The correct answer is A. drainage filters.
Drainage filters are used to control seepage through embankments in an earthen dam. They are placed between the embankment and the foundation to prevent water from flowing through the embankment and eroding the foundation.
Drainage filters are made of a material that is more permeable than the embankment material, but less permeable than the foundation material. This allows water to flow through the filter, but prevents it from flowing through the embankment.
Drainage filters are an important part of the design of any earthen dam. They help to ensure the stability of the dam and prevent it from failing.
The other options are incorrect because they do not directly control seepage through embankments.
B. Relief wells are used to control uplift pressure in an earthen dam. They are installed in the foundation of the dam to allow water to flow out of the foundation and reduce the pressure on the dam.
C. Drain trenches are used to collect seepage water and direct it away from the dam. They are installed in the embankment of the dam to collect water that has seeped through the embankment.
D. Provision of downstream berms is used to reduce the risk of flooding downstream of the dam. Berms are constructed on the downstream side of the dam to raise the elevation of the land and reduce the amount of water that can flow downstream.