Network Water Quality Modeling With Stochastic Water Demands And Mass Dispersion

A new computer model, ADRNET, is developed to predict the spatial and temporal distribution of disinfectant in a pipe network, considering stochastic water demands and unsteady mass dispersion. An Eulerian-Lagrangian scheme is combined with a numerical Green's Function technique to solve the advection-dispersion-reaction equation efficiently in network conditions. In a comparison with the industry standard advection-reaction water quality model (EPANET), ADRNET exhibits better agreement with field observations at locations where laminar flow is prevalent. Implementation of the ADRNET model is preceded by three ancillary studies. The first study investigates the effect of temporal averaging on stochastic pipe flows to identify the appropriate time scales for water quality modeling of distribution networks. For this purpose, a non-homogeneous Poison Rectangular Pulse (PRP) process is utilized to simulate high resolution residential water demands in a distribution network. Two water demand models are successfully established to demonstrate variability and frequency of regimes for PRP flows as function of time scale. The results show that the variance of time-averaged PRP random flows is inversely proportional to the time scale; the frequency of flow regimes depends on both the time scale and the mean of the random flows. The second study investigates the conditions under which mass dispersion is important in pipe networks through comparison of numerical simulations with and without dispersive transport. The results show that mass dispersion is always important in laminar flow zones, and the importance of dispersion increases with increasing pipe diameter but decreases with increasing of reaction rate coefficient. Finally, the effect of temporal scale on unsteady dispersion is studied through both theoretical analyses with periodic binary flow pulses and numerical simulation with PRP random laminar flows. For small diameter tubes, unsteady dispersion decreases with increasing time scale in unsteady laminar flows. For an actual network pipe, however, the time scale has little effect on unsteady dispersion in completely laminar flows.