Modeling of Water Distribution Networks

This page is supposed to give a very brief overview of the modeling and terminology of water distribution networks (WDNs).

Topology

The structure/topology of a WDN is modeled as a graph, where edges model links/pipes and nodes model junctions – see the following Figure for an illustration.

Edges

Edges (e.g. links/pipes) have certain parameters such as length, diameter, roughness coefficient, etc. There exist different types of links:

Type	Description
Link/Pipe	Transporting water
Pump	Moving water from one segment (i.e. node) to another by adding hydraulic head to the system
Valve	Blocking or letting water pass through – can also control (i.e. reduce) pressure in the network

Nodes

The nodes in the graph do not only model junctions but also consumers – i.e. locations where water is taken (i.e. consumed) from the WDN. Consequently, different nodes might have different elevations which makes the use of pumps necessary. Water consumption is modeled by demand patterns that describe how much water is consumed over time – each node in the graph can have its own demand pattern. Furthermore, there exist different types of nodes:

Type	Description
Reservoirs	“Infinite” source of water (e.g. a lake or river)
Tank	Storing water
Junction	Intersection of links/pipes and consumption point (i.e. water is taken from the network)

Simulation

There are two types of dynamics that are relevant in a WDN: 1) hydraulics and 2) quality.

Hydraulics refers to quantities such as flow rates, pressures, etc., while quality refers to chemical concentrations. Hydraulics depend not only on the topology of the WDN but also on demands (i.e. water consumption) as well as pump and valve operations. Building on the hydraulics, quality dynamics depend not only on the hydraulics (in particular flow rates) but also on chemical reactions (e.g. pipe wall reactions) and injections (e.g. chlorine injection or contamination events).

Also, there exist two different types of demand models that can be used for simulating the hydraulics: Demand-driven analysis (DDA) and a pressure-driven analysis (PDA) – note that pressure-driven analysis (PDA) is more robust in extreme situations but requires specifying additiona parameters such as the minimum pressure and the pressure exponent.

The units of measurement are set globally and are either in US customary or SI metric. The units are set by specifying the flow and pressure units – more details can be found in the EPANET documents on units.

EPyT-Flow is based on EPANET and therefore uses a steady-state simulation of the hydraulics, on which the quality dynamics are computed. Details can be found in the EPANET documentation.