Building better integrated network data

Drawing on experience from the UK, Tony Andrews of Wallingford Software believes that the integration of GIS technologies with hydraulic modelling software is a powerful solution to help water authorities meet their responsibilities relating to river catchments, urban drainage, and water distribution.


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In the UK, numerical Hydraulic Modelling of the urban environment, water networks

and rivers plays a vital role in providing the UK Water Industry with solutions

for protecting the environment, meeting UK Government and European Regulations,

meeting OPEX and CAPEX business targets, and improving the efficiency of Water

Companies in managing their assets.

However, new data extraction and cleansing techniques together with better

linkages between GIS and modelling software, have produced good quality geographic

data enabling modellers to build bigger networks faster and more reliably

There is growing evidence that the closer integration of GIS with hydraulic

modelling software can assist water authorities to meet regulatory requirements,

achieve financial targets, carry out design work, and improve the operational

and environmental management of rivers, water distribution networks and collection

systems.

Integrated models

The basic system architecture of an ‘Integrated Network Model’ links

data storage using a GIS to an hydraulic modelling software suite such as InfoWorks1.

Specific data requirements are different between the three modelling areas

of drainage, water supply and rivers, but the maintenance, versioning and auditing

of ‘static’ asset data are fundamental requirements of an ‘Integrated

Network System’. GIS vendors and the many specialist asset information

database suppliers now provide data models that can be adopted in the drainage,

supply and river sectors

Typical GIS data requirements for a wastewater hydraulic modelling study comprise:

• Network asset data (i.e. con duits, manholes and ancillaries).

  • Sub-catchments (contributing areas)
  • Surface area breakdown (road/roof polygon areas) from impermeable area study

    for area take off calculation.

  • Population data (address point).
  • Rainfall profiles from Thiessen polygon analysis.
  • Viewing geographic information data types and image formats as background

    mapping layers.

An excellent example of the integration of GIS and wastewater modelling can

be seen in the surface area breakdown from an impermeable area study for area

takeoff calculation. Impermeable area surveys are conducted to establish an

understanding of the distribution of impermeable and permeable areas in catchments

in order that the correct ‘surface type’ can be assigned to features

in the urban environment. This is typically carried out through a survey of

the catchment, and represented digitally in a GIS using a combination of data

acquired from the UK Ordnance Survey and aerial photography. The analysis of

the different areas is conducted using GIS, with the hydraulic modelling software

providing area take-off tools to calculate the runoff surface areas and the

contributing area for a subcatchment using the data imported from the GIS (see

Fig.1).

Water supply systems

In the water supply environment, GIS and GI data assist modellers through the

incorporation of sup porting asset information (pipe condition, class, material,

age etc.). It provides the functionality to assign elevation to nodes and customer

points using digital elevation data, and to associate spatial information such

as bursts and customer complaints with hydraulic data.

Hydraulic modelling software is designed to streamline the modelling process

by automating the most repetitive tasks and providing flexible links to all

the source data. The functionality of modelling software has extended well beyond

just simulation; examples include:

  • GIS data cleanup and connectivity checking.
  • Links to logger and telemetry in their own formats.
  • Automatic demand allocation.
  • Automatic setting of elevations.
  • Look-up tables to set asset attributes (e.g. pipe diameter and roughness).

The main purpose for providing the direct link between GIS and modelling

software is to facilitate model building and automatically allocate demand using

a combination of GI data, Microsoft Office data files such as Access or Excel,

and text files (e.g. commaseparated variable). The most fundamental requirement

of any hydraulic modelling package is the provision of tools to enable the:

  • Automatic derivation of elevations at all nodes, spatial data (e.g. bursts,

    complaints) and customer points.

  • Automatic allocation of demand at any node and/or pipe using georeferenced

    seed point information such as address point (see Figure 2)

  • Incorporation of geo-referenced information to support the model ling process

    such as customer com plaints and pipe bursts. These can then be allocated

    to the nearest main and pipes graded by structure as well as hydraulic condition.

However, it is the process of allocating demand on the water supply network

that has benefited the most from the incorporation of GIS technology and GI

data in the network modelling products. This is where the water supply modelling

community have been able to automate tasks and save precious resources in building

demand into the model.

Figure 2 illustrates the incorporation of address point data to allocate

demand at nodes. The address point data was imported into InfoWorks WS from

GI data, having been prepared using a GIS. A base demand is applied for unmetered

customers in appropriate units (e.g. litres per property per day) or for metered

consumption demand can be extracted from the billing data.

River modelling

The key data requirements for river models are the cross sectional profiles

and elevation data relating to the river flood plain. Profile data represented

by a series of x, y, z-values (z representing elevation) does not have to be

managed and served to the modelling system using a GIS, but the preparation

of a digital elevation “ground model” of the flood plain is perhaps

the clearest example of the necessity for integrating GIS technology.

Digital elevation data will be familiar to most hydraulic modellers and should

be familiar to all GIS specialists. Elevation is represented as a matrix of

points or more commonly in a regular grid raster pattern. In order to analyse,

display terrain features and fit surfaces to the elevation data, the grid data

is converted using GIS technology to a ‘triangulated irregular network’

(TIN) dataset. GIS specialists will be familiar with this data, but to river

modellers TIN data will be even less familiar than the grid dataset.

A TIN dataset represents a surface derived from irregularly spaced sample

points and breakline features, with the points comprising x, y, and surface

or z-values, and a series of edges joining these points to form nonoverlapping

triangles. The triangular mosaic forms a continuous faceted surface. TINs offer

an alternative to the raster data model for representing surfaces.

Using TIN/GRIDDED elevation data in modelling software such as InfoWorks

RS enables the direct takeoff of elevation data to facilitate the extraction

of model sections and floodplain storage properties based on overlaid section

locations and boundaries.

The TIN/GRID is also used to generate and display ground level contours, and

forms the basis for dynamic flood mapping. River modelling products now have

full flood-mapping capability based on sophisticated floodinterpolation models

overlaid onto a TIN/GRID based ground model.

The floodinterpolation model enables:

  • Instantaneous flood mapping of any simulated event, typically including

    the additional ability to replay dynamic results in animation, or display

    flood maximum extents.

  • Contouring of flood depths.
  • Flood graph of water level and depth at any point within the flooded envelope.
  • Interaction with imported georeferenced seed point data (addresspoint) to

    produce reports of flooded-depth and duration at specified locations.

The future

Hydraulic Network Modelling software in the UK has been essential in meeting

expected levels of service and in reducing costs. Clearly, closer integration

of GIS and modelling software will advance the capability of water authorities

to achieve regulatory requirements, meet financial targets, carry out design

work, and improve the operational and environmental management of rivers, water

distribution networks and collection systems.

Recognising this, GIS service implementers and middleware providers have formed

partnerships with businesses in the water industry, whilst GIS vendors dedicate

teams of specialists to focus on the water business. Likewise, hydraulic modelling

vendors continue to add new features and tools to automate much of the previous

manual work of building models, and to ensure that their product is a component

of the ‘integrated network modelling’ strategy.

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