Hydraulic Design

Roads and Bridges have evolved over time from their roots in footpaths and log bridges into modern transportation routes capable of carrying vast amounts of goods and services around the nation. Today's roads and bridges provide the physical connections that are the taproot of our society, and the safe operation of these roads and bridges is vital to our nation's prosperity. Approximately 86% of all bridges in the United States are built over streams.

What is hydraulic design?

According to Webster's Dictionary, hydraulic means operated, moved, or effected by the means of water. In a transportation context, this refers to drainage structures such as bridges or culverts. The purpose of hydraulic design is to ensure structures are of sufficient size that natural flooding is not worsened and to ensure that the structure can withstand the design flood and remain traversable. This is required in order to protect the property and residents upstream and downstream of a highway structure and any motorists who use the roadway. Hydraulic designers also must account for scour. Scour refers to the tendency of soil in a streambed to be washed away by flowing floodwaters.

Earth is a world of water. Roughly three-quarters of this planet is covered by water. The interaction between the sun and the water is the force behind life on this planet. Rain, falling one drop at a time, can produce tragic results. Since 1990, nearly all presidential declared disasters in Tennessee involved precipitation of some kind. Most have involved flood damages.

In the design of bridges and roads, one main thing to remember is that STREAMS and RAINFALL are DYNAMIC. No two stream crossings are exactly alike and no two floods are exactly alike.


Interstate 55 over the Mississippi River in Memphis, TN. This picture was taken during normal conditions in August 1996. Water surface elevation is 192 feet above mean sea level.


Responsibilities of the Hydraulic Design Section

A brief history of hydraulic design at TDOT

Downloads (pdf format)

Design Procedures for Hydraulic Structures 2012

Hydraulic Design Summary form (English) as required on all hydraulic designs

CADD submittal form (English) checklist for hydraulic preliminary

Sample project file (8.57 MB)

Sample Hydraulic Layout


Interstate 55 over the Mississippi River in Memphis, TN. This picture was taken during flood stage in March 1997. Water surface elevation is 224.53 feet above mean sea level.