Use of the discharge-weighted average velocity in studies of the frictional energy loss of streamflow

✍ Scribed by Lewis, Nathan K.

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 38 KB
• Volume: 22
• Category: Article
• ISSN: 0360-1269
• DOI: 10.1002/(sici)1096-9837(199704)22:4<329::aid-esp669>3.0.co;2-k

✦ Synopsis

The discharge-weighted average velocity of streamflow is proposed as an alternative to the more commonly used areaweighted average for uses where frictional energy losses are evaluated. Using experimental data from Mink Brook, NH, and data published by Marchand et al. (USGS Open File Report 84-733, 1984), the theoretical framework developed here indicates that, through the use of the area-weighted average velocity, Manning's n overestimates frictional effects by 2-156 per cent in certain common situations. Variance in the vertical axis, from a sample of various streams in Colorado, creates an additional overestimation of 6-25 per cent. A sample velocity distribution for a smooth walled, straight, trapezoidal channel creates an overestimation of 24 per cent. Similar overestimation may partially explain the roughness multiplier applied to the Nikuradse K in gravel-bed streams where particle size approaches or exceeds mean depth. A generalized resistance equation is proposed that may assist in evaluating the range of conditions found in the natural world.