The Efpec~S O F Tidal Fewer Development on the Pergsieal

The EfPec~sof Tidal Fewer Development on the PErgsieal Oceanography of the Bay of Pundy and Gulf of BPne

David A, Greenherg

Coastal Oceanography Redford institute of Oceanography P,O, Box 1006 Dartmouth, Nova Scotia BJA 4A2

ABSTRACT

Predicted changes in physical oceanography due to the installation of Cidal power barriers in the upper Bay of Fundy are reviewed. Away from the barrier site, the changes induced are small compared to the natural variation In tile system, but in many areas still of potential significance. Changes in the vicinity of the barrier and in the headpond would be more dramatic and depend on the type and level of installation.

Key words: tidal power development, physical oceanography, Bay of Fundy, Gulf of Maine.

Daas le prgsent article, on gtudie les variations pr4vues des conditions oc6anographiques physiques, qu'entrafnera lqam6nagement des di~ues dPunc usine mar4motrice dans 1%partie sup4rieure de Pa baie de Fundy. A une certaine distance du site de l'endiguement, les variations cr66s seront faihles par rapport aux variations naturelles du syst6me, mais peut-&re notables dans de nombreux secteurs. AUK alentours de l'endiguement et dans 4es eaux de retenue, les modifications risquent dP@trebeaucoup plus impor- tantes, ee ddpendront du type dqem&nagement et de son niveau.

INTRODUCTION

Although tldal power has been studied for some time, with scheines considered in Passamaquoddy (see for example IPEB l961), and in the upper Bay of Fundy (ATPPB 1969) it was not until the study of the Bay of Fundy Tidal Power Review Board (BFTPRB 1977) that wider issues of the environmental effects of the schemes in the upper Bay were addressed (Daborn 1977)- Lt was also realised around this time that the changes in tidal response would be more far reaching than previously ti-ioug'i~t(Heaps and Greenberg 1974)-

In this paper possible changes in the physical oceanography of the Kay of Fundy due to tidal harriers are described and compared the natural variation in the system. This paper updates some of the predictions made In Garrett (1977) and Greenberg (1997)- The changes in tidal sea levels, as found in numerical model studies (Greenberg 1979), are presented and some implications of these changes are disci~ssed,

Changes in the tidal response of sea Level in the Bay of Fundy and Gulf of Plaine due to tidal power development have been calculated using a ~~umericalrnodek (Greenberg 197581, These are accounted far in terms of the free period and energy characteristics of the system, The barrier locations most favored are in upper Ghignecto Bay across Shepody Bay, across Cumberland Basin and in Minas Basin at Economy Pt, (Fig, 11,

Barriers across rhe mouths of Shepody Bay and Cumberland Elasin would give rise to very similar changes in tidal regime, The M2 tidal. amplitude of the sea level elevation (Fig, 2) decreases at the barrier and throughout the upper Bay of Fundy, The magnitude of this change dimintshes from the head of the Bay changing to an increase in tidal amplitude in the lower Bay and throughout the Gulf sf Maine, There seems to he 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-Gulf of Maine sys- tems. Resonant amplification occurs aihen a system hs forced near its preferred period of oscillation. The Bay of Fundy has a natural period of oscillation sf about 9 hrs. (Wao 1958), 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, 19741, Shortening this period brings it closer to the tidat forcing period, thus increasing the reasonant ampkificatlon, 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 in- creases in tidal amplitude throughout the Bay and Gulf (Pig, 3) except Tor the area very close to the barrier, The difference in the regimes result- ing from these two barrier locations is the result of the reduced transport at the Economy Point barrier site being felt domstream 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 barrjer decreases further the tide at the barrier because increased flow Leads to more energy dissipated by Cape Split, Changes in the capacity of Shepody and Cumberland barriers had lirtle effect at the barriers and in all cases capacity changes had little effect downstream, Similarly, differences in types of generation (see "Headpond Tidal Affects" below) would have compar- able effects away from the barrier slte, ATLANTIC OCEAN

I 6 I I 70" 68' 66' 64"

