The rehabilitation of dams often requires spillway capacity upgrades. Replacing a less hydraulically efficient linear weir with a labyrinth weir can be an effective way to increase discharge efficiency (discharge at a given upstream head) for a fixed-width channel. Labyrinth weirs are linear weirs folded in plan view to increase total spillway crest length (which in turn increases discharge efficiency within a channel). Labyrinth weirs potentially have limitless geometric configurations. This study was performed to analyze the effects of varying certain geometric parameters on discharge efficiency and design method predictions. Due to limited cross-sectional flow area near the upstream apex, labyrinth weirs experience nappe collision and local submergence that potentially reduce discharge efficiency. The increase of upstream apex width may be a feasible method to decrease the negative effects of nappe interference, which in turn may increase discharge efficiency. This was analyzed in this study by testing a series of eight laboratory scaled labyrinth weirs (with sidewall angles of 12°), with various upstream apex widths. Upstream apex width tests were performed in a fixed and varied channel width setting. The design method developed by Crookston and Tullis is based on laboratory scaled physical models. This method is very useful in the estimation of performance for geometrically similar prototype labyrinth weirs. However, due to difficulty in obtaining data on completed prototype weirs, design method predictions are rarely verified. To help validate Froude scaling and design method predictions of prototype weirs, a series of physical model tests (with sidewall angles of 15°) were performed with varying scale sizes (0.5 to 3.0 compared to the size of weir used in the design method). To expand the applicability of the design method to common geometric variations, tests were performed on weirs of varying weir height and cycle width (with sidewall angles of 15°). These variations were applied independently and analyzed to determine their effects on discharge efficiency and design method predictions. A correction factor is then presented to be used in conjunction with Crookston and Tullis’s design method for these geometric variations. All conclusions are presented in this thesis.