Modifications of the dam need to be undertaken to reduce the level of the phraetic line. Which statement best summarizes the recommended action?

• A. Modifications of the dam
• B. Increase the crest width
• C. Add a downstream toe drain
• D. Install an upstream filter

Answer: (A)

Reducing the phreatic line requires addressing seepage paths inside the dam and its foundation, which is achieved by changing the dam’s overall design and drainage approach. The best summary is that modifications to the dam as a whole are needed, because lowering the seepage surface usually involves a combination of geometry changes, drainage improvements, and filtration practices rather than a single isolated measure.

Single options like increasing crest width, adding a downstream toe drain, or installing an upstream filter are specific tactics that might be part of the solution, but they don’t by themselves capture the required broad action of addressing seepage through the dam system as a whole.