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Estimation of effective rainfall threshold on the start of runoff in arid zone of central Iran (Case study: Sanij watershed-Yazd)
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Mahtab Alimoradi   , Mohammadreza Ekhtesasi * , Arash Malekian , Farshid Jahanbakhsi |
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Abstract: (406 Views) |
Introduction
One of the most important features of any watershed is the threshold of the start of runoff, which can reflect the different characteristics of the watershed and is an important factor in identifying and determining the flood status of the watershed. Accurate estimation of the amount and duration of runoff due to rain events, followed by the starting point of the flood, is one of the main points of interest in hydrological studies of watersheds. The runoff threshold is the amount of effective precipitation that is required during a certain period of time at the level of a certain watershed to start a flood at the outlet of the drainage channel of that level. The purpose of this research is to determine the minimum rainfall, or in other words, the effective rainfall on the start of runoff, in the Sanij watershed in the province of Yazd. By determining the height of the minimum rainfall for the start of runoff in the mentioned basin or other basins, one of the main and effective components in studies related to flooding and flood risk zoning is provided.
Materials and methods
The study area in the current research is the Sanij watershed, 30 km from Yazd city in Taft city, Yazd province, with an area of 153.173 square kilometers and geographic coordinates 31°32°48 to 31°18°42 north latitude and 36°54° north latitude. 53 to ˝54 ˊ03 ° to east longitude. Its annual rainfall is 220 mm, the average annual temperature is 11.2 degrees Celsius and the average relative humidity of the basin is 42%, the maximum height of the basin is 4036 meters and the lowest point is 2020 meters high. The concentration time of the area (Tc) according to the Bransby-Williams method is 5.18 hours. The stations targeted in this research are the Faizabad hydrometric station at the outlet of the Sanij watershed to provide flood discharge data, the Bidakhoud rain gauge station for hourly rainfall data and the Faizabad climatology station to provide 24-hour rainfall data. daily) whose data was available for the period from 1370 to 1400. To achieve the goal of the research, the relationships between maximum 24-hour rainfall and runoff threshold were investigated. Also, the compatibility of the corresponding hydrographs and hyetographs was studied in order to estimate the minimum rainfall for the start of runoff, and the intensity of rainfall was checked in the time base of 1 hour. Then EXCEL software was used to analyze statistics and information.
Results and discussion
The results of investigating the relationship between the runoff threshold and the maximum 24-hour rainfall, whose data was a combination of 24-hour rainfall and torrential rainfall, showed that their function is y=0.9131x+ 14.01 and the minimum amount of precipitation with 82% of R2 is equal to 14.01 mm. It also showed the results in the adaptation section of water patterns and corresponding rain charts; The average height of precipitation for the start of runoff is 18.9 mm. Finally, the average value for the minimum precipitation height in both study methods was 16.45 mm. Also, the intensity of precipitation in the time base of 1 hour was estimated as 13 mm; Therefore, if the intensity of precipitation is more than 16 mm in the time bases above 1 hour, it is expected that runoff will be produced at the outlet of the basin.
Conclusion
The aim of the present research is to determine the threshold of effective precipitation that leads to the flow and start of runoff in a complete basin in the arid regions of central Iran..By knowing the threshold of the start of runoff in watersheds, one of the main components in hydrometric studies and optimal flood management is provided. The results showed that if the duration of rainfall in the basin is more than one hour and its amount is more than 16 mm, the runoff will flow at the outlet of the basin. It is also important to know the threshold of effective precipitation in the beginning of runoff in watershed plans, optimal use and management of precipitation, as well as the design of rain catchment surfaces to absorb precipitation. It should be noted that the results of this research depend to a large extent on the direction of the entry of rain-producing systems as well as its distance from the outlet of the basin, which is suggested to be investigated in future researches. |
Article number: 2 |
| Keywords: Hydrograph, Threshold, Hyetograph, 24-hour rainfall, Runoff. |
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Full-Text [PDF 1341 kb]
(156 Downloads)
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Type of Study: Research |
Subject:
Special
Received: 2023/05/16 | Accepted: 2024/05/6 | Published: 2024/07/30
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