Tarakan city is one of city that is growing in the province of North Kalimantan. In an effort to promote the development and economic development of the town of Tarakan, Juwata Airport is in airport that needs to be upgrade the capacity. The research on the water flow in drainage Juwata Airport is expected to determine the capacity of the drainage channel on. This research uses a rainfall data calculation method partial series and log normal distribution and the analyzed debit calculation where the calculation of the flow rate using the manning formula and then the calculation of input on HEC-RAS 4.1.0. Based on the calculation, obtained the discharge design 0.367 m3/s with a bottom width dimension of the channel plan (B) = 0.64 m: channel height (H) = 1.08 m with high water = 0.56 m while the existing channel bottom width (B) =1.04 m ; channel height (H)= 0.67 m with high water =0.721 m, which in these conditions is not able to accommodate the existing channel of the water discharge.