Frequently Asked Questions (FAQs)

If you are looking to learn a bit more about dams or dam terminology, one of the best places to start might be the Terms and Definitions page, or the Illustration Gallery. Also visit our Fact Sheets section of the Owner/Consultant Info to get information on legal responsibilities, erosion, and more.

If you have any questions that you would like answered, or you think would be helpful to other people, please email Meg Galloway.

What are some common problems with dams as they age?

Many of the dams in Wisconsin were built in the late 1800´s and early 1900´s. Over time, water pressure and weathering will slowly break down a dam. Dams need constant maintenance and repairs. If dams are allowed to naturally degrade, they have a greater risk for problems such as sudden breaks in flood conditions. The possibility for loss of life and property make dam maintenance an important issue. Dams left to deteriorate in place can also pose a threat to the life and health of the public using waterways for swimming and boating.

The most common problems are undesirable woody vegetation on the embankment, deteriorated concrete, inoperable gates, and corroded outlet pipes.

What are the environmental impacts of dams?

Dams are built to temporarily slow the flow of water, and create an artificial impoundment, or lake, just upstream of the dam. Water held by the dam is often warmer than the natural water temperature, and attracts different fish and mammal species. Fish such as carp prefer the warm water of dams, while trout prefer the cooler, flowing water of a river. Dams prevent native fish from utilizing different stream segments which can be important seasonally or during different stages in their life. Beavers and muskrat are also attracted to dams. Naturally flowing rivers are often cleaner and clearer in water quality than water held by a dam, since nutrients and sediment can be naturally discharged in flowing water. Impoundments created by dams sometimes need to be dredged to remove sediment build up behind the dam.

What benefits are gained by removing dams?

Dam removals are often a necessity caused by the high cost of dam reconstruction and maintenance. Removing a dam also often removes a hazard to swimmers and boaters in the area and those who live downstream. Recent removals of dams in Wisconsin have also shown a decrease in carp populations and increase in trout species in the area of removal, and have shown a higher water quality and biodiversity after removal. For more information on removals, see our Dam Removal page.

What role does a dam play in heavy rainfalls or flooding situations?

In heavy rainfall or flooding, some dams are designed to hold back some of the water flowing downstream, protecting people and property downstream from higher water. This naturally results in higher water upstream of the dam, but emergency spillways are designed to pass excess flood waters downstream, and most dams in the state are not designed to function as flood control structures. They are run of the river dams designed to hold relatively stable water levels in the impoundment. However, flood situations can sometimes exceed the capabilities of either type dam, resulting in a failure and a more drastic and sudden flooding of downstream property. Constant maintenance of the dam, and awareness of dam operators is essential to protecting the public in flood situations.

Why and when are dams "open" or "closed"?

A dam operator can usually control the flow of water and size of impoundment by opening or closing gates. Gates might be opened when water levels are high and the impoundment needs to be lowered, and may be closed if water levels in the impoundment are low. Dams must maintain a minimum downstream flow to protect aquatic resources. All dams should have a written plan for when it is appropriate to open or close gates. This plan is known as an Operation and Maintenance Plan.

I am interested in buying some property that has a dam on it. What are some of the liabilities and responsibilities I will be acquiring?

In Wisconsin, prospective dam owners must be able to prove that they are financially capable of maintaining a dam before ownership can be transferred. Contact your local Engineer or WMS for more information. You may also check out our Liability Fact Sheet (coming soon) for more information about the legal responsibilities faced by dam owners.