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Figure A-15 (page A-29) shows a method of installing a temporary boazd dam at the • inlet of a culvert. This method can be used in those locations where space is not available at the outlet end to install adequate temporary measures. Also, many locations are usually available where this method can be used to temporarily pond runoff in medians and ramp loop areas. The basin created by this dam should be periodically cleaned. Hay bales may be used in conjunction with the boards if adequate measures (such as staking) are taken to prevent them from clogging the culvert. At lazger stream or river crossings, temporary dams in the channel are generally not feasible or practical, except under special conditions. In these instances, eroded materials should be intercepted before they reach the waterway. Figure A-16 (Page A-30) shows three types of protection that can be installed to trap sediment. Dumped stone_or riprap protection is also needed between the outlet and the waterway. Most highway plans show the location of ditches and include a typical aoss section detail However, no special details are generally included for those locations where ditches join and in many cases the junctions are indicated as 90 degree intersections. At junctions, heavy concentrations of flow may result in the water leaving the ditch and eroding the adjacent earth. Ditch junctions should therefore, be designed and constructed to accommodate the runoff and side slope at junctions should be steepened to more effectively direct the flow. • nrainaE intr~~ Unprotected drainage inlets, catrhbasins, and other minor structures often times empty silt laden runoff directly into waterways or ditches leading to waterways. Runoff should be intercepted before it reaches these drainage structures and the silt and other materials removed. Figures A-17 and A-18 (pages A-31 and A-32) suggest methods that can be used to minimize the amount of sediment entering these structures. Periodic cleaning is necessary to maintain their effectiveness and au accumulated silt must be removed before constructing the pavement structure. When water is discharged from a pipe, erosion often results. While permanent splash pads, energy dissipators, or other special treatment may be required, often times they aze not constructed until some time after the pipe is installed. In these situations, dumped stone should be used as shown in Figure A-19 (page A-33) for temporary or permanent erosion control The quantities of stone required should be determined depending on conditions such as the anticipated discharge and velocity. A-8