TWC2
Civil/Environmental
- Mar 11, 2011
- 2
Does anyone have a study of velocities in extreme slope channels (20 to 45% slope). The county I am working in allows engineers to use overland flow equations for up to 6000 feet because the shallow concentrated flow and channel flow equations give ridiculous results.( > 20 ft/sec). I have spent the last four years measuring flow in mountain streams. These streams are pool riffle and the average velocity even during spring runoff is about 3 feet per second. The problem is that the equations for velocity were created on slopes < 10%. Also, they assume the channel is uniform, which they are not!
The maximum velocity AT A POINT ever recorded in a river was 22 ft per second and the average velocity at that cross-section was 11 feet/sec. So all of those RAS results showing >10 ft/sec are bogus. There is nothing wrong with the model or the math, it is the assumption that the slope is constant! You can't take xsections every 100 feet or 1000 ft. You would have to take xsections at the top and bottom of every vertical drop.
The problem is that everyone wants an equation to back up our results.
The maximum velocity AT A POINT ever recorded in a river was 22 ft per second and the average velocity at that cross-section was 11 feet/sec. So all of those RAS results showing >10 ft/sec are bogus. There is nothing wrong with the model or the math, it is the assumption that the slope is constant! You can't take xsections every 100 feet or 1000 ft. You would have to take xsections at the top and bottom of every vertical drop.
The problem is that everyone wants an equation to back up our results.