Boundary Line Through a Shifting Sandbank
You are advising on a maritime delimitation between two adjacent coastal states. The agreed provisional equidistance line runs through a submerged sandbank that has migrated 1.2 km over 15 years, according to historical charts and recent multibeam data. One state argues the sandbank is a 'special circumstance' that should deflect the line; the other argues it is irrelevant because it is fully submerged at all states of tide. The relevant treaty text is silent on sandbanks. Baseline points on both coasts are well established, but one basepoint sits on a low-tide elevation that is 0.4 m above chart datum at spring lows and has a small lighthouse. You must produce a technical position paper.
1. How should the migrating sandbank be treated in the delimitation analysis, and what is the legal-technical reasoning?
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Treatment: A fully submerged feature that is never above water at low tide is generally not a basepoint and does not generate maritime entitlements. Its migration is therefore usually not a 'special circumstance' that deflects an equidistance line, because it does not affect the location of baselines or the geography that the line is measured from.
Reasoning:
- Under UNCLOS, basepoints derive from the low-water line of the coast and from low-tide elevations only where they meet the relevant tests (e.g., within the territorial sea of a coast, or where they have been appropriated).
- A permanently submerged bank is part of the seabed, not the coast; its movement does not shift entitlements.
- If, however, the bank is claimed to affect navigation, resources, or security, it may be argued as a non-geographic special circumstance - but that is a policy argument, not a technical one, and must be distinguished clearly.
Recommendation: Treat the sandbank as legally irrelevant to the equidistance geometry, but document its migration as a factual matter and note that any charted depiction used for basepoints must be current.
2. The low-tide elevation with the lighthouse is contested as a basepoint. How do you assess it, and what does the lighthouse change?
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Assessment of the low-tide elevation (LTE):
- An LTE is a naturally formed area of land above water at low tide but submerged at high tide. If it lies wholly or partly within the territorial sea of a coast, its low-water line may be used as a baseline.
- The 0.4 m height above chart datum at spring lows is marginal; verify it is above water at all low tides (not just spring lows) and that it is natural, not an artificial structure.
Effect of the lighthouse:
- A lighthouse is an artificial structure. Artificial structures do not generate baselines or basepoints, and their presence does not convert a submerged feature into a basepoint.
- The lighthouse may, however, be relevant to the 'special circumstances' analysis (e.g., navigation aids) and to any argument about appropriation of the LTE, but it does not itself create entitlement.
Recommendation: Use the LTE as a basepoint only if it satisfies the natural-formation and low-water tests; otherwise rely on the mainland low-water line. State the evidence (tidal records, survey heights) explicitly.