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Younos: Stream daylighting: The 21st century green water infrastructure

Younos: Stream daylighting: The 21st century green water infrastructure

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Twenty-first century America is approaching a turning point in its approach to urban stormwater management, i.e. stormwater runoff collection and drainage from imperious land surfaces. The 20th-century engineering that made rapid land development possible is often failing and creating a host of problems. Cracked and collapsing pipes cause major urban floods as undersized culverts fail to handle the stormwater runoff generated during heavy rainfall events on impervious surface areas such as roads and parking lots. Today, keeping natural streams underground to facilitate land development remains a common practice, and many municipalities continue to replace and/or expand the underground piped stormwater drainage system. Fortunately, current trends in environmental awareness and stewardship are making it possible and imperative to imagine and build sustainable water management systems for our cities and to preserve rivers, streams, creeks and natural ecosystem. Movements toward implementing “green water-infrastructure” such as low impact development (LID) and environmental best management practices (BMPs) are gaining ground in public debate, policy making, and land use management and planning. Stream daylighting is a LID approach which is trending toward increased implementation.

The word ‘daylighting’ is often unfamiliar to most people, who confuse it with bringing daylight into the interior of a room or building. The term daylighting describes stream restoration projects that deliberately expose part or all of a previously covered stream, river or stormwater drainage pipes and restores the underground waterway to open air. Measurable benefits of stream daylighting include improved riparian habitat and water quality along newly created stream banks; reduced flood impacts by increasing storage capacity in comparison with underground culverts; reduced urban “heat island” effect - built up areas that are hotter than nearby rural areas resulting in increased summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions, and heat-related illness and mortality; and adding valuable public open space to dense urban communities which consequently enhance aesthetic environment, increased property values and business investment opportunities.

Our research of several case studies shows that stream daylighting projects have successfully reduced urban flooding and enhanced aesthetic value of built environments. The physical constraints of a given location yield three common stream design options and outcomes - artificial streams, channelized streams and naturalized streams. Artificial streams are usually established in highly built urban environments where little space is available for a meandering and shaded stream bed. Its function is limited to controlling water's flow path without restoring the stream's basic ecological function. Channelized streams are typically found in urban or suburban areas where large vacant parcels facilitate a higher degree of ecological function and aquatic habitat. Naturalized streams are typically found on large pieces of property such as school fields and campuses where greater land area exists to re-establish floodplains, wetlands, ponds, and wider stretches of riparian plantings and forest buffers. Naturalized streams offer the highest degree of ecological function and typically see the largest number of returning fish and insect species within their channels.

Though the first stream daylighting project occurred in 1984 along a section of Strawberry Creek in a Berkeley (California) park, today there is an increasing trend toward implementing stream daylighting projects across the country. Stream daylighting has proved to be a viable green water-infrastructure alternative to traditional stormwater management approach. In appropriate situations, daylighting and open streams are becoming a successful retrofit method for controlling specific types of urban floods and consequent damage that we often observe and experience. Although stream daylighting initial cost is perceived to be high, in many cases long-term daylighting cost can be less than expanding and installing new underground pipes. Stream daylighting and environmental preservation can also result in community warm-glow feeling and emotional reward. Our planners, engineers, and municipalities need to reevaluate high cost and less effective stormwater management projects, and where feasible, consider a stream daylighting option as an alternative approach for stormwater management and flood control. Acknowledgment: Tracy Buchholz Strickland, a landscape architect and former graduate research assistant at Virginia Tech, conducted research on stream daylighting and co-authored a book chapter on this topic.

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