a low broad crest weir is installed in a wide, rectangular channel to reduce the flow velocity. the channel is 60ft wide, the channel slope is 1 to 2000. Manning's roughness coefficient n=0.014. the discharge per unit channel width is q=60 cfs/ft. the depth directly upstream of the weir is 12ft. What are the critical depth and the normal depth at the given discharge? How far does the backwash extend upstream if the rise of 10% above normal depth is taken as the limit?