Emergy valuation of diversions of river water to marshes in the Mississippi River Delta

River diversions within the Mississippi Delta deliver river water and associated sediments and nutrients to interior marshes that were previously isolated from river inputs by elevated levees. When isolated from river inputs. the marshes subside and deteriorate to open water, resulting in ecological and economic losses, River diversions are an ecological engineering method to reverse this trend by restoring controlled flows of river water through modified levees. This study compares the cost of constructing and operating the diversions with potential benefits to determine whether the diversions yield a net public benefit. The Caernarvon and Davis Pond river diversions were evaluated using emergy analysis to provide a common basis to quantify and compare economic and ecological costs and benefits. The analysis quantified high concentrations of natural resources inherent to deltas and demonstrated benefits produced by investing economic resources in river diversions to capture and utilize renewable resources. The diversions resulted in large net emergy yield ratios (33.2 and 9.36) that varied depending on the rate of marsh gain produced by the diversions. (C) 2002 Elsevier Science B.V. All rights reserved.