Understanding the Connection Between Surface Water and Groundwater in Tennessee

In Tennessee, we have more than 50,000 miles of winding, biodiverse rivers and streams – along with more than a half-million acres of lakes and eco-diverse marshes. With such an abundance of natural resources, approximately 90% of Tennesseans live within one mile of a river, stream, or waterway. But our water resources go far beyond what we can simply see. Tennessee is also home to the Memphis Sand Aquifer, which is an unparalleled natural resource spanning more than 7,000 square miles across portions of eight states. Many people might not realize that surface water (like rivers and lakes) and groundwater (stored in underground aquifers) are closely connected. This connection is vital for maintaining the quality and availability of water across the state.

What is surface water?

Surface water is found in rivers, lakes, streams, and reservoirs. It’s the water you see every day! In Tennessee, about 68% of the population relies on surface water for their drinking water needs. This water is collected from various bodies of water, treated, and then distributed to homes and businesses. In fact, having cleaner water in our rivers and reservoirs actually makes it easier and cheaper for a water treatment plant to supply tap water to our homes.

What is Groundwater?

Groundwater is found underground in the spaces between soil, sand, and rock. These underground reservoirs, called aquifers, are accessed through wells. An aquifer is a layer of sand, silt, or porous rock underground that contains water. The aquifers in our area are primarily composed of sand, where the spaces in between sand grains hold water.

The Memphis Aquifer is made up of multiple alternating layers of primarily sand, and clay, with a bit of silt and gravel mixed here and there. It likely began as rain that fell thousands of years ago, slowly infiltrating the ground through the layers of sand.

Groundwater is essential, especially for rural areas where it may be the primary source of drinking water. In Tennessee, about 32% of the population depends on groundwater for their daily needs. It is particularly important in Western Tennessee and the city of Memphis, which is the largest U.S. city that relies 100% on groundwater to meet its every need.

How Are Surface Water and Groundwater Connected?

Rainwater can seep into the ground, replenishing aquifers in a process known as recharge. Similarly, groundwater can flow into rivers and lakes, maintaining their levels, especially during dry periods. Depending on the time of the year, we can actually characterize streams and rivers by whether they are “losing” or “gaining” water from an aquifer.

Typically, in the hot and dry summer, the groundwater table drops and water from a river flows through the ground into the aquifer, this is called a “losing” stream. The opposite occurs during the wet season when the groundwater table is elevated and water is allowed to flow from the aquifer into a stream, called a “gaining” stream.

As well, Tennessee is characterized by its unique karst geology, which is marked by soluble rocks such as limestone that create a landscape of sinkholes, caves, and underground streams. This significantly influences how water moves between the ground and surface.

Water moves quickly through these underground channels, which means that contaminants on the surface can easily reach groundwater sources. Many streams in Tennessee actually “disappear” for stretches because they are completely contained within a karst feature underground and pop up to the surface after several hundred meters or even a mile or two. Therefore, protecting surface water from pollution is crucial for safeguarding groundwater.

Types of Water Use in Tennessee

In Tennessee, water is used for a variety of purposes, including:

Public Supply: This includes water provided to households, businesses, and industries by public water systems. Surface water is the primary source for these supplies.
Irrigation: Agricultural activities require significant amounts of water, both from surface and groundwater sources, to irrigate crops.
Industrial Use: Industries use water for processes such as manufacturing, cooling, and cleaning. Both surface and groundwater are utilized, depending on the location and industrial needs.
Thermoelectric Power: Power plants use large quantities of water, mainly from surface sources, for cooling and generating electricity.
Domestic Use: In rural areas, many households rely on private wells tapping into groundwater for their domestic water needs.

Understanding these different uses helps highlight the importance of managing both surface and groundwater resources sustainably.

Why This Connection Matters

The connection between surface water and groundwater ensures a stable and sustainable water supply. Understanding this relationship helps us appreciate the need for comprehensive water management practices that protect both surface and groundwater resources. Efforts to reduce pollution, manage water use efficiently, and conserve natural habitats all contribute to the health of our water systems, which are central to the mission of protecting clean water and rivers in Tennessee.

By understanding the relationship between surface water and groundwater, particularly in regions with karst geology, we can better appreciate the importance of protecting both. Through collective efforts in conservation and sustainable water management, we can ensure that clean, safe water is available for all Tennesseans now and in the future.

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