Why is the design of storm drainage systems unique compared to sanitary systems?

The design of storm drainage systems is unique compared to sanitary systems primarily because storm drainage relies on gravity flow rather than full hydraulic pressure. In storm drainage systems, the primary goal is to efficiently manage and redirect surface water runoff following rain events. Because the water is usually collected from various surfaces like roofs, roads, and yards during precipitation, it flows naturally under the force of gravity through channels, pipes, or catch basins, rather than being pumped under pressure as is typical with sanitary drainage systems.

Sanitary systems, on the other hand, are designed to transport wastewater, which can include solids and requires a certain level of hydraulic pressure for effective movement through the system. Thus, storm drainage focuses more on volume and gravity, allowing for design considerations that differ significantly from those used in sanitary plumbing systems.

The other options do not accurately portray the key differences between storm and sanitary systems. For example, storm drainage systems are designed to handle varying flow rates depending on rainfall intensity and area size rather than just small flows. They do not necessarily need to be buried deep underground as design depth depends on site conditions, and the systems do not require only one outlet; they are often designed with multiple inlets and outlets to effectively manage large volumes of water.