研究提出之計算方式，保水指標值較具一致性，改進了指標值偏高之問題；而在設計降雨延時之選取上，則建議以目前颱風降雨之設計降雨延時24 小時為計算依據。

Traditionally, saturated soil hydraulic conductivity coefficient is used to calculate the amount of infiltration during rainfall period in water conservation indicator. But during rainfall period, soil is not saturated most of the time. Therefore, when soil hydraulic conductivity coefficient is smaller, the value of water conservation indicator tends to be higher and reaches the minimum requirement standard easily. Also, water conservation indicator is sensible to rainfall duration. Even with same soil hydraulic conductivity coefficient, values of water conservation indicator vary with different rainfall durations. Hence, this research tries to assess the impacts of infiltration and time parameters to water retention indicator in green building with mechanics of rainfall-runoff and groundwater theory. From the Green-Ampt infiltration model, the final infiltration rates can be obtained for different soil conditions. These standards will be used to calculate the values of water conservation indicator for selected soil conditions and rainfall durations. From the obtained results, calculation the value of water conservation indicator using final infiltration rate instead of saturated soil hydraulic conductivity coefficient can effectively improve the consistency of this value and current existing drawbacks. For the factor of rainfall duration, 24 hours is recommended which is often used in design.