Environment and Economics

9.1 Tidal Power and the Environment

But for the in depth environmental assessment conducted by T. Shaw and his collaborators, little or no environmental study has been carried out prior to the con­struction of Rance or Kislaya plants.[230] Ex post facto examinations were conducted on both schemes. At the Rance site the only milieu considerations were to protect the plant, and to insure a minimum of perturbations for the entrance to the port of St Malo. In fact the major changes have been the loss of lanzons (Ammodyti – dae), the disappearance of some species and the take-over by others. High speed currents have been created near sluices and powerhouse, surges occur occasionally suddenly, sandbanks have disappeared, range of tides has decreased. Pool levels and navigation patterns have changed. Overall it appears that the TPP has affected the environment less than hydro-electric plants do.

Fisheries, an important aspect of St Malo-Dinard and surroundings economic life, have not been affected, industrialization has moved in, population has in­creased, tourism has not decreased. One can expect that no plant will ever be built again without a comprehensive assessment. Such a study would at least encompass following topics: water quality, wading birds, migratory fish, fish species elimina­tion, development of intertidal algae, navigation, sediment movements, mudflats – marshes and sandbanks modifications, stratification increase, changes of pool water level, tidal regime modification[s].

In the case of the Bay of Fundy, shad has been slightly affected—notwithstanding the fish-path-way included in the plant—speed of current and range of tides some­what reduced. Marsh drainage has been slightly unfavorably affected but storm damage reduced. A pre-construction study held that impacts would be kept at a minimum. Several impacts of biological nature would be eliminated if a scheme would not include a barrage.

As no barrage is needed, the plant requires less capital investment. A “removable barrage” scheme, which involves also re-timing has also been designed by Gorlov (1979, 1980). He proposes to use compressed air to insure re-timing; electricity can be generated directly or compressed air can be stored for later power production. The usual dam is to be replaced by a thin plastic barrier hermetically anchored to bottom and bay sides. A cable stretched across the bay or inlet, attached to several floats, would support the plastic barrier and hold it above water level. Environmental impact would be benign, though a pool of stagnant water may be created behind the barrier; pulled to one side, the barrier would allow evacuation of the impounded water and even navigation.

Most sites suitable for the construction of a tidal power plant are also locales of complex ecosystems, among others wintering and migratory birds. Intertidal flats which they use as feeding-grounds can be submerged by barrage-impounded water, and salt-marshes flora may be lost. Assuming that land pollution sources impact upon an estuary, the latter’s impoundment may result in deterioration of water qual­ity. Evidently effluent treatment before and after construction of the barrage may represent a non-entirely negligible additional cost, as tidal currents will be affected. Relief may however come through the presence of a larger mean volume of water (Parker 1993).

Lesser impacts, more site-specific, are related to coastal protection, flood con­trol and groundwater. As co-lateral uses are looked for so as to lower the capital investment, or provide immediate additional returns, tourism development may be considered but is not necessarily in harmony with nature conservation (Table 9.1).

Assessments of environmental implications, ex post facto, have been numer­ous for the Rance River plants (e. g. Parker 1993, Retiere 1994). At least thirteen theses have been presented on the topic of environmental equilibrium in the area (Clavier 1981, Dauvin 1984, Grall 1972, Han 1982, Lacalvez 1986, Lang 1986, Lechapt 1986, Priou 1947, Retiere 1979, Rivain 1983). In fact the placing of cof­ferdams during construction, which cut the estuary, was the most damaging, a fact not reported in the Electricite de France’s post facto assessments. Once in the op­eration stage things changed and an increasingly diverse fauna and flora colonized the area, showing a variable degree of biological adjustment; the ecosystems re­main nevertheless strongly dependent on the operating conditions of the power station.

An environmental assessment was also conducted years after the Kisgalobskaia plant was constructed (1963-1968) and had operated for some twenty years. A first observation is that the water exchange between the bay and the open sea has been considerably reduced, salinity dropped in the upper fifteen meters of the water col­umn while hydrogen sulfide accumulated below that level.

Additionally to those chemical modifications, the pre-construction bio-ecosystem seems to have been totally destroyed. When in 1987 water exchange was brought up to 30-40%, it triggered a slow-paced restoration of the ecosystem; by 1992-1993 fauna and flora did not differ substantially in distribution in and out the bay. The study conducted by Marfenin et al. (1997) reveals that the construction of tidal power centrals may have impacts which are far from benign and that a pre­construction impact study is absolutely necessary, at least where small plants in narrow entrance bays are concerned. The difference in parasite fauna in cod and pollock were studied for Kislaya and Ura inlets near Murmansk (Karasev et al.

1996). Ecosystem research was further conducted by Semenov in 1997. It would be quite interesting, for comparison purposes, to have results of environmental studies—providing some were undertaken—of small Chinese power plants.