Fig. 1, The Bay of Fundy and Gulf of Maine CHANGE IN M2 TIDAL AMPLITUDE (cm)

r;, I - 0 5 0 0 _I_I__C I BLOCK ISL. HYANNIS CAPE COD BOSTON

PORTLAND LUNENBURG C. SABLE BAR HBR. YARMOUTH EASTPORT WESTPORT CENYREVILLE ST. JOHN

MARGARETSVILLE

C. D'OR

C. ENRAGE gn

P A C. BLOMINDON GRINDSTONE PP9

FIVE ISLANDS I' I

I ECONOMY PT. CHANGE IN M2 TIDAL AMPLITUDE ('10) - 0 V, 0 ul XI _I_r_l_ BLOCK ISL. ; HYANN IS 'i CAPE COD BOSTON

PORT LAND LUNENBURG C. SABLE BAR HBR YARMOUTW EAST PORT WESTPORT CENT REVILLE ST. JOHN

MARGARETSVILLE

C. D'OR

C. ENRAGE

C. BLOMINDON GRINDSTONE

FIVE ISLANDS Iv) 1 f. 1 I1 I I ECONOMY PT. !

Pig. 2, Absolute and percentage change in tidal amplitude along the coast, due to a barrier installed at the mouth of Shepody Bay. The solid line is for the New Brunswick and New England coasts, the broken line is for the Nova Scstian coast. CHANGE IN M2 TIDAL AMPLITUDE (cm) N - - 8 0 0 0 0 E 8 BLOCK ISL. HYANNIS CAPE COD BOSTON

PORTLAND LUNENBURG C. SABLE BAR HBR. YARMOUTH EASTPORT WESTPORT CENTREVILLE

ST. JOHN

C. L'OR m C. ENRAGE 0 0 C. BLOMINDON GRINDSTONE 8 FIVE ISLANDS ZE

ECONOWlY PT. CHANGE IN M2 TIDAL AMPLITUDE ('lo) as D BLOCK ISL. XI HYANNIS X) CAPE COO , BOSTON ;FI LUNENBURG PORT LAND C. SABLE BAR HBR. YARMOUTH EASTPORT WESTPORT CENTREVILLE

ST. JOHN

C. D'OR

I C. ENRAGE C. BLOMINDON GRINDSTONE

FIVE ISL.ANOS

ECONOMY PT.

Fig. 3, Absolute and percentage change in tidal amplitude along the coast, due to a barrier installed across the Minas Basin at Economy Point. The solid line is for the New Brunswick and New England coasts, the broken line is for the Nova Scotian coast, CONFIDENCE IN CALCULATIONS

Error limits on the changes given in Figs, 2 and 3 are diff i cult, if not impossible to derive, Confidence in the predictions is gained 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, Garrett and Greenberg (1977) and Garrett and Toulaney (1979) showed that any errors due to open boundary effects would be rninimal (of order 1%) for the barrier cases now under consideration, Garrett (1974) showed in his normal mode study that the shortening of the Ray of Pundy changed the shape of the Pundy-Maine oscillation. Although his grid was coarse and the equations were simplified, he predicted a reduction in a,nplification at the head of the Bay and an increase at the mouth and in the Gulf as is suggested in Greenberg (1979) on which this paper is based.

More recently, Duff (1981) has obtained similar patterns and percentage changes to those of Greenberg (1979) using a numerical model that telescoped to include much of the North Atlantic, This also showed mini- mal change along the edge of the continental shelf where Greenberg (1979) specified tidal elevations unaltered when barriers were simulated, The? magndtude of the changes predicted by Duff did dif fer, but Ct is thought that this was due to poor calibratfon of the model, it being up to 30 cm out in amplitude and up to one hour out in phase of the tide, Duff did get results different from his full model when using a cut-down conttnental shelf model, using inappropriate open boundary conditions in which currents were specified not to change when barriers were simulated,

The Bay of Pundy-Gulf of Maine model referred to here has gone through a considerable development from its first trials in Greenberg (1975) (Fig, 4) to its present form (Greenberg 1979, Fig, 5)- This has lead to some revision in the magnitudes of the predicted changes but little difference in the pattern of the change, Among the steps in this evolu- tion, some of which are obvious from the diagrams, are the following:

