The National Academies

NCHRP 24-36 [Final]

Scour at the Base of Retaining Walls and Other Longitudinal Structures

  Project Data
Funds: $500,000
Research Agency: University of Minnesota
Principal Investigator: Fotis Sotiropoulus
Effective Date: 11/15/2012
Completion Date: 5/31/2016


In many locations in the United States, new construction, rehabilitation, and/or reconstruction is requiring the use of retaining walls to minimize the impact of fill into a channel or floodway. Other longitudinal structures (e.g., embankments) that encroach into floodplains need to be protected from erosion and failure by designing and installing countermeasures to protect the face and/or bottom of the structures.  What is missing in both of these design situations is the ability to accurately determine the depth of scour at the base of the retaining wall or longitudinal structure such that their foundations can be set at elevations that prevent failure due to undermining. In recent years, there have been several significant retaining wall failures caused by undermined foundations because a reliable method of estimating scour is not routinely used by the engineering community.  Either the potential scour at the base of the structure is not considered or estimates are made based on “rule-of-thumb” guidance that may not be reliable. This is particularly important in building MSE (mechanically stabilized earth) walls in environments where the ultimate depth of scour is not known or cannot be determined. There is an urgent need for research in this area so that retaining walls and other longitudinal structures being placed in a riverine environment can be designed with a higher level of confidence.


Research was performed under NCHRP Project 24-36 by University of Minnesota to develop predictive methods that can be used to estimate scour at the base of longitudinal structures including vertical and sloping walls in a riverine environment with varying (a) flow characteristics; (b) approach angles; (c) structure lengths, shapes, and roughnesses; and (d) streambed/sub-surface soils. The completed work is documented in the Agency's Final Report and available at:


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