Description Lamb Drove is a residential development of 35 affordable homes (developed and owned by Cambridge Housing Society) on a one hectare site. The aim of the Lamb Drove SuDS scheme was to showcase practical and innovative sustainable water management techniques (incorporating SuDS and property flood resilience and resistance) within new residential developments.
The project intended to demonstrate that SuDS are a viable and attractive alternative to more traditional forms of drainage and to deliver practical solutions for new housing areas.
A range of SuDS components were used to demonstrate different available techniques and the application of management train from prevention to site control and regional control components. The measures include:
detention and wetland basins
Permeable Paving The pavements within the residential roads is of permeable construction (see Figures 1 and 2). Gaps between the paving allow water to enter porous storage zones and to filter out pollutants.
Figure 1 Permeable paving (Royal Haskoning)
Figure 2 Permeable paving (Royal Haskoning)
Green Roof – A small demonstration green sedum roof is included to reduce and treat runoff (see Figures 3 and 4).
Figure 3 Green roof on bike shed (Royal Haskoning)
Figure 4 Green roof on bike shed (Royal Haskoning)
Swales Most of the excess water from the site will be fed into a series of shallow open channels, further slowing the flow of water and continuing the water treatment process (see Figures 5 and 6).
Figure 5 Swale (artist impression)
Figure 6 Swale (Royal Haskoning)
Detention Basins Sculpted depressions in open spaces help to slow down the runoff rate and store water on a temporary short-term basis during extreme events (see figures 7 and 8).
Figure 7 Detention basin (Royal Haskoning)
Figure 8 Detention basin (Royal Haskoning)
The concept of the management train was adopted for the site. The management train uses drainage components in series to improve the water quality and controls the quantity of runoff incrementally by reducing pollution, flow rates and volumes. It mimics as much as possible the natural pattern of drainage prior to development and uses a hierarchy of components within an integrated framework, to manage runoff as close as possible to the source.
Water management was considered from the point at which it falls on land and buildings to the point at which it leaves the site.
At Lamb Drove components and features have been kept simple, natural and visible. The aim is to control the runoff starting as close as possible to its source. The use of source control features within the housing development areas manages most pollution and deals with the day-to-day runoff storage requirements.
Roofwater is collected in water butts, for use in gardens, or flows directly to grass swales or under-drained swales. Rain falling on roads or paths will pass through the permeable block paving, where it is filtered and stored in the permeable layer of crushed rock below, or flows into under-drained swales where water is treated and conveyed. Water then travels downstream through a series of swales, detention basins and wetlands till it reaches a final retention pond. Here it is stored before being released to a local drainage ditch outside the development site.
When the capacity of source control components are exceeded the excess water is safely stored and treated in larger SuDS components integrated within public open space until the flood risk has passed. Such components also contribute to the provision of green space, green infrastructure, visual amenity and promoting wildlife. Throughout the site, blockage free and simple flow control structures as well as overland flow paths were provided to cater for more extreme flood events.
The driving force behind the project is the growing pressure for new housing in the UK. Cambridgeshire in particular is a key growth area under the governments housing strategy, with up to 50,000 new houses planned to be built by 2016. It is also a relatively low-lying county where flooding in river valleys and urban watercourses is a major concern.
The project was part of a European funded programme (FLOWS), which featured 40 projects throughout Germany, the Netherlands, Norway, Sweden and the UK.
Once Lamb Drove had been chosen as the site for the project (in January 2004) it took just over two years to design and then install the system, with residents moving in during spring/early summer of 2006. Royal Haskoning were employed as drainage consultants and used their advice and guidance to help design the SuDS scheme at Lamb Drove.
Project time-scale constraints meant that the design principles and layout of the site were already set and the SuDS had to be built around it.
Figure 9 illustrates the initial SuDS proposals developed for Lamb Drove. It clearly shows the range of SuDS components (permeable paving, swales, detention basin etc) and demonstrates the principles of the management train and source control, detailed above.
The scheme and components that were chosen were derived from the site topography and the pre-development drainage patterns, which ensure two key overland flood routes through the site.
Figure 9 Initial SuDS proposal (Royal Haskoning)
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In order to provide a 1:100 year return period volume with an extra 20% allowance for probable climate change, it became apparent that the peripheral public open space would be required to achieve a reasonable hierarchy of storage. Therefore recreational space in the LAP area within the site and in adjacent greenway and golf course were designed to contain SuDS.
The use of public open spaces, including adjacent, off-site open spaces, provides a viable solution to the problem of accommodating softer landscaped SuDS within housing developments.
In the early stages of the design, it was found that the full attenuation of runoff to a 1:100 year standard, with allowance for climate change, could be accommodated within the site boundary. However, this would have required the use of below ground storage techniques, which are costly and relatively more difficult to manage and maintain.
Figure 10 Final design of SuDS system (Royal Haskoning)
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