Mississippi River diversions, coastal wetland restoration/creation and an economy of scale

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We tested the hypothesis that there is an economy of scale in ecological engineering projects designed to create or restore wetlands by using examples of coastal restoration/creation projects in the Louisiana coastal zone. Land gain and project cost are directly related to the amount of riverflow diverted from the main channel, as expected. However, the $/ha gained was dramatically and directly related to project size. A 1000 fold increase in project size is matched by a 100 fold increase in the cost/ha gained. The smallest river diversion projects ($20,000 each) create land at slow rates (@5 ha/year) and tend to be very cost effective ($20-$500/ha). These low cost/ha gained are in sharp contrast to that of the larger river diversion projects and most other local wetland restoration/creation projects funded by state/federal sponsored programs ($1000 to $100000/ha) on this coast. There is a 15 fold increase in $/ha gained as project size increases by a factor of 10. This situation of decreasing returns ($/ha gained) with project increasing costs may be called an 'inverse' economy of scale. We propose that there are generic economies of scale inherent to similar environmental management approaches that represent a compromise of at least three attributes: attempts to control ecosystem behavior (predictability and use), ecosystem complexity, and incomplete ecosystem knowledge.

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Ecological Engineering

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