How about if you build 72 housing units at the top of the hill and you have neighbors and wetlands that will all suffer if the amount of water that runs down the hill either increases or decreases? Then you have to go beyond swales...you have to build complicated drainage, storage and infiltration systems to get exactly the right amount of water back into the water table...at a price tag of several tens of thousands of dollars.

How do I know this? Don't ask...