A barrier would do the job, but it may be too dear

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From Terry Thuillier.

I REFER to the proposal for a tidal barrage in St Aubin’s Bay as reported in the JEP on 9 January.

I was initially surprised at the size of the proposed scheme, as I imagined a barrier going directly from Noirmont Point to the end of Elizabeth Castle breakwater – a straight line distance of 3.4 km. However, the proposed scheme shows a horseshoe-shaped barrier extending 3 km to the south-east of Noirmont and then returning north to the Elizabeth Terminal – an overall distance of just over 8 km.

While I appreciate that this doubles the area of the basin and the resulting potential for power generation, I would seriously question the cost of such a barrier and, therefore, the economics of this proposal. The highly successful Rance barrier has a similar tidal range, capacity and power output (240 mw) to that proposed for St Aubin’s Bay, but unlike St Aubin’s Bay it has several distinct advantages – it is a short barrier, it is in a sheltered location and as a bonus it provides an important road link.

While I hesitate to make direct comparisons, as the situation and construction methods would be very different, the fact remains that the Rance barrier is only 750 metres long, compared with 8 km, or at best 3.4 km, for St Aubin’s Bay. This means that the ratio of basin area to barrier length is not very encouraging.

I would guess that by far the greatest cost of the St Aubin scheme would be in the barrier itself, perhaps as much as 80 per cent. The remainder would be in the caissons housing the turbines, locks and sluices, etc.

The exposed nature of the St Aubin barrier would mean that it would not be maintenance-free and severe storms may necessitate remedial work to the outer boulder armouring. Alderney breakwater is an extreme example of this. While the resulting enclosure would no doubt provide some additional marine leisure benefits, a public road on top of the barrier would not be of any real benefit and would not easily link up with the Noirmont headland and could possibly be detrimental to the natural beauty of the area.

At low tide, the barrier would also not be very attractive, especially on the sea approaches/gateway to St Helier and would possibly compromise Elizabeth Castle’s unique setting. The proposed Severn barrier has been extensively studied and costed in great detail. The present-day cost is estimated at £13 billion for a barrier length of 16 km, resulting in a huge basin area of 185 square miles and a generating capacity of 8,640 mw.

This is massive by comparison, but sections of this barrier would possibly share many features with that required for the St Aubin’s Bay scheme.

I would therefore suggest, if not already carried out and before embarking on extensive geological sea-bed surveys, that a detailed study be carried out on comparative costings for the barrier, which I believe may show this bold and imaginative scheme to be too costly for the power generated.

On a more positive note, the proposed tidal current turbines for the Alderney Race look very promising. While admittedly they may not be in the same league as tidal barriers and may not cater for all our energy needs, they do not require massive structures and are just fixed to the sea bed.

These, I believe, have the potential to make a very significant and cost-effective contribution to a Channel Island grid with the bonus of minimal environmental impact.

La Niche,

Rue de Samarès,

St Clement.

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