Abstract:

Experience in ecological storm water management has been gathered since 1985 from various completed projects now in operation ranging in size from 2 ha to 30 ha, as well as from projects which are currently in the planning stage, which range in size from 80 ha to 20 km².

The storm water management projects have employed various techniques, including collection, storage, and purification of street runoff, followed by its discharge through various pipe systems for reuse. In other projects, the storm water runoff from sidewalks, bicycle lanes, parking lots, and private roads is conveyed to the groundwater through infiltration trenches. Also proven to be successful has been the purification of polluted runoff from roads for subsequent storage in ponds, making it available for eventual reuse or infiltration.

Zero runoff has been achieved in three separate storm water projects. This has been accomplished through the reuse of storm water for drinking water substitution.

Viable economic solutions have been developed for our various German projects. A project currently being designed will completely satisfy the entire water needs for a city of 50.000 inhabitants from harvested rain water. This project will also incorporate the reuse of the waste water.

The incorporation of the various modern storm water management components into the initial municipal planning stages is urgently needed in order to improve the quality and viability of integrated municipal projects.

Introduction

Present day municipal sanitary supply and disposal in Germany has been controlled for years by powerful interest groups that up to now have allowed the application of alternative systems only in storm water disposal. The model projects of the 1980’s demonstrated many alternatives, but none have ever been further developed.

Until the mid-90’s, all storm water was treated as contaminated surface runoff and diverted away in drainage systems. Drainage took precedence over infiltration. However, with the amendments in the state water laws, the water resource management objectives became reversed, and decentralised infiltration began to take precedence over drainage. In the 70’s, the general practice was to discharge municipal storm water into combined systems. Till today, the largest portion of existing networks are combined systems. The increasing pollution load in lakes and rivers from the discharge of these combined systems led to the construction of improved overflow structures, holding tanks, and sedimentation tanks, as well as to larger sewer systems and more extensive treatment of both storm water and waste water in the treatment plants.

In the 80’s, the construction of separate systems began. However, the preliminary treatment of storm water prior to its discharge into the downstream water body was, as previously, the exception. The rapid discharge of storm water from impervious areas through storm drains into the rivers brought about increasing problems under extreme precipitation events. Finally, due to the frequency and high water levels of floods, as well as the lowering in groundwater levels and the reduction in the wetlands, a reversal in storm water management objectives was begun. In the second half of the 1980’s, stemming from the international housing exhibit in Berlin, model projects were realised. Their aim was, among others, to demonstrate methods that reduce the need to draw upon conventional water supplies.

In addition to the presentation of water-saving sanitary technology, the natural purification of wastewater with the use of rootzone treatment technology for reuse, and drinking water substitution, exemplary solutions with regards to storm water issues were also presented. The objectives of the model projects included prevention of runoff, the reduction in peak flows, reuse, and infiltration (z. B. Berlin-IBA Block 6, 103). New housing projects cannot ignore these developments any longer, and current legislation provides, now more than ever, the means for the implementation of these new water resource management objectives.

Storm water management in urban areas is basically subdivided into that for private lots and that for public property, including streets, public squares, parks, or other open areas. It is primarily carried out through retention, reuse, and infiltration. Drainage of storm water as wastewater can now be seen as outdated. Storm water management intended to relieve the sewer network, infiltration to enhance groundwater recharge, and on a limited scale, the storm water collection for reuse, are finding increasingly more application in modern development projects.

Storm Water Harvesting and Reuse Projects in Germany

Project “Berliner Straße 88”, Berlin-Zehlendorf
In 1992 the construction of project Berliner Straße 88 was begun. The storm water from 160 housing units is collected in three cisterns making up a total storage capacity of 650 m³. The water is then reused for irrigation. The runoff is discharge into an artificial water course and a storm water pond of 1000 m². The pond water is recycled through the water course by solar and wind energy and continuously cleaned in a root zone treatment plant. The excess water is infiltrated through ground water recharge units. No storm water leaves the premises.

Project “Schweriner Hof” Berlin-Hellersdorf
This project was recognised as an exemplary model of an ecological project in the Habitat II Conference in Istanbul in 1996. The storm water runoff from the roofs is stored in a 600 m³ cistern and reused for irrigation and for the regulation of a rain water pond.

The external water, as well as the surface runoff, is infiltrated through an infiltration trench system into the ground, which was actually declared to be unfit for infiltration.

Project “Landsberger Tor” Berlin-Marzahn
In this large project (30 ha, 1.800 units), the storm water runoff from the roofs is infiltrated into an infiltration trench system. The storm water runoff from the roads is collected in a conventional storm water drain and discharged into a storm water treatment and infiltration facility, located in a public park. The facility consists of a separate unit for mechanical treatment, a rain water lake, and a root zone treatment plant for the biological treatment. The outflow is infiltrated through ditches. The total surface area of the facility is 5.000 m². The project design is the outcome of an international competition.

Project “Teltow-Mühlendorf”
This project area is 29 ha, comprising 1.800 housing units.

