Water Boundaries and Riparian Rights
Ownership limits
California water boundaries turn on navigability and tide. The state holds title to tidelands and the beds of navigable waters in trust for the public. The upland boundary is the ordinary high water mark for tidal waters (the mean high tide line) and the ordinary low water mark for navigable nontidal rivers. On nonnavigable streams, the upland owner typically owns to the thread or center of the stream unless the deed or patent provides otherwise. A meander line is an artificial line run for area computation and is never the legal boundary.
Ambulatory boundaries
Accretion (gradual and imperceptible) and reliction move the boundary with the water and benefit the upland owner. Avulsion (sudden and perceptible change, such as a flood cutting a new channel) does not move the boundary; the old channel or water line remains the ownership line. Erosion correspondingly shrinks the upland.
Traps
- Moving the boundary after an avulsion.
- Using the meander line as the boundary.
- Applying tidal high-water rules to nontidal navigable rivers (where the low water mark controls).
- Assuming the public trust easement disappears whenever the state conveys the fee.
Riparian rights
Riparian owners hold usufructuary rights to reasonable use and to natural flow; these are appurtenant to the land, not ownership of the water itself. Groundwater is governed separately, including under the Sustainable Groundwater Management Act.
Worked example
A river migrates 40 feet over 25 years of gradual bank erosion: the boundary follows the water. A single storm cuts a new channel 300 feet away overnight: the boundary stays in the old channel.
Rule of thumb
Gradual and imperceptible - the boundary moves. Sudden and perceptible - the boundary stays.