Develop a new flood routing method for rectangular cross sections based on the Muskingum and storage indication techniques. Instead of using the Muskingum storage equation S = f(K, x, I, Q), use Manning's equation in the form where a and m are constants. Assume prismatic channel conditions at each time step, and derive the necessary equation for flood routing in a given rectangular channel with length L, inflows I1 and I2, channel width B, and outflows Q1 and Q2. Manning's equation takes the form Q = aym.