The inclusion of the shallow area at the head of Cobequld Bay. The inclusion of advective terms in formulations of the equations in the Minas Ras-in and flinas Channel, The creation of a new, finer grid for the Mirlas Basirn and Minas Ghannel area, Recalibrations carried out along with the above three changes resulted in the lowering of the frictlsn co- efficient from an unusually high h,4 x to within a normal range at 2-1 x 10- 3 , The medium size grid was extended out to the mouth of the Ray of Fundy, The coarse grid was extended out to the edge of the continental shelf and to the northeast and southwest along the shelf, Variations due to map projection and the changes with latitude of the CorioLis parameter were allowed for in the coarse grid. Fig, 4. The grid outline of the earliest version of the Bay of Fundy - Gulf of Maine numerical model (from Greenberg 1975).

8, An extensive data collection program was undertaken which permitted a precise specification of the open boundary tides and very accurate calibration of the model.

Calculations using the above mentioned models all gave similar qualitative results, but quantitatively there was an increase in effect, The tide change at Boston, for example, increased progressively from s 6% rise to a 10% rise as the more accurate schemes were incorporated, The change in tide phase at Boston differed only from a 6 minute delay to a 4 minute delay in the later calculations.

A further test was carried out to see whether barrier effects would be poorly predicted because of the coarse resolution of the Gulf of Maine coastline, The depths around the coast of the Gulf were doubled, and simu- lations were run with and without barriers, The percentage change in tides due to barriers was found to be the same as predicted with realistic depths. It was reasoned that if such gross errors did not alter the predicted change, then more comprehensive modelling of the Gulf would give more detail, but not increase the accuracy of the prediction,

BARRIER EFFECTS AND NATURAL VARIABILITY

The changes in M2 tide should be considered in conjunction with the natural variability of sea level in the system,

Computer runs have been made simulating the major tidal constituents for 30 days to examine the complete monthly variation in tides, The hourly output from the model was analyzed using a standard tidal analysis package and the simulated constituents were compared for cases with and without barriers. Times and heights of high and low water were also interpolated. The results (e.g, Table I, Economy Pt, Barrier) indicate the largest change in amplitude for the M2 constituent, Away from the head of the Bay, the other constitutents are changed principally in phase, Ex- cept in the immediate vicinity of the barrier, there were no changes in mean sea level. The average of the mean differences in high and low water are very close to the change in M2 amplitude, although there are differences in the changes at high and low water, This could be real or due to inaccuracies in the interpolation scheme, particularly near the barrier, where the opening and closing of sluices and turbines could dis- proportionately influence results, This requires further investigation,

Changes in tidal sea level elevations of a few centimeters might tend to be camouflaged by surface waves, storm surges and even the natural tidal variation, It would be the extremes, spring and neap tides, that would be most noticeable (see Fig. 6)- In a period of neap tides, low areas that would normally not be exposed and higher areas that would normally not be covered for one or more tidal cycles, would be covered and exposed respectively every tide. During a period of spring tides, areas that would never be exposed or covered by the natural tides would be included within the outer range of tidal variation, T4IILI.: 1, Difference between model run wlth an Economy Point b8rrie-c and withatlt barri~rs,of high and low water heights and times, and of thc major constituents simulated,

At Barrier Grinds tone Saint John Bosfron

PP ------P -- - -- HW Mean Difference - 53.1 cm - 31.4 min +- 37,4 - 6,2 + 20,9 - 2-6 + 12.0 + 0.9 Standard Deviation 6,8 cm - 2.7 min 4-7 2,8 1,R 2-1 0,6 1,4

IJW Mean Difference + 25.5 cm - 29,3 min - 20-0 - 8,8 - 19,7 - 6,5 - 15,8 + 7,2 Standard Deviation 9,s cm - 3.0 min 3-3 1,6 2.6 2 -0 1.2 3*4

1 12 em 143" 12 143" 7 1 129" 10 142" Iliff erence - 1 cm 7" 0 - 2" 0 - 1" 0 0"

