A watershed is the land area that drains water above and below the surface to a single water resource. It’s often named for the resource it drains into, like Richland Creek.
The force of gravity carries water across the land, and the landscape topography determines the path. Long ago, over a period of time, these trails became stream beds, as the water carved its way over the landscape.
In Nashville, there is karst topography, and water naturally makes its way underground where it gets stored in water-bearing layers of rock, called aquifers. Groundwater eventually makes its way back to the surface as a spring, supplying our waterways with their daily base flow of cool, clean water.
We all live in a watershed and our properties determine the function of the watershed and the health of its waterway! A watershed has natural hydrologic, ecologic, chemical and biologic functions. When the land area is covered with hard surfaces, impervious to water, then all the rainwater is directed into the stormwater system. This urban process prevents water from making contact with soil and recharging groundwater sources below. It also causes us to miss out on the benefit of the free, natural purification system that is soil. In the urban setting, each rain event quickly generates large amounts of stormwater draining into our waterways. It’s warm, dirty, and fast! So in addition to losing the recharge of groundwater and the purification by soil, the surfacing of stormwater causes other issues to occur, such as pollution, erosion, riparian tree loss, and flooding. Whether the water is dirty or clean, eventually all water ends up as part of the water cycle, But when we take advantage of a watershed’s free attributes, we get cleaner water, natural flow regimes in our waterways, a healthier ecosystem, and a flood control tool to use. Preserving the functions of a watershed benefits us all!
The Hydrologic Cycle
The hydrologic cycle, which replenishes our water resources, is a system of land, air and water interactions. Temperature and wind speed affect the rate of evaporation from surface storage (streams, rivers, wetlands and lakes). Underground flow can surface as springs or seeps and provide flow to streams throughout the year.
Richland Creek is an urban watershed with 5 major tributaries:
- Unnamed Tributary
- Jocelyn Hollow
- Vaughn’s Gap
- Belle Meade
- Numerous smaller spring branches
Where does our pollution come from?
Urban watersheds have significant land area covered with impervious landscape (rooftops, roads, parking lots, structures). These nonabsorbent surfaces collect all types of pollutants that flow to streams as stormwater run-off. Adding to the mix is excess lawn and turf applications, construction sites without adequate soil erosion protection, illegal discharges and the trash dumped, or not disposed of properly. The stormwater system collects it all and takes it all to our streams, unfiltered and untreated, during each wet-weather event.
When storm runoff is permitted to flow over undeveloped land, such as across riparian buffers, swales and into rain gardens, there is diffusion through soil layers that filtrates pollutants out, naturally. Some types pollutants often found in urban runoff are oil, grease, dirt, trash, chemicals, and other harmful substances that drip from vechiles, get spilled that degrades water quality and harm aquatic ecology.
Groundwater flows beneath the surface, through unseen pathway. Dissolution of the soluble bedrock (limestone) layers overtime create karst landscape—geologic formations of caves, tunnels and sinkholes. Surface runoff can enter and contaminate groundwater resources more easily in karst topography. Aquifers provide groundwater storage and keep our streams flowing healthfully year-round.
“The world has no more fresh water than it did 2000 years ago, when the population was less than 3% of its present size.” – Earth Island Journal, “Water Wars, Water Cures”, Spring 2000.
Water supply is limited. Of the enormous amount of water on the planet only 1% is suitable for consumption—97% is sea water and 2% is ice. Of that 1%, only 10% is accessible— 60% of water resources are where only 40% of the global population resides. Water demand is growing at an unsustainable rate while much of our supply is returned polluted.
Our sustenance, health and economy are dependent on clean water for drinking, agriculture, fisheries, energy production, manufacturing, recreation and many other uses that support our way of life. Streams are important no matter where they are located and keep the system flowing. Surface runoff replenishes the water cycle and needs regarded as a valuable water resource, even in an urban watershed.
The Clean Water Act tells us our waters are impaired. Richland Creek watershed streams are federally listed as “impaired” due to sewage collection failure, urban run-off and habitat alteration — 20+ stream miles are not meeting the regulatory, designated requirements—aquatic habitat and recreational uses.
The Federal Water Pollution Control Act Amendment of 1972 was enacted due to excessive industrial discharge into water resources. The U.S. Environmental Protection Agency was created to protect human health and the environment by writing and enforcing environmental regulations based upon laws passed by Congress. This legislation addressed point-source pollution.
Urban run-off (non-point source pollution) degrades streams’ water quality, is of major concern, and generates more run off pollution as the landscape develops more intensely. Our local stormwater management manual was recently updated, and now (Feb 2016) requires develoment manage the first inch of runoff, to help reduce stormwater pollution.
The Division of Water Pollution Control at the Tennessee Department of Environment and Conservation (TDEC) has compliance responsibility for protection of Tennessee waters. TDEC issues permits to cities and industries that want to use our resources or discharge into waterways. The Tennessee Wildlife Resources Agency comments to TDEC for protection of Tennessee’s wildlife.
Nashville is currently under a Consent Decree mandating infrastructure improvement to address sewage discharges and overflows into the river and streams. The old sewage collection system in Nashville is in need of repair and updating, with some sections 100 years old. Capital improvement of system will reduce these pathogens from flowing into our waterways and significantly improve water quality.
We all contribute to pollution… and can take actions to improve the water quality of our streams.