The border between Iowa and Nebraska was defined as the middle channel of the Missouri River.
Between 1851 and 1877, the Missouri River changed course so that it occupied a very different bed and flowed through a different area.
Procedural History:
SCOTUS held that the old line was valid.
Issues:
What property rules apply when a border of property is along a river or other body of water.
Holding/Rule:
When the border of a property is along a river or other body of water, there are two possible property rules…
Rule of Accretion - When the banks are changed gradually, the boundary remains on the river (land can be gained or lost based upon accretion).
Rule of Avulsion - When the river suddenly abandons its old bed and seeks a new bed, the boundary remains where it was before the change.
Reasoning:
These two rules come from authority; accretion means the boundary varies; avulsion means the boundary is fixed.
The law of accretion holds for the Missouri River, in general. Thus, the boundary between the two states can vary.
However, in regard to the change in the river in 1877, that movement was an avulsion; thus, the boundary there remains where it was set before the change.
