مجله علوم و مهندسی آبخیزداری ایران
پیاپی 40 (بهار 1397)

Determining the relative contribution of sediment sources is the first step in planning for soil conservation programs. This study aimed to compare two methods of water sediment source tracing (including fingerprint technique and field measurements of erosion) in Vartavan catchment. Discriminant analysis and multivariate mixing model were used for determining the optimum combination of tracers and contribution of sediment sources. Sediment trapper was also used for measuring the erosion of various lithological units. The result showed that the contributions of sedimentary, calcareous and volcanic sources in the outlet sediments were equal to 47.6, 37.4 and 15.1 % respectively and the relative importance of these sources (in terms of specific sediment) were equal to 1.58, 1.04 and 0.48, respectively. The average of minimum and maximum weight of accumulated sediments in trappers were also 2/13 and 6/221 gr for orbitolina and plagioclase limestone. respectively. In totalæ the results and efficacy of fingerprinting, was approved by field measurements. As well, differences between the results of direct and indirect methods are due to the differences in the area of units and the lack of spatial and filtering resistances in the indirect methods.

Rill erosion which occurs as a result of runoff concentration on a hillslope is one of the major soil erosion types in arid and semi-arid regions, especially where plant cover is poor. For this reason, understanding the factors affecting them is a high priority. Rill erodibility indicates the ease of soil particles detachment and transport by water shear force in a rill. The study was conducted to investigate the effect of rainfall intensity on the flow characteristics and rill erodibility (Kr) in a marl soil. A laboratory experiment was carried out in ten rainfall intensities from 10 to 100 mm.h-1 at three replications. Soil samples were taken from a semi-arid region in west of Zanjan and placed into a flume with 0.4 m × 9 m in dimensions. Rill erodibility (Kr) was determined using the WEPP model at three artificial rills. The results showed that flow characteristics (velocity, discharge and shear stress) and rill erodibility were affected significantly by rainfall intensity (P

Study of turbulent flow and sediment transport pattern in rivers, especially erodible reach is utmost importance. With regard to the complex process of sedimentation and erosion in meander reach and significance role of the flow velocity and shear stress forces on river bank erosion, two-dimensional numerical modeling as CCHE2D was performed to simulate flow and sediment patterns of a meandering river reach located in the downstream of the Minab dam (Hormozgan province, Iran). Using topographic data obtained from field surveys and then the geometry model and the computational mesh (grid) with different dimensions and also field measurements of flow and sediment characteristics such as velocity, depth and suspended load, the two-dimensional hydrodynamic model was run. Simulated data were compared with observed ones in order to assess the velocity horizontal profile gradients, the distribution of shear stress and the flow depth condition, erosion and deposition in curved parts of the river channel. Furthermore, two statistical criteria (RMSE and MAPE) were used to evaluate the performance of the model. The results indicated that the simulated values are in good agreement with the field measurements. Also, results showed that simulating the flow pattern, by k-ε model has a better performance in predicting of turbulence closure areas in concave portions of the river bends than Eddy Viscosity model.

Investigation of sediment load, runoff, and evapotranspiration in watersheds is necessary for efficient use of soil, water resources, and design of appropriate management options. In this study, we used a SWAT model in Soltani basin at Baft to simulate runoff, actual evapotranspiration, and sediment load for two management scenarios during 1979 to 2012. The simulation results were evaluated using NS, R2 and BR2. For the calibration step, we obtained (0.74, 0.77, and 0.68) for runoff; (0.78, 0.81, and 0.69) for actual evapotranspiration; and (0.75, 0.73, and 0.66) for sediment load, respectively. The results indicated that, all three parameters were simulated quite well in calibration step. In validation step, were obtained (0.71, 0.7, and 0.59) for runoff; (0.74, 0.72, and 0.62) for actual evapotranspiration; and (0.68, 0.69, and 0.56) for sediment load, respectively. This again indicated a good performance of SWAT model. Two scenarios of land-use change and filter strips in the river banks, led to 7% and 38% reduction in sediment load, respectively.

Recognizing quality of groundwater as one of the most important and vulnerable sources of water supply in recent decades is a necessary and important issue. Water purification is sensitive and time consuming; therefore, investigation of the quality of groundwater supply is essential. In this research, in order to study chemical compounds of groundwater, 21 observed wells were sampled in the summer of 2013 year and important parameters of samples were measured and calculated for agricultural and drinking uses. Also Piper diagram was used to determine hydrochemical facies of the groundwater area. The results showed that dominant type of groundwater hydrochemical facies of region was calcium sulfate (Ca-S04). According to World Health Organization standard, among wells of region just H9, L15, O12, and L6C wells was suitable for drinking use and these wells in terms of sodium hazard and change of soil structure for agriculture use, had a good to admissible situation . Also, groundwater of that region had moderate permeability index; therefore, it should be used for soil irrigation with sufficient permeability and cultivation of salt tolerant plants.

