Accretion, Avulsion and the Ordinary High Water Mark on a Northern Idaho Lake
You are retained to establish the lakeshore boundary of Lot 7, Block 3 of a subdivision platted in 1972 on the west shore of a large natural lake in northern Idaho. The plat meanders the shoreline and shows Lot 7 with 82.4 ft of waterfront; the meander line was run at the water's edge as it existed in 1971. The current ordinary high water mark (OHWM) lies an average of 31 ft lakeward of the platted meander line at the north end of the lot and 9 ft lakeward at the south end. Aerial photos from 1971 through 1995 show a gradual, fairly uniform recession of the low bluff. In February 1996 a single storm event collapsed a 25-ft section of bank overnight, toppling six mature cedars that today stand rooted in the water. The adjoining owner has had a surveyor flag a line 20 ft landward of the current OHWM, asserting that the 1996 event froze the boundary at that location. Your client wants a survey showing the full 31-ft gain.
1. What rule governs the location of the lot line here, and how does it apply to the 1996 storm?
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The platted meander line is not a boundary. It was run to show the water's edge for area and closure purposes. Where a natural lake is meandered, the upland title runs to the ordinary high water mark, and that line moves with the water under the common-law doctrines of accretion, reliction and erosion.
The controlling distinction is gradual versus sudden:
- Accretion - imperceptible, gradual change - belongs to the riparian owner. The 1971–1995 aerial record shows exactly this: a slow, uniform recession of 31 ft at the north end and 9 ft at the south. That gain is your client's.
- Avulsion - a sudden, perceptible change - does not move the boundary. Where the 25-ft section of bank collapsed overnight in February 1996, the boundary remains at the OHWM as it existed immediately before the storm.
So the lot line is a composite: the current OHWM along the portions that changed gradually, and the pre-February-1996 OHWM across the avulsed reach. The six mature cedars now standing rooted in the water are strong physical evidence of avulsion; gradual submergence would not leave mature trees upright and rooted in that condition. Note too that the neighbor's theory is inverted - avulsion preserves the old line, so a 20-ft landward flag is not supported by the very event cited to justify it.
2. What evidence would you gather to establish the pre-avulsion OHWM, and how do you establish the OHWM itself?
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Separate the two questions: where is the OHWM now, and where was it in 1996?
Establishing the OHWM is a field exercise using the physical indicators of ordinary, as opposed to flood or seasonal, water: the natural scour line, the landward limit of the water's erosive action, the boundary between upland and aquatic vegetation communities, the lower limit of perennial vegetation, soil characteristics, and staining or undercutting on bank exposures. On a regulated or regulated-lake-level water body, long-term gauge records are essential to keep a seasonal high stage from being mistaken for the OHWM. If the state has published an OHWM elevation or line for this water, use it and cite it.
Reconstructing the 1996 line requires: sequential aerial imagery (1995, immediately post-storm, and current) at a known scale, rectified to your control; bluff-profile cross sections; soil borings to distinguish intact bank from storm-deposited material; tree-ring or scar evidence on the toppled cedars; testimony from long-time residents; and any prior survey or state map of the shoreline. A distinctive storm deposit is often the best physical marker of the pre-storm toe.
Document all of it on a record of survey: the plat meander line, the current OHWM, the reconstructed pre-avulsion line across the 25-ft reach, the basis and evidence for each, the datum for shore elevations, and the neighbor's flagged line labeled as a claim of record by others. The surveyor locates and reports; navigability, state ownership of the bed, and title are for counsel and the court.
3. The client demands a survey showing the full 31-ft gain, and the neighbor's surveyor has already flagged a competing line. How do you proceed?
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Do not draw a line the evidence does not support, and do not draw the client's line because the client asked. The evidence supports 31 ft of accretion at the north end and 9 ft at the south, with the pre-avulsion line held across the 25-ft collapsed reach - that is what the map shows.
Handle the competing flag geographically rather than dismissively: locate it, dimension it from both the platted meander line and the current OHWM, and label it as a boundary line claimed by others with the date and the name of the surveyor who set it. A notation of that kind is a factual statement, not an endorsement.
In the transmittal, tell the client plainly: (1) the meander line does not bound the lot; (2) gradual recession is the owner's; (3) a sudden collapse does not move the boundary; (4) the surveyor's map records the evidence, and if the parties disagree about title, that is resolved by negotiation, agreement, or court, not by the surveyor's opinion. Recommend counsel. Recommend a written boundary line agreement if both owners can be persuaded, since an agreement removes the avulsion uncertainty cheaply.
Finally, record the survey. A shoreline boundary built on a reconstruction of a 1996 event is exactly the kind of determination that must be documented for the next surveyor, and an unfiled opinion on a disputed line invites the dispute to be re-litigated from scratch.