مجله تحقیقات آب و خاک ایران
سال چهل و پنجم شماره 1 (پیاپی 16، فروردین و اردیبهشت 1393)

A large number of authors have studied to find out how to control scouring around a pier along direct stream. The objective of this research is then to study a scour pattern around such piers on curves rivers due to the fact that there may be a difference between a flow pattern on a direct line and the meander. Thus, this study tries to check whether the use of cable and collar alone and in a combination of cable and collar affects scouring around bridge pier group constructed on rivers meander. In this study two thickness of cable 0.2D and 0.4D and three steps 0.2D, 0.5D and D are used. The results showed that more scouring depth is decrease as a cable diameter increases and the pitch of helix decrease. About pier groups that are in the direction of water flow, scour depth for first pier is more than single pier, that represents increase of reinforcing phenomenon, also scouring depth for middle and back piers due to sheltering phenomenon, is less than single pier. About piers perpendicular to the flow direction, the maximum scour depth is observed in middle pier, also at this case scour depth is reduced by increasing distance between piers. Using collar is more effective than cable for small distances between piers. Also it is found that using a combination of cable and collar results the most reduction in scoring depth.

Application of outflow water from treatment plants for irrigation as a non-usual water resource is being developed due to the lack of usual water resources in Iran. Activated carbon as a conditioner in water treatment procedures causes undesired changes in hydraulic properties of porous media and soil degradation. In this paper, the effects of activated carbon concentration on hydrodynamic properties of a sand soil were studied through a physical modeling activity. Variation of saturated hydraulic conductivity, bulk density and porosity of the sand was measured for two categorical tests. First, for the flowing of fresh water through a soil-carbon mixture with 1 to 7 mass percent and the other for the mixture of water-carbon with 0.5 to 2 mass percent through the sand. The results showed that the saturated hydraulic conductivity of sand decrease 80 percent due to mixture of 7 percent sand-carbon and reduced from 0.06 cm/s to 0.014 cm/s, porosity was reduced from 0.44 to 0.426 and bulk density was increased from 1.5 to 1.507 g/cm3. Also, reduction of 91.5% and 6% for saturated hydraulic conductivity and porosity, respectively and an increase of 0.71% in bulk density were observed due to flowing water-carbon through the sand column with concentration of 2%.

Modeling in arid regions to better manage water resources is very important. Groundwater is an important water resource in arid regions. The purpose of this study was to assess the performance of adaptive neuro fuzzy inference (ANFIS) and time series models to predict the water table. In this study, groundwater levels of Shiraz plain for one month ahead were forecasted by using time series models and ANFIS model. In the ANFIS model has been used Gamma and M-test for determine of the optimal input combination and training and testing data length. Performance of different models was compared with the parameters of the error and Taylor diagrams. ANFIS model results showed that this model with membership function of Π-shaped has better performance than the rest of membership functions. Performance comparison of the models indicated very suitable performance of the ARIMA (2, 1, 2) model than ANFIS models with different membership functions.

The assumptions considered in developing the Saint-Venant equations limit their application in many practical situations. The modified Boussinesq equation was presented to overcome the limitation imposed by Saint-Venant equation due to the presence of non-hydrostatic pressure distribution and steep slope. In this paper a computational model was developed for solving the modified and the traditional Boussinesq equations for unsteady flow condition. Verification of the numerical results was accomplished by compiled discharge experimental data in the range 7 and 30 l/s. The relative errors associated with the results of both equations were calculated. The average relative errors were 4 and 18 percent respectively for the modified Boussineq and the traditional one in predicting discharge. This highlighted the importance of the slope impact on the accuracy of the results. Also, the modified equation is able to produce the stage-dischrge relationship for trapezoidal weir with high accuracy.

In this study, Hydraulic properties of low pressure drip irrigation systems were studied under laboratory conditions and using of the pipes that exist in Iran. Therefore, effect of various heads from 0.45 to 1.8m was evaluated for lateral pipe with outside diameter 32mm and length of 16, 30, 60 and also the lateral pipe with length 16 and outside diameter of 16, 20, 25 and 32mm, on hydraulic characteristics consist of average emitter discharge, variation coefficient, uniformity and loss. Emitters used in this study were micro-tube with length of 0.7m and outside diameter of 3mm that inserted to the lateral at 1m intervals. Results showed low pressure trickle irrigation system supplied necessary discharge in all of the lateral length and diameters to the end of it. Moreover, examine effect of lateral length and diameter on emitter coefficient uniformity indicated that desirable uniformity obtain in the lateral with length of 89m and outside diameter of 16mm and also the least head.

