Hydraulic failure of earthen dam is due to?

Earthen Dam failures are mostly attributed to hydraulic failures....

some are mentioned herein under

1. Exposure of the phreatic line (Atomospheric exposure line)

2. High hydraulic conductivity of core 

3. Inadequate drainage of slope (insufficient turfing and drains) inducing slope failures

4. High uplift pressure thereby increased pore-water pressure at the base line of the Dam, conjestion of weep holes

5. Degeneration of rip-raps thereby increased wave action

6. Earthquakes..etc. etc.