Journal of Arid Biome
Year:2010 | Volume:1 | Issue:1|Papers Count:7

One of the most important tasks in catchment hydrological analysis is flood and flooding, and therefore estimation of river peak discharges is necessary. Peak discharge estimation as design flood is the base and necessary element of water related projects and designs. In ungaged catchments where no enough measured data is available, empirical approaches are usually applied to estimate the maximum flood discharge. They are usually based on one or more factors such as drainage area that cause flood, and most of these methods have been proposed for a certain area with specific physical and climatic conditions. To use these methods in other areas with different conditions, evaluation and analysis of the sensitivity of their parameters seems to be necessary. In this research a simple new and efficient method has been used to carry on sensitivity analysis of ten empirical flood estimation methods including Creager, Diken, Fuller, Fanning, Inglis, Coutange, Mayer, Horton, USGS and German, in which some of them are the most famous existing methods. The results show high sensitivity of all equations to area in its lower ranges. In other word, small changes in catchment area for small watersheds cause large variation in model output (peak discharge). Also in most of the equations, the role of area is decreased in comparison to the C coefficient in large watersheds. It means that as the area of catchment increases, its role on peak discharge decreases. In some equations such as Fuller, the output is also very sensitive to return period especially in the range lower return periods.

The main objective of this study was application of spatial statistics as a tool for model based prediction of vegetation types.Sampling method was randomized-systematic. Quadrate size was determined for each vegetation type using the minimal area; hence suitable quadrate size for different species was determined 1*2m–10-10m (2-100 m2). Within each unit 3-5 parallel transects with 300-500 length, each containing 30-50 quadrates (according to vegetation variations) were established. Soil samples were taken from 0-30 and 30-80 cm in starting and ending points of each transect. Measured soil properties included gravel, texture, available moisture, saturation moisture, organic matter, lime, gypsum, pH, electrical conductivity and soluble ions (Na+, K+, Mg2+, Ca2+, Cl-, CO2-3, HCO-3 and So2-4). Logistic Regression (LR) techniques were implemented for predictive modeling of Cornulaca monachantha. To mapping soil characteristics, spatial statistical methods of point-Kriging, Normal Distance Weighting and Inverse Distance Weighting were used to predict soil factors by using GS+ and ArcGIS softwares. Finally, cross validation technique were used for comparing the above mentioned methods by considering the statistical parameters of MAE and MBE. It can be concluded from the results that the point Kriging method is the best method among the others in all of the factors. Results shows that the point Kriging method by MAE 1.56 and MBE -0.048 in gypsum, and gravel factor by MAE 0.176 and MBE 0.006 (0-30 cm depth) is better than the others and sampling method is effective in accuracy of geostatistical method. Predictive map of C. monachanthawhich has narrow amplitude, with 98% Kappa coefficient, has high accordance with the actual vegetation map prepared for the study area.

Iran is a part of the world’s arid and semi-arid areas and encounters severe lack of water resources. Evapotranspiration is a major components of the hydrological cycle and its precise determination has a high importance in the studies of hydrological balance measurement, design and management of irrigation systems, product yield simulation and design and management of water resources. At present, there are various methods for calculating the reference evapotranspiration. As previous researches have shown that, after Lysimeter weight method, FAO-Penman-Monteith method is the most accurate one for the estimation of both dry and wet weather conditions. In this study, the amount of reference evapotranspiration was calculated, using FAO-Penman-Monteith method, in 29 selected synoptic and climatology stations of Yazd. Then, they were classified in two ways: firstly, through an establishment of the relationship between evapotranspiration parameters and the height, and secondly, through inverse distance weighting method or IDW. Finally, the variations in different land levels throughout the province were analyzed. Maps of reference evapotranspiration showed that the degree of evapotranspiration is higher in central, southern and some western areas of the province than in the northern and eastern areas.

