Abstract: The aim of this study was to apply a hydraulic model for the gap flow in the Sepeed Rood valley to assess the roles of factors such as sea breeze affecting the flow in the gap. The valley is considered as a narrow passage in Alborz mountain range in which the remarkable air flow causes intensive winds in its route cities such as Rood Bar and Manjil. Since the gap winds are considered as the condensed air flow in low levels which are horizontally limited by the channel rims and vertically by temperature inversion, it is similar to the flow in a channel and the hydraulic model can be applied for it. The application of scale analysis indicates the strength of F0 term related to the contribution of heat forcing circulation such as sea breeze which plays a role for creating the winds with the average daily velocity much bigger than the night most especially in summer days. Moreover it indicates the validity of Bernoulli equation application in winter most especially when the regional circulations are weak and synoptic forcing is the dominant factor in the gap wind, while in summer the effects of regional circulations such as sea breeze are more noticeable.