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White Cart Water Flood Prevention Scheme


Client:


Glasgow City Council Consulting Engineers: Halcrow


Contractors: Volker Stevin - Urban flood defences Carillion - Flood Storage areas


White Cart - A brief history


• Over 20 significant floods since 1908


• 1984 – over 500 homes flooded twice in 12 days


• 1990 – Severe flooding • 1994 – River burst it’s banks • 1999 – Severe flooding • 2006 – Flood scheme approved • 2011 – Scheme fully operational


The Scheme


White Cart is Scotland’s largest completed flood prevention scheme and provides protection from an up to a 1: 200 year storm. It has reduced the risk of flooding for around 1,750 homes and businesses


as well as providing an improved wildlife habitat.


The total cost of scheme was £53 million and includes the worlds largest hydro-brake, at 8m long and 6m high.


The scheme was divided into two parts: Flood Water Storage


Construction of the 3 flood storage areas began in 2008 after 33 possible locations were reduced down to the final 3; Blackhouse (Earn Water), Kirkland Bridge (White Cart Water) and Kittoch Bridge (Kittoch Water). The storage areas were formed by constructing earth embankments across the river valley. The river passes through the embankment in a reinforced concrete culvert which contains a vortex flow control limiting the volume of water that can pass through the culvert with the excess water being held back in the storage areas. Together the three flood storage areas have the capability to hold back more than 2.6 million cubic metres of flood water. Each dam is capable of storing over 0.7M cubic metres of water, with the largest storing 1.1M cubic metres,


Water is then released downstream at a controlled rate so that it does not overspill the new flood defences protecting the city.


Flood Defences Blackhouse flood storage area Kirkland Bridge flood storage area


The construction of the defences began in January 2009 and was completed in October 2011. It comprised the construction of approximately 4.5km of flood defence walls and embankments together with the raising of two footbridges and the construction of six underground pumping stations.


The design philosophy was to make sure that all accessible parts of the river were not severed by high flood fence walls and with an average height of 0.85m above ground level, this has been comfortably achieved. Particular attention was paid to the alignment of the flood defence wall and where possible the alignment sought to maximise the retention of the natural flood plain and follow existing boundary walls and features to avoid the reduction in size of private gardens.


Active Consultation Kittoch Bridge flood storage area 12


The project has involved active consultation and participation of a range of stakeholders from affected land owners to the general public and various statutory and non statutory consultees. Through one-to-one discussions, workshops and an extensive public exhibition, the views and opinions of affected parties were obtained and, where appropriate, incorporated within the final design. Stakeholders were kept fully informed of the development and progress of the project through the distribution of regular newsletters, meetings


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and the creation of a dedicated project website. The concerns of the affected stakeholders primarily related to the visual impact of the flood storage areas, traffic impacts and also the impact on the local ecology and water environment. Despite the size and scope of the project, only limited objections were received, all of which were subsequently resolved through discussion without the need for a Public Local Inquiry, a first for a flood prevention scheme of this size.


Flood Defence


Normally a shallow river, the White Cart Water is prone to flash flooding. As little as 12 hours of rain can cause water levels to rise by up to six metres with the potential to turn the river into a raging torrent as it gathers momentum downstream towards the vulnerable suburbs of the city.


Iain Macnab, Glasgow City Council Alan McGowan, Halcrow


Environmental Consideration


The development of engineering designs for the scheme were complemented by the creation of an environmental working group (EWG) comprising stakeholders from the Scottish Environment Protection Agency, Scottish Natural Heritage, Scottish Water, local angling/ fisheries groups and the Royal Society for the Protection of Birds as well as environmental professionals from the three local authorities involved. The establishment of the EWG was a unique approach and an early example of effective collaborative working. The work of the EWG helped to minimise the environmental impact of the scheme, and, where possible, to enhance the natural environment and assist in developing a sustainable flood prevention scheme.


Upstream water storage to hold back the water during storm events would enable downstream flood defences along the river in the urban areas to be reduced in height and length. This reduction in height and length has significant benefits not only in engineering terms but more importantly in the associated visual and environmental impact. High walls would have created a barrier between the river and its wildlife and those that live and work alongside.


The dams and culverts have been designed to ensure they do not prevent the movement of fish and mammals up or downstream. The base of the culverts incorporate baffles and boulders to ensure a varied flow pattern and to retain a minimum depth of water for fish passage in low flows.


The flood storage areas were used to enhance biodiversity through the creation of artificial wildlife habitats, woodland, scrub, and over 90,000 m2 of species-rich wet grasslands, shallow scrapes and ponds.


Wildlife


The scheme has been responsible for new habitat creation. The wet grassland at Kirkland with its pond and scrapes, has proven popular with a wide variety of different birds including swallows, sand martins, various geese species, plover, oystercatcher and lapwings. As well as species which are less common in the UK, as a whole, but which are flourishing along the White Cart. These include the dipper, kingfishers and grey wagtails. An artificial sand martin wall, with nest tunnels provided, was built at Kirkland Bridge and has been successful in encouraging the sand martins back to the area. Artificial otter holts were constructed attracting otters and bat boxes and Dipper nesting boxes have also been extremely effective.


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