Importance of demand modelling in network water quality models: a review

Abstract

Abstract. Today, there is a growing interest in network water quality modelling. The water quality issues of interest relate to both dissolved and particulate substances. For dissolved substances the main interest is in residual chlorine and (microbiological) contaminant propagation; for particulate substances it is in sediment leading to discolouration. There is a strong influence of flows and velocities on transport, mixing, production and decay of these substances in the network. This imposes a different approach to demand modelling which is reviewed in this article.For the large diameter lines that comprise the transport portion of a typical municipal pipe system, a skeletonised network model with a top-down approach of demand pattern allocation, a hydraulic time step of 1 h, and a pure advection-reaction water quality model will usually suffice. For the smaller diameter lines that comprise the distribution portion of a municipal pipe system, an all-pipes network model with a bottom-up approach of demand pattern allocation, a hydraulic time step of 1 min or less, and a water quality model that considers dispersion and transients may be needed.Demand models that provide stochastic residential demands per individual home and on a one-second time scale are available. A stochastic demands based network water quality model needs to be developed and validated with field measurements. Such a model will be probabilistic in nature and will offer a new perspective for assessing water quality in the drinking water distribution system.

Accumulation and modeling of particles in drinking water pipe fittings

“…If there are no suspended particles transported to the end of a pipe, which may settle, then there is also deposit formation; (3) the topography which is indirectly confirmed by the number of customer complaints about water quality in undulating terrains compared to those in flat terrains (Polychronopolous et al, 2003); (4) diameter of pipes where increased particle concentration in trunk mains, which in the network acts as sedimentation tanks, has been previously shown Saldarriaga et al, 2010). (5) An incontrovertible factor that affects the concentration of particles is the maximum daily velocity, which can be related to particles by applying "bottom-up" demand modeling, has been described earlier (Blokker et al, 2008). The same opinion is postulated in the cohesive transport modeling approach called PODDS (Boxall et al, 2001;Boxall and Saul, 2005;) which predicts that the particle deposits on pipe walls are conditioned by shear stress.…”

“…Analyses of the impact of daily maximum velocity on washed out mass of particles normally should be done by applying a careful hydraulic analysis using a "bottom-up" demand allocation principle, e.g. SIDMEUM (Blokker et al, 2008), rather than the "top-down" approach used in this study.…”

Review of applications for SIMDEUM, a stochastic drinking water demand model with a small temporal and spatial scale

“…It was expected that one of the main applications for SIMDEUM would be in modelling water quality in the DWDS (Blokker et al, 2008b). Added value was shown in residence time modelling (Blokker et al, 2010a(Blokker et al, , 2011a, especially in the periphery of the DWDS ( Fig.…”

“…The models were introduced in papers, along with a discussion on their potential applications. For the small temporal and spatial scale models, the main application was assumed to be in water quality modelling (Blokker et al, 2008b) related to discolouration, chlorine decay and contaminant propagation. However, the predicted applications are rarely re-examined.…”

The use of high resolution monitoring in the management of water quality failures caused by discolouration

“…Some studies have suggested that the difference in flow between trunk mains and normal distribution pipes could be as high as a factor of a hundred (Blokker et al, 2008). The lower velocity makes distribution networks Gaffney and Boult, 2011. an ideal location for sediments to accumulate and therefore a possibility of resuspension during, say a sudden hydraulic change.…”