15.1. Submittal Review 15.1.1. Review Drainage Impact Analyses (DIAs), construction plans, and hydrologic/hydraulic models submitted by developers. 15.1.2. Confirm that models include timing analyses for 5-, 10-, and 100-year storm events. 15.1.3. Verify that HEC-HMS/HEC-RAS or approved equivalent software is used, with parameters consistent with Atlas 14 rainfall data. 15.2. Peak Flow Timing Evaluation 15.2.1. Evaluate the synchronization of site runoff peaks with downstream receiving systems. 15.2.2. Confirm that detention routing adequately attenuates and staggers peaks to avoid coinciding with regional system peaks. 15.2.3. Ensure hydrographs demonstrate “no increase” in peak flow timing impacts at all outfalls compared to pre-development conditions. 15.3. Detention & Routing Analysis 15.3.1. Verify that detention facilities are designed not only for volume requirements (0.55 acre-ft per acre minimum) but also for timing control performance. 15.3.2. Confirm that outlet structures and stage-storage-discharge tables are consistent with both County detention standards and timing requirements. 15.3.3. Ensure that pumped detention or non-standard controls are justified, limited, and approved by the County Engineer.