Terrain Modelling
This newly developed concept assumes that all of the storm water and the necessary excavation is to stay on the project site. Using the displaced earth (250 000 m³), the terrain has been modelled so that the surface water can be diverted to a centrally located pond, resulting in a rise of about 1 m in the ground level in the centre of the project. A considerable environmental stress has been prevented by not hauling away the excavated earth, which would have require approx. 25 000 truck loads.

Storm Water Disposal for Traffic Ways
The major goal of this design is to minimise the interference of the natural water regime within the project area. In spite of the high percentage of paved and otherwise sealed areas, the precipitation remains within the boundaries of the project. The storm water runoff from sidewalks, bicycle paths, parking lanes, pedestrian walkways, green areas and playgrounds is conveyed to the subsoil through local infiltration. The runoff from the streets is intercepted in lateral gutters and conveyed to three storm water purification facilities and, after being extensively biologically treated, fed to a central storm water pond.

Surplus storm water is infiltrated when complete filling of the pond forces water over the edge into infiltration trenches located in the banks. The overflow is also biologically treated prior to the infiltration in vegetated filters.

Storm Water Disposal on Residential Lots
The precipitation from all rooftops is stored in cisterns and from there made available to the residents to be used as non-potable water substitution. The surplus water is to be led to infiltration trenches. The pond water will be circulated through four natural-looking channels (flowing brooks), which run through the residential areas. The resulting cooling effect on the immediate surroundings, as well as the enhancement of the living conditions through simultaneous aeration of the lake, are the primary goals of the design concept.

Project “Former Airfield Böblingen-Sindelfingen”

In this 85 ha project, the entire storm water runoff is proposed to be collected, treated and reused as a substitute for drinking water used in recreation, irrigation, toilet flushing, washing machines and still further uses where drinking water quality is not required. The excess water is discharged to a river bed.

The basic aim here is that all of the storm water will be reused within the project area.

Water Management FOR THE CITY OF AUROVILLE in India
A solitary banyan tree stands on a low barren hill of red laterite, about 60 m above the sea which lies 5 km to the east near Pondycherry in South India. This tree is to become the centre of the city. Buildings will spiral outwards from it in the form of a galaxy, surrounded by a belt of dense tropical forest. Vegetation will extend inwards again to the centre between the arms of the spiral, acting as the ‘green lungs’ for the city.

On the crown of the hill will be gardens, surrounded by a large lake. Within the gardens, an amphitheatre, a large spherical building, and the ancient banyan tree will mark the centre of the city, which is meant one day to accommodate 50,000 inhabitants.

Even in drought years, precipitation over the city area corresponds to more than ten times the amount of drinking water needed. But the rainy season lasts only a few months.

The upper layer of relatively impermeable laterite, together with the uppermost aquifer, form the entire plateau on which the city stands, and both slope gently towards the sea. Therefore, all of the water that percolates within the city area moves gradually above sea level towards the coast.

Rainwater falling on roofs can be collected in cisterns and used for drinking water and various household and gardening purposes. The surface runoff from roads, tiled surfaces, and open areas, can be collected and stored in reservoirs within the greenbelt up to the boundaries of the city. After filtration, through rootzone treatment plants the stored rainwater can be slowly pumped up into the central lake, a distance of no more than 20-30 m, by means of solar energy. From here, percolation into the groundwater table will take place. In this manner, the water level of the lake will be kept constant, providing optimal conditions for high quality landscaping and park areas, along with desirable climatic effects.

Sewage from the densely developed areas can be centrally purified in the greenbelt, and then be re-used for irrigation purposes. Sewage, as well as secondary runoff if necessary, from the less densely developed areas can be purified in root-zone treatment plants and reused on site for irrigation.

In this way, the geological and geographical "disadvantages" of the city's site, make a regime of rainwater conservation possible which would provide a plentiful water supply for both drinking and irrigation, even if the underlying groundwater becomes completely salinated. The average rainfall is not only sufficient enough to support a vigorous tropical vegetation, but would provide enough surplus to supply the surrounding areas. However, this will be successful only if the residents of the city protect the first aquifer from contamination.

The upper strata of earth beneath the city functions as a reservoir, and must therefore be protected. Drinking water can be obtained from wells in the greenbelt which tap the groundwater before it flows beyond the city limits towards the sea.

The extreme degradation of life’s basic elements through over exploitation of this area’s natural resources, has threatened the existence of human settlements. This water management concept enables the residents of the city to live unaffected in the midst of a degraded environment, so long as they, themselves, avoid polluting the ground and the water which together form the basis for their survival.

Conclusion
An alternative ecological supply and disposal system of water offers possibilities particularly in new residential areas, contributing to a considerable improvement in the quality of life and to a reduction in costs. Such a new and unusual venture would, however, require expressed public interest and strong support especially throughout the permit acquisition process.

Considering the expected problems in drinking water supply for a growing population, as well as the change in precipitation patterns due to climate change, the collection and reuse of storm water (“Rainwater Harvesting”) grows increasingly important.