In a part of the USA where I once lived there are salt marshes . The program you mentioned dug trenches in the marshes, perhaps to drain them in order to reduce the number of mosquitos. Nowadays small fish swim up the trenches when the tide is high and retreat as the tide recedes. Was this intended? I don't know. It is said to be an estuary area. Considered waterfront property today, the local authorities spray it from above with pesticides to reduce the number of mosquitos. Some very wealrhy and/or famous people live nearby who, I am sure, would complain if the mosquitos became more numerous.
"Forest" is misleading. This areas were savannahs, primarily grass and trees with shrubs. Permaculture has a tropical bias hence it's obsession with swales and trees
