Table 6, Qualitative comparison of the environmental performance of a hypothetical linked-basins TPP of the flow-through type, as described in this section vis–vis the chosen standard of comparison, a single-basin, double-effect TPP, Type Z, at Fundy s Cumberland Basin. The tabulation shows which of the two types scores highest for optimum environmental performance.
Environmental effects
A
B
C
E
F
Type of TPP
Linked-Bs, SE, flow through type at an imaginary site
Single-basin, DE, at Fundy Cumberland Basin. Tyoe Z
Size of linked-bs too small to affect tidal regimes
TPP parameters
Mean, natural tidal range
5.64 m
10.0 m
Mean tidal range within hign basin as % of natural tide
49%
68 %
Z
Z
Mean tidal range within low basin as % of natural tide
46%
68 %
Z
Z
Mean water level within high basin, compared to natural conditions
+1.28m
-0.12m
Z
Z
Mean water level within low basin compared to natural conditions
-1.02m
-0.12m
Z
Linked-Bs
Number of passes through turbines for a fish going in-and-out of TPP
1
2
Linked-Bs
Plant operation at or close to the rhythm of the natural tide
no
yes
Maximum head across turbines
3.68m
4.62m
Linked Bs
Maximum water velocities through turbines
11.47m/sec
11.9m/sec
Linked-Bs
Stagnant flow within high basin % of the time
35%
18 %
Z
Stagnant flow within low basin % of the time
35 %
18 %
Z
Simplicity and effectiveness of flow patterns
See Fig. 6
linked Bs
Total scores for Linked-Bs, SE plant, through-type layout
10
0
3
1
Total scores for Type Z, DE
4
4
0
1
NOTE: Re D, Sea-mammal survival: TPPs should be designed and operated to keep sea mammals away from the hydraulic turbines. This applies equally to both types B and Z and therefore does not affect a comparison between the two. DE = double-effect; SE = single effect; HB = high-basin; LB = low-basin Linked-Bs = linked-basins
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