Hydrological studies have become more important in recent years to estimate flow discharges in the valleys. The study area of Al-Ghadaf Valley was chosen due to the absence of surface runoff information for this valley. This research studied the watershed of Al-Ghadaf (GW) by using the SWAT model. It wasn’t possible to perform calibration and verification for the model due to the absence of actual discharges in the Al-Ghadaf valley. The area of the catchment was 8567.25  and the weather data used in this model was for three actual stations, Rutba, Ramadi, and Al-Nukhaib, for 13 years from 2009 to 2022. I wasn’t able to choose a period larger than 13 years because some of them are missing. Despite this, one of the features of the period that was chosen is that the years 2019 and 2013 fall within the chosen period and are considered flood years by the Iraqi Ministry of Water Resources. The results show that the maximum daily flow discharge for Al-Ghadaf that outflows into Al-Razzaza Lake was 312.1 /s, the maximum surface runoff depth (mm) for all watersheds was 6.62 mm, and the average curve number for the basin was 88.4. These results will help future researchers in this study area and decision-makers in the Ministry of Water Resources to know the amount of water coming from this basin and feeding Al-Razzaza Lake, especially since there are no previous studies about this basin showing the amount of water falling on the basin and coming to the lake.