Accumulation of floating woody debris at flow control structures can result in reduced discharge efficiency. Labyrinth weirs may be more likely to catch debris on the crest than other weirs due to their ability to pass large discharges with relatively small heads. Therefore, prompted from field data at Lake Brazos Dam, a laboratory-scale hydraulic model study was performed to evaluate the floating woody debris blocking sensitivity of labyrinth weirs in channel and reservoir applications, including arced labyrinth weirs. Experimental test results noted debris entrapment locations on the crest and that debris blockage probability is primarily a function of trunk diameter and upstream head. Debris accumulation tests indicated that lower heads are more sensitive to debris blockage than higher heads. Specifically, for smaller flow depths the initial or reference head (without debris) increased by up to 17% with debris, while at higher reference heads the head increase due to debris was approximately 7% or less.