California Department of Transportation
 

DIB 83-02 - 4.1 End Treatment and Other Appurtenant Structure Repairs and Retrofit Improvements

DESIGN INFORMATION BULLETIN No. 83-02
CALTRANS SUPPLEMENT TO FHWA CULVERT REPAIR PRACTICES MANUAL

4.1 END TREATMENT AND OTHER APPURTENANT STRUCTURE REPAIRS AND RETROFIT IMPROVEMENTS
  4.1.1 Headwalls, Endwalls and Wingwalls
  4.1.2 Outfall Works
         

4.1 End Treatment and Other Appurtenant Structure Repairs and Retrofit Improvements

4.1.1 Headwalls, Endwalls and Wingwalls.

Selecting an appropriate end treatment for a specific type of culvert and location requires the application of sound engineering judgment. Design guidance for culvert entrances and exits is given in Topics 826 and 827 of the HDM. If bank erosion is evident, a review of the original design may be warranted, particularly if the original selection was the same standardized type for both the headwall on the upstream end and the endwall on the downstream end. Straight headwalls and endwalls should be limited to locations with low approach and exit velocity not requiring inlet or outlet protection against eddy action. However, at the outlet to some cross culverts in narrow riverine canyons where there is a free outfall, it may be necessary to consider using a straight endwall to prevent erosion.

Example of combined straight headwalls and concreted RSP upstream end treatment
Example of combined straight headwalls and concreted RSP upstream end treatment

4.1.2 Outfall Works

The outfall works should provide a transition for the 100-year flood or design event from the culvert outlet to a section in the natural channel where natural stage, width, and velocity will be restored. If an outfall structure is required for transition, it will not typically be a counterpart of that required at the entrance. Wingwalls, if intended for an outfall transition, should not flare at an angle (in degrees from the stream axis) greater than 150 divided by the outlet velocity in feet per second (ft/s). For the 100-year flood or design event, warped endwalls can be designed economically to fit trapezoidal or U-shaped channels, as transitions for moderate to high velocity (10-18 ft/s). For extreme velocity (exceeding 18 ft/s) the transition can be shortened by use of an energy-dissipating structure. At large culverts where stream channel degradation is present, countermeasures may be needed to prevent embankment failures and loss of pipe support at the outlet where the high-energy waterfall can undermine the embankment toe quickly in heavy runoff. For example, see photograph on page 70, Index 7.1.4. HY-8, the FHWA culvert software program provides designs for energy dissipators and follows the FHWA Hydraulic Engineering Circular No.14 method for design.

Energy dissipator plunge pool and bank protection at large diameter culvert outlet
Energy dissipator plunge pool and bank protection at large diameter culvert outlet

Energy dissipator with flared wingwalls and bank protection
Energy dissipator with flared wingwalls and bank protection

Refer to FHWA Culvert Repair Practices Manual Volume 1, Chapter 5, and Volume 2, Appendices B-16 through B-22.

For bank protection design, in lieu of the guidance shown in Chapter 870 of the HDM, refer to the California Bank and Shore Rock Slope Protection on-line publication available at: http://www.dot.ca.gov/hq/oppd/hydrology/ca_riprap.pdf


This page last updated June 30, 2003