Assessing the effects of catchment‐scale urban green infrastructure retrofits on hydrograph characteristics

Abstract

Abstract:Run-off from impervious surfaces has pervasive and serious consequences for urban streams, but the detrimental effects of urban stormwater can be lessened by disconnecting impervious surfaces and redirecting run-off to decentralized green infrastructure. This study used a before-after-control-impact design, in which streets served as subcatchments, to quantify hydrologic effectiveness of street-scale investments in green infrastructure, such as street-connected bioretention cells, rain gardens and rain barrels. On the two residential treatment streets, voluntary participation resulted in 32.2% and 13.5% of parcels having green infrastructure installed over a 2-year period. Storm sewer discharge was measured before and after green infrastructure implementation, and peak discharge, total run-off volume and hydrograph lags were analysed. On the street with smaller lots and lower participation, green infrastructure installation succeeded in reducing peak discharge by up to 33% and total storm run-off by up to 40%. On the street with larger lots and higher participation, there was no significant reduction in peak or total stormflows, but on this street, contemporaneous street repairs may have offset improvements. On the street with smaller lots, lag times increased following the first phase of green infrastructure construction, in which streetside bioretention cells were built with underdrains. In the second phase, lag times did not change further, because bioretention cells were built without underdrains and water was removed from the system, rather than just delayed. We conclude that voluntary green infrastructure retrofits that include treatment of street run-off can be effective for substantially reducing stormwater but that small differences in design and construction can be important for determining the level of the benefit.

Factors Contributing to the Hydrologic Effectiveness of a Rain Garden Network (Cincinnati OH USA)

“…Cities have used the constellation of green infrastructure (GI) technologies as a governing concept and flexible management technique to transform and connect landscapes, with an emphasis on stormwater management [1][2][3][4][5][6]. As pointed out by Green et al [2], a great deal of urban vacant land area is available (e.g., via land banks), especially in post-industrial cities, and this land mass can be leveraged toward implementation of GI, and rendering an expanded suite of ecosystem services.…”

“…These services to humans include not only stormwater management and reducing loads on ageing wastewater infrastructure, but also providing recreational spaces, expanded patches of habitat, increasing biodiversity and pollination services, and contributing to mitigation of urban heat island impacts, among other services. In this way, GI practices can re-integrate the urban landscape, and render ecosystem services that link social equity, economic stabilization, and environmental quality in areas historically lacking in these attributes [2,3,6].…”

“…Rain gardens, a type of GI, are constructed plant-soil systems that combine infiltration and storage processes to maximize retention capacity for at least the smallest and most-frequent storms, with some emphasis on improving the aesthetics of the urban landscape [1,3,5]. These stormwater control measures provide hydrologic losses through redistribution of soil moisture in the rooting zone, enhanced transpiration via vegetation, and temporary storage of infiltrated runoff volume in engineered rooting zone soils and gravel-filled underlayers [5,6].…”

“…In the design process, best-known estimates of engineered soil hydraulic conductivity are used to create a rain garden that meets the situational, site-specific expectations for overall capacity, infiltration, and complete draw-down of storm volume within 24-48 h [3,5,7]. Underdrains are often employed to ensure drainage of the plant rooting zone and timely drawdown [3,5].…”

“…Underdrains are often employed to ensure drainage of the plant rooting zone and timely drawdown [3,5]. Due to mulching and washing through of organic matter and soil particles, and development of soil biotic communities, the soil profile is in a constant state of development, influencing soil hydraulics.…”