Demand Loading Conditions: To What Extent are They Representative?

A common practice in water distribution systems management is to classify its problems into three hierarchical levels: (1) layout (analysis of system connectivity/topology); (2) design (system sizing given a layout); and (3) operation (system operation given a design), with reliability/risk/water quality considerations inherently related to all three. In most of the cases in reality the layout, design, and operation phases are solved separately with an implicit assumption that if certain constraints are fulfilled at a specific phase, then at the next stage the system will prevail (i.e., will be able to accomplish its tasks). This is the case at the design stage in which selected loading conditions are used instead of the full extended period demand cycle: it is implicitly assumed that if a system is designed for a number of chosen loading conditions (e.g., peak, low, average), then it will function properly for any other loading conditions sequence. This hypothesis is explored in this manuscript through comparing different designs with different loading conditions, to using the full extended period demand cycle. The Cross Entropy (CE) method for optimal design of water distribution systems, developed recently by the authors, is used as the optimization tool. Two example applications are explored. This paper was presented at the 8th Annual Water Distribution Systems Analysis Symposium which was held with the generous support of Awwa Research Foundation (AwwaRF).