iGeo 2017, Писмен тест — Задача 4. Section D: Tides

1. Answer (point marking – 0.5 marks for each correct factor):
Tidal constituents:

• Moon’s gravitation,
• Sun’s gravitation,
• Earth's rotation,
• Inertia (on the side of the Earth away from the Moon, inertia exceeds the gravitational force, and the water tries to keep going in a straight line, moving away from the Earth, also forming a bulge),
• The position of the Moon and Sun relative to the Earth,
• Moon’s distance from the Earth (when the Moon is closest, at perigee, the tidal range increases, and when it is at apogee, the range shrinks),
• Earth’s distance from the Sun (the elliptical shape of the Earth's orbit around the Sun),
• The obliquity (tilt) of the Earth’s Equator and rotational axis,
• Lunar altitude (elevation) above or below the Earth’s Equator: Moon’s declination (angle from Earth’s Equator ranging from 28°N to 28°S over the course of a month),
• The Moon’s orbit inclination from the ecliptic (the plane of the Earth's orbit around the Sun): Moon’s inclination is about 5°, and the direction gradually changes over an 19-year cycle, alternately adding to or subtracting from the 23.5° tilt of the Earth’s axis,
• Sun’s declination (ranging from 23°N to 23°S over the course of the year),
• Gravitational effects of other celestial bodies,
• The placement of landmasses on Earth,
• The amphidromic systems of the oceans,
• Bathymetry,
• The shape of the coastline,
• The shallow depth of water relative to wavelength of tides,
• Distance from the landmass: conversely, mid-oceanic islands not near continental margins typically experience very small tides of one meter or less,
• The latitudinal variation of the rotational velocity of Earth,
• The Coriolis Effect,
• Local wind and weather patterns (low and high pressure systems).

2. Answer (point marking):

Adapted from: http://www.canaturalist.com/2016/01/23/bogus-terminology, https://manoa.hawaii.edu/exploringourfluidearth/physical/tides/tide-formation-and-gravitational-pull, https://www.flickr.com/photos/donkeyhotey/5679642883, http://www.thehoodwitch.com/blog/2017/3/11/full-moon-in-virgo-3122017.

• The Sun, Earth, and Moon form a line (a condition known as syzygy) and the Moon is in correct position (1 m).
• Solar and lunar tide bulges augment each other (coinciding) (called spring tide) (1 m).
• Subsolar tide and antipodal lunar tide and antipodal solar tide and sublunary tide are coinciding on opposite sides of the Earth (1 m).
• Earth’s anticlockwise rotation duration and orbit (0.5 m) and the Moon’s counter clockwise movement on its orbit (0.5 m).
• Annotations (explaining rotation durations and including labelling of Sun, Earth, full moon, (sub)solar tide, (sub)lunar tide and antipodal tides) (1 m).

3. Answer (point marking – 1 mark for each correct suggestion):

• These radical measures were launched because the unique characteristics of Mont Saint-Michel were being heavily degraded and France has international responsibilities to maintain the character of world heritage listed sites: the insular character during high tide that attracted tourists was being lost due to accumulating silt deposits. Due to increased siltation/silt deposits the castle was no longer surrounded/cut off by the sea at high tide which attracted tourists:

  • The raised (permanently dry) causeway prevented the tide from scouring the silt around the mount. Replacement of the causeway with a bridge has restored the flow of water around the island.
  • Land reclamation on coastal flats (polders) and grazed salt marsh meadows decreased the distance between the shore and the island allowing less and not so deep free water movement having less force to clean the area from disposed sediments.
  • The canalized river reduced the spread of water (dispersion of the flow of water) to wash away accumulated silt from the (area). A hydraulic dam uses the waters of the river Couesnon and the tides to help remove the accumulated silt.

4. Answer (point marking – 1 mark for each correct suggestion):

Strengths – are internal characteristics of the project that give it an advantage over other projects

• Unlike some other renewable sources of power, tidal power is predictable.
• They can be constructed in areas where the coastal landforms mean that the old type of tidal power plant is not feasible.
• In areas vulnerable to flooding and coastal erosion, increasingly as a result of climate change, tidal lagoons can act as a barrier to potentially damaging and disruptive storm surges and waves that threaten coastal communities and infrastructure.
• Because it would be a landmark, it will be in instrumental in instigating/initiating regeneration and other developments.
• Renewable clean zero carbon (no $\mathrm{CO_2}$ during operation) year round cheap energy.
• Jobs in building and managing.
• It does not take land space because it is built on the water (no waste of arable land).

Weaknesses – are internal characteristics that are a disadvantage relative to other projects

• It is only feasible in areas with a high tidal range.
• Enormity of the project, high cost, procurement of right kind of building materials such as rocks, gravel and sand.
• As a first of its kind, none of the real impacts on environment, economy and socio-cultural life is known.
• The stability of the seawall is not strong enough to endure severe weather conditions.
• The understanding of coastal processes, of physical (e.g. influence on the currents) and biological origin may still have some blind spots.
• Although it is not standing water, it may need cleaning from algae.
• The fact that it is in a marine environment, makes it more difficult to deal with potential accidents (motor oil spills) or diseases, epidemics, e.g. bird flu.
• Difficulty of cleaning and repairing broken (corrosion?) turbines in the marine environment.
• Limits commercial shipping and navigation so may not get government approvals (meaning extra harbours need to be built on either side of the lagoon – instigating/initiating unplanned and unforeseen developments).

Opportunities – are external elements that the project could use to its advantage

• Increasingly stringent government regulations on greenhouse emissions favour clean energy.
• Society now expects new power plants will be non-polluting, favouring power plants such as the new type.
• Maximizing return on investment by developing associated aquaculture (lobster and oyster hatchery, edible seaweed, cockle and mussel farming and further development work around Integrated Multi-Trophic Aquaculture (IMTA) – a way of a number of different species living together for environmental and economic benefit), also creating new jobs.
• Establishing good relations with the local community by developing recreation (walks on the wall, cycling, running, playgrounds, sporting events, angling, swimming, canoeing, rowing and sailing), tourism, edutainment and environmental projects.

Threats – are external elements that could cause difficulties for the project

• A change in government policy could undermine the economic viability of the project.
• Changing self-regulatory environment to totally human-controlled environment can backfire on many unpredictable levels and scales.
• Severe weather conditions may damage the seawalls.
• Negative changes to the environment (such as to coastal processes, water quality, flooding and hydrology, intertidal and subtidal benthic ecology, fish, marine mammals, birds, terrestrial ecology, seascape and landscape, heritage, salinity, sedimentary deposits) may lead to government fines and loss of community goodwill.
• Natural hazards like earthquakes, tsunamis etc.