Freeboard Clearance beneath Pavement Structures
To reduce the influence of water on the asphalt pavement, it is necessary to provide a certain freeboard beneath the pavement structures. The lowest elevation of the asphalt pavement is at -0.45 m MSL, therefore a 60 cm freeboard would imply that the water level in the subgrade sand would have to be kept at -1.05 m MSL, which is close to the bottom elevation of the secondary canals. It would be difficult to achieve this magnitude of freeboard by means of the gravity flow system. Sump pits with water pumps would be inevitable as the best option available, but the associated cost and the effort could be significant.