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Stream ‘Daylighting’ Offers Benefits, Challenges

Saw Mill River
In December 2011, a 10-year, $19-million project led by the Saw Mill River Coalition to daylight a portion of the Saw Mill River near the plaza was completed, creating 13,775 sq ft of aquatic habitat and revitalizing a portion of the downtown area. Courtesy of Groundwork Hudson Valley

A new report reveals that the process of daylighting buried rivers and streams as part of urban renewal efforts has gained momentum, and a database of best practices would further encourage the practice.

September 3, 2013—Although the practice known as stream daylighting is beginning to receive greater attention from communities seeking to improve water quality and reduce flooding, numerous obstacles continue to hinder efforts to return buried streams to a more natural condition. In addition to ongoing research and the monitoring of stream daylighting projects, a comprehensive database of such efforts would “vastly improve” scientific understanding of the practice and help communities decide whether to pursue the option of stream daylighting, according to the report Daylighting Streams: Breathing Life into Urban Streams and Communities, released in mid-July by American Rivers, which is headquartered in Washington, D.C.

Throughout the United States and other industrialized nations, urban development frequently resulted in the burial of small streams within underground pipe networks. Such actions have had wide-ranging, long-term hydrologic and environmental effects, some of which have come to be understood only in recent decades. For example, urban areas tend to have higher concentrations of impervious surfaces, leading to increased volumes of pollutant-laden storm-water runoff. This runoff, rather than making its way to small streams, is typically directed to the conveyance systems that have replaced the original waterways, systems that are designed to quickly route the flows to larger streams or, in older cities, to a combined sewer system. In turn, the larger receiving streams experience “flashy” conditions characterized by “more frequent, larger flow events with faster ascending and descending hydrograph [readings],” according to the report. Altered channel stability, biological degradation, and increased levels of nutrients and other contaminants are other symptoms of what the report dubs “urban stream syndrome.” Meanwhile, the rapid runoff of storm water reduces infiltration in urban areas and contributes to lower groundwater levels.

In certain situations, these problems can best be addressed through daylighting, which the report defines as the practice of revitalizing streams “by uncovering some or all of a previously covered river, stream, or storm-water drainage.” Although such efforts typically take the form of restoring a stream to a more natural condition, daylighting may sometimes entail what the report calls “architectural or cultural restoration” instead. The report defines architectural restoration as “restoring a stream to the open air while confining the channel within concrete walls.” Cultural restoration “celebrates a buried stream through markers or public art used to inform the public of the historic path, although the stream remains buried,” according to the report. The American Rivers report focuses on restoring streams to as natural a condition as possible, because this approach “provides the most benefits,” the report states.

The potential benefits associated with daylighting projects include flood reduction, better water quality, and lower operating and maintenance costs. “Daylighting results in numerous benefits, including increased hydraulic capacity for flood control, slowing water velocity to reduce downstream erosion, [and] removal of water from combined sewer systems, resulting in fewer sewer overflows, community and ecological revitalization, as well as water quality improvements,” the report states. “Daylighting may also be quite cost effective when compared to repairing a failing culvert,” according to the report. For communities seeking to reduce combined sewer overflows, daylighting offers an attractive alternative to the conventional approach of sewer separation. By restoring a buried stream and some of its associated floodplain, daylighting can provide an aesthetically pleasing amenity that helps to create a landmark and define a community. 

Larkin Plaza circa 1950s

During the 1920s, the Saw Mill River was buried beneath Yonkers,
New York. By the 1950s it flowed beneath Larkin Plaza before
joining the Hudson River. Courtesy of Groundwork Hudson Valley

Despite its many potential benefits, stream daylighting poses multiple challenges for communities implementing the practice. In many cases uncovering a buried stream is a major effort, and it is not the only issue to be addressed. “Not only does daylighting require excavation of unwanted material, but restoration of some floodplain would provide the greatest benefit and is sometimes not physically possible in highly developed areas due to constraints imposed by adjacent infrastructure,” the report states. Meanwhile, funding and permits also may present significant, though not insurmountable, obstacles. “These challenges, like any met with implementing new projects, can be solved with careful design, planning, and outreach,” according to the report.

As a relatively new practice, stream daylighting would benefit significantly from “additional scientific research and comprehensive monitoring,” according to the report. “Monitoring efforts will improve scientific data on daylighting, allowing for more comprehensive guidance for future projects.” More detailed modeling and scientific information regarding headwater streams, nutrient retention, and hydrology “would vastly improve the mechanisms for how daylighting sites are chosen,” according to the report. At the same time the creation of a daylighting database having a “set of standardized, measurable values would vastly improve not only stream daylighting but our understanding of urbanization effects on ecosystems,” the report states. Such a database “would improve daylighting implementation, making it easier for interested communities to access the successes and failures of daylighting, thereby improving future projects,” according to the report.

Early public engagement in daylighting projects is of the utmost importance. “Many citizens likely have no knowledge that buried streams even exist in the area,” the report states. “Proper communication and education will ensure more meaningful results.” To this end, American Rivers notes that some communities, including Oakland, California, Baltimore, and Portland, Oregon, have created maps of buried streams as a means of educating the public about the existence of these largely forgotten waterways. Such maps “give citizens a sense of where streams exist within the community while emphasizing the sense of place within a watershed,” according to the report.

In some cases federal and state policies could be changed to encourage stream daylighting. For example, as part of the Clean Water State Revolving Fund, which it administers, the U.S. Environmental Protection Agency should direct more funding to daylighting projects, according to the report. Meanwhile, states “should revise their funding criteria to take environmental restoration into account to ensure that such projects can compete fairly for funds against bigger projects,” according to the report.

Federal flood policy also needs to better account for stream daylighting, American Rivers contends. For example, grant programs administered by the Federal Emergency Management Agency (FEMA) within the National Flood Insurance Program should seek to ensure more funding for daylighting projects as part of broader efforts to reduce flood risks. “Protection of headwater streams or restoration efforts such as daylighting, along with watershed scale planning, can lessen the frequency or severity of localized flooding and thus should all be considered by FEMA as eligible strategies for funding under FEMA’s hazard mitigation programs,” according to the report.

The report, which highlights successful daylighting projects in such cities as Dubuque, Iowa, Kalamazoo, Michigan, and Yonkers, New York, is available online.



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