numerical model studies (Greenberg 1979), are presented and some implications of these changes are discussed.

Tidal Elevation

Changes in the tidal response of sea level in the Bay of Fundy and Gulf of Maine due to tidal power development have been calculated using a numerical model (Greenberg 1979). These are accounted for in terms of the free period and energy characteristics of the system. The barrier locations most favored are in upper Chignecto Bay across Shepody Bay, across Cumberland Basin and in Minas Basin at Economy Pt. (Figure 1).

Barriers across the mouths of Shepody Bay and Cumberland Basin would give rise to very similar changes in tidal regime. The M2 tidal amplitude of the sea level elevation (Figure 2) decreases at the barrier and throughout the upper Bay of Fundy. The magnitude of this change diminishes from the head of the Bay changing to an increase in tidal amplitude in the lower Bay and throughout the Gulf of Maine. There seems to be little change away from the Gulf along the continental shelf.

These widespread changes are caused by the shifting of the free periods of the Bay of Fundy and of the combined Fundy-Maine systems. Resonant amplification occurs when a system is forced near its preferred period of oscillation. The Bay of Fundy has a natural period of oscillation of about 9 hrs. (Rao 1968). A barrier which shortens the Bay, decreases this period, moving it further away from the forcing tidal period of 12.42 hours, which decreases the amplification from the mouth to the head of the Bay. The period of the Bay and Gulf combined is about 13 hours (Garrett 1972, 1974). Shortening this period brings it closer to the

tidal forcing period, thus increasing the reasonant amplification.

In the

Bay of Fundy these two effects compete causing the tidal sea level decrease which dominates at the head of the Bay and the increase which dominates at

the mouth.

A barrier in the Minas Basin at Economy Point leads to larger increases in tidal amplitude throughout the Bay and Gulf (Figure 3) except for the area very close to the barrier. The difference in the regimes resulting from these two barrier locations is the result of the reduced transport at the Economy Point barrier site being felt downstream near Cape Split releasing energy that is dissipated by friction in the natural system. Increased capacity would necessitate more or larger turbines and greater flow. Consequently, an increase in capacity of the Economy Point barrier decreases further the tide at the barrier because increased flow

Similarly,

leads to more energy dissipated by Cape Split. Changes in the capacity of Shepody and Cumberland barriers had little effect at the barriers and in all cases capacity changes had little effect downstream. differences in types of generation (see "Headpond Tidal Affects" below) would have comparable effects away from the barrier site.

Confidence in Calculations

Error limits on the changes given in Figures 2 and 3 are difficult,
Confidence in the predictions is gained

if not impossible to derive.

Garrett and

through an understanding of the physics involved, by noting the consistency of the nature of the change with other researchers, and by obtaining similar results with the progressive refining of the model. Greenberg (1977) and Garrett and Toulaney (1979) showed that any errors due to open boundary effects would be minimal (of order 1%) for the barrier cases now under consideration.

Garrett (1974) showed in his normal mode

Fig. 3.

due to a barrier installed across the Minas Basin at Economy Point. Absolute and percentage change in tidal amplitude along the coast,

LUNENBURG

C. SABLE
YARMOUTH
WESTPORT

CENTREVILLE

-15

-10

BLOCK ISL.

HYANNIS
CAPE COD
BOSTON