KI 15 cm 137" 15 129" 13 124" 12 136" Difference - 1 cm- 8" 0 0" - 1 -i- I" 0 0"

N2 92 cn 336" 86 321" 58 311" 29 326" Difference - 1 cm - 15" 4- 3 - 2" + 2 -- I" -4- I -+- 3"

''? ? 553 cm 1" 50: 349" 32 2 340° 150 358 O Difference - 29 cm - 16" + 25 - 3" + 19 - 2" + 13 + 3"

S% 88 cm 46" 8 1 30" 5 1 18" 2 2 31" Ilif ference - I cm- 17" + 4 0" -i- 2 C I" 0 + 6" SPRING TIDE NEAP TIDE LAND COVERED 7-INFREOUENTLY

I I SPRING NEAP $ f~p"~~~~AND TIDE ,& EVERY TlDE 1 I !

EXPOSED LLg WATERINFREOUENTLY

Fig. 6. The changes in spring and neap tide ranges and shoreline impact due to an increase in tidal amplitude. Changes are exaggerated for clarity. There are marry instances where tncreased tidal amplitudes could have an tffecr. Imparcs which could be felt include:

I, Areas sensitive to present high water: those having low beach slope, already bothered by stor- surges, salt marshes, or built up close to present high water would be most affected. 2, Shore1 ines sensitive to wave attack would find the waves con- sistently hitting higher and lower levels of the beach, but diktused over the wider tidal range, 3, t4arginal. ship passage would he more rfsky for the lower half of the tidal cycle but safer during the higher fialf, 4, The flood risk in the lower Sainr John river valley may be more severe if higher high waters further retard high runoff in the spring.

TTDAL EFFECTS LN THE HEADPOND

The largest changes from the present regime, due to the Pnstalla- tions of a tidal power plant, would be behlnd the barrier, The preferred type of installation known as ebb generation, consists of an enclosed reservoir or headpond, which is fif led through sluices on a rising tide and drained through turbines on a falling ride generating electricity (Pig, 7). Other generation modes have been considered, with two way generation being a possibility, but flood generation is uneconomic. The tidal sea Level changes in the headpond would be reduced to one half to one third their present range rmder any mode. The mean level of the reservoir depends on the particular generation mode (Fig. 8), being higher than normal for ebb generation, lower for flood generations and only slightly raised for two- way generation, The level of installed capacity also has an effect (Table 21, Greater sluice capacity tends to increase the mean headpond level, and higher turbine installation tends to increase headpond range. The mean level In ebb generation tends to mimic the variation in high water (Fig. 9) due to the higher resistance to flow of turbines compared to sluices. This effect is similar to that of Reverslng Falls on the water levels in. the lower Saint John River, The mean level in flood generation would tend to follow the Low water variation but would vary less in two way generation,

Two-way generation is the only mode where some power can be had on demand for short periods, To achieve this, the demand must be sufficiently forecast and in such instances it might be necessary to give up some energy to have the basin level optimized at the correct time. For maximurn power production, a two way scheme would be generating in an ebb generation mode during priods of low tldes and in both directions during medium and high tide periods. Both of these factors could lead to a more irregular variation in mean reservoir level and in the extent of the intertidal area.

From the above, we can see that changes in the headpond tidal regime will impact the area in two different ways, by changing the mean sea level and by cha~~gingthe regularity and extent of the intertidal area. Factors that could depend on the mean water level include changes in the level of, and salt intrusion into, the watertable of the surrounding land, KCSERVOIR LEVEL TIDE FALLING RESERVOIR FALLING RESERVOIR LOWEST RESERVOIR FILLIFIG

OPERATE TURBINES

Fig, 7. The different stages of operation in an ebb generation power scheme relative to tide and reservoir levels. EBB GENERATION EXISTING HIGH TIDE / HIGH TlDE f ______------T - NEW MEAN WATER LEVEL------// I! I NEW LOW TlDE ' TIDAL BARRIER ----..I.--- LOW TIDE INTERTIDAL ZONE FLOOD GENERATION

- -YEW RANGE NEW MwL_/1 --- _____-_--

TWO WAY GENERATION

Fig. 8. Reservoir levels for different generation modes. 'TABLE 2, Variations due to different installation Levels. Experiments were done with a11 early version of the model, and barriers operating characteristics have evolved, so exace numbers would differ, but trends should be the same, Present thinkil~gcalls for even higher installation levels.

