Shirin Mohammahkhan; Hamid Ganjaeian; Laila Garosi; Zahra Zanganetabar
Abstract
Extended Abstract
Introduction
The land subsidence is the descending or collapse of the land under the influence of natural and human factors. The land subsidence is one of the issues that are being exacerbated by human factors, including excessive exploitation of groundwater. Subsidence can affect ...
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Extended Abstract
Introduction
The land subsidence is the descending or collapse of the land under the influence of natural and human factors. The land subsidence is one of the issues that are being exacerbated by human factors, including excessive exploitation of groundwater. Subsidence can affect many constructions and facilities, causing problems for the industry, the environment, etc. This phenomenon is one of the most important environmental hazards that have been less considered than other natural phenomena due to the low human losses. The Qorveh plain is considered as one of the plains which have been introduced as a forbidden plain in the province of Kurdistan in recent years due to the over-exploitation of groundwater. Considering the amount of groundwater level drop and its direct impact on the subsidence level of the region, the present study evaluates the subsidence rate of the Qorveh plain during the period of 2017.12.19 to 2016.01.11. In this research, in order to evaluate the status of the groundwater drop, the statistical data from the Regional Water Organization of Kurdistan province has been used, and the Sentinel-1 images and the SBAS method were used (due to the unique capabilities of this method in terms of dimension, cost, time and accuracy compared to other remote sensing techniques) to estimate the subsidence rate of the region.
Material and Methods
In this research, first, the status of the groundwater of the Qorveh plain and the drop rate of its level has been investigated. Then, the subsidence rate of the area and its relation with the groundwater drop has been investigated. Radar interferometry and SBAS were used to evaluate the subsidence of the study area. Radar interferometry method is one of the most powerful tools for monitoring the subsidence phenomenon. By comparing the phases of two radar images taken from a region at two different times, this method can determine the land surface changes at that time interval. The phase taken from a feature on the land surface is proportional to its distance to the radar sensor. Therefore, making any changes in this distance affects the measured phase. In this research, the Sentinel-1 images (2017.12.19 and 2016.01.11) have been used to perform the radar interferometry.
Discussion and results
The hydrograph of the alluvial aquifer of the Qorveh plain has been provided for the water years of 1966-1676 to 2010-2011. During the 24 yeas, the groundwater level fluctuations in this plain are -13.29 meters, with an annual average of -0.55 meters. The least rate of dropping in the wells is in the wells located south of the Qorveh plain, and the rate increases toward the eastern and northeastern parts. In this research, the subsidence rate of the Qorveh Plain was estimated from 2017.12.19 to 2016.01.11 using the SBAS method. The final map indicates that during this period, the study area subsided between +61 and 216 cm, with the lowest subsidence occurring in the southern areas of the Qorveh plain, which corresponding to the sedimentary heights and slopes of Badr and Parishan and the rate has increased toward the east and west of the Qorveh plain.
Conclusion
The results of this study indicate that Qorveh Plain has witnessed a sharp drop in groundwater level over the recent years. Considering that the southern parts of the Qorveh plain corresponds to the heights and slopes of Badr and Parishan, and the rate of exploiting groundwater in these parts is lower, the rate of subsidence is less. The plain has also subsided further towards theeastern, western and northern parts and the outlet of the Shoor River, due to the growing increase of exploitation. The results indicate that the rate of subsidence is consistent with the rate of groundwater drop so that in the southern part which corresponds to the Badr and Parishan slopes, the rate was less than 10 millimeters during the period of 2017.12.19 to 2016.01.11. The results of the SBAS method indicate that the study area had subsidence of 216 mm during the 2 years and also a 61 mm uplift. Based on the final result, the highest rate of subsidence was related to the eastern and western parts of Qorveh plain and on the outskirts of the city of Dezaj and the villages of Ghasem-Abad, Shokuh-Abad, Avangan, Ganji, and others. A series of the aforementioned factors suggests that the Qorveh plain subsides about 20 centimeters per year. This is due to the over-exploitation of the groundwater. Unlike some areas where the displacement (subsidence and uplift) is due to the tectonic conditions, the results of this study have shown that in the Qorveh plain, the subsidence has a direct relationship to the drop of the groundwater. Therefore, it is necessary to monitor the use of groundwater, especially in the agricultural sector, and the rate of the exploitation should be proportional to the amount of recharge because in addition to the water shortage problems, the continuous use of the groundwater can lead to the irreversible risks of subsidence.
parviz panjehkoobi; Abolfazl Masoudian; Abdolazim Qangherme
Abstract
Extended Abstract Introduction Runoff is considered to be an effective variable in the formation and intensity of floods, and water balance. It is also considered to be a very important parameter in water resources management. Surface runoff is formed due to a combination of different parameters, such ...
