Isle of Wight Council Coastal Management
Coastal Cliff Instability Problems on the Isle of Wight
Peter Marsden Principal Coastal Engineer Simplified geology of the Isle of Wight Landsliding at Woodside, Wootton Cliff fall at Bembridge Cliff falls in Sandown Bay Cliff falls in Sandown Bay Cliff falls in Sandown Bay Cliff falls in Sandown Bay Cliff falls in Sandown Bay, last Sunday Cliff talus failure, Shanklin Remedial measures – cliff top trimming / battering Installation of rock bolts and netting behind property Installation of rock bolts, shuttering and netting below property
Remedial measures – Rock catch fencing Remedial measures – Improved drainage Remedial measures – Warning Signs Cliff Stabilisation – risk reduction
• Removal of undermined rock slabs or overhanging buttresses • Cliff top trimming or re-profiling • Removal of talus at the cliff base • Installation of timber shuttering • Installation of rock bolts and netting • Improved cliff top drainage • Construction of rock catch fencing • Placing of warning signs • Prevent inappropriate development adjacent to the cliff, either top or bottom • Copparding or removal of trees • Vegetation control or removal
Sandown Bay –Failure of existing cliff stabilisation Clean face and install grouted rock anchors Attach geotextile and netting Construct new timber shuttering Fill void with light weight fill, compacted in layers Top off with topsoil And re-open Landslide and ground movement at Bonchurch Chalk cliff fall at Bonchurch The Isle of Wight Undercliff 1991 Department of the Environment study of Ventnor
• Ventnor identified as the largest urban development in an area of active landsliding • Reviewed existing database on landsliding • Undertake field investigations • Develop landslide model • Develop a set of maps for use by planners, developers and landslide managers, covering Land Use, Geomorphology. Ground Behaviour and Planning Guidance 1991 Department of the Environment study of Ventnor
The maps used the Ordnance survey base map and then over- layed the site mapping to produce the relevant plans. The maps and the digital database are still in use today. The report recommended installation of ground movement monitoring. Ventnor Cross Section Ground movement monitoring in the Undercliff Automatic weather station to provide rainfall data Landslide Susceptibility to Rainfall Annual GPS monitoring in central Ventnor Annual GPS monitoring in central Ventnor
Monitoring equipment on the Isle of Wight
• Inclinometers, up to 150m deep • Tiltmeters • Extensometers • Crackmeters • Piezometers • Standpipes • Weather station • GPS point network
In total nearly 200 pieces of equipment
DEFRA funded schemes involving slope stabilisation
Wheelers Bay, Ventnor, 2000 - £1.5M, rock revetment with upper slope stabilised using 14.5m long soil nails DEFRA funded schemes involving slope stabilisation
Castle Cove, Ventnor, 1994
£2.6M, 230m rock revetment, Slope stabilised with an array of no fines concrete shear drains, up to 6m deep DEFRA funded schemes involving slope stabilisation
Castlehaven 2003 - £6.5Million, 650m rock revetment, 170 siphon wells, Landsliding along Undercliff Drive, Niton Landsliding along Undercliff Drive, Niton Landsliding along Undercliff Drive, Niton
Taken yesterday Coastal erosion on the SW coast
Around 1900 ChaleChale TerraceTerrace #5 Coastal erosion on the SW coast
2013
ChaleChale TerraceTerrace #5 Coastal landsliding - Brook Landsliding at Compton Coastal cliff instability at Afton Down – A3055 Coastal cliff instability at Afton Down – A3055 Coastal cliff instability at Afton Down – A3055 Totland landslide – Started Christmas 2012, still moving Totland coastal landslide Totland coastal landslide – Seawall position Totland coastal landslide – CCO Laser survey
Coastal slope instability at Yarmouth Cowes to Gurnard Coastal Instability Study Geomorphology Ground Behaviour Planning Guidance Managing coastal slope instability
• Improve ground conditions by installing slope stabilisation or construction of coastal defences / toe weighting. • Preventing or reducing water leakage into the ground. • Preventing inappropriate development through planning process. • Improving building standards. • Control of construction activities. • Encouraging property owners to undertake repairs and maintenance. • Monitoring ground movement and antecedent weather conditions.
Thank you