Using InfoWorks CS in Berlin to evaluate the impact of CSOs
Monday, 21 January 2008
InfoWorks CS is enabling Germany’s largest water supply and wastewater disposal company to carry out crucial flow and pollution calculations to ensure that Berlin’s rivers are able to cope with Combined Sewer Overflows (CSOs). A large section of the city’s system has been modeled in a case study. "We needed a tool for use in the evaluation of combined sewer overflow impacts in terms of nutrients and the effects on water quality in the rivers," says Erika Pawlowsky-Reusing of Berliner Wasserbetriebe. InfoWorks CS was chosen as that tool.
Berliner Wasserbetriebe is Germany’s largest water supply and wastewater disposal company. It serves a total area of 900km2 (348 square miles), which is home to 3.4 million inhabitants of Berlin and a population of 600,000 in the surrounding region.
InfoWorks is being used to model a substantial case study area, which covers an area of 5,500 hectares (13,590 acres), with 1.1 million inhabitants and 13 pump stations.
Berlin’s drinking water abstraction has historically been carried out almost exclusively within the city boundaries and the wastewater disposal and treatment is also managed within the same area. Central areas are served by a combined sewer system, while wastewater in the outer regions is collected by a separate system.
Every drop of the Berlin’s wastewater is collected at a pump station: the system has 63 main pump stations and 86 booster pump stations. Berlin’s dry weather flow is 635,000m3 per day (168 million gallons a day). Six wastewater treatment plants are located on the outskirts of the city. Wastewater from the 63 main pump stations is delivered to the treatment plants by an extensive pressurized mains network, which is 9,000km (5,600 miles) long.
Sensitive waters
Long stretches of navigable rivers run through the city, but flow levels in them are low and water can stagnate in summer. The water authority has already set stringent governing emission standards for the wastewater entering the rivers and further requirements will also be imposed under the European Union’s Water Framework Directive.
The receiving waters of the rivers Spree and Havel are particularly sensitive, with a risk of a build-up of chemical nutrients. Approximately 25% of the phosphorus entering these rivers in central Berlin originates from CSOs.
Berliner Wasserbetriebe has put measures in place to ensure that present and future standards are met. One aspect of this is the upgrading of the wastewater treatment plants to reduce the phosphorus concentration to a mean level of 0.05 mg/l. In parallel, an enlargement of the storage volume within the combined sewer system will be carried out over the coming years.
It is vital that Berliner Wasserbetriebe ensures that these measures will also prove sufficient for the water quality orientated demands of the Water Framework Directive. A study has therefore been set up to develop the tools and standards for the evaluation. The work is being carried out at KompetenzZentrum Wasser Berlin (Berlin Centre of Competence for Water), with the participation of Berliner Wasserbetriebe, a limnologist and a consulting engineer.
The intention is to study the effects on the water quality in the sensitive river system caused by CSOs. The research project covers an extensive catchment area around the River Spree, which is ideal for the research as the CSOs discharge into a basin that can be isolated by locks and weirs.
Extensive case study
The sewer network model consists of 13 catchment areas and wastewater for each is collected at a pumping station. Each serves between 31,000 and 263,000 people, giving a total of 1.1 million inhabitants. The mean dry weather flow of the pumping stations varies from 10,000 m³/day to 41,000 m³/day (2.6 million to 10.8 million gallons per day).
InfoWorks CS has been used to model the “skeletonized” network including all the special structures such as weirs that enable storage of storm water within the existing sewer system or within storm water tanks. InfoWorks has enabled the management strategies to be modeled accurately to represent precisely the approach used during actual events.
A detailed analysis of the ecosystem was carried out to formulate the water quality criteria for the discharge of the CSOs into the canalized water bodies. In particular, oxygen and ammonia were highlighted as the main parameters for detection of the critical conditions during overflows of the combined sewers. Validation of the results is ensured through the integration of existing river monitoring stations.
The next, still ongoing, step is the simulation of the pollution load from the sewer system together with the nutrient impact and processes in the receiving water.
It is vital that Berliner Wasserbetriebe ensures that these measures will also prove sufficient for the water quality orientated demands of the Water Framework Directive. A study has therefore been set up to develop the tools and standards for the evaluation. The work is being carried out at KompetenzZentrum Wasser Berlin (Berlin Centre of Competence for Water), with the participation of Berliner Wasserbetriebe, a limnologist and a consulting engineer.
The intention is to study the effects on the water quality in the sensitive river system caused by CSOs. The research project covers an extensive catchment area around the River Spree, which is ideal for the research as the CSOs discharge into a basin that can be isolated by locks and weirs.
