The water issue

More water
The reasons for concern over the world's water can be summarized in the following three key matters: water scarcity, water quality and water-related disasters. (UN World Water Development Report: Water for People, Water for Life, 2003). Today we have taken our point of departure in four different ways of looking at water in relation to the sustainable urban planning: Water supply, urban storm water management, urban waste water management and the amenity value of water. Yet, some crucial questions are still left unanswered: How can cities and municipalities implement efficient water technologies and approaches that are financially, socially and environmentally sustainable?

It is estimated that stormwater runoff is responsible for 70% of all water pollution in lakes, rivers and creeks. Less stormwater runoff reduces the impact on surrounding water bodies and minimizes erosion while increasing groundwater recharge. Stormwater runoff is created when rain falls on paved surfaces, can impair streams, reduce water quality and cause flooding. When rain falls on paved surfaces, a much greater amount of runoff is generated than when rain falls over a forested area.

Water management
Large volumes of water can decrease the health of streams, cause damage to existing structures and decrease water quality through pollution, erosion and flooding. To encounter these effects, municipalities must adopt regulations, create infrastructure and draining systems that can manage and reduce the negative effects of stormwater runoff. Looking at Denmark in particular the most dominating topics on the agenda regarding water are concerned with water quality, water pollution, microbial processes, waste water management, and control of water in the city and peri-urban areas.

With the above-mentioned water-perspectives, we recognize that urban water use and local management is closely linked to the socio-economic situation of the given city: Regarding poor cities, sufficient water and sanitation may be the main issue. To wealthier cities in the Western part of the world water management may be more related to clean water and the securing the water quality for recreational purposes due to create livable urban environment.

A lesson from Denmark
In Denmark the overall goal regarding water management is to optimize operation of integrated storm- and wastewater systems while securing water quality with regard to: Changing performance demands - i.e. to ensure that waste water systems are adapted to new legislation and customer demands, and that the performance of existing systems benefit from new technology. Also making the built environment act like the natural environment and natural ecosystem in order to treat stormwater runoff and reduce flooding in a way which improves the water quality and cost less than traditional stormwater management technologies. However, implementing effective and sustainable stormwater management in a municipality or city requires legislation and most importantly cross-departmental coordination between the local storm water agency, erosion and sediment control agency, enforcement authority and zoning authorities.

Thus, looking at new mixed-use area of Amager, Copenhagen, named Ørestad, it has recently become a site for testing new waste water management technologies. Together with the municipality of Copenhagen, CPH City & Port Development directly supports the development of a treatment technology targeting road runoff. Today, a new IPR-protected concept for road runoff treatment, entitled “Dual Porosity Filtration” (DPF) are being tested in the Ørestad area. The treated water are required to meet high standards in terms of suspended solids, heavy metals and organic micropollutants. Technically speaking a DPF-plant is constructed from several layers of layered filter materials, through which the road runoff passes in a hori¬zontal flow. In Ørestad, the DPF-plant is comprised of high-porosity nylon nets of a few millimetres thickness, separating layers of 1 cm thick filtering mats.

The water flows freely through the open nylon layers and while passing the filter gravity forces suspended solids downwards towards the underlying limestone filtering mat, where the hydraulic conductivity is low and the water almost standing still. Clogging is avoided in DPF because the particles are collected in a different compartment to the primary flow, and the entire retention capacity of the limestone mats can be used before replacement or regeneration is necessary. The method cleans solely by natural physical-chemical and biological processes, and is not dependent on the addition of polymers or precipitation agents. The filter has been placed underneath the soil surface, under one of the area’s green recreational spaces.

No water no (city) life
Although the proof of the concept is still on-going the first results are promising. The greyish and dirty runoff water from the roads is turned into clear water with a low content of heavy metals and or¬ganic micro-pollutants. The technology of DPF appears to be robust, easy to operate and with an expected life span comparable to other traffic-related infrastructures such as road pavings. The general aim for the water quality is that flora and fauna in the area should thrive in the water bodies. The hope is for the fragile habitats in the water bodies to continue flourishing and evolve into clear-water robust aquatic habitats. Besides that the aesthetic appeal of clean water is striking. Water gardens in the urban space can contain a variety of plants, shrubs and grasses, providing vital green – and blue space for the local community. There is no life without water!