Calibrating Pipe Wall Demand Coefficient for Chlorine Decay in Water Distribution System

Abstract

Methodology and algorithm to calibrate pipe wall demand coefficients for chlorine decay using an input-output model framework are developed and applied. An input-output model of water quality in water distribution systems developed previously provides information that is not available using traditional simulation approaches: the various flow paths between particular input sources and output nodes, and their associated time delays and impacts on output node water quality. Such information constitutes a complete description of the input-output behavior under typical assumptions of first-order chemical decay or production reactions. With the input-output model, the chlorine concentration at output locations can be expressed explicitly as a function of the concentrations at upstream input locations, and pipe wall demand coefficients. Thus the sensitivity of water quality at the outputs to wall demand coefficients can be derived analytically and calculated efficiently. The sensitivity information is also used to study uncertainty in wall demand coefficient estimates that are caused by chlorine measurement errors.