Morad Darabi; Hossein Malekinezhad; Ali talebi; masoumeh hidari
Abstract
1-Introduction Floods have historically been the most common, deadliest and most expensive hazards among natural hazards. The risk of flooding has increased over time, especially since countries have allowed changes in the land uses and land coves in floodplains and plains. In Iran, like the other ...
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1-Introduction Floods have historically been the most common, deadliest and most expensive hazards among natural hazards. The risk of flooding has increased over time, especially since countries have allowed changes in the land uses and land coves in floodplains and plains. In Iran, like the other flood-prone areas of the world, the severity of floods and the extent of their damages have increased dramatically in recent decades. Land use and vegetation play an important role in the production of runoff due to its effect on infiltration, erosion, evapotranspiration and transpiration. 2-Methodology Khorrambid watershed having an area of 88.7 km is a part of the Sivand Dam watershed. The average rainfall of this basin is 228 mm and it has a semi-arid climate in the view of Domarten. Khorrambid metropolitan basin consists of 12 smaller sub-basins in the study area with three main waterways named A, B and C that cross the city upstream of Khorrambid and pass through the city. In this study, the design, purpose, and efficiency amount of the flood and runoff output amount have been evaluated and finalized from the hydrographic network. The set of Management, Biological and Structural works carried out in the Khorrambid urban basin of the Sivand Dam Branches include: management excavation, piling, seeding, Dry working forage, Dry Stone Structures, rock and PVC mesh, rock and earth dams. Detailed studies and implementation of Khorrambid urban watershed was carried out in 1999 and the implementation of watershed management projects started in 2002 and by the end of 2010 about 33% of the projects were implemented in the study phase. At the same time, the evaluation process regarding the effect of these projects on flood and runoff control took place. This study aimed to evaluate the performance of projects (management, biological and structural) on the runoff and water resources in Khorrambid watershed in Fars province. In this study, first, the height of the dams, the length of the reservoir and the slope of the canals were measured under the basins where structural projects were carried out to determine the route of the new water movement. Then the new concentration time was calculated using the Branse-Williams method. In the next step, soil cover layer data such as the percentage of canopy cover, hydrological groups and vegetation status were obtained to determine the number of curves and maximum holding and infiltration potential in the soil. Then using SCS method and Hyfa software, modeling the flood volume and outflow runoff for sub-basin were estimated. 3- Results and Discussion By analyzing the results of statistical analysis of changes it can be said that there were many changes in all land use and land cover as well as the implementation of structural and biomechanical projects in the studied area. To investigate the effect of land use and structural changes on the hydrological regime of the studied basin, SCS method was utilized. This model was formulated using GIS techniques. The results showed that due to the increase in rangeland land use (from poor to good condition) and the construction of watershed structures, flooding in the area has decreased in case there were 24-hour rainfall. This amount of runoff reduction in the basin A and C was 41% and 72%, respectively. 4- Conclusions It is suggested that by evaluating the projects, if the performance of these projects could be evaluated in appropriate ways and from various technical and engineering aspects, the results would lead to finding the causes of the proposed operation failure and presenting appropriate solutions to address them. On the one hand, this could improve the quality of implementation of watershed management activities, on the other hand, it would increase operational efficiency, and the learnt lessons would enhance future plans. On the other hand, it is recommended that since watersheds are in fact considered as a natural-human system as well as a planning and work unit, comprehensive management of these watersheds is essential for achieving sustainable development goals. Watershed management is a complex process whose practical goals should be in line with the promotion of stakeholders` interests and stakeholders` engagement at all levels of planning and decision making. Integrated Watershed Management requires a flexible process that taking into account the challenges and constraints of the Watershed System, makes good use of its opportunities and potential conditions to ensure the social and economic well-being of its stakeholders while maintaining the security of water, food and environment in order to meet its goals of sustainable development.
Morad Darabi; Hossin gharehdaghy; Masod Nejabat
Volume 5, Issue 14 , June 2018, , Pages 199-218
Abstract
IntroductionMan's undue interference, livestock overgrazing, soil texture disorganization, and change in the geometry of channels are the main factors which could destroy the hydrologic balance of the watershed in an ecosystem. The systematic imbalance in a watershed could destroy the earth crust and ...
