Datos de Teledetección

typical aquatic vegetation, because the turbidity in the discharge area consists of fine sand that is also commonly carried by sea currents. No impacts are expected to extend outside the turbidity area.

In other areas, the project will have only minor impact on aquatic vegetation. The seabed will change in areas where dredging will take place. The temporary turbid- ity caused by dredging is not estimated to cause any harm to the distant Takaranta habitat types with typical aquatic vegetation. Due to the quality of the dredging mass (sand), no sedimentation detrimental to the natural values of the Siikalahti area is expected either. The sand turbidity that will spread during dredging will not differ from normal migration of sand in the area. At times, tur- bidity caused by finer sediments may spread to Siikalahti during the work. However, such brief periods of turbidity do not usually cause any permanent harm to bottom veg- etation. No changes in vegetation were observed in the follow-up to the dredging and waste soil dumping work in the marine spoil area at the Hamina harbor, for exam- ple (Leinikki 2011).

The benthic fauna found in the Hanhikivi headland sea area are species typical to the Bothnian Bay. The dredging will destroy the benthic fauna in the immediate dredging area, but the fauna will recover fully within a few years.

Impact on fish stocks and the fishing industry

Fish stock

The most significant impact factor during construction will be the noise caused by excavation and other hydraulic construction works. The most immediate effects will be caused by the blasting. The pressure waves will kill fish within a 20-meter radius and may cause physical injuries to fish several dozens of meters away. Noise may drive fish away and change their behavior. The serious impact zone for the noise and blasting has been set at one kilometer and the potential impact zone five kilometers from the work locations.

The hydraulic construction work will result in the loss of approximately 40 hectares of seabed habitat. The area to be dredged includes spawning areas of sea-spawning whitefish and Baltic herring as well as fry habitats of Baltic herring, sea-spawning whitefish and vendace. The Hanhikivi sea area has many spawning areas of these species, so the destruction of some spawning areas will have no significant impact on the overall fry production in the area. The impact of the loss of habitat on the fishing industry was assessed as moderate. The impact of breakwaters and other fixed structures on the flow rates will remain low. Such structures may also create new sheltered habitats for fish. The impact area has only few reproduction areas of spring-spawning fish, which means that the construction works will have no significant impact on these stocks.

Increased solids content may damage or destroy fry and spawn. Turbidity will make feeding more difficult for fish and harms their food such as the zooplankton. The adverse impact of turbidity rapidly disappears outside the work targets. The overall harmful impacts were assessed as minor,

and the impact was estimated to extend no further than two kilometers from the work location.

In the spring, the grayling migrates to the Liminkaoja river located near the hydraulic construction sites. The pro- ject may therefore have an impact on the migration of the grayling, if excavation is carried out during the migration season.

There are no important salmon or trout spawning riv- ers in the Pyhäjoki or Raahe districts. Migration routes of salmon and common whitefish do, however, pass the Han- hikivi headland. The noise and water quality changes may change some of these routes, but will not affect the ability of the fish to find their spawning rivers.

Fishing

The project’s impact on fishing during the construction phase will be significant. Fishing at the construction areas and in their immediate vicinity will not be possible during the construction phase. The construction activities in the sea area may also drive away fish from a larger area and possibly influence their migration routes. Excavation, in particular, will cause powerful underwater noise that may drive away fish from an extensive area. Significant impacts are likely in an area extending at least one kilometer from each blasting site. Changes in fish behavior may appear as far as five kilo- meters from blasting sites.

The hydraulic construction work will destroy spawn- ing areas of sea-spawning whitefish and Baltic herring in the dredging areas, and will certainly affect the spawn- ing of Baltic herring in three consecutive construction years. The fishing activities in the area are mainly based on whitefish. Whitefish come to the area to feed on her- ring spawn. Thus, the project may have a negative impact on the fishing of whitefish in the project site’s immediate vicinity.

While fishing may be possible near the work locations, turbidity will cause increased soiling of fishing equipment. The dredged soil does, however, contain only little organic material, which will probably keep the soiling down and limited to a small area, no more than a few kilometers from the work locations.

7.4.3.2 The impact of waste soil dumping into the marine spoil area

In the following, the impact of dredging waste dumping operations on the waters and fishing industry is examined based on the water permit applications that concern the marine spoil area (Fennovoima Oy 2013c).

Impact on water systems

The impact is related to turbidity caused by the dumping operations and the effect that the turbidity will have on the fish stocks and the fishing industry. The marine spoil area is located in open sea approximately 9.5 kilometers to the west from the Hanhikivi headland. There are no islands within a 10-kilometer radius of the marine spoil area. The surface area of the marine spoil area is approxi- mately 190 hectares.

