HEC-RAS: Its history, benefits, drawbacks, and alternatives

For much of human history, rivers were one of the most prevalent resources to civilization, serving as the liquid highways for goods and providing needed water for irrigation. It’s no wonder then why the world’s top minds have long toiled over how to control rivers and understand their flow.

While understanding rivers presented persistent toil for engineers of past, in today’s world of computer simulations and digital computation, the problem has been solved – to an extent. 

Understanding how humans understand the flow of rivers today demands some backstory on a place known as the Hydrologic Engineering Center (HEC), and their work creating a tool known as HEC-RAS (Hydrologic Engineering Center-River Analysis System).

What the HEC is HEC-RAS?

While we’ll spend a good portion of this article examining the history of HEC-RAS through its creation and into today, it’s worth starting with a quick summary of what the tool is. HEC-RAS is a software developed by the U.S. Army Corps of Engineers that models the hydraulics of water as it flows through rivers and channels. It performs one-dimensional and two-dimensional hydraulic calculations on natural and man-made channels, floodplains, and other topography. In essence, HEC-RAS is a tool that engineers often leverage to perform flood studies and river analysis.

At its core, it can help you perform:

• Water quality analysis
• Quasi-unsteady or fully unsteady flow calculations
• One and two-dimensional unsteady flow simulations
• Steady flow calculations

Just how HEC-RAS does these calculations and the history of how engineers came to understand rivers owes itself to more backstory. One that we’ll pick up in the year of 1824.

The history of HEC-RAS

The first glimmers of an official Army Corps were initially formed before the United States even existed as an independent nation, on June 16, 1775, with a chief engineer being put in place with two assistants. Eventually, by 1802, a dedicated Corps of Engineers was formed by the government, tasked with fortifying coastlines and building defensive positions for the US mainland. Which, glaringly, didn’t include managing rivers.

The history of the U.S. Army Corps of Engineers and their involvement with water infrastructure begins a few decades later after the Congress in 1824 authorized the agency to remove obstructions and snags in the Ohio and Mississippi rivers. The US had come to the same conclusions that countless civilizations had arrived at before it – properly managing their waterways was paramount to the nation’s defenses and potential for prosperity. The 1824 authorization from Congress was part of the Army Corps of Engineers’ first civil works project and would mark the first of many projects to come that were focused on water management.

Surprisingly, it wasn’t until a century later, in 1936, that the Flood Control Act gave the Corps authority to manage flood protection infrastructure across the US. Naturally, being tasked with such an impossible mission meant venturing into the unknown world (at the time) of computational modeling and simulation. By the 1950s and 60s, with the emergence of computers, the earliest versions of HEC software programs had emerged, leveraging computers to calculate complex hydrologic equations. 

How the HEC did they do it?

A man by the name of Bill Eichert began to develop software known as HEC-2 by 1964, which would serve as the technological foundation to the first HEC-RAS program. This initial tool ran step-backwater analysis, essentially a method of calculating flow at various stations along a river with known cross sections. Think of it like very complicated long addition.

HEC-2, as we previously mentioned, initially rolled out with a name only a mother could love: “Backwater Any Cross Section.”

By 1968, the backwater model was formally released as HEC-2, with new computational functionality being added in years later.

It’s worthwhile to note how primitive these early hydrologic software tools were. HEC-2 was written in FORTRAN and used punch-cards as the user interface. If a user didn’t input data correctly on the punch-card, the program wouldn’t work correctly. Ultimately, this complexity and barrier to use meant that only large government or academic institutions ran models on these tools.

By 1981, IBM introduced their personal computer and paved the pathway for desktop hydraulic analysis. Within the next decade, HEC-2 became the international standard for water surface elevation calculations in addition to FEMA, the Federal Emergency Management Agency’s flood insurance study standard.

Over the next several decades, the capabilities of HEC software slowly grew and by 1995, we saw the first appearance of HEC-RAS, with version 1.0 release on Windows. 

HEC-RAS was formally designed by a man named Gary Brunner, who led the software development team, but it’s important to note how collaborative the process was, with input from not only HEC, but other branches of the Army Corps. This early version of HEC-RAS could run steady flow water surface profiles, unsteady flow computations, sediment transport computations and more.

The HEC-RAS of today continues to build off all of these prior advances, offering up modern 1D and 2D flow simulations.

1D vs 2D: To the non-hydraulic modeler reading this, 1D flow is calculated through a series of cross sections along a river or path, whereas more complex and intensive 2D simulations (seen here) run through a mesh, solving flow one cell at a time. Designing in 2D means using polygons, which are more flexible and can more accurately represent the real world.

Additionally, modern HEC-RAS has features such as water quality modeling, mixed flow calculations, dam or levee analysis, and other complex hydraulic analyses needed for accurate river and floodplain modeling. HEC-RAS has, and will likely continue to be, the baseline for hydraulic modeling tools, but it’s worth noting how far the hydraulic modeling industry has come.

InfoWorks ICM or HEC-RAS?

It’s hard to speak about hydraulic modeling without underscoring the work done by the U.S. Army Corps of Engineers and HEC-RAS. As time has gone on, private companies, like Autodesk, have worked to develop more powerful tools for hydraulic modeling built off these foundations. InfoWorks ICM, Autodesk’s ‘Integrated Catchment Modeling’ software, stands above the rest in terms of its power – so let’s examine some of the benefits of HEC-RAS and why a modeler or engineer might eventually want to switch to InfoWorks ICM.

The benefits of HEC-RAS

• Specifically built for river and floodplain analysis
• Trusted tool for bridge and culvert analysis
• Aligned with FHWA guidelines 
• It’s free to download!
• Recommended for certain government studies

When to switch from HEC-RAS

• Speed: HEC-RAS currently doesn’t run on GPU; InfoWorks ICM also offers optional access to cloud runs, significantly improving user workflows
• Complex catchment hydrology: 15+ methods in ICM, 0 in HEC-RAS
• Urban pipe networks: HEC-RAS is only for cross drainage
• Incorporation of WQ elements / Sustainable Drainage Designs (SuDs): HEC-RAS does sediment transport but not WQ or SuDs (called LiDS by some in the U.S.) 
• Workgroup capabilities: data flags, version control, multi-user, unlimited undo functionality
• Cloud capabilities: InfoWorks ICM’s access to the cloud for users means complex simulations can be done faster, and without taking up local hardware, improving workflows and giving users access to more powerful functionality.

It’s important to note that HEC-RAS is a fantastic hydraulic modeling tool. This said, our team at Autodesk has built, and is committed to advancing, the most comprehensive storm, sewer, and flood tools inside of InfoWorks ICM.

As noted above, there are certain things that are just done better, and that only a tool like InfoWorks ICM can do in the world of hydraulic modeling.