Jenny Watts Coastal Process Scientist, Plymouth Coastal Observatory The South West Regional Coastal Monitoring Programme North Devon and Somerset – Woolacombe Dune Study Jenny Watts Coastal Process Scientist, Plymouth Coastal Observatory Hello everyone, so today I am going to talk to you about some on-going work we have undertaken looking at the dune system at Woolacombe in North Devon.

Study Area Located in Morte Bay a NWN facing bay in North Devon, the Woolacombe Warren is an approximately 3 km long dune system owned by the national trust. The dunes are sandwiched between the beaches Woolacombe and Putsborough Sands and Woolacombe Down. The dunes are considered an important habitat and sits within the North Devon Coastal AONB. For all three shoreline management epochs the proposed plan for the site is No Active Intervention, leaving natural processes to continue. However, dune management is still undertaken as necessary to address any issues relating to damage resulting from recreational pressures. As a result, loss of the dunes through erosion is expected – however it is still important to monitor the rate.

Study Aim Aim: Assess long-term changes to the dune and beach morphology at Woolacombe Analysis includes: Profile volume changes Topographic difference models Beach volume changes Dune toe position Storm event identification and energy analysis Extreme water level analysis The aim of this study was to evaluate the morphological long-term changes occurring within the dune system. In order to do this a range of different analyses were undertaken, including profile volumes, topographic difference models, beach volume changes, dune toe assessments and assessment of hydrodynamics including storm and extreme water level event analysis.

Aerial LiDAR Covered by five LiDAR flights since 2007 Accuracy of 10-15 cm in the vertical and 40 cm in the horizontal Date Organisation Resolution Coverage 15/03/2003 EA 2m Full to MLW 29/09/2007 SWRCMP 1m Full to MLWS 09/03/2009 17/09/2009 20/06/2014 23/02/2016 As part of the SWRCMP we fly aerial LiDAR surveys, these are currently flown on a two-yearly basis. At Woolacombe we have six sets of LiDAR covering the area, with another set being collected this flying season. This is of huge benefit for sites which also do not currently receive RTK-GPS topographic surveys, such as Woolacombe. While the accuracy of the data is lower and the interval between surveys is larger, LiDAR data is still key in enabling us to monitor processes over the long-term and effectively fill in gaps within out regular topo schedule.

Hydrodynamics – Storms and Extreme Water Levels The nearest Wave Buoy at Bideford began recording in 2009. I extracted all the events during which the storm threshold was crossed, and plotted them according their energy level as shown in the top graph. These indicate that, as expected, winter 2013/14 represents the most energetic winter for this period with significant storm clustering as well as the single highest energy event. Extreme high water level has been assessed, and shows extreme events where levels exceeded a 1-in-1 year water level, with events over 5.3 m shown in red. These also indicate that a cluster of extreme height water level events above 5.3 m occurred during winter 13/14. To further improve these results it would be key to assess storm direction.

Topographic Difference Models – 2007 to 2016 2007 - 2016

Topographic Difference Models – 2009 to 2014 2009 - 2014 In light of the hydrodynamics, this first topographic difference model shows the difference in beach levels experiences. A central band of erosion is apparent across the beach foreshore, as well as a more focused strip of erosion across the dune frontage. Evidence of dune roll-back and accretion can also be seen towards the area of dune to the north of the dune complex.

Dune and Beach Zones Dune Backshore Foreshore To further assess morphological changes, the system was split into three areas – the dune system, backshore and foreshore using defined tidal levels. The toe of the dune was taken to occur at around the point of the highest astronomical tide as has been observed in other study sites.

Beach Volume Analysis

Profile Analysis

Profile Volume Analysis

Dune Toe - Contours Say what I have used - HAT

Dune Toe Position Changes – 2009 to 2016 Show where these profiles are

Human Impacts – Pathway Erosion

Discussion and Conclusions Results: Erosion was the predominant process between 2009 to 2014. This corresponds with the increased storminess experiences during Winter 2014/14. As whole, it is the beach foreshore that has undergone the most erosion while the dunes appear to have stabilised. Analysis: LiDAR data is a useful tool for assessing dune stability It is particularly useful in areas not covered by the SWRCMP’s topographic survey schedule The automated processes used in this analysis (e.g. toe position identification) could be easily used over both large and small study areas

Thank you for listening – any questions?