Whilst the importance of integrated modelling of urban wastewater systems is ever increasing, there is still no concise procedure regarding how to carry out such modelling studies. After briefly discussing some earlier approaches, the guideline for integrated modelling developed by the Central European Simulation Research Group (HSG - Hochschulgruppe) is presented. This contribution suggests a six-step standardised procedure to integrated modelling. This commences with an analysis of the system and definition of objectives and criteria, covers selection of modelling approaches, analysis of data availability, calibration and validation and also includes the steps of scenario analysis and reporting. Recent research findings as well as experience gained from several application projects from Central Europe have been integrated in this guideline.

The sewer system of the city shows predominantly low gradients and partly high inline sewer capacities. A historically founded system of 63 pump stations is used for the delivery and distribution of combined water and wastewater from the collection systems via long force mains to six wwtps. Simultaneously, in case of rainfall events the pumps act as variable throttles on the outflow of the combined sewerage and activate the inline sewer capacities. High demands are formulated by the water authority to the emissions out of the waste water system into the sensible water bodies. Five of six wwtps of the city are situated in the surrounding area of Berlin. Due to the long distances between the pump stations in the inner city and the wwtps, the time until the dilution effect of the stormwater will be noticed at the inlet of the wwtp may last several hours. Due to the increased delivery rate at the pump stations of the combined sewer system during stormwater runoff (twice the dry weather peak flow), the pollution load at the wwtp increases immediately in the same amount. Due to the enlargement of storage within the combined sewer systems until the year 2020 to meet higher demands of the water authority, the total duration of a raised inflow to the wwtp during and after rain events will increase. To furthermore keep the processes at the wwtp stable (especially the nitrogen removal) the construction of a storage tank at the inlet of the wwtp (=outlet of the pressure main) as an option shall be taken under research. The volume of the storage tank is not only determined by the quantity but also by the quality of the inflow To provide evidence, that the new version of InfoWorks 9.5 CS® is able to calculate the flow and pollution processes in the pressure main network, a diploma thesis is carried out at the Berlin Centre of Competence for Water with the participation of the Berliner Wasserbetriebe

An international review of the market, current practices and R&D projects on the topic of rainwater harvesting management was performed. The review highlighted leading countries in different regions of the world, but also the variety of practices and acceptance. Current R&D issues and further research needs are identified and discussed. The application of RWHM techniques at household level seems to be mature, but sanitary risks exist when rainwater is used inside homes and also reserve on economical an environmental aspects can be drawn when drinking water supply is available. Promising concepts are being developed and demonstrated at larger scale such as industrial or commercial buildings or even urban catchments where the use of rainwater and the operation of the systems are under full control. For schemes of this scale, the integration and optimization of several beneficial aspects such as –traditionally- additional water supply and stormwater management, but also urban planning with water and green spaces, energy compensation in buildings and in the cities or ecological enhancement seems to be promising. Specific expertise will be required to best plan these schemes according to the local conditions and targets and to operate, maintain and upgrade them over their entire life time.

Combined sewer overflows (CSO) can have a strong impact on the quality of surface waters. A common measure to reduce CSO is the construction of storage tanks. The objective of this study was to determine the required volume of a storage tank by means of a numerical long-term simulation and to assess uncertain input data. Particularly, the influence of the considered rain series’ length on the calculated storage volume was investigated. Engineering standards usually recommend the use of at least 10 to 15 years of rain series. Here, the hydraulic behaviour of the studied sewer system was simulated in a 30 year hydrodynamic simulation. Special effort was made to calibrate an available model by use of currently measured data. The quality of calibration was evaluated by means of the Nash-Sutcliffe model efficiency coefficient. The analysis of input data uncertainty revealed that applying a 10 year series results in tank volumes that differ between -12 % and +19 %, respectively from the dimensioning result achieved by applying the 30 year rain series.