A rock whose highest point sits at roughly chart datum. Charts use separate symbols for rocks that dry (with a drying height), rocks awash at chart datum, and underwater rocks with a known or unknown depth. Getting the category right matters, because a rock awash is hidden at most states of tide. Surveys confirm it by lidar, by levelling to it at low water or by sonar passes near high water.
Charted rock awash is actually 0.4 under datum, recode it as an underwater rock with a sounding.
Also heard as
- rock awash at chart datum
Related terms
Drying height
Height above chart datum of a rock, bank or flat that dries at low tide, shown on charts as an underlined figure.
Chart datum
The low-water level from which charted depths are measured, set so actual depth is seldom much less than shown.
Least depth
The shallowest depth over a wreck, rock or other feature, which is the value that gets charted.
Obstruction
A submerged object that hinders vessels or fishing and is not a wreck or natural rock, such as piles or debris.