Wet weather discharges from urban catchments are widely recognised as a major cause of unsatisfactory receiving water quality. Among stormwater discharges the impact from combined sewer overflows (CSO) plays a prominent role. The dynamic character of the discharge events lead to particular stress on the water bodies. Legal requirements for CSO follow the precautionary principle and usually set emission standards. Within the Urban Waste Water Treatment Directive 91/271/EEC of May 1991 it is written that “member states shall decide on measures to limit pollution from storm water overflows”. The directive does not give standards but solely proposes that “such measures could be based on dilution rates or capacity in relation to dry weather flow, or could specify a certain acceptable number of overflows per year”. The European Water Framework Directive 2000/60/EC of October 2000 goes beyond and asks for a combined approach to river basin management. On the source side, it requires that all existing technology-driven source-based controls must be implemented as a first step. On the effects side, it provides a new overall objective of good status for all waters, and requires that where the measures taken on the source side are not sufficient to achieve these objectives, additional ones are required. To assess the impact of CSO on the Berlin receiving water the research projects MONITOR and SAM-CSO are carried out in cooperation between Kompetenzzentrum Wasser Berlin, the Berliner Wasserbetriebe and the Senate Department of Environment Berlin. The objective of the projects is to identify and make available receiving water parameters (immission parameters) for the decision making process concerning the optimisation of the urban drainage system. Further on, a method for the evaluation of measures of combined water treatment on the basis of these immission criteria will be defined. The evaluation shall be based on both, available measurement data from the sewer system and the receiving water and simulations with an integrated model for the coupled drainage-river-system. The paper will present the methodology of the project. Special focus is on the description of the processes within the Berlin water bodies (stagnant lowland rivers) and the compilation of relevant physical-chemical and ecological parameters for the assessment of CSO.

Nachdem in den vergangenen dreißig Jahren in Deutschland durch den Bau und Ausbau von Kläranlagen ein hohes Niveau der kommunalen und industriellen Abwasserreinigung erreicht wurde, gewinnt die Problematik der Gewässerbelastung durch Regenwassereinleitungen aus Siedlungsräumen an Bedeutung. Menge und Zusammensetzung der über den Pfad der Regenwassereinleitung in die Gewässer eingetragenen Schmutzfrachten hängen von der Flächenart des Entwässerungsgebietes sowie dessen Nutzung ab. Verschmutzungsquellen sind beispielsweise die atmosphärische Deposition, Bremsabrieb und Ölverluste des Straßenverkehrs oder auf Gebäudefassaden angewandte Materialschutzmittel. Der auf die undurchlässigen Flächen gelangende Niederschlag trägt diese Substanzen ab und wird in Trennkanalisationssystemen meist ohne vorherige Behandlung in die Vorflut eingeleitet. Durch den Stoffeintrag entstehen teilweise erhebliche Verunreinigungen in den Gewässern, die z.B. Eutrophierung, eine erhöhte Schadstoffbelastung im Sediment und ökotoxikologische Auswirkungen zur Folge haben. Klassische Schmutzfrachtmodelle berechnen Nähr- und Schmutzstofffrachten im Regenabwasser auf Grundlage von mittleren Konzentrationen oder jährlichen Flächenabträgen. Dabei ist die detaillierte Herkunft der Stoffe bei der Planung von Maßnahmen der zentralen Niederschlagswasserbehandlung unerheblich. Bei der dezentralen Regenwasserbewirtschaftung hingegen ermöglichen Informationen zur räumlichen Verteilung der Stoffquellen und -ströme eine gezielte Abstimmung der Maßnahmen auf den örtlichen Handlungsbedarf. Der Modellansatz SEWSYS (implementiert in der Software STORM ermöglicht eine solche räumlich differenzierte und dynamische Simulation von Stoffkonzentrationen. Die für den Einsatz von SEWSYS erforderlichen ortsspezifischen Eingangsgrößen (z.B. Verkehrsbelastung, Anteil der Metallflächen) liegen für Berlin jedoch noch nicht in geeigneter Form vor. Auch ein Vergleich von SEWSYS mit dem herkömmlichen Ansatz der Schmutzfrachtsimulation unter Berücksichtigung der Unsicherheiten der Modelleingangsdaten steht bislang aus. Im Rahmen der Diplomarbeit soll das Modell STORM/SEWSYS verwendet werden, um beispielhaft für das Einzugsgebiet Ruschegraben in Berlin den Transport ausgewählter Stoffe im Niederschlagsabfluss von urbanen Flächen räumlich differenziert abzubilden. Im Einzelnen sind folgende Punkte zu bearbeiten: (i) Recherche und Aufbereitung von Eingangsdaten für den Modellansatz SEWSYS (allgemeine, stoff- und quellenspezifische Daten sowie ortsspezifische Daten des Einzugsgebietes), (ii) Durchführung von Langzeit-Schmutzfrachtsimulationen für ausgewählte Stoffparameter, (iii) Vergleich von SEWSYS mit dem herkömmlichen Ansatz der Schmutzfrachtsimulation und Diskussion der Ergebnisse und (iv) Aufzeigen von Unsicherheiten bezüglich der von SEWSYS verwendeten Eingangsdaten und Analyse ihrer Auswirkung auf die Simulationsergebnisse

