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.
Starlings may form part of a buttress for the vertical load of the bridge piers, and so are symmetrical. Examples such as at the Old Wye Bridge, Chepstow are on lower stretches of rivers which are tidal and that require a starling in both directions. Other starlings may be asymmetrical, so that the upstream aspect of a pier is larger as it a face sloping outwards, whilst downstream is vertical.
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 or curved extreme sometimes called the nose. The cutwater 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 part-submerged ice flow tends to lift the solid ice translating horizontal force of the current to a vertical force shearing the ice allowing the icy flows to pass on either side. A sloped, ice-cutting starling is known as a starkwater.
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- Urquhart, Leonard Church (1959). Civil Engineering Handbook (4th ed.). New York: McGraw-Hill Book Company. pp. 8–75.
- Raymond, William G.; Riggs, Henry E.; Sadler, Walter C. (1937). The Elements of Railroad Engineering (5th ed.). New York: John Wiley & Sons. p. 163.