Energy and Climate Change CommitteeSupplementary written evidence submitted by Evans Engineering & Power Company Ltd

Matters arising from evidence submitted to the DECC 2013 Committee on 30th January addressing the Tidal Power Projects in the Severn Estuary Currently under consideration.

1. Executive Summary

This documents seeks to counter any claim that the REEF Tidal Concept is unsound from an engineering perspective, and to show that it is superior to all other proposals, in the light of evidence given by the author and others including Hafren Power to the Select Committee. The original “Evans Engineering Concept” considered in a report by W.S.Atkins for the R.S.P.B is still valid, and it is only aspects of “some possible engineering solutions” that have been questioned. The Hafren Power Barrage now uses the REEF bi-directional low-head operating concept, but does not go far enough to mitigate the environmental and commercial shipping impacts. Further, the developers have admitted to the Select Committee that it is not their intention to see the Barrage built, but to sell on the project after three years to a Sovereign Wealth Fund. So my continued objections to the Cardiff to Weston Hafren project are that it is the wrong structure, in the wrong location and the developers are not interested a “Public Participation” in a “Green Legacy Project”.

2. Background

The “Tidal Power Reef”, or the “REEF” was, at the behest of the RSPB, studied by consultants W.S.Atkins.1 The findings of this independent study affirmed the claim that the Reef would do far less damage to the environment than the Severn Barrage and estimated that it could produce as much or more power than a conventional design of Cardiff to Weston Barrage. Lord Porritt, now an official advisor to Hafren Power, said of the new Hafren Power Barrage in an e-mail to my colleague Dr Brian Mathew(18^th January 2013) “as you said in your paper, this proposal is now in many respects closer to the idea of the Reef initially developed by Rupert, and you must be (to a certain extent!) gratified by that” The Hafren Power Barrage however, differs from the REEF in several key respects, resulting in the continued concerns of both environmental and shipping interests. The REEF uses a lower differential head, which in turn reduces the environmental impacts. The lower “solidity” presents less resistance to the tidal flow, smaller change in navigation depth and greater operating flexibility.

3. The Operating System

The Severn Estuary has one of the highest tidal ranges in the world. It is the differential head across the barrage structure and the inherent delay to the natural tidal cycle that causes the difficulties, but reducing this head/delay also reduces the commercial viability of any scheme. It is a fundamental premise of the REEF Concept that the environmental and shipping interests dictate the envelope into which any project fits. The Hafren Power Barrage patently approaches this from the traditional perspective of a commercial project seeking to “Mitigate” any environmental problems. In the case of the highly complex systems that exist in the Severn Estuary, this is not possible. Evidence presented to the Select Committee suggests that providing compensatory habitat with a similar hyper-tidal range and scale would in effect require the construction of another Severn Estuary! Hafren, on their own admission did not even contact Bristol Ports, so could hardly have included their requirements into their engineering proposals.

4. Fish Migration

The REEF system, is a totally new concept, it is based on a relatively light impounding structure spanning the 12-mile estuary that maintains a small but constant head difference between the outer sea level and the inner estuary. The very low head differential totally removes any risk to fish resulting from the pressure change through the turbines. The free discharge of the water is about 6 metres per second and the relative speed of the turbine runner to any fish passing through it, can be significantly lower. Smooth internal passages and the total lack of “pinch points” means that a totally “fish friendly” turbine can be built. There is no reason to believe that a turbine cannot be designed that presents less of a danger to migrating species than a natural river obstruction of the same height such as rapids or a small waterfall. There will undoubtedly be some trade off against power output but there is no other feasible mitigation measure.

5. Navigation

The favoured location for the REEF is between Minehead in Somerset and Aberthaw in South Wales. Others have been considered but this route offers the best power output with the lowest impact, because it is possible to offset some efficiency in favour of lower environmental impacts and easier navigation.

