Thursday, July 28, 2016

HEC Software Workshop London - Oct 25-26, 2016.

Would you like to meet the Director of HEC, Chris Dunn and the lead developers of HEC-RAS (Gary Brunner) and HEC-HMS (Matt Fleming)?

They will all be coming across to London on 25 and 26 October to meet with leading users of the software. It’s a great opportunity to learn more about the software and its future development path, and to exchange knowledge on how these products are used in Europe and the USA for flood risk management and also water resources and channel restoration work.

Over the two days there will be plenty of opportunities to speak to Chris, Gary and Matt and learn from the experts. Demonstrations and interactive workshops will feature the latest thinking, giving you practical solutions to take away with you.

There is also an opportunity to showcase your projects where the HEC software has been used focusing on the new functionalities and efficiencies. If you would like to submit a poster the deadline is 31 August, please email us in the first instance to register your interest and we will send you further guidelines for the poster submission.  

During the two days you will:
  • Learn how to build a HEC-HMS catchment model from scratch
  • How to apply the HEC software in hydraulic engineering, flood forecasting, flood risk mapping and catchment modelling projects
  • Explore how HEC-RAS Sediments (and some of the ‘hidden’ utilities) can help in your hydromorphology studies, scour, bank erosion and maintenance.
  • Discover how the reservoir system simulation software (HEC-ResSim), can be used to model reservoir operations at one or more reservoirs for a variety of operational goals and constraints.
To see the full programme of the workshops clickhere

Social Event – 25 October

image courtesy of Chris Wheal via Flickr Creative Commons

On the evening of 25 October there will be an optional social event to visit the largest movable flood barrier in the world - The Thames Barrier, followed by a buffet. Your guide will cover topics including the history of the river and the risk of flooding in London, the environment and wildlife of the Thames.

When: 25 - 26 October 2016

Where: Chartered Institution of Water and Environmental Management (CIWEM), London

If you’d like to join us and would like to find out more and book your place, please visit

Chief Executive
Jeremy is the Executive Chairman of JBA Consulting.  He has over 33 years’ water engineering, management and hydrology experience working in the UK and internationally.  He has published and lectured widely on these subjects.

He has been involved in the feasibility and detailed design of irrigation, drainage, flood walls, and storage reservoirs, ranging from culvert replacements to multi-million pound flood alleviation and land drainage schemes.

Jeremy has particular interests in computational hydraulics and hydrological modelling and is an acknowledged expert on the assessment and management of scour risk to engineering structures.

Wednesday, July 27, 2016

Controlling HEC-RAS using MATLAB

Please check out this journal paper written by Professor Arturo Leon of the University of Houston and myself on using MATLAB to control HEC-RAS for gate optimization on a multi-dam river network.

The preprint can be downloaded from:

The MATLAB code can be downloaded from:

or from

Tuesday, July 26, 2016

HEC-RAS Dam Breach course in New Zealand and Round 2 of HEC-RAS 5.0 2D courses across Australia!

Dam breach course in New Zealand and Round 2 of HEC-RAS 5.0 2D courses across Australia!

We had a great turnout for our first HEC-RAS 2D course in Melbourne back in April, and I’m excited to be returning to the southern hemisphere in November to teach a 3-day HEC-RAS Dam Breach course to be held in Auckland, New Zealand.

November 29 - Dec 1, 2016

Our agenda will cover unsteady flow, level pool versus dynamic routing, breach parameters, setting up a dam breach model, diagnosing and fixing dam breach models, and presentation of 1D and 2D case studies.

Register your interest in this course here:

The course will be facilitated by Krey Price, who organised our Melbourne course and has wrapped up a full round of HEC-RAS 5.0 2D courses around Australia over the last three months; due to the overwhelming demand, Krey has now scheduled a second round of 2D courses across Australia:

·         Hobart 11-12 August 2016
·         Brisbane 25-26 August 2016
·         Sydney 1-2 September 2016
·         Adelaide 15-16 September 2016
·         Perth 6-7 October 2016
·         Melbourne 20-21 October 2016

Why not combine your HEC-RAS training with a New Zealand or Australian vacation? All courses are open for registration for local residents as well as international attendees. International participants can contact Krey for a visa invitation letter or further details.

