Pages

Tuesday, March 31, 2009

Stage-discharge curve for Dam Breach modeling

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2009. All rights reserved.

In the NWS DAMBRK model, a single stage-discharge curve could be constructed external to the program and used as a method for defining the reservoir. Though this is an easy and stable way to define a reservoir, it lacks the ability to account for submergence effects, which could significantly affect the results once the breach has fully developed. My guess is this is why HEC-RAS does not allow for a stage-discharge curve to be used to define a reservoir.

If you use cross sections to define your reservoir (full dynamic hydraulic drawdown routing), then you can use an inflow hydrograph at the upstream-most cross section. If you use a storage area to define your reservoir (level pool drawdown routing), then a simple stage-storage curve is required. A storage area can also have a lateral inflow hydrograph attached to it. You also have the option to determine your breach hydrograph external to HEC-RAS and just enter it as the upstream boundary to a cross section. That way you could avoid modeling the reservoir in HEC-RAS altogether.

A family of stage-discharge curves (rating curves) CAN be used at the inline structure to define flow through the structure prior to the breach. This can be used to describe a complicated gate strcture or spillway-one that is not available explicitly in HEC-RAS. However, the weir equation will be used to define flow through the breach-in addition to any other outflow you may have at the dam. And this is not the same as using a stage-discharge curve to define the reservoir.

2 comments:

  1. Hi Chris, I am simulating a simple 2D dam breach and leaning towards using a generated breach hydrograph as the upstream boundary condition, instead of using storage area for the reservoir route, because the reservoir data (Elev. v Storage curve) will not be always available to me currently.

    My question on here is, is attaching upstream BC to a cross-section the only available option even in the newly released 5.0? If so, I figured it will give me just as inaccurate/rough results as I would use the estimated Elev v. Storage curve from my terrain data, because I will have to roughly sketch the cross-section too, as this is not always available to me as well... Thanks for your help...

    ReplyDelete
    Replies
    1. No, you can establish an upstream boundary condition right on the perimeter of a 2D area using BC Lines.

      Delete

Note: Only a member of this blog may post a comment.