Further evidence of dredging induced coastal erosion

Tyndal Working Paper 97 of December 2006 authored by Mike Walkden and P.K. Stansby, entitled ‘The effect of dredging off Great Yarmouth on the wave conditions and erosion of the North Norfolk Coast’ (including all references). It is a research paper by the Crown Estate, prepared in conjunction with ABPMer, British Geological Survey and HR Wallingford.

The reference for this paper is : 2008 Report by The Crown Estate ref: Cooper, W.S., Townend, I.H., and Balson, P.S. (2008); A synthesis of current knowledge on the genesis of the Great Yarmouth and Norfolk Bank Systems. The Crown Estate, 69 pages, February 2008. ISBN: 978-0-9553427-8-3.

Website link:
www.thecrownestate.co.uk/media/5745/gy_norfolk_bank_systems.pdf .

Content

It is a detailed paper study containing a plethora of historical data and information relating to the tide and sand movement, rich in charts and diagrams, although rather thin on actual empirical evidence. It explains the otherwise apparent anomalies of the currents and tides around the Norfolk offshore sandbanks through history, and may be downloaded from www.tyndall.ac.uk/sites/default/files/wp97.pdf

Strangely, the research paper concludes with ‘No significant difference was found in the nearshore wave climate or the shoreline erosion due to the dredging scenario’ which you will be aware are certainly not MARINET’s findings who, backed by much existing scientific evidence have long opposed the granting of marine aggregate dredging licences off the East Anglian coastline. We are now able to show this further evidence of the link between offshore aggregate dredging and coastal erosion given within this study, the very opposite of the rather strange conclusion reached and given at the termination of this paper. Perhaps that was more political than scientific.

MARINET also intend to bring this to the attention of the Marine Management Organisation (MMO), who have long claimed that there is no coastal erosive impact due to offshore aggregate dredging, and readily pass each and every application for a dredging licence in this area off our East Anglian coastline.

This Crown Estate paper describes the rather complex details of the offshore banks and the current state of knowledge on their formation and movement, and its findings do in fact establish the link between offshore aggregate dredging and sandbank and coastal erosion, as evidenced by the following extracts:

3.5.3

“The Great Yarmouth Banks lie sub-parallel to the modern Norfolk coast. The most nearshore of these banks appear to be attached to the shore-face at the location of small headlands, known locally as nesses. Thus, Caister Shoal extends northwards from Caister Ness, and Holm Sand is attached to Lowestoft Ness. The nearshore banks are smaller, much more closely spaced and are generally set much higher in the tidal frame (and are in places inter-tidal) than the more offshore banks. Banks are between 4 and 15km long, 1.5 to 3km wide and are mostly between 10 and 20m high above the surrounding sea floor. Sandbanks such as Holm Sand and Scroby Sands may have much shallower depths on their landward margins than on their seaward sides which are prone to breaking waves. The nearshore banks such as Scroby Sands are within 2 to 3.5km of the modern coastline”.

MARINET’s Comment: That extract establishes the physical connection between the near shore banks (e.g. Scroby Sands, close to the dredging sites) and the actual coastline. The migration of sand from the coastline is going to these sandbanks. Hence, as we have erosion of these offshore sandbanks due to aggregate dredging, we have a direct link to coastal erosion itself. The paper gives evidence of a dynamic link between the inner sand banks and the outer sand banks i.e. a transfer of material.

The Crown Estate paper further states:

3.8 Great Yarmouth Banks Formation

“Another notable feature of the Great Yarmouth Banks is that they are interlaced with flood and ebb channels, as identified by Robinson (1966). Two features are particularly notable. First, the main flow direction is west north west to west south east along the North Norfolk coast to the north of the Great Yarmouth Banks and north north east to south south west along the Suffolk coast to the south. Consequently, the location of the Great Yarmouth Banks is a turning point for the tidal flow. Secondly, the ebb and flood channels cut through the banks at relatively regular intervals, forming what appears to be a series of meandering channels that cross each other at each end of the bank”.

MARINET’s Comment: Here we are shown the sand wave travel route and the route method of migration of coastal and inshore sands to offshore sites.

The following observation is made by models which seek to explain offshore sand bank formation:

5.1.4 Model 1.4

“The Great Yarmouth Banks are a sink for cliff erosion that is transported to the area by littoral drift and nearshore residual drift”.

MARINET sees that there is substantial evidence in this report showing that coastal erosion is linked to aggregate dredging. Increased wave height due to reduced sand banks (greater depth of water allowing larger waves to form) is working in conjunction with the pits remaining following offshore dredging which are being in-filled by sand from adjacent sandbanks which in turn are linked to each other in a serial chain which ultimately leads back to the coast. Thus sand eroded from the coast is ending up in dredged sites, aided and abetted by a process that demands sand in order to replace the sand that has been excavated and removed.

This issue has heightened in importance as we are now seeing much serious damage from rapidly escalating erosion over coastal East Anglia by way of the loss of coastal housing, nature sites, tourist amenity, popular seaside beaches and coastal sited trade, enhanced due to the denial of sea defence funding and the restrictions on these imposed by the Shoreline Management Plan.

MARINET will again ask the MMO to include in the EIA/EA a requirement for a sand tracking survey using fluorescent granular beads or sand granules labelled with a short lived isotope scattered along the low tide line, such as was employed for a survey hosted by Lancashire County Council when they lost half-an-inch of sand from Blackpool beach. Similar research was performed in the USA. Both found it in the landed sand from the dredgers. Such a study would surely prove the point. Much of our East to North East beach has lost over 100 times this!


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