10.2 Accretion, Reliction, Erosion & Avulsion

Gradual versus sudden

"Imperceptible" means the process cannot be seen while it happens, even if the total change over years is large. In County of St. Clair v. Lovingston, 90 U.S. 46 (1874), the U.S. Supreme Court treated accretion as imperceptible even though the change could be measured over time. Heavy deposits during high water are still accretion. Avulsion requires the stream to leave its channel suddenly.

Why the rule is fair. A riparian owner bears the risk of loss by erosion, so the owner gets the benefit of gain by accretion, and keeps access to the water. Avulsion is different because the land is still identifiable after a sudden change, so title stays where it was.

On the coast. The Public Trust Tidelands Act writes the doctrine into Mississippi's tidelands law. The trust boundary is ambulatory: natural inland expansion of the tide increases trust lands, while natural accretion and reliction diminish them and increase the contiguous upland owner's property (§ 29-15-7). Artificial fill is treated differently from natural accretion (Section 10.3).

Dividing accretion among riparian owners

When several owners front a bend that builds out, their new frontage must be divided so that each keeps access to the water. Extending the old upland lines straight out often makes the lines cross or cuts an owner off.

Proportional shoreline method. Give each owner a share of the new shoreline proportional to their share of the old shoreline, then connect each owner's old shore corner to the matching point on the new shore:

New frontage for a tract = total new shoreline × (tract's old frontage ÷ total old frontage)

Example: tracts A, B, and C had 400, 200, and 400 feet of old frontage (1,000 feet total), and the new shoreline is 1,500 feet. B receives 1,500 × 200/1,000 = 300 feet; A and C receive 600 feet each.

Where the shore and channel are nearly straight, courts and surveyors also use lines perpendicular to the thread or to the general shoreline. Whichever method applies, document it on the plat and note that the allocation is subject to the owners' agreement or a court decision.

Avulsion on the Mississippi River

The lower Mississippi River has changed course many times by cutoffs across the necks of meander loops, some natural and many engineered. After a cutoff, the abandoned bend often becomes an oxbow lake; Lake Washington and Eagle Lake in Mississippi are examples.

• Interstate boundary. The boundary between Mississippi and Louisiana or Arkansas follows the river's main channel, the thalweg, and moves with accretion and erosion. After an avulsion it stays in the abandoned channel as it ran before the cutoff. In Mississippi v. Arkansas, 415 U.S. 289 (1974), the Supreme Court applied these rules to decide which state held disputed land on the river. Earlier cases such as Nebraska v. Iowa, 143 U.S. 359 (1892), and Arkansas v. Tennessee, 246 U.S. 158 (1918), established the same accretion–avulsion framework.
• Consequence. Land cut off by an avulsion stays in the state, county, and ownership it belonged to before, even if it now lies on the "wrong" side of the river.

Islands

Title to an island depends on who owns the bed it forms on. In non-tidal Mississippi waters the beds belong to the riparian owners (Section 10.1), so an island arising from the bed generally belongs to the owner of that part of the bed, divided by the thread if it straddles it. In tidal waters the bed is public-trust land, so a new island is generally trust land unless it forms by accretion to an existing upland. On the Mississippi River itself, with its interstate boundary, federal works, and long histories of accretion and avulsion, island and batture titles are fact-specific. Research the channel history before drawing conclusions.

If an island and the mainland accrete toward each other until the slough closes, the usual rule divides the joined land along the line where the two accretions met.

Proving what happened

Accretion and avulsion are facts that must be proven, usually in chancery. Evidence includes:

• GLO meander lines and plats (showing the original position of the water);
• Mississippi River Commission and U.S. Army Corps of Engineers channel surveys and hydrographic maps;
• historic aerial photography and USGS topographic maps;
• dated vegetation, such as the age of trees on the new land compared with the old bank;
• soils and sediment evidence; and
• testimony about floods and cutoffs.

The surveyor's plat should show the historic lines relied on and their sources (Rule 7.3, item 9), and for tidal or lake boundaries it should meet the Rule 7.5 elevation tolerances.

Exam traps

• Rapid flood deposits are always avulsion. No: deposits are accretion unless the stream suddenly left its channel.
• After a cutoff, the state line moves to the new channel. No: avulsion leaves the boundary in the old channel.
• Extend the upland lines to divide accretion. Only if the result is equitable; the proportional method avoids cutting owners off from the water.