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.

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

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