Example the River Tyne CFMP

The Tyne is a catchment in north-east England containing two main tributaries, the Rivers North Tyne and South Tyne, and a number of small streams (Fig. 16.8). The lower reach of the main River Tyne and short sections of its smaller tributaries, the Ouseburn, Team and Don, are tidal. Upstream of the tidal reach the topography and river channels are steep. The catchment is made up of sedimentary carboniferous rock overlain by relatively impermeable glacial sediments. Soils in upland areas are generally peaty with good water retention properties but their overall effect on runoff is complex.

Over three-quarters of the Tyne catchment is rural. Arable farming is limited to small areas of available floodplain. Most upland areas are managed grasslands. Urban and commercial areas are concentrated in the lower reaches of the catchment with Newcastle and Gateshead having a population in excess of 900 000. The catchment relief is predominantly steep slopes. With its shallow soils and short contributing streams, this leads to high runoff rates and rapid flood travel times, although there is storage and attenuation within the lower floodplains.

16.5.1.1 Current flood risks and management

The catchment has experienced a number of extreme flood events, with most parts of the River Tyne system experiencing flooding at some time. In recent times there have been few instances of significant flooding to residential property. The larger events have generally happened in winter. Snowmelt has contributed to some of the most extreme flood events on record, although it is not a common source of flood risk.

There is a significant number of people and properties in areas mapped as having a 1 per cent or greater annual probability of flooding in the lower reaches of the catchment, especially in Haydon Bridge, Hardaugh near Warden, Hexham, Corbridge, Low Prudhoe/Ovingham and areas of the Tyneside conurbation along the tidal Tyne, Ouseburn, Team and Don rivers. The potential agricultural damages are much less

Fig. 16.8 River Tyne CFMP policy appraisal.

than property damages throughout the CFMP area. Important communication routes cross significant sections of the floodplain within the River South Tyne and River Tyne sub-catchments and are therefore vulnerable to the risk of disruption through flooding. Table 16.5 is a summary of some current indicators of flood risk for the CFMP area. This is expressed in terms of the potential consequences of flooding within outlines that correspond everywhere to the specified annual exceedance probability (AEP). It is important to be aware that these represent notional catchment-wide outlines and not an individual flood event of the given AEP.

Flood risk management measures discussed in the CFMP comprise an extensive flood warning system and lengths of engineered, structural flood defences. Most measures are implemented for the key areas at risk concentrated along the lower reaches of the River South Tyne and reaches of the non-tidal River Tyne. There is about 50 km of flood

Table 16.5 A summary of the consequences of flooding for notional flood outlines of different annual exceedance probability (AEP), River Tyne catchment flood management plan (CFMP) (June 2009)

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