The present study “Literature review on impact-based guidelines for stormwater treatment” provides an overview of international guidelines, which evaluate acute impacts of combined sewer overflows (CSO) on receiving surface water bodies. The overview should serve as a basis for the assessment of measured and simulated CSO impacts on Berlin surface waters within the projects “Monitor-1” and “SAM-CSO”, which are currently carried out at the Berlin Centre of Competence for Water. In contrast to the classical approach of sewer emission thresholds, impact-based guidelines focus on possible effects of CSO in the receiving surface water. Impact-based guidelines aim at deriving locally adapted measures to minimize CSO impacts to surface waters. Thanks to this local approach, potential protection measures can be planned dependent on the state of a specific river, reservoir or lake. The following study focuses on acute CSOimpacts, which were identified as relevant for the biocenosis of the River Spree in Berlin within the KWB project ISM: (i) Increased levels of unionised ammonium (NH3) through ammonium input. (ii) Low levels of dissolved oxygen (DO) through the input of degradable organic components, which lead to DO consumption. Guidelines from Germany, Austria, Switzerland, United Kingdom, France and USA are considered along with the approach by Lammersen, which assembles a number of scientific publications. The Austrian guideline (ÖWAV-RB 19) stops at distinguishing whether further investigations are necessary. In the US “CSO control policy” further analysis is delegated mostly to local institutions. The French “Arrêté du 22 juin 2007” also asks to take into consideration the local situation of the receiving water but does not give any limit values. The remaining four approaches provide a detailed evaluation scheme for critical NH3 and DO conditions, using duration-frequency-relationships. These relationships assume that pollution events of a specific duration may only occur in defined recurrence intervals (e.g. Figure 4.1). The Swiss guideline (STORM) is not suitable for dammed lowland river systems such as the Berlin River Spree, since it focuses on fast flowing rivers with salmonid fish populations. As a result there remain three approaches, which are interesting for the Berlin situation: the UPM guideline from the UK, the BWK-M7 guideline from Germany and the Lammersen-approach, which summarizes various scientific results. Apart from the dependency of critical concentrations on event duration and recurrence frequency, influence of temperature, pH and concurrent NH3-concentrations or DO-minima are considered by UPM and the Lammersen-approach. The relationships used by the three approaches for NH3 and DO are similar (see Figures 4.1, 4.3 and 4.4). Nevertheless, their comparability is limited, as the approaches generalize various local situations and cannot be derived strictly scientifically. As a first step we therefore recommend applying the three approaches to existing data from the River Spree and count the respective numbers of critical events. Based on the results it is possible to assess to which extent each approach is applicable for the situation in Berlin. As a second step experts need to evaluate the resulting critical events to distinguish suboptimal from lethal situations. For instance, the Lammersen-approach judges both (i) a two-day period with DO < 5 mg L-1 and (ii) a 30-minutes event with DO < 1.5 mg L-1 as critical. However in the Berlin River Spree (i) occurs basically continuously throughout the summer season and is tolerated by local fish species, whereas (ii) would probably lead to a major fish kill. As a consequence the prevention of (ii) should be given first priority. Based on the experience gained from the assessment of river monitoring data, simulation results can be evaluated in a third step. All the considered guidelines propose numerical simulation of sewer and receiving surface water systems. However only simple model approaches are discussed in detail, while specialized literature is suggested for complex cases. If numerical simulations are used for the planning of concrete measures, model uncertainties must be indicated to avoid feigning accuracy of results that cannot be provided. The Swiss STORM guideline suggests using Monte-Carlo simulations to calculate probabilities of the recurrence of critical events for possible management measures. We suggest a similar approach for the Berlin situation. Thus, decision makers could weigh cost against probability of success for proposed measures.

