Simulating Hurricane Storm Surge in the Lower Mississippi River under Varying Flow Conditions R. C. Martyr, M.ASCE 1 ; J. C. Dietrich 2 ; J. J. Westerink, M.ASCE 3 ; P. C. Kerr 4 ; C. Dawson 5 ; J. M. Smith, M.ASCE 6 ; H. Pourtaheri 7 ; N. Powell, D.WRE, M.ASCE 8 ; M. Van Ledden 9 ; S. Tanaka 10 ; H. J. Roberts 11 ; H. J. Westerink 12 ; and L. G. Westerink 13 Abstract: Hurricanes in southeastern Louisiana develop significant surges within the lower Mississippi River. Storms with strong sustained easterly winds push water into shallow Breton Sound, overtop the river’ s east bank south of Pointe à la Hache, Louisiana, penetrate into the river, and are confined by levees on the west bank. The main channel’ s width and depth allow surge to propagate rapidly and efficiently up river. This work refines the high-resolution, unstructured mesh, wave current Simulating Waves Nearshore + Advanced Circulation (SWAN þ ADCIRC) SL16 model to simulate river flow and hurricane-driven surge within the Mississippi River. A river velocity regime– based variation in bottom friction and a temporally variable riverine flow-driven radiation boundary condition are essential to accurately model these processes for high and/or time-varying flows. The coupled modeling system is validated for riverine flow stage relationships, flow distributions within the distributary systems, tides, and Hurricane Gustav (2008) riverine surges. DOI: 10.1061/(ASCE)HY.1943-7900 .0000699. © 2013 American Society of Civil Engineers. CE Database subject headings: Storm surges; Mississippi River; Hurricanes; Rivers and streams; Hydrodynamics; Numerical models; Simulation. Author keywords: Storm surge; Mississippi River; Hurricanes; Rivers; Hydrodynamics; Numerical models; Storm surge generation; Propagation and attenuation. Introduction The central Gulf coast’ s geographical features and location make it particularly vulnerable to large storm surge during hurricanes. Southeast Louisiana is defined by low-lying topography, with many floodplains, marshes, and interconnected lakes (Fig. 1). The Mississippi River meanders through the region, and its southern reach is surrounded by shallow bays and lakes, such as Lake Borgne, and shallow open waters to the east. The river’ s delta protrudes to the edge of the continental shelf and contains many distributaries and interconnected fresh-water and brackish marshes. The city of New Orleans is bounded by Lake Pontchartrain to the north and the river to the south. Plaquemines Parish, the southern boundary of the state, encompasses the southern portion of the river and its delta, which are also surrounded by extensive marshes and sounds, such as Caernarvon Marsh and Chandeleur and Breton sounds to the east, and Barataria Bay to the west. These features define the geography of the region and are interconnected to the Gulf by the river, natural and artificial channels, and the low-lying floodplain. Periodic flooding and navigational demands prompted levee development along the river. These levees extend downriver to Pointe à la Hache, Louisiana, on the east river bank, and continue further southward to Venice, Louisiana, on the west bank. Due to the regional geography, hurricane storm surge is effectively cap- tured by the western river levee. Hurricanes, such as Betsy (1965), Katrina (2005), and Gustav (2008), pushed surge from the southeast and east into Breton Sound and flooded the narrow marsh and eastern river banks of lower Plaquemines Parish, Louisiana (Westerink et al. 2008; Bunya et al. 2010; Dietrich et al. 2010, 2012). The western levees that extend 60 km farther south along the river enable an efficient buildup of surge. The river’ s width and depth facilitate the propagation of this surge upriver to New Orleans and Baton Rouge, Louisiana. The Mississippi River experiences interannual and intra- annual variations in flow due to many factors including seasonal 1 Dept. of Civil and Environmental Engineering and Earth Sciences, Univ. of Notre Dame, Notre Dame, IN 46556 (corresponding author). E-mail: rmartyr@nd.edu 2 Institute for Computational Engineering and Sciences, Univ. of Texas, Austin TX 78712. 3 Dept. of Civil and Environmental Engineering and Earth Sciences, Univ. of Notre Dame, Notre Dame, IN 46556. 4 Dept. of Civil and Environmental Engineering and Earth Sciences, Univ. of Notre Dame, Notre Dame, IN 46556. 5 Institute for Computational Engineering and Sciences, Univ. of Texas, Austin TX 78712. 6 Coastal Hydraulics Laboratory, U.S. Army Engineer Research and Development Center, Vicksburg, MS 39180. 7 New Orleans District, U.S. Army Corps of Engineers, New Orleans, LA 70118. 8 New Orleans District, U.S. Army Corps of Engineers, New Orleans, LA 70118. 9 Haskoning Nederland B.V., Rotterdam, The Netherlands. 10 Earthquake Research Institute, Univ. of Tokyo, Tokyo 113-0032, Japan. 11 ARCADIS INC., Boulder, CO 80301. 12 Dept. of Civil and Environmental Engineering and Earth Sciences, Univ. of Notre Dame, Notre Dame, IN 46556. 13 Dept. of Civil and Environmental Engineering and Earth Sciences, Univ. of Notre Dame, Notre Dame, IN 46556. Note. This manuscript was submitted on December 6, 2011; approved on November 2, 2012; published online on November 5, 2012. Discussion period open until October 1, 2013; separate discussions must be submitted for individual papers. This paper is part of the Journal of Hydraulic En- gineering, Vol. 139, No. 5, May 1, 2013. © ASCE, ISSN 0733-9429/2013/ 5-492-501/$25.00. 492 / JOURNAL OF HYDRAULIC ENGINEERING © ASCE / MAY 2013 J. Hydraul. Eng. 2013.139:492-501. Downloaded from ascelibrary.org by University of Texas At Austin on 04/14/13. Copyright ASCE. For personal use only; all rights reserved.