Erosion Hazard Zone

January 30, 2017 by Brittany Lankford

What is Erosion?

Erosion is the action of water flow that removes soil, rock, or dissolved material from one location then transports it away to another location.  Some results of erosion consist of slope failure, gully formation, channel down-cutting, or widening.

What is an Erosion Hazard Zone?

An Erosion Hazard Zone (EHZ) can be defined as an area where stream channel erosion is likely to result in damage to or loss of property, buildings, infrastructure, utilities or other valued resources.

Where are EHZ’s located?

EHZ’s are typically located near streams, channels, flood plains, and other waterways.  The City of Austin conservatively defines an EHZ as a 100-ft setback from centerline of stream but recommends a ‘Level 1 analysis’ to determine the EHZ’s exact location.

What is a Level 1 analysis?

A Level 1 analysis is a 7-step procedure that estimates the limits of the EHZ.  See below steps:

  1. Identify and Delineate Location and Stream Reach
  2. Identify and Delineate Meander Belt
  3. Determine Existing Channel Width (Wex) and Depth (Dex)
  4. Estimate Potential Future Incision Depth
  5. Delineate Estimated Future Incised Bed Level and Bottom Width (Bult)
  6. Delineate Sideslope Projections
  7. Delineate Erosion Hazard Zone

For more detailed information regarding Erosion Hazard Zones and a Level 1 analysis, please reference City of Austin’s Appendix E in the Drainage Criteria Manual: https://www.municode.com/library/tx/austin/codes/drainage_criteria_manual

What is a Level 2 analysis?

A Level 2 analysis may be performed if the Level 1 analysis results in being too conservative.  A Level 2 analysis is a more detailed study and requires more information such as hydrology of stream, soil data, and channel geomorphology over a 30-year period.  This information can be determined by a professional geotechnical engineer.

In Summary, the limits of an Erosion Hazard Zone can be determined by using a Level 1 Analysis.  The City of Austin has applied this procedure to a number of locations and found the criteria to be an adequate approach when determining the limits of an EHZ.  It is preferred that all new construction be set outside the EHZ to ensure no threat due to future stream erosion.

We encourage you to contact BIG RED DOG Engineering | Consulting about your next civil engineering project to see how we can help make it a great success.

Written by Brittany Lankford

Brittany Lankford

Brittany is a Project Engineer in the Austin office. Originally from Las Cruces, New Mexico, Brittany attended New Mexico State University. After earning a Bachelor’s of Science in Civil Engineering, she worked for a private civil engineering firm in San Jose, CA. Her experience includes school, single-family, subdivision, and commercial projects. Brittany and her fiancé recently moved to Dripping Springs, Texas, where they like to spend time with their two Labrador Retrievers, Stoney and Ryley.