Estimation of the Ability of a Forest Watershed to Conserve and Regulate Water by a Baseflow Approach

The ability of forest watersheds to conserve and regulate water has received much attention recently. Much research has tried using different approaches such as the infiltration capacity, porosity of soil layers, recession-curve-displacement analysis, and water budgets to estimate the water conservation ability of a watershed. However, many factors are involved in the ability to conserve water, and therefore it is difficult to use some physical quantities to give accurate estimations. Baseflow is the discharge of water that drains from deeper subsurface runoff or originates from the groundwater system, and it is the best and more direct index to describe the ability of a watershd to conserve water. This study used the variable-slope baseflow separation method to analyze rainfall events of the Lienhuachih no 5 experimental watershed to estimate the quantiles of conserved water of the target watershed. From results of 46 rainfall event analyses, the average daily baseflow discharge was about 1.164 (range, 0.474~3.265 mmd^(-1)), which is equivalent to 11.64 m^3d^(-1)ha^(-1) or 4284 tonsha^(-1)yr^(-1) and accounts for 21% of annual rainfall. Combining the estimated baseflow amount and temporal rainfall distribution can give a more-reliable estimate of the ability of a forested watershed to conserve water.

關鍵字

water conservation ； baseflow ； baseflow separation ； Lienhuachih

並列摘要

森林集水區的水資源涵養功能日益受到重視，但此一功能定量性的分析卻始終為一爭論的課題。已有許多研究者以集水區地表滲透率、土壤孔隙率、退水曲線及水平衡方法進行推估；然而影響集水區涵養水資源功能的因素眾多，難以簡單的物理量就可得到精確的數值。基流為源自較深層的次地表逕流或源自地下水系統的流量，最能反應集水區涵養水資源的能力。本研究分析蓮華池五號集水區的降雨事件，以變動斜率法進行基流分離，進而求得各場降雨的基流量，藉以評估森林集水區涵養水資源的能力。經分析46場暴雨事件，獲知該集水區平均基流量約為1.164 mmd^(-1) (0.474至3.265 mmd^(-1))，相當於公頃每天可排出11.64 m^3的水量，每年每公頃由基流供應的水量約為4284公噸，約佔全年降雨量的21%。由所推估的基流量，再配合降雨的強度及時間分佈，當可有效推估森林涵養水資源的水量。

並列關鍵字

水資源涵養；基流；基流分離；蓮華池試驗集水區

國際替代計量

Estimation of the Ability of a Forest Watershed to Conserve and Regulate Water by a Baseflow Approach

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