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May 18

If the Alabama-Georgia border be a river and rivers can change over time...

If the Alabama-Georgia border be a river and rivers can change over time, then does that mean the state governments and the federal government all have to acknowledge that state borders can change because of Mother Nature and Father Time? 2601:545:C780:56C0:15C6:350C:9D1E:1439 (talk) 12:19, 18 May 2022 (UTC)[reply]

Yes and No. A lot depends on the specific language used when the borders were formed. In some cases, the borders are defined as simply being the middle of a river… and, in these cases, if the river changes course then the borders would change with it. However, in other cases, the border is defined as being the middle of the river as it was at a specific point in time… and in these cases, the borders remain the same even if the river changes. Several good examples of the latter can be found along the Mississippi River… where several states that are on one side now have exclaves on the other side due to the river changing course. Blueboar (talk) 12:53, 18 May 2022 (UTC)[reply]
In general, when a river is chosen as a border, the border is defined as some specific part of the river, such as the midline or the thalweg, or occasionally as one bank or the other. The border is allowed to drift along with the river's meandering so long as the river remains in the channel it is in, and the channel migrates gradually. When the river abandons an old channel for a new one (which can be a natural process, or it can be man-made), the border becomes fixed at the old channel. This explains the deviations of the border along the Mississippi; in places where the Mississippi has drifted gradually, the border remains in the river. In places where it has jumped from one channel to another (look for oxbow lakes), the border remains at the old channel. This can vary however, as the border may be defined differently depending on the specific document that created the border. --Jayron 32 13:46, 18 May 2022 (UTC)[reply]
Jayron32 Many thanks for introducing thalweg as a word and concept. Both new to me, much appreciated! Tribe of Tiger ^{Let's Purrfect!}

There have been several modifications of the boundary line between Georgia and South Carolina over the years because of alterations along the Savannah River, including erosion, the accretion of islands and banks, and changes in the river course itself. From Boundaries of Georgia.

See also Tennessee–Georgia water dispute. Alansplodge (talk) 13:49, 18 May 2022 (UTC)[reply]
The Tennessee–Georgia border dispute is over the definition of a line-segment border, not over a border defined by a river. As with many disputes, it comes down what are sometimes vague descriptions of borders in the legislation that created them several hundred years ago; when the border is surveyed and marked in the field, that can often have deviated from the definition on paper, and in this case the border de facto differs slightly from the border de jure, and the claim by Georgia is that the de jure border would give them access to a waterway that the de facto border does not. Access to that water way means that Georgia has water rights to it; however this is distinct from situations where the river is used itself as a definition of a border. In this case, it was not, --Jayron 32 14:12, 18 May 2022 (UTC)[reply]
Quite right, it was lazy editing on my part. However, one of the disputed elements is a river boundary now under a reservoir called Nickajack Lake. Alansplodge (talk) 14:06, 19 May 2022 (UTC)[reply]
Sort of... One of the disputed elements was the Alabama-Georgia-Tennessee tripoint, which was defined by law based on a confusing set of different statutes; the Alabama-Georgia border was defined as running north to the location known as Nickajack at the southernmost bend of the river, and from there along the river's western bank until meeting the southern border of Tennessee. The problem is that the southern border of Tennessee, defined as the 35th parallel north, was surveyed at the time to pass south of Nickajack, meaning that the Alabama-Georgia border (and thus the tripoint) was located south of the river itself, obviating the part of the defined boundary that included part of the river in Georgia. Doubly unfortunately, the survey was wrong, and the 35th parallel actually does cross the river. Tennessee's claim is that the border was settled by the survey, and that deviations from the 35th parallel were ratified into law when the border was established. Georgia contends that the border should be pegged to the actual 35th parallel. If you look at most current maps, such as Google Maps, you see the contention: the dotted line is drawn south of the river, but clicking the line confirms that the line is somewhat south of the 35th parallel. The tripoint, according to Google, is at about 34.984661 N, while the 35.000000 line does cross where the river had been before the lake was formed. Alabama, for its part, doesn't really give a shit because a significant portion of the Tennessee River flows through Alabama anyways.--Jayron 32 14:25, 19 May 2022 (UTC)[reply]

Much of the border between the Australian states of New South Wales and Victoria is defined as the southern or left border of the Murray River. Well, that's the simple version. There's actually a 24 page document clarifying the situation. It involves British derived law plus precedent from the USA. A murder case where the location of the body mattered a lot led to more clarification. If you have time, it's worth a read. There's some great pics of the river. https://www.spatial.nsw.gov.au/__data/assets/pdf_file/0006/25935/NSWVic_v3.pdf HiLo48 (talk) 10:18, 19 May 2022 (UTC)[reply]

That sound similar to the border irregularity sometimes known as the Idaho Murder Strip. --Jayron 32 12:30, 19 May 2022 (UTC)[reply]

See Ötzi#Border dispute. 2A02:C7C:365E:E700:8123:7A3F:B448:E090 (talk) 11:45, 20 May 2022 (UTC)[reply]

The U.S. Supreme Court ruled in 1933 in the case of Vermont v. New Hampshire that the boundary between those two states is the west bank of the Connecticut River at the mean low-water mark. Michael Hardy (talk) 05:01, 21 May 2022 (UTC)[reply]

Which part of the bank? What about flood times? And those places where tributaries enter? What if the river moves? HiLo48 (talk) 05:05, 21 May 2022 (UTC)[reply]

See above. If the river moves, it depends on how it moves; if it abandons its channel, the general idea is that the border stays at the old channel. Gradual erosion generally causes the border to move with the river. For the Connecticut River between New Hampshire and Vermont, this is not a meandering river, so it is unlikely to cut new channels in such a way as to make this a problem. Mean low water is usually defined by regulation based on datum taken from some official body; NOAA manages this data, eg. [1]. --Jayron 32 11:57, 23 May 2022 (UTC)[reply]