Author(s): Marcelo H. Garcia; J. Ezequiel Martin; Blake J. Landry; Andrew R. Waratuke; Nils Oberg
Linked Author(s): Marcelo García
Keywords: Levees; Flooding; Backwater computations; HPG; HEC-RAS. 1
Abstract: The Mississippi River and its delta have a history of experiencing periodic catastrophic flooding conditions. During the most recent event in 2011, levees were breached at many locations to prevent the flooding of towns and cities along the length of the lower Mississippi River. It has been suggested that levees may tend to raise flood levels (Chris and Shock, 2001). In some cases the confining effect of levees may act as a bottle-neck on flow and lead to flooding upstream. This is obviously counterproductive with regards to their stated purpose – to prevent flooding. Despite this problem there are few simple techniques for readily assessing the effect of levees on flooding. At the same time there has been a lot of discussion in the literature regarding the hydraulic effectiveness of levees and their role in flood control. An approach based on the Hydraulic Performance Graph (HPG) method is presented with the goal of providing a technique to assess the effectiveness of levees for flood control, to explain to the public the impact of levees on flood conveyance and to facilitate floodplain management by local, state, and federal agencies. Two examples of the technique are provided to highlight both the ease of use of the method, and how the method can be applied to both simplified reaches using simple backwater calculations (the Mississippi River at Chester, IL) and more complex systems (the Mokelumne River in central California) using the Army Corps of Engineer ’s HEC-RAS.