Hydraulic scaled model tests for the optimization of approach channel excavation and approach flow conditions of haraz morning glory spillway

Haraz dam under construction is located along Tehran-Amol road, 20 km upstream of the Amol city. A tunnel has been designed to detour the traffic temporarily around the dam site to avoid any closure of the main road. This tunnel will be integrated in the morning glory spillway of the dam. According to the road design constraints and the tunnel layout, the morning glory entrance is located next to the dam abutment. This is the main challenge in Haraz spillway in comparison with conventional morning glory spillway approach channel. A spillway hydraulic model was set up in Tehran Water Research Institute and the corresponding tests were performed on it subsequently. According to the test results and as expected, some disturbances in the stream lines were observed of the approach flow nearby the abutment which had some negative impacts on the spillway capacity and its performance. Several alternatives were studied to optimize the hydraulic conditions using the hydraulic model. Finally, taking advantage of piers in a specific position on the ogee crest was found to be the most promising solution for reducing flow disturbances. This method could be an innovative solution for morning glory spillways, which have to be located close to the abutments.