Dry drainage could be considered as a natural system which evaporates water from fallow areas to control water table depth and soil salinity in neighboring cropped area. The technique requires the retirement of part of the irrigated land. One of the most notable design criteria for this system is to estimate the ratio of cropped to fallow Strip width. A Plexiglas physical model with the dimensions of 60 cm length, 20 cm width and 50 cm height designed and built. The model was divided into two equal parts in which the first half was regularly irrigated while the other left fallow during the test. A précised scale was used to measure the evaporation. The minimum evaporation rate was 2.7 mm per day when the soil was mainly covered with salt crusts. As this measured value is close to the common drainage coefficient in most parts, hence with a low risk, the ratio of 50% fallow area to 50% cropping was recommended. It seems however, that with a good management and salt scraping one can expect a higher ratio of cropped to non-cropped ratio.

Up to now, different methods have been applied to calibrate electromagnetic induction data. Therefore, at present research, we applied multi-linear regression (MLR) and artificial intelligence techniques (i.e. ANFIS, GA, ANNs) to calibrate the apparent electrical conductivity (ECa)- measured using an electromagnetic induction instrument and electrical conductivity (ECe)- measured in saturation paste. 600 soil samples collected from Ardakan in central Iran and divided into two subsets for calibration (80%) and testing (20%) of the models. To evaluate models, some evaluation parameters such as root mean square, average error and coefficient of determination were used. Results showed that the ANFIS model gives better estimation than the other techniques whereas this model increased accuracy of predictions about 9, 9, 5 and 2% for EC15, EC30, EC60, and EC100, respectability. Higher performance of ANFIS to predict soil salinity might be because of uncertainty. After ANFIS model, GA and ANN had better accuracy than multivariate regression. As a whole, results indicated that artificial intelligence methods had higher performance than regression technique to calibrate electromagnetic induction data.

Salinization and alkalization are the most problem in the arid and semi-arid regions, where precipitation is low than evapotranspiration. Under such a climatic condition, soluble salts are accumulated in the soil, which cause lessening of the soil productivity and fertility. So, the identification of the salt affected areas is essential for sustainable soil management. The specific objective of this research is mapping of saline soils by the Hyperion EO-1 satellite images in the Uremia Plain. In this study, spectra responses of the 40 saline soil samples were conducted by the Spectroradiometer Fieldspace 3 and Hyperion image in order to mapping of the soil salinity was acquired from the United State geological survey (USGS) archives. Results indicated a significant correlation (R2= 0.89) between Soil saline Content (SSC) and reflectance percent at the 42 and 219 bands. A soil salinity spectral index (SSI) was constructed from Continuum Removed Reflectance (CR-Reflectance) at 0.762 and 2.345 micrometers. Then, a model for estimation of SSC with SSI was constructed using univariate regression. Model validation yielded a Root Mean Square Error (RMSE) of 1.23 ms/cm and an R2= 0.8. The model was calibrated with a Hyperion reflectance image, on a pixel-by-pixel basis, and reasonable agreements with overall accuracy of 75% and Kappa Coefficient of 0.65. The findings of this project suggest that the satellite hyperspectral data have potential for predicting SSC in this study area.

Rainfall erosion processes a long with the rainfall characteristics can be affected by soil properties. The study was conducted to investigate the susceptibility of the aggregates in different soil textures to the rainfall erosion processes. The experiment was done on thirty soil samples recognized in four soil textures with different replications as the completely randomized design. Ninety boxes were filled with aggregates (6-8 mm) and were exposed to the simulated rainfall for 30 minutes. Results indicated that there were significant differences among different soil textures in the aggregate breakdown (P< 0.001), soil compaction (P< 0.001), and soil particles splash (P< 0.01). The highest aggregate breakdown was observed in sandy loam soils, whereas the highest soil compaction and soil particles splash occurred in clay loam soils. The aggregate breakdown was significantly affected by silt particles (r= -0.63, P<0.01) and clay particles (r= -0.70, P<0.01). Nevertheless, the soil compaction and particles splash were significantly increased by silt and clay particles. Sand contrary to other soil particles (silt and clay) had different effect on the rainfall erosion processes.

Soil colloid particles influence soil chemical and physical properties by their surface electrical charge. With respect to the importance of this issue from both agricultural and environmental points of view, charging behavior of a kaolinite sample was studied in the pH range of 4 to 10 and at three background electrolyte concentrations, including 0.005, 0.05, 0.5 M NaCl, by potentiometric titration. Using a combination of mass and electrolyte titrations, kaolinite point of zero charge (PZC) was determined to be at pH=7.6. Increase in pH from the initial value of 4 caused at first a gradual decrease in positive surface charge and then a gradual increase in negative surface charge, indicating a net positive surface charge at pHPZC. Increase in ionic strength reduced positive surface charge at pHPZC. The adverse effect of ionic strength on the surface charge at pH Keywords: adsorption, ion, exchange, point of zero charge, surface charge