Cost-benefit considerations for stormwater wetlands Revision as of 18:54, 14 December 2012 by Chochstein (talk | contribs) (Created page with "Cost factors for stormwater management ponds are extremely sensitive to site conditions. Availability of materials for embankment construction, outlet protection, cost of exca...")
Cost factors for stormwater management ponds are extremely sensitive to site conditions. Availability of materials for embankment construction, outlet protection, cost of excavation, liner materials, and land costs are significant factors. Maintenance and inspection costs for mowing and periodic dredging are post-development factors. Other technologies such as infiltration trenches may be more cost-effective in smaller drainage areas due to construction and long-term maintenance costs (Young et al.,1996). Costs for ponds typically include costs for embankment, riser and spillway structures, outfall protection, vegetative stabilization, excavation, and grading. Additional costs for site preparation can include soil amendments, precision grading, plant materials and creation of occluding layers in coarse-textured soil types if wetlands systems must be created on upland sites due to project constraints. Project costs can be lowered if existing pre-construction site conditions are carefully considered and isolated areas with hydric soils contained within the footprint of the project are utilized as stormwater management facilities.
Additional maintenance costs may be incurred until the establishment of the wetland ecosystem. Invasive plants must be culled and dead plants replaced. The outlet structure may have to be adjusted, based on seasonal observations, to achieve the proper water surface in the pond. (FHWA, 1997).
Detailed Cost Estimate
The most appropriate technique for determining the cost to construct and maintain a specific BMP will be to apply unit costs to each component of construction, operation and/or maintenance. Table 12.WETL.6 represents the typical components for stormwater wetlands. This table presents those components of a construction project that are unique to this best management practice. Costs that would be associated with all aspects of a construction site, such as erosion and sediment control, mobilization, or traffic control, are not presented as unique costs.
Designers are encouraged to use the cost worksheet included in Appendix D to estimate their BMP construction cost.