Monday, November 22, 2010

A Case for Open Stormwater Systems (Part I): Western Harbour, Malmö

In Scandinavia, sustainable developments that address environmental health of both land and water are called "green and blue". Blue refers to measures that help protect water quality adjacent to urban areas. One of the biggest efforts that is being made to help protect urban waterways is the separation of stormwater and sewage. Combined sewage and storm systems are an issue all over the world, as they were the most cost effective way of transporting wastewater before cities developed sewage treatment systems. Now, the rate of treatment is controlled by how fast a treatment plant can handle water intake.

Sewage treatment plants, which often rely on living systems are not equipped to deal with fluctuations in the volume or nutrient-concentration of water they receive. The raw sewage produced by a city on a daily basis is fairly predictable, except during periods of heavy rain. During these times, systems become overloaded, and overflows occur. These overflows dump sewage directly into urban waterways, full of pollutants.

The alternative to combined sewage systems is to completely separate stormwater from sewage systems. Often, stormwater is regarded as clean and unharmful to urban waterways, and is allowed to drain freely without any filtration. However, stormwater that passes over contaminated surfaces such as roads and parking lots can contain many contaminants as well.

A trend in stormwater management is the 'open system'. Open stormwater systems can include many different approaches to dealing with stormwater: swales, open gutters, reservoirs, permeable pavers, greens roofs can all be part of a system designed to manage water on site.

The Western Harbour in Malmö incorporates many of these strategies into a newly developed mixed-use housing district. Here are some of the systems at work:

Small alleys are lined with open gutters that transport stormwater to larger canals. The gutters also create a buffer zone next to people's homes and windows for better privacy, and provide an opportunity for plants to climb the walls. Changes in paving indicate when cyclists and pedestrians are near the gutter to prevent accidents. The gutter is covered in places where people must cross to enter a building.

In larger 'streets', small gardens act as swales, and help filter the water. These gardens also serve as traffic calming devices, and help to indicate parking spaces (for the few inhabitants who own cars).

Building layouts are staggered slightly to create opportunities for small filtration pools and gardens. They provide green spaces for the neighborhood, and break up the monotony of a solid street wall. This effort is aided by the fact that most of the buildings are very small (2-4 units) and are designed by many different architects, to avoid feeling like a monolithic housing complex.

One benefit of an open stormwater systems is that beyond the initial cost, maintenance is cheaper because all problem areas are open and accessible. In the case of the Western Harbour, Bo01, most components are made of small masonry/block units that can be replaced individually when repairs are needed.

All of these measures are taken to help protect the quality of water in the Øresund. The waterfront of the Western Harbor was designed with bathing in mind: Seating oriented toward the sun, unlimited access to the water, and a lovely boardwalk. I should also add that though I took these photos on a sunny day, the temperature was well below freezing, so there were not many people outside.

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