Long term experiences with decentralized infiltration

11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
Long term experiences with decentralized infiltration-systems in
Germany
H. Sommer1*, H. Sieker1, U. Zweyenert1
1
Ingenieurgesellschaft Prof. Dr. Sieker mbH, Rennbahnallee 109A, D-15366 Hoppegarten,
Germany
*Corresponding author, e-mail h.sommer@sieker.de
ABSTRACT
In the last 15-20 years numerous project for onsite storm water management have been
realised. Even there are no statistics available it can be assumed that the amount of area
managed by storm water systems is several km². This amount of disconnected area reduces
the runoff into the receiving waters significantly.
Many of these systems were built without reviewing the results after a certain period. In this
paper a few projects are mentioned were measurements were done after realisation of the
projects to verify the correct function according to the original plans.
The experiences of a trough-trench-system in the commercial area of Hoppegarten, close to
Berlin, are presented. The first systems were built in 1992. More than 15 years of experience
were collected during this period. All together 160 ha are managed with storm water systems.
The measurements confirm that even with an infiltration rate of ~5*10-6 m/s of the
precipitation can be retained in the area and slowly discharged into the receiving water.
Maintenance is provided by a private company. This includes the parts on the surface and the
sewer system.
During a minor oil spill it could be shown that the trough-trench system is capable to retain
the oil fraction in the topsoil layer of the trough. After several weeks is biodegraded by
microorganisms.
These results can be confirmed by other project results. It can be stated that infiltration
measures like trough-trench-systems can be a suitable measures for on site storm water
management, flood protection and treatment of storm water runoff.
KEYWORDS
Infiltration, BMP, SUDS, Heavy Metal, Organic Contaminants, Stormwater, Surface Runoff,
Treatment, Urban drainage
INTRODUCTION
A lot of BMPs and SUDS have been constructed in several catchments over the last 10 to 15
years. Within this period the onsite storm water management became a standard measure in
urban drainage. Especially in new developed urban areas infiltration and retention is
considered in an early stage. (Sieker, 2006)
Sommer et al.
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11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
In the early period of establishing these systems projects to evaluate the hydraulic efficiency
were made. Also studies for pollution removal have been worked out. These projects and
studies deliver many results. It was assumed that infiltration measures have a high efficiency
in flow reduction and ground water renewal and pollution reduction. Several studies were
made to evaluate the results in early stages up to 5 years. Only from one project longer data is
available. Real long term evaluation have not made in the last years.
One example with the longest perspective was undertaken in the commercial area of
Dahlwitz-Hoppegarten. This study should evaluate if the hydraulic system is working
according the proposal, which was based on simulations and the operation and maintenance of
the system. (Sieker, 2001)(Zweynert, 2007)
EXPERIENCES
From several projects experiences will be shown. These sites are:
• Sustainable Storm Water Management in a commercial area in Dahlwitz-Hoppegarten
• Measurements on Swale-Trench-System in Berlin-Rummelsburg
• Swale-Trench-System Schüngelberg Siedlung
Commercial area of Dahlwitz-Hoppegarten
The commercial area of the municipality of Hoppegarten has a size of 160 ha and is located
east of Berlin. 40 ha already existed before 1990. The rest was newly developed after the
reunion. For the whole area the maximum yearly peak discharge to the small receiving creek
Wernergraben was set to 400 l/s by the regional water authority. The discharge of the already
existing area was already 360 l/s. So the allowed discharge for new developed area was 40 l/s,
which is comparable with the natural discharge of the area. Solutions solving this hydraulic
limit are conventional sewer with large end of pipe storage volumes or decentralised BMP’s.
The soil in this area is glacial loamy soil with low infiltration rate of app. 5*10 -6 m/s. A layer
of low permeability in a depth of 3-5 m leads to temporary ground water levels in rainy years.
This can result in water coming up to the ground in low part of the ground.
