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CHAPTER 6 TECHNIQUE SELECTION SYSTEM SELECTION STRATEGY AND APPROACH Greenbank is a rule-based selection software program developed for use by DOT or consulting engineers. The gov- erning rules relate the strengths and weaknesses (hydraulic, geotechnical and environmental) of each technique to the rel- evant site conditions and project constraints. The knowledge base is contained in a matrix that allows the user to examine the rules and the basic rationale or reasoning behind each technique. Such an approach avoids the controversy associ- ated with selecting techniques based on a particular stream classification system. This approach also allows the user to conduct sensitivity analyses when reach descriptors are based on estimates. This software is roughly patterned on an earlier expert sys- tem known by the acronym ENDOW (Environmental Design of Waterways) developed in the mid-1980s at the U.S. Army Engineer Waterways Experiment Station (Shields and Aziz, 1992). The new selection system, Greenbank, was developed using a Windows-based tool known as Exsys CORVID. The CORVID system allowed the development of a tailor-made, interactive decision-making tool. As noted previously, some 44 discrete techniques were iden- tified and adopted. Design criteria for some (Level I Tech- niques) are highly developed, with abundant studies in flumes, field experiments, and mathematical analyses. Others (Level II and Level III Techniques) are less well documented and are supported only by anecdotal or qualitative observation. The rule-based system allowed the application of the current knowl- edge for each technique. In the case of hydraulic criteria, for example, there is a tabulation from the literature prepared by Fischenich (2001b), as well as others. Geotechnical criteria are well known in some cases, unknown in others, and sometimes not applicable. Due to regional differences in ecosystems, much of the environmental criteria must be general and generic. In any case, the Greenbank system is intended not to provide detailed design criteria, but rather to offer a list of techniques that match (1) dominant erosion processes and (2) environ- mental resources of special concern at the site in question. GREENBANK DECISION SUPPORT TOOL The Greenbank decision support tool can be run using a web browser (i.e., recent versions of Internet Explorer or 14 Netscape). The program, which contains rules to screen all 44 techniques and all attendant files, may be read from the accompanying CD. (Once the CD is started, an icon at the lower right corner of every screen opens the support tool.) A typical Greenbank consultation begins with the software asking the user to provide information about the proposed project. Specific aquatic habitat requirements can be taken into account in a systematic manner. The user is asked to specify environmental resources or aquatic attributes of interest from a list of 11 possibilities: (1) benthic habitat, (2) decreased sedimentation, (3) enhanced bed stabiliza- tion, (4) fish rearing habitat, (5) holding areas for adult fish, (6) in-stream and overhead cover, (7) pool and riffle enhancement, (8) public acceptance potential, (9) riparian habitat, (10) velocity refugia for fish, and (11) water qual- ity improvement. Based on this initial response, the system asks for more specific information about environmental issues. The user is then asked to characterize the erosion problem as (1) gullying, (2) erosion or scour by stream flow or wave wash, or (3) mass wasting (i.e., slope failure). If the user is uncertain about the nature of the erosion at his or her site, links are provided with text and photos to help the user iden- tify the dominant erosion process(es). In the case of erosion or scour by stream flow, the user can also input hydraulic criteria (i.e., design velocity and boundary shear stress), which allows Greenbank to compare these criteria with available published allowable values. A worksheet is pro- vided to assist the user in computing estimates of velocity or shear stress. The user is also asked to classify the spatial extent of the problem as local or general. If the erosion is general, the user must identify the parts of the stream channel cross section that appear to be eroding: top bank, middle bank, toe, or channel bed. Through this dialog, the user is led to identify the dominant erosion mechanisms operative at the site in question. Up to 4 erosion mechanisms may be selected from a master list of 12 processes. The user is then asked to spec- ify the maximum acceptable unit cost (relative to a riprap blanket). Greenbank then assigns a score to each of the 44 tech- niques based on the techniqueâs overall feasibility. This fea- sibility score takes into account suitability for a particular type of erosion problem, spatial location of the problem, environmental attributes specified as important, and price the
user is willing to pay. The top techniques are then output to the user, who may elect to change any or all of his or her pre- vious responses and obtain new recommendations. Each technique recommended is linked to the corresponding tech- 15 nique guideline within the manual portion of the CD, so that the user can learn more about the recommended technique. The logic flow, or selection methodology, used in Greenbank is described in more detail in Appendix B.
