Extract the answer to the question from the following context. Question: What is a shared characteristic of most of the damaged dams? Context: The Zipingpu Hydropower Plant (simplified Chinese: 紫坪铺水库; traditional Chinese: 紫坪鋪水庫) located 20 km east of the epicenter was damaged. A recent inspection indicated that the damage was less severe than initially feared, and it remains structurally stable and safe. The Tulong reservoir upstream is in danger of collapse. About 2,000 troops have been allocated to Zipingpu, trying to release the pressure through spillway. In total, 391 dams, most of them small, were reported damaged by the quake.
The answer to this question is:
most of them small