By Clint Calhoun
It has been awhile since I have focused my writings solely on lake issues, but due to the overwhelming number of questions I get related to water quality of the lake, as well as the natural changes that occur within the lake, I think that the timing is good to shift some focus to the very thing that is the namesake of the Town of Lake Lure. My goal in launching this series of writings is to improve understanding of the overall health of the lake, the processes that occur within lakes, and why it’s necessary to manage the lake. Some of it could get a little dry at times, so I will try to keep it as interesting as possible.
Did you know that lakes are not created equally? They are divided into two groups: natural and manmade. The first group, the natural lakes, are found all over the world and are generally the results of some type of natural phenomenon such as glaciation (the Great Lakes), volcanic activity (Crater Lake), tectonic shifting (Lake Tahoe), flooding (oxbow lakes of the Mississippi basin), or dissolution of soluble rock formations (many Florida lakes). North Carolina has a few natural lakes known as Carolina Bay Lakes which are believed to have formed during times of rising sea levels, where wave and wind action eroded ancient shorelines. As sea levels decreased during the last Ice Age, these eroded depressions in the ancient seabed became landlocked and filled by ground water. These mysterious lakes are all roughly oriented in the same direction and are all found in the coastal plain of North and South Carolina. Carolina bay lakes are the only natural lakes in the Carolinas. All other lakes fall into the second group which are the manmade lakes. These are the ones I will be focusing on in this series.
Manmade lakes are more typically referred to as reservoirs (particularly water supply lakes) or impoundments. Most lakes in the southern U.S., from coast to coast, fall under this classification. These lakes are created by damming or impounding a large stream such as a river, mostly for the purposes of creating water supply, hydroelectric generation, flood control, or some combination thereof. Lake Lure is the result of impounding the Broad River. The dam was constructed at an area of the river known historically as Tumbling Shoals, financed by the Carolina Mountain Power Company. Lake Lure was built as the centerpiece for what would become the resort town of Lake Lure. Lake Lure was constructed primarily for recreational use with hydroelectricity generation as a secondary use.
Manmade lakes differ greatly from natural lakes in terms of the natural processes that affect them, although all are subject to issues such as eutrophication (a term we will discuss in a future article), invasive species infestation, shoreline erosion, and other anthropogenic associated issues. Probably the most common issue associated with impoundments that is not typically associated with natural lakes (but does occur) is that of sediment collection. Rivers and streams naturally transport sediment, and certain amounts of sediment are vital for maintaining aquatic ecosystems. On the other hand, too much sediment has exactly the opposite effect and can be quite detrimental to aquatic ecosystems and water quality, so balance is very important. Naturally occurring sediments are created by erosive forces within the watershed and the collection of organic matter. The Upper Broad River Watershed produces a large amount of natural soil sediment due to the highly erodible soil types and steep topography of the 94 square mile drainage area, particularly during large storm events as water serves as the primary transport mechanism. The large amount of forest land within the watershed contributes massive amounts of organic matter such as leaves and woody debris. Throw human impacts into the mix and the amount of sediment increases exponentially. Shortly after the construction and impoundment of Lake Lure, the sedimentation issue quickly became apparent as a delta began to form at the mouth of the river. This was noted in Lee Powers’ memoirs where he detailed a letter that was sent out to upstream landowners by Dr. Morse, asking them to do everything possible to reduce sedimentation in the upper reaches of the watershed to slow down the filling in of the newly created lake.
When impoundments are created, it changes the natural hydrology of the stream that is impounded, in this case the Broad River. Sediment transport relies on velocity to keep the suspended soil particles moving. The interruption of a steady current results in the settling out of suspended soil particles, creating the sand deposits that gradually fill in large areas of the lake. This is a common problem with nearly all impoundments, particularly the ones that have large feeder tributaries and large drainage areas. A good example is the Glen Canyon Dam which impounds the Colorado River near Page, Arizona to create Lake Powell. This dam so drastically changed the hydrology of the Colorado River that it impacted the ecology of the river downstream by starving the river of sediment. At the same time, the sediment loads in the upper reaches of the Colorado River are so high that the dam has a high risk of failure due to how quickly the lake is filling with sediment. Sedimentation is the biggest problem that Lake Lure currently has in terms of water quality, and as we will explore in the future, it impacts more than just depth.
Another important thing to know about manmade impoundments is the requirement of maintenance and management. It requires a great deal of expense, resources and effort to continually maintain and manage an impoundment. Infrastructure maintenance is the largest expense item when it comes to managing an impoundment. Whether it’s hydroelectric plants, water treatment facilities, or the dams themselves, there are always significant costs when it comes to properly managing and maintaining an impoundment. This will be explored in the future as well.
My hope is that this series will clear up a lot of questions that our readers may have about Lake Lure as the series moves along. The more lake users know about the lake they love, the better it gets taken care of. Next time I will discuss some basic limnology (the study of lakes) and terminology that is important to know when managing lakes. I hope everyone has a Happy New Year!
Clint Calhoun is a naturalist, biologist and Certified Lake Manager and has worked in Hickory Nut Gorge for over 20 years. He is currently the Environmental Management Officer for the Town of Lake Lure. Check out Clint’s blog at http://clintcalhounadventures.blogspot.com.