Logan Bayer defended his thesis on Wednesday, October 30
MS in Engineering, Emphasis in Environmental Engineering
“Redefining the Bounds of approximations to the Sant-Venant Equations for Overland and Riverine Flows in Compound Flood Simulations”
Abstract: Floods are extremely destructive and affect many people every year. For example, Hurricane Ian in 2022 was responsible for over 150 deaths and over $112,000 million (USD) in damage, making it the costliest hurricane in Florida. With the effects of climate change, coastal watersheds will be subjected to additional flood stressors, resulting in catastrophic effects from compound flooding – a phenomenon which occurs when storms cause concurrent extreme meteorological tides and precipitation (Bevacqua et al., 2020). Numerical modeling of compound flood events allows for the design of risk-mitigation strategies but requires simulations of several flooding scenarios. Current modeling techniques cannot simulate multiple processes simultaneously and may lose accuracy when modeling events with numerous flood drivers. We present a tightly coupled model for simultaneously simulating overland and riverine flows using the equations and their approximations, such as the kinematic wave (KWE) and diffusive wave (DWE). The overland module uses 2D KWE, while the riverine module can employ the full equations (SVE), as well as different approximations like the KWE and DWE. The 1D and 2D governing equations are discretized in space with the weighted residual method and in time with implicit time discretization methods, similar to the ADCIRC (ADvanced CIRCulation) model. This study investigates conditions where the approximations to the Saint-Venant equations for overland flow and riverine flow are applicable. A sensitivity analysis is performed for the overland flow module, and the channel flow modules are run on hundreds of simulations. The Froude and kinematic numbers for each approximation are analyzed and new bounds for when to use approximations to the SVE for compound flood simulations are developed using these findings. Lastly, the physical channel characteristics are compared to the average values of each term in the diffusive wave approximation and we found that longer rivers with higher slopes result in higher values of the pressure gradient term, indicating the DWE results in better approximations than the KWE in these conditions. This research allows modelers to know when approximations can be used to model complex flows in low-lying coastal areas, and lays out a framework for implementation into the ADCIRC model. Ultimately, it is a stepping stone for better approximations to compound flood scenarios, which in turn could reduce the money spent on damages and alert the populations of coastal areas prior to these events occurring.
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Stevens Charles defended his thesis on Thursday, October 31st
MS candidate in Environmental and Civil Engineering, Emphasis in Civil Engineering
(DU Natural Infrastructure Graduate Fellow)
“Impact of Controlled Overtopping on Wetland Rehabilitation and Flood Mitigation”
Abstract: Riverine wetlands along the Mississippi River are critical habitats for migratory waterfowl and provide essential ecosystem services. However, efforts to control frequent flooding along the river have led to infrastructure developments that reduced wetland habitats and altered flood frequencies. In the spring of 2008, significant rain events caused severe flooding along the Mississippi River, resulting in levee breaches at multiple sites, including the Henderson Creek State Fish and Wildlife Area (HCSFWA) in Illinois. A major flood event, with a return period of about 25 years, caused the first breach, allowing water from the Mississippi River to flood a large portion of agricultural land and form an unintended wetland. The accumulation of water behind the levee led to a second breach in the southern part of the site, allowing water to flow uncontrolled into the Henderson Creek tributary, bypassing a U.S. Army Corps of Engineers (USACE) Lock and Dam system on the Mississippi River. This project seeks to capitalize on the levee failure and utilize the seasonal flow patterns of the Mississippi River to mitigate flooding while enhancing the ecosystem services provided by the site. Using hydraulic modeling tools, this study aims to analyze the hydrodynamics of the HCSFWA, focusing on water residence time to create optimal wetland conditions. Additionally, flood depths upstream and downstream of the site will be examined to assess the broader impacts of the levee breach on the Henderson Creek tributary and the Mississippi River. The findings will offer insight into the role of controlled overtopping in flood mitigation. By aligning with the natural flood cycles of the Mississippi River, this approach could help reduce flood risk along the river and its tributaries, while restoring vital wetland habitats that benefit both nature and society.
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Media by: Olivia Allen.