The study of Manning’s n roughness coefficient in Klong Muang, Nakonnayok Province

Abstract

          The objective of this study is to investigate Manning’s n coefficient of Klong Muang canal in Nakonnayok Province. The procedures of study are as followings : 1) calculate exhaustive Manning’s  n coefficient by direct step method, 2) calculate approximate Manning’s n coefficient by assuming the water flow in the canal is uniform, 3) compare Manning’s  n  coefficient between exhaustive method and approximate method from 2 measurement  locations, point 1 and 2.  At point 1, the results indicate that the average Manning n’ coefficients from exhaustive method is about 0.02460 and the average Manning’s n coefficients from approximate method is about 0.02516. The difference between the minimum value and maximum value are about 0.12 and 5.17 percent, respectively, and R² is about 0.9857. For the measurement results at point 2, the average Manning’s n coefficients from exhaustive method is about 0.02171 and the average Manning’s n coefficients from approximate method is about 0.02162. The difference between the minimum value and maximum value are about 0.00 and 2.09 percent, respectively, and R² is about 0.9829. By comparing the results of Manning’s n coefficient between 2 points, it is found that the average value is in the range of 2.22 and 0.76 percent and the difference of the results between the 2 methods is about 1.49 percent. Thus, the average Manning’s n coefficients from approximate method is more practical in the fieldwork since it is far more convenience and less time consuming.