Draft

if sea:
	sea was removed
	restore sea, set owner to water
	(set canal not on river)

if bare land:
	self canal was removed
	restore canal, set canal to self
	set canal not on river
	
if river && canal on river:
	self canal was removed
	restore canal, set canal to self
	set canal on river

if river && canal not on river:
	(it's a real river)
	maintain river, maintain owner
	(maintain canal not on river)
	
if canal && canal not on river:
	(it's not our canal)
	maintain canal, set canal to its owner
	(maintain canal not on river)
	
if canal && canal on river:
	(it's not our canal)
	maintain canal, set canal to its owner
	(maintain canal on river)