نشریه پژوهش های آبخیزداری
پیاپی 95 (تابستان 1391)

Optimal use of water and soil resources has always been the aim in agricultural development in order to achieve maximum productivity by using of minimum land and water resource consumption. Nowadays، remote-sensing technology represents a powerful tool for researchers and policy makers. In particular، the availability of an ever increasing number of remote sensing satellites makes it possible to consider new advanced applications of remote sensing، ranging from monitoring and management of natural resources، mapping of land-cover/land-use (e. g.، monitoring of agricultural areas، etc.) to economical investigation of production. In this study Landsat (TM7) and panchromatic band of IRS-1C data were used for extraction of rice planted area of Some-Sara district، Iran and its villages using RGB-HIS fusion method and NDVI deference’s employed in this research. Evaluation was performed by field observation and by analyzing the classification results using a maximum likelihood classifier for both fused image resulted from fusion method and NDVI deference’s images. The accuracy of these methods were compared. The results was shown that the NDVI deference’s of two landsat images acquired with 45 days interval، yields higher accuracies (Overall accuracy=92. 4%، Kappa =0. 83%) than the fusion method using RGB-HIS transformation (Overall accuracy= 87. 47%، kappa=72. 76%) method. Meanwhile، total estimated rice planted area is about 26675. 30 ha which is corresponded to the area reported by agricultural organization of Gilan province.

Determination of flow resistance is an essential parameter for flow hydraulic computation in open channel. Flow resistance in open channels with coarse materials on bed is mostly due to grain roughness. Over the past decades many studies have been conducted to estimate the flow resistance coefficient to the particle size but the effects of particle shapes are not clear so far. In this experimental research for determination of flow resistance coefficient eight types of particles; four naturally nearly rounded and four angular particles have been tested under different hydraulic conditions in a flume of 10 meter long، 25 cm wide and 50 cm height and constant bed slope of 0. 0005. By applying experimental data، the manning roughness coefficient has been calculated and equationes for prediction of roughness coefficient have been proposed. The results showed that parameters such as relative submergence (R/Ks)، Froude number (Fr)، energy grade line (Sf) and flow hydraulic radius (R) have significant effects for precise estimation of flow resistance coefficient.

Greenhouse gases (GHG) is a serious threat to humans and the environment. Greenhouse gases have different sources، but main factors are fossil fuels، industrial processes، deforestation and agriculture. Carbon sequestration is capture atmospheric carbon dioxide by plants and other life forms in planet. The aids of this study are estimation amount of carbon sequestration by Atriplex canescens، determination of the economic value of carbon sequestration and determination of soil and plant carbon sequestration contribution. In order to measure organic carbon in soil and plant respectively Walki Black and combustion methods were used. The results showed that 41. 626 kg of carbon per hectare is sequestrated، which about 36. 204 kg and 5. 422 kg of carbon in soil and Atriplex canescens respectively. Role of soil in carbon sequestration is 87 %. So we can conclude that the soil in ranglands is considered as، most organic carbon reservoir.

Today، flood is considered as one of the destructive factors which devastates human communities adversely and remains bad effect on human life. Therefore establishment of appropriate structures in places with high potential of flooding can reduce flood damages. In this study، in order to identify of effective places on flood peak generation، we use RS&GIS techniques، hydrological model of HEC-HMS and two flooding indices (of F% and f) in Jiroft Dam basin. The results of F% index showed that K4 and soltani sub-basins are the first priority of flooding potential with values of 16. 12 and 13. 24 respectively. But in prioritizing of flood potential according to the f index that area factor of basins is eliminated and special discharge is considered، results showed that sub-basins of K6 and Hanjan are first places from flood generation point of view with values of 0. 76 and 0. 74 respectively. Results showed that the rate of flooding potential increases from downstream to upstream and upward streams play an important role in generation of outflow. On the whole، results show that performance of management programs and construction of hydraulic structures in upstream areas could reduce flood damages markedly in Jiroft Dam basin.

This research was conducted to study the negative allelopathic effects of Thymus kotschyanus on seed germination of Agropyron elongatum. Also to find what chemical materials are able to decrease the mentioned effects. The chemical treatments were three levels of giberlic acid (GA3) (250، 500، 1000 ppm)، KNO3 (0. 1، 0. 2 and 0. 3%) and salicylic acid (100، 200 and 300 mg/lit). Allelopathic treatments were 5 levels of 0، 5، 25، 50 and 75 % concentrations of Thymus kotschyanus aerial parts extractions. Results showed that solution extracted from Thymus kotschyanus had a negative effect on seed germination of Agropyron elongatum while in contrast chemical stimulators improved germination. GA3 had the highest positive effect. Interaction of stimulators and allelochemicals had a significant (P <0. 01) effect on properties of germination speed، root length، shoot length، plant length and seed vigor index while no significant difference was observed for seed germination of Agropyron elongatum.

Drought is one of natural disaster that unlike of others has gradually essence. It causes economic، social and environmental damages such as famine، waning civilization and ecosystem changes. Drought analyzing has a main role to recognize its essence that leads to reduce harmful effects. In this paper the meteorological drought has been analyzed in Karkhe، Karoon and Dez basins. In outset monthly rain was modeled by a method that includes empirical orthogonal function’s (EOF)، stochastic modeling and Kriging interpolation. Based such method the homogenous regions were determined in mentioned basins. The four regional time series of PC that explained 86. 9% of variance were modeled by stochastic modeling then time series of monthly rain was produced as long as 1000 years for every 291 cells. Meteorological drought was analyzed by method of truncation level (at 70% level) for every one of cells and drought characteristics includes of severity، duration، effected area، total of deficit volume، and relative deficit volume were calculated. After classifying drought according percentage affected area return periods of droughts، duration and deficit volume were calculated by fitting the best probability distribution models. Then severity-area-frequency (SAF) and duration-area-frequency (DAF) curves were concluded.

