The first two steps of the scour calculation are the same as the first three steps of the riprap calculation. If you are doing these analyses together, use the results from the riprap analysis (or visa versa). If you are only using the calculator to compute scour, see Step 1, Step 2, and the Radius of Curvature section of Step 3 in the riprap portion of the manual. This section includes some scour-specific implications for these analyses where the steps differ from the Riprap Calculator.

Hydraulic Scour Parameters

The Scour Calculator imports more hydraulic results from the HEC-RAS results file (e.g. p01.hdf) than the Riprap Calculator. Each of the seven scour equations uses a small subset of these parameters. But the ensemble approach requires a range of hydraulic inputs. Apart from the Neill equation (which requires manual bankfull data), most of the data for these equations come from the HEC-RAS hydraulics.

The Calculator automatically computes results for each when the required data become available. In most cases, the model results are sufficient for General Scour results (with a categorical sinuosity parameter that has a default) and the Bend Scour results require a manual radius of curvature.

Selecting a Design Flow

Design flow selection for scour analysis follow similar principles as riprap analysis. See that section for reference. However, most of these equations were based on flows at or below bankfull. Maynord 1996 (from Thorne) notes empirical methods are valid up until significant interaction between main-channel and overbank flow. Overbank depth should not exceed 20% of channel depth.