Abstract
Executive Summary
This report, one of three reports produced for CREW to verify the current state of knowledge on NFM, focuses on establishing the effectiveness of SUDS measures for flood management in urban areas, particularly in relation to performance under saturation conditions and long term efficiency as a device becomes established.
Although it is explicitly recognised that SUDS can also deliver water quality and amenity benefits, this report focuses only on runoff detention and retention. Specifically, this report examines the performance of devices with high or moderate potential for runoff volume reduction in detail (green roofs, rainwater harvesting, pervious paving, infiltration devices and swales), reviewing the available evidence relating to the impact that these different SUDS measures have on managing flood scenarios.
The review focused on SUDS performance with respect to the following key hydrological processes:
1.Retention - where flow is not passed forward (including infiltration)
2.Detention/attenuation – temporarily slowing or storing runoff.
3.Conveyance - the transportation of surface runoff away from the original source
4. Water harvesting - the direct capture and use of water from its
source.
A key outcome of the review has been to highlighted the uncertainty associated with the performance of SUDS devices. In some case this is due to the contrasting research methodologies and metrics. However, equally significant is the design, main tenance and catchment characteristics associated with the devices considered.
The research review also found that, regardless of the SUDS device considered, a number of environmental factors influence the performance of the device in managing runoff:
- The length of any preceding dry period: saturated systems are less efficient.
- The prevailing climate: devices perform differently in hot and cold climates depending on air temperature, wind conditions, humidity etc.
- Seasonal variation: performance varies throughout the year.
- The characteristics of a rain event: intensity and duration, temporal spacing of multiple events and intensities during an individual event.
With the exception green roofs, it was found that the devices considered could operate well during and/or soon after extended periods of rainfall. Although green roofs can retain significant volumes of rainfall, the research reviewed suggested that lightweight “extensive” roofs readily become saturated and then offer only modest detention. As highlighted in Table 1, one stratagem to mitigate against these problems on other types of device has been to update design methods to allow for a loss of efficiency over time or due to saturation. This approach, although it comes at a cost, underlies the design of permeable paving systems and its success is evidenced by their widespread use and
relatively low maintenance requirements. An alternative to this may be to provide additional retention / detention downstream.
This report, one of three reports produced for CREW to verify the current state of knowledge on NFM, focuses on establishing the effectiveness of SUDS measures for flood management in urban areas, particularly in relation to performance under saturation conditions and long term efficiency as a device becomes established.
Although it is explicitly recognised that SUDS can also deliver water quality and amenity benefits, this report focuses only on runoff detention and retention. Specifically, this report examines the performance of devices with high or moderate potential for runoff volume reduction in detail (green roofs, rainwater harvesting, pervious paving, infiltration devices and swales), reviewing the available evidence relating to the impact that these different SUDS measures have on managing flood scenarios.
The review focused on SUDS performance with respect to the following key hydrological processes:
1.Retention - where flow is not passed forward (including infiltration)
2.Detention/attenuation – temporarily slowing or storing runoff.
3.Conveyance - the transportation of surface runoff away from the original source
4. Water harvesting - the direct capture and use of water from its
source.
A key outcome of the review has been to highlighted the uncertainty associated with the performance of SUDS devices. In some case this is due to the contrasting research methodologies and metrics. However, equally significant is the design, main tenance and catchment characteristics associated with the devices considered.
The research review also found that, regardless of the SUDS device considered, a number of environmental factors influence the performance of the device in managing runoff:
- The length of any preceding dry period: saturated systems are less efficient.
- The prevailing climate: devices perform differently in hot and cold climates depending on air temperature, wind conditions, humidity etc.
- Seasonal variation: performance varies throughout the year.
- The characteristics of a rain event: intensity and duration, temporal spacing of multiple events and intensities during an individual event.
With the exception green roofs, it was found that the devices considered could operate well during and/or soon after extended periods of rainfall. Although green roofs can retain significant volumes of rainfall, the research reviewed suggested that lightweight “extensive” roofs readily become saturated and then offer only modest detention. As highlighted in Table 1, one stratagem to mitigate against these problems on other types of device has been to update design methods to allow for a loss of efficiency over time or due to saturation. This approach, although it comes at a cost, underlies the design of permeable paving systems and its success is evidenced by their widespread use and
relatively low maintenance requirements. An alternative to this may be to provide additional retention / detention downstream.
| Original language | English |
|---|---|
| Publisher | CREW - Centre of Expertise for Waters |
| Commissioning body | Centre of Expertise for Waters |
| Publication status | Published - 2012 |
