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RAINWATER HARVESTING IN GERMANY
- NEW CONCEPTS FOR THE SUBSTITUTION OF DRINKING WATER, FLOOD CONTROL AND IMPROVING THE QUALITY
OF THE SURFACE WATERS
INTRODUCTION Urbanisation is increasing worldwide. To reduce the environmental impact e.g. increase of water consumption, flood risk and polluted surface waters, a combination of decentralized rainwater management measures is available. They consist of greening yards and roofs, partly sealed surfaces, artificial lakes, active infiltration systems and rainwater utilization systems. Besides saving drinking water for the toilet flush, the retention of rainwater becomes more and more a second important advantage of rainwater harvesting. That means a reduction of the rainwater input in the sewerage system during rainfalls, cutting the peak load, avoiding an overload of the system, which might cause flooding and serious health problems.
Potsdamer Platz:The new center of Berlin under construction (1997)
Measurements of the surface runoff and groundwater recharge of partly sealed surfaces at the Techn. University Berlin
Increase of urban areas in Germany from 1981-1993 (+14,9%), the loss of agricultural areas (-3,1%)
Filling of the constructed wetland in the southern part
The risk of flooding in cities, which is increasing in many cities due to a ground sealed by buildings, asphalt and concrete, can be diminished. The annual floods of the rivers Rhine, Mosel and Main in Germany show that there should be a high priority for decentralized measures to retain rainwater. One recent example of water harvesting with this purpose is the Potsdamer Platz in the centre of Berlin, where 99% of the rainwater has to be evaporated or used at the building site. A second interesting example is a cultural centre in the south of Berlin, where most of the rainwater is stored in a former waterworks station in the underground. A third example is a project, financed by the city administration of Berlin, where the water of the roofs and a public street is collected to supply the toilet flush of 87 flats and some areas for gardening.
1. Example: Potsdamer Platz (DaimlerChrysler) The example of the construction-site of the Potsdamer Platz Project shows the importance of integrating all aspects regarding ecology already in the planning process. As a part of an integrated ecological concept from energy-purposes to the use of environmental-friendly building materials a large water-management concept was realized. A condition dictated by the city council was the compliance of a maximum draining of 3 l/sec /ha for this specific area, this means 1% during stormwater events. The idea behind was a reduction of the runoff to avoid the overload of the mixed sewerage system. To comply with this regulations, the following measures are implemented for the management of 23.000 m³ rainwater of 19 buildings per year: • extensively and intensively
greened roofs • collecting of roof-runoff to be
used for toilette flushing and irrigation of green areas including intensively greened roofs
• Refilling an artificial lake 3500 m³ of storage capacity is corresponding to 15% of the annual precipitation (Berlin 580 mm). The urban water covers a total area of 13,042 m² and has a volume of 15,000 m³. The water is divided into 4 independently functioning parts and systems. The completion and handing over to the public took place in October 1998. It took 6,100 m³ of concrete, approx. 3 km piping and approx. 3km of cables. The level of the urban lake may be changed by 30 cm, that is corresponding to a storage capacity of 17% of the annual precipitation.
Rainwater management at the Potsdamer Platz, Berlin
extensively and intensively greened roofs 40.000 m²
Rainwater cistern 3500 m³ (15%)
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Artificial lake 13.000 m²
Constructed wetland for rainwater treatment 1900 m²
Advanced technology controls the constant quality of the water. 19 pumps and 2 filters are to be found in 2 underground control stations below the DaimlerChrysler Services building. The cleaning and filtering of the water is achieved naturally through the cleaning biotopes, a modified constructed wetland which is planted mainly with Phragmites.
The water circulates continuously with a maximum filtering capacity of 30 m³/h to 150 m³/h for the different parts of the lake. Additionally, there are multi layered filters through which the water can be fed by 3 pumps in the control stations with a maximum combined capacity of 125 m³/hr. The mechanism of the pumps and measuring devices are controlled by 2 programmable automatic systems (Siemens SIMATIC). The water quality has a low nutrient concentration and a high transparency all the year round.
Until today there is no monitoring to evaluate the ecological and economical benefit of the project. Therefore no additional information of the cost/ benefit-ratio is available.
2. Example: Cultural Center UFA-Fabrik in Berlin-Tempelhof
© Uta Berndt
In the south of Berlin a cultural center, the former copy center of the UFA-Film factory in 1920, implemented varous ecological projects. Besides photovoltaic plants of 70 kWh (peak) and combined heating systems an integrated rainwater management project was founded. The water of various greened and non-greened roofs together with the runoff of the streets is stored in a former waterworks station in the underground.
UFA-Fabrik Berlin Tempelhof
Non-greened roofs: 3100 m²
Greened roofs: 2600 m²
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Sealed courtyards and streets: 1900 m²
Irrigated area: 6000 m²
The system has a total storage capacity of 240 m³ in two cisterns, these are 7,3% of the annual precipitation. The rainwater is collected of the former sewerage system. The main cistern has no outlet, the rainwater runs of externally. This concentrates the nutriens in the system, one main ecological benefit. The rainwater is used for the toilet flush and for gardening. Because of the big amont of gardening area and 45% of greened roofs the drinking water of the public supplier is with 45% quite high. On the other hand, the amount of 72% of the total runoff is relatively high.
