Mahdis Amiri; Hamidreza Pourghasemi; Gholam Abbas Ghanbarian; Sayed Fakhredin Afzali
Abstract
Gully erosion is one of the most important advanced (accelerated) forms of water erosion; so, identification and consideration of effective factors and its zoning is one of the important tools for controlling this phenomenon. The main purpose of the present study is spatial modeling and assessment of ...
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Gully erosion is one of the most important advanced (accelerated) forms of water erosion; so, identification and consideration of effective factors and its zoning is one of the important tools for controlling this phenomenon. The main purpose of the present study is spatial modeling and assessment of gully erosion using a probabilistic Weights-of-evidence (WofE) model and its different scenarios for selecting the location of gullies identified in Maharloo Watershed, Fars Province. For this aim, first, using extensive field observations, points of headcut, end, and also the boundary of the gullies (gully polygons) were identified and the gully inventory map for the study area was prepared. Then, thematic layers such as percent slope, slope aspect, plan curvature, elevation, Topographic Wetness Index, average annual precipitation, NDVI, land use, lithological units, distance from river, distance from road, drainage density, and some soil characteristics (percent silt, percent clay, EC and pH) were identified as effective factors on gully occurrence and their maps were prepared and classified in GIS environment. In the next step, using WofE algorithm, the relationship between effective factors and three different scenarios according to gully locations (head, end and gully polygons) were determined and the weight of each factor's classes was calculated. Ultimately, gully erosion zonation maps were prepared in the ArcGIS software environment. Evaluation of three gully erosion zoning maps using the ROC curve and 30% of unused gullies in the modeling process indicated that the accuracy of the models prepared based on three scenarios are 0.847, 0.861 and 0.792, respectively. Also, results of layer weighting using WofE model indicated that rainfall increasing, high drainage density, high silt percentage, low altitudes, southern directions, low distances from roads and river, Asmari, Aghajari, Razak, Gachsaran, Mishan and Sachun geological formations, as well as bare lands, have played an effective role in the occurrence of gully erosion in the study area. In order to control and prevent this kind of erosion in the Maharlo Watershed, the protective measures and watershed management were performed in the early stages.
Mahdis Amiri; Hamid Reza Pourghasemi
Abstract
The current study aims to investigate the relationship between hydrological and meteorological droughts in the Maharloo Watershed, Fars Province. In order to assess the hydrological drought, Standardized Water-Level Index (SWI) was used, calculated from piezometric groundwater level data from 60 observation ...
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The current study aims to investigate the relationship between hydrological and meteorological droughts in the Maharloo Watershed, Fars Province. In order to assess the hydrological drought, Standardized Water-Level Index (SWI) was used, calculated from piezometric groundwater level data from 60 observation wells within 15 years (2000-2014). The Standardized Precipitation Index (SPI), calculated from the 15 years of rainfall data from 18 stations was used to assess meteorological drought in the study area. Two geostatistical techniques were employed to create drought zonation maps namely Inverse Distance Weighting (IDW) and simple kriging. Correspondingly, three criteria were chosen to evaluate the results including Mean Absolute Error (MAE), Mean Bias Error (MBE), and Root-Mean-Square error (RMSE). Furthermore, the Mann-Kendall test was used to assess the temporal trends of hydrological and meteorological droughts. As a result, trends in hydrological drought were increasing in a significant manner, while meteorological drought trend was decreasing at first and increasing afterwards so that it did not follow any particular trend. With regard to the results of hydrological drought assessment, the driest period has been occurred in 2000 with the SWI value of about 2.25, while 2003 had the highest SWI value equals -2.66 as the most significant wet period. Moreover, the most intense drought and wet periods have been occurred respectively in northwestern and southwestern to central parts of the study area. The results of meteorological drought assessment indicated that the Komehr station has had the most intense wet period in 2000, however; it turned to have the most intense drought periods later on. As regards the evaluation of interpolation techniques, the IDW method with the lowest MAE value of 0.2688 and the lowest RMSE value of 0.0629was chosen as the best interpolation method compared to simple kriging. Also, the drought map obtained from the SPI method with the lowest values of MAE (0.2688) and MBE (-0.000051) found to be the most desirable method to assess the drought behavior in the study area.
