What is your experience in using runoff models in small gaged and ungaged catchments (less than 50 km2)? How did you asses the accuracy of the model you used? What was the input data used in the process?
I suggest ATHYS and HEC-HMS, Both models used DEM and Land cover and other inputs data as Rainfall, CN...
You could use Nash and Sutcliffe, Percent Bias coefficient (PBIAS), and RMSE-observations standard deviation ratio (RSR) to evaluate the output of these models.
HEC-HMS is my recommendation. You can download the software for free here: "https://www.hec.usace.army.mil/software/hec-hms/downloads.aspx". To get you off the ground and running, check out these 5-10 minute YouTube videos: "https://www.hec.usace.army.mil/confluence/hmsdocs/hmstr/hydrologic-modeling-with-hec-hms-march-2021-42175930.html". Also, check out these tutorials and guides for examples and step-by-step instruction on setting up a simple model: "https://www.hec.usace.army.mil/confluence/display/HMSGUIDES/Creating+a+Simple+Model". Hit me up with any questions you may have.