HYDRAULIC MODELLING

 

 

 

 

 

FUNCTION

 

Scope and Use

 

The hydraulic modelling scope considered here is water distribution

modelling, in the form of a software package performing extended-

period simulation of hydraulic and water-quality behaviour within a

pressurised pipe network. Water network hydraulic modelling is used

for both network engineering and network operation:

 

  • Used in utility planning/engineering departments for network design and planning, rehabilitation, maintenance and improvement, or training

  • Used at utility control centres for hydraulic supervision and system control, alarming, leak detection or optimisation purposes, as well as training.

 

Water Model and Water Modelling Software

 

The model is the schematic representation of the real system, combining the physical system (e.g. pipe network and special elements) and physical rules (e.g. mass, energy conservation), enabling the construction of a numerical model generating results according to boundary conditions. The network scheme is made of nodes (e.g. junction nodes, reservoirs, storage tanks, air chambers), links (e.g. pipes, pumps, valves) and operation rules (e.g. pump status dependent on a reservoir level). 

 

A water modelling software includes: 

 

  • A Graphical User Interface, that can be a stand-alone interface or GIS based

  • A database based on standards (e.g. Access, Oracle, etc.)

  • Open data models

  • Hydraulic simulation tools, like EPANET (US EPA) or similar + dynamic simulation

  • Advanced Tools, for data processing and model simplification, demand distribution and allocation, results presentation, calibration

 

When used in a network operation context, water modelling software has to be integrated with other systems such as Geographical Information System (GIS), Customer Information System (CIS), SCADA, Leakage Management, or Optimisation applications.

 

Model Building

 

Water modelling software provides capability to build model from scratch or to automatically import and build the model from the following data sources:

 

  • GIS/mapping data

  • Demand data/profiles/geo-coding

  • Elevation data

  • Calibration data – pressure, flow, level and water quality

 

Network Analysis

 

Water modelling software allows utilities to perform feasibility studies and scenarios to evaluate the effect of new residential areas or industrial sites, increased demands, maintenance and rehabilitation work, fluctuations in consumption. This is to design the network to meet future demand or to comply with regulations while improving service, avoiding bottlenecks and optimising investment.

 

Typically, the following analysis can be performed:

 

  • Hydraulic: Quickly assess current network performance and evaluates the effects of modelling changes (e.g. pressure, flow, level, etc.).

  • Water Quality: Quickly evaluates how various operating conditions influence water quality. Common water quality problems such as taste and odour can be tracked down using the age-of-water model. Quality analysis can also be used to track any pollutant in the system, and to separate the zones to avoid spreading of the pollutant.

  • Surge (transient): Performs surge simulations to establish the reasons for a pipe burst. Many water companies estimate that surges cause as much as 50% of pipe bursts in the network.

 

Network Management – Real-Time Application

 

Water modelling software is traditionally used as a planning tool.  The ability to run the water network hydraulic modelling in real-time (online) mode improves network operation, transforming it into a decision-making tool, used in the network day-to-day operations. The model uses live SCADA data, which is automatically added to the model after being pre-processed and validated to avoid flawed data and replacing faulty instrumentation with emulated values. Historic views, real-time views, and predictions may be combined in the same user interface to obtain the network’s pressure, flow and water quality (e.g. age, chlorine concentration) for any past, present, or future point in time.

 

Contingency Management - Pollutants

 

Water modelling software is able to perform a trace, performing a forward analysis of a situation from any given time, or a diagnostic trace, performing a backward analysis of a situation from any given time.

 

Optimisation Modules

 

Water modelling software may include optimisation modules such as:

 

  • Leakage management 

    • Leakage detection on distribution networks, using techniques like night line measurement. This requires DMAs to be in place. 

    • Leak detection (and location) of transmission networks.

 

  • Pressure optimisation

Pressure optimisation utilises the real-time hydraulic model for set-point generation. It takes into account the fluctuation of consumption in the network, and automatically provides the set-points for the pumps or pressure control valves. This ensures an adequate supply pressure. The set point scheme is sent back to the SCADA system automatically.  Pressure optimisation reduces water loss and its associated costs of pumping, production and chemical treatment, in addition to reducing the subsequent CO2 emission. 

 

  • Pump and reservoir optimisation

In water distribution systems, pumping costs often constitute the major part of the operating costs, and pump and reservoir optimisation minimise these costs. It determines the optimal pumping schedule for a pipeline system for a given period of time (user-defined), while taking into account demand schedules, storage capacities of reservoirs, power costs (unit costs may vary over time), other operational costs, capacity and availability of pumps and other equipment, pump efficiency, and pumping curves. The results are flow set points or pressure set points for each pumping station that are sent back to the SCADA system automatically.

 

BENEFITS

 

Benefits from implementing hydraulic modelling cover both network system design and operation of a utility:

 

  • Improved network planning and design

    • Deep understanding of network hydraulics and water quality

    • Better planning and definition of operational procedures

 

  • Improved operators and technical staff efficiency

    • Better trained staff and support to decision-making (e.g. "what if" scenarios) 

    • Monitoring of network performance and detection of malfunctions, complementing SCADA

 

  • Improved water quality

    • Allow assessment of water quality over the network, ensuring that water is safe to drink

    • Pollution incidents tracking

 

  • Improved customer service

    • Reduction in failure detection time

    • Better reactivity following an incident

  • Reduced Non-Revenue Water

    • Leakage detection informs operator, advises which zone to prioritse

    • Pressure optimisation reduces leakage through existing leaks and occurrence of new leaks

 

  • Energy optimisation (save energy – save CO2 - save money)

    • Pump optimisation is always looking at minimum costs

    • Pressure optimisation also reduces pumping costs

 

 

SYSTEM REQUIREMENTS

 

To assess the suitability of water hydraulic modelling in a particular system, utilities should first carry out a series of tasks, including:

 

  • Provide general data of the current network and its existing management system:

    • Size, structure of the network, number and location of flow and pressure transmitters in the network, level of implementation of district metering areas (DMAs) and pressure zones.   

   

  • Confirm availability of data necessary to build a model of water transportation and distribution network.

 

Those data can be grouped into three categories:

 

  • Geographical data:

Ideally, data for all pipes and equipment should be available in a GIS system. In the absence of GIS data, up-to-date CAD drawings and P&IDs are used. The data required must include a pipeline layout (coordinates and elevations), pipe characteristics (e.g. inner diameter, length, material, roughness, year laid etc.), elevation data, and special locations. Equipment must be registered as points (e.g. coordinates and elevation).

 

  • Equipment specific data

Pumps (e.g. curves, pressure measurements, pump status and speed if VFD), surge devices, valves (e.g. characteristics, status, opening degree, etc.), tanks /reservoirs, quality equipment (e.g. Chlorine), flow meters, pressure meters.

 

  • Consumption data and other time dependent data:

Consumption at all consumption points as historical record of time- series, or as the total consumption for a given period together with the consumption pattern for the period. 

 

  • Confirm availability of required telemetry data and remote control via SCADA.

     

    • Implementation of inbound and outbound interfaces between SCADA and hydraulic modelling software must be further studied, but are typically done via OPC, a SCADA database, web services or some other exchange file format.

 

  • For pump optimisation modules, identify opportunities in current and alternative energy tariffs offered.

 

  • Understand the culture change process that on-line hydraulic modelling is likely to require from a planning tool to a planning + daily operation tool, therefore not only used by hydraulic specialists.