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<br />Armorlng Technique. . <br /> <br />e <br /> <br />cutting, handling, storing, preparing and installing them. In addition, there must be an <br />adequate and suitable supply of plant materials nearby. Care should be taken to evaluate <br />the impact of mature tree growth upon the flood conveyance of the channels. <br /> <br />FIGURE 4.4 <br /> <br />Staked Riprap <br /> <br />Soil Layer <br /> <br />Varies <br /> <br /> <br />Dormant Willow Stakes <br /> <br />J <br /> <br />N.W.S.\ <br /> <br /> <br />Concrete Mattresses - Used almost exclusively for underwater revetments on large <br />rivers, concrete mattresses are approximately four feet by 20 feet slabs of concrete <br />connected by corrosion resistant wire. This allows multiple slabs to be connected to <br />form a mattress. The purpose of the wire, other that to hold the slabs together, is to allow <br />some flexibility to the mattress. Figure 4-5 shows a typical section of a concrete <br />mattress. <br /> <br />Concrete mattresses. shown in Figure 4 - 5,are capable of conforming to irregular <br />shapes of the stream bank and scour pockets. During increased hydnwlic flow, concrete <br />mattresses provide effective control of erosion; however. some bank material may erode <br />through the joining sections. Concrete mattresses must be economically justifiable due <br />to the specialized equipment they require. <br /> <br />The costs of concrete mattresses vary from $150-300 per linear fool. and may have high <br />annual maintenance costs from $10-25/ft/yr. <br /> <br />Concrete Rubble - Concrete rubble, derived from sidewalks 01' roads for example, can <br />be used in a similar manor as riprap. Concrete rubble is useful when stone riprap is <br />uneconomical or not available. Design and placement of concrete rubble annOI' is <br />similar to that of riprap. 1\\10 important considerations in the use of concrete rubble are <br />that all reinforcement be cut flush and that it be properly graded. LaIge slabs are not <br />desirable and generally lead to failure. <br /> <br />. <br /> <br />Colorado Erosion Control Manual <br /> <br />31 <br />