The Impacts of Demand Variability on Distribution System Hydraulics and Transport

A stochastic water demand generator (PRPsym) and a well known distribution system network solver (EPANET) were linked together to analyze the impact of water demand variability on the underlying hydraulics and transport in a distribution system. The modified EPANET example 2 network model was used as a template and test network model for both hydraulic and water quality simulations at three different temporal aggregations (1-hour, 10-minute, and 1-minute). The mean, standard deviation and coefficient of variation at each hour for both hydraulic and water quality parameters were calculated for all nodes or links. Results showed that decreasing temporal aggregation of the water demands leads to increased flow rate variability. The increase in flow rate variability is related to the increased demand variability and the localized flow reversals that alter the travel path. The increase in flow rate variability was more evident in the links located at edges of the system rather than the main trunk lines. In addition to the hydraulics, water age simulations — used as a water quality surrogate — indicate that increased demand variability can significantly impact water quality simulations by altering residence times and travel paths. These preliminary results suggest that there are likely portions of a distribution system where typical modeling assumptions do not adequately represent localized water quality conditions.