Abstarct: Abstract Every year, floods in different parts of the country cause a lot of damage to economic resources. the occurrence of floods and the resulting damage in iran has been increasing in recent years; however, not much attention has been paid to it. every year, some of the buildings and facilities downstream of the country's rivers suffer a lot of damage due to seasonal floods and the release of streams larger than the healthy capacity of the rivers. Occurrence of flood in a catchment area is subject to many variables. These variables do not have constant conditions and values every year. one of the parameters that can be effective in flood control is the use of vegetation in the river bank to reduce the energy. due to the importance of the subject in this research a numerical study was conducted on flood energy reduction through a protection forestin , at first, validation was performed with laboratory results with flow3d software, and then five tree planting arrangements of protected forests by changing the distance to the diameter under different velocities of the flow are examined, which by reviewing the results show that afforestation arrangement is very effective on reducing energy. on average, changing afforestation arrangement was about 54.7 percent effective on reducing energy.