Journal of Spatial Analysis

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Land degradation in arid, semi-arid and sub-humid areas, leads to  desertification and land degradation is a concept that refers to any reduction of soil potentials. In Iran, that 85 percent of its area is classified in arid and semi-arid climates, and  one percent per annum growth rate of desertification and its increasing trends, finding ways to evaluate this phenomenon and its causes in the form of models seems essential. In Iran, especially southern areas due to their arid climatic conditions, are considered to be areas prone to desertification. This study aims to evaluate and analyze the vulnerability of desertification in the Mond watershed located in the northern coast of the Persian Gulf.

     In order to evaluate the potentials of desertification in the Mond watershed, geological, the erosion (water erosion potential), rainfall, slope, elevation levels and land use maps are used.  To identify vegetation cover conditions Landsat ETM + sensor data and normalized vegetation index (NDVI) are used.

     Where in reflected in the near-infrared band (Band 4, Landsat ETM+) and the reflection in the visible band (band 3 sensor ETM+) respectively. Overlaps and combines the above criteria is done using E-VIKOR (VIKOR developed) a method of multi-criteria decision-making models (MCDM). This method is based on a compromise plan proposed in the compromise solution is justified determines solutions that are as close to the ideal solution and has been created through special credit decision-makers. VIKOR use linear approach normal. The normal value in VIKOR  is not related method unit of measure. Also standardization effective indicators of desertification has been done using a linear scale.

      In this study, the ANP method (Analytical Network Process) was used for weighting criteria. Analysis method Network, is one of the popular methods of multi-criteria decision problems. This method complex relationship between and among the elements of the decision by replacing hierarchical network structure considers. Table 1 shows the weights of the effective criteria in desertification. In this study 7 criteria are used that results show criteria’s of climate and vegetation, have the most effective measures in the area of desertification and erosion (water and wind) have the least amount of importance in the region.

Table 1: weight criteria of effectivein desertification

criteria	vegetation	erosion	Precipitation	Landuse	Geology	Slope	Elevation levels
weight(W)	0.21	0.18	0.15	0.14	0.13	0.11	0.08

    After mapping the effective indicators in evaluating desertification separately, Standardization of maps, weighting the index, To obtain amount and   , Finally, the amount of , was produced Zoning map of desertification that in it Mond watershed in the province Bushehr in terms of desertification is divided into five ratio and the area is provided in Table 2.

Table 1: Percentage and  area zone of desertification

amount vulnerabilities	Area (ha)	Area (in percent)
Very low	516300	11
low	598900	13
Average	1438025	30
High	2168675	46
Very High	40825	1

    Studies show that more than half of the Mond basin have on the surface with average risk of desertification and In the continuation of the current trend of soil degradation, desertification prone zones and will be reduced all lead to the deterioration of the natural ecosystems and human life quality.

