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|Title:||Lake Pontchartrain and Vicinity Hurricane Protection Plan. Report 3, Numerical model investigation of plan impact on the tidal prism of Lake Pontchartrain|
|Authors:||United States. Army. Corps of Engineers. New Orleans District.|
Butler, H. Lee.
|Keywords:||Chef Menteur Pass|
Inner Harbor Navigation Canal
|Publisher:||Hydraulics Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Technical report (U.S. Army Engineer Waterways Experiment Station) ; HL-82-2 rept.3.|
Abstract: A comprehensive study to evaluate effects of the Lake Pontchartrain and Vicinity Hurricane Protection Plan on the tidal prism and circulation in Lake Pontchartrain, hurricane surge levels, and water quality is being conducted by the U.S. Army Engineer Waterways Experiment Station under sponsorship of the U.S. Army Engineer District, New Orleans. This report, third of a series, presents results pertinent to a detailed investigation of effects of proposed structures in the two major arteries (The Rigolets and Chef Menteur Pass) connecting Lake Pontchartrain with the Gulf of Mexico and the lock/structure system between the lake and the Inner Harbor Navigation Canal (IHNC). The basic approach to simulating the impact of structural alterations on the Lake Pontchartrain tidal prism can be outlined as follows: (A.) Develop a numerical model of the three basin system (Lakes Pontchartrain, Borgne, and Maurepas). (B.) Obtain and analyze field data to aid in calibrating and verifying the lake system model (Report 1 of the subject series, Outlaw 1982). (C.) Perform sectional model studies of each pass (Report 2 of the subject series, Butler et al. 1982) to provide descriptions of structure hydraulic characteristics to the numerical tidal prism model. (D.) Calibrate and verify the tidal prism model and test plan impact under mean, spring, and neap tide conditions. Preliminary calculations with these tide conditions indicated difficulty in assessing the true impact of the hurricane protection plan on the tidal prism of Lake Pontchartrain. Consequently, a follow-up investigation of the effect of tidal range variation was made by simulating the structure system impact over a spring-to-neap-to-spring tidal period (semilunar month). In addition, computations were made to simulate the effect of a Bonnet Carre Floodway operation. In the development of the numerical model, a new boundary condition treatment was formulated for the IHNC to permit simulation of construction changes in the model interior without being forced to move the model boundary beyond influence of the changes. The tidal prism model was shown to accurately portray tidal behavior through the passes and to reproduce observed astronomical surface elevations throughout the region. Impact of the proposed control structures and the Seabrook Lock on the tidal prism of Lake Pontchartrain was shown to be minimal. Approximate percentage reductions in the tidal prism for the individual entrance passes are: Rigolets (9 percent), Chef Menteur (12 percent), and IHNC (21 percent). Model results showed a net reduction of 10 percent in the lake tidal prism with the barrier plan. When a 2 percent adjustment for omitting shallow navigation channels in The Rigolets and Chef Menteur plans is taken into account, the total impact of the barrier plan on net tidal exchange with the lake is to reduce the tidal prism about 8 percent. It was found that lake circulation is unaffected by installation of the structures except in areas local to the individual structures. Impact of the proposed hurricane protection barrier plan during a Bonnet Carre Floodway operation is minimal. Simulation of a floodway operation (to full capacity) under existing conditions showed that a 1.5 ft rise in average lake stage would occur. With the barrier plan in place the average lake stage rose about 1.8 ft, an increase of only 0.3 ft. Report reviews by project consultants are provided verbatim in Appendix B.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Technical Report|