Wednesday, July 13, 2016

Dam Breach Modeling and the Assessment of the Self Rescue Zone

An interesting and informative paper by Mr. Bruno Neves of Brazil on HEC-RAS dam breach modeling and determining the self rescue zone, as well as the timing for alerting residents of the self-rescue zone.  The concept is tested using HEC-RAS with hypothetical 2D breach scenarios of the Santa Branca Dam in the Paraíba do Sul River in São Paolo State, Brazil.  Included within the paper is a comprehensive review of some of the most widely used parametric breach equations used today.

 Bruno NEVES


Saving lives during dam break events is the main topic of this article, considering that a precise definition of the self-rescue zone (area in which authorities supposedly are not able to provide support to the population at risk in case of dam break, within the first minutes of the event) is crucial for planning mobilization of population in case of flood inundation. This paper presents a comparison of hydrographs, highlighting their dispersion through the self-saving zone, and sheds some light on issues of the hydraulic model.   


Despite the low probability of a dam break situation, around 0.0001 per year, this sort of hazardous event may cause significant damage and considerable loss of life (Medeiros, 2008).

In Brazil, federal law 12.334/2010 has set the National Policy of Dam Safety which defines obligations to the stakeholders of dams. Through National Agencies of Natural Recourses, details of this regulation are being defined.

ANA (National Water National Agency) and ANEEL (Electric Energy National Agency) agree in their regulations on the definition of the Self Rescue Zone, as follows: The downstream region of a dam where authorities are not able to provide assistance prior to the arrival of the flood wave in case of dam break alert, which is assumed to be 10 kilometers or the distance the front end of the rupture wave can travel in 30 minutes.
Colorado Department of Natural Resources (2010) regulates that the simulation of dam break events shall take place to characterize and identify locations which may be potentially threatened.

The bibliography shows diversity in modeling methods of breach opening which may lead to equally diverse results regarding potential damage in the self-rescue zone.
This paper cites details that may be considered when modeling a dam break event and sheds some light on results acquired from different breach opening equations. The US Army Corps of Engineers software HEC-RAS 5.0 (Hydrologic Engineering Centers River Analysis System) was used and applied to Santa Branca Dam, an earthen dam located in São Paulo state in Brazil.

Monday, July 11, 2016

Weir Equations in HEC-RAS

Written by Christopher Goodell, P.E., D.WRE
Copyright © The RAS Solution 2016.  All rights reserved. 

HEC-RAS has the ability to simulate flow at hydraulic controls in a variety of ways.  
Bridges, culverts, inline structures, lateral structures, and SA/2D area connections can all act as hydraulic controls.  Effectively, they break up the conservation equations used between cross sections in a 1D reach and/or cells in a 2D area with empirically derived (and usually very stable!) equations.  Weir equations can be used to define flow over an obstruction and are available with all of the 5 hydraulic controls identified above.  However, there are a number of options to consider when selecting simulating weir flow in HEC-RAS.  HEC-RAS approaches weir flow with three different cases:  Ungated Inline Weirs, Ungated Lateral Weirs, and Gated Weirs.  They all begin with the same standard equation:


Where:  Q = discharge, C =weir coefficient, L = weir crest length, H = Energy head over the weir crest.

But each of the three cases apply the weir equation slightly differently. 

Before I continue, I should discuss the difference between the weir coefficient and the discharge coefficient.  I see both of them used interchangeably, but they ARE different.  The weir coefficient (as shown above in the weir equation) is a lumped parameter that includes the discharge coefficient, the gravitational constant, and constants based on geometric properties. 
Where Cd is the discharge coefficient.  

