Calibrate the constrained data to develop unconstrained annual hydrographs

Suibing Liu, Susan E. Moisio, Pedro Quiros Pierce and James B. Ferguson


CH2M is managing the Miami-Dade County Water and Sewer Department’s (WASD) $ 5.7 billion Ocean Outfall Legislation (OOL) Program. The 11-year OOL Program is the culmination of a regulatory mandate by the Florida Legislature to reduce all wastewater treatment plants (WWTP) outfall discharge to the ocean by 95% by 2025. The OOL program will reverse the County’s WWTP effluents away from the ocean outfalls, reroute flows to a new WWTP, and redistribute the flows among the three existing WWTPs as well as the new one. The future annual inflow hydrograph for the WWTPs and conveyance systems is one of the key components for the capital improvement projects (CIP) evaluations.

The 2010 monitored inflows at the WWTPs were utilized to develop the future annual inflow hydrographs. However, the WASD’s collection system was constrained during large wet weather events with under-capacity pump stations throughout the system. A simple PCSWMM model was built with one hydrologic subcatchment and minimal hydraulic networks to represent a WWTP’s service area. The 2010 to 2014 composite 15-minute rainfall for the WWTP service area was loaded into the model. Then the RTK method was used to calibrate the 2010 to 2014 monitored WWTP data. The unconstrained smaller events were identified and selected for calibration. The calibrated RTKs were used to simulated the large wet weather events to generate the unconstrained hydrographs. The simulated unconstrained hydrographs were combined with the rest of the 2010 monitored hydrographs to create 2010 unconstrained annual hydropaths. The unconstrained annual hydrographs were regressed with the projected future dry weather flows, annual average daily flows and peak wet weather flows to create individual annual hydrographs at the loading nodes (896 or 1604 loading nodes for two model versions) to the InfoWorks collection system hydraulic model. The collection system model has been using these annual inflow hydrographs to simulate the annual hydrographs for the WWTPs and the conveyance systems for CIP evaluations.

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