مجله مهندسی و مدیریت آبخیز
سال هفتم شماره 1 (بهار 1394)

In the past decades، the study of soil erosion has gained considerable attention by many researchers. This was thorough understanding of soil erosion processes and variable factors affecting it which is essential for making land management decisions. The aim of this study was to investigate the spatial-temporal coefficient of variation of soil erosion and flow hydraulic parameters in top-down conventional ploughing rills with 20 percent average slope. The artificial rills were produced with a length of 10، 20 and 30 meters. Hydraulic parameters and sediment concentration were measured at three equal time and distance intervals after applying 10، 15 and 20 Lmin-1 inflow rates for 10 minutes. Consequently، sediment detachment and transport rates were calculated. In addition، relative errors (RE) of these parameters were calculated in order to investigate the coefficient of variations. The results showed that there was a significant difference (P<0. 01) between sediment (soil detachment rate، transport rate and sediment concentration) and hydraulic parameters. Stream power was significantly different with sediment detachment and transport rates (P<0. 05). Temporal evaluation revealed that coefficient of variations in the first and final time intervals of RE values of detachment and transport rates were more than middle time slot. This is perhaps due to stochastically movement of available sediment in the first step and undercutting and bank failure of rills in final stage. Spatial variability showed that the RE in the primary section is significantly (P<0. 01) greater than following sections، whereas there was no significant difference between second and third sections.

Assessment of suspended sedimentgraph (SG) and rating loops are important tools for analyzing the behavior of watersheds and successful implementation of watershed management measures in reducing sediment. However، the development and analysis of SGs and rating loops and influencing factors need more attention in watershed-scale. Therefore، the present study aimed to conduct the analysis of 13 observed and simulated sedimentgraphs (SGs) during October 2011 and November 2012، in Galaz-Chai Watershed with an area of 103km2 located in West-Azarbaijan Province، Iran. Towards this attempt، the SG of observed events was derived using instantaneous unit sediment graph (IUSG) concept، and the effects of different land uses were investigated. Also، the variation and patterns of the simulated sedimentgraphs (SGs) and rating loops were plotted and interpreted with the respective land use types. Based on the results، anearly peak occurred in SGs with respect to the observed hydrograph peak rates and consequently had clock-wise pattern. Increase in falling limb of hydrograph could be attributed to the participation of sediment production from agricultural land inwatershed upstream. The model predicted SGs with good accuracy according to the Nash-Sutcliffe criterion (70%). Analysis of results indicated that the type and distribution pattern of different land uses had significant effect on the shape of SGs and sediment rating loops.

Cluster analysis methods are one of the most efficient approaches of regionalization of watersheds for Regional Flood Frequency Analysis (RFFA). Fuzzy regionalization is a kind of regionalization in which each site of interest may be assigned to more than one region simultaneously. In order to perform regionalization، a variety of cluster analysis algorithms named fuzzy clustering are used that fuzzy c-means algorithm is most wellknown of them. Also Self-Organizing Feature Maps (SOFM) are a special class of Artificial Neural Networks (ANN) that has found several applications in the areas of pattern recognition. Capability of this class of networks in areas of pattern recognition and data clustering using their attributes has make some hydrologist interested in testing ability of these maps for regionalization of watersheds in order to perform regional flood frequency of analysis. In this study self-organizing feature maps have been used to determine initial centroids of clusters in fuzzy c-means algorithm for regionalization of Sefidrood watershed. Results of this study showed that this approach has an acceptable performance in formation of homogeneous regions and providing suitable estimates in regional flood frequency analysis using L-moment algorithm in interested watershed. Furthermore it is observed that fuzzy clustering may provide longest reliable flood estimates. Also based on fuzzy clustering validity measures it’s seemed that two or three regions is appropriate number of regions for regional flood frequency analysis in this watershed.

Sand transport by erodible winds is one of the most important wind processes in arid and semi-arid regions. In this study، in order to determine the wind regime، different indices of same wind aspect index (UD)، sand transport potential index (DP)، erodible winds direction resultant index (RDD)، transport potential resultant index (RDP) were studied and compared with sand dunes morphology index in Semnan Plain. Garmsar، Semnan، Damghan and Biarjomand synoptic stations anemometer data and sand rose graph software were used to analyze wind data، sand transportation potential and sand rose drawing. Results showed that wind sand transportation potential is relatively high at all studied stations and more than 3000 vector unit (VU) throughout the year، according to six m/s threshold velocity which presents highly potential of wind erosion and sand transportation in the region. Annual (UD index is more than 0. 9 in Damghan station and varies between 0. 3 to 0. 8 in other stations. RDD index is also reflecting wind direction changes from 130 to 180 degree. These two indices are representing barchan sand dunes، barchanoid and or silk shape longitudinal dunes in Semnan_Garmsar plain that are formed along north-northwest to south-southeast winds. This condition show the close adaptation with Alborz mountains cold and high pressure condition at the north part of the region and southern situation of Gramsar، Damghan and Semnan plain and also with topography pathway of the region. Sand dunes moving index shows that they are moving and their current vegetal coverage is the result of de-desertification activities.

