نشریه پژوهش های آبخیزداری
پیاپی 114 (بهار 1396)

Land use change has a significant effect on soil physical and chemical characteristics and subsequent changes in hydrologic responses such as runoff volume and sediment concentration. Although numerous studies have mentioned vegetation cover impacts on soil erosion, relatively a few studies have quantified the temporal variation of hydrological response of runoff and sediment production under different land use and rainfall intensities. A replicated field-based rainfall simulation were performed at two selected intensities (51 and 86 mmh-1) in 1m2 plots on four types of land cover (rangeland, bare soil, straw mulching, and lentil filed) at Gonbad University research site. Behaviors of runoff and sediment concentrations during 30 min rainfall simulation test were made at every 6 min intervals. The ANOVA results showed that there were significant differences between the hydrological response of the soil depending on the vegetation covers and rainfall intensities over time. The different land uses in this study resulted in runoff volumes ranging from 2.3 lit to 24 lit and from 6.38 to 46.8 lit at 30 min for 51 and 86 mmhr-1 rainfall intensity, respectively. On the other hand, bare soil was most easily detached, followed by straw mulching, lentil, and rangeland. Although Student's t-test showed that there were significant effects of rainfall intensities in runoff volume on all plots except on bare soil plot. These differences are all significant at the P = 0.05 level. Moreover, only there was a statistically significant difference in sediment concentrations of rangeland plot.

Flood control and storage are the main factors in combating desertification especially in arid and semi arid regions. This study aims at recognizing suitable sites for flood spreading by coupling fuzzy inference systems and RS & GIS techniques. In this resarch, Davarzan watershed selected as a one of the most flood prone area in northeastern Iran because of its strategic location in upstream of Etka agricultural regions. Various thematic maps of the study area including slope map, surface infiltration, pollution generating potential of each formation type, runoff volume and aquifer depth on 1:50000 scales were selected as inputs and analyzed using ARC GIS 9.3 package. Land use map on 2002s ETM image after field measurement and identifying training sites in ENVI 4.8 software is also extracted. For weighting and integration of information layers, any techniques such as index overlay, Boolean logic and fuzzy logic model has been used. Results showed that fuzzy gamma 0.9 and index overlay with maximum overlaying surface with the control sites (5 and 4% respectively) are the most appropriate methods. Screening output maps, it is revealed that alluvial fan located in upstream of Etka agricultural regions was unsuitable. It is mainly due to accelerated erodibility of formations PLc and K1l, lying on the outlet section and resulted in aggregated marl sediments on the alluvial fan which made it unsuitable for flood spreading.

85 % of Total moving sands in the world are in ergs which cover about 32000 Km2. Traditional qualitative methods for geomorphological surveys are based on the field observations which due to harsh condition in deserts are time and money consuming. Lut desert in eastern part of Iran includes the mega dunes which are very interesting landforms but unreachable. This paper presents a new approach using a Self Organizing Map (SOM) as an unsupervised algorithm of artificial neural networks for analysis and identification of Lut mega dunes. The latest version 1 arc second SRTM/X band DEM were re-projected 30 m UTM grid and used to generate 22 morphometric parameters of first order (e.g. slope), second order (e.g cross-sectional curvature, maximum curvatures and minimum curvature) and third order( extreme curvature)by using a bivariate quadratic surface. The five optimum parameters are selected based on Optimum Index factor (OIF) and used in a SOM to identify morphometric features (or landform). The number of landforms was determined by Davies-Bouldin Index. The ETM bands of landsat satellite data also included to input data for increasing the potential of SOM to extract features. The result showed that all mega dunes could clearly be recognized and classified by this method when their width is larger than the DEM resolution. The results also demonstrate that a SOM is a very efficient tool for analyzing geo-morphometric features as Aeolian landforms under a hyper-arid environmental condition.

