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3.4. Mitigation Alternatives • based on the previous analyses, alternatives have been developed to mitigate the potential erosion of the drainage channels. These mitigation measures are necessary where it is evident that erosive velocities are occurring in the channel or channel slopes are much greater than the average slopes presented in Table 3.2. The measures developed to mitigate the potential channel erosion locations include: 1. Install structural controls such as riprap, check dams or drop structures. Procedures for determining the size, thickness, gradation, filter requirements and placement techniques for riprap protection have been developed given the discharge, channel shape and slope. The riprap would increase the channel roughness, increase the flow depth and decrease the flow velocity. Constructing a series of stable check dams or drop structures would reduce the effective slope, increase the flow depth and reduce the flow velocity. Procedures for determining the height and spacing of the check dams or drop • structures have been developed and can be applied to restore channel stability. It is assumed that the drop structures or check dams would be constructed of riprap or materials not likely to erode during the 10-year, 24-hour storm. 2. Reduce the channel slope by regrading the existing topography. 3. Reduce the channel flows. This can be accomplished by rerouting a portion of the design discharge to a more stable drainage channel or establishing stock ponds capable of storing a significant portion of the design discharge. In each case, the existing topography must be evaluated and the effectiveness of the mitigation measure determined. Any one of the above mitigation measures will be sufficient for abatement of the potential channel stability problems identified by this study. Further analysis and evaluation of site-specific information will be necessary to determine the design details of each recommended mitigation measure. 38