- In the United States, the scour depth around a bridge pier is calculated by using the HEC-18 equation described by Richardson and Davis in 2001. This equation was developed for piers founded in sand, and there is a sense that in clay the depth of scour is not as large. A study was made to develop a method for clays, silts, and dirty sands. The SRICOS-erosion function apparatus (EFA) method was developed on the basis of flume tests, numerical testing, and erosion testing of the soil. The EFA was built for engineers for testing the soil for credibility in the laboratory. The output of the simple SRICOS-EFA method is a scour depth after a given time. If a hydrograph is used as input, the extended SRICOS-EFA method can be used and results in a scour depth versus time curve. All the details for this method and the software that automates the calculations are available from ceprofs.tamu.edu/briaud/sricos-efa.htm.