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23 pages, 6364 KiB

Open AccessEditor’s ChoiceReview

Urban Flooding Mitigation Techniques: A Systematic Review and Future Studies

by Yinghong Qin

Water 2020, 12(12), 3579; https://doi.org/10.3390/w12123579 - 20 Dec 2020

Cited by 79 | Viewed by 24715

Urbanization has replaced natural permeable surfaces with roofs, roads, and other sealed surfaces, which convert rainfall into runoff that finally is carried away by the local sewage system. High intensity rainfall can cause flooding when the city sewer system fails to carry the amounts of runoff offsite. Although projects, such as low-impact development and water-sensitive urban design, have been proposed to retain, detain, infiltrate, harvest, evaporate, transpire, or re-use rainwater on-site, urban flooding is still a serious, unresolved problem. This review sequentially discusses runoff reduction facilities installed above the ground, at the ground surface, and underground. Mainstream techniques include green roofs, non-vegetated roofs, permeable pavements, water-retaining pavements, infiltration trenches, trees, rainwater harvest, rain garden, vegetated filter strip, swale, and soakaways. While these techniques function differently, they share a common characteristic; that is, they can effectively reduce runoff for small rainfalls but lead to overflow in the case of heavy rainfalls. In addition, most of these techniques require sizable land areas for construction. The end of this review highlights the necessity of developing novel, discharge-controllable facilities that can attenuate the peak flow of urban runoff by extending the duration of the runoff discharge. Full article

(This article belongs to the Special Issue Rainwater Management in Urban Areas)

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16 pages, 3139 KiB

Open AccessArticle

Hydrological Performance of LECA-Based Roofs in Cold Climates

by Vladimír Hamouz, Jardar Lohne, Jaran R. Wood and Tone M. Muthanna

Water 2018, 10(3), 263; https://doi.org/10.3390/w10030263 - 3 Mar 2018

Cited by 26 | Viewed by 7791

Abstract

Rooftops represent a considerable part of the impervious fractions of urban environments. Detaining and retaining runoff from vegetated rooftops can be a significant contribution to reducing the effects of urbanization, with respect to increased runoff peaks and volumes from precipitation events. However, in climates with limited evapotranspiration, a non-vegetated system is a convenient option for stormwater management. A LECA (lightweight expanded clay aggregate)-based roof system was established in the coastal area of Trondheim, Norway in 2016. The roof structure consists of a 200 mm-thick layer of LECA^® lightweight aggregate, covered by a concrete pavement. The retention in the LECA-based roof was estimated at 9%, which would be equivalent to 0.27 mm/day for the entire period. The LECA-based configuration provided a detention performance for a peak runoff reduction of 95% (median) and for a peak delay of 1 h and 15 min (median), respectively. The relatively high moisture levels in the LECA-based roof did not affect the detention performance. Rooftop retrofitting as a form of source control may contribute to a change in runoff characteristics from conventional roofs. This study of the LECA-based roof configuration presents data and performance indicators for stormwater urban planners with regard to water detention capability. Full article

(This article belongs to the Special Issue Sponge Cities: Emerging Approaches, Challenges and Opportunities)

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