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<br />Where a block is checked for a given countermeasure under an environmental <br />./ characteristic, the countermeasure is considered suitable or has been applied <br />successfully for the full range of that environmental characteristic. <br /> <br />The checked block means that the characteristic does not influence the selection of <br />the countermeasure, Le., the countermeasure is suitable for the full range of that <br />characteristic. For example, guide blinks have been applied successfully in braided, <br />meandering, and straight streams; however, bendway weirs/stream barbs are most <br />suitable for installation on meandering streams. <br /> <br />3.4.3 Maintenance <br /> <br />The maintenance category identifies the estimated level of maintenance that may need to be <br />allocated to service the countermeasure. The ratings in this category range from "Low" to <br />"High" and are subjective. The ratings represent the relative amount of resources required <br />for maintenance with respect to other countermeasures within the matrix shown in Table 1. <br />A low rating indicates that the countermeasure is relatively maintenance free, a moderate <br />rating indicates that some maintenance is required, and a high rating indicates that the <br />countermeasure requires more maintenance than most of the countermeasures in the <br />matrix. <br /> <br />3.4.4 Installation/Experience by State Highway Agencies <br /> <br />This category identifies SHAs for which information on the use of a particular counter- <br />measures was available. These listings may not include all of the states which have used a <br />particular countermeasure. Information for state use was obtained from three sources: <br />NCHRP 24-7 Questionnaire (University of Minnesota survey); Brice and Blodgett, <br />"Countermeasures for Hydraulic Problems at Bridges, Volumes 1 and 2," (1978); and <br />personal correspondence with SHA staff. It is expected that additional information on <br />state use will be obtained as this matrix is distributed and revised. Certain <br />countermeasures are used by many states. These countermeasures have a listing of <br />"Widely Used" in this category. Both successful, and unsuccessful experiences are reflected <br />by the listing. <br /> <br />3.4.5 Design Guideline Reference <br /> <br />Reference manuals which provide guidance in countermeasure design have been developed <br />by government agencies through research programs. The FHWA has produced a wealth of <br />information through the federally coordinated program of highway research and <br />development. The design guideline reference column identifies reference manuals where <br />guidance on design of the countermeasures can be obtained. The references are <br />symbolized by numbers in this column. The numbers correspond to the numbers of the <br />references listed on the second page of the matrix (see also Section 6.0 References). <br />Countermeasures for which design guidelines are provided within this document are <br />referenced using DG#, where # represents a number assigned to the design guideline (see <br />Section 5.0 Design Guidelines). <br /> <br />4.0 COUNTERMEASURE DESIGN PHILOSOPHY <br /> <br />, <br />, <br />i <br />I <br />J <br /> <br />I <br /> <br />4.1 Investment in Countermeasures <br /> <br />While it is sometimes possible to predict that bank erosion will occur at or near a given <br />location in an alluvial stream, one can frequently be in error about the exact location or <br />magnitude of potential erosion. At some locations, unexpected lateral erosion occurs <br /> <br />8 <br />