The topography map was used to identify low spots within the watershed that are internally drained and which might therefore be prone to flooding and ground subsidence. These internally drained areas correlate closely with vacant lands. In some neighborhoods, most vacant land and vacant buildings are within the old floodplain or along the current sewer alignment. The WPLP proposed that the city acquire these vacant "floodplain" areas and use some of them to detain stormwater runoff in order to eliminate combined sewer overflows from the watershed. It was further proposed that the city of Philadelphia apply for federal funding to map the floodplain of the Mill Creek and to develop a plan for sewer, stormwater, and parkland management similar in principle to that implemented in Denver, Colorado. (See The West Philadelphia Landscape Plan: A Framework for Action.)