Experiment 1 2 3 4 ------M2 hpin Front (cm) 548 538 563 546

M2 hpBehind (cm) 167 227 94 171

Mean Level nif f erence Across Barrier (cm) 340

Generation Time (min,) 364 339 402 374

Sluice Time (mine) 222 249 183 2 PO

Number of Turbines 70 105 35 70

Number of Sluices 70 7 0 70 100 ------

and the drainage of aboiteaux, Changes in intertidal area could lead to changes l'n erosion, sedimentation and biology,

OTHER FACTORS

Changes in tidal currents can be expected in similar magnitudes to changes in tidal elevations. A relationship has been found connecting the strength of the tidal current and the water depth to whether or not an area is well mixed or stratified. In an analysis of tidal mixing, Garrett et al, (1978) found that the Great South Channel changed from being marginally outside tile critical range for a tidally mixed area, to marginally wlthin this range (Fig. 10) when tidal power barriers were simulated. This could have implications for water mass exchange through the Channel. The study also indicated the headpond area would tend eo stratify in the summer. Holloway's (2981) study suggested a significant decrease in salinity in the headpond which would tend to increase any tendency to stratification, but little effect on salinity was predicted for the area outside of the tidal reservoir,

The placement of a barrier could have a locally significant effect on waves, The long channel fetch would be reduced, decreasing the energy level 05 the waves downwind from the barrier, Reflections of waves at the barrier could cause a Local increase in wave energy.

Several factors relating to a barrier's installation could affect ice conditions. These include: decreased breaking forces on the ice due to lower wave activlty, lower salinities, tidal range and tidal currents, limited tidal excursion due to the barrier and possibly greater ice forma- tion due to decreased mixing, These factors could induce the present large quantities of drifting ice to form a more solid ice cover, Whether this could lead to complete fast-ice cover in the headpond has not been deter- mined, The subject of ice is more completely covered in Cordon and Desplanque (1983)-

CONCLUDING W,PILARKS

The predicted changes in tidal elevations and tidal currents due to the proposed installation of a tidal power dam in the upper Bay of Fuady are now fairly well understood, Although, away from the barrier, the changes may seem small compared to the natural variation in the system, they still could be significant in many areas, Good quantitative analyses on how these changes could impact flooding, shipping, mixing etc, have not been made, Perhaps estimates should be made on a site specific basis. An attempt has been made here to give some qualitatfve ideas on impacts based on what is quantitatively understood. Fig, 10. The mixing parameter, Depth Dissipation, in the Gulf of Maine when a barrier is simulated at Economy Point (from Garrett et al. 1978). The Great South Channel is included in the mixed region. This should be compared to Figure 6 in Greenberg (this volume). REFERENCES

ATPPB (Atlantic Tidal Power Programming Board). 1969, Feasibility of tidal power development in the Bay of Fundy. Board Report and Committee Report, Halifax, Nova Scotia, 5 vols,

BFTPRB (Bay of Fuady Tidal Power Review Board). 1977. Reassessment of Furldy Tidal Power, Reports of the Bay of Fundy Tidal Power Review Board and Management Committee, Ottawa, 516 p.

Daborn, G,R,, ed. 1977, Fundy tidal power and the environment. Acadia Univ. Inst, Publ. No. 28, 304 p.

Duff, G.F,D, 1981. A gulf and ocean model of the Bay of Fundy tides, and their response to barrier construction and operation. Utilitas Math. 19: 3-80,

Garrett, C,J,R. 1972. Tidal resonance in the Bay of Fundy and Gulf of Maine, Nature 238: 441-443.

Garrett, C.J,R. 1974, Normal modes of the Bay of Fundy and Gulf of Maine. Can, J* Earth Sci. 11: 549-556.

