Kyle of Durness - Marine Litter Study

This computational fluid dynamics (CFD) study of marine plastic distribution around Cape Wrath was carried out in collaboration with colleagues at plastic@bay, based near Balnakeil on the Kyle of Durness.
 

7-days of SW wind are modelled followed by a 3-day storm coming from the NW.

The initial background particle distribution in the sea was 20 particles per km^2 [1]. The particles were spherical of 5 cm diameter and density 970 kg/m^3.

A combination of coastal topology, tides, Earth spin and change in wind direction show a growing cluster of plastic off Cape Wrath which is transported into the Kyle of Durness in more substantial quantities on the back of the NW storm wind.

The model predicts an average daily plastic amount arriving on Balnakeil beach of 5.1 kg over the first 7 days of SW wind. This rises to 8.5 kg over the following 3-days of NW storm.

These results are in reasonable agreement with the observations of plastic@bay before and after the storm [2].

The CFD model also predicts similar plastic deposit levels on remote beaches such as Sandwood and Eoropaidh on Lewis.

Figures 4 and 5 show the concentration of marine litter (particles per m^3). Two cases were considered: a weak 4 mph wind and a stronger 20 mph wind. In both cases there were 11-days of SW wind followed by 9-days of NW wind. The initial particle concentration was 20 particles per km^2 with each litter particle 5 cm dia and density 970 kg/m^3.

For the 20 mph wind case, the competing effects of wind, tides and earth spin combine to generate a cluster of litter debris off Cape Wrath. This cluster is then driven on North coast beaches such as Balnakeil on a NW wind.

References:

[1] Turrell, W. R. (2020) Estimating a regional budget of marine plastic litter in order to advise on marine management measures, Marine Pollution Bulletin, https://doi.org/10.1016/j.marpolbul.2019.110725.
[2] https://www.plasticatbay.org/2020/03/19/balnakeil-pollution-report-15-03-2020/?v=79cba1185463

List of Figures:

Fig. 1: 7-days of SW wind.

Fig. 2: Focus on the vicinity of Balnakeil.

Fig. 3: 7-days of SW wind followed by NW storm wind.

Fig. 4: Weak wind study: 11-days of SW wind at 4 mph followed by 9-days of NW wind at same speed.

Fig. 5: Strong wind study: 11-days of SW wind at 20 mph followed by 9-days of NW wind at same speed.

Ballater Flooding 2016
Fig.1 - 7 Days of SW Wind
Ballater Flooding 2016
Fig. 2 - Focus on Kyle of Durness

Figure 1 Flood prediction using commercial code.

Ballater Flooding 2016
Fig.3 - Effect of NW Storm Wind
Fig. 4 - Litter concentration - weak wind study
Fig.4 - Litter amount - weak wind study
Fig.5 Litter Amount - strong wind study