نشریه پژوهش های حفاظت آب و خاک
سال هفدهم شماره 4 (زمستان 1389)

In this study, the effect of flow depth on water content and solute distribution was assessed in furrow irrigation. Two series of field experiments including small and large scale furrow experiments were conducted. In large scale, four experiments were carried out. One experiment was conducted under free-draining (FD) conditions in which bromide was applied during the entire irrigation event and three experiments were carried out in blocked-end furrows in which bromide was injected either during the entire irrigation event (100%), the first half of the irrigation (FH), and the second half of the irrigation (SH) event. In small scale, five field experiments were conducted on short blocked-end furrows. Three experiments were carried out, each with the same duration but with different amounts of water and solutes resulting from 6, 10, and 14 cm furrow water depths. Two more experiments were performed with the same amounts of applied water and solute and, consequently, different durations, on furrows with depths of 6 and 10 cm of water. Soil water contents at different times and locations in furrow cross-section were measured with neutron probe tubes and TDR. Soil samples for bromide analysis and gravimetric soil water contents from all the experiments were collected at different depths up to 1.80 m, 5 days after the irrigation at three locations near the inlet, in the middle, and close to the outlet of the experimental furrows. Results in large scale experiments showed substantial non-uniformity in solute distribution along the monitored furrows, with the degree of non-uniformity depending upon flow depth and solute application time. The effects of flow depth and irrigation/bromide application time on soil water contents were more pronounced in the soil surface layers and were found to be relatively minor at deeper depths. Water and solute deep percolation rates also showed dependency to flow depth and solute application/opportunity time and gradually decreased along the furrows. In small scale experiments, results showed that both the water level and the duration played an important role in distributing water and solutes in the soil profile. A positive correlation was found between water level and infiltrated amount of water or solute. Irrigation with the 14 cm water level and short application time improved the distribution of water and solutes within the soil profiles, while also causing relatively less deep percolation of water and solutes as compared to low and moderate water levels and relatively long duration times.

The uncontrolled groundwater extraction, low precipitation and falling water table depth cause a modification of natural flow systems and induce seawater intrusion from the coast finally resulting in the groundwater quality deterioration. The principal aim of this study is to determine the extent of seawater intrusion in the aquifer, characterize the hydrochemistry of the Ghalghachi aquifer, and identifying the main processes that occur in the system. In order to achieve this aim, chemical parameters of the area during May and September 2006 were measured, such as electrical conductivity, pH, anions and cations concentrations. In this study, the seawater intrusion or salinization in a coastal aquifer was evaluated using groundwater chemistry data, ionic ratios and calculation of indices. A large proportion of the groundwater is classified as Na-Cl, Ca-HCO3 and Ca-Cl types. The Na-Cl types represent effects of seawater intrusion. Major ionic compositions effectively indicated effects of the seawater intrusion and especially Cl and EC are the simplest indicators for the salinization process. The Cl concentrations and EC levels are highly positively associated. Lower ratios of Na/Cl and SO4/Cl than the seawater ratios indicated the seawater encroachment. The analytical results obtained in the hydrochemistry study were interpreted using ion correlations with chloride, and calculations of the saturation indices (SI) and ionic deviations (Δ). The results of calculation of the saturation indexes (SI) and ionic deviations for cation of coastal groundwater showed that the saturation index for carbonate minerals is positive and for sulfate minerals is negative. The ΔNa+ is usually negative and the ΔCa2+ and ΔMg2+ are positive and samples plot below the mixture line and seawater intrusion in the aquifer. The most remarkable process was found to be the inverse cation exchange.

Nowadays it is very important in watershed management to consider the participation of people particularly ranchers in rangeland restoration. It seems that for greater participation of ranchers in vegetation restoration it is necessary to consider people needs, provide inputs and financial supports, education and extension, and control, monitoring, and supervising of projects. The aim of this study is to assess the role of support services and extension on the participation of ranchers in rangeland restoration projects in mountain rangelands of Baladeh in Mazandaran. Statistical population includes 102 ranches, of them 72 ranches were sampled where rangeland restoration projects were performed at least for three years. Each ranch is a defined area of rangeland used by a number of ranchers for raising livestock. The sampling was done using questionnaire in random-stratified method. Result of this study showed that there was a significant relationship between ranchers` participation and support services and extension of ranchers in rangeland restoration, soil and water conservation. Also we found that as the number of ranchers increased in each ranch there was a decrease in support services such as inputs, financial supports, education, and extension. There was not a significant relationship between the number of ranchers in each ranch and the control and monitoring services. Finally the result of this study showed that in many ranches the support services and extension are not enough to support the success of rangeland restoration projects.

