Comparison between Some Dry Weather Flow Calibration Packages

Hazem Gheith and Gibson Chen


This paper presents a detailed comparison between different dry weather flow (DWF) packages used to deconstruct and generate DWF parameters for collection systems continues simulation. Flow in combined and sanitary collection systems is composed of a dry weather flow and a wet weather flow (WWF) portions. The WWF portion in combined collection system is usually generated from storm runoff, snow melt. The WWF portion in sanitary collection system is usually generated from illicit storm water connections, downspouts, and foundation drains. A delayed portion of the WWF in both combined and sanitary collection systems is also generated from rain dependent infiltration which took place immediately after the storm events and lasts for few hours to few days. The DWF portion is the flow collected by the collection system in a dry day that was not influenced by the storm events that took place immediately before the dry days. The DWF is composed of base wastewater flow (BWWF) and groundwater infiltration (GWI). The BWWF can be sewage that is collected from residential and/or industrial wastewater, especially from heavy water users industries. The GWI is generated in the collection system due to the rise of the groundwater table (GWT) in the vicinity of the collection system and due to the existence of defected joints and cracked pipes in older segments of the collection system.

A comparison between different vendors and consultants for calculating the two DWF components is presented. These different procedures vary in terms of ease of use, time of processing the flow data, and quality of DWF calibration results. Calibrated DWF values and patterns were tested against monitored data. Parameters for the calibrated DWF were calculated from applying several procedures available to the authors. Deconstruction packages available to the authors included CAPE (Brown and Caldwell), PCSMM (CHI) Slicer (ADS), SSOAP (US-EPA) and an in-house procedure used by the first author at Brown and Caldwell. Effort and quality of generating and calibration both components of the DWF (GWI and BWWF) were compared. The tests included flow metered sewersheds at different Midwest cities; including Columbus-Ohio, Pittsburgh-Pennsylvania, Ft Wayne-Indiana, … Some of the sewersheds were close to the rivers and others were in hilly or distant areas from the river. Some sewersheds were dominated by residential while others were dominated by heavy water user industries. Also some of the sewersheds were separate flow basins while others were combined flow basins.

Quality of the simulated peak flow and total mean daily DWF were compared to the monitored data. Seasonal DWF and weekdays versus weekend flow sand patterns were also compared.

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