The Hydraulic Design, Riprap and Scour Calculator has two components that track the two main tasks associated with bank-protection design.

  1. Size the Rock and Select an Available Gradation
  2. Compute the Potential Scour to Determine the Depth of Toe Protection


HEC developed these calculators together because these computations are often used in tandem to determine the size of rock required and the volume of launchable stone required to protect the toe.

Riprap Calculator:

Size Rock and

Select Gradation



Step 1

Run HEC-RAS Steady Flow Hydraulics (or compute flow depth and width externally).

Step 2

Identify Upstream "Reference" or "Crossing" Cross Section

Step 3

Compute Radius of Curvature and Enter Data

Step 4

Compute d30 of Stable Rock Gradation

Step 5

Select Appropriate Riprap Gradation and Compute Thickness


Scour Calculator:

Compute Key Depth

or Launchable Volume



Step 1*

Run HEC-RAS Steady Flow Hydraulics (or compute hydraulic parameters externally).

Step 2* 

Identify Upstream "Reference" or "Crossing" Cross Section

Step 3*

Compute Radius of Curvature and Enter Data

Step 4

Select Appropriate Equations

Step 5

Compute Ensemble Scour Depths

Step 6

Visualize Results: Select a Toe Station to Plot Bend Scour

Step 7

Select a Reasonable Scour Depth Based on Calculations, Regional Geology, and Engineering Judgement

Step 8

Use Selected Scour Depth to Compute Volume of Launchable Rock or Depth of Stone Key

  • The Riprap and Scour calculations share steps 1-3