Bridges are more important structures that have been used by human from old times. Destruction of bridges always has irreparable fatal and financial losses and their strength is very important. Crossing these structures over the rivers needs locating of piers on the river bed and their strength ensure the stability of the bridge. On the other, locating of each structure in front of flow, changes the flow pattern and has same effects. One of these, are local scour around piers that causes bed excavating and resulting the protrusion of the pier foundations that risks the stability of the bridge. Therefore, scour examination in piers and finding a way to its reduction seems very important. Today, using of several piers in bridges is common and measures to reduce scour in group piers is considered. In this context, there are a lot of research on the application of any protective measures, such as a collar, slot, piles and etc., but a few studies have been conducted to examine the effects of combining them. In this study with the aim of investigation of collar-slot combination in scour reduction, in first step, several experiments was conducted on piers with 6cm diameter in a 90cm width flume on D 50 =0.75mm sediment particles and then time development of scour depth was compared for each. First, these experiments were done in separate application for each of these protective measures for collars with 1.5D, 2D, 2.5D and 3D (D: Diameter of Piers) in the three positions of above, below and on the floor and two shapes of circular and square. Also, efficiency of two slot types with length of half depth and equal in 0.25 of pier diameter constant width were examined. Then, experiments were done on 6 treatments obtained from combination of collar and slot in single pier and finally, application of two combinations of these was studied in group piers with a pier distance of 2D, 2.5D and 3D. In the following, velocity, turbulence and Reynolds stress components were obtained for a combined model to help of ADV (Acoustic Doppler Velocimeter), and flow structure around this was studied. Obtaining results show that increasing the size of collar and slot length improves the performance of these two protective measures in scour reduction. Also, locating of collar in below the bed and using square collars increases delay time in beginning of scour process and shows better performance. Application of combined model in single pier with weakening the down flow and absorb the rising flow causes 25 to 100 percent of scour reduction. Effect of this model in group piers boosted with increasing distance of piers and caused 34 to 63 and 58 to 100 percent of local scour reduction in front and back of pier respectively. Keywords: Local Scour, Bridge Pier, Group Pier, Flow Structure, Collar-Slot Combined Model