This study aimed to analyse the design of spillway in curved plan and downward angle of convergence. In this plan the effective length of the spillway is reduced from the crest to the toe for several times. Tests were carried out in two stages. In the first stage، a physical model of the real sample was prepared for a specific site in the scale of 1:50. In this stage، experiments were performed for eight different discharges making up to 25 to 150% of the design discharge of the real sample. The spillway demonstrated a satisfactory performance up to the discharge of 1. 13Qd (Design Discharge). Gradually an increase in the discharge led to a decrease in the performance of the spillway so that with a discharge of 1. 26 Qd the spillway was fully submerged and the downstream channel took control of the discharge. Observations and experiments indicated that one of the factors contributing to the swamp of the spillway was a severe variant of the guide wall (120 degrees) as well as the considerable decrease in the ratio of channel length (Lch) to crest length (L)، i. e. Lch/L=0. 214. In the second stage، the effect of variation of convergence angle of the guide walls of the spillway was studied. To this end، a physical model with three convergence angle of the guide walls، including a 0- degree angle and ratio of Lch/L=0. 98،; a 60-degree angle with ratio of Lch/L=0. 32; and a 90-degree angle with ratio of Lch/L=0. 26 was tested. The effect of variations of angles in discharge coefficient was reported to be negligible before the swap. At the 0-degree angle with ratio of Lch/L=0. 98، the highest discharge was 1. 99 because the model was not submerged in a discharge equal to the PMF discharge of the real sample. In all angles، the static pressure on the crest was reduced while it was increased in the shoot and toe. So that، in the crest a ratio of Hp/Hd=-0. 217was recorded for a discharge of 1. 13 Qd. At the angles of 90 and 120 degree، higher discharges led to swamp of the spillway and a change of the current flowing on the spillway from supercritical to subcritical. The high pressure was reported to be Hp/Hd=4. 35 of the 120-degree angle for a discharge of 1. 5Qd. Since at the 60-degree angle (Lch/L=0. 32)، the length of the crest was smaller (45% less than the 120-degree angle with Lch/L=0. 214)، it was selected as the proper angle. Key words: Angle of convergence، Critical discharge، Discharge ratio، Physical model، Static pressure

Acquiring sufficient knowledge about soil structure of the river side wall and arrangement quality of its layers will be helpful to prevent soil erosion and distraction. The main purpose of this research is to find a proper way to decrees effects of river bank erosion with regard to studying the effects of clay on the rate of the river bank erosion. To conduct the research، some experiments have been performed by using an experimental model with 14m length، 90cm width، and 50cm depth. The results demonstrate the major role of clay in decreasing the rate of side wall erosion and the depth of scour. In the final analysis، the research comes to this conclusion that there is an inverse relationship between the increasing percentage of clay and the side wall erosion rate and scour depth. By increasing the amount of clay materials، adhesives، wall scour depth profiles، the declining trend is involved. So that the figure in clay materials 7/5% to almost zero. Scour depth at the top of the wall to increase the adhesion of materials resulting from the addition of bentonite clay to 7/5%، compared to non-clay materials has decreased by about 97% And at the beginning of the clay wall materials 7/5% of the action occurring is very low

One of the most important problems of water resources operation systems, specifically surface reservoirs in confronting hydrologic variability, is considering drought phenomenon effects on operation methods. As well as flow variations relative to average flow, duration of the drought is another important factor. One way to resist the drought is suitable operation of water resources during drought conditions. There are several models developed for water resources management such as WEAP software. But such models do not have water resources modeling capability during drought conditions. Therefore, developing such capability on WEAP model is highly important for water resources engineers. Developing the hedging rules for operation based on WEAP software was investigated by this research by which an extension program was developed in WEAP software. Developing such model would enable us to jointly optimize and simulate on basins. In order to test the capability of the complementary program, modeling was performed on operation of Gorganrood river reservoirs. Then the results of the developed model were compared to the ordinary WEAP software results. The results indicated 1 to 38 percent increased capability of WEAP software on modeling for hydrologic drought conditions. It is worth mentioning that the complementary model was developed as a general model by which the model can be used on different basins.

Landslide with Morphotectonic indices is related. Morphotectonic indices applicable tools for probability estimation and seismic planning of area. Landslides events are the most common natural threats that have been recorded in the Iran. Landslide hazard zonation planning is required for the sustainable management plan. Therefore، application of morphotectonic indices to estimate landslide risk in the selected areawas the aim of this research. The selected area comprises seven sub catchments at the south west of Iran which historically has experienced several earthquakes ranging between 2. 5 to 6. 5 magnitudes in the Richter scale. Morphological indices such as river length–gradient index (SL)، the catchment، drainage basin asymmetry (AF)، transverse topographic symmetry (TP)، factor hypsometric integral (HI) and index of drainage basin shape (BS) were applied for seismic planning of study area. As a result، different indices were converted to the tectonic activity index (IAT) in the three categories. Besides، the resultant morphotectonic zoning map was compared with landslide risk event، and calculated showed that a good correlation between morphotectonic indices and landslide risk event map was demonstrated in this study.

Investigations show that in some cases the distance between check dams are decreased due to wrong ultimate slope. In this Study، a survey and investigation implemented on Gush and Bahreh catchments، Kartian، Kameh and Dasht watersheds which are located on upstream of Kardeh، Torogh، Shahid Yaghubi and Golestan dams، respectively. In this way، longitudinal section profile، ultimate slope، location، distances and height of dames with acceptable performance about upstream ultimate slope has been measured. Meanwhile، characteristics related to bed aggregates has been sampled and determined. Then، with the measure of dimensions regarding the ultimate slope، some equations which were based on primary slope of river direction has been developed. Our investigations claim that unsuitable design in ultimate slope had been lead decreasing the distances between dams; consequently، some of upstream weirs had been buried under sediments. To wrap it up، we have to argue that definition of distance between dams based on the measured ultimate slope could result 25. 4 percent descend in expenses of all studies weirs and dams construction and protection.