عنوان مقاله [English]
Changes in climatic variables affect the hydrology of basins. Evaluating the trend of seasonal changes in runoff is important in the water management of watersheds, especially when drought and flood hazards occur. This research studied the seasonal changes of Runuff under hydrological characteristics in Gharaghom Catchment located in northeastern Iran.
The Gharaghom Catchment is the sixth watershed of the country with 14 dub basins and is located in the northeastern part of Iran with an area of about 43925 square kilometers. The study area is located at latitudes between 36° 07΄ and 37° 41΄ North, and longitudes between 48° 51΄ and 61° 13΄ East on the border of Afghanistan.
In this research, the hydrological status of the Gharaghum basin was investigated by estimating the runoff in its 14 sub-basins using the SCS-CN experimental model of the American Soil Conservation Organization. The maximum runoff flow was estimated using digital model data at a height of 30 meters, precipitation and temperature data of climatic stations, and network data of temperature and precipitation.
Results and Discussion
The assessment of physiographic indicators of the basin showed that in some sub-basins the ability to produce runoff was high and the analysis of the model results in runoff production showed that the spring season with 117 mm of rainfall in the sub-basin of Keshaf Rood with the largest area compared to other sub-basins can produce peak flow. It has up to 2379.3 cubic meters per second, and in general 88% of all spring rains turn into the runoff. The state of the soil hydrological group and permeability, vegetation cover, rainfall, and catchment area create different conditions for the potential of runoff production in different seasons. The summer season, with the lowest average rainfall of 6 mm can produce less runoff than other seasons due to the effects of the basin area. In the autumn season, due to the less vegetation and the increase in the amount of precipitation to 28.9 mm, the soil hydrological group had a greater effect on the runoff production than in other seasons, and as a result, 63% of the autumn precipitation was converted into the runoff. In the winter season, the average rainfall reached 71 mm, and 82% of the rainfall turned into the runoff. Of course, solid precipitations occur in the winter season and their melting at the end increases the ability to produce runoff in the winter.
The evaluation of the physiographic indicators of the basin showed that in some sub-basins the ability to produce runoff is high and the spring season with 117 mm of rain in the sub-basin of Keshafrood with the largest area compared to other sub-basins can produce a peak discharge of up to 2379.3 cubic meters per second, and in general 88% of all spring rains turn into the runoff. In the autumn season, due to the less vegetation and the increase in the amount of precipitation to 28.9 mm, the soil hydrological group had a greater effect on the runoff production than in other seasons, and as a result, 63% of the autumn precipitation was converted into the runoff. In the winter season, the average rainfall reached 71 mm, and 82% of the rainfall turned into runoff. In general, hydrological group C with low soil permeability and a high amount of CN causes significant runoff production potential in the spring season in this watershed and the management of surface water resources is essential.
The lowest rainfall is for the summer season with 6 mm, of which 17% becomes runoff. Vegetation has reached its peak growth in this season and even with the effects of the soil hydrological group, the potential of runoff production is at the lowest possible level.
In autumn, the amount of precipitation increases to 28.9 mm, and also the vegetation is less than in summer. The result of these changes is an increase in the peak discharge so that 63% of this season's rainfall turns into the runoff. Due to vegetation reduction in autumn, the effects of hydrological groups become more visible and increase the potential of runoff production in the sub-basins. The highest peak flow rate in the Kashf Rood sub-basin is estimated to be 396.6 cubic meters per second in the autumn season, and the lowest peak flow rate is estimated to be 26 cubic meters per second in the Sheikh Canal sub-basin. The winter cold turns precipitation into the snow, the vegetation is very weak and the effect of soil hydrological groups is more visible than in other seasons, the average seasonal precipitation reaches 71.7 mm. This causes the peak discharge to increase and the limiting factor of runoff production is precipitation in solid form. In the Gharaghom catchment area, snowmelt occurs at the end of the winter season, and due to the effect of other mentioned factors, 82% of the precipitation is converted into runoff and increasing the ability to produce runoff in the winter season. Therefore, based on the seasonal difference of runoff in the Gharaghom catchment and the significant amount of the peak discharge, the need to manage the flood risk in this basin seems necessary. Protecting the areas of the sub-basin, taking into account the existing hydrological situation, can prevent the wastage of surface runoff, and manage the runoff, It can lead to an increase in artificial nutrition with the penetration of runoff into the ground.