Hydraulic engineers Alam and Willson use physical modeling to test river management measures
The February 2009 edition of the quarterly publication Louisiana Civil Engineer features two related articles that should be of great interest to readers of this blog. They both pertain to the challenge of designing a new way to manage the lower Mississippi River to retain the 140 million tons of sediment that is currently disappearing into deep water every year.
The cover article is by Sultan Alam, Hydraulic Engineering Consultant, and the related article is by Clint Willson, PhD, PE, LSU associate professor of civil engineering. Both articles describe the design and operation of what is called a small scale physical model of the lower Mississippi River. This unique tool, which was designed by Alam, is housed at LSU and managed by Willson. In his article Alam describes creating a similar physical model of part of the Old River Control Complex to overrule critics of the design of the hydroelectric power plant, which is shown in the above photograph.
I recently reminisced about my youthful love of model ships, trains and planes and I noted that in today’s world models that simulate the behavior of real world objects or systems are primarily constructed of mathematical algorhythms interpreted by digital computers producing endless series of zeros and ones. Such numerical models can perform extraordinary feats, including calculating the trajectory of a meteorite that could collide with earth centuries from today.
Nevertheless the science of simulating the behavior of chaotic fluid systems, such as turbulent river water carrying sediments, is not a precise science – it requires lots of approximations. For that reason, with respect to predicting the detailed behavior of flowing water and sediments there are still a few old school proponents of the use of physical simulation models, in addition to numerical simulation models. Sultan Alam is one of those proponents.
Physical models that use geometrically accurate scaled down reaches of river beds with real flowing water have several obvious advantages over numerical modeling. To observe water flow and sediment erode and accumulate under the influence of actual gravity confers a visual credibility that the most sophisticated mathematical models lack. In addition, physical models are easy to manipulate like sand boxes, using trial and error experiments that can quickly and cheaply test alternative management strategies.
Experiments using physical models also have great public relations value and persuasive power with respect to critical stakeholders and policy makers who may be uncertain about signing on to expensive and politically sensitive public works projects that change familiar conditions.
The lynchpin of comprehensive coastal restoration for the deltaic plain is the diversion of most of the river flow upstream of Head of Passes. Achieving approval among stakeholders for such a radical change in management of the lower part of the largest river in North America will require an extraordinary “marketing” campaign. I believe that a working physical model of the lower river (a larger and more sophisticated version of the existing model) will be a necessary part of that campaign.
I predict that the final management design for the lower river will be based on a combination of physical and numerical modeling and I hope that Sultan Alam oversees the physical modeling component of that effort. I also hope that Clint Willson’s considerable skills and experience are utilized for the same effort.
The person who deserves credit for recruiting both Alam and Willson to consult on delta management is Chris Knotts, PE, the president-elect of the Louisiana Section, American Society of Civil Engineers. Chris serves as the director of the engineering division of the newly-formed Louisiana Office of Coastal Protection and Restoration.