What is a wall-like concrete structure across a river designed to back up water, also known as a Low-Head Dam?

• A. Low-Head Dam
• B. Weir
• C. Dike
• D. Floodwall

Answer: (A)

A wall-like barrier that spans a river and holds back water upstream is a dam. A low-head dam is a small dam built across a river with a low crest, appearing like a solid concrete wall, whose purpose is to back up water and create a shallow upstream reservoir. This fits the description precisely, whereas a dike is an embankment along land to keep floodwaters out, and a floodwall is a barrier protecting land from floods. A weir does raise water across a stream, but the term that matches the description given is the low-head dam.