Assertion: thames barrier | /r/HasProperty | lowered at ebb tide
Facets:
value: to release the water
type: PURPOSE
Source sentences:
text: It needs to be raised (closed) only during high tide; at ebb tide it can be lowered to release the water that backs up behind it.
text: It is raised (closed) only during high tide; at ebb tide it is lowered to release the water which backs up behind it.