A hydrologic determination is the scientific and legal method for determining if a watercourse in TN is a wet weather conveyance or a stream. The resulting identification dictates how the resource is regulated.
Types of Resources
There are many different kinds of water resources, both on the surface of the ground (called surface waters) and underneath the surface (called groundwater). Surface waters form drainage patterns based on the topography of the ground. Areas where the large amounts of waters collect, such as lakes, aquifers, and oceans, are called “sinks”. As waters move across the surface of the ground towards sinks, the concentrated flow can erode through the soil and create channels. These channels convey flow linearly, from upstream to downstream, with flow levels and intensity varying based on hydrology inputs. There are different classifications of channels, based on these flow patterns.
Ephemeral, Perennial, and Intermittent Streams
For example, if the only input hydrology is temporary, then then flow a channel conveys will also be temporary. These are commonly called “ephemeral streams” or “ephemeral flow”. However, if the hydrology inputs are more permanent, then a channel’s flow will be semi-permanent or permanent. Permanent hydrology can come from connections to groundwater sources, such as seeps or springs, or from draining a large enough area to provide consistent flow. Channels which permanently have flow and are almost always flowing are called “perennial streams”. Channels which have semi-permanent flow are called “intermittent streams”. These channels get hydrology inputs from permanent sources, but only during certain times of the year. Often, intermittent streams occur in places where droughts significantly lower the availability of water in the channel’s drainage area or in the groundwater table.
Waters of the State of Tennessee
Legally, Tennessee divides these three types of watercourses into only two categories: wet weather conveyance (WWC) or stream. Technically, both are jurisdictional features and are considered “waters of the state”. However, the law makes provisions to authorize alterations to wet weather conveyances without a permit or notification when certain conditions are met. So, if you are planning a project on a property with one of these resources on it, it is important to complete a jurisdictional determination for that resource. If the resource is a stream, a hydrologic determination will be required to get the appropriate permits.
What is a Wet Weather Conveyance (WWC)?
The legal definition of a wet weather conveyance (WWC) is found in the Tennessee Code Annotated §69-3-103 (49) and reads as follows:
(49) “Wet weather conveyance” means, notwithstanding any other law or rule to the contrary, man-made or natural watercourses, including natural watercourses that have been modified by channelization:
(A) That flow only in direct response to precipitation runoff in their immediate locality;
(B) Whose channels are at all times above the groundwater table;
(C) That are not suitable for drinking water supplies; and
(D) In which hydrological and biological analyses indicate that, under normal weather conditions, due to naturally occurring ephemeral or low flow there is not sufficient water to support fish, or multiple populations of obligate lotic aquatic organisms whose life cycle includes an aquatic phase of at least two (2) months;
What is a Stream?
In contrast, the legal definition of a stream, found in §69-3-103 (42) reads:
(42) “Stream” means a surface water that is not a wet weather conveyance;
How Do You Know Which is Which?
It may sound simple to differentiate between a stream and a wet weather conveyance, but looking at a real feature, it can be a lot less clear. At different times of the year, channels in Tennessee can show widely different traits. Helpfully, state law also required that TDEC establish rules for consistently determining if a watercourse is a wet weather conveyance and a certification process for professionals who want to be trained to make those determinations. In response, TDEC developed the “hydrologic determination” method and the Qualified Hydrologic Professional certification.
What Is a “Hydrologic Determination?”
A hydrologic determination is a methodical assessment of indicators of flow regime which a trained professional conducts to evaluate the hydrologic classification of a watercourse in accordance with Tennessee’s legal definitions. These indicators include hydrological, geomorphological, and biological factors which provide information about the flow regime of the channel. The indicators used in the methodology have observable, predictable patterns corresponding either with sporadic ephemeral flow or with more consistent intermittent or perennial flows. The method is designed to be effective even for intermittent streams which don’t have flow at the time of assessment.
Hydrology
“Hydrology” simply means “the study of water”, but more specifically refers to the study of the movement of Earth’s water. In the context of water resources, “hydrology” is often used to refer to the source of water for a feature. Professionals conducting a hydrologic determination evaluate the hydrology of the channel to assess how permanent or impermanent it is. Indicators include recent precipitation records, presence or absence of water within the channel, connections to groundwater, presence or absence of water-saturated soils, and signs of flow moving sediment and debris.
Geomorphology
“Geomorphology” means the study of the origin and formation of the form of the Earth’s surface. In the context of water resources, it’s used to refer to the shape of the ground in, around, and beyond water resources. For channels, professionals assessing geomorphology look at the characteristics of the bed, banks, riparian zone, and drainage area. The geomorphology indicators are features that develop over time in response to different types of flow such as formation of a defined bed and bank, sorting of substrate, in-channel structures, recent deposits of sediment, and shape of the drainageway.
