CS17B - Concurrent Session 17B: Land O’ Lakes Inundation Mapping: Challenges of Modeling and Mapping an Above Ground Reservoir

Abstract Description: Dam breach modeling and inundation mapping for above ground reservoirs can present a variety of challenges. A ring-dike impoundment may have multiple potential breach locations, leading to additional modeling and mapping efforts when compared to a traditional dam breach analysis. These impoundments are also commonly near residential structures and water treatment plant infrastructure, assigning them with a high-hazard classification. One such impoundment, located in Land O’ Lakes, Florida, is currently being studied by Hazen and Sawyer to update inundation mapping for inclusion in an EAP.
Land O’ Lakes Reservoir is a 100 MG reclaimed water reservoir, impounded by an earthfill dam. Two of the reservoir’s five sides are connected to reject ponds encompassed by their own earthfill dams. One challenge setting up this dam breach model was determining how a breach from the main reservoir would enter a reject pond, and if the pond’s outer embankment could also breach. A conservative approach is typically desired for emergency planning, but questions arose as to what scenarios would be physically probable.

For the simulated storm in progress breach, initial inundation around the reservoir was due to pluvial flooding. Ponds and low-lying areas fill during large storm events, and it was essential to establish this as a model initial condition to ensure there wasn’t an unrealistic amount of storage available to detain the breach wave. This conservative modeling approach introduced a challenge to inundation mapping, because there needed to be a differentiation between pluvial flooding and that caused by the breach wave.

Above ground reservoirs also pose the distinct challenge that dam breaches are possible around the entire perimeter of the embankment, producing numerous potential inundation zones. Judgement had to be made to determine several dam breach locations that would paint the full picture of potential inundation. The question then arose of how to illustrate these various breach scenarios on inundation maps. First responders need to quickly and easily understand the maps and the potentially impacted areas of a breach in progress, even at a location that may not have been modeled. For this reservoir, a balance was found between minimizing the number of breaches to improve readability for emergency responders while ensuring all potentially inundated structures are accounted for.

This presentation will outline these unique modeling considerations as needed for an above ground reservoir to create equally probable and conservative breach modeling and subsequent mapping.