نشریه پژوهش های آبخیزداری
پیاپی 99 (تابستان 1392)

In this research at first، gully erosion sites were studied in Zanjan province and their boundary drawn. Climates map by modified Demarton''s method prepared and two gullied regions with more than 500 ha area were selected from each climate. In each region one representative gully & 2 replications were chosen for measuring physical and morpho_metetric characteristics، gully initiation and development causes، land use & soil sampling region. Results revealed that there are 57 gully affected regions (552. 7 km2) and 9 climates by modified Demarton''s method in Zanjan province. Gullies are distributed in three of climates such as cold semi- arid، very cold semi- arid and moderate semi- arid climates. Cold semi- arid climate contains most of gullies (64. 91%) in Zanjan province. Gullies have clay، clay loam and loam clay soil texture dominantly and are lateral and formed along drainage ways. Most of the gullies are located on hills and some on plains. The view plan of gullies is dendritic and linear. The headcuts of gullies are digitated and pointed and the vertical plans of headcuts are generally vertical and inclined. Their cross section are V and U shaped. In viewpoint of their depth، they are in the intermediate class (1-10m). Dominant causes of gully formation include degradation of vegetation cover، land use change، soil erodibility and improper irrigation management. The gullies damages to rangelands، cultivate lands and roads and total damages were estimated about 2226. 9 billion Rials in Zanjan province.

The area of rangeland which surrounds a permanent watering point is seen as a management unit and has been described as a ''piosphere''. Investigation of quality and quantity of vegetation cover in this area to range management is necessary. In this study the impact of watering point provision on the vegetation cover، composition، yield، trend and range condition was investigated in three piosphere in Middle Taleghan. To this target three watering points (with high، medium and low grazing intensity) was selected. Then we measured the vegetation cover، composition، yield، trend and range condition in two aspects (with high and low grazing of livestock) and distances (250،500 m) from central point of each point. For measuring based data، 100 m transects and 1m2 quadrate have been used. The data were analyzed by spss. The results show that maximum vegetation cover، composition and yield of Plants with class I is related to watering point with low grazing intensity. vegetation cover، yield and composition of Plants with class I in aspect with low grazing of livestock is more then aspect with high grazing of livestock in watering points with medium and low grazing intensity. composition (watering point with high grazing intensity) and vegetation cover (watering point with low grazing intensity) of Plants with class I increased as distance from water increased، while on watering point with medium grazing intensity vegetation cover، yield and composition of Plants with class III increased as distance from water increased. Range condition increased as distance from water increased on watering points with medium and low grazing intensity.

Flood is one of the most important natural disasters that threats human life and wealth. Application of rockfill dams is one of the low-cost methods for flood controlling. The use of these dams is resulted in higher peak discharge and shorter time in output flood hydrograph than those in input hydrograph. Artificial neural network (ANN) is one of the methods which can predict complex and non-linear processes at desirable level of accuracy. However، the accuracy of its prediction depends on the type of used learning algorithm and threshold function. In this study for estimation of flow through rockfill dam based on experimental data، multilayer perceptron model with different learning algorithms and threshold functions was evaluated. Afterwards، the output discharge values predicted by ANN method were compared with the values computed by two-dimensional numerical model. The results showed that the Multilayer perceptron model using Delta-Bar-Delta learning algorithm and Tanh threshold function with mean square error equal to 0. 00011 predicted the output discharge from rockfill dam with high accuracy. The ANN method with a R2 of 0. 962 performed as good as the numerical model (R2 =0. 984) for estimation of the mentioned parameter. Therefore، the drawback of the time-consuming and complex numerical methods analysis in estimating the output discharge of the dams can be overcome by using artificial neural network.

Biomass is an important structural parameter for investigating for ecosystems dynamic، the level of biodiversity، carbon cycle and ecosystems sustainability. In addition، the quantification of biomass resources is required in many studies، such as the analysis of fixed-emission of CO2. This research focused on quantifying the influence of grazing intensity on aboveground and belowground biomass on the arid shrublands that is covered by Artemisi sieberi. Intensity levels were quantified as non-grazing، moderate and heavy based on the rate of vegetation utilization. In all treatments، aboveground and belowground (0-25، 25-50، 50-75 cm) were sampled. To estimate aboveground and belowground biomass، their relationship and effect of grazing intensity in biomass compartments، simple biomass equations were extended in each treatment. There were strong linear relationships between volume and aboveground biomass and also between aboveground and belowground biomass in all the treatments. These relationships and functions could be used in similar studies. Although the result showed aboveground and belowground biomass and their relationship can be affected by livestock grazing، the dimension of these changes was highly depended on grazing intensity. Aboveground and belowground biomass was decreased significantly by grazing intensities in both heavily and moderately grazed sites in comparison with non-grazing treatment. It was seen that grazing not only had a potential to change the amount of aboveground and belowground biomass in ecosystem، but also could change the allocation of these elements and relative allocations of belowground that were increased by grazing intensity. In our study، although heavy grazing reduced the amount of biomass، moderate grazing didnot respond to plant biomass in this area.