UFA-Fabrik Berlin Tempelhof
Rainwater cistern 240 m³ (7,3 % = 42 mm)
Average daily use 4,8 m³ (3-11m³) = 0,85 mm
Percentage of drinking water 45 % (Simulation)
Usage of total precipitation 72 % (Simulation)
Reduction of Nutrients > 90 % (geschätzt)
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Constructed wetland for rainwater treatment 25 m²
3. Example: The building estate Belss-/ Luedeckestreet In this project the water of the roofs and a public street is collected to supply the toilet flush of 87 flats and some areas for gardening. The relation between roofs and the potential consumption of rainwater just allows to connect one third of all inhabitants. In addition, the public street is connected to the system.
The building estate Belss-/ Luedeckestreet
with rainwater supplied flats: 87
Irrigated area: 1100 m²
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Connected roofs: 7325 m²
Connected streets and parking lots: 4450 m²
The rainwater is stored in the underground of the building. The storage capacity of 180 m³ is related to 3 % of the annual precipitation. The rainwater is treated in a modified constructed wetland inside of the building. With 2,5 m² the treatment capacity for 9 m³ every day means a treatment period of 40 minutes. At the ufaFabrik in Berlin Tempelhof the treatment capacity is 24 hours. In this project in addition the water is radiated by UV.
The building estate Belß-/ Lüdeckestreet
Start of the project: March 2000
Storage capacity: 180 m³ (3% = 15 mm)
Average daily usage: 9,1 m³
Percentage of drinking water: 31 % PPrr oo
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Constructed wetland for rainwater treatment 2,5 m²
Simulation process of water harvesting projects The simulation of a water harvesting system is an important step in the planning process. For the simulation in Germany rainfall data is used in steps of 5 minutes over 10-30 years. 5 minute data is nessesary for the calculation of the stormwater runoff of water harvesting systems. In flat regions data may be used of a 15 minute database because of the slower flow in the sererage system. For some regions 5 minute data may be calculated out of daily precipitation data and local parameters for stormwater events. The simulation of projects may optimize the storage capacity of the pond for an optimized drinking water substitution and stormwater management in an economic variant. The overall economic efficiency of water harvesting will set the frame for the expenditures which can be invested into the storage and water distribution structures. The basic physical interrelationships must be available in order to decide on the relative economic worth of planning variants. Especially for irrigation the storage capacity is of high importance. The following simulations show the effect of the increase of the soil moisture by an irrigation of a pond with a storage capacity of 20 mm and 40 mm. In this example of a semi-arid region in Africa (530 mm annual precipitation) a storage capacity of a pond of 20 mm for irrigation reduces the yield reduction by 50%. The individual runoff and irrigation events can be expressed independent of the areas, in [mm]. The volume of water available in the pond is expressed as a percentage of the yearly rainfall. 100 % would be a storage volume equivalent to the total runoff from the runoff area during the year. The irrigated area can be expressed in relation to the runoff-area, e.g. 2:1.
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Choma 1991/92 Simulation of the soil moisture with Water Harvesting for additional Irrigation by a Pond of 20mm and 40mm (5a Rainfed agriculture in Comp.)
German law and instruments to implement rainwater projects 1) The National Nature Conservation law reduces the environmental impact by defining decentralized measures, e.g. roof greening 2) The city water administration may refuse the draining into the sewerage system or the surface waters 3) Since 2000 a charge is raised in Berlin as well as in many German cities for the diversion of the precipitation into the sewage system. Before 2000 the fee was charged just for the wastewater treatment by 3,85 DM, calculated with the consumption of drinking water. Nowadays the fee was splitted into 3,15 DM for the wastewater treatment and 2,50 DM for each sealed squaremeter every year. This is an important monetary motivation for owners to save this charge by rainwater harvesting projects.
Literature Diestel, H., J. Bobert, R. Schliep, M. Schmidt: Development of modules for a decision support
system for water harvesting with ponding and supplemental irrigation. Gutachten im Auftrag der FAO, Rom 3/ 1998. 51 S.
Schmidt, M. und K. Teschner: Auswahl von geeigneten Substraten in Bezug auf die Reinigungsfähigkeit eines geplanten Reinigungsbiotops für Regenwasser sowie die Minimierung des Nährstoffaustrags von extensiven Dachbegrünungen. Gutachten i.A. von debis Immobilienmanagement, Projekt Potsdamer Platz, 4/ 1998. 59 S.
Diestel, H. und M. Schmidt: Wasserwirtschaftliche Vision: Die abflußlose Innenstadt – ein richtiger Ansatz? In: Senatsverwaltung für Stadtentwicklung, Umweltschutz und Technologie 1998: Zukunft Wasser, Tagungsband zum Symposium zur Nachhaltigkeit im Wasserwesen vom 17.-19.6.98.
Schmidt, M. und H. Diestel: Regenwassernutzung als dezentrale Strategie zur Vermeidung von Nähr- und Schadstoffeinträgen in die Oberflächengewässer. In: fbr-Wasserspiegel 4/98, S. 18-19.
Teschner, K. und Schmidt, M.: Kombination von Regenwasserbewirtschaftungsmaßnahmen: Ergebnisse der Voruntersuchungen für das Projekt Potsdamer Platz - Teil 2: Regenwasserreinigung über ein Reinigungsbiotop. In: gwf 11/2000, S. 773-779.
Adress
TU Berlin, Institute of Landscape Architecture and Environmental Planning Dipl. Ing. M. Schmidt Albrecht-Thaer-Weg 2, 14195 Berlin, Tel: 049/ 30/ 314-71307; Fax: 049/ 30/ 314-71228 www.tu-berlin.de/~Wasserhaushalt, email: [email protected]
