2.7.0 Physical Processes
2.7.1 Background
The Medina Estuary is the product of the flooding of a pre-existing narrow, and relatively deep, river-eroded valley caused by sea-level rise during the past 10,000 years, following the last glacial period. The estuary as we see it today has been formed by the physical processes associated with the coast, the hydrography and hydraulic regime of the estuary and surrounding areas and the associated sediment transport or accretion.
The estuary is tidal with the River Medina, which flows from St Catherine's Down, making a very small contribution to both water volume and sediment transport within the estuary. Cowes Harbour and the upper estuary are influenced by the high energy conditions which result from coastal waves, currents and the tidal regime, which declines rapidly inland. As hydraulic gradients weaken, sediment mobility diminishes and marine influences, in general, become weaker. As a result, over several millennia, there has been a net input of sediment into the estuary.
The hydraulic regime of the Medina Estuary may be regarded as substantially natural with local modifications due to waterfront development, the dredging of the main channel and the installation of protection structures.
Erosion: Erosion of the banks and saltmarshes adjacent to the estuary is variable, but is occurring predominantly within the middle and upper reaches of the estuary. Some sites are known to have been receding progressively since the 1940s. Preliminary examination of aerial photography indicate approximate losses of between 5 and 17 metres since the mid to late 1960s. The cause of the erosion is unknown and will require investigation to substantiate the cause.
Flooding: Flooding is of concern in the urban areas of Cowes, East Cowes and Newport. A recent assessment of the vulnerability of low lying areas of Cowes has determined that flooding is due to the combination of high tide levels and rapid run off from steep slopes above the settlements. Flooding events in Newport are related to high tides.
Shoreline Protection: Shoreline protection in the estuary consists of concrete and timber walls, piers, quays and pontoons. Continuous defences exist within the urban areas and sections of the middle reaches are protected by defence structures. The main protection feature within Cowes Harbour is the breakwater which primarily reduces the input of sediment derived from the shrape mud and other sediment sources within the Solent and has contributed to the stable channel configurations within Cowes Harbour. A variety of options have been considered for improvements to the breakwater.
Dredging: Maintenance dredging is undertaken in Cowes and Newport Harbours by the Harbour Authorities for navigation purposes and amount to approximately 10,000 tonnes and 2,000 tonnes per annum respectively. Dredging of wharves and marinas also occurs depending upon need. The effects of dredging on the physical dynamics of the estuary require further research.
Regulation: Sea defence is the responsibility of the Environment Agency (EA) under the 1991 Land Drainage Act which empowers the EA to construct defences to protect low lying coastal land from flooding. The Isle of Wight Council is responsible for coastal protection under the 1949 Coastal Protection Act which empowers the Council to construct defences against erosion in consultation with all interested parties. Dredging is regulated by Cowes Harbour Commissioners (CHC) in CHC jurisdiction and by Isle of Wight Council in the jurisdiction of Newport Harbour.
2.7.2 Issues
2.7.2.1 Knowledge and understanding of the Physical Processes
Knowledge about the physical processes within the estuary is limited. Historically, data has been generated by specific and relatively short-term requirements. Longer-term co-ordinated monitoring of almost all aspects of the physical environment of the Medina is absent, making accurate description difficult and evaluation highly problematic. Requirements include the need for investigation into:
• suspended and bedload sediment transport within the estuary and along the adjacent coast;
• sediment budget;
• the tidal regime of the estuary;
• the impact of dredging;
• erosion; and
• sea level rise.
In 1999 ABP Research & Consultancy Ltd. commenced work to analyse the bathymetric changes in the River Medina. To be completed in March 2000 this study will improve the understanding of the ebb / flood dominance of the system and will aid decision making for dredging applications.
Further research in the estuary includes the possible support from 2 EU LIFE bids.
2.7.1 Background
The Medina Estuary is the product of the flooding of a pre-existing narrow, and relatively deep, river-eroded valley caused by sea-level rise during the past 10,000 years, following the last glacial period. The estuary as we see it today has been formed by the physical processes associated with the coast, the hydrography and hydraulic regime of the estuary and surrounding areas and the associated sediment transport or accretion.
The estuary is tidal with the River Medina, which flows from St Catherine's Down, making a very small contribution to both water volume and sediment transport within the estuary. Cowes Harbour and the upper estuary are influenced by the high energy conditions which result from coastal waves, currents and the tidal regime, which declines rapidly inland. As hydraulic gradients weaken, sediment mobility diminishes and marine influences, in general, become weaker. As a result, over several millennia, there has been a net input of sediment into the estuary.
