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Strategic Environment Assessment -Environment Objectives

Environment monitoring report

Project Overview 1&2

Project Overview 3&4

Construction Display

CAD and GIS

Hydraullic model

Geology

Engineering Solutions

Piling removal

Erosion monitoring

Condition monitoring

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The Project

What is the BFAP?

The Broadland Flood Alleviation Project (BFAP) is a long-term project to provide a range of flood defence improvements, maintenance and emergency response services within the tidal areas of the Rivers Yare, Bure, Waveney and their tributaries.

Appointed by the Environment Agency Broadland Environmental Services Ltd deliver these services and, in partnership with the Agency, it is now implementing the 20-year programme of works.

This contract was awarded in May 2001 as a Public Private Partnership Programme, and is the first of its kind to provide flood defences on this scale.

The Project area

Situated in East Anglia, Broadland is one of the finest areas of wetland in Britain. It includes both open water ,The Broads themselves, and the low-lying marshland surrounding the tidal reaches of the River Yare, The Waveney, Thurne, Ant, Chet and the Bure. The rivers reach the sea at Great Yarmouth

For many centuries, the rivers of Broadland played an important role transporting goods and equipment for trade and industry. Today, Broadland is still busy, although in a different way. Fifty percent of the land is given over to traditional farming with the remainder being used for residential, industrial, commercial and conservation purposes.

 

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The rivers remain a major inland navigation, which, together with the Broads, provide access to 125 miles of waterway.

Recreation and tourism have become very important, with thousands of holiday makers visiting each year. In response, the boat hire industry now makes an important contribution to the local economy.

This unique and environmentally sensitive area is home to plants and animals that are found in few other places in Britain. The Project Area contains around 28 sites of Special Scientific Interest. These amount to over 7000 hectares in total, all of which benefit from protection under European Law, either as Special Protection Areas (SPAs) or Special Areas of Conservation (SACs). In 1988 the whole of Broadland was designated as having equivalent status to a National Park.

Conservation bodies own or manage some of these sites but most of Broadland is productive farmland. Much of the land is now used for traditional summer livestock grazing.

Following extensive drainage programmes during the 1970s and early 1980s, moves were undertaken to encourage more sustainable farming practices. Funded by DEFRA farmers are encouraged to undertake Environmental Stewardship (ES) . This is a scheme designed to conserve and enhance the high environmental value of the area via improved farming practices.

Why is flood alleviation needed in Broadland?

Some 240km of floodbanks protect approximately 21,300 hectares of Broadland containing more than 1700 properties of which more than 1000 are residential. Most of the original material used for the construction of these floodbanks was silty clay and as a result many have deteriorated over time.

Combined with changes to river channels many of the banks have become susceptible to seepage and erosion which places them in danger of being undermined and/or subject to breaching. The erosion of riverbanks is caused by wind and waves, boatwash, normal river flows and the action of the tides.

Over time floodbanks settle putting them at risk of being overtopped by even fairly small tidal surges. Sea level rises are officially predicted to be 6mm per annum at Great Yarmouth. The combination of these effects works out to be the same as an average settlement rate of about 25mm/year.

Many areas have been protected in the past by steel or timber sheet piles, much of this was installed between the 1960's-2000 meaning it has come to the end of its natural life.

What are the Project's aims in Broadland?

The main aim of project work has been to strengthen existing flood defences and restore them to a height that existed in 1995 (a level defined by the Environment Agency) and make additional allowances for sea level rise and future settlement of the floodbanks. The Broadland Flood Alleviation Project works will not prevent all future flooding as land that flooded in 1995 will still be subject to periodic flooding at the end of the Project.

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The project must carry out the major improvements within the first 12 years of its work and maintain the improved system for a further 8 years. Beyond the end of the Project the flood defence improvements must have a further life of 7 years. The improvement works are being implemented through a phased programme through:

bulletStrengthening the existing floodbanks, restoring them to agreed levels where excessive settlement has occurred
bulletReplacing existing erosion protection that is in a poor condition using more environmentally acceptable methods wherever possible
bulletProviding new protection where erosion is currently threatening the integrity of the flood defences
bulletCarrying out works at undefended communities

These improvements are maintained by:

bulletMonitoring crest levels (height of the floodbank) and raising banks again (crest raising) in places where further settlement has
taken place;
bulletMonitoring the condition of existing and any new erosion protection and extend or replace if necessary.

How will the project achieve its aims?

Within the contract the solutions available to the Project are:

Floodbank strengthening

This is usually used where there is still a good band of rond between the river and the floodbank.

It involves strengthening the existing floodbanks in their present locations by putting material on the back and/or front slope.

The crest (top of the floodbank) is also raised to provide the agreed 1995 level. The increase in height can be between approximately 30-40 cm depending on how poor they are when compared to 1995 standards.

Floodbank setback

This is usually used where the river is already hard up against the floodbank and the flood defence is protected by erosion protection, such as piling. This solution involves building a new clay floodbank inland from the river edge with the floodbank set back far enough from the existing line of flood defence so that a new rond can be created and natural vegetation established. The existing erosion protection will then be removed once the new floodbank is in place and the new rond has become established.

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Floodbank rollback

This solution is similar to setback, however, the distance the floodbank is moved inland is considerably less (dependent on position of existing soke dyke, ground conditions and width of folding).

It is the preferred solution when rond/erosion protection is insufficient to allow for just bank strengthening and where ground conditions do not permit full setback.

Erosion protection

Floodbank erosion protection is used in various locations to stabilise the floodbanks and the edges of the rond. Several types of erosion protection can be used depending on local circumstances these include asphalt matting, coir (coconut husk) rolls or matting, alder poles, reed based products and new sheet metal piling. Wherever possible the material required is found locally, e.g. by widening existing soke dykes close to where work is being carried out; by creating new marsh dykes or by using stockpiled, or new, dredgings.

Hydraulic model

A computer model of the Broadland river system has also been developed using detailed survey information of river channel shape, bank height etc., as well as predictions of sea-level rise. This hydraulic model is used to determine what effect, if any, a particular scheme of works might have on water levels, flows and the frequency of flooding in any other part of the Project area. It is an important tool to help the project decide exactly what to do, where and how their programme of works should be phased and to test other options, e.g. informal washlands. The predictations made by the model have been thoroughly checked throughout the Project and has proven to be extremely accurate.

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Project budget

Another important aspect of the project is that it is cost limited. This cost ceiling means that all individual schemes within the project have to be strictly designed to be cost-effective and within the planned programme. Any excessive spending in one area will result in a shortfall elsewhere. With careful management the Project hasl improved the area security against flooding and significantly reduced the risk of damage to the Broadland environment as a whole.

 

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