Time of concentration is one of the most important hydrological variables which plays crucial role in designing the flood control structures، spillways and so on. However، enough investigations have not been taken place about this important variable. The purpose of the study is to evaluate the application of empirical equations including Kirpich (1940) California (1944)، NRCS (1972)، Yen-Chow (1983)، Haktanir-Sezen (1990) and Zomorodi (2005) for estimating shallow concentrated flow travel time in the upper channels of Manshad and Deh-Bala watersheds located in Yazd province، Iran. Therefore، the estimations made by the equations were compared to measured values provided by Nacl 75 g/lit solution gulp injection. The estimations made by the equations were evaluated using statistical criterion including absolute percentage error (APE)، root mean square error (RMSE)، coefficient of determination (R2)، and correlation coefficient. The results showed that Haktanir-Sezen and Zomorodi revealed acceptable estimations of accumulated (sum of the travel times estimated for reaches) as well as partial (travel time measured per reaches) overland flow travel time. While none of equations presented a reasonable estimation of total travel time (travel time estimated using mean values of slope and roughness of the whole studied stream length)، although the estimations of Haktanir-Sezen، California and Zomorodi showed higher accuracy than others. Most of the equations underestimated overland flow travel time in comparison the measured values.

In some windy، dry areas of Iran tree species such as Tamarix spp are used as windbreak to reduce soil erosion. Tamarix accumulates salt in its leaves، and then excretes it onto the leaf surface. These salts accumulate in the surface layer of soil when plants drop their leaves. Therefore some farmers are not interested to plant Tamarix as windbreak around their fields. The objective of the present paper was to evaluate the effect of Tamarix as tree windbreak on the soil salinity of the agricultural lands of Ardakan city. Soil samples were taken in the depth of 0-20 cm at different locations (beginning، middle and end) of each plot. The experiment for both sites (with and without windbreak) was carried out as randomized complete block design with four replications. Soil samples were then analysed for EC، SAR، K-، Na+، Cl-، Ca+2، Mg+2، HCo3-2 in laboratory of Natural Resources Faculty of Yazd University and mean of three locations of sampling was recorded. Results showed that rate of soil salts at region with windbreak were more than the region without windbreak. So that wind breaks increased EC of soil 15 percent compared with lands without windbreaks. Also the concentration of Na+، Ca+2 and Mg+2 of the soil near the windbreak were significantly higher than lands without windbreak، In the other hand، the concentration of Cl-، SAR، HCo3-2، K- of soil did not show any significant difference in both sites investigated in this research.

One of the important necessities for grazing systems is informed for favorability of rangelands to provide daily requirement of grazing animal. Therefore in this study، favorability of habitat rangelands of Taleghan; that is spread in 39º، 50´، 20 «to 36º، 21´، 30» north latitude and 50º، 20´، 5 «to 51º، 11´، 22» east length in 110 kilometer from west of north of Tehran; to provide daily requirement of grazing animal in different grazing season stages، is determined. For this purpose، if the amount of metabolism energy in weight unit of plant type، was more than 8 Mj/KgDM، the plant type is considered very desirable; but if it had less than 5 Mj/KgDM، it is undesirable and if metabolism energy in weight unit of plant type was between 5-8 Mj/KgDM، it is desirable. Also، if the amount of crude protein in weight unit of plant type، was more than 7%، the plant type is considered very desirable; but if it had less than 5%، it is undesirable and if metabolism energy in weight unit of plant type was between 5-7%، it is desirable. The results showed; with progress of phonological stages، favorability of habitat rangelands became less. But، none of the plant types to provide daily requirement of grazing animal in different grazing season stages، were undesirable. Also the results showed; favorability of habitat rangelands to provide crude protein requirement of grazing animal، in the end of grazing season، is less than the first and middle of grazing season. In the 44. 98% of rangelands of Taleghan، the amount of crude protein in weight unit of plant type، in the end of grazing season was less than 5%. Therefore in this situation، these rangeland to provide crude protein requirement of grazing animal are undesirable and recommend that supplement alimentary used for protection of status of animal requirement. Therefore، the time of grazing is effective on daily requirement and it is necessity to determine animal requirement in each phenoligical stages. It is clear that forage quality is changed with variation of weather، but due to the expense of determination forage quality is very high، can use the results of this research for estimate of animal requirement in different years.

