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e Channel Side Slopes $ For purposes of safety, construction, maintenance, and erosion resistance, it is suggested that channel side slopes be kept as flat as possible. Ideally, side slopes should be 3:1 or flatter for erosion resistance. Still flatter slopes may be necessary for safety or other reasons. . Analysis of the NCHRP Report No. 108 riprap design method demonstrates that if a riprap lined channel has 3:1 or flatter side slopes, there is no need to check the sides for scour. With steeper side slopes, the combination of velocity against the stone and gravitational effects may dislodge the stone on the sides before the channel bottom is disturbed. e The SCS (5) recommends maximum 3:1 to 4:1 side slopes on vegetative lined channels for ease of construction, mowing, and crossing the channel with equipment. In the Louisiana research (4), eroded field test channels were reconstructed with side slopes no steeper than 3:1. Therefore, all design charts are for channels with side slopes of 3:1 or flatter. For rock riprap, a method of designing steeper side slopes is presented in the Design Procedures Section. Channel Freeboard Channel freeboard should be evaluated based on the consequences of overflow of the channel banks. In a usual situation, about one foot of freeboard, measured vertically should be adequate for small drainage channels, although in some cases more should be used and in some cases no freeboard is necessary. When freeboard is provided, the depth of flow may exceed ~x and then scour of the channel will occur. M 'i Most lining materials should extend to the top of the bank or at least two feet above the design water level, measured along the slope. In large channels, wave height may define freeboard requirements. Wave height determinations are beyond the scope of this circular. e 13