The hydraulic regime of the Medina Estuary may be regarded as substantially natural with local modifications due to waterfront development, the dredging of the main channel and the installation of protection structures.
Erosion: Erosion of the banks and saltmarshes adjacent to the estuary is variable, but is occurring predominantly within the middle and upper reaches of the estuary. Some sites are known to have been receding progressively since the 1940s. Preliminary examination of aerial photography indicate approximate losses of between 5 and 17 metres since the mid to late 1960s. The cause of the erosion is unknown and will require investigation to substantiate the cause.
Flooding: Flooding is of concern in the urban areas of Cowes, East Cowes and Newport. A recent assessment of the vulnerability of low lying areas of Cowes has determined that flooding is due to the combination of high tide levels and rapid run off from steep slopes above the settlements. Flooding events in Newport are related to high tides.
Shoreline Protection: Shoreline protection in the estuary consists of concrete and timber walls, piers, quays and pontoons. Continuous defences exist within the urban areas and sections of the middle reaches are protected by defence structures. The main protection feature within Cowes Harbour is the breakwater which primarily reduces the input of sediment derived from the shrape mud and other sediment sources within the Solent and has contributed to the stable channel configurations within Cowes Harbour. A variety of options have been considered for improvements to the breakwater.
Dredging: Maintenance dredging is undertaken in Cowes and Newport Harbours by the Harbour Authorities for navigation purposes and amount to approximately 10,000 tonnes and 2,000 tonnes per annum respectively. Dredging of wharves and marinas also occurs depending upon need. The effects of dredging on the physical dynamics of the estuary require further research.
Regulation: Sea defence is the responsibility of the Environment Agency (EA) under the 1991 Land Drainage Act which empowers the EA to construct defences to protect low lying coastal land from flooding. The Isle of Wight Council is responsible for coastal protection under the 1949 Coastal Protection Act which empowers the Council to construct defences against erosion in consultation with all interested parties. Dredging is regulated by Cowes Harbour Commissioners (CHC) in CHC jurisdiction and by Isle of Wight Council in the jurisdiction of Newport Harbour.
2.7.2 Issues
2.7.2.1 Knowledge and understanding of the Physical Processes
Knowledge about the physical processes within the estuary is limited. Historically, data has been generated by specific and relatively short-term requirements. Longer-term co-ordinated monitoring of almost all aspects of the physical environment of the Medina is absent, making accurate description difficult and evaluation highly problematic. Requirements include the need for investigation into:
• suspended and bedload sediment transport within the estuary and along the adjacent coast;
• sediment budget;
• the tidal regime of the estuary;
• the impact of dredging;
• erosion; and
• sea level rise.
In 1999 ABP Research & Consultancy Ltd. commenced work to analyse the bathymetric changes in the River Medina. To be completed in March 2000 this study will improve the understanding of the ebb / flood dominance of the system and will aid decision making for dredging applications.
Further research in the estuary includes the possible support from 2 EU LIFE bids.
- EU LIFE – Nature, ‘Living with the sea: Managing Natura 2000 Sites on Dynamic Coastlines’. Funding has been approved for this project
- EU LIFE – Environment, ‘Beneficial use of dredgings in intertidal recharge’. Bid submitted Nov. / Dec. 1999
A North-West Coast Strategy Study has been proposed for the Island and includes the stretch of coast from East Cowes to the Needles. It is hoped to commence by the beginning of 2000, is part grant aided by MAFF, and will provide a framework for the management of the Process Unit over the next 50 years.
The North-East Coast Strategy is aimed to be completed by May 2000 and covers the area from Old Castle Point, East Cowes, to Culver Cliff. Both NW and NE strategies need to recognise the Medina Estuary in its entirety and take on board the policies within the EMP and vice versa.
| Objective P1 To develop a comprehensive knowledge base about the physical processes to inform and facilitate decisions. |
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2.7.2.2 Flooding and shoreline protection
The Isle of Wight Council and the Environment Agency have devoted considerable resources to the monitoring and maintenance of protection structures and the prevention of flooding within the developed parts of the estuary. Maintenance, monitoring and improvement of shoreline protection within the developed areas of the estuary is required. Extensive parts of the estuary, both developed and natural, are in private ownership and protection of certain areas of the estuary is dependent upon the private owner, thereby fragmenting comprehensive coastal protection.
| Objective P2 To ensure the co-ordination of appropriate coastal protection and flood relief. |
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Page last updated on: 04/09/2001
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