Intensive grazing and continues trampling and presence of livestock in rangeland ecosystems can cause soil degradation. In this research the effects of various grazing intensities on some soil properties including Percent of Soil Moisture Content، Bulk Density، Electrical Conductivity (EC)، pH، and Percent of Sand، Silt، Clay particles in conditions such as non-grazing area، moderate grazing and intensive grazing areas (critical area) as vicinity of village، livestock pen area and watering point area were studied in Chaharbagh rangelands of Golestan province. After soil sampling in two depth (0-20 and 20-40 cm) and each five site via random-systematic strategy of sampling and laboratorial measuring of parameters، one-way analysis of variance and Duncan test were used for testing of all parameter means equality and grouping of treatments respectively. Results of analyses demonstrate that livestock grazing has caused more changes in first depth than second depth. Statistical analyses showed that implementing of rangeland enclosure with upper than ten years can improve soil properties in comparison with moderate grazing area due to good precipitation and climate condition in this region as such enclosure has decreased soil bulk density of first soil depth and pH of two depths and has increased the moisture content of first depth and there is no changes in soil particles percents. With ignoring of pen area for facing with exceptional condition because of accumulation high amount of dung on it، as increasing grazing and livestock trampling intensity، soil bulk and soil moisture content of first depth density increases، as such، vicinity of village due to concentration of all livestock of rangeland has more undergoing in declining soil quality. The soils of pen area have faced with problems such as increasing EC and bulk density. According to the results of key area، if the grazing intensity be on a moderate level، soil properties will face less declining of soil quality than critical areas and finally it could have sustainable production. In this region، implementation of grazing exclusion due to its good proved effects is suggested for rehabitation of high grazed areas especially in vicinity of village in this area. Reducing of livestock density in critical areas through increasing amount of watering points and pen areas is of other ways of reducing destruction intensity in these sites.

Rock falls are one of the speed movements in dry and continuous material. They are natural process of activities geomorphic on steep slope in mountainous terrains. At this research، Rock fall Hazard Mapping was generated by Logistic Regression، Frequency Ratio and Overlay Index models at a long 11 kilometer of the Salavat Abad road in eastern Sanandaj، Kurdistan، Iran. Dependent variables is occurrence and non-occurrence rock falls and independent variables including; slope degree، slope aspect، slope curvature، elevation of sea، lithology، distance from road، distance from fault، land use. The maps which were generated with three models، compared and verified with rockfalls situation using Success Rate Curve (SRC). Results showed that the logistic regression model، Frequency Ratio model and Overlay Index model have an accuracy of 85. 09، 76. 76 and 81. 44 percent of the Area under Curve (AUC)، respectively. So، Logistic Regression is more proper than the other models for determining regions prone to rock fall in the case study.

Sheep fescus is the important perennial grass in country''s rangelands for establishing pastures and producing fodder in cold climates، are growing in northern provinces، Alborz and Zagros mountains. The objectives of conducting this research، were to assessment the 12 genotypes of sheep fescue to find the suitable populations at the point of view of forage yield and quality in dry and irrigated conditions، as well the investigation if the relationships between traits and populations classification according to the studied traits. During the 2007، 12 genotypes of Festuca ovina were established in a squared lattice design at the Kheirabad experimental station in Zanjan. Forage yield، qualitative and quantitative traits were analysed during 2008-2009. Simple and combined analysis of variance was applied to the collected data. Combined analysis of variance showed that in rein fed cultivation genotype No. 10042 with 1475 Kg/ha. and in irrigated conditions genotype No. 140502 with 3224 Kg/ha. considering their forage yield should be recommend at the condition of Zanjan province. Finally during determining the genetic distance and grouping، all genotypes were arranged in 2 clusters; therefore، considering the goal of grouping these species، genotypes of cluster No. 1 recommend for inducing of forage production.

This study aimed to investigate the effect of habitat kind on soil seed density and richness، and finally introducing the best habitat as a soil seed source for vegetation recovery. Therefore، three habitats were selected in central Alborz viz. forest، rangeland and the ecotone between forest and rangeland. In each habitats، 7 transects perpendicular to the slope were established. Soil samples were collected along transects from 70 2*2 m plots in each habitat and for two depths: 0-5 and 5-10cm. Soil samples were then spread in green house and seedlings were identified and removed for a 6-months period. GLM، ANOVA and post hoc tests were used to study the effect of habitat kind، depth and the interactions on soil seed density and richness. The results showed that the kind of habitats، depth and interaction between habitat and depth were significantly affected on both richness and density of soil seed bank. In upper layer، the highest value of seed richness and density were related to ecotone، rangeland and forest، respectively. In deeper layer، the highest seed richness was related to rangeland and ecotone and the highest seed density was related to rangeland. In total، it can be concluded that ecotone was a suitable habitat to act as a source of soil seeds. The manager could rely on ecotone as a genetic memory and a source for introducing seeds for recovering the eroded areas particularly in rangeland.