For draining the area of 100 ha of newly developed area a swale trench system was
considered for the public roads and the private properties. The maximum discharge was
limited to 1 l/(s*ha). This can only ensures a management of the temporary ground water
table. Runoff from roofs, pathways and roads are managed by the system.
In the whole area different structures exist:
• 40 ha of old commercial area with conventional sewer system
• 15 ha of new commercial area with conventional sewer system
• 32 ha of new commercial area with conventional sewer system in roads and
decentralised storm water management on private properties
• 60 ha of new commercial area with decentralised storm water management on private
properties
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Long term experiences with decentralized infiltration-systems in Germany
11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
runoff in conventional sewer
conventional sewer +
storm water management
40ha
32ha
storm water management
60ha
15ha
outlet
Central retention area
Wernergraben
Additional retention basins
Figure 1. Hoppegarten, commercial area with retention measures
Conventional sewer system versus onsite storm water management
For the end-of-pipe retention of storm before discharge into the Wernergraben a central
retention volume of about 20.000 m³ would have been necessary for 100 ha. Furthermore the
sewer sizes must be bigger than with decentralised storage systems. This results in big
differences regarding the water flow in the area and the pollution load to the Wernergraben.
Table 1.
Hoppegarten, commercial area, storage volume with decentralised storm water
management
Building Step
Drainage System
Connected Area
Swales
Trenches
Storage
Top Soil
Storage
Filling
[m³]
[m³]
[m³]
[m³]
Filling material
[m²]
1
181
1220
172
344 Lava
8715
2
202
825
170
340 Lava
10139
3
113
430
100
200 Lava
2200
4
176
730
175
350 Lava
7172
5
79
275
78
234 Gravel
3962
751
3480
695
Sum
Sommer et al.
1468
32188
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11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
Figure 2 + 3. Hoppegarten, retention measures on private properties and public roads
The german water act (Wasserhaushaltsgesetz WHG §1) demands that the capability of the
natural water system should be preserved. This includes the infiltration and evaporation. The
water balance in the natural state shows that only 7,5 % of the precipitation is discharged,
37,1 % is infiltrated and 55,4 % is evaporated. With a conventional sewer system the
discharge would rise to 51,9 % while the infiltration is highly decreased to 7,4 %. The
evaporation is 40,7%. With an onsite storm water management with swale-trench-systems the
deficit in infiltration can be minimised. Infiltration is rising again to 27,8 %, evaporation is
going up to 45,5 % and discharge is decreased to 26,7 %. It has to be mentioned that this
discharge still consists the runoff of 60 ha conventionally drained area. Even the values for
the natural state before the development of the area cannot be reached a considerable changed
back to the natural conditions can be achieved by the storm water management system. The
peak discharges of the system is also minimised by the decentralise solution.
100%
90%
80%
70%
40,7
45,5
55,4
60%
evaporation
7,4
50%
infiltration
27,8
40%
30%
37,1
discharge
51,9
20%
26,7
10%
0%
7,5
natural state
conventional drainage
onsite storm water
management
Figure 4. Water balance of different management scenarios compared to the natural water
balance in the state of no development.
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Long term experiences with decentralized infiltration-systems in Germany
11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
It has to be stated that with the conventional solution a high load of particles (TSS) and also
pollution load (COD, P, N) is discharged into the receiving water. The treatment efficiency of
central sedimentation tanks is low. The treatment efficiency with decentralised soil filters
(swale-trench-systems) is much higher. The runoff of TSS and especially heavy metals can be
significantly reduced.
A central soil filter can have a similar effect on pollution load reduction, but does not have a
positive effect on the water balance because soil filters are often sealed on the bottom and the
specific infiltration area is lower than in decentralised system.
Evaluation of success
To evaluate the success of the realised systems following questions had to be answered:
• Are the infiltration sites clogged?
• Is the runoff slowed down according the plans and simulations?
• Is the temporary ground water affected by the system?
• Is the system capable to retain the maximum discharges?