Identifying plant distribution is very important to select appropriate sampling strategy. This study aimed to compare different indices of vegetation distribution in three rangeland areas dominated by Festuca ovina، Bromus tomentellus and Prangos ferulacea. Random-systematic method was conducted using 5 transect with 100 meters long each. 30 points were located in each transect and plant spatial patterns were measured in 20 points. Distance from nearest plant and second neighbor plants were measured. Spatial indices of plant distribution sample (Johnson and Zimer Index، Pielou Index،Hopkines Index، Eberhart Index and Holgate Index) were calculated. Also 1 meter square plots were established in any random point and plant densities were counted in any plot. Then، distribution quadrate indices (Index of variance /mean Ratio، Green Index، Lloyd Index of patchiness and Morisita Index of Dispersion) were calculated. The results showed that Festuca ovina had patchy distribution and two other species (Bromus tomentellus and Prangos ferulacea) had a random distribution pattern. The results also showed that the distribution of distance indicators in most cases a plant species shows a pattern that to have more accurate indicators of the quadrate. Low accuracy in indicators quadrate due to the impact number، shape and surface of quadrates.

Pasture management may increase or decrease the cementing agents incorporated into soil primary particles through changes in the amount and composition of cover vegetation، the quality of organic C inputs to soil، soil organic matter (SOM) decomposition rate. To investigate the influence of ecosystem management and land use changes on organo-mineral complexes and SOM fractions، several physical fractionation techniques have frequently been performed، because these methods are considered to be less destructive to SOM than the traditional chemical fractionation methods. However، the complete dispersion of soil aggregates and particles is a central prerequisite and assumption in physical fractionation methods for obtaining reliable results. Thus، the objective of our study was to assess the efficacy of an ultrasonic dispersion procedure to separate soil primary particle-size fractions in protected pasture ecosystems with different grazing regimes in Central Zagros. Soil samples were collected from 0-15 cm depth of freely grazed and long-term ungrazed regimes in three native pasture sites including SabzKouh، Boroujen and Sheida areas. Sub-samples were analyzed for particle size distribution (texture) by both physical (i. e.، ultrasonic instrument) and chemical (i. e.، Calgon) methods. The Calgon method using hydrometer was considered a standard analysis for soil texture. Results showed that the ultrasonic dispersion energy necessary for complete dispersion varied from 386 to 1545 J ml-1، depending on pasture management and C contents in the bulk soil and in the fractions. The complete dispersion of primary particles for free grazing and ungrazing regimes was achieved at ultrasonic energy of 902 and 1545 J ml-1، respectively، in SabzKouh pastures. The necessary energy for complete dispersion of primary particles in Boroujen pastures was 386 for grazed pastures and 644 for ungrazed pastures، whereas in Sheida area the complete dispersion of primary particles occurred at 644 and 1159 J ml-1 ultrasonic energy، respectively، for free grazing and ungrazing regimes. Briefly، results of the current study demonstrate that (1) the calibration of energy output from ultrasonic instrument for given soil type with results obtained from a standard method (e. g.، Calgon) is indispensable and the existence of a strong correlation between the two methods is imperative، and (2) ultrasonic dispersion procedure resulted in a complete dispersion of soil aggregates and particles necessary for SOM studies.

Mathematical models are widely used in water engineering as valuable tools to simulate the qualitative and quantitative aspects of water flow conditions. In This study، mathematical relationships derived from the physical models were used where the roughness coefficient was as a function of water depth and speed، and type of vegetation، to simulate the water flow by FASTER model in Karoon river. The hydrographic data of years 2003 and 2004 in three hydrometric stations were used as the minimum، maximum and average values for measurement of the model accuracy. Comparing the water level simulated by the FASTER model with fixed roughness coefficient of 0. 03 and variable coefficient and corresponding values measured by the model، indicated that the variable “n” can be improved the model accuracy. The results showed that the predicted surface roughness obtained from the FASTER model was well fitted by observed values. In this case، the correlation of surface roughness of the mathematical model with variable coefficient is equal to R2=0. 932 and with a constant roughness coefficient is R2=0. 799. This means the estimations of the mathematical model was closed to actual conditions of the river values with high accuracy.

Irreversible losses of natural crisis in Iran are need to proper understanding of the causes and solutions to reduce them. In this regard، identifying the severity of the various aspects of vulnerability; environmental، social، economic، cultural، psychological، and society readiness against them is presented as the main determinants crisis. Karaj city turn as the center Alborz province and increasing immigration and residence in the city are important subjects in the new province of Alborz. The most substantial action in order to damage restriction is to be informed about the quality and quantity of possibilities and limitations of the natural environment including the regional characteristics of water resources and natural hazards. By this، for modeling of the risk and vulnerable zones of Karaj privacy، base layers were formed from the natural base maps that include; geology، fault، soil، slope، aspect، hydrology and vegetation. In this research the survey factors are calculated in way of mutual، comparison and weight of the items of sensation grade by the use of AHP method. Regarding weight quantity of each factor، weight plot prepared and finally the vulnerability map by use of each item weight layers and weight ratio prepared. Based on evaluated criteria and overlaying in GIS، the most important environmental factors in vulnerability are including to earthquake، flood and mass movement. Concentration of natural risk factors; as faults، steep slopes and numerous waterways in the mountainous region of Karaj has been caused to the northern and northeast parts of the Karaj area by high vulnerability in different aspects. In contrast، central and southern parts، with plain features and moderate slopes are specified in lower vulnerability.