PROJECT DESCRIPTION
BACKGROUND
The city of Dordrecht is situated in the West of what can be described as the lower region of the Netherlands. Distinguishing features of this environment are the clay-peat soil and a high groundwater level. Creeks, ponds and rivers form an integral part of the landscape. In the municipality of Dordrecht the following drainage-related problems can be listed: • The quality of the open water does not meet the standard requirements of the purification authority. • The drainage capacity of the sewerage system is inadequate to cope with large supplies of storm water. • Groundwater reaches unacceptably high levels. • Vegetation is insufficient. • It is the policy in the Netherlands to reduce unnecessary transportation of clean storm water to water treatment plants for purification. Traditional solutions to these drainage problems are for example, the use of storage tanks for controlling quantities and equalizing flows, enlarging pipe diameters to increase capacity; laying drains and planting vegetation to control groundwater levels. In general if the problem is approached from a wider perspective, opportunities can be taken advantage of to manage an integrated water management system. A study group comprised of participants from the Dordrecht City council, the purification authority “Hollandse Eilanden en Waarden” (ZHEW) and the district water board “Waterschap de Groote Waard” (WGW), has developed a new concept, based on the infiltration and transportation of storm rain water. The theory has been analyzed thoroughly and a feasibility study has been carried out with positive results.
OBJECTIVES
The objective of the project was to implement, under the site specific conditions, storm rain water transport and infiltration systems, including: • the adoption of an integral approach to implement the infiltration system in the district of Kinkelenburg and Luchtenburg; • the acquisition of an insight into the functioning of different infiltration systems; and • the validation the theoretical models applied to the water system. Based on a former study, the Municipality of Dordrecht decided to adopt an infiltration-transport system (IT system).
RESULTS
The principal design characteristics of the Infiltation Transport (IT) technology used during the project were as follows: • The storm water which falls onto the paved surface is drawn across the road surface and then, via ducts to the infiltration bed. • In the infiltration strip (a sunken area of the surface), the first quantity of water can be stored. The infiltration strip is planted with grass or other plants. • From the infiltration strip, the precipitation water sinks down into the infiltration bed. This is a sand bed enriched with organic material and lutum. It should be low enough to allow any impurities in the infiltrated water to attach themselves to the adsorption complex, and yet high enough to avoid overflows or the need of an absurdly large system. The root growth and the soil biota in the infiltration strip ensure that the infiltration rate is maintained throughout the life of the system. • The water percolates through the infiltration bed and ends up in the transport part of the IT system. In sizing the transport part it is important to get the coefficient of storage high. This should be less than the porosity, so that some adhesive water always remains behind in the soil matrix as a result of capillary action. A high coefficient of storage and a high transport rate ensure that the infiltration strip situated above the storage area does not remain permanently damp. • The water travels from the transport part and enters the drain. There is also an interchange between the groundwater inside and the ground water outside the transport part. • In order to stabilize the water-table, use is made of a sublevel drainage system. The drainage pumps runs on electricity generated by solar cells. The project had to tackle several unexpected problems. The first objective –construction of the IT system- has been partly achieved by the implementation of the infiltration system at one out of the two foreseen districts: the district of Luchtenburg. The rain pipes of the houses have been disconnected and the zinc gutters have been coated with EPDM in order to prevent zinc contamination of the water. The residents of the second district -Kinkelenburg- did not support the implementation of the concept in their district. The major reason was that they were not so motivated because they had fears of high groundwater levels which might inundate their houses. - The second objective of getting data on the functioning of the newly implemented system was only partially achieved as the monitoring system has not been implemented due to insufficient remaining time. - The validation of the theoretical model (the third objective) has not been achieved. However, the project has made some progress in this field and brought forward recommendations for further projects on integrated sustainable urban drainage. - It can be concluded that it is technically and economically possible to apply infiltration and transport (IT) technology in already developed residential areas. One of the major restrictions is the fact that the IT system is not always applicable to an existing infrastructure. - The communication with the residents of the area is vital for the success of the project, because of the socio-economic impacts of the project. - The outcome of this project may be interesting for policy makers in other EU Member States as it refers to water management in urban areas. It is expected that a major transfer of knowledge could take place via a major commercial consultant involved in acquiring and executing similar types of projects in the Netherlands and across the EU.
