allings 18. a. Determine the head water depth of a 800 mm by 1000 mm concrete box culvert operating under inlet control with a stream flow of 3 m 3 /s. The culvert has wingwalls at 450 flares. If the entrance invert elevation is 117.13 m, what is the headwater elevation? (3) b. Explain how you would approach this if the inlet control is unknown (1)