Lake Fayetteville Spillway Study

What is this project?

This project is an engineering study to determine the capacity of the Lake Fayetteville spillway. Per state regulations, the Lake Fayetteville spillway must be capable of safely passing 100% of the Probable Maximum Flood - a theoretical storm event. FTN Associates Ltd. was consulted to study the lake watershed hydrology as well as the lake and spillway hydraulics. The State of Arkansas' Dam Safety Section of the Natural Resources Division has recently reviewed the findings and concurred that the existing spillway passes approximately 70% of this theoretical storm event.

View the capacity study document (PDF).

Why is it important?

Being able to safely pass the Probable Maximum Flood through the Lake's spillway safeguards against the over-topping of the earthen dam embankment, which could lead to failure and downstream flooding. Since the City of Johnson is situated downstream of the lake outfall, the lake is classified by the State as "High Hazard" and must be able to pass 100% of the Probable Maximum Flood.

What is the current status?

FTN has completed the engineering study of the Lake's hydrology and hydraulics, determining that 70% of the Probable Maximum Flood can pass through the existing spillway. This is more than was expected, as older studies appeared to indicate only 50% could be safely passed. The State has reviewed this document and concurred with the findings.

The next step in this project is to move from a study to an engineering design of concepts that could resolve the capacity issues. The options that will be considered include, but are not limited to:

  • Increasing dam height to consistent elevation,
  • Increasing length of spillway crest, 
  • Lowering lake level (permanently or temporarily) to increase storage capacity, and 
  • Any combination of the suggestions above.

When is completion expected?

Engineering design and analysis is ongoing. No construction would occur until a design were approved by the State that could address capacity without any harmful impacts upstream or downstream of the lake.

How was this project funded?

This project is funded from the Water & Sewer Rate Operations Study account.