Legal Concepts of River Boundary Delimitation With Emphasis on Navigable Rivers
The Middle East has experienced some of the most persistent political disputes. Approximately 90 percent of the region’s water resources are transboundary.
The Islamic Republic of Iran, located in a strategic region and connected to numerous international rivers, is not an exception to these realities.
Principles of International Law in Determining River Boundaries
The Concept of an International River
Grotius and Vattel first articulated the theory of the internationalization of rivers. In earlier approaches, rivers were generally considered to fall under the sovereignty of states within their territories and along their banks.
International rivers are navigable rivers that pass through more than one country. An international river is a river that flows through the territory of two or more states. In such a case, each state exercises sovereignty over the portion of the river that passes through its territory.
International rivers are commonly categorized into two groups:
- Boundary rivers that mark the boundary between two states. Examples include the Arvand Rud (Shatt al Arab) as a boundary river between Iran and Iraq, and the Aras River as a boundary river between Iran and Armenia and Azerbaijan.
- Rivers that traverse the territory of two or more states, such as the Nile and the Rhine. The Nile flows through multiple countries, including Sudan, Egypt, Ethiopia, and others.
Hydropolitics
A review of the world’s natural and political geography shows that political borders do not necessarily align with water systems. Approximately 50 to 60 percent of each continent’s area consists of shared waters.
Shared bodies of water cover more than 45 percent of the Earth’s surface, and globally, 261 rivers are shared by two or more countries.
In practice, several approaches are used in the creation of river boundaries:
- Approach 1: Using One Riverbank as the Boundary: Under this approach, one of the riverbanks is designated as the boundary between the two states. As a result, sovereignty and control over the river effectively shift from one side to the other. This method provides limited practical control over changes affecting the river boundary.
- Approach 2: Midline Delimitation: This approach is derived from Roman private law and later reflected in the legal systems of various European states. The midline is defined as a line where each point is at an equal distance from the nearest point on each of the two riverbanks.
- Approach 3: The Thalweg Line: Under this approach, the boundary follows the thalweg, meaning the line that divides the river’s surface into two parts. In many rivers, however, a deeper channel exists that is safer and more suitable for navigation. Boat operators commonly use that deeper channel when crossing. This navigable channel does not always coincide with the geometric midline and is often closer to one bank.
The Principle of Absolute Territorial Sovereignty
Under this principle, the portions of international rivers that flow through a state’s territory are treated as internal waters, and the state may attempt to alter the flow of the river.
At the same time, international law limits such conduct where it causes harm to other states. Under generally recognized principles, no state should stop or divert the natural flow of waters that naturally pass from its territory into the territory of another state, nor use those waters in a manner that harms the neighboring state or prevents its use.
The Principle of Absolute Territorial Integrity
Under this principle, riparian states must allow the natural flow of the river to continue and have no right to alter the river’s waters. Max Huber and Oppenheim are identified as supporters of this approach.
The Principle of Common Ownership and Shared Use
Under this principle, neighboring states share joint sovereignty over an international river. In other words, all relevant states have an equal right to use the river’s waters.
The river is treated as an economic unit, and the waters are considered to belong to all riparian states rather than being limited by political borders.
Limited Territorial Sovereignty and the Principle of Equitable Utilization
Under this approach, each riparian state’s sovereignty is limited by the obligation not to cause harm to other riparian states. Use of the river must be equitable and balanced, taking into account the rights and interests of all concerned states.
Frequently Asked Questions About River Boundary Delimitation With Emphasis on Navigable Rivers
An international river is a navigable river that flows through the territory of two or more states. Each state exercises sovereignty over the portion of the river within its territory, and such rivers may either form a boundary or traverse multiple territories.
Key principles include absolute territorial sovereignty, common ownership, limited territorial sovereignty and equitable utilization, and technical delimitation approaches such as the midline and the thalweg.
It suggests that a state may exercise sovereignty over the segment of a river within its territory, but this authority is restricted by international law obligations not to alter the natural flow in a manner that causes harm to neighboring states.
It holds that riparian states have joint rights over an international river and that all concerned states may use the river’s waters on an equal basis, treating the river as a shared economic unit.
Under this principle, each state may use the river but must do so fairly and in a way that does not cause harm to other riparian states, with utilization balanced among competing interests.
The midline is defined as a line equidistant from both riverbanks. The thalweg follows the deepest and most navigable channel used for safe passage, which may not align with the geometric midline and often lies closer to one bank. What is an international river and what are its characteristics?
What international law principles are used to determine river boundaries?
What does the principle of absolute territorial sovereignty mean in the context of rivers?
What is the principle of common ownership of international rivers?
How does limited territorial sovereignty or equitable utilization operate?
How are the midline and thalweg used in river boundary delimitation?
If a river forms the border between two countries, who owns the river itself?
The legal status of a river used as an international boundary depends on agreements between the countries involved and principles of international law. In some cases, the boundary may follow the middle of the river, the main navigable channel, or another agreed line. The specific arrangement depends on treaties and historical practice.
If a river changes its course naturally, does the international border move with it?
Changes in river courses can create complex legal questions. Whether a boundary moves with a river depends on the original agreement, the type of change, and the rules applied by the countries involved. Some legal systems distinguish between gradual natural changes and sudden changes in the river’s course.
Can one country build a dam on a border river without approval from the other country?
Activities affecting shared rivers can involve international legal considerations, especially when they may impact another country’s rights or interests. The obligations of each state depend on applicable agreements, international principles, and the specific circumstances of the project.
How do countries decide exactly where the boundary line is in a river?
Countries may use different methods to determine river boundaries, including the geographic middle of the river, the middle of the main channel, or the riverbank, depending on the agreement and circumstances. Clear demarcation is important to avoid future territorial disputes.
If two countries disagree about a river boundary, can an international court decide it?
Yes, some river boundary disputes have been addressed through international courts or arbitration when countries submit the matter for resolution. The outcome usually depends on treaties, historical evidence, maps, and principles of international law.
Does a country have full control over the part of a river that is inside its territory?
Control over international rivers can involve balancing territorial rights with the interests and rights of other states sharing the water resource. The legal position depends on treaties, customary international law, and the specific relationship between the countries involved.
What happens if the river boundary changes because of flooding?
Flooding and natural changes can create difficult boundary questions. The legal effect depends on whether the change is temporary or permanent and on the rules governing that particular boundary. Historical agreements and evidence about the original boundary may become important.
Can people living near a border river use water from both sides?
The rights of individuals and communities near international rivers depend on domestic laws, international agreements, and any arrangements between neighboring countries. Shared water resources are often managed through legal frameworks designed to balance different interests.
Why are river borders sometimes harder to define than land borders?
Unlike fixed land features, rivers can naturally change over time, creating questions about the exact location of a boundary. Legal systems have developed different approaches to address these geographic changes and maintain certainty in territorial limits.
If a country has used a river boundary for many years, can another country later challenge it?
Long-term practice can be relevant in territorial disputes, but it is not the only factor considered. Courts and international bodies may examine treaties, official records, maps, state conduct, and other evidence when evaluating a boundary claim.