Starling (architecture)

In architecture, a starling (or sterling) or, more commonly, cutwater is a defensive bulwark, usually built with pilings or bricks, surrounding the supports (or piers) of a bridge or similar construction. Starlings are shaped to ease the flow of the water around the bridge, reducing the damage caused by erosion or collisions with flood-borne debris, and may also form an important part of the structure of the bridge, spreading the weight of the piers. So the cutwaters make the current of water less forceful.

One problem caused by starlings is the accumulation of river debris, mud and other objects against the starlings, potentially hindering the flow. The starling has a sharpened upstream edge sometimes called the nose. The cutwater edge may be of concrete or masonry, but is often capped with a steel angle to resist abrasion and focus force at a single point to fracture floating pieces of ice striking the pier. In cold climates the starling is typically sloped at an angle of about 45°  so current pushing against the ice tends to lift the downstream edge of the ice translating horizontal force of the current to vertical force against a thinner cross-section of ice until unsupported weight of ice fractures the piece of ice allowing it to pass on either side of the pier. A sloped, ice-cutting starling is known as a starkwater.

...
Wikipedia