Map showing the proposed location of the Reef in green and the Barrage in blue, this also graphically illustrates the difference of the impounded areas of the two schemes, with the Reef exploiting almost twice the volume of water.

Navigation has always and will continue to be vital to the community and commerce along the Severn estuary. Evidence has been presented outlining concerns over safety and transit times through any structure. Conventional locks would result in different sizes of vessel congregating in a restricted area with consequent dangers of collision or grounding. A REEF structure located much further to the West, has several advantages. Large container ships can be scheduled to pass directly through the REEF during and for an hour or so each side of “slack water”. Should they wish to “lay to” before moving across the REEF, there is ample room in the estuary. If they wish to cross the REEF and “lay to” before proceeding up the estuary, there is also ample room. With a Cardiff-Weston barrage, they simply isn’t enough room for several large vessels to manoeuvre in safety in poor weather conditions.

The navigation structures would comprise two large ship pounds measuring approximately 200 metres in width by a kilometre in length. Controlling gates that do not have to form any watertight seals (because of the low head) would rise (aided by compressed air) from the seabed (similar to the Mose Project currently under construction to protect Venice from storm surges). Even at times when the gates would normally be closed, some ships could pass through without having to tie up or require tug assistance. The evidence of Hafren Power suggests that their design would introduce a delay of 45 minutes or more for a large container ship. Transiting the REEF would only require a reduction in speed or a delay of ten to fifteen minutes.

Above right: how the Reef might look from above, showing how ships could pass through openings in the structure.

The navigation depth will be reduced on account of the energy extracted, but given that the REEF presents very little “parasitic” loss/friction, it would be possible to “free flow” the system when appropriate to achieve the required water depth at Avonmouth. Evidence was given that cast doubt on the economics of “free flowing” or even “pumping” to maintain navigation depths. Since this aspect is of a commercial nature, it is a relatively straight forward procedure to determine whether the cost of a delay is greater than the loss of generation, so compensation is appropriate according to the state of the tide and time of the day. For example, on a particular tide it might be economic to delay generating for an hour in order to coincide with navigation requirements or meeting an evening peak generation requirement. The REEF is thus a more “flexible” and adaptable option than the Hafren Power Barrage.

6. Reef Structure

The REEF is not so much a “power station built in the sea” as a chain of ships or floatable structures sitting on the seabed. The key to reducing both short-term risk and “future proofing” the whole project is flexibility. The Hafren Power Proposal is for a conventional fixed structure with a finite operating system and life. The REEF by contrast is built, maintained and “future proofed” by its modular “demountable” design. Should the operating requirements or technology change over the years, the REEF can change to meet them. Changes in sea level, materials or estuary morphology, may make it necessary to alter or even remove the structure. This is possible with a REEF but very difficult with a conventional barrage.

7. FLOOD ALLEVIATION

Evidence has been heard that suggests that storm surges coming up the estuary will spill onto the Somerset Levels if there is a barrage between Cardiff and Weston, as there is no where else for the water to go. Hafren Power are suggesting an increase in the bund height in Bridgwater Bay, but the capital cost might be better spent on a REEF structure further to the West to stop the problem in the first place. The REEF between Minehead and Aberthaw is better able to offer a buffer to surges and river flooding on account of the larger enclosed area.

8. National Vision

Galvanising the many interested groups and getting the “nation” behind this project is the only feasible way forward. The Hafren Power proposal is in danger of being divisive and out of touch with public opinion. It may increasingly fuel conflicts with environmental groups, shipping interests and the general public, who would not tolerate an effective privatisation of the Welsh and English coastline for private profit. A significant part of the capital investment and “direction” should come from the people of Britain. Both the Welsh and the English have major parts to play and would benefit from very significant numbers of jobs, both during construction and for ongoing maintenance. Hafren appeared to sate at the second of the Select Committee hearings (30/01/2013) that they intend to sell out after three years and have already indicated that the majority of the finance would come from overseas investors, who may be less inclined to use UK contractors and labour.

February 2013