Plant cover may be the most important factor in conserving the soil from water and wind erosion. Wise management of plant cover needs accurate and sufficient information from vegetation and soil seed bank capacity. Evaluation of changes in vegetation and soil seed bank after a restoration operation can show the role of land management. The relation between these two indicates the necessity of study the areas after restoration operation. To determine the species richness and similarity of plants and soil seed bank, sampling was done in ungrazed 18 year old Atriplex cultivated area and natural exclosure non-cultivated area. In the fall of 2010 randomized-systematic sampling of seed bank was conducted along four 200 m transects in each region. Five one-square-meter plots with 50 meter intervals along each transect (total of 20 plots in each region) were deployed. Soil samples from the depth of 0-5 and 5-10 cm were collected using auger and transferred to the greenhouse for planting in the proper beds. Plant cover was also estimated and recorded in the fall and spring of 2011 in each plot. Sorenson’s quantitative index was used to measure the similarity between soil seed bank and vegetation cover in each plot. To compare the characteristics of soil seed bank, containing seed bank similarity to vegetation, seed bank richness, palatability classes and life forms, between two regions, unpaired t-test, and between two depths of each region paired t-test were applied. One-way ANOVA and Duncan's test were used separately to compare the palatability classes and life forms in each region. The results showed that, similarity of plant cover and soil seed bank, also soil seed bank richness in the depths of 0-5 and 5-10 cm had significant difference between planted and non-planted areas. The results also showed that similarity of soil seed bank and plant cover in the planted area is 60% for the first depth and 24% for the second depth. It’s 84% in the first and 40% in the second depth of non-planted area. All palatability classes showed significant difference between two regions. All kinds of life forms except Hemicryptophytes had significant difference between two areas.

Development and improvement of soil erosion estimation schemes with providing feature to examine various strategies effects of land management on soil losses is essential to land science experts. The Universal Soil Loss Equation (USLE) is one of the primitive empirical models in estimation of erosion that is used continuously. In this study, the efficiency amount of USLE and some of its versions include MUSLT¡USLEM¡MUSLE-E¡MUSLE-S, AUSLE and AOF are evaluated in North Khorasan semi-arid rangelands in event base and for 20 selected events. For this goal, the measured sediments due to 20 events in three plots with same characteristics include range land use and without protective measures are considered and compared with estimated values for each version. The results show that the estimated obtained from MUSLT, MUSLE-E, MUSLE-S and USLEM methods have significant correlation with the observed sediment and the modeling procedure in these methods is logical than others. The MUSLT has the lowest Relative Root Mean Square Errors (RRMSE = 4.257) and greatestMean Efficiency(ME=0.011) has a relative efficiency in estimating of observed sediment in event base in the studied area. Other considered methods estimate non-reasonable sediment values.

Haloxylone is a common shrub for stabilization sand dune in Iran.The objective of this research were to investigate the effect of Haloxlylon on the physicochemical properties of soil and the possibility of fertile islands formation in Yahyaabad, Sabzevar. Firstly, based on field observations and vegetation inventory, two regions with good and moderate Haloxylon coverage were identifies and 4 and 5 sampling sites in the good and moderate coverage were selected, respectively. To examine soil morphological and physicochemical characteristics, in each site, two soil profiles under and between plants canopies (totally 18 soil profiles) were described and sampled from genetic horizons. The results showed that the amount of Pa, Nt, and SOC in fertile islands are considerably higher than between plants, especially in surface layers in good coverage regions. Coordinated changes of HCO3- and SOC indicating their close relationship. Because of high mobility of Na, K, and Cl- and HCO3- the amount of these ions and consequently EC and SAR have increased in all soil layers under canopies in comparison to between canopies . The composition of Haloxylone leaves indicated that decomposition of falling leaves is the main factor of increasing the mentioned characteristics. The low amount of Mg2 and Ca2 in leaves explained insignificant changes of these ions under canopies. Among the physical properties, only the saturation percentage (SP) has been increased in surface layer due to close relation of this parameter to SOC. The results of this study confirmed the formation of fertile island under Haloxylon which extended with less intensity to subsurface layers.

During the past decades due to population growth and urbanization , urban runoff has increased and lead to different Environmental problems such as inundation risk, release the environmental pollutions and risks of flooding.Sensitivity analysis is used to determine the important input parameters which caused run off. Basically, the aim of this study was determine the important input parameters of SWMM model and the reliability of this model Performance in the Mahdashttown. Therefore, 10 parameters including percentage of impervious area, slope, width, N-Manning for impervious area, time of concentration, curve number, N-Manning for pervious area, depth of depression storage on impervious area, depth of depression storage on pervious area and percent of impervious area with no depression storage reduction, the first account of abovementioned parameters was increased and decreased 15 and 30 percent and flood peak discharge was selected as the dependent variable. For calibration and validation process model, corresponding to three event rainfall runoff measured at the output of the basin and was compared with runoff simulated by the model. The results showed there is good agreement between simulated and observed runoff discharge and depth.So this model can use to predict the inundation risk, design and prioritization areato fixing the inundation problem.