Developments in Wastewater Modelling
Hydraulic modelling is now enjoying rapidly increasing use across the water industry - in wastewater collection, water supply, and river management. Given that the technique of modelling has been around for a very long time - mathematical modelling can be traced back at least 60 years - what are the reasons behind the current growth in water industry modelling? David Fortune, Director of Product Management at water management software company Wallingford Software Ltd, explains all.
The two primary drivers for using modelling in the wastewater industry act like a carrot and a stick. The carrot is the ease of use of the best current modelling software; and the stick is the regulatory pressure for improved performance of utilities, coupled with ever-tightening financial constraints.
Modelling improvements owe much to the increasing power of the desktop PC. Where once even simple models had to be painstakingly built by experts in primitive languages or packages, the best of the current packages mean that modelling is a cost-effective approach to a wide range of water engineering decisions, with the engineer as the hands-on user.
The key improvements in the best modelling software over recent years are:
- easy model building and data input; easy input of data from existing engineering data sources, such as GIS systems (this applies both to building the model - the network model can be created from the GIS data on nodes and pipes - as well as the data sets for the various runs of the model and weather radar);
- easy user interface - Windows-style graphical user interfaces with pull-down menus and clicking options means engineers can use the models themselves, without needing a modelling expert to 'chauffeur drive';
- large models - the closer a model is to the real network, the fewer the assumptions required, and the easier it is to understand and act on the results; the increasing capacity of the best packages mean that models with tens of thousands of nodes can be built quickly and easily from direct GIS import and built-in validation;
- ease of distribution of output - easy links to other PC software mapping, word processing and spreadsheets - simplifies the understanding of the results of the model;
- good housekeeping - good computing practice of version control and audit trails is managed by the package itself, allowing model results to be more accountable than ever before;
- modelling of real-time controls - the model can include rules that change capacities and controls within the network to reflect such real-life changes at different performance levels;
- acceptable run times - with the power of PCs the best packages can use the best industry-proven equations (in the wastewater area this is the St Venant equations) and still deliver results within acceptable run times;
- 'sustainable models' - where once one-off models were built for the specific evaluation required, water authorities now tend to build one model for each part of the network, or even the whole network, and to maintain that model into the future.
All around the world, regulatory and financial pressure is increasing in the wastewater industry. CMOM in the United States and the pan-European AMP initiatives are mirrored in many other countries. Modelling enables utilities and their consultants to address these and other requirements.
Issues that modelling is used to address include:
- reducing the number and the impact of incidents of flooding of sewers;
- reducing overflows from sewerage systems to meet and improve on the statutory limits that are being set on spills to rivers and other outlets.
- the impact of any possible changes to the topology, loading or capacity of the network and its storage and pumping capability on reducing the number and severity of incidents;
- the performance of the network under extreme conditions, and thus the probability of future incidents occurring;
- the impact of a change in operational policies - rules for holding and venting wastewater, whether manually operated or using real-time controls in the network.
Given that the two drivers of increased use of modelling - legislative pressures, plus ease of use through greater computing power - will not go away, neither will the take-up of modelling software. Hydraulic modelling is here to stay, and will be used even more widely throughout the water industry in the future.
Wallingford Software Ltd is a global leader in the development of water management software solutions. Wallingford Software's products include data management and network modelling software to support planning and operations in water distribution, sewerage provision, river management and coastal engineering.