136 7 Assessment methods, the present state of the environment and the assessed environmental impacts

Most of the material to be dumped (90 %) is rough and fine sand that settles quickly. Based on model cal- culations, the turbidity caused by the dumping opera- tions will decrease to 1 % within significantly less than 24 hours. The impact of turbidity mostly remains within the marine spoil area. If the grain size of the mass to be dumped is finer, the turbidity may extend to 2–4 km from the marine spoil area. In such cases, turbidity is mostly found in the water layers near to the seabed. The most extensive turbidity impacts caused by dredging waste being dumped into the sea have been observed within 3–4 km from the actual marine spoil site. It is unlikely that any turbidity will be observed in shore areas or near them. (Luode Consulting Oy 2012.)

The quality of the seabed at the marine spoil area also has an impact on the quantity of solids that mix with seawater. Based on samples obtained from the sea off the Hanhikivi headland, the seabed at the marine spoil area is hard sand that will not mix with the water extensively when dredging masses are dumped on top of it. Any resus- pended sand will settle quickly and is not likely to spread with currents. Based on the results, the maximum dis- tance traveled by the turbidity caused by dumping would remain at the level of 2 km even at the fastest measured flow rates when the settling rate of the dumped mass was set at 0.8 mm/s, which corresponds to the settling rate of the finest observed grain size used in the cooling water simulation. Turbidity would also be strongly diluted due to mixing with water masses. Experience has shown that the hard clay found in the seabed is not easily broken by dredging or dumping.

The currents near the bottom may carry dumped materials towards the shore even after the dumping oper- ations have been completed. Flow measurements carried out in the marine spoil area show that the hardest cur- rents flow towards the north-east and south-west, which means that the migration of solids to the shore is very unlikely.

The marine spoil area is too deep for any aquatic vegetation. Therefore, no valuable underwater habitats can be harmed.

The benthic fauna of the marine spoil area will be bur- ied under the dumped mass. The benthic fauna will recover fully in a few years after the completion of the dumping operations.

Impact on fish stocks and the fishing industry

According to a preliminary plan, dredging waste created during the construction phase will be dumped into the sea in three years. After this, dredging will be carried out approximately every ten years to maintain the channels, and dredging waste will be dumped accordingly. The impact of dumping noise, solids, loss of habitat and changed flow con- ditions on the fishing industry was estimated to be minor. There are no fish reproduction areas in the marine spoil area or in its immediate environment. Migration routes of salmon and, most likely, common whitefish pass near the marine spoil area, and dumping operations may cause temporary changes to these. Turbidity caused by dumping operations is mainly limited to the deepest waters near the

seabed. Migrating fish stay closer to the surface, where the impact of turbidity is minor. Therefore, the detrimental effect of turbidity was estimated to be rare and to have little significance.

No fishing takes place in the planned dredging waste marine spoil area, but it is possible that the noise and tur- bidity disturb or prevent fishing near the marine spoil area or the transportation route. Some commercial gillnet fish- ing takes place within the estimated maximum impact area of turbidity, but fishing operations are mainly focused on the shallows around the marine spoil area.

7.4.3.3 Other impacts

The blasting, excavation and stone crushing carried out during the construction phase will increase the solids and nitrogen load in drained rainwater. Oil might also typically be found in the rainwater drained from con- struction sites. Loading can be reduced by leading drain water first to sedimentation wells and oil separators. If such water protection measures are adequate, solids and oil are not estimated to cause any significant harm to the marine ecosystem. The impact of inorganic nitrogen load also remains minor even at the worst case due to the temporary nature of the construction work and the fact that phosphorus is the most important factor limiting the increase of primary production in the Hanhikivi sea area. The inorganic nitrogen content of drained rainwater is also quickly diluted in the open sea.

The noise caused by the construction of the nuclear power plant and carried from land to sea may drive fish away from the immediate vicinity of the project area.

7.4.4 Operation phase impacts

The impacts on water systems include the impact of cool- ing water, treated process and washing water, and water intake. The treated process and washing water will be drained into the sea together with the cooling water. Sani- tary waste water will be treated at a municipal water treat- ment plant.

7.4.4.1 The impact of cooling water Sea currents

The cooling water intake and discharge will have a local impact on the sea currents in the area. These impacts were assessed by Suomen YVA Oy using a model which presented the currents as the difference between the implementation alternative and the zero option. Average currents of June 2012 were used as the starting point of the current simulation, and changes in currents were examined at six different depths (0–1 m, 2–3 m, 3–4 m, 5–7 m, 7–9 m and 9–11 m).

The impact of cooling water discharge on currents was obvious in the surface layer (0–1 m). The impact of cooling water intake, on the other hand, was more definite below the surface layer (Figure 7-19). In the deepest layer (9–11 m), no impact could be detected.

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