Hebridean Coastline
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What's Happening Now?

South Ford Hydrodynamics Study

Work on the hydrodynamics study is now complete with field work and computer modelling already having been completed. The study consists of a number of sections of work and is undertaken in stages. Some of this work has been carried out by contractors with other sections being done by Joint Client Group member organisations.

A public meeting was held on 23 November 2011 in Iochdar, South Uist where the results and findings of the South Ford Study were presented to members of the local community. The presentation can be found by clicking here.

Survey work

Trimble 5800 GPS Survey SystemOn-site survey work has been undertaken by staff from the Aberdeen Institute for Coastal Science and Management at Aberdeen University as the first stage in acquiring the present day Digital Elevation Model (DEM). This was carried out using a Trimble GX 3D (terrestrial LiDAR) advanced surveying and spatial imaging sensor that uses high speed laser and video to capture millions of coordinates and image data Trimble GX3D Terrestrial Laser Scannervery quickly.To ensure the survey data was accurately located, ground control points were fixed using two Trimble 5800 GPS receivers. This equipment was also used to survey the more level areas of South Ford.To integrate all of the above described datasets, they need to be geographically referenced in the same coordinate system and this will be the standard British National Grid generally adopted for Scottish surveys.

Measuring changes (part 1, part 2)

The objective of constructing two Digital Elevation Models dating present day and from 1984 is to undertake a comparison and to measure the change which has taken place in the South Ford since the causeway was built. Powerful computer software, BAE Socetset, has been used to produce the 1984 DEM from the aerial photos. Since both DEMs are in digital format, they can be compared in 2 and 3 dimensions to enable changes in the South Ford to be analysed. This has been done using Geographical Information System (GIS) software and has produced both comparisons of changes in the volume of sand in the South Ford, and changes in location of shoreline – erosion and accretion.

Change map
Sediment analysis & dating

Another important aspect of the study is to determine the rate over time and the composition of sediment or sand which forms the bed of the South Ford. Samples of sediment have been taken by coring into the seabed and the resulting cores have been analysed in Dundee. This was done to establish how quickly sand is building up and where this sand is coming from so that trends can be determined for future years.

Hydrodynamic modelling

The flooding observed during the January 2005 storm was a result of extreme conditions in tide height, storm surge level and wave set-up. A hydrodynamic modelling system has been developed that includes the simulation of all three processes. This model is used in various configurations for three modelling tasks, which are:

1. To determine the change in hydrodynamic behaviour due to the construction of the causeway and subsequent sediment build-up.

2. Examine the impact of various scenarios of erosion in Gualan Island on hydrodynamic behaviour.

3. Assess how continuing sediment build-up and barrier island erosion may affect local hydrodynamic processess after 20 years.

Flood risk assessment

Assessments of past flooding have been made which involved people living on the coasts of the South Ford and learning from their experience of past storms. Research has been undertaken on daily air pressures going back to 1869 and from these an analysis made of past storms. Using computer visualisations from the scenario models and local knowledge, consideration is being given to future flood risk which will form the basis for how these risks can be managed.

People were asked to answer a few questions and encouraged to give their opinion on storms and flooding and how these affect them. A public consultation meeting was held during November 2011 to gather information and to present the findings of the study. Local residents were encouraged to provide relevant comments on the findings of the Study and these, together with comments made at the public meeting, have been incorporated into the final Study Report.