A DNR dam construction permit may be required to construct a dam, modify an existing dam, drawdown the water level, or remove a dam.
The thresholds for when a Flood Plain Permit from this department is required are outlined in 567 Iowa Administrative Code Chapter 73.3 and are listed below. The thresholds are primarily based on both dam height and water storage volumes. The height of a dam is defined as the vertical distance from the top of the dam to the lowest elevation at the downstream toe of the dam, typically the streambed.
Any dam with a height of at least 25 feet and a storage volume of at least 15 acre-ft
Any dam with a storage at the top of dam of at least 50 acre-ft and a height of at least 6 feet.
Any high hazard dam (see dam classifications).
Modifications to existing dams also require permitting:
Modification or alteration of any dam or appurtenant structure beyond the scope of ordinary maintenance or repair, or any change in operating procedures, if the dimensions or effects of the dam exceed the applicable thresholds above. Changes in the spillway height or dimensions of the dam or spillway are examples of modifications for which approval is required.
Estimating storage volumes:
An acre-foot of water is equal to a one foot depth of water over 1 acre, or also equal to 43560 cubic feet. The volume of a pond can be estimated by using the following formula:
Normal Pond Storage in acre-feet = (Surface area in acres at normal pool elevation) X (max depth in feet at normal pool elevation) X 0.4
Top of Dam Pond Storage in acre-feet = (Surface area in acres at top of dam elevation) X (max depth in feet at top of dam elevation) X 0.4
Example: A 4 acre pond is proposed with a 30 foot tall dam, the normal water level is expected to be 5 feet below the top of dam, if water rose to a top of dam elevation it would cover 6 acres (areas can typically be estimated by looked at topographic maps. We would estimate normal storage at 4 acres x 25 feet x 0.4 = 40 acre-feet. The flooded pool at top of dam is expected to be 6 acres, we would estimate top of dam storage to be 6 acres x 30 feet x 0.4 = 72 acre-feet. This pond would need a permit.
To apply for a dam construction permit visit our PERMT Online tool.
Please submit this checklist with the permit application: Earth Embankment Dam