Tt for Open Channel
Tt for Open Channel
(OP)
TR-55 states that "Average flow velocity is usually determined for bank full elevation."
Would this be considered the most conservative approach to calculate a sub-basin's Tc when using the rational method & IDF curves to determine a peak flow rate from a basin for a culvert design?
Or would it make sense to assume a Tc to get a flow rate from the sub-basin then use that flow rate to determine the channel depth and then in turn find the avg. velocity and Tt of the channel segment (the channel geometry is known). After finding this Tt based on the assumed Tc & flow rate use this Tt to determine a new Tc & flow rate and repeat the process until the numbers converge?
Would this be considered the most conservative approach to calculate a sub-basin's Tc when using the rational method & IDF curves to determine a peak flow rate from a basin for a culvert design?
Or would it make sense to assume a Tc to get a flow rate from the sub-basin then use that flow rate to determine the channel depth and then in turn find the avg. velocity and Tt of the channel segment (the channel geometry is known). After finding this Tt based on the assumed Tc & flow rate use this Tt to determine a new Tc & flow rate and repeat the process until the numbers converge?
RE: Tt for Open Channel
RE: Tt for Open Channel
In TR-55 you can use the kinematic wave method or any of several other methods described in the literature to calcualte Tc.
RE: Tt for Open Channel
Just curious how others solve for travel time (Tt) in open channels seems to be a few choices:
1. Assume the channel is at a "bank full elevation"
2. Assume a velocity (would the assumed velocity change based on the channel slope?)
3. Or an iterative solution based on a initial assumption of flow depth.
RE: Tt for Open Channel
Given a trap. grass swale of b=2, D=1, z=3 and slope =.020, capacity is 11.8 cfs. Full flow yields a Manning's of .063 and v = 2.37.
Same swale with 1 cfs yields a Manning's of .134 and v = 0.70.
I don't like Rational on anything over a couple of acres, and really don't like it for hydrographs at all.
Signature under construction, sorry about the mess - Steve