Pre- and post-development peak discharges Return Period (yr)
The InfoSWMM scenarios that produced these results are EX1-PRE and EX2-POST, respectively. The pre-development peaks were determined in Example 1 (Table 1-9 in Section 1.5) and post-development peaks were determined in Example 2 (Table 2‑7 in Section 2.5). Table 3-1 shows the discharges to be controlled by the pond. It is required that the pond reduce the peak discharges of the 2-, 10- and 100-yr storms to those of the undeveloped site, and that extended detention be provided for a specific water quality capture volume.
Based on the results of these scenarios, it is now required to design a detention pond immediately downstream of the planned urban development to both prevent flooding and protect water quality in a receiving stream. Total site runoff for the 2-, 10- and 100-yr design storms was computed for both the pre- and post-development conditions. Additional scenarios were constructed to estimate the site’s post-development runoff both without flow routing (Example 1) and with routing through a surface collection system (Example 2). In Example 1 a model was built to estimate the pre-development runoff from a 29 acre site. Facilities must control not only the extreme runoff events to prevent flooding, but also the more common smaller events that produce a “first flush” pollution phenomenon and thereby impact the quality of receiving water bodies. The design criteria for storage structures have changed over time due to an improved understanding of the effects that urban runoff has on the environment. Storage is widely used in urban runoff quantity and quality control, providing both peak flow reduction and suspended solids removal. The urban catchment studied in Examples 1 and 2 will also be used in this example. Storage units, orifices and weirs will be used to model a multi-purpose detention pond built to detain a water quality capture volume (WQCV) and control peak post-development release rates to their pre-development levels.
This example illustrates how to define, design, and evaluate a detention pond using InfoSWMM H2OMap SWMM InfoSWMM SA. Detention Pond Design in InfoSWMM and InfoSWMM SA