Document Type : Research Paper
Authors
1 Postdoc Researcher, Department of Reclamation of Arid and Mountainous Regions, Faculty of Agriculture and Natural Resources, University of Tehran, Karaj, Iran
2 Assistant Professor, Soil Conservation and Watershed Management Research Department, Lorestan Agricultural and Natural Resources Research and Education Center, Agricultural Research, Education and Extension Organization (AREEO), Khorramabad, Iran
Abstract
Introduction
Watershed management measures are implemented to maintain or restore the ecological functions of watersheds by reducing the impacts of events such as floods, landslides, and erosion in downstream areas, while also enhancing resource productivity and improving local livelihoods. These measures become effective when they identify, restore, or reinforce areas of high ecological value that must be protected from degradation or conversion to other uses. Therefore, it is essential to assess the effectiveness of watershed management measures (both in research and implementation phases) to develop a model of their positive or negative impacts, guiding decision-makers in planning and executing successful watershed management projects. Project reports often emphasize the strengths and positive outcomes of these measures, while their inefficiencies are less frequently highlighted. This study reviews and evaluates recent watershed management projects to examine both their strengths and weaknesses.
Materials and methods
In this study, the effectiveness of several recent watershed management projects implemented in different watersheds of Iran was assessed based on the latest available documents. The evaluated watersheds include Behshahr-Galoogah, Maragheh (Markazi Province), Khaveh-Delijan, Asiaborud (Chalus City), and Faryab-Golashgerd (Kerman Province). The state of water resources in these areas was also analyzed.
Results and discussion
The findings indicate both positive and negative outcomes for each project. In the Behshahr-Galoogah watershed, sub-basins where a combination of different structures was implemented along the stream network experienced reduced peak discharge and increased concentration time. However, in sub-basins with few check dams relative to their area and stream length, the measures did not significantly alter stream length, concentration time, or peak discharge, but they did help stabilize the stream's longitudinal profile. In the Maragheh watershed (Markazi Province), specific erosion and sediment rates before and after the implementation of watershed measures were recorded as 10.78 and 3.14 (Ton/km²), and 3.1 and 66.9 (Ton/km²), respectively. The effectiveness of watershed measures in the Khaveh-Delijan watershed was also evident. The construction of check dams led to a reduction in peak discharge for different return periods (5, 10, 20, 50, and 100 years), with values decreasing from 3.9 to 0.6, 4.9 to 2.7, 9.4 to 5.1, 14.6 to 8.0, and 22.4 to 12.4 m³/s, respectively. Additionally, base time and lag time of the hydrograph increased by approximately 3.5 hours. The Asiaborud watershed project demonstrated that, following the implementation of watershed measures, specific erosion was recorded at 3.89 Ton/ha/year, and specific sedimentation was estimated at 1.87 Ton/ha/year. Hydrological studies from 2000 to 2019 indicated a decrease in curve number (CN), an increase in concentration time, and reductions in both peak discharge and flood volume (by 1078.49 mm³). Consequently, financial losses caused by floods in this watershed decreased due to the reduction in flood volume. Similarly, findings from the Faryab-Golashgerd watershed project indicated a significant increase in concentration time and a reduction in peak discharge across all studied return periods.
Conclusion
Overall, the results show that most of the implemented watershed management projects had significant positive effects, including reduced peak flood/runoff discharge, decreased erosion and sedimentation, and increased concentration time. However, maintaining the long-term effectiveness of these measures depends on proper care and maintenance. Additionally, integrating suitable biological measures alongside mechanical interventions in watersheds plays a crucial role in sustaining the effectiveness of these measures.
Keywords
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