The Effects of Watershed Pattern on the Time of Concentration

• Main Authors: Yung-Neng Hsieh, 謝永能
• Other Authors: Su-Chin Chen
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/60836650285141186212

碩士 === 國立中興大學 === 水土保持學系 === 91 === Abstract Commonly, the time of concentration equations used in Taiwan which have derived by abroad scholars. Most of these are empirical, and limited to site specific conditions under which they were developed, but can’t respond the changing of time of concentration for various basin configurations. In this study, the time of concentration is calculated using the Kinematic-wave equations. From the sensitivity analysis, the most effects of small scale watershed pattern on the time of concentration are slope, land-covered and slope length. The time of concentration in channel has little effect and depends on the channel length. The parameter of channel length can be replaced by form factor. Then the time of concentration can be expressed by the following equation： tc=0.8*(n1^2*l1^2/s1)^0.3*(1+kF^-0.6) where tc represents the time of concentration (min) and n1 is land-covered (Manning''s n)；l1 implies the slope length and s1 is the slope；k is the topographic factor, the value is about 1*10^-1 ～4*10^-1 ；F is the form factor. This equation is not only equivalent to calculate the travel times for overland and channel flows but also show the relationship between the form factor and the time of concentration. Furthermore, after analyzing the value of k in Shui-li Creek watershed, it is found that the value of k is about 0.09~0.21.The results for taking the k values into the equation and compares with the time of concentration in the Lien-Hua-Chi No.3 experimental watershed has good accuracy. Finally, the paper collects about 20 time of concentration equations and uses Microsoft Visual Basic language to compiles a Windows-based program. We can use it to compare with the different equations and help us to make convenient design.