Rocks in the nature have various resistance to erosion. Each one has different potential to erosion and sediment production. Knowledge of geological landforms is a suitable means to manage the watershed in combating erosion. This research has focused on geological formation of Hableh Rood Basin in North of Garmsar. The objective of this research is to prioritize the potential to erosion by rational, semi distribution and comparison with the amount of measured sediment from lithological units using rain simulator. First, field monitoring of geological formation and identification of 12 lithological groups have been carried out. Results of rain water simulator measurements and semi empirical models such as; PASIAC, EPM and semi distribution model of SWAT have been evaluated. Results show that PASIAC has in good agreements with measured sediment from sediment station. Also, Specific sediment yield from rain water simulator with one single rain event has suitable accuracy in the basin.

Cylindrical weir is one of the hydraulic structures used in open channels and reservoirs to regulate and control the water levels. Compared to the other shapes of structures, cylindrical weir has some advantages such as easy flowing of floating objects over it, simplicity of its design and construction, less loss, and greater discharge coefficient. Much work has been long done on the hydraulic of cylindrical weirs in non-roughness conditions. However, the effect of the roughness of the structure body that can affect discharge coefficient, flow loss, and formation of the critical depth as well as the characteristics of the boundary layer has received little attention and lack of comprehensive research on this is quite evident in previous studies. Therefore, in this study, the effect of roughness on the hydraulic of cylindrical weirs has been analyzed in details with different diameter, discharge and roughness in the laboratory and finally the obtained results was compared to other researchers. Experimental model is composed of full cylinder with three different diameters and four levels of roughness of PVC, 1.5, 3 and 4.5 mm for each diameter. The results show that for the same cylinder and with the equal flow rate, an increase in the roughness of surface of the weir from PVC to 4.5 mm, results in a reduction of discharge coefficient(cd) value around 10.7% and leads to an increase of energy loss about 22.3%. Moreover, it has been concluded that the critical depth formed about 78.8% closer to the crest. While the effect of roughness on the discharge coefficient in smaller diameters is more visible, the effect of roughness on energy loss doesn’t depend on the diameter of cylinder. Furthermore, there is a decreasing in cd and energy loss value with increasing of the cylinder diameter under the same surface roughness. By increasing of the inlet discharge, discharge coefficient increases and energy loss decreases and the distance of critical formation point from crest, increases. The achieved results regarding the dimensionless ratio of crest depth on the critical depth (Hcrest/Hc) is in conformity with the results achieved by Chanson and Montes`s research in the case of non-roughness.

In this study, hydrological indices variability due to land use change were assessed in the Marboreh watershed. In order to prepare land use maps, maximum likelihood method was used in the ENVI software. It was created land use scenarios based on land use maps and climate data. Then, after the SWAT calibration and validation, flow discharge data, and hydrological indices were simulated and extracted for each scenario, respectively. Statistical analysis carried out using Mann-Kendall and t-test for hydrological indices. The results of Mann-Kendall test showed that in the first scenario, hydrological indices related to high flow including high flow pulse duration, high flow pulses days per normal flow days and high flow pulses duration per high flow has decreasing trends at the 1% significance level. All indices (except maximum September flow, low flow pulses duration per low flow counts and high flow pulse count) in the second scenario, and high flow pulse count in the third scenario and also except maximum September flow in the fourth scenario, had decreasing trends at the 1 & 5% significance levels. The results of t-test revealed that minimum April flow and maximum September flow in the first scenario altered at the 5% significance level with scenario #2 and #4 scenarios, respectively. Low flow pulse count, low flow pulse duration, high flow pulse duration, low flow pulses days per normal flow days had altered between #1 and #4 scenarios, and high flow pulses days per normal flow days altered between #1 with #2 and #4 scenarios at the 1% significance level. Generally, the results of this study in the Marboreh watershed revealed that hydrological indices related to the minimum and maximum flows were decreased and increased due to land use changes, respectively. Also, impacts of land use change on hydrological indices related to the minimum flows was higher than hydrological indices related to the maximum flows.