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IntroductionMan's undue interference, livestock overgrazing, soil texture disorganization, and change in the geometry of channels are the main factors which could destroy the hydrologic balance of the watershed in an ecosystem. The systematic imbalance in a watershed could destroy the earth crust and increase flooding. It could also result in the erosion and soil sedimentation behind the reservoir dams and the destruction of the agricultural lands, roads, and villages. In addition, it could reduce the production ability of productive sources. Soil erosion is one of the environmental problems that threatens natural resources, agriculture, and the environment. The objective of the present study was to evaluate the biological, managerial, and constructional watershed projects and their effects on reducing erosion, sedimentation, and parameters of land protective cover. This study was conducted between 2001-2010 in the Khorrambid urban watershed from the Sivand dam in Fars province.Methodology A. Primary Collection MethodThe preliminary data for Khorambid urban watershed from Sivand dam was collected by the executive detailed reports (Natural Resources and Watershed Management Office of Fars Province, 2001).B. Estimating the parameters of land cover layer, erosion, and sedimentation before implementing the watershed projectsBefore implementing the watershed projects, the vegetation parameters, erosion, and sediment yields in the executive and detailed reports were used to evaluate the parameters.C. Estimating the parameters of land cover layer, erosion, and sedimentation after implementing the watershed projectsIn the first step, the vegetation classification mapping was prepared and the vegetation parameters were sampled in the paired plots. It must be mentioned that one of the most effective items in estimating the erosion and sedimentation is to know the land cover parameters. To determine the rates of erosion and sediment exited from the network, it was required to calculate the rate of erosion and sediment on the domain. It was also required to calculate the controlled sediments on the waterway or at the rear of structures. In the first step, the locations of all structures executed in the intended sub-basins were specified by GPS to determine the sediments trapped at the rear of the structures. Meanwhile, their types, structural materials, and location maps were prepared. In the second step, the waterway slope, overflow height, reservoir length, waterway width, reservoir volume, and sediment volume were respectively determined by preparing some special forms via clinometer and meter. In addition, to estimate the erosion and the sedimentation of the domain, the experimental model of MPSIAC, modified by ArcGIS10, was used. When the nine layers of the MPSIAC model were combined and overlapped, the homogeneous units map was prepared. Next, the scores of nine factors were estimated and calculated to extract the sedimentation degree of each homogeneous unit according to the following equation:Qs = /253 e0.036R (Equ.1)When the sedimentation map was prepared, the erosion rate was calculated by the Sedimentation Delivery Rate (SDR) equation in the level of homogeneous unit. Regarding the factor of the basin area ( based on square mile), the following equation was used to determine the percentage of SDR.Log SDR = 1.8768 – 0.14191 log(10A) (Equ.2)To evaluate the differences between sedimentation changes in the sub-basins for the pre and post watershed operations, the normality test and Paired T-test in SPSS software were used.DiscussionThe results indicated that the factors’ score of river erosion and surface erosion which were respectively 30.77 % and 30.51% had the most effects and the land cover factor, with 15.05%, had the least effect on reducing the sedimentations to 21.97%. Also, the area of sediment class of 75-100 was 1375 hectares, which was equivalent to 15.78% of the basin's area. Indeed, in terms of the spatial distribution, it was located in the basin outlet and changed to class 50-75. The sediment class of 50-75 was 7339 hectares, equivalent to 84.22% of the basin's area. It reduced to 28.09 % and changed to the lower class of 25-50. Since there was a significant change in the sedimentation of the sub-basins in 0.05 levels, the results of this study indicated that the watershed projects were efficient in reducing the sediments. To manage the water and soil resources, to raise the effectiveness of watershed operations in reducing erosion and sediments, and to raise the land cover layer in Khorrambid watershed, the combination of both biological and constructional programs and treatments undertaken in the basin should be applied.ConclusionWith regard to the findings of this study, before the watershed operation, the sedimentation degrees in two classes of 75-100 and 50-75 were respectively 15.78% and 84.22%. According to the sedimentation class map, the sedimentation degree of 75-100 was located in the basin outlet. Since the structural watershed operation has been extended more than biological watershed operation, the sediment class with the area of 1375 hectares experienced lower sediment degree and changed to 50-75 class after the watershed operation. The sediment class of 50-75 was 7339 hectares before the watershed operation; however, by implementing biological programs, 2447 hectares of that class changed to the lower class of 25-50. Therefore, 15.78% of class 75-100 before the watershed operation reduced to 0% after the watershed operation. In addition, 84.22% of class 50-75 was reduced to 71.91%. Regarding the equation of SDR based on the area factor, the rate of SDR for the basin was 33.03%. Thus, the sediment rates for pre and post watershed operations were respectively calculated as 23755 and 14390 tons, which indicated 39.42 % drops in the total sediments. The results of this study showed that the watershed operation, which was a combination of protective, managerial, and biological programs, was implemented well in the measures of domain and waterway (structural) in the basin. Consequently, the sedimentation mean in Khorambid watershed decreased to 39.42%. The findings of this study are in line with the findings of researchers such as Roghani (2012), Salmanpour (2013), Azami Rad (2013), and Agharazi (2016).