Event from 25.10.1997, N
V gem = 127.17 m
Runoff [l/s]
vben = 0.20 mm, v
muld
3
ges
= 11.2 mm
, V sim = 138.59 m
= 0.10 mm, psi
0
= 0.30, psi
e
3
= 0.58, kf = 10
-6
m/s
14
Precipitation
[mm]
0
Precipitation
Runoff, measured
12
Runoff, simulated
n=3
10
0.5
1
1.5
t f,Kana =1min
vf,Ober =0.041m/s
2
8
2.5
6
3
3.5
4
4
2
4.5
0
5
11:
00
13:
25
15:
55
18:
20
20:
45
Time
Figure 5. Runoff curve at the end of the system, comparison of measured and simulated
curve
Following results can be stated:
• Flow measurements showed that the runoff in the sewer system is comparable to the
predicted simulated runoff. The measured runoff was lower than the considered runoff
of 400 l/s.
• The dry wheather situation in the Wernergraben is improved. The water from the
storm water management system is prelonging the throttled discharge for several days.
• A management of temporary ground water was observed by flow measurements and
water level measurements in the trenches.
Operation and Maintenance
For a safe operation of the system regular maintenance is essential. For the development area
a maintenance plan was developed. This included regular inspection of the complete system,
maintenance of the swales, mowing of grass, removing sedimentations along the roads etc..
• The maintenance of public area is done by a contractor.
• The maintenance on the private property is regulated by the charter of the developer.
Following observations were made:
• Clogging of the swales and trenches was not observed.
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11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
•
•
Quick frost and thaw changes in winter due to changing weather conditions in winter
do not to a failure or overload of the system.
No sedimentation of iron ochre could be observed in sewers, trenches or manholes.
An advantage of the system was observed after a minor oil spill. The oil flew into a swale
trench system and was retained in the first 10-20 cm of the topsoil layer. While no serious
concentrations in the outflow of the swale-trench-system were observed there was no need to
excavate the contaminated soil. During 2-3 months of observation and measurements of
hydrocarbons (HC) in the runoff the concentrations decreased to a normal level. It can be
stated that minor oil spills can be retained in the topsoil layer. The oil is degraded by
microorganisms in aerobic conditions.
Following advantages of the system in comparison to a conventional system are obvious:
• With infiltration measure a contamination is obvious and will not be discharged into
the receiving water without any notification. The source can be easily localised.
• The contamination is retained and measures for removal can be considered.
• Microbial degradation for HC is available and effective
Financial aspects
Through the decentralised system the investment cost in the development state in the
beginning of the process is lower than if the investment for the infrastructure has to be
realised at once in the beginning. This is an advantage for the developer of the commercial
area. The total investment is 25% lower and can be stretched according to the development of
the area.
The investments for storm water management on the private properties are made by the
private investors themselves when the investments start and be realised according to their
demands. The decentralised storm water management is fixed in a contract. This includes a
flow retention to 10 l/(s*ha) into public sewers. The area required for storm water
management is available in the 20% of free green area, which has to remain on the private
properties.
Conclusion
The runoff from 100 ha of the commercial area is discharging into a small ditch
(Wernergraben). The capacity of the ditch for the commercial area was limited to 40 l/s. The
soil conditions stated that the hydraulic conductivity is low due to loamy soil deriving from
the ice age. This forced the implementation of retention measures such as decentralised and
semi-centralised swale-trench-systems. With the combination of these systems it was possible
to reduce the flow to the required rate.
After 10 years the system is working well during heavy summer rainfall events as well as in
winter frost-melt conditions. An oil accident could be handled by the topsoil layer of the
swale. Also experiences were made with the maintenance of the drainage system. Until now
visitors from China, Mexico, Spain, England, Korea, Taiwan and other countries visited this
area.
Swale-Trench-System in Berlin-Rummelsburg
In a development area in Berlin-Rummelsburg, close to the city center, swales and swaletrench-systems were introduced for the handling of storm water from streets and roofs. 200
hectares of sealed areas are handled by those BMP since the mid of 1990’s.