Garrett, C.J.R. 1977. Tidal influences on the physical oceanography of the Bay of Fundy and Gulf of Maine. In: Daborn, G.R., ed. Fundy tidal power and the Environment. Acadia Univ, Inst. Publ. No. 28, pp. 101-115.

Garrett, C.J.R, and D-A, Greenberg, 1977, Predicting changes in tidal regime: the open boundary problem. 3, Phys. Oceanog., 7: 171- 181,

Garrett, C.J.R,, J.R, Reeley an3 D,A. Greenberg. 1978. Tidal mixing versus thermal stratification in the Bay of Fundy and Gulf of Maine. Atmosphere - Ocean 16: 403-423,

Garrett, C,J,R. and B, Toulany. 1979. A variable depth Green's function for shelf edge tides. J. Phys. Oceanog. 6: 1258-1272.

Gordon, D,C. Jr, and C. Desplanque. 1983. Dynamics and environmental effects of ice in the Cumberland Basin of the Bay of Fundy. Can. f, Fish, Aquat, Sci, 40: 1331-1342,

Greenberg, D.A. 1975, Mathematical studies of tidal behaviour in the Ray of Fundy, Ph,De thesis, University of Liverpool, 139 p.

Greenberg, D,A. 1977. Effects of tidal power development on the physical oceanography of the Bay of Fundy and Gulf of Maine. In: Daborn, G.R,, ed, Fundy tidal power and the Environment. Acadia Univ. Inst. Publ. No. 28, pp, 200-232, Creenberg , D.4,. 1979, A numerical model inves tigation of tidal phenomena in the Bay of Fundy and Gulf of Maine, Marine Geodesy 2: 161-187.

Heaps, N,S, and D,A. Greenberg. 1974, Mathematical model studies of tidal hehaviour in the Ray of Pundy, Proceedings of the IEEE Lnterna- ttonal Corlference on Engineering in the Ocean Environment 1: 388- '399 *

NoPloway, P,E, 1981, Longitudinal mixing in the upper reaches of the Ray of Fundy. Est. Coast. Shelf Sci, 13: 495-515.

IPEB (Interaational Passamaquoddy Engineering Board), 1961. Report of the International Joint Commission United States and Canada on the International Tidal Power Project, Washington-Ottawa. Rept, Intern. Joint, Comm, Docket 72, Invest. Intern. Passamoquoddy Eng. Fish. Bd,

Rao, D,H, 1968. Natural oscillations of the Ray of Fundy. J. Fish. Res. Bd. Can. 25: 1097-1114,

QUESTIONS AND COMMENTS

-G, Daborn: You mentioned the possibility of stratification occuring in the headponds, Have you pinpointed the likely degree to which this might occur?

D. Greenberg: Pete Holliway did his calculation of horizontal. mixing based on salinity values and he came up with a value he thought the new mean salinity would be in the headpond. Now that is a mean overall average. I an not sure of the exact numbers but it's a good four or six parts per thousand less than what are found there now. 1 am under the impression lche change will be greater on top and less at the bottom within the stratified area at Least during summer, In the winter I am sure it will be all well ;mixed with the exception if there is complete ice cover, Just meterology should mix it up, if it mixes the Gulf of Maine it should mix a shallow headpond.

D, Scarratt: One of your comment areas was effects on water tables and drainage but there is one thing- nobody has get addressed and that is there are a number of communities which are dependent on the ocean for sewage disposal, Has anyone begun to study the municipal engineering problems that might be created by altered and perhaps unpredictable tidal amplitudes changes?

D, Greenberg: This question may be answered by some of the later speakers, otherwise I know of no one who is examining such problems.

D, Bray: With regard to waves in the area upstream of the barrage might you not consider only the wave height but also the duration the waves wLll have to erode a certain Length of shoreline when the level of the reservoir is held constant for three hours? What addftional effect will this have on sedimentation? D, -Greenberg: Yes, this is a new departure that some of the sedimento- logfi-ki--canilook at. There have been studies done that do suggest how things might happen when you dam a river and change the system into another regime all at once, The idea of changing a variable regime, however, has not been studied.