Biology
“Biology” means “the study of life and living organisms”, and it means the same thing in the context of water resources. In the HD method biology indicators are used to assess the normal conditions of a channel, because different living organisms have different habitat needs. The indicators include presence or absence of different vegetation, amphibians, fish, macroinvertebrates, and certain fungi and bacteria which rely specifically on either wet or dry conditions to live.
How Do You Get an HD?
To get an HD completed on your property, you need someone who has completed the HD training. This can be a fully-certified Qualified Hydrologic Professional (QHP) or a Qualified Hydrologic Professional In-Training (QHP-IT). A QHP is someone who has a degree in a related field, has passed the HD training course, and has practiced conducting HDs for 5 years. A QHP-IT has all of the above, but has not yet completed his or her 5 years of experience.
If you are a commercial or public entity, you’ll need to hire an environmental consultant who is a QHP or QHP-IT to complete your determination. If you hire a consultant, they will come to your property and conduct assessment following the method. Then, they’ll prepare and submit the required report to TDEC for review. TDEC will review the submitted report and either provide a letter confirming their concurrence, or agreement, with your consultant’s call, or they will work with your consultant to make any corrections or clarifications.
If you are a private residence or family farm, you can request an HD from TDEC. They offer the service free of charge to private property owners.
Hydrologic Determination vs. Aquatic Resource Inventory
This is one of several cases where common vocabulary for something TDEC does causes confusion. The term used widely by the public, and even within TDEC, is often *technically* incorrect. An aquatic resource inventory is a report surveying the resources on-site and applying the appropriate determination method to each one. The inventory includes HDs for any channels on-site AND any other applicable determinations such as those for wetlands, ponds, or reservoirs. However, most people in Tennessee don’t use the name “aquatic resource inventory.” Tennessee started conducting HDs first, and as we started adding other determinations, “HD” became the common umbrella term.
When you submit an HD, TDEC really wants an inventory of all the aquatic resources on your project site which might be impacted by your activity. If they spot another resource on your property that isn’t called out in your determination report, they will want data for it before they consider your HD submittal complete. Logistically, it just makes sense to go ahead and complete jurisdictional determinations for all the features at once. It saves time for everyone—the consultant, TDEC, and the property owner. When all the potentially impacted features are included, the property owner gets the most accurate information possible for planning his or her project and permitting.
It is standard practice for consultants to complete the full inventory and submit it all at once with the HD, and most offer the services together automatically. However, not all consultants are trained and experienced in all of the jurisdictional determination methods and not all QHP-ITs and QHPs automatically expect you to need a full resource inventory. If you have any non-channel resources on-site, knowing you need a consultant who can conduct an aquatic resource inventory, not just an HD, can potentially save you time and money.
Similarly, if you are requesting an HD from TDEC for a private residence that has a wetland on-site, you may still need to hire a consultant. TDEC will do “wetland determinations” which just tells you if a location is wetland and is jurisdictional. For permitting, you’ll also need to know its size, and sometimes its resource quality.
Get Help with Your Property
Do you need an HD for your property? Depending on your entity type and the resources on site, multiple types of help are available to you.
- Local TDEC Environmental Field Office
TDEC has numerous offices across the state to help Tennesseans navigate the regulatory programs. You can find your closest field office and phone numbers for the main office reception line at this link. TDEC Field Offices
- Environmental Consultant
If you need someone to conduct one of the required scientific assessments or to complete a permit application for you, you can hire an environmental consultant. You can find consultants online using the related program and assessment keywords. It’s usually not necessary to hire the most expensive consultant, but it can be worthwhile to avoid hiring the least expensive.
- TN Environmental
Whether you’re planning to hire a consultant or handle your permitting yourself, TN Environmental is here to help you navigate the process with clarity and confidence.
Check out our ARAP resources page here, and don’t forget to join our email list. We’ll send updates straight to your inbox, so you’ll always know when we’re launching a new helpful post or resource. Right now, subscribers get a free 17-page guide to Step #1 for ARAP. If you’re ready to get started, you can get your copy here.
Helpful Links
- TDEC Rules (including HD certification rules)
- Tennessee Water Quality Control Act
- TN Environmental ARAP Program Page
- Free Guide to Jurisdictional Determinations
- Work with TN Environmental
References
Wikipedia contributors. “Biology.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 29 Sep. 2025. Web. 10 Oct. 2025.
Wikipedia contributors. “Geomorphology.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 19 Aug. 2025. Web. 10 Oct. 2025.
Wikipedia contributors. “Hydrology.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 25 Sep. 2025. Web. 10 Oct. 2025.