Permitted dams in Iowa and associated attributes, as recorded by the Floodplain Section of the DNR. The dams regulated are those with the parameters listed below: a. Any dam designed to provide a sum of permanent and temporary storage exceeding 50 acre-feet at the top of dam elevation, or 25 acre-feet if the dam does not have an emergency spillway, and which has a height of 5 feet or more. b. Any dam designed to provide permanent storage in excess of 18 acre-feet and which has a height of 5 feet or more. c. Any dam located in or within 1 mile of an incorporated municipality, if the dam has a height of 10 feet or more, stores 10 acre-feet or more at the top of dam elevation, and is situated such that the discharge from the dam will flow through the incorporated area. d. Also regardless of dam height and storage, any urban area dam situated across a stream that has a drainage are of more than two square miles and any dam in a rural area situated across a stream that has a drainage area of more than 10 square mile. The generally known threshold is any dam that has a height of five feet or more and a permanent water storage volume of more than 18 acre-feet. The height is measure from the top of the dam to the lowest point on the downstream side of the dam, usually the streambed.