Dr. Schumacher Ingenieurbüro für Wasser und Umwelt wurde im Rahmen des Projektes SAM-CSO beauftragt, eine Langzeitsimulation der hydraulischen Verhältnisse in der Stauhaltung Charlottenburg (Spree und Kanäle) für die Abflussjahre 2002 bis 2007 durchzuführen. Diese Simulation erfolgt mit der Software HYDRAX und ist die Grundlage für die Simulation der Gewässergüteprozesse, die dann mit der Software QSIM durchgeführt wird. Da bisher im Rahmen des Projektes eine Gewässergütesimulation lediglich für den September 2005 erfolgte (Fokus auf 2 Starkregenereignisse mit Mischwasserüberlauf), konnten noch keine allgemeinen Aussagen zur Güte der Simulation des Gewässerbasiszustandes über längere Zeiträume getroffen werden. Die Simulation des Basiszustandes (unter Vernachlässigung der Mischwassereinleitungen) und die Anpassung des Modells an die Berliner Gewässerverhältnisse ist ein wichtiger Schritt, bevor die spezifische Situation während Mischwasserüberlauf betrachtet werden kann. Zusammenfassend ist festzuhalten, dass nach Korrektur der Zuflüsse über die Spree eine in Bezug auf den Referenzpegel Sophienwerder stimmige Durchflussbilanz erreicht werden konnte. Die aufgrund der instationären Berechnung verbleibende Bilanzdifferenz spiegelt gut das (im Vergleich zu den Stauhaltungen Mühlendamm/Kleinmachnow, Spandau oder Brandenburg mit ihren großen Seen) geringe Retentionsvermögen der Stauhaltung Charlottenburg wider. Unter Berücksichtigung der Messunsicherheit werden auch die Wasserstände für alle Durchflussverhältnisse in guter, für die anschließende Gütesimulation mit mehr als hinreichender Genauigkeit, berechnet. Hingewiesen sei darauf, dass bei einer Änderung der Zuflusssumme, z.B. durch die Berücksichtigung der bisher inaktiv gesetzten Mischwassereinleitungen, auch ein erneuter Bilanzausgleich vorgenommen werden sollte, da der Stauhaltung derzeit die vernachlässigten Größen indirekt über die Korrektur der Spreezuflüsse im Rahmen des Bilanzausgleichs zufließen. Folgerung für das Projekt: (i) Die Grundlage (Hydraulik) für die Gewässergütesimulation des Basiszustandes der Spree liegt nun vor. (ii) Die Gewässergütesimulation wird in Abstimmung mit Herrn Dr. Schumacher am KWB durchgeführt. Es erfolgt eine Identifikation, welche in QSIM simulierten Prozesse an die Berliner Situation angepasst werden müssen und in welcher Weise. (iii) Daraufhin erfolgt die Anpassung in Kooperation mit der BfG (Herrn Kirchesch).