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Simulation of floodplain zones in Tehran's metropolitan watershed (case study: Kaan basin)
Ezaatollah Ghanavati, Associate prof. Geographical science faculty, Kharzmi University
Ali Ahmmadabadi. Assistance prof. Geographical science faculty, Kharzmi University
Negar Gholami, MA in Geomorphology, Geographical science faculty, Kharzmi University
Extended abstract
Floodplains and adjacent rivers are always at risk from flood events due to their specific circumstances. Flood prone area identification in the watersheds is one of the basic solutions for destructive flood control and mitigation. Flood mapping is one of the best methods for flood prone area planning and identifying. Considering the importance of flood hazard, it is important to understand the role of uncertainty and incorporate that information in flood hazard maps. The hydrodynamic modeling approach is suitable for accounting various uncertainties, and thus lends itself to creating probabilistic floodplain maps. For  this purpose,  flow  boundary  conditions,  peak  instantaneous  discharge with  different  return  periods,  cross  sections and their distance and roughness coefficients for each cross section were entered to HEC-RAS hydraulic model in Kaan watershed  located  in  the Tehran  province,  Iran,  and  this model was  then  run  and  flood water surface profile at different return periods were estimated. In the Kaan Basin, most residential and agricultural lands are located in a very small distance from the river bed. The rapid growth of construction, human activities and land use change in the downstream of the basin have caused a change in the hydrological cycle and runoff production. Floodplain mapping using hydrodynamic models is difficult in data scarce regions. Additionally, using hydrodynamic models to map floodplain over large stream network can be computationally challenging. Some of these limitations of floodplain mapping using hydrodynamic modeling can be overcome by developing computationally efficient statistical methods to identify floodplains in large and ungauged watersheds using publicly.
The aim of this study is to determine flood areas within 20 kilometers of the Kaan River by using the HEC-RAS model and Arc GIS software to identify flood lands in different return periods.
The Kaan basin is located in the central Alborz Mountains. This basin is limited to south, north, east and the west respectively to Tehran, Jajrood Basin, Darakeh Basin and Karaj River Basin. The most important River in the area is the Kaan River and originated from high mountains.
Most commonly, the hydrodynamic modeling approach is used to create flood hazard maps corresponding to a rare high flood magnitude of 100-year return period or higher. Although this approach can provide very accurate floodplain maps, it is computationally demanding. As a result, the modeling approach to flood hazard mapping works well for individual streams, but its efficiency drops significantly when used to map floodplains over a large stream network. In this research, floodplain areas in the Kaan basin in return periods of 2 to 20 years are determined using the HEC-RAS model and the HEC-geoRAS extension. For this purpose, digital maps 1: 25000, DEM (10m), discharge values of Sulaghan Station, morphological characteristics of the river bed and cross sections have been used. Digital Elevation Models (DEMs) play a critical role in flood inundation mapping by providing floodplain topography as input to hydrodynamic models, and then enabling the mapping of the floodplain by using the resulting water surface elevations. Finally, the data is entered into the HEC-RAS software and analyzed. After determining the flood ranges in the various return periods at each cross-section, enter the results to the Arc GIS software and the flood zoning maps were obtained.
In this research roughness coefficients (Maning^,s coefficients) for each cross section were obtain be the
n= (nb+n1+n2+n3+n4) m                                                             (Eq.1)
Geological map and field observations have shown that the main difference between the widths of the valley in the study area is related to the type of rock. The results of the hydrodynamic model show that in the river upstream, the increase in discharge had led to the water level increase and expansion in the floodplain surfaces. But in the middle and low slopes in the downstream of the river, due to the reduced discharge, the river has a larger lateral extension and the flood areas are larger than the upstream of the river. Also, for a longer period of return, the discharge rate and the water level increase and the flood plain was more extensive. The results show that in the downstream of the basin due to instability the bed, existence of wide and eroded chanels, high ability in sedimentation, erosion of the channel bed, and low impact of vegetation, this section They can be restored and regenerated and constantly changing. Due to the location the Tehran-North high way from the Kaan basin, had the construction of roads and structures, the flood plain areas of the river should be fully observed or retrofitted.
 
Key words: Environmental hazards, Flood, Flood areas, Kaan River, HEC-RAS
 
 
 
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Introduction: Assessing the vulnerability and pollution of the aquifer is necessary for the management, development and allocation of land use, quality monitoring, prevention and protection of groundwater pollution. The purpose of this research is to identify and analyze the qualitative vulnerability of the Mashhad plain aquifer in order to monitor and manage underground water resources and prevent its future pollution.
Methodology: Mashhad plain is located in the northeast of Iran between Binaloud and Hezarmasjed mountains and in the watershed of the Kasfroud river, and its area is 2527 square kilometers. In this research, the vulnerability of the Mashhad Plain aquifer was evaluated with DRASTIC and SI models, and ArcGIS was used to analyze the parameters and prepare the vulnerability map. DRASTIC model is one of the overlap and index methods. In this method, the seven measurable parameters for the hydrogeological system include the depth of the groundwater level(D), net recharge(R), aquifer environment(A), soil environment(S), topography(T), Impact of the unsaturated Zone(I) and hydraulic conductivity(C) is used. The ratings for the sub-layers of each criterion vary from one to ten depending on their impact on the vulnerability potential. In SI method, five parameters of groundwater depth(D), net recharge (R), aquifer lithology(A), topography(T) and landuse(LU) are used for aquifer vulnerability. After preparing the SI model layers and weighting each of the layer classes using the functions available in the ArcGIS, the sensitivity index is obtained from the weighted sum of the mentioned parameters.
Conclusion: Study area is divided into four zones with very low vulnerability(21.85%), low(32.09%), medium to low(31.05%) and medium to high vulnerability(14.59%). Also, based on the results of the SI model, the study area is divided into five areas with very low vulnerability(0.4%), low(24.63%), medium to low(23.98%), medium to high(18.71%) and high vulnerability(32.25%). In general, the vulnerability of the aquifer increases from the southeast to the northwest.For verification, statistical method and calculation of correlation coefficient between vulnerability maps and TDS layer was used in TerrSet software and the results showed that both DRASTIC and SI models have high accuracy in zoning the vulnerability of Mashhad plain aquifer, so that the correlation coefficient of vulnerability maps with index The quality of TDS in Drastic model is (0.996) and in SI model (0.995); Therefore, the results of the following research can be used in environmental assessments and analysis of various pollutions and can be used as a basis for management decisions.

