May 24, 2024
Multiple Opening Analysis
Did you know that if you have a bridge opening and one or more culverts at a single river crossing a Multiple Opening Analysis is required?
Flow/Conveyance Distribution
Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2009. All rights reserved.
In HEC-RAS conveyance for a given cross section is divided into the main channel, left overbank and right overbank. The distribution of conveyance is controlled by geometric features of the cross section itself, such as the terrain, bank station locations, ineffective flow triggers, and Manning’s n values. The latter three are typically subjective in how they are defined at any given location. It is important for the modeler to define these parameters to accurately define the hydraulics in the cross section, but also to maintain numerical stability for unsteady flow modeling.
Copyright © RASModel.com. 2009. All rights reserved.
In HEC-RAS conveyance for a given cross section is divided into the main channel, left overbank and right overbank. The distribution of conveyance is controlled by geometric features of the cross section itself, such as the terrain, bank station locations, ineffective flow triggers, and Manning’s n values. The latter three are typically subjective in how they are defined at any given location. It is important for the modeler to define these parameters to accurately define the hydraulics in the cross section, but also to maintain numerical stability for unsteady flow modeling.
A convenient way to check for appropriately defined conveyance distribution is a quick scan of Standard Table 2, in the Profile Output Table. Standard Table 2 displays the flow in the left overbank, main channel and right overbank (Q Left, Q Channel, Q Right). The modeler should view this table and look for cross sections that show a sudden change in distribution. Any sudden change is a good indication of poorly placed bank stations or ineffective flow triggers.
The attached table illustrates how Standard Table 2 can be used to locate areas of sudden changes in flow or conveyance distribution.
Comments
Angana Borah
on April 6, 2016Is there any way to input rating curve when discharge and stage data are not following an increasing or decreasing trend but rather changes unpredictably with each other.
Angana Borah
on April 6, 2016Is there any way to input rating curve to hec ras when stage and discharge are not following an increasing or decreasing trend but rather changes unpredictably with each other with time?
Chris Goodell
on April 6, 2016Are you talking about inputting observed data? Why would you want to input a rating curve?
Fiamma Buchinger
on October 25, 2016Hi Chris,
I'm modeling in steady flow downstream with boundary conditions (Known W. S.), but there is a sudden change in distribution (as you said) on the first interpolated cross section after cross section downstream. And then follows a consistent pattern.
How to solve this? It would be a geometry error?
Chris Goodell
on October 26, 2016Check your ineffective flow areas. Make sure they are all either on or off for a given profile. Also, make sure your bank stations are placed properly.
امیر
on June 8, 2018But what is implication of defining the poorly placed bank stations?
ashwini chaudhari
on August 8, 2018Hi chris,
I am modeling in steady flow with formation of bar by changing bed level elevation. Is it correct or I should requir some other changes.
VIVEK KUMAR BIND
on January 14, 2019i want to calculate conveyance from 1D modelling if anybody know about that can we discuss on teamviewer
POOJA SINGH
on January 16, 2019In my hec ras system negative conveyance is coming so what does it means
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