Recognition of source areas of sand dunes is very important in wind erosion control projects. Due to the difficultes in application of traditional methods in recognition and determination of the share of sediment sources in sediment production, fingerprinting methods, sediment tracery or in other wards, source identification are alternative and suitable methods which are considered by different researches. In this method, by investigation of physical and chemical characteristics of sediments, rocks and soils of different sources, the source areas of sediment are determined.In this research, sediment tracery by geochemical elements, source areas and the shares of these sources in eolian sediment production in one of the most important eolian critical centers of sistan plain were identified. First, granolumetric and mineralogical studies were performed on eolian sediments of sistan province. then, step-wise source identification method was performed on Niatak eolian sediments. Then. by using determination analysis method and suitable composition of geochemical elements, Organic carbon, Phosphorous and Nitrogen which can differentiate lithological, land use and geomorphological units in Niatak critical center and by using composite multivariate methods, the importantance and share of sediment sources were determined. The results indicated that transport distances have been between 20-50 kilometers and the most important sources were sediments of Hamon lake and then barren lands that 92% of particles have originate from Hamon lake and River bed and 69% of particles from barren lands.87% of particles have originate from NQts unit (upper Miocene– Pliocene fine – grained alluvial sediments of Hamon lake), having the highest share and QK unit (the youngest lucastrine sediments of Hamon) having the lowest share.

Saline soils are common in different ecological sites of Iranian rangelands. Vegetation distributions in saline soils are correlated with soil properties, so knowledge of vegetation changes with soil characteristics is necessary for management and restoration of saline rangelands. The aim of this study is to identify main halophyte communities and their relationship with soil properties rangelands of Sorkhdeh Damghan in Semnan province. Systemathic-randomised sampling was done in each homogenous unite of vegetation for both standing vegetation and soil. We recorded cover percentage for vegetation and measured the soil properties in laboratory. Results of cluster analysis showed that there are five halophyte communities. Analysis of variance indicated that all five communities are significantly different according to soil properties. We also found that species richness and diversity were significantly greater in Hypocylix kerneri-Salsola dendroides than others. Multivariate analysis showed that soil significantly influenced the species distribution and it is possible that with any changes in soil properties the vegetation community may transfer to others. EC, K, Caco3 and texture were the most dominant factors shaping vegetation distribution.

Estimation of time of concentration have important and considerable role in physiographic and hydrologic studies of watersheds. Especially it affects on estimation of peak discharge in hydrological studies of watersheds. However there are many various equations for computation of time of concentration, they have not been analyzed by sensitivity analysis. So, in this study, beside of introduction of new straightforward method for sensitivity analysis of simple equations, four common applicable time of concentration in Iran, e.g. kirpich, California, Bransly Williams and SCS, have been surveyed by sensitivity analysis. Results show that the very low changes in the slope amounts, especially in low slope reaches, have considerable effect on time of concentration. While, with increasing in the slope of stream, the effect of stream length or CN (curve number) parameters is increased on the output. In the other hand, the effect of circularity coefficient on time of concentration is not so considerable. Generally the results show that the measuring or estimation of stream slope, length and curve number need to more attention and correction.

Playa lakes are an important source for aeolian and dust storm sediments, because of their location in low land, arid and desert regions with strong wind systems and existence of fine and unconsolidated sediments. Jazmourian playa (Hamun Jazmourian) is an ephemeral lake with a large catchment has located in the Southeast of Iran. During the last 10 years, the playa was dried because of drought. In this study, 26 surface sediment samples were taken for sedimentology and sedimentary geochemistry analysis. Sieve for the samples, laser, calcimetry, mineralogy, morphoscopy, morphometry and chemical analyses have been done. Results show that the sediments with the size of silt and clay are dominated which are potentially suitably for wide distance and long time transportation. The most important minerals are calcite, quartz, feldspar and halite. Distributions of minerals in playa have a regular pattern. Montmorilonite, chlorite and Illite are the major clay minerals whereas Kaolinite is the minor one which is autogenic. Sedimentary geochemistry results show there are two main debris sources for the elements including igneous, ophiyolite omelange, and evaporate sediments. Elements Ca, Sr and Na mostly precipitate by chemical process in the playa. Because of morphology, climatology and sedimentology conditions, the Jazmuriyan playa is an important source of aeolian sediments and dust storm in the southeast of Iran and southearn Asia.