Quantitative analysis of the impacts of watershed management activities on catchment hydrological status

Evaluation of the impacts of past watershed projects provides useful insights for future projects. In this study, the hydrology and water resources status of Akujan Catchment of Qazvin Province has been the object of the study in which the effects of various measures of watershed managements were evaluated. For this purpose, the changes of water resources discharge, increased infiltration, water storage, peaks and volumes of catchment floods, were compared before and after the implementation of watershed management projects. Results showed that 114000 m3</sup> more runoff storage has been carried out by watershed management operations that 20.1% of this volume was related to the structural operations and 79.9% of it was due to biological and biomechanical projects of the catchment. Results of the flood analysis indicated that the role of structural measures in the change of time of concentration is low and even negative. Therefore the reduction of the peak flow and flood volume at the outlet of the catchment is due to the implementation of biological and biomechanical measures which reduces the peak flows by 42.7, 25.4, 20.8, 17.1, 15.3 and 13.8% and flood volumes by 41.8, 24.8, 20.2, 16.5, 14.8 and 13.3% respectively for the return periods of two, five, 10, 25, 50 and 100 years. Another observation is that the effect of watershed management practices on the reduction of flood peak and volume decreases when the return period of flood is increased.