Oak forests in the Zagros, west Iran, are suffering from severe unusual dieback phenomenon which has been developed throughout forest area. However, combating this event needs short terms measurements for return soil moisture in soil profile during dry seasons. The objective of this research was to evaluate the effect of runoff harvesting through micro-catchment. The research work was conducted in the Kalehzard site, Kermanshah, Iran. The treatments include a Crescent Shaped Bund Preservation (CSB), Preservation treatment (PT), Crescent Shaped Bund without Preservation CSB-P and Control treatment (CT), resulting in a total of 12 plots. Each plot measured 50 ×30 meters performed in September 2012. The ground cover was estimated using a 1 m2 quadrate and all dried trees was recorded within plots every year. Soil moisture was measured in three layers (10, 30 and 50 cm) using time domain reflectometry (TDR). Finally, all data statistically were analyzed using SAS6.12 software. The result explored that dieback ratio was 30%, while there was increased during second year in CT. The data from TDR showed that CSB significantly enhanced soil moisture and consequently attributes in re-vegetation of dried tree (19 tree/ha) as well as reduction in dieback (37 tree/ha) compared to control treatment. Although the preserved treatment affects severity of dieback, there only curtail tree mortality rate (38 tree/ha), while CSB-P had minimum effect on forest mortality (6 tree/ha) due to absence of protection measures. In addition, significant increasing of plant cover and plant litter was found via CSB and PT. It is concluded that CSB can be considered as the possible adapted measure combating Zagros forest mortality through drought tension and climate change.

Drought is one of the known environmental phenomenon and impartible part of change climate that occurs in each geographic region. In this study was used Standardized Precipitation Index (SPI) and streamflow drought index (SDI) for assessment and analysis of droughts incidence temporal. For this purpose, were used monthly statistics of 10 rain gauge and 5 hydrometric stations in Karkheh watershed and indicators investigated in 3 timeframes (12, 24, 48 months). At the first, relationship of precipitation and runoff investigated for drought effect study on surface water resources. Then the standardized data rate (SDI) with SPI time series at varies temporal interval using Pearson correlation was studied in the whole of basin and sub basin also compared separately. The results showed that temporal relationship of hydrological and meteorological drought occurrence is meaningful in level of 99 % with together and this correlation is maximum in 48 months. Drought occurrence in case study showed its effect on surface water resources with a delay of 2 months or 1 month that due to the karstic region.

Dust storm is a stochastical event that depends on several parameters, therefore, multivariate analysis of this event is really important. In this study, importance and shortage of multivariate analysis of natural disasters such as dust storm is investigated. For this purpose, Copula theory is used for bivariate analysis of dust storm. Copulas function are useful tools for multivariate frequency analysis of natural disasters. One of the main advantages of Copula theory is that there is no limit to select the type of marginal distribution. In order to perform bivariate analysis of dust storm, severe dust storm was selected based on definition of WMO from 1982 to 2014 in Yazd province. 34 dust storm events were extracted and maximum wind speed and geopotential heights were determined corresponding to stormy days. Finally, the bivariate return period was calculated based on maximum wind speed and geopotential height using the t-student Copula as the best function. Also, univariate return period of dust storm was calculated based on maximum wind speed and geopotential height, separately for comparison with bivariate return period. The results showed bivariate analysis of return period of dust storm is more accurate than univariate return period.

Flood spreading on the conical sections that located at the existing openings flood way in the aquiferous area of dry and semi dry zone with purpose of savings floodwater is a suitable way for utility of dry rivers, seasoning river(ephemeral) and extra flow of perennial rivers. Identification of suitable location for flood spreading and penetrating it in the undergrounds water is one of the most important steps in these kinds of projects. The purpose of this research is finding the location of flood spreading in the Padva aquiferous domain for preserving water subterranean canal, well and spring at the dry zone with the multi critical sitting evaluation techniques for overcoming with drought crisis. Therefore, Padva aquiferous domain in the west Bam with 7692-hectare area was selected. In this research, the spatial economical factors such as; vicinity to the road, fault, subterranean canal, well and river with these factors are analyzed with new techniques: gradient, geology, geomorphology and lands efficiency, so that in the multi_critical sitting evaluation way, these factor with the phases value are standardized. Weight of factors is also identifying with various ways such as, ranking. At the next step combination of layers with designing of tree shaped was done in the ILWIS software and the result was: index plan combined with phase value from 0 to 1 as a result suitable area of flood spreading with the value around 1 is equivalent 5626/58 hectare and include 75/64 percent of domain measurement. For elevation this way, the index plan combined with design plan flood spreading carried out and gave in the cutting zone which this had suitable overlapping with carried out flood spreading plan, therefore the usage of above way for exact and fast identification of flood spreading for similar zone in the country is advised.

In this study, Probable Maximum Precipitation (PMP) and the corresponding return period were estimated. Then HEC-HMS model was calibrated to estimate the characteristics of the PMF in the Eskandari watershed, branch of Zayandehroud River. Firstly, using Hirschfield method and statistical distribution, maximum 24-hour rainfall amounts in different return periods were determined as well as PMP. Then, the next step by using two events with the best model efficiency coefficient, HEC-HMS model calibrated and then the model evaluated by two various other events and was obtained acceptable results. Also, the estimation of PMF characteristics showed that precipitation of 240.6 mm and 596374 year return period can generate flood peak of 3079.5 m3/s and volume of 178.1 Mm3.