The lithology underlying the dam is a metamorphic rock called gneiss, this rock type is known to be relatively impermeable meaning that there is no significant groundwater flow within the rock unit also it does not allow water to penetration the ground.
The lithology underlying the dam is a metamorphic rock. This was what this rock type is known to be relatively impermeable meaning that there is no significant groundwater flow within the rock unit also it does not allow water to penetration the ground. This metamorphic rock is called gneiss.