The term 'daylighting' has multiple meanings and applications. It's often used to denote the practice of placing windows effectively on a building, allowing the entrance of natural light to maximize internal illumination. It may also refer to the removal of a tunnel's roof to expose the underlying roadway or railway to the sun. But in urban planning, daylighting is the redirection of a stream or creek for the purposes of restoring it to a more natural state.

Daylighted Saw Mill River in Yonkers, New York, previously buried under a parking lot, image by HamTech87 via Wikimedia Commons

In urbanized areas, development and human alterations can result in the degradation and loss of environmental and recreational assets, with pollution, erosion, and flooding exacerbating those issues. Realizing the damage done to the landscape, cities around the world have taken efforts to protect and restore the natural functions of streams, mitigating harsh impacts to the watershed.

Cheonggyecheon River restoration, image by Flickr user riNux via Creative Commons

The City of Edmonton, gifted with a long and winding river valley system, is rehabilitating and re-establishing the natural surface flow of the downstream reach of Mill Creek, a tributary of the North Saskatchewan River. This section of the waterway had been diverted to a tunnel and concrete outfall structure above the river in the 1960s and 1970s to accommodate the development of a freeway system. This modification meant that Mill Creek no longer flowed directly to the river but instead underground to a discharge point upstream from the original discharge point. The City says these alterations have greatly damaged terrestrial and aquatic ecosystem functions, leading to an overall decline in watershed health.

Mill Creek daylighting study area, image via City of Edmonton

The project aims to restore fish and wildlife habitat, create new points of access to fish spawning and rearing habitat, improve air and water quality, enhance recreation and educational opportunities, and create better transportation links across the river valley. A similar story is playing out in Vancouver, where over 50 wild salmon streams pierced the city in the 1880s. But with industrialization came the introduction of impervious surfaces that gradually replaced the natural ground cover. Vancouver has partially rediscovered its stream network by undertaking daylighting projects at Hastings Creek and the Spanish Banks, whose riparian habitat has largely been restored.

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