The purpose of this study was assessment of drought impacts on social – economical situation of wheat-producers and extension- educational solutions for decreasing of its impacts in Nehbandan county. This study was a sort of Survey research. The statistical population of this research included all wheat-producers households in Nehbandan County which were equal 3817 Households. Using Morgan table، the number of statistical sample was determined to 308 Households which were selected through random sampling in the first stage and stratified sampling in the second stage. A questionnaire was used as research tool which constituted of four sections included Individual، economical، social and farming characteristics in the first section، The impact of drought on economical situation In the second section، The impact of drought on social situation In the third section and extension- educational solutions for decreasing of drought Impacts in the fourth section. The questionnaire validity was confirmed through supervisor and advisor professor opinions and other experts related to this issue in Jihad-e-agriculture Management and its reliability also was confirmed using Cronbach’s Alpha which was estimated upper (= 0. 92). After collecting data، they were analyzed using SPSS software. The results of correlation showed that there is significant negative relationship between perceived drought by farmers and variables like literacy level، Income and participation in extension-educational courses. In addition، paired sample t test results showed that average area under cultivated of wheat، total annual production of wheat and the number of sheep، goat and cow in usual year were more than drought year. Also the number of annual irrigation in the drought year was more than usual year as these differences were statistically significant. According to Man-Whitney Test results، average of perceived drought between farmers who are satisfied and unsatisfied from amount of credits had significant difference. According to Kruskal-Wallis Test average of perceived drought among farmers whit different irrigation transmission canal had significant difference. The results of factor analysis of economical impacts of drought showed that these impacts can be classified into 5 category namely increasing production costs، decreasing wheat production، increasing economic ability of farmers، decreasing productive ability in future by farmers and exit from agriculture sector. Besides social impacts of drought showed that these impacts can be classified into 5 category namely increasing social challenges، decreasing the level of Hygiene and tuition، mental impacts of drought، social involvements and creating poverty in society. Lastly، The results of factor analysis of Extension- Educational Solutions for Decreasing of drought Impacts showed that these solutions can be classified into 5 categories namely extension of appropriate farming operations، education of farming management options، encourage of farmers to defend with drought، education and empowerments of farmers and establishment of data base of drought.

Soil water retention curve (SWRC) is an important hydraulic property in the studies of water and solute movement in soil and its direct measurement is time consuming and expensiveness. Therefore many indirect procedures like pedotransfer function and empirical models have proposed by soil scientists. In this study، a model based on fractal theory، was used to estimate water retention curve. For estimating Fractal dimension (D) that used in this model، it was tried to find out a simple relation between this parameter and feasible soil properties such as، soil particle size distribution (PSD) fractal dimension، clay، silt and sand content، ρb، dg، by applying stepwise regression analysis. The SWRC was measured for 40 soil samples، which included all soil texture classes، by pressure plate. the measured DSWRC for 33 soil samples، used for regression analysis and 7 soil samples was used for model validation. The regression analysis showed a linear relationship between DSWRC and DPSD and dg with goodness of fit، R2 = 0. 95. Estimation SWRC for 7 soil sample whit replacement estimated D by linear model، showed that the model had a good estimation، especially for light texture soils. Also there is an overestimate that can be modified by model calibration.

During recent decades، many rangelands have suffered degradation. To preserve these valuable resources، monitoring and evaluation is important. A proper assessment requires a precise sampling of the study area. In this study، different methods of sampling in terms of accuracy and time were analyzed in three sites in Taleghan rangelands. The optimum number of plots were investigated by evaluating different equations and determined the ideal plot shape and size according to the percentage cover of dominant species. Our data showed that the formula is the most appropriate method for determination of suitable plot numbers in estimation of canopy cover in terms of accuracy and saving time. According to this formula، use of 40 plots for Thymus kotschyanus، 30 plots for Astragalus microcephalus، and 40 plot for Bromus tomentellus give the best results for canopy cover estimation. The most appropriate plot shape and size were determined quadrate (2 × 2 m2) for T. kotschyanus and A. microcephalus and quadrate (1 × 1 m2) for B. tomentellus.