Some parts of it seem like it would be rape, but other parts sound more like about nature and death, Im really not sure though.
Ive thought about this a lot, since the BWP album is themed around disgust for humanity I think, here are some possibilities:
Bleak may be about some type of sickness or disease.
Harvest is possibly about grief, bereavement/from a funeral maybe.
The Drapery Falls, I have no idea, maybe depression?
Dirge for November seems to be about suicide and depression.
Funeral Portrait seems to be about a murderer/serial killer.
Blackwater Park is sort of a climax and culmination of the whole album, and basically "confessor of the tragedies of man, lurking in the core of us all" sums it up I guess. There is evil and dark things within all of us.
Some of these could be way off and completely wrong but I think the important thing is not to try and disect every line and translate it to something, but maybe an overall theme or idea. Or whatever the songs mean to the listener, as they can mean different things to everyone.