The 1937 flood was a disaster of unparalleled magnitude for Paducah and many other cities in the Ohio Valley and the lower Mississippi Valley. Over a million people were displaced, nearly 400 lives were lost and millions of dollars in damage to industries, businesses and communities were reported [4]. Although levees and floodwalls are critical infrastructure in protecting cities, industries and agricultural lands, the flood of 1937 demonstrated the need to control tributary and upstream runoff volume and velocity. Further, it became rather clear that the Ohio and Mississippi river basins were interconnected and needed a unified, comprehensive engineering and land use plan encompassing watershed and basin scales.

Eroded hillsides from years of poor cultivation practices (Figure 11) and depressed agricultural markets made it almost impossible for rural families to produce and sell enough agricultural products to meet their basic food and housing needs. During the 1800s timber and tobacco were main income sources in the Tennessee River Valley. However, by 1937 much of the land had been cultivated too intensively without good conservation practices resulting in eroded and depleted soil unable to produce sustainable crop yields (Figure 11). As agricultural yields declined so did farm incomes. Concurrently, the timber industry peaked and declined as the best of the hardwood forests had been clear cut. However, controlling main stem inland river flooding and tributary back flow were not the only problems facing central United States in the 1930s. Many rural areas lacked rural electricity, year around passable roads, and other public infrastructure. Malaria and yellow fever carried by mosquitos breeding in swamps and wetlands and cholera from contaminated drinking water caused illnesses and deaths. Rural poverty and joblessness were exacerbated by the Great Depression [4].

In 1930s the country was in the Great Depression, President Roosevelt created the “New Deal” to help America recover. TVA was founded to help the hard hit Tennessee River Valley recover and improve the quality of life the people living in the valley. The TVA’s mandate included controlling flooding on the wild Tennessee River. TVA’s first task was to even out the flooding and drought extremes by building a system of dams and lakes to generate power, control flooding and create a system of water management for the greatest possible public good.

Faced with a large portion of the U.S. population unemployed and unable to support themselves, President Franklin Roosevelt and Congress created a number of social, environmental, and economic government programs. Legislation in 1933 authorized the TVA, a public-private institution designed to produce low-cost electricity using hydropower and revitalize poor rural regions throughout the south. The largest public power provider in the United States, TVA served an area covering 207,200 km² ranging from Tennessee, parts of Alabama, Kentucky, Georgia, and Mississippi to Virginia and North Carolina (Figure 2). During World War II, TVA hydropower produced electricity for critical war industries including aluminum plants that built bombs and airplanes. At its peak production in 1942, 12 steam plants and hydroelectric projects were under construction at the same time; and design and construction efforts employed 28,000 labors [7]. Today, TVA directly produces electricity for 56 industries and federal facilities and 155 local distributors who provide power to over 9 million people.

The first chairman of the TVA, Arthur Morgan, was an engineer with a vision for large scale, comprehensive planning that integrated building dam projects, public works employment and the transformation of poor rural communities in the Tennessee valley [8]. Morgan’s social engineering and dam projects on the Miami River (Ohio) after the flood of 1918 offered a prototype for his problem-solving approach to address resource management and community development. The TVA attempted to balance social, economic, land use and natural resource management of the region in the development of electric power production, flood control, navigation, malaria prevention, erosion control reforestation, and employment. The TVA continues to operate on the principle of integrated solutions even as issues have changed over time.

TVA’s River Forecast Center, located in Knoxville, Tennessee, is staffed 24 hours a day to monitor the river to control flooding and to provide water quality, availability and water demand data. In 1933, the TVA headquarters was required by a Congressional mandate to be created on the banks of the Tennessee River and not on a tributary, such as the Holston River [7]. For this reason, the headquarters was moved from Lenoir City to Knoxville and the confluence of French Broad and Holston Rivers.

Dam construction to harness the region’s rivers was the cornerstone of the TVA (Figure 12). The dams controlled floods, generated electricity, improved navigation and provided jobs. Concurrent to building dams and rural electrification, TVA undertook rural development by teaching farmers erosion control practices to prevent soil loss and introducing fertilizers that improved crop yields. TVA also invested in the replanting of forests, better forest fire management, and preservation of wildlife habitat. Electricity generated by TVA dams (Figure 13) modernized rural farms and homes by providing electricity for lights, motors, and other power equipment.

