What is the design criterion for storm water sizing?

The design criterion for storm water sizing focuses on the rate of discharge from any collection area. This is primarily important because effective stormwater management relies on understanding how much water is expected to flow from a given area during a storm event. By calculating the required rate of discharge, designers can appropriately size the stormwater drainage system to handle potential peak flows, thereby preventing flooding and ensuring proper drainage.

Sizing based on discharge rates also takes into consideration factors such as runoff coefficients, rainfall intensity, and the geographic characteristics of the area, which influence how quickly water will move into the drainage system. This approach ensures that the infrastructure can accommodate stormwater runoff effectively while mitigating the risk of environmental damage.

Other options focus on aspects that do not directly determine the capacity needed for stormwater systems. For instance, the depth of stormwater in each pipe is a consequence of the design rather than a sizing criterion. Similarly, the total area of green space impacts water absorption and runoff but does not alone dictate system sizing. Lastly, the type of drainage material used is relevant for construction but does not contribute to the calculations needed for effective stormwater discharge sizing.