Daylighting (streams)

In urban design and urban planning, daylighting is the redirection of a stream into an above-ground channel. Typically, the goal is to restore a stream of water to a more natural state. Daylighting is intended to improve the riparian environment for a stream which had been previously diverted into a culvert, pipe, or a drainage system. In the UK, the practice is also known as deculverting.

The term also refers to the public process toward such projects. A general consensus has developed that protecting and restoring natural creeks' functions is achievable over time in an urban environment while recognizing the importance of property rights.

Natural drainage systems help manage stormwater by infiltrating and slowing the flow of stormwater, filtering and bioremediating pollutants by soils and plants, reducing impervious surfaces, using porous paving, increasing vegetation, and improving related pedestrian amenities. Natural features — open, vegetated swales, stormwater cascades, and small wetland ponds — mimic the functions of nature lost to urbanization. At the heart are plants, trees, and the deep, healthy soils that support them. All three combine to form a "living infrastructure" that, unlike pipes and vaults, increase in functional value over time.

Some efforts to blend urban development with natural systems use innovative drainage design and landscaping instead of traditional curbs and gutters, pipes and vaults. One such demonstration project in the Pipers Creek watershed reduced imperviousness by more than 18 percent. The project built bioswales, landscape elements intended to remove silt and pollution from surface runoff water and planted 100 evergreen trees and 1,100 shrubs. From 2001 to 2003, the project reduced the volume of stormwater leaving the street in a 2-year storm event by 98%. Such a reduction can reduce storm damage to water quality and habitats for species such as the iconic salmon. Unfortunately, the engineering alternatives have a relatively expensive initial price, since they are usually replacing existing structures, albeit life-limited ones. Further, conventional systems generally do not consider full cost accounting. The NDS alternatives can also provide returns on investment by improving urban environments.

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