Flood Alleviation

The activity that ranges from the undertaking of major works to reduce the risk of flooding, often to extensive developed areas, to the creation of sustainable urban drainage systems (Suds) to control the risk of flooding to adjacent areas.

Flooding occurs as a result of the over-spilling from channels from high sea/tide levels, uncontrolled flow directly from land (agricultural and developed), or through the surfacing of groundwater.

 

Types of Flooding in the UK

 Various solutions are applied to deal with the ensuing over-spilling, the most readily available being containment, the construction of flood defences, both hard and soft, alongside channels, and/or increasing their flow carrying capacity. In some situations diversion channels, and the creation of floodwater space alongside channels can be the most practical approach. On some smaller catchments the provision of flow attenuation reservoirs may be the best option.


Spurnhead 2014SEA & TIDAL FLOODING can be the most extensive and devastating flooding with the greater potential for loss of life. It threatens the low-lying areas alongside the coast and tidal rivers, many of which, particularly in eastern England extend a considerable distance inland.

 

 

 

 

 

Somerset 2014OVERLAND FLOWS (inland flooding) are the most frequently experienced in the UK and can occur due to exceptional rainfall or rapid snow melt reducing the rate of absorption. Agricultural land is at its most vulnerable when crusted after prolonged dry weather or is frozen.

In urban areas overland flows will occur when the capacity of drainage systems is exceeded.Flooding tends to be localised and of short duration. But such flows can, with more widespread conditions, contribute to major events. 

 

 


groundwater floodingGROUNDWATER flooding occurs when prolonged rainfall causes the water table to rise. Underground aquifers can become surcharged emerging as surface flows. The flows from an acquifer can continue for long periods, such is the lag of the water passing through the underlying permeable rock, due to this the timing of such flooding and it’s duration are difficult to predict. Solutions are based on controlling the emergent flows through channel creation and improvement.

 

 


Alleviating the flood risk 

Various solutions are applied to deal with the ensuing over-spilling, the most readily available being containment, the construction of flood defences, both hard and soft, alongside channels, and/or increasing their flow carrying capacity. In some situations diversion channels, and the creation of floodwater space alongside channels can be the most practical approach. On some smaller catchments the provision of flow attenuation reservoirs may be the best option.

The approach to tidal flooding is the construction of defences in the form of concrete walls, earth embankments and barriers through which the tide can be excluded from tidal rivers.

DATA COLLECTION – of the flood event itself, followed by investigation of the catchment characteristics, its topography and hydrology.

DESIGN – establishing the conditions against which protection should be based, interpretation of the event, modelling, reviewing options, and their costs. The preparation of the specification and tender documents.

WORKS - The engagement of skills and equipment appropriate to the work content. Civil Engineering. Mechanical/Electrical Engineering, Environmental and other specialists, together with the necessary Plant and Equipment.

As with all infrastructure flood alleviation, and the reduction in flood risk is highly dependent on works being maintained to a satisfactory standard. Such maintenance includes that necessary to maintain the flow carrying capacity of channels.

 

Responsible Bodies

With few exceptions flood alleviation works are carried out by public bodies, in particular the,

Environment Agency (England and Wales)
Rivers Agency (Northern Ireland)
Local Councils  (Scotland)
Internal Drainage Boards and Local Authorities (England and Wales)  

Flood protection to individual properties is in the main carried out by the owners of the buildings, although they can form part of a wider, and publicly funded flood alleviation scheme. 

 

 


ffSee the recent Feature from the May edition of Managing Water Magazine on temporary flood barriers. Click the image:

 

 

 



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