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See maps, tables and summaries from the Government consultation
Estuary Tidal Reef
flood risk by breaking storm surge before it reaches low-lying
increases flood risk by damming the estuary above low-lying
|Average output (TW-hrs a year)
7% UK elec
|likely appr. 15% higher
average output than barrage, also generated over a period
of 18+ hours per day, 85% usable
5% UK elec
|lower output, generated
over a period of 6 hours per day in 2 three-hour blocks,
thus only 25% usable
(MW @ optimum)
|16+ hours per day
4-5 hrs on, 1-2 hrs off, generating
on both ebb and flow tides. Output varies between 5000
MW at spring tides and 2000 MW at neap tides*
|8 -12 hours per day
3 hrs on, 9 hrs off, generating on
ebb tide only. Estimated 8600 MW output when operating**
||Could be constant
||If a lagoon or tidal
coffer dam is included to kick in at the high & low
tides, supply could be constant at all times.
||Very expensive to provide
major backup from other sources for most of the cycle.
|Est. Build Costs
||£2 bn less than the barrage, using
the same costing methodology. Saving is in weight of concrete,
foundations, and installation.
||Due to massive size and consequent knock-on
effects & time involved, Government would have to
subsidise it initially.
||Tides function; scouring / silting unchanged;
habitats are preserved - little overall change.
||Habitats upstream are changed; clyces
will be needed; silting and scouring patterns will change
a lot. See Fundy
|Generation Start Date
||2 years after construction
start - does not need to be complete to start production
||Estimated 7 years to build; expected to
start operating 2020 or even 2030**
||Likely to be upwards
of 100 years; no decommissioning costs
||Silting could seriously
limit life span & cause other problems - see Fundy
||Very low profile as it rises and falls
with the tide
||Massive fixed structure - will cut right
across visual skyline.
|Shipping and Silting
||Ships will be able to
pass through at all times. Channel will not become silted.
||Ships' passage times
will be severely restricted. Also, serious silting may
||This "early" barrier can inhibit
side-wash seiche effects, storm surges, and be adapted
to sea level rise issues if necessary.
||May cause side-wash that could flood the
Somerset levels. No protection from storm surges or sea
|Practicality of design
||Likely to be good
||Needs funding for modelling
R&D. But standard turbines used in new overall design.
Little environmental protective work needed.
||Massive funding needed
for R&D, environ't protection, and shipping locks.
More concrete, more road wear, no railways.
||Many small turbines - can easily be repaired
at relatively low cost
||There are many unknown questions, due
to severe environmental disruption: shipping, silting,
river sluices, etc.
||Smaller units can be
made locally, by competing firms, and can be more easily
||Such a monolithic and
disruptive scheme can play into the hands of distant multinationals