In Zurich, urban drainage faces a variety of challenges: Continuous settlement development and topographically pronounced structures require exact hydraulic calculations. The goal is optimal drainage and a water balance that is as close to nature as possible. BaSYS HydroCAD for hydrodynamic sewer network calculation enables a targeted analysis of weak points here. Measures to minimize the negative impact of settlement development on the natural water balance can be planned sensibly.

With a population of approximately 396,000, Zurich is Switzerland’s largest city and its most important economic, scientific and social center. The city is characterized by dynamic urban development: In the last 50 years, residential areas have grown at an enormous rate into the surrounding areas of the city. Many new building areas have been created, some of them in areas on slopes and with steep gradients. According to the specifications of the General Drainage Plan (GEP, in Switzerland the official planning guideline for public authorities), ERZ Entsorgung + Recycling Zürich (ERZ) has the task of reducing the negative effects of settlement development on the natural water balance.

No simple task on this scale – and hardly manageable without a powerful management and calculation tool. After all, the drainage network of the city of Zurich consists of around 3,000 km of private sewers and 920 km of public sewers, through which up to 80 million cubic meters of wastewater flow each year to the Werdhölzli sewage treatment plant and from there back into the Limmat River as treated water. In order not to pollute groundwater and water bodies, the hydraulic capacity of the constantly growing sewer network has to be calculated precisely.

Therefore, many years ago, Abwasser ERZ decided to use the proven hydrograph volume method (GVM) of Dorsch International Consultant GmbH, which is integrated as calculation core in BaSYS HydroCAD. All runoff processes are mapped realistically within a time span from the first raindrop to the drop of wastewater. The calculations are efficient, detailed and realistic. The results can be visualized in thematic plans and animated in dynamic longitudinal sections. Users can identify weak points in the sewer system, for example overloaded reaches or areas subject to overflow, in the first step and then analyze them specifically. “By using BaSYS, the network can be continuously adapted to settlement development. Only in this way can the necessary resources be used in a targeted manner.” reports the responsible project manager Niculin Cathomen from ERZ. BaSYS has thus also become an indispensable tool for planning new construction areas: With BaSYS HydroCAD, the effects on the existing wastewater network can be hydraulically tested before construction begins and the sewers can then be dimensioned accordingly.

For use in conjunction with other systems, BaSYS HydroCAD adapts precisely to the requirements. For ERZ, BART HAUER Consulting configured the necessary interfaces and carried out user-specific adaptations. As a result, data from other GIS systems can be transferred 1:1 to and from HydroCAD without data loss. “The tracking is very efficient and we can adapt the planning to the current conditions” is the satisfied statement from ERZ. In line with the multi-platform philosophy, the system can be combined with other solutions such as Intergraph and WinCan, allowing its users to always have the most suitable tool at hand in each specialist area. And becoming a BaSYS HydroCAD professional is not that difficult: after just a few in-house training sessions, the water experts in Zurich, as the employees rightly call themselves on their website, have also become HydroCAD experts.