Extensive case study
The sewer network model consists of 13 catchment areas and wastewater for each is collected at a pumping station. Each serves between 31,000 and 263,000 people, giving a total of 1.1 million inhabitants. The mean dry weather flow of the pumping stations varies from 10,000 m³/day to 41,000 m³/day (2.6 million to 10.8 million gallons per day).
InfoWorks CS has been used to model the “skeletonized” network including all the special structures such as weirs that enable storage of storm water within the existing sewer system or within storm water tanks. InfoWorks has enabled the management strategies to be modeled accurately to represent precisely the approach used during actual events.
A detailed analysis of the ecosystem was carried out to formulate the water quality criteria for the discharge of the CSOs into the canalized water bodies. In particular, oxygen and ammonia were highlighted as the main parameters for detection of the critical conditions during overflows of the combined sewers. Validation of the results is ensured through the integration of existing river monitoring stations.
The next, still ongoing, step is the simulation of the pollution load from the sewer system together with the nutrient impact and processes in the receiving water.
Gathering data
The project’s first step was to perform a check on the model, using data from a carefully chosen rainfall event. This needed to be an intense event to represent a high load within the sewer and the receiving water. The rainfall of 11 September 2005 was found to be the most suitable. "We had 16 days of dry weather before this rain event and we found it was one of the most even periods of rainfall," says Ms Pawlowsky-Reusing. This ensured that the conditions in the receiving water could be considered as stable.
One of the key control mechanisms in the study area is a large descending weir in a major combined sewer. It has been in operation for many years, and works well, she adds. The weir’s control strategy is carefully planned so that it is lowered to deliver greater flow whenever a defined set point level is reached. "If we have a very severe rain event, then the weir is capable of going down very fast," she says. Once the water level reduces again, the initial position is resumed.
The weir’s real-time control file is modeled within InfoWorks to incorporate the required operational rules. Comparison of the measured flows and simulated flows at the pump station showed that the model copes very well with a real flow situation regarding the flow, she adds. Closely matching results were also obtained for measured and simulated water levels.
"It is very important for us to have a good result for the water level," says Ms Pawlowsky-Reusing. Most of the storm water tanks are filled by pumps. The real-time control file within InfoWorks for the filling and emptying of the tanks had to be set up correctly, as this has a major influence on the resulting emission into the receiving water. At several catchment areas, the overflow at the storm water tank represents more than 80% of the mean annual total overflow volume.
Pollution simulation has also been carried out. The resulting hydrographs of the flow and pollution are used as input for the simulation of the nutrient processes within the water body. The pollution parameters and the daily distribution were derived from calibrations in one of the catchment areas and were transferred to the other twelve. Various parameters were calculated, including the chemical oxygen demand concentration. InfoWorks will also be used as part of further work that is planned in 2008 to extend the level of information available about the system’s behavior.
One of the key control mechanisms in the study area is a large descending weir in a major combined sewer. It has been in operation for many years, and works well, she adds. The weir’s control strategy is carefully planned so that it is lowered to deliver greater flow whenever a defined set point level is reached. "If we have a very severe rain event, then the weir is capable of going down very fast," she says. Once the water level reduces again, the initial position is resumed.
The weir’s real-time control file is modeled within InfoWorks to incorporate the required operational rules. Comparison of the measured flows and simulated flows at the pump station showed that the model copes very well with a real flow situation regarding the flow, she adds. Closely matching results were also obtained for measured and simulated water levels.
"It is very important for us to have a good result for the water level," says Ms Pawlowsky-Reusing. Most of the storm water tanks are filled by pumps. The real-time control file within InfoWorks for the filling and emptying of the tanks had to be set up correctly, as this has a major influence on the resulting emission into the receiving water. At several catchment areas, the overflow at the storm water tank represents more than 80% of the mean annual total overflow volume.
Pollution simulation has also been carried out. The resulting hydrographs of the flow and pollution are used as input for the simulation of the nutrient processes within the water body. The pollution parameters and the daily distribution were derived from calibrations in one of the catchment areas and were transferred to the other twelve. Various parameters were calculated, including the chemical oxygen demand concentration. InfoWorks will also be used as part of further work that is planned in 2008 to extend the level of information available about the system’s behavior.
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The new Vista Plus and Octopus loggers from Halma Water Management combine the unique measurement and data logging technologies and experience of Hydreka S.A. and Radcom Technologies.
The high performance TR Muncher from Mono® NOV, Europe’s leading designer and manufacturer of pumps, parts, grinders, screens and packaged systems, has been installed by Thames Water to improve efficiency at Bracknell Sewage Treatment Works by preventing pump blockages and minimising down time.