As is often the case with a new technology, or one applied at greatly different scale than previously, there are many more questions about the potential environmental impacts of Fundy tidal power than there are answers. We believe the report forthcoming from the Maine State Planning Office represents an important first step in identifying areas of significant concern and should prove very useful to agencies trying to formulate responses. However, this report is only a beginning Much research is needed. In my opinion, which I believe will be shared by the project's proponents, environmental research should proceed before substantial investments are made in design or construction aspects. In this way, if studies indicate that the net environmental consequences are unacceptable, vast amounts of money and effort can be saved. If studies are begun in the near future, I am sure many of the environmental questions can be resolved without causing debilitating delays in the project. We are fortunate in some areas to have both the scientific expertise and necessary data bases available to address some potential problems very quickly, i.e. within a year or two. For example, the question of how significant are the projected changes in estuarine flushing rates. This must be addressed on an estuary by estuary basis because of their individual characteristics. An estuarine flushing model is operative at the Bigelow Laboratory. Information on flow rates, volume and tidal ranges of the various estuaries is also available. The model could be run for each Gulf of Maine estuary, the output field checked and the results interpreted in perhaps eighteen months. Some insight into the significance of increases in current velocity could be gained by examining longterm tidal cycles. Tidal currents may vary by as much as 5% over some of these cycles and at least some fishery biologists believe the cycles in fishery landings are correlated. Long-term tidal records, temperature records and catch statistics exist and could be analyzed for relevant correlations by the proper experts. could produce an early indication of the potential impact of current changes on fisheries. This Another useful exercise that could be accomplished quickly is a detailed case study of one or more coastal communities. A group of experts including a geologist, ecologist, hydrologist, civil engineer, waste water engineer, real estate appraiser, etc. could walk the shore and assess changes that may result from the advent of Fundy tidal power. A rather accurate dollar value could be assigned to the potential changes in that community. This value could then be used to estimate a total cost of possible damage or mitigative measures over a wider area. Other information gaps will require a longer time to fill. For example, the relationships between increased tidal mixing, primary productivity and fisheries are complex. Significant progress has been made in recent years but much remains to be done. Large multi-investigator projects of the sort required to address problems of this magnitude may take five to seven years before anything approaching a definitive answer can be attained. Indeed, any predictions concerning large-scale biological systems will always be surrounded by a great deal of uncertainty. 116 POTENTIAL ENVIRONMENTAL CONSEQUENCES Peter F. Larsen Bigelow Laboratory for Ocean Sciences In the last decade, the increasing costs of fossil fuels and concern about the public safety of nuclear power have spawned a growing interest in alternative sources of energy. Where oceanographic conditions are appropriate, a considerable amount of this interest has been focused on large-scale tidal power development. Tidal power has several advantages over conventional energy sources. It is aj renewable source of energy that is not influenced by seasonal water levels, floods or droughts as is conventional hydropower. Although most operational modes only produce power on an intermittent basis, and therefore, tidal power facilities must be integrated with other systems, power production is predictable years in advance. Since it uses no fuel, problems associated with fuel acquisition and waste product disposal are avoided. Potential sites for tidal power development must fulfill two basic needs. First, a tidal range large enough to produce a sufficient head is required. Secondly, the embayment to be impounded must provide a large surface area, while *Contribution No. 81012 Bigelow Laboratory for Ocean Sciences Reprinted from OCEANS, September 1981 its connection to the sea should be relatively narrow to minimize construction costs. On a worldwide basis, there are generally considered to be about fifty sites suitable for development (1). Presently, the 240 MW LaRance project in France is the only major operational tidal power facility. Other major projects have been considered since early in this century, but development has always been postponed because the high construction costs have invariably outweighed the benefits of low-cost power production when compared to the cost of development of other energy sources. Presently, however, the world economic climate, especially in terms of energy costs, seems to be more favorable for tidal power development and several projects are receiving attention around the world. CH1685-7/81/0000-0908 $00.75 1981 IEEE Georges Bank Moon Cove project, a 12 MW development advanced by the Passamaquoddy Tribe, has undergone lengthy feasibility studies and could enter into final liscensing procédures in the very near future. Other, much larger, proposals for Cobscook Bay are being considered by the U.S. Army Corps of Engineers, but it is not clear how quickly they will proceed. Current Canadian attention is focused on the upper Bay of Fundy (Fig. 1), where the potential for projects in Cumberland Basin and Minas Basin is being studied (Fig. 2). These would be large facilities, being rated at 1,085 and 3,800 MW respectively (2), which is roughly equivalent to one to four nuclear plants. They would address regional power needs, including those of the northeastern United States. ment. Whereas tidal power is non-polluting in the traditional sense, it does have several environmental consequences that deserve detailed evaluation early in the planning phase (3, 4). These environmental consequences can be conveniently divided into those that occur within, or in the immediate vicinity of, the impoundment and those that occur well outside the impoundI refer to these effects as internal and external consequences, respectively. Internal consequences are principally those associated with local current changes and restricted water exchange between the tidal basin and the open sea. Examples are altered sedimentation patterns, loss of intertidal habitat and water quality modifications (5). These effects, which are generic to tidal power development, and by definition, are geographically limited, are the focus of most impact considerations. External consequences, on the other hand, occur seaward of the tidal barrier and may influence a considerable geographical area. The exact effect depends upon the size and location of the barrier within the entire tidal system. In some cases, such as the defunct U.S. - Canadian project involving Passamaquoddy and Cobscook Bays, the effect would be caused by reduced frictional dampening because of decreased water exchange. Tidal ranges would be affected by about 1% with a maximum increase of 0.7 ft. occurring at the head of the Bay of Fundy (6). In other cases, where barriers are to be located near end of a closely resonant basin, tidal modification could be significant, the actual change being determined by whether, and to what degree, resonance is enhanced or decreased. the The proposed Fundy tidal power development will enhance the natural tidal resonance of the Bay of Fundy and Gulf of Maine by shortening the basin, bringing its period closer to the natural period of the tidal wave (7). Far-reaching changes in tidal patterns and hydrography could result. Present estimates indicate that an increase in tidal range of from two to thirty cm. would be produced from the southern Bay of Fundy to south of Boston, Massachusetts (7). The increase in range will depend on which project is constructed, but if more than one is built, the effects are expected to be additive (7). The consequences of altering the tidal regime of northern Gulf of Maine are legion, diverse in scope and range widely in time-scale of development. To date, although the work of Greenberg and others has produced sophisticated numerical models of modifications in tidal behavior induced by tidal power development in the upper Bay of Fundy, little attention has been given to consideration of the resultant environmental consequences. this presentation, I will address some of the most obvious environmental concerns. It is not my intention to be comprehensive or definitive, but only to begin a dialogue that will help to insure that environmental concerns are given adequate evaluation on a time-scale to allow maximum possible mitigation of projected impacts. ENVIRONMENTAL CONSEQUENCES In The environmental consequences of tidal power development seaward of the tidal barriers can be categorized as those caused principally by the changes in tidal range and those caused principally by changes in tidal currents. These categories are obviously different manifestations of the same phenomenon, but since tidal range effects will be most pronounced at the coastline, and tidal current effects will be felt over a wider area, it is a convenient distinction for the purposes of discussion. It should be noted that mean sea level remains unchanged. Effects of Tidal Range Changes The predicted increases in tidal range will cause alterations in the extreme upper and lower portions of the intertidal zone, that productive region of shoreline which is alternately covered and exposed by the sea. Even modest changes in tidal range will mean that points near the present tidal extremes will be submerged or exposed on a more frequent basis. This will lead to a restructuring of the resident biological communities near high and low water. These communities are finely tuned to, and limited by, the rhythmic pattern of immersion and submersion. The best example is perhaps the salt marshes which can be large in extent and which exhibit marked zonation of community types over a limited vertical gradient, i.e. large horizontal distances are associated with small elevation changes. The zonation is caused principally by the dominant plant's tolerance to submersion - plants tolerant to frequent submersion living at lower tidal heights and less tolerant plant's dominating at higher tidal heights with intolerant plants completely excluded from the tidal zone. The projected increases in tidal range will increase the frequency of unundation and, over an undefined period of time, result in an upward 1.e. shoreward, movement of plants of the intertidal zone. The higher water levels at mean high tide will reach elevations not previously inundated and marsh plants will displace terrestrial vegetation. In effect marsh area will be increased along landward borders. Analogous effects will occur in all intertidal habitat types and also at the lower end of the tidal range where more hardy intertidal species will replace specialized subtidal forms in the expanded lower intertidal zone. A significant expansion of the tidal range also could have implications for the human population. Higher tides, as noted above, will cause the loss of terrestrial habitat at the immediate shoreline. The absolute loss will depend on the type, slope and wave exposure of the shore. It may be of no consequence on steep rocky shores, but could be significant in lowlying areas. Manmade structures, such as piers, docks, low-lying roads and bridges, designed for existing high tide levels will be more closely approached by the higher modified tides. This consequence could take on great importance when a storm. surge accompanies an enhanced spring tide and lead to increased property damage for a storm of given magnitude. There is some suggestion, however, that the higher tidal range will reduce the amplitude of storm surges (8). Beach erosion, already a problem in southern Maine, could be accelerated especially if storm waves associated with the higher tidal levels are able to undercut sea walls designed for present tidal levels. The increased tidal levels could, in local situations, cause water table fluctuations and lower the quality of well water in the immediate coastal zone. . Depending on the extent of tidal range. alteration, reduced low tide level could also have human impacts. In many small New England harbors, navigation is already difficult near low water and many docks and piers are marginally useful at periods of low tide. Reduced water levels could |