RAINWATER HARVESTING IN GERMANY
- NEW CONCEPTS FOR THE SUBSTITUTION OF DRINKING
WATER, FLOOD CONTROL AND IMPROVING THE QUALITY
OF THE SURFACE WATERS
Measurements of the surface runoff and
groundwater recharge of partly sealed
surfaces at the Techn. University Berlin
Potsdamer Platz:The new center of
Berlin under construction (1997)
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.
Increase of urban areas in Germany
from 1981-1993 (+14,9%), the loss of
agricultural areas (-3,1%)
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
Project data
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
Filling of the constructed wetland in the southern part
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
Rainwater cistern
Artificial lake
40.000 m²
3500 m³ (15%)
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
Connected
Area
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
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.
Project data
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)
Constructed wetland for rainwater treatment
25 m²
3. Example: The building estate Belss-/ Luedeckestreet
Connected
Area
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
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.
Project data
The building estate Belß-/ Lüdeckestreet
Start of the project:
Storage capacity:
Average daily usage:
Percentage of drinking water:
Constructed wetland for rainwater treatment
March 2000
180 m³ (3% = 15 mm)
9,1 m³
31 %
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.
© M. Schmidt 1998
20
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.)
30.03.82
20.03.82
10.03.82
28.02.82
18.02.82
08.02.82
29.01.82
19.01.82
09.01.82
30.12.91
20.12.91
10.12.91
30.11.91
20.11.91
80
10.11.91
60
31.10.91
5b) Soil Moisture + Pond in mm
80
21.10.91
11.10.91
01.10.91
5c) Soil Moisture + Pond in mm
5a) Soil Moisture Rainfed Agriculture
100
80
60
40
20
0
120
100
Storage 20 mm
Soil Moisture 20
40
20
0
140
120
100
Storage 40 mm
Soil Moisture 40
60
40
0
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]