Stromflow characteristics of the Chungliaoshi forested watersheds in southern Taiwan

Stormflow characteristics of the Chungliaoshi upstream and mainstem forested watersheds were monitored to detect effects of large and small forest cover area on stormflow from 2004 to 2008. Based on analysis of 5-yr stormflow data by year, stormflow rates of the upstream forested watershed were 34.18%, 37.08%, 54.02%, 49.06%, and 33.01%; stormflow rates of the mainstem forested watershed were 21.80%, 28.70%, 41.02%, 46.32%, and 28.80%; and stormflow rates of the upstream forested watershed differed from those of the mainstem forested watershed as follow 1.57, 1.29, 1.32, 1.06, 1nd 1.15. Stormflow rates of the upstream forested watershed were larger than those of the mainstem forested watershed, illustrating the effetcs of large forest cover area in reducing stormflow rates were larger than the effects of small forest cover area. The stormflow volume increased as storm rainfall increased and could be estimated from a simple regression equation of stormflow volume to storm rainfall. The peak flow was estimated from a multiple regression equation of peak flow for both storm rainfall and average intensity, and was calculated from the beginning of stormflow to the time of the peak. However nonlinear regression equations were better than linear regression equations for estimating the stormflow volume.The curve numbers of the Chungliaoshi upstream and mainstem forested watersheds were determined using the SCS runoff curve number methods, measuring 57 and 48, respectively. The ranges of peak flow coefficients in the rational formulae for the Chungliaoshi upstream and mainstem forested watersheds were 0.006~0.449 and 0.004~0.601, respectively.