Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2005
Publication Date: 6/17/2006
Citation: Li, H., Barkdoll, B., Kuhnle, R.A., Alonso, C.V. 2006. Parallel walls as an abutment scour countermeasure. Journal of Hydraulic Engineering, 132(5): 510-520 (doi 10.1061/(ASCE)0733-9429(2006)132:5(910)).
Interpretive Summary: Streams in agricultural watersheds are often plagued with unstable channel boundaries. Erosion of the unstable channel boundaries may threaten valuable agricultural lands and structures such as bridge supports. Erosion protection measures have the potential to preserve structures and adjacent agricultural lands. A study was conducted in the laboratory using a model stream channel to develop methods to prevent erosion near a model bridge support located on a stream bank. Several successful designs of vertical walls and walls composed of gravel were developed to protect bridge supports from erosion in this study. These results will provide useful guidance for the design of erosion-prevention structures in the streams of agricultural and other watersheds. This knowledge will provide another method in the tools available for managers to control the erosion of structures and lands. This type of information is necessary for effective environmentally-aware management of watersheds.
Technical Abstract: Scour at bridge abutments can cause damage or failure of bridges and result in excessive repairs, loss of accessibility, or even death. To mitigate abutment scour, clear-water and live-bed laboratory experiments in a compound channel were performed using parallel walls. Two types of parallel walls were tested: the first was made of a solid thin wood plate and the second was made of piled rocks. Solid parallel walls consisted of a series of rectangular straight plates of different lengths attached to the upstream end of a wing wall abutment parallel to the flow direction. The velocity for the three cases was 0.9, 1.5 and 2.3 of its incipient motion value for bed sediment movement. The bed material was sand with a mean diameter of 0.8 mm and a standard deviation of 1.37. All the plates were seated at the bottom of the compound channel bank slope and were even with the abutment face. Straight plates thus situated were able to move the scour hole away from the upstream corner of the abutment and were effective as a countermeasure to prevent scour. As the length of the plate increased, the scour at the abutment declined. A length of 1.6L, with L being the length of the abutment perpendicular to the flow, caused the scour to be eliminated at the abutment for a velocity ratio of 0.9 (clear-water scour). Similarly, a 1.6L long wall can eliminate the time-averaged scour depth at the abutment 100 percent for a velocity ratio of 1.5, and 70 percent for a velocity ratio of 2.3. For parallel rock walls, various values of wall length and protrusion length into the main channel were tested. A wall that did not protrude into the main channel with a length of 0.5L minimized scour at the abutment for all three different velocity ratios (0.9, 1.5, and 2.3).