نشریه خشک بوم
سال یکم شماره 1 (پاییز 1389)

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 basic 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 maximum flood discharge. They are usually based on one or more factors such as drainage area that causes 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 sensitivity of their parameters seems to be necessary. In this research, a new simple and efficient method is used to carry on sensitivity analysis of 10 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 in small watersheds cause high variation in model output (peak discharge). Also in most of the equations, the role of area is decreased in comparison with C coefficient in large watersheds. It means that while 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 lower range return periods.

The main objective of the study is application of spatial statistics as a tool for model-based prediction of vegetation types. Method of selecting Samples was systematic-randomized. Quadrate size was determined for each vegetation type using the minimal area method; hence suitable quadrate size for different species ranged from 1 2m to 10 10m (i. e., 2-100 m2). Within each unit, 3-5 parallel transects with 300 to 500 m long, each containing 30-50 quadrates (according to the vegetation variations) were established. Soil samples were taken at soil depth of 0-30 and 30-80 cm at the starting and ending points of each transect. Measured soil properties include gravel, texture, available soil moisture, saturation moisture, organic matter, lime, gypsum, pH, electrical conductivity and soluble ions (such as Na+, K+, Mg2+, Ca2+, Cl-,, and). Logistic Regression (LR) technique was applied for predictive modeling of Cornulaca monachantha. To map soil characteristics, spatial statistical methods of point-Kriging, Normal Distance Weighting and Inverse Distance Weighting were used to predict soil factors using GS+ and ArcGIS softwares. Finally, cross validation technique were used to compare the above mentioned methods by considering the statistical parameters of MAE and MBE. It can be concluded that the point Kriging method is the best method among the others in all of the factors. Results show that the point Kriging method by MAE of 1.56 and MBE of -0.048 in gypsum, and gravel factor by MAE of 0.176 and MBE of 0.006 (0-30 cm depth) is better than the others and the sampling method is effective in accuracy of geostatistical method. Predictive map of C. monachantha which has narrow amplitude, with Kappa coefficient of 0.98, has high accuracy in 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 component 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 water resources management. At present, there are various methods for calculating the reference evapotranspiration. According to some researches, FAO-Penman-Monteith method is the most accurate method for the estimating of both dry and wet weather conditions after lysimeter weight method. In this study, the amount of reference evapotranspiration was calculated using FAO-Penman-Monteith method in 29 selected synoptic and climatology stations in Yazd. Then, they were classified in two ways: Firstly, through an establishment of a relationship between evapotranspiration parameters and height, and secondly, through Inverse Distance Weighting (IDW). Finally, variations of reference evapotranspiration in different land cover throughout the province were analyzed. Method Reference evapotranspiration maps show that the amount of evapotranspiration is higher in central, southern and some western areas of the province than in northern and eastern areas.

Recognition of origin of sand dunes is very important in wind erosion control projects. Due to the difficulties in application of traditional methods in recognizing and determining the share of sediment sources in sediment yield, fingerprint method, sediment tracery, or in other wards, source identification are alternative and suitable methods which are considered by some researches. In this method, by analysis of physical and chemical characteristics of sediments, rocks and soils in different places, source areas of sediment yield are determined. In this study, sediment tracery by geochemical elements, source areas and the shares of these sources in eolian sediment yield in one of the most important eolian centers of Sistan plain were identified. First, granulometry and mineralogical studies were performed on eolian sediments of Sistan province. Then, step-wise source identification method was performed on Niatak eolian sediments. Using determination analysis and composite multivariate methods and also selecting suitable composition of geochemical elements, organic carbon, phosphorous and nitrogen which can differentiate lithological, land use and geomorphological units in Niatak, importance and share of sediment sources were determined. Results indicate that the transport distances are between 20 to 50 Km and the most important sources were sediments of Hamon lake (92%) and bare land (87%). 87% of the particles originates from NQts unit (upper Miocene – Pliocene fine – grained alluvial sediments of Hamon lake), which has the highest share and QK unit (the youngest lucastrine sediments of Hamon) has 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 recognition 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 of rangelands of Sorkhdeh Damghan in Semnan province. Systemathic-randomised taking sample was selected in each homogenous unite of vegetation for both standing vegetation and soil. Cover percentage for vegetation is recorded and soil properties are measured in laboratory. Results of cluster analysis show that there are five halophyte communities. Analysis of variance indicates that all five communities are significantly different according to the soil properties. We also found that species richness and diversity were significantly greater in Hypocylix kerneri-Salsola dendroides than others. Multivariate analysis shows that soil significantly influences the species distribution and any changes causes in soil properties may transfer the vegetation community to others. EC, K, Caco3 and soil texture are the most dominant factors forming vegetation distribution.

Estimation of time of concentration has considerable role in physiographic and hydrologic studies of watersheds. Especially, it affects on estimation of peak discharge in hydrological studies. However, there are many various equations for computating of time of concentration, which have not been analyzed by sensitivity analysis. So, in this study, beside of introducing of new straightforward method for sensitivity analysis of simple equations, four common applicable equation of time of concentration in Iran (e.g. Kirpich, California, Bransly Williams and SCS) have been analysed by sensitivity analysis. Results show that very low amount of changes in the slope, especially in low slope reaches, have considerable effects on time of concentration. While, increase in slope of stream, the effects of stream length or curve number (CN) parameters on time of concentration increases. In the other hand, the effect of circularity coefficient on time of concentration is not so considerable. Generally, results show that the measuring or estimating 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.