Water flows in a rectangular channel of bed width 4 m at a discharge of 6.0 m/sec and a water depth of 1.5 m. a. A bridge is proposed to cross this channel. What is the minimum allowable bed width at the proposed bridge site in order to keep the upstream water conditions unchanged? Find the change in the water depth due to that contraction in bed width. b. If it is decided that the channel bed width at the reduced section will be 3.0 m only, what is the required rise or drop in the bed elevation at the reduced section in order to keep the water level unchanged through this channel.