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Planning And Preliminary Dealgn e h. Morphdogic Trends - A proposed solution may be appropriate ~or today's conditions; however, projected changes in the system which might render it ineffective in the future must be Cl msidered. See Chapter 2 for a review of the criterion to be considered. i. Project] .ife . Part of the economic evaluation, this factor carries technical significance as well. If the need is to stop erosion during an emergency, longevity of the constructed wol1cs maJ not be a prime factor. In very dynamic alluvial sellings (highly braided rivers for example), erosion may be the result of a temporary anomaly in the channel. Protecting the bank until the next major flow causes a change in the channel conditions may be all that is necessary. 5.4.2 Colorado Rivers . It would te very convenient to have a table listing each of the rivers in Colorado with the "best" solution to erosion for each. Unfortunately. the diversity of these systems (and indetd individual reaches on a single river), as well as the complexity of the other factors tole considered, prohibit such a simplistic approach. That is not to say that little can be lelll1led from erosion control wol1cs elsewhere on a system. Such information must be tempered with an evaluation of the specific case at hand. 5,4.3 Envlronrnental Considerations - Koowledge of potential environmental effects is as much a part of the basic data needed for sound. responsible p1anrting and design of river woB:s as are hydrologic, hydraulic. geologic, seismic, and other physical data. All stabilization projects should include an evaluatio~ of environmental impacts. In addition, every effort should be made to incorporate environmental features into the complete project. Potential solutions to such considerations can be developed into an artificial intelligence program. Such a program is describ<:d in Appendix D. 5.4.4 Past Failures and Successes. Success and failure of streambank erosion control structures contribute to the quality of future p~iects. Success has always been built on past failures. Thus, it is very important to examine why a structure failed its designed purpose. From that, one can learn from the deficie ncy and generate the proper facility. Care must be taken not to generalize the structures themselves. The engineer must differenti~Je the river environment in wbich the existing and proposed erosion control structures reside. Only then can comparison of success and failure between similar reaches arod their structures begin. 5.5 Economic and Financial Evaluation - Two mon"tary evaluations are used in project formulation and justification; economic analysis and financial analysis. Economic analysis is an indicator of project feasibility: a Would b<:nefits equal or exceed costs if the project were constructed? Financial _ 64 CoIOradl) Erosion Control Manual