The discharge coefficient is dimensionless and therefore it is the same in both English (U.S. Customary) Units and SI Units.  The weir coefficient, since it is a function of the gravitational constant, is not dimensionless and therefore has different values depending on which unit system you are using.  For example, a weir coefficient (C) of 3.00 in English Units would be 1.66 in SI units.  But both share the same discharge coefficient (Cd) of 0.56.  For convenience, to convert an English weir coefficient to an equivalent SI weir coefficient, multiply the English weir coefficient by 0.552.  
Be very cautious when considering C versus Cd.  They are different but are often mistakenly used interchangeably.  In fact, you’ll see the coefficient Cd labeled occasionally in the HEC-RAS software and literature when discussing weir coefficient. 

Ungated Inline Weirs. 
When defining inline flow over an “ungated” obstruction (bridge, culvert embankment, inline structure, SA/2D area connection), you have two options for computing weir flow:  Broad Crested and Ogee.   
Figure 1.  Inline structure weir embankment editor.

Both use the same standard weir equation presented above in equation (1).

The only difference between the Broad Crested Option and the Ogee Option is that for the Broad Crested option, the user enters a weir coefficient for C.  For the Ogee option, the user enters a spillway approach height and the ogee’s design energy head, and HEC-RAS will compute the weir coefficient for you.  This may sound convenient, but as the name implies, this option should really be used only for ogee-shaped spillways.  And you would have to know what the design energy head is, a design parameter that is not usually easy to come by, unless you have the hydraulic design report for the spillway.  With both options, submergence reduction of the discharge is automatically calculated with their own respective methods (FHWA ,1978 for broad crested, and COE, 1965 for ogee).

Ungated Lateral Weirs.
Lateral weirs are entered in the lateral structure editor.  Inside the lateral structure’s weir embankment editor, you’ll see two options for weir computations:  Standard Weir Eqn. and Hager’s Eqn.

Figure 2.  Lateral Weir Embankment Editor.

In version 5.0.1, the Standard Weir Eqn. provides four options for the weir crest shape:  Broad Crested, Ogee, Sharp Crested, and Zero Height.  Caution!  Zero Height is NOT used when Standard Weir Eqn. is selected.  This is a bug and will most likely be fixed for future versions.  If you do select Zero Height and Standard Weir Eqn. together, HEC-RAS will just use the weir coefficient you provide with the broad crested methodology.  Sharp Crested is not fully functional in Lateral Structures for version 5.0.1.  You’ll notice that no additional input options (like Rehbock and Kindsvater-Carter, as discussed under the next section, “Gated Weirs) are available when you select Sharp Crested in the lateral weir embankment editor.  My guess is that if you select Sharp Crested, it too will default to the broad crested methodology. 

Broad Crested and Ogee work the same as with the ungated inline structures.

With Hager’s Equation, all four weir crest shapes are available, including the zero-height weir.  The same weir equation is used, but an adjusted weir coefficient is computed based on physical and hydraulic properties.  Each of the four weir types has its own method for computing the adjusted weir coefficient.  There is an input box for “default weir coefficient”.  This is only used for the first iteration of solving Hager’s Equation.  Since Hager is a function of hydraulic properties, it must be solved in an iterative fashion.  After the first iteration, the adjusted weir coefficient will be computed and used.  Page 8-18 of the Hydraulic reference manual discusses Hager’s equation and how the adjusted weir coefficient is computed. 

Zero-height weirs are used for cases where flow will leave a channel laterally, but there is no defined obstruction or hydraulic control separating the two.  Commonly this is used to simulate flow from a main channel up a tributary that is being modeled using a lateral structure and a storage or 2D area.  The HEC-RAS 2D manual has a table of lateral weir coefficients (Table 1). 

Table 1.  Lateral Weir Coefficients (from the HEC-RAS 2D Manual, page 3-50).