One of the most powerful weapons for averting flood disasters and reducing the

maximum height of floodwater downstream is the network of reservoirs and dams built on tributaries hundreds of kilometers upstream in the headwaters of the Ohio and Mississippi river basins [4] [6]. The Kentucky Dam is on the Tennessee River (Figure 14) and 34 km upstream from Paducah and the Ohio River. The dam is one of the largest human constructed reservoirs built to store excess floodwater and produce electricity (Figure 15). In the late 1800s the most pressing inland river policy issues focused on encouraging industrialization, westward expansion and assuring navigation on the Ohio and Mississippi rivers [6]. Although high water was an expected seasonal occurrence, large flood events (Figure 16) only became a major concern as they collided with increasing settlement and industry development along river valleys. The disastrous flood of 1937 caused a number of United States politicians, engineers, and citizen leaders

to reimagine river basins as unique ecological units and to more purposefully manage them as watersheds. A 1908 report by the Inland Waterways Commission called for multipurpose dams, but it took another 30 years and a sequence major river flood disasters (1913, 1927, 1936-1937) before the Federal government, with public support, took leadership in constructing the system of dams and reservoirs we have today in the Ohio River basin [4] [5] [6].

During the 1937 flood, many communities along the Ohio River experienced water 4.5 m above previous records in their downtowns; loss of lives and property; disruptions to railroad traffic and the regional economy in the eastern half of the United States; and loss of telegraph connections and communication functions throughout much of the Ohio Valley. Paducah, Kentucky, at the confluence of the Tennessee and Ohio rivers, evacuated more than 27,000 of their 33,000 population [4] and lost most of their downtown. Paducah today is a thriving city which owes much of it character and revival to the painful destruction of its city in the 1937 flood. Its back-to-the-river renaissance now celebrates its river history with new industries, downtown redevelopment, riverfront stores and museums, and a floodwall which documents historical river events [6]. This spirit of recovery for Paducah is made possible by the 4 m floodwall (Figure 6) and 1940’s construction of the Kentucky Dam (Figure 15) [7], a 294 km long reservoir which holds back and stores 494,378 hectare-m from the Tennessee River before releasing it into the Ohio River.

Upstream dam and reservoir construction is the most straight forward strategy for downstream flood protection. Dams hold back high volume runoff water from upland spring snow melt and extreme and prolonged periods of precipitation. This allows for the slow release of water downstream thereby managing river height and velocities and limiting potential flood damage. Five dams built in the early 1900’s in the Miami Valley (Ohio) by a consortium of public and private interests withstood the 1937 flood in the Ohio River valley and demonstrated the effectiveness of river surveys, topographical maps, a network of gaging stations, and well sited reservoirs [4]. Lessons learned from the construction and management of these early dams provided the TVA with engineering and survey mapping knowledge and reaffirmed the value of comprehensive planning.

As early as 1920s and before the flood of 1937, area communities along the Tennessee River and their leaders lobbied Congress to have a dam constructed. The Kentucky Dam, a hydroelectric dam on the Tennessee River on the county line between Marshal County and Livingston County and within the state of Kentucky, was located in Gilbertsville after extensive geological and soil evaluation. The dam is 35 km above the mouth of the Tennessee River, which empties into the Ohio River at Paducah, Kentucky (Figure 2). After merging with the Tennessee River, the Ohio River flows another 74 km before draining into the Mississippi River at Cairo, Illinois. The Kentucky Dam (Figure 16), started in 1938 and completed in 1944, is the lowermost of nine dams including the Watts Bar lock and dam (Figure 17 and Figure 18) and the Fort Loudon lock and dam (Figure 19 and Figure 20) designed to hold back the Tennessee River. About 17 m above the original river, the dam controls the release of water into the Ohio River and helps manage the fast rise of the Ohio and Lower Mississippi Rivers during spring snow melt and rains.

The Kentucky Dam at 63 m high and 2567 m long is the widest dam (Figure 21) on the Tennessee River and in the TVA system. The dam impounds Kentucky Lake which covers 65,000 ha; making it the largest of the TVA reservoirs by area and the largest artificial lake in eastern United States. Kentucky Lake has 3322 km of shoreline and the most flood storage capacity, 4944 Gl of any lake in the TVA system.