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Analysis of the behavior changes of hydrological response units due to Residential development
(Case Study: Cheshmeh Killeh Tonekabon Basin)

Ezatollah Ghanavati ^*[1]
Ali Ahmadabadi^[2]
Amir Saffari^[3]
Masoud Rajaei^[4]


Abstract                                                                                                                                          
Land use and vegetation changes directly lead to changes in the hydrological regime, especially runoff coefficient and maximum instantaneous discharge changes. Much of the land use change has occurred due to residential development, which has led to a decrease in residential and rangeland lands and agricultural lands in the northern regions of the country; This has led to an increased risk of flooding in these areas and downstream urban areas. Cheshmeh Killeh basin as one of the catchments in the north of the country in the last decade has witnessed the occurrence of various floods; Therefore, in this study, by extracting the hydrological response units of Cheshmeh Killeh catchment in order to identify changes in vegetation and land use of these units and the effect of these changes on the hydrological behavior of the basin, the runoff coefficient is one of these behaviors in this period of 29 years (1991-2018). paid. Therefore, in this research, hydrological response units have been identified and extracted as a working unit to determine the runoff production potential of Cheshmeh Killeh catchment. In order to monitor changes in density and vegetation cover using satellite images of the study area in 1991 and 2018, the normalized plant difference index was used; Then, by combining the layers of hydrological groups and land use, the amount of curve number was determined for each of the hydrological response units. According to the values ​​of the obtained curve number for each hydrological response unit, the amount of soil moisture holding capacity was extracted. Finally, by calculating the average monthly values, the amount of runoff from rainfall for 1991 and 2018 was estimated. The results of the study indicate a decrease in the amount and density of vegetation, an increase in the number of curves, a decrease in soil permeability and also an increase in runoff height during a period of 29 years (1991-2018) in Cheshmeh Killeh catchment (especially the northern parts of the catchment); In other words, settlement development, land use change and weakening of vegetation have intensified flooding in the basin; Therefore, it is necessary to carry out watershed management operations upstream to increase permeability.

 Keywords: Hydrologica response unit, Cheshmeh killeh, Runoff, Normalized vegetation difference index, SCS-CN model.
 

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The process of erosion and sedimentation on river banks is often accelerated by natural events and human activities, which lead to natural hazards. This process has also faced serious risks in Jajrud river, urban and rural settlements, agricultural lands, construction structures around the river. The Jajroud River has important importance and effects in securing agricultural water rights, feeding underground aquifers, providing drinking water in the region and the green and natural spaces of Fashm, Migun, Lavasanat and downstream, which has been subject to many changes in recent years due to direct and indirect human interference. including the expansion of urban and rural construction, river engineering operations and wall construction along the river, encroachment on the river boundary and changing the course of the river channels, the use of non-native vegetation on the banks of the river, and as a result, the eco-hydro geomorphological conditions of the river have become unstable. The phenomenon of erosion and sedimentation in Jajroud river has brought negative consequences such as changing the bed, accumulation and settling of large amounts of sediment and overflowing of canal water and as a result the risk of flooding.
 

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In order to plan, manage and exploit water and land resources, awareness of the spatial variability of resources, as well as understanding the response behavior of the watershed in order to model physical processes, has an identical significant role. Due to its location in arid and semi-arid areas, special climatic and geomorphological conditions, Qom-Roud basin is prone to flash floods. Due to the lack of hydrometric and topographical data with high accuracy in the basin, the use of hydraulic models does not lead to accurate results of the hydraulic characteristics of floods. In such a situation, the methods based on the geomorphological features of the basin can be advantageous. In this article, Variable flood stage method (VFS) method is used, which combines the hydraulic characteristics of the river with the geomorphic characteristics of the basin in order to estimate the water depth in the river caused by floods with different return periods. The water depth was investigated for different return periods of two, five, ten, twenty-five, fifty and hundred years. In each period, the highest water depth was in the parts near the outlet and the lowest water depth was in the upstream parts of the river. The research illustrations there is a direct relationship between the depth of water and the area of the sub-basin. The results of this research can be used for basins without hydrometric and topographic statistics with high accuracy in order to estimate the peak speed and flood depth.