All ditches would remain open and could slowly fill in over time or be blocked by beaver dams, if beavers stay active in the area.
(All ditches; would remain; open) (All ditches; could slowly fill in; T:over time) (beavers; stay; active; L:in the area)
All ditches All ditches beavers
would remain could slowly fill in stay
open
T:over time
active L:in the area