Six Reasons Why Morganza "Leaky Levees" Are Unproven Storm Protection
This VOICE of the WETLANDS joins with the objections to the “Leaky Levee” Morganza proposal as stated by the
Louisiana Coastal Area (LCA) Program Science Board Report. December 13-14, 2006 and as submitted to the Program Management Team, January 5, 2007
VOICE of the WETLANDS quotes:
- There are large uncertainties about the effects of leaky levees on enclosed tidal wetlands, including the degree of interference with water-level variations, vertical soil accretion and migration of fishery species; entrapment of saline waters if overtopped or breached and fresh waters from storm water runoff; and other water quality issues. Although they were designated to stabilize vertical fluctuations of water level, marsh management schemes have often had deleterious effects on wetland sustainability, fishery habitat value and entrapment of saline or fresh water.
- Cases where a large portion of the estuarine basin is enclosed by a leaky levee (e.g. the Barataria Basin) are more problematic than where smaller areas of wetlands are so enclosed because of the technical and practical challenges of managing large volumes of water exchange.
- The compensation of diminution of sediments subsidies from the marine side by river diversions into the upper basins, as envisioned in the State Master Plan, is an intriguing but untested concept.
- Strong state laws and policies would be required to prevent development of low-lying areas protected by leaky levees. Otherwise, expanded development in subsiding polders would just bring more disasters.
- Despite the existence of leaky levees, for example along portions of the Morganza-to-Gulf alignment, surprisingly little scientific information is available on their effects on tidal exchange, sheet and subsurface flow, water-level fluctuation, wetland soil and plant dynamics, water quality, and ingress and egress by fishery species. Evaluation of these effects through field research, monitoring, and modeling should be a very high priority.
- In some regions the leaky levees have alignments that take into account physical processes and long-term evolution of the landscape. In others the alignments appear to be determined primarily for human infrastructure or political reasons. Where leaky levees are adopted, the alignments should be based on assessment of how the landscape will evolve around the new obstructions.
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