關刀溪森林集水區降雨與逕流關係之研究

Study on the Relation of Rainfall and Runoff in Guandaushi Forest Watershed

本研究係以關刀溪森林集水區為對象，就1995年7月至1998年2月間所收集之42場降雨事件，探討各流量參數間之關係，同時藉不同臨前水文參數值之分析，初步建立影響直接逕流總量之關係式，茲將分析結果摘要如下：1.本集水區以退水常數法分離基流量而分析出水文反應值平均約為1.64%，顯示本集水區降雨時之直接逕流量甚低。2.就降雨型態而言，在所收集之降雨事件中，本集水區之降雨型態以中峰型降雨為主，達22次；而後峰型降雨所造成之水文反應值最大，達1.76%。若以降雨延時作為分類之依據，則降雨延時在10hr內之降雨事件中，其水文反應值呈現較為分散之情況，在降雨延時大於10hr之降雨事件中，其水文反應值有隨降雨延時增加而增大之趨勢。3.最大時雨量與尖峰流量呈現高度相關，因此在推求尖峰流量時，似可將最大時雨量之影響納入考慮。4.以臨前基流量或前期降雨指數均能有效推估直接逕流量，惟前期降雨指數可自降雨資料直接獲得，易於推估一場降雨之直接逕流量。 According to the 42 rainfall events collected from Jul. 1995 to Feb. 1998 in Guandaushi Forest Watershed, this study was going to realize the relation between rainfall and runoff. And a regression equation was derived with different antecedent hydrological parameters to estimate the direct runoff during rainfall. The analyzed results were obtained as follows: 1. Using the recession constant method to separate baseflow, the average hydrologic response value in Guandaushi Watershed was about 1.64%. It showed that the direct runoffs were very low in this watershed. 2. The main type of rainfall in Guandaushi Watershed was middle peak type with 22 rainfall events. The back peak type of rainfall caused higher value of hydrologic response with 1.76 %. While the duration of rainfall was less than 10 hours, the hydrologic response values varied with a wild range, and while the duration of rainfall was longer than 10 hours, the hydrologic response values increased with the duration of rainfall. 3. Based on the analysis between maximum rainfall intensity and peak flow, maximum rainfall intensity was highly related to peak flow. Therefore, maximum rainfall intensity should be adopted as an influence factor to estimate peak flow. 4. The parameters of antecedent base flow and antecedent precipitation index could be effectively used to estimate the direct runoff discharge. The antecedent precipitation index could be easier obtained than the antecedent base flow to estimate the direct runoff discharge.

According to the 42 rainfall events collected from Jul. 1995 to Feb. 1998 in Guandaushi Forest Watershed, this study was going to realize the relation between rainfall and runoff. And a regression equation was derived with different antecedent hydrological parameters to estimate the direct runoff during rainfall. The analyzed results were obtained as follows: 1. Using the recession constant method to separate baseflow, the average hydrologic response value in Guandaushi Watershed was about 1.64%. It showed that the direct runoffs were very low in this watershed. 2. The main type of rainfall in Guandaushi Watershed was middle peak type with 22 rainfall events. The back peak type of rainfall caused higher value of hydrologic response with 1.76 %. While the duration of rainfall was less than 10 hours, the hydrologic response values varied with a wild range, and while the duration of rainfall was longer than 10 hours, the hydrologic response values increased with the duration of rainfall. 3. Based on the analysis between maximum rainfall intensity and peak flow, maximum rainfall intensity was highly related to peak flow. Therefore, maximum rainfall intensity should be adopted as an influence factor to estimate peak flow. 4. The parameters of antecedent base flow and antecedent precipitation index could be effectively used to estimate the direct runoff discharge. The antecedent precipitation index could be easier obtained than the antecedent base flow to estimate the direct runoff discharge.