If all the water in Park Hill flows north, how would flooding be reduced by a retention basin to the southwest of Park Hill in City Park? I was referring to surface flow, but the storm drainage maps show something different. However, contrary to what David says, all the sewer drainage in Park Hill south of MLK runs south or west, across Colorado and eventually into City Park, where it exits to the NW. It never runs north as you and David claim. North of MLK, the storm drainage runs north or west, and never toward City Park. And, south of MLK, surface water, like sewer, flows south, and during flooding turns 17th and Colfax into rivers. As water from North Park Hill does not drain into City Park, and as water from south Park Hill and City Park drains to the NW and not through neighborhoods to the north, it's still not clear how building a retention pond in City Park will do anything to improve flooding to the north and east of City Park in the neighborhoods you mention.