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Extended Abstract Introduction Runoff is considered to be an effective variable in the formation and intensity of floods, and water balance. It is also considered to be a very important parameter in water resources management. Surface runoff is formed due to a combination of different parameters, such as severe precipitation, a sloping ground, and saturated soils. It is especially important to predict and determine the amount of runoff produced and transferred to the basin outlet. Generally, different parts of large basins may experience a higher or lower than average precipitation, and thus different spatial distribution of precipitation. Empirical formulas may sometimes give us an inaccurate estimation of the surface runoff volume. Radar and rain gauges are the most common tool used for collecting rainfall data. Together, they can be useful for estimation of rainfall volume and its distribution in a wide area. Integrating high resolution radar based rainfall estimation with hydrological models makes a highly efficient tool for flood prediction. Materials and Data Baghu Basin is considered to be one of Gorgan Gulf sub basins. It covers an area of 24.4 square kilometers. Its perimeter is 23.2 kilometers. The length of its main river is 10 kilometers. The maximum altitude of the main river is 2080 m and its minimum altitude is 80 m. The river channel has an average slope of 20%. Data used in this research includes: 1-data received from east Caspian radar; 2- precipitation and daily evaporation data received from different weather stations around the basin, including Bandar Gaz, Bandar-Torkman, Hashem-Abad and Gorgan stations; 3- discharge value in previous floods of Baghu basin. Geographic coordinates of the basin were obtained using GIS. Geographical coordinates of the basin perimeter were also extracted by radar and the basin area was defined for the radar. Then using the radar software, total amount of precipitation and runoff were measured in the basin. These were used in (1) to calculate runoff coefficient, as a percentage of rainfall: (1) Where C is runoff coefficient, P is precipitation elevation and R is direct runoff. Discussion and Results It is important to consider the effect of climatic and meteorological factors on runoff formation in basins. Severity of precipitation is the first factor. Radar based rainfall estimates indicated that increased rainfall intensity results in increased hourly runoff in the basin. The same phenomenon has been observed in some of previous floods in Baghu basin. In these cases, a sudden increase in precipitation resulted in a severe runoff increase. These floods exhibited long sharp-crested hydrographs. Spatial/temporal distribution of rainfall intensity was the second factor with a significant effect on the amount of runoff produced. Thus, the effect of rainfall distribution was also analyzed. Results indicate that rainfall distribution has affected the amount of runoff produced in different parts of the basin in different ways. Rainfall continuity was the third climatic factor with a significant role in the production of increased runoff. This factor was investigated in winter (cold seasons) floods. Apart from the intensity and volume of precipitation in these floods, precipitation continuity was the most influential factor in the production of a large amount of runoff. This shows the effect of rainfall continuity on runoff increase. Temporal distribution of rainfalls was the fourth factor influencing runoff production, and thus soil moisture. In winter, soil moisture is usually high and there is little evaporation. So soil maintains its moisture and remains wet for a longer time. In this way, a moderate and low amount of rainfall over a short period of time results in soil saturation, and runoff increase. This was investigated in Baghu basin precipitations. According to the findings of this study, increased soil moisture has resulted in runoff increase. Several climatic factors contribute to increased runoff coefficient. In high intensity floods which occur due to large volume of precipitation over a longer period of time, a huge amount of runoff would form. And if as a result of successive precipitation these factors combine with soil moisture, runoff coefficient would be even larger. In cold seasons, three factors - rainfall continuity, soil moisture and poor vegetation- results in increased runoff. However, dry soil and vegetation during warm seasons reduce the effect of intense precipitation on increasing runoff volume. Conclusion Based on the findings of the present study, it is not possible to consider a single constant runoff coefficient for the total area of a basin. Thus, it is better to determine a range of runoff coefficients for each basin. It should also be noted that each flood has its own runoff coefficient, which depends on precipitation severity, temporal/spatial distribution, rainfall duration, intensity variations during precipitation, time intervals between each rainfall occurrence and season rainfall coefficient. Respective severity or weakness of different factors, combination of various factors affecting runoff, and the amount of runoff in similar precipitation may also vary. The present study indicated that due to severe and sudden rainfalls, warm season floods had long sharp-crested hydrographs. In winter, rainfalls were continuous, but with lower intensity. Thus, their hydrograph was wider than warm season floods. In small areas with less than an hour concentration time, the effect of spatial/temporal dispersion of rainfall on the amount of runoff is important. In Baghu basin, 8 to 25 percent variation was observed in runoff coefficient of eight different floods.
Parham Pahlavani; Mahdi Hasanlou
Abstract
Abstract
Nowadays, the combination of data and images obtained from different remote sensing sources is considered as an optimal solution for extracting more information, since these data, with their own wide vision, digital format, their periodically preparation, and high temporal resolution provide ...
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Abstract
Nowadays, the combination of data and images obtained from different remote sensing sources is considered as an optimal solution for extracting more information, since these data, with their own wide vision, digital format, their periodically preparation, and high temporal resolution provide researchers with a variety of information about the land surface. In this regard, the passive optical sensors are widely used in mapping horizontal structures. Given that, radar data can often be collected 24-hours a day and Independent of atmospheric conditions, and also some ground structures and artificial targets have a specific response in the radar frequency, they complete the capabilities of optical images. LiDAR airborne data can also provide sample measurements from vertical structures with very high accuracy. As a result, the simultaneous use of optical, radar and LiDAR data can provide more information in a variety of applications. In this research, by simultaneously applying these three categories of data, we tried to identify the urban specific features in an optimal way. In this regard, by utilizing and producing various descriptors (57 descriptors), and using the feature extraction methods (including PCA and ICA) and estimating the intrinsic dimensions of the data (including SML and NWHFC), an optimal space for the supervised classification was created. After classifying (K-NN method) using the obtained results, descriptors (information layers) produced to identify specific urban features including buildings, roads and vegetation were obtained and grouped according to the classification accuracy. The numerical results indicate the high efficiency of the proposed procedure as well as the applied methods of estimating intrinsic dimension and extracting the features.
