Yellow Tacks – Minor Obstructions
Red Tacks – Dams
Dark Blue Streams – Metro Waterways
Highlighted Blue Streams – Metro Segments that have already been walked for the inventory.
Green – Mill Creek Watershed Boundary
Many dams in the Cumberland Basin no longer serve their intended purpose. Yet, these outdated dams obstruct aquatic species passage and degrade water quality. In some cases, these dams are even at risk of failure and may represent a safety or flooding hazard.
In Nashville, it may come as a surprise that a complete picture of the location and number of dams does not even exist. Working with area volunteers, we are walking streams and inventorying dams. In so doing, we’re taking the first steps towards the eventual removal of those dams that are outdated and unnecessarily impacting water quality. With your help we can begin to reconnect our waterways!
Interested in helping with the effort?
Please contact Gray Perry and specify “Dam Inventory” in the subject line.
Segments within Mill Creek Watershed that are NOT highlighted in neon blue still need to be walked for the inventory. Please check in with Gray Perry before walking to ensure you are looking at the most recent data.
The Benefits of Dam Removal
Improved natural flow variations and stream bank habitat
Dams alter natural flow variations. Under unaltered conditions, streams have seasonally varying, high and low flows, and many native animal and plant species are adapted to this natural variation. Dam removal can help restore natural flow variations and natural stream bank habitat.
Improved natural temperatures and nutrients levels
Dams alter stream temperature and nutrient levels. When water above a low-head dam pools, it alters water temperatures and pools nutrients. Many aquatic species are sensitive to temperature changes and nutrient loading. Dam removal can help restore natural temperatures in a stream and prevent nutrients from pooling above obstructions.
Restored natural sediment deposition
Streams and rivers naturally experience sediment deposition. Faster waters carry more sediment downstream, while slower waters
carry less. Because dams slow down water, they cause sediment to drop to the bottom of the stream, behind the dam. Dam removal can restore natural sediment deposition, reduce siltation of important spawning and feeding habitat, and allow debris and small rocks to pass through waters, as they do in healthy stream habitats.
Unobstructed species passage
Dams disconnect the natural flow of water thus altering the natural life cycles of aquatic species. Migrating fish and mussel species, for example, are unable to pass, and as a result, populations become isolated. Strategic dam removals can open miles of new habitat to the many species that rely on free-flowing waters to live and reproduce.
No increased risk of flood
While concerns are often expressed over increased risk of flooding, in fact, only a small percentage of dams provide flood control benefits and these are generally from dams that were constructed explicitly to provide these benefits. Dam removal can sometimes even decrease the risk of flooding, as flow is no longer obstructed and risks of dam failure (and sudden flooding) are eliminated.
Improved river recreation
Poorly maintained dams can also be a safety hazard for river users. Dam removal can enhance recreation and safety on area waterways and provide paddlers with unobstructed passage.
Maintenance costs for an older dam often outweighs the cost of removing it.1 In addition, American Rivers notes that “Economic studies have found that property values are higher along free-flowing streams and rivers than they are next to impounded water.”2 For those dams that may be increasing the risk of flooding in an area, the economic benefits of removal are even greater.