Quantcast 5 Costs of Bioengineering

 
  
 
Appendix B: Bioengineering for Streambank Erosion Control -- Guidelines
5 Costs of Bioengineering
Bioengineering treatments are normally much less expensive than traditional methods of
streambank erosion control, e.g., riprapped revetment, bulkheads, but not always depending
on the environmental setting and the project objectives. Costs can vary tremendously by
availability of materials, hauling distances, prevailing labor rates for the geographic area, and
a host of other factors. Table 3 illustrates cost comparisons of actual costs for a couple of
bioengineering installations compared to estimated costs of riprapped revetment for the same
locality under similar conditions. You will note that the first method, the dormant post
method, installed in northwestern Illinois, was about one-fourth the cost of riprapped
revetment. The vegetative geogrid installed in California was about 4 times the cost of
riprapped revetment. In the first case, riprap was in short supply and cost much more which,
in part, contributed to a higher cost than in the California example. Also, the dormant post
method required cheaper materials and less labor than the vegetative geogrid in California.
Riprap in the California example was fairly cheap and the slope distance to cover the bank
was not great, contributing to a cheaper installation than the vegetative geogrid. Also, the
vegetative geogrid was fairly labor intensive. Labor accounted for 66 percent of the overall
costs. However, what is not shown in the California example is that the site is next to a
valuable golf course and the sponsor is also trying to provide shaded riverine aquatic (SRA)
habitat for native brown trout. The vegetative geogrid can be installed on nearly a vertical
slope without much sacrifice to the adjacent land and it will provide the SRA habitat by
providing willow that overhang the banks. The riprapped revetment option does not provide
overhanging vegetation for good SRA habitat and does require more land to accommodate
shaving the bank to an acceptable construction standard for riprap. It would have required
eliminating some of the valuable golf course land. Thus, one must consider the project
objectives and potential benefits and impacts when considering comparison of bioengineering
methods with other traditional techniques.
When comparing bioengineering methods with traditional engineering applications,
Coppin and Richards (1990) stated that each must be considered on its merits, comparing life-
cycle costs, i.e. the net present value of investigation, design and construction, plus future
management and replacement. As mentioned earlier, bioengineering will require a higher
investment early in the project life to ensure that the living system is established. Then,
maintenance drops off and the vegetation in the bioengineering treatment continues to grow,
spread, and strengthen the streambank through its various attributes mentioned early
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