Hydrologic Determinations

Commercial, utility, and mining projects frequently require environmental permitting.  But when is a stream hydrologic determination needed?

A Hydrologic Determination may be required if your project crosses or is adjacent to a watercourse in Tennessee. The Hydrologic Determination is required to meet state of Tennessee and metropolitan area MS4 stormwater rules.  Below are some answers to commonly asked questions about Hydrologic Determinations in Tennessee.

1. What does “Hydrologic Determination” mean?

A Hydrologic Determination (HD) is an on-site study by a Qualified Hydrologic Professional (QHP) to determine whether a watercourse is regulated as a “stream” or as a “wet weather conveyance”. Each of these is a “Waters of the State” designation and are protected natural resources in Tennessee.

Hydrologic Determinations

2. Why are hydrologic determinations necessary?

In 2009 Tennessee Chapter 464 was adopted requiring rules that would require hydrologic determinations for permitting, establish protocols for performing hydrologic determinations, and establish a Qualified Hydrologic Professional Certification in Tennessee.  

A hydrologic determination provides the state jurisdiction of the watercourse and provides the required information for:

At least one of the above permits or processes are generally required for most residential and commercial site development, utility expansions, and mining projects.   

3. What will the Qualified Hydrologic Professional Do While On-Site?

The QHP will collect data on the hydrology, geomorphology, and biology of the watercourse.   The method of hydrologic determination is spelled out in the Tennessee Department of Environment and Conservation (TDEC) – Division of Water Pollution Control, Guidance for Making Hydrologic Determinations.  Data is collected on the Hydrologic Determination Data Sheet. The QHP will record 28 natural characteristics of hydrology, geomorphology, and biology and give the watercourse a score.  A score of 19 or above generally, but not always, indicates the watercourse is a stream. A score less than 19 generally indicates the watercourse is a wet weather conveyance. 

4. When Are They Needed?

A hydrologic determination is generally required:

  • When complying with the General ARAP for altering wet weather conveyances
  • When applying for an ARAP to impact a stream
  • When encroaching within 60 feet of a watercourse
  • When impacting a watercourse with an unknown regulated status
  • When the buffer distance from a watercourse is needed for a development, public utility, mining, or another project that encroaches upon a watercourse.

5. What are excluded from hydrologic determination requirements?

The following aquatic resources are excluded from requiring a hydrologic determination:

  • Lakes – the rule covers linear watercourses
  • Ponds – the rule covers linear watercourses
  • Wetlands – wetlands are regulated by the TDEC and Corps of Engineers under different regulations.
  • Non-regulated Drainage – drainage features not following topography, such as a roadway ditch not following natural slope.

6. Are ephemeral streams considered wet weather conveyances or streams in Tennessee?

TDEC does not use the terms used by the Corps of Engineers, such as ephemeral, intermittent, or perennial in their guidance.  Remember, if you are working under a TDEC permit your watercourse is “Waters of the State” and either a stream or wet weather conveyance.  If you are working under a Corps of Engineers permit your watercourse is “Waters of the US” and either non-jurisdictional or jurisdictional and described as ephemeral, intermittent, or perennial.

7. Who may complete hydrologic determinations?

Hydrologic determinations may only be completed by an individual listed by TDEC as having passed the Hydrologic Determination Training and fulfilling other requirements including having a Bachelors of Science Degree in the Natural Sciences, five years project experience, and passing the TDEC Hydrologic Determination Certification Class.

8. Who has the final say on the determination of my stream?

TDEC does, but a report by a Qualified Hydrologic Professional is required to obtain their decision.  TDEC reviews the hydrologic determination report submitted by your hydrologic professional and will either concur or not concur with the findings. 

9. What is presumptive correctness?

If your hydrologic determination report is conducted by a Certified Hydrologic Professional in Tennessee and submitted with the presumptive correctness requirements, then the hydrologic determination report will be presumed correct by TDEC, unless there is a significant question. 

10. Can TDEC complete the hydrologic determination?

TDEC no longer completes Hydrologic Determinations for commercial projects.  Instead, they review the HD report submitted by the hydrologic professional. 

11. How can I determine whether an HD has already been completed on my stream?

A list of Hydrologic Determinations confirmed by TDEC may be found at the Division of Water Resources Hydrologic Determination Map Viewer.  The viewer shows the location and results of completed hydrologic determinations.

12. How quickly can the results be obtained?

Most Hydrologic Determination reports can be completed within one week.  TDEC has 30 days to respond to the HD report if there are any significant questions.  If there is no TDEC response on a submittal from a Certified QHP then it is presumed that TDEC agrees with the findings of the report and it may be attached to the environmental permit or be used in Metro Nashville buffer distance determinations.

13. How much does a hydrologic determination cost?

The cost depends on the length of the watercourse and the number of observations required. For more information, call Lord and Winter staff in Nashville at (615) 953-9490or email us at info@lordandwinter.com.  We have a Qualified Hydrologic Professional ready to answer your questions.

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