Navigating Hydrologic and Hydraulic Modeling Challenges for Dam and Levee Projects: GZA's Expertise and Solutions

Hydrologic and Hydraulic modeling is a powerful tool for evaluating the safety and efficacy of dams and levees. At GZA, we use multiple approaches, developed by government institutions and carefully tested, to help our clients with their dam and levee safety programs. Learn about the tools we use, and why they’re effective.

Why use models?

Dams and levees are complex systems, particularly at the hydrological level, whose behavior often cannot be predicted well through simple intuition. Changing the flow of water requires absorbing or redirecting an enormous amount of kinetic energy from the water itself. Similarly, the amount and rate of water in the system can change quickly and dramatically through rainfall combined with seasonal changes and climate change. And because dams and levees are part of a larger, interconnected watershed system, modifications to a dam or levee can also affect the broader watershed, upstream and downstream of the structure.
  
To keep a dam operating safely, and to keep people who live near and downstream of dams and levees safe, we also model events with a very remote chance of occurring in a given year.  These types of events probably haven’t been historically observed at the dam, requiring us to simulate them using models.

As a result, dam owners and operators need a clear understanding of possible vulnerabilities and possible changes to the system to operate their structures, assess contingencies, and plan for possible emergency scenarios. Models are also useful at large and small scales: Our modelling projects have focused on some of the largest river systems in the United States, such as the Mississippi, Arkansas, Hudson, Connecticut, and Delaware Rivers, as well as small tributary streams, urban flood scenarios, and sudden precipitation events.

What does ‘dimension’ mean in computer modeling?

In hydrological modeling, “dimension” refers to the direction of flow in the model. A one-dimensional (1D) model shows water flowing in a single path, like a flume or a channel. The flow can only go upstream or downstream.  A two-dimensional (2D) model can represent flows in multiple directions. While both are useful tools depending on contexts, 2D models are more useful in complex situations such as flood risk assessment of floodplains.

For dams and levees, the value of a 2D model is that it can more clearly depict extreme scenarios that overflow the banks of a river and it can directly simulate objects like roads, bridge abutments, and other construction that can redirect flood flows. The most common tool kit for these models is the U.S. Army Corps of Engineers (USACE) Hydrologic Engineering Center - River Analysis System (HEC-RAS).

Public data

Any model is only as effective as the data put into it, and most hydrological models are built using publicly available data from multiple sources, including Geographic Information Systems (GIS) data generated by state and federal agencies, FEMA, and stream/tidal gauge networks managed by USGS and NOAA. The wealth of information available today enhances our understanding of flood hazards and strengthens the foundation of our modeling efforts.

What are hydrologic and hydraulic models used for once they’re built?

We utilize model results for a range of purposes, from upgrading, repairing, or removing dams and levees to vulnerability assessments to emergency action planning. By estimating flood conditions during storms, predicting the impacts of sea-level rise and climate change, and evaluating proposed projects' effects on surrounding areas, our clients have more insight into their risk profiles and we can provide better guidance on reducing those risks.

The challenges inherent in hydrologic and hydraulic modeling for dam and levee projects are substantial, but with the right expertise, these challenges can be effectively addressed. Hydrological models help us empower our clients make informed decisions based on the best available science to better protect their assets and our communities.