Nowadays, the catchment areas of impermeable surfaces increase due to urban development and construction of various buildings on permeable soils. It increases the volume and intensity of runoff. Consequently, the capacity of existing drainage systems for flood control is inadequate and their designs should be modified, accordingly. In drainage systems of urban runoff, water channels have little slopes to limit the velocity of flow. Drop manholes are usually provided to offset the elevation differences between the channel slope and the ground slope. This special structure should be used to reduce the energy as well as current level. The aim of this thesis is to investigate the performance of drop manholes to reduce the energy of flow and increase the flow capacity. The scheme combines drop manhole and pipe outlet structure. Pipe outlet structure usually consists of hanging baffle and end sill. A physical model of drop manhole was constructed in the Hydraulics Lab, Isfahan University of Technology. It was consisted of a 2 m pipe with diameter of 0.19 m upstream and a 2.5 m rectangular channel after a drop of 0.345 m height. A hanging baffle was implemented which was capable to move in horizontal and vertical direction. In order to generate a free surface flow, Jet Box was used with two nominal opening ratios of 50 and 80%. Discharge ranged 10 to 38 L/s and Froud number was between 1 and 4. Different flow regimes and hydraulic characteristics of flow were investigated. Using OpenFOAM, open-source software, the flow was simulated numerically. To only investigate the performance of hanging baffles, end sill was not used. To verify the results, the first set of experiment was conducted on a model without hanging baffle and the experimental and analytical results were compared with the existing rectangular vertical drops. In the second phase of experiments, a model with hanging baffle is used. Results show that the efficiency of energy dissipation in the drop manhole with no sills ranges about 40 to 80 percent, which is 50 percent higher than those of the rectangular vertical drop. In addition to energy loss, other factors such as the depth and length of the pool, the air concentration and the downstream depth are compared with previous experimental results. In the second set of experiments with a hanging baffle, four types of flow regimes are identified based on the location of the water jet impact, opening of the hanging baffle, and pool depth. Results in terms of energy loss are similar to the model without hanging baffle and are about 50 to 80 percent. Using the momentum equation, a semi-analytical relation for estimating the pool depth upstream of the hanging baffle is presented that provides good agreement with the experimental data. It is found that the coefficients of contraction and discharge of the system were less than those in sluice gates. Numerical simulation results also showed that the OpenFOAM software has good capability for estimating the hydraulic parameters. Key Words Manhole, Pipe outlet structure, Vertical drop, Flow regimes, Energy dissipation, OpenFOAM