Within the project SAM-CSO it shall be tested if the Open Modelling Interface and Environment (OpenMI) can be applied to link models of the Berlin sewerage (modelled in the urban drainage software InfoWorks CS,Wallingford Software) to a river water quality model. This report gives an overview on the OpenMI and its application. Chapter 1 outlines the general background of integrated water management and integrated modelling as it is aimed at by the European Water Framework Directive. The development process, which resulted in the release of the OpenMI is summarized in chapter 2. An introduction to the objectives, the concept and the technology of the OpenMI is given in chapter 3. Chapter 4 lists case studies in which the OpenMI has been applied. In Appendix B, each of the reported studies has been described in generalized form. A matrix showing all model links, which have been established within the case studies, has been developed. Finally, in chapter 5, an overview on other model linking approaches is given. This report shows that in many use cases the Open Modelling Interface could be used successfully for model linking. Even out of Europe, at a workshop of the U.S. EPA it is stated that, in terms of the ability to go between different temporal and spatial scales, a framework such as OpenMI might have the necessary flexibility. Actually, it was found that in many cases models of the InfoWorks software family have been part of the OpenMI linked systems. In cases of many interaction points between models, the OpenMI mechanism may not be applicable. In the Berlin case the impact of combined sewer overflows on the water quality of the receiving river shall be examined. With far less than a hundred interaction points between sewer model and river model it is assumed that the OpenMI could be used for a successful model linking. The difficulty within the SAM-CSO project may be to find an apropriate river quality model, which is ready to be linked to InfoWorks CS using the OpenMI. Unfortunately, there are few use cases reported in which a freely available river water quality model was involved. The water quality model QSIM of the German Institute of Hydrology (BfG) that is used within the project is currently not equipped with OpenMI. Nevertheless, using the OpenMI mechanism for model linking is assumed to be a promising approach. It is expected to become an internationally accepted standard. As the OpenMI specification is fully free, anyone may contribute to its further development. The OpenMI Association will give advice to modellers and will be open to discussions on improvement of the OpenMI. With the OpenMI linking mechanism not only models can be linked. Modules for calibration, optimization, statistical evaluation etc. can be part of an OpenMI system as well as components for generic data access or visualization. It will be tested, if the integration of such a module for statistical evaluation into the CSO impact assessment method (to be developed within the project SAM-CSO) is applicable and useful.

Rainwater Harvesting (RWH) is the process of collecting and storing rainwater for a later use. This technique could be an alternative water source in response of a climate change context. In this review, the state of this practice worldwide was studied. Some discrepancies between countries have been highlighted. First, between developed and developing countries, gaps concerning techniques and regarding the main purposes (water savings for the first ones and drinking purposes for the last ones) were reported. Then, within developed countries themselves, acceptance and standards of RWH installations are different, with precise guidelines and norms for countries leading the way on RWH practices. The scale of applications (RWH for households – up to 50 inhabitants, for large buildings and for urban area) is discussed and the state of the technique showed that there were more potential of technological development and challenges for large scale systems than for households. Finally, this report draws the attention to the needs in terms of Research and Development projects. Six main aspects were highlighted: drinking water, energy compensation, environmental impacts, economical aspects and the integration of stormwater management and rainwater harvesting. The last feature concerns hygienic aspect, but the report do not focus on this consideration.

In recent years considerable progress has been made in numerical weather prognosis. Special progress has been made in doing local forecasts up to five days of temperature, wind and atmospheric pressure and al so o f the weather det erminant flow s ystems. In contrast, the local prognosis of precipitation (liquid and ice phase) has not been improved. T his circumstance has lead to the DFG p rogram “Quantitative rainfall prognosis”. I t co vers broadly base d activities that ai m on the i mprovement o f t he knowledge on t he pr ocesses of r ainfall f ormation and t heir num erical pr ognosis. The main objective is to improve the routine prognosis of the German Weather Association (DWD). The program covers the modeling of microphysical processes as well as the description of essential meteorological conditions in different temporal and spatial scales. Especially, co nvective c loud sy stems that ar e often responsible for e xtreme r ainfall situations are studied. In a G ermany-wide monitoring campaign in the year 2007 comprehensive measurements are conducted. The gained information and data will be used to improve process description and to support model evaluation. The st udy at hand describes the anal ysis and pr ognosis of temporally (5 m in) and spatially (500 m) highly distributed rainfall data for the Berlin area. The data will be used in the frame of the EVA project of Kompetenzzentrum Wasser Berlin to analyse and evaluate the potential of online rainfall measurement and forecast to support the operation of wastewater pump stations.