What is a requirement for ensuring proper hydraulic design of sewer pipes?

To ensure proper hydraulic design of sewer pipes, it is essential to lay pipes crown to crown when size changes occur. This practice helps maintain a smooth flow transition from one pipe diameter to another, minimizing turbulence and potential blockages. When pipes are connected at differing diameters, aligning the crowns allows for uninterrupted flow, reducing the risk of sediment buildup and ensuring efficient sewer operation. By facilitating a consistent flow path, this alignment helps maintain hydraulic efficiency throughout the sewer system, supporting optimal drainage and system performance.

The other options don't address the hydraulic design as effectively. Maintaining a minimum velocity of 1.5 feet per second is important for preventing sedimentation in sewer pipes, but it does not directly relate to the design considerations of connecting varying pipe sizes. Keeping the cover over piping constant is not specifically tied to hydraulic design; rather, it pertains more to protection and maintenance ease. Lastly, using only one size of pipe throughout the system might simplify construction but can lead to inefficiencies in flow and may not accommodate the required capacities for varying flow rates in different sections of the system.