Discharge missing data, is an important challenge facing water resource project designers and hydrologists, as it leads to error in design studies and implementations with enormous financial and safety considerations. When the number of hydrometric stations is limited in an area of concern, this challenge becomes more serious. Therefore, this data needs to be completed statistically for practical purposes. Several methods have been proposed for predicting such missing data. In this article, fuzzy linear regression is compared with simple linear regression, multi-linear regression, graphical method and normal ratio method, for reconstruction of annual discharge data in Great Karoon river basin in south-west Iran. For this purpose, observational discharge data from 27 stations in a set of 11 groups were analyzed. By deliberate exclusion of real annual data for each station, the excluded data was reconstructed using the above methods and the error in calculation was measured using RMSE index which was found to be 17.41, 16.05, 21.00, 119.60 and 17.60, respectively. Hence, simple linear regression was found to be the superior method for reconstruction of annual discharge data for this basin. Fuzzy linear regression was also shown to be the second most appropriate method in this regard.

Evapotranspiration is one of the most important parts of water cycle in the nature but, the measurement of actual evapotranspiration (via Lysimeter as an exact measurement instrument) is so difficult and not practical. Therefore, equations that can estimate the value of evapotranspiration only by using meteorological data are necessary. In this study, four different reference crop evapotranspiration of Penman-Montith FAO56 (PMF56), Penman-Montith FAO with Irmak Radiation (PMFI), Jensen-Hais1 (JH1) and Jensen-Hais2 (JH2) have been assessed in a semi-arid climate of Iran to estimate the ETo. The investigations showed that, when the data of radiation, temperature and wind changed by 5% and 10%, the radiation was more effective than other parameters. Therefore to calculate the short wave radiation, radiation models of Angstrom, Sabbagh, Gelever-Mc Culoch and Black have been used. Calibration of obtained results with data of three weighting microlysimeter during the growing season (May to October) duration 95 days by using different statistical parameter such as coefficient of determination (R2), Root mean square error (RMSE), Mean bios error (MBE) and t-test criteria of 0.781, 0.625, 0.038 and 0.468 respectively, indicated that PMF56 model with radiation models of Angstrom is the best model for estimation of reference evapotranspiration and the models of JH1 and PMFI have low exactness for this climate. The finding of the present research reveal that in all investigated evapotranspiration models, the models that used Angstrom radiation have high accuracy and radiation models of Sabbagh, Gelever-Mc Culoch and Black are in next orders.

Use of unsuitable tillage practices and undesirable tillage tools has resulted to soil physical erosion and reduction in its fertility. In order to investigate the effect of different tillage methods on soil physical properties in wheat-fallow rotation, a study was conducted in a rainfed subtropical farm in Gachsaran in a factorial-based RCB design with 4 replications and 5 treatments for 3 years. Treatments consisted of A (Chisel plow +Disk harrow + Grain drill), B (Non moldboard plow +Disk harrow + Grain drill), C (Power harrow + Grain drill), D (Sweep + Disk harrow + Grain drill), E or control (Moldboard plow + Hand broadcasting seed and fertilizer + Sweep). The results showed that the effects of depth, treatment and their interaction effects on soil bulk density were significant at 0.01 level. Also, the effects of depth at two stages and the effect of treatment and their interaction at flowering stage on soil moisture were significant at 5% level. Although tillage methods E and D had the lowest effect on soil bulk density (1.49 gr/cm-3), but the lowest soil compaction was observed in the 0-10 cm layer by using chisel plow (1.37 gr/cm-3). Study of treatment effect at flowering stage on soil moisture showed that E and D treatments had the highest and the lowest values, respectively. However, toward the end of cropping season and at the ripening stage, maximum humidity was recorded (8.8%) for A treatment (Chisel plow +Disk harrow + Grain drill) and minimum humidity (8.2%) was observed for E treatment (Moldboard plow + Hand broadcasting seed and fertilizer + Sweep). Considering these results, we can conclude that A method could maintain more humidity in soil. Based on the results, tillage method A (Chisel Plow + Disk harrow) compared to E method resulted in an increase in soil relative humidity in 0-40 cm layer up to 7.3%. Therefore, it could be recommended for subtropical climate of Iran and similar regions.

The effect of land use type on soil functioning within an ecosystem can be assessed and monitored using soil quality attributes. Such studies, which are carried out to create a balance between the biological production and the maintenance and improvement of land resource quality, provide a framework for land degradation control and also for identification of sustainable management. In order to study the effects of different land uses on soil quality indicators, a loess hillslope was selected in eastern Golestan Province, Agh-Su area. Four profiles in four land uses including pasture; Quercuse natural forest; Cupressus artificial forest and a cultