The Dynamic Coast at Montrose Bay

The coast is highly dynamic. A particular beach-dune system can show extensive change in just a few hours as a result of a single storm so the extent of change in a coastal landscape over the course of a human lifetime can be remarkable. These changes reflect the sensitivity of the coastal margin to changes in climate, sediment supply, sea level and, particularly over the last century, human activity (Hansom & Rennie, 2004).

Having experienced widespread and dramatic change in recent decades, Montrose Bay is a particularly good example of a dynamic coastline. Since the 1980s there has been persistent beach-dune erosion at the southern end of the bay. This has most notably resulted in 10s of meters of shoreline retreat in the dunes fronting the Montrose Medal Links golf course. The unstable, scarped dunes at this location are a signature of this on-going erosion.

Cliffed dunesScarped Dune_Mar10

Meanwhile, towards the northern end of the Bay at St Cyrus, the beach has been gradually building up over the same period of time. This has resulted in the development of a healthy and growing dune belt in sharp contrast to that in the south.

View north from St Cyrus (2)St Cyrus dunes and relict cliff line

What has caused this pattern of coastal change? At any given site there is normally a range of contributory factors to erosion, both natural and man-made. However, in exposed, sandy coastal systems such as Montrose Bay, the wave-driven transport of sediment along the beach, known as longshore drift, usually exerts an overriding control on erosion and accretion. Thus, in recent years a dominant northward transfer of sediment in the bay via longshore drift has resulted in the current trend of erosion at the south of the bay, and growth in the north.

There is an old adage used in coastal geoscience which sums up perfectly the influence of longshore drift on shoreline evolution: one beach’s loss is another beach’s gain. This certainly rings true for Montrose Bay!

Reference

Hansom, J.D. & Rennie, A.F. 2004. Establishing the rate and sense of medium term coastal changes: St. Cyrus, Scotland. Littoral 2004. 20-22 September. Aberdeen. Scotland.

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Posted in Photos, Science

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