Document Type : Research Paper
Authors
1 Assistant Professor, Department of Range and Watershed Management, Faculty of Natural Resources and Environment, Ferdowsi University of Mashhad, Mashhad, Iran
2 Graduated Ph.D. in Watershed Science and Engineering, Department of Reclamation of Arid and Mountainous Regions, Faculty of Natural Resources, University of Tehran, Iran
3 Graduated Master's degree in Watershed Management, Department of Reclamation of Arid and Mountainous Regions, Faculty of Natural Resources, University of Tehran, Iran
Abstract
Introduction
In recent decades, the increasing trend of natural hazards and the destruction of natural resources under the influence of natural and human factors have become increasingly intense. One of the important methods in controlling and reducing surface runoff to mitigate flooding and peak discharge is the implementation of watershed management measures, including management and protection measures, biological and mechanical interventions. Although valuable watershed measures have been implemented in the country in recent years, unfortunately, the scientific documentation and studies regarding their performance, weaknesses, strengths and effectiveness are very little. By studying and evaluation the watershed management measures effects on the important factors of a watershed, such as discharge and water flow, we can take steps to strengthen the strengths and reduce the weaknesses. Therefore, the present study aims to evaluate the performance and effects of biological and mechanical watershed management measures on the peak discharge of treatment and control watersheds in Zidasht Taleghan, Alborz province.
Materials and methods
The paired Zidasht Taleghan watershed, comprising a treatment watershed (104 hectares) and a control watershed (92 hectares), is located inside within a representative watershed with an area of 2750 hectares. In the treatment watershed, along with the protection of the entire area, banqueting along with seeding has been implemented on the area of about 12.5 hectares. In the mechanical measures section, 943 and 72.5 m2 of gabion structure and dry stone structure were implemented in the treatment watershed, respectively. The total reservoir created by the gabion and dry stone structures was 13,550 and 125 m2, respectively. In this research, to consider the importance of vegetation cover effect on runoff and peak discharge through curve number in modeling, study and field measurement of vegetation cover changes during the last 5 years (2018 to 2019) in two treatment and control watersheds are presented. In order to investigate the impact of watershed management measures on the peak flow of the control and treatment watersheds, meteorological and discharge data were used from the meteorological station and outlet flumes of the paired watersheds. In addition to comparing the observational data of the peak flow at the outlet of both control and treatment watersheds, rainfall-runoff modeling with the HEC-HMS model was used.
Results and discussion
The evaluation of changes in vegetation under the effects of watershed measures showed that the percentage of vegetation and plant production is about 8% and 265 kg on average in the treatment watershed (on average, 51% vegetation and 777 kg/hectare production) more than the control watershed (on average, 43% vegetation percentage and 512 kg/hectare production). In the discussion of reducing the peak discharge of the treatment and control watersheds, the results of the evaluation of observational data showed that the peak discharge of the treatment watershed under the effects of watershed management measures was 65% lower than that of the control area (without the implementation of watershed management measures). The results of flood modeling showed that in the treatment watershed, the peak flow has decreased about 40% with the implementation of biological measures and 66% with the implementation of biological and mechanical measures compared to the control watershed. The flood volume has also decreased by 30% on average under the effects of biological and mechanical watershed management measures in the treatment watershed compared to the control watershed.
Conclusion
As a result of the implementation of biological and mechanical measures, in addition to reducing the peak flow, the time to peak flow in the treatment area has also increased (discussion of increasing concentration time). And the peak flow occurred with a longer time delay than the hydrograph of the flood in the case of no watershed management measures in the control watershed. As a result, it can be reported that under the influence of watershed management measures, in addition to reducing flood damage by reducing the peak discharge, with a delay in the time of runoff and flood, more water is infiltrated and stored in the area. The highest amount of peak discharge in these areas occurred in the state without implementation of watershed measures (without structures). Also, considering that the base flow in the treatment watershed was higher than the control watershed in most of the year (on the contrary to the peak flood discharge), the richness of the vegetation cover in the treatment watershed can be considered an important factor in the higher base water flow.
Keywords
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