With respect to the importance and considerable extent of the Kosar irrigation and drainage network, the environmental issues of the network are investigated. The purpose of this study was to evaluate the environmental effects of Kowsar irrigation and drainage network located in the central basin of Karkheh in Khuzestan province, using two methods: conventional and modified ICOLD matrices. To study the environmental parameters, three physical, biological and socio-economic environments were used. Then, using two methods of conventional and modified ICOLD matrices, the effect of each of the project micro-activities on the environmental factors of the study area was measured in the operation phase separately for the three mentioned environments. Thus, a matrix was designed according to all three environments, which was completed by environmental experts and the average score of the evaluation criteria was considered. The results showed that the most positive effects are related to the socio-economic environment. It should be noted that the sum of positive values using conventional and modified ICOLD matrices was 793 and 458.9, respectively, and for negative values was 447 and 285.8, respectively. Therefore, both matrices showed reasonable and good fitness in estimating the impacts and thus the implementation of the Kawser irrigation and drainage network is verified
