Channel flow control and prediction of waterbodies reaction on heavy rainfalls or rapid snowmelt become critical when forecasting the flood risk in urban catchments. A very good example of both problematic and carrying a real threat to urban infrastructure is the Strzyża Creek in Gdańsk. In years 2011–2013 undertook the implementation of storm water monitoring system in the Strzyża Creek basin in Gdańsk. Since that time, it has become possible to collect valuable hydrological data on rainfall and flows in the strongly diversified urbanized districts of the city. Currently, the work is underway to extend the Strzyża Creek monitoring system. The ongoing research project is being realized again in years 2015–2017. The main aims of a project are: development of the methods of flood control, expansion of the existing rainfall-runoff and storage monitoring system in the basin and integrated water quantity and quality analysis, since the Strzyża Creek is one of the main stormwater collectors in Gdańsk. The article presents an example of using continuous data collected by the hydrological monitoring system to determine the annual runoff coefficient. The results were compared with the same parameter estimated on the basis of monthly instantaneous flow measurements and rainfall observations from the precipitation gauge localized in the vicinity of the analyzed catchment.