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Long term experiences with decentralized infiltration-systems in Germany
11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
Figure 6. Development area of Rummelsburger Bucht, Berlin
This long term experience shows that all measures are working according the plans. In a
separate swale-trench-element measures were made to evaluate the hydraulic capacity and the
pollution reduction. A high hydraulic efficiency and pollution reduction can be confirmed.
(Sommer, 2007)
Figure 7. Examples of swale-trench-systems, covered with grass and with small bushes
Experiments with swales covered with bushes and shrubs instead of grass showed positive
result too. (Sommer, 2007)
Schüngelbergsiedlung
This project was one of the first larger projects carried out in the Emscher Region. (Sieker,
1997) Several swale-trench-elements were built mainly for roof drainage. These elements
were evaluated after construction. The evaluation considered hydraulic parameters such as
hydraulic conductivity of the topsoil layer and the functionality of water management. In a
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11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
second step the removal of pollutants were evaluated. The results of evaluation showed
comparable result to the projects above:
• The hydraulic conductivity is according the simulations.
• The runoff is according to the predicted values.
• The pollution removal is high for TSS and heavy metals.
Other projects
Besides these studies, the authors have knowledge of several other locations. In Hanover a
large development was constructed for the EXPO 2000, which implemented BMPs. This area
is working satisfactorily after 8 years.
A separation of a combined sewer system on a hospital site of 30 ha in Berlin was realised
with onsite infiltration measures in 2001. The runoff is slowed down according the restriction
from the sewer network. The system is working confidently.
Measurements with several infiltration sites including the INNODRAIN®-System showed
good retention of TSS and heavy metals. (Sommer, 2007)
CONCLUSIONS
Within the last years a wide range of projects with BMPs and SUDS have been realized in
Germany. Some of them were assessed after a significant period and several questions have
been answered. This knowledge allows detailed observations on the behaviour and long term
function to be made.
Following results can be concluded:
•
•
•
•
•
•
Evaluations for infiltration measures were made mostly within in first years after
construction.
Studies report that this measures a working very well in the first period of operation.
Infiltration capacity is stable and according recommendations in this period.
Reduction of pollution is high due to the low rate of infiltration.
Minor oil spills can be handled by infiltration systems.
More long-term evaluations will be necessary for long-term behaviour.
ACKNOWLEDGEMENT
The studies and results were partially funded by the Federal Environment Agency (UBA) in
Germany and the German Environment Foundation (DBU).
REFERENCES
Sieker, F., et.al., (1998), Untersuchung und Weiterentwicklung der naturnahen Regenwasserbewirtschaftung am
Beispiel des Mulden-Rigolen-Systems in der Schüngelbergsiedlung, Gelsenkirchen, Universität
Hannover, gefördert von der Deutschen Bundesstiftung Umwelt
Sieker, F., et.al., (2001), Naturnahe Regenwasserbewirtschaftung Gewerbegebiet Dahlwitz-Hoppegarten,
Abschlußbericht, Ingenieurgesellschaft Prof. Dr. Sieker mbH, Ingenieurgesellschaft Prof. Dr. Dr.
Rudolph & Partner mbH, gefördert vom Umweltbundesamt UBA (German EPA)
Sommer, H. (2007), Behandlung von Straßenabflüssen, Dissertation an der Leibniz Universität Hannover,
Fakultät für Bauingenieurwesen und Geodäsie
Sieker, F., Kaiser, M., Sieker, H., (2006), Dezentrale Regenwasserbewirtschaftung im privaten, gewerblichen
und kommunalen Bereich, Fraunhofer IRB Verlag, 236 Seiten
Zweynert, U., Sieker, H., Hagendorf, U., Kirschbaum, B., Wunderlich, D., (2007),
Dezentrale
Regenwasserbewirtschaftung ist Stand der Technik, 12 Jahre Erfahrungen mit einem großen
dezentralen System in schwierigem Gelände, Korrespondenz Abwasser, September 2007
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Long term experiences with decentralized infiltration-systems in Germany