252 - Effects of Sampling Interval on Understanding Storm Characteristics

When monitoring stormwater management systems, it is imperative to have a clear and accurate depiction of inflow and outflow. This is especially important to understand storm intensity as they relate to erosion potential. Utilizing a model created in SWMM to simulate a stormwater management practice (SMP) bioswale located in Philadelphia. Observed rainfall data was collected from a nearby weather station. The focus of this study was to determine the optimal sampling interval for data collection. The SWMM model was used to simulate inflow and outflow at different sampling intervals (i.e., 1-, 5-, 15-, 30-, and 60-minutes). The results of the study concluded that changing the sampling interval did not make a significant difference for total runoff volume. However, for peak flow rate data, there was a significant difference between the different sampling intervals. With the larger sampling intervals (15-, 30-, and 60-minutes) the more the peak flow rate is underestimated. In contrast, the shorter the interval, the more defined the resulting hydrographs were, such that they had higher peaks and deeper valleys. These results show that having a sampling interval small enough to capture momentary peaks (i.e., 1- and 5-minute intervals) that could be missed by larger sampling intervals as it affects monitoring design and operation of SMPs and their downstream receiving systems.