Spatial Assessing of cost-effectiveness of check dams in controlling sediment load (Case study: Kond watershed)

Extended abstract 1- Introduction Evaluation is a process of assessing the degree of achievement to determined goals. In the meantime, choosing the right method for evaluating the effects will have a significant role on the results and management strategies. Therefore, considering the importance of check dams in watershed management programs in Iran, in this study, performance of check dams in Kond watershed in Tehran province is evaluated with a new economic approach named Cost-Effectiveness Analysis. 2- Methodology At first, the cost associated with check dams is Actualized based on 2019. Then, their effectiveness in controlling sediment load is determined by calculating the volume of stored sediment in their reservoir by Nakhjavani method. Next, Economic evaluation of check dams done using Cost-Effectiveness approach and their spatial distribution is obtained. Finally, the most cost-effectiveness and optimal type and height of check dams in the Kond watershed is determined. 3- Results Obtained results showed that the effectiveness of check dams in the Kond watershed was equal to the control of 131782 t of sediment load, which is a high value. Overall cost-effectiveness of these check dams is equal to 317180 IRR per each ton of controlled sediment load. Their effectiveness-cost is also equal to 0.00000315 ton of controlled sediment load per each IRR, which is a small amount. The results show that the cost-effectiveness criterion increases as the height of check dams up to 4.5 m in the study area. After height of 4.5 m, the cost effectiveness decreases due to the change of the type of check dams from gabion to Masonry. In fact, the cost of sediment load control in check dams with a height of 4.5 meters is about nine times less than that of the check dams with a height of one meter. Accordingly, it is found that sediment load control in this case study has been done with high cost. One of the main reasons of high cost-effectiveness is the large number of check dams in the height range of 1 to 1.5 m (43%) where the cost of sediment load control with them is very high. Obtained results by considering the type of check dams also showed that Gabion check dams with 4.5 m height and cost-effectiveness equal to 134615 IRR per each ton of sediment load have the lowest cost-effectiveness and are the most economical and optimal types of check dams for sediment load control. In contrast, masonry and gabion check dams with heights of 1 and1.5 m also have highest cost-effectiveness and the cost of sediment load control in this type of dams is very high. 4- Discussion & Conclusions This result indicates that the choice of right type of check dams in the management plans will have a significant impact on the efficiency of cost of sediment load control. Also these results show that watershed management approach in Iran needs to change its attitude. In fact, if it is necessary to control the sediment load on the stream, the choice of a less number of check dams with optimal height and type, will load better results than choosing a large number of small check dams.