Notice the last category is “non elevated” overbank terrain.  If you wish to use the weir coefficients in this table to simulate a non-elevated weir, do not use the Zero-Height weir.  That is strictly for Hager’s equation and Hager’s method automatically computes the weir coefficient.  Instead, use the broad crested standard equation and enter in the non-elevated weir coefficient there. 

Gated Weirs. 

When modeling gated spillways at inline structures or lateral structures, users can provide a weir coefficient for flow over the spillway when the gate is completely opened, and out of contact with the flow (Figure 3). This is different from the discharge coefficient used for flow over the top of the inline structure (Figure 1). 

Figure 3. Inline Gate Editor

With gated spillways, the user has three options for the weir shape:  Broad Crested, Sharp Crested, and Ogee (Figure 4).  Broad Crested and Ogee work the same as previously discussed.  The Sharp Crested option also uses the standard weir equation but gives you three options for determining the discharge coefficient:  user-entered, compute with the Rehbock equation, or compute with the Kindsvater-Carter equation.  For both the Rehbock and Kinsvater-Carter methods, the weir coefficient will be computed independently at each time step. So you can have a varying discharge coefficient for varying heads. 

Figure 4.  Inline Gate Editor.

The Rehbock equation for the discharge coefficient was developed for rectangular weirs and is as follows:
Where P = Spillway approach height.  This value must be entered to use the Rehbock equation.  HEC-RAS will then compute the weir coefficient, C using equation (2).   According to Ippen (1950), this equation holds up well for values of H/P up to 5.  And it performs with fair approximation for H/P values up to 10. 

The Kindsvater-Carter method was developed in English units only and is as follows:


Where Ce = effective weir coefficient, ft1/2/s
                kb = a correction factor to obtain effective weir crest length, ft
            kh = a correction factor with a constant value of 0.003 ft

The effective weir coefficient, Ce is a function of two ratios:  L/B and H/P, 

Where  L = Weir crest length
            B = Average width of the approach channel
            H = Energy head over the weir crest
            P = Spillway approach height

Ce is a function of both the relative width and relative depth of the approach channel and is taken from the following chart (note that the chart uses the variable h1 for H.  They are the same):

Figure 5.  Effective Weir Coefficient

kb is used to determine the effective length of the weir crest and is a function of the relative width of the approach channel.  It is taken from the following chart:

Figure 6.  Correction factor kb.

To use the Kindsvater-Carter method in HEC-RAS for a gated spillway, first select the weir shape as “Sharp Crested”.  Then select “Compute with Kinsvater-Carter eqn as the Weir Method.  You must then choose a relative approach channel width (L/b) and enter the spillway approach height, P (note, b is used in the HEC-RAS Inline Gate Editor for B.  They are the same). 

Figure 7.  Kindsvater-Carter Weir Method.

Remember, the Kindsvater-Carter equation was developed and is presented here in English units.  When using SI units, HEC-RAS will automatically convert the units appropriately.  So you can still enter a spillway approach height in meters if you are using SI units. 

The Kindsvater-Carter weir equation is built for rectangular weirs and “is particularly useful for installations where full crest contractions or full end contractions are difficult to achieve.”  (USBR 2001)  More information on the Kindsvater-Carter equation, including its limitations, can be found here:

Federal Highway Administration (FHWA), 1978.  Hydraulics of Bridge Waterways, Hydraulic Design Series No. 1, by Joseph N. Bradley, U.S. Department of Transportation, Second Edition, revised March 1978, Washington D.C.

Ippen, A.T. ,1950.  Channel Transitions and Controls, Chap. VIII in Hunter Rouse (editor): Engineering Hydraulics,” John Wiley & Sons, Inc., New York.  pp.496-588.

Unites State Bureau of Reclamation (USBR), 2001.  Water Measurement Manual,

U.S. Army Corps of Engineers (COE), 1965.  Hydraulic Design of Spillways, EM 1110-2-1603, Plate 33.