Change in tidal amplitudes, phases spectral composition of sea-level oscilla­tions, tidal currents parameters are but a few of the modifications observed in the sea area around the power plant. These and other phenomena, such as suspended matter transport and movements of bottom sediments, can be estimated by model­ing of tidal characteristics prior to tidal power plant implantation. Examples have been furnished for large plants that could be possibly constructed in the White and Okhotsk seas (Nekrasov and Romanenkov 1997).

The inner Bay of Fundy’s estuaries—like other large amplitude estuaries—are home to numerous migratory fishes, such as the endangered sturgeon, herring, shad, bass, salmon but also to squids, sharks, seals and whales. Studies have shown that fishways at the Annapolis-Royal (Nova Scotia) power plant are not very effective in sparing marine life and mortality reaches, depending on such factors as species, size and turbine operation, 20 to even 80%. Were marine currents harnessed in the open ocean the impact of power stations may be such that a very serious decline in bio­populations could ensue. Dadswell and Rulifson’s (1994) study follows up earlier ones by G. L. Duffett (Tidal Power 1987 p. 101) and by W. E. Hogans on mortality of adult fishes (American Scientist 1985 and 1987).

Never to be discouraged, opponents of a Fundy power plant raise the spectre of major ecological changes—besides fisheries losses—were a large station implanted in the upper reaches of the Bay. Variations in high (drop) and low tide (rise) sea level would compress the intertidal zone. New water levels for salt marshes would mod­ify these habitats and modify primary production, which, however, would increase. Such changes would affect abundance of intertidal invertebrates, fish and migratory shore-birds (Gordon 1994).

Modelisation of water circulation in Passamaquoddy Bay was carried out, with a model forced by tidal height variations at the oceanic boundary, fresh water run­off from rivers and parameterized fluxes of heat and momentum at the sea surface and sea bottom. The natural system shows strong tidal currents in channels and passes, but near zero residual flow in the bay itself. If the tidal flood is reduced in the modified system, a significant tidal-residual flow passes from Passamaquoddy into Cobscook bay; freezing at the surface is more common with a power plant, but mainly due to a lower heat flux from the bay bottom. It thus looks as if some environmental impacts that had been mentioned as deterrents for a plant construc­tion may well be less important than stated in the past (Brooks 1992, Holmes 1955). Tidal residual currents have also been modelized recently for the Juan de Fuca Strait and the Southern Strait of Georgia (Foreman et al.).

Retiere has examined repeatedly the environmental impact of the Rance River TPP and came to the conclusion, based on 20 years of operation, that the construc­tion phase, during which the estuary was isolated, proved particularly environment damaging. However, once the plant was put into operation, a diverse flora and flora established itself. Their grouping into ecological units and their interrelationships, show a varied degree of biological adjustment. The operating conditions of the plant influences the fragile new ecological equilibrium, even though migratory organisms are able to pass through sluices and turbines. Little quantitative data is available that covers the pre – barrage situation. The comparisons of species distribution are thus based upon the known penetration into the estuary when there was no barrage. (Little & Mettam). Though these authors do not share the viewpoint that the reason for the small number of TPP is to be attributed to environmental concerns,—in his view the reasons are predominantly economic—one will agree that EIAs are use­ful tools to identify the impacts, and indeed applications of modern appropriate technologies might help abate the objectionable effects of a tidal power plant (Salequzzaman).

The environmental benefits of harnessing tidal power, among such other sources as hydro-electricity and extracting natural gas in the Russian Federation’s Far East­ern region, were pointed out by Streets (2003). Neighboring areas are “choking” in the fumes emanating from coal-fired and bio-fueled electricity plants; cities in China, Mongolia, both Koreas and Japan would find present relief, not even men­tioning considerable future benefits.

If Gibrat proposed a scale, or better formula, to rate the suitability of sites for location of a TPP, Sergey (2003) established a semi-quantitative rating of environ­mental disturbance brought about by power generating schemes. The thermal power industry is, according to that scale, the most damaging (coefficient 74) and the wave energy capturing industry the most benign (coefficient 31). Second to best is tidal power with a score of 42, just one point “better” than that of solar power.

Environmental and ecological assessments have been conducted in many in­stances and for different sites, thus sometimes before sometimes after construction of a TPP. Many of these “studies” are listed in this book’s bibliography. Table 9.1 refers the reader to the “General Bibliography”.

The project also named Roosevelt Island Tidal Energy Project (RITE) includes an impact study covering fish movement and concomitant protection of the biological resource (primordial concern), river navigation potential encumbrance and security, effect—if any—on the recreational and historical resources, and water quality. At the tip of the turbine’s blunt rotor with a speed of 7.6 m/s there should be no impact upon fish. Further away from the rotor the speed is still lower. Furthermore turbines are spaced 12-30 m apart.[231] A protected area is foreseen around the system that covers in total 5,700 m2.