Flow routing in the parallel pipes of a combined sewer system
A parallel pipe model has been constructed and successfully applied to a twin pipe sewer system. The model predicts flow and level for each of the parallel pipes and deals with the complex behaviour which occurs at cross-connections. The model DUPPERS is an enhancement of the single pipe simulation model DUCTS developed at Dundee Institute of Technology. It has been rigorously tested using a variety of artifical parallel pipe system configurations and input discharges. Obtained results showed that the model was operating satisfactorily. The model was applied to the Lyneburn system in Dunfermline, Scotland, with three models being constructed : two sub-models and a full system model. Comparison between observed and predicted hydrographs for both flow and level were in close agreement. Percentage differences for peak flowrates, runoff volumes and levels were all within ±20% of observed and simulated values. A review of flow routing procedures, above-ground hydrological models and the major commercial sewer simulation packages is also included. In addition to the tailored parallel pipe model, single combined pipe models for the system based upon the commercial package WASSP and the in-house model DUCTS were also constructed. The simulation outputs from these two models were found to be close to the observed flow data. However, the lumped pipe models only predicted the combined flow for the twin pipe outfalls. The construction of these models verified that the Sewered Sub-Area model could be applied to the study catchment. Furthermore, the model DUCTS was shown to perform satisfactorily. Catchment data such as contributing areas, sub-catchment type and paved areas used in the lumped pipe models were subsequently used in the parallel pipe model. The data collection techniques are described in detail. A sequential flow logging procedure was used and found to be an effective and economic method of data collection, especially where a limited number of loggers was available. The model was successfully used to examine the storm runoff for the Lyneburn parallel pipe system and also the complicated hydraulic behaviour in cross-connections. The numbering system for the parallel pipe networks, the chosen equations to represent the different flow patterns for cross-connections, together with the level computation procedure form the major enhancements incorporated into DUPPERS.
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