The construction of Kentucky Dam and its reservoir resulted in the public purchase of 129,598 ha of land including 19,625 ha of forest, which had to be cleared. Prior to the flooding of the land to create the reservoir, over 3390 graves, 2600 families, and 587 km of roads had to be relocated. Bridges over some roads needed to be rebuilt and sixty-five new ones were constructed on the new roads. The Illinois Central Railroad was rerouted to cross the top of the Kentucky Dam (Figure 22). Several small communities were submerged by the new reservoir and a dike was constructed around Big Sandy, Tennessee to protect the town from reservoir backwater [8]. Kentucky Dam, located in the New Madrid Seismic Zone, was built to withstand 7.0 - 7.9 magnitude earthquakes. Construction was finished on August 30, 1944, at a cost of nearly $118 million [8].

Railroads relocated include the Illinois Central (now Louisville & Paducah) railroad and the now abandoned Louisville & Nashville railroad. During WWII, the United States needed to build aluminum bombs and airplanes, and plants required electricity. To provide electricity for such critical war industries, the TVA created one of the largest hydropower construction programs ever undertaken in United States. Early in 1942, when the construction reached its peak, 12 hydroelectric projects and steam plants were being built at the same time with the design and construction activities employing 28,000 people. Public funding of the Tennessee Valley Authority power program ended in 1959 and its environmental and economic development activities were phased out by 1999 [8]. Electricity sales and other power initiatives currently fully fund all the TVA’s activities.

By the end of the WWII, TVA had created system of dams and locks on the 1005 km long Tennessee River navigation channel. The locks and dams have a significant impact on the economy of the region. Historically, goods were shipped by rail or truck. The use of barges reduced shipping cost by about $500 million each year depending on volume and year [9]. The railroads reduced shipping costs to stay competitive with barge transport. This meant lower prices and costs for consumers. One 15 barge tow can carry the same amount of freight as 216 rail cars and six locomotives or 1050 large semi-trucks [10]. Water transportation reduces labor costs, highway traffic, air pollution, fuel consumption, highway maintenance and the number of tires placed in landfills.

The Tennessee River originates at Knoxville, Tennessee (Figure 1) and drops 156 m before it joins the Ohio River at Paducah, Kentucky. Much like the Ohio River prior to the construction of the lock and dam system, the Tennessee River depth had a great deal of variability. Shoals and rapids made navigation almost impossible depending on drought, seasonal rainfall and timing of snowmelt. The Tennessee River has nine main-river locks and dams (Figure 17 and Figure 20) which create a continuous series of pools the length of the Tennessee River and enable navigation. River navigation is possible from Knoxville, up river on the Ohio River to Pittsburgh, Pennsylvania (Figure 23), or downstream to the Ohio-Mississippi river confluence at Cairo, Illinois (Figure 24) and south to the Gulf of Mexico (Figure 25). Commercial navigation occurs on three major tributaries of the Tennessee: up the Cinch River 98 km; up the Little Tennessee 46.7 km; and up the Hiwassee River 35 km. Recreational boating is popular on

the river and over 13,000 recreational craft annually lock through the system. In addition to the 2.74 m channel commercial vessels use, about 600 km can be used by recreational boaters but are too shallow for commercial traffic. River ports have become regional centers of social and economic vitality and sources of industrial activity. River transportation of food products for processing has proved to be inexpensive and efficient, reducing the price of groceries in the Southeast and across the United States.

TVA dam construction on the Tennessee river and tributaries has re-aligned the river flow patterns, temperatures and sediment transport thereby modifying aquatic and terrestrial habitats [9] [11] [12]. Hydropower demands resulted in timed water releases to meet power production needs without regard to aquatic ecosystem impacts. Consequently, water depth and velocities in tail waters below the dam before it flows into the next reservoir during non-generation periods declined to very low levels. Further, reservoir conditions and the dam structure produced low dissolved oxygen (DO) concentrations the low tail waters exacerbating the aquatic ecosystem conditions [11]. In 1991, TVA put in place a Reservoir Releases Improvement Plan to address deteriorating ecological conditions in the Tennessee watershed. Modifications included the installation of fish ladders and experiments in adding DO and changing the minimum flow to tail waters by modifying timing, velocity, and quantity of periodic water releases. A variety of strategies are used to increase DO including pumps, turbine venting, air blowers, forced air turbine venting, infuser weirs, and line diffusers [11].

A number of studies have begun to monitor dam modifications and impacts on abiotic and biotic conditions and the abundance and diversity of fish species to better understand the extent to which these modifications mitigate and restore the ecology of the river. Of particular interest are changes in discharge fluctuations into tail waters associated with peaking hydropower operations. Monitoring data below nine dams showed yearly and mean minimum velocity and mean DO increased following dam modifications. Flow changes alone had a smaller benefit than the combined effects of increased flow and increased DO [11].

The Cumberland and Tennessee river basins-considered a single aquatic ecoregion-contains one of the most diverse temperate freshwater species in the North America, including 231 fish species, mussels, crayfish, and salamanders [9]. However, urbanization, mining, logging, agriculture, river channelization and dams have accelerated erosion and sedimentation, changed stream flows, and degraded or destroyed aquatic habitat putting many of these species at risk. Research on ecological flows of the Tennessee River and their tributaries [9] is examining how changes in climate, land cover, soil properties and physiography drive stream flow responses. Knight et al. [9] found basin characteristics explained over half of the variation in streamflow with daily temperature range, rock depth and geology being other co-variables. One of the most influential factors is regional climate variables—mean monthly precipitation, daily temperature range, January precipitation, and August temperature. The relationship between flow and aquatic ecology is complex and not yet well understood [12]. The TVA continues to monitor and use research findings as feedback loops to adaptively manage not only their lock and dam network but also the land and river uses throughout the Tennessee River basin.

The silver carp (Hypophthalmichthys molitrix) (Figure 26), also known as the flying Asian carp [10], began migrating through the Mississippi River, Ohio River and into the Tennessee River and have now enter both the Kentucky and Barkley Lakes [12]. The carp escaped the Arkansas fish farms and began migrated up the Mississippi River system. The carp can jump above water and can grow to 23 kg. The carp were first introduced, with the approval of the Environmental Protection Agency (EPA) in the 1970s, to help consume algae in catfish farm ponds within Arkansas [12]. The carp remove the bottom of the food chain for indigenous species and displace the native species of filter feeding fish. Harvesting the carp for food has been one of the most successful approaches to date (Figure 27).

There are several kinds of Asian carp that have spread (or are spreading) around North America, and the two that have garnered the most attention at present are the bighead carp (Hypophthalmichthys nobilis) and silver carp and (personal communication, Dr. Cory David Suski, NRES, ACES, UIUC) [12]. Dr. Suski suggested “the carp do not displace native fishes and he is not aware of any displacement to date”. Dr. Suski noted “that the Asian carp out-compete the native fish for food, and several species of fishes (particularly filter feeding fishes) have experienced reduced conditions, likely through competition” [13]. There are other carps (grass carp, black carp) but of less concern than bighead and silver carp.

Known as North America’s Next Regional Trail System, the Tennessee River Line project [14] was started in 2016 and headquartered in Knoxville, Tennessee. The School of Landscape Architecture at the University of Tennessee’s College of Architecture and Design started work on the concept in 2016. The pilot program was set up at five sites in 2019 (Figure 6). The program included efforts to create more access points from the water into communities from Paducah, Kentucky to Knoxville, Tennessee. The potential for economic development and recreational tourism is huge. There are 48 million ha of public parklands (Figure 28 and Figure 29) along the Tennessee River pathway. The next phase, a River Towns program has the potential to link communities via the River Trails program. The River Line Partnership now has the support of Tennessee Valley Authority, the River Discovery Center of Paducah and the National Parks, marinas (Figure 30) and other conservation and environment groups such as The Nature Conservancy.

“The Tennessee River Line trail project was started to create a network of trails to paddle, hike and bike along the 652 river mile length of the Tennessee River. The project is now taking the next step, by signing the first batch of River Towns to participate in the project” [14]. The Tennessee River Line trail project

which started in Knoxville is now “Flowing” to Alabama, Mississippi and Kentucky with ready to sign up for the River Towns program. The first batch of River Towns were announced on October 23 of 2020. The inaugural cohort of Tennessee River Towns program included both Paducah-McCracken County (Figure 31 and Figure 32) and Calvert City in the group of 15 communities selected.

The River Line Partnership is a “generational project” created to increase recreational usage of the Tennessee River and watershed. The program goal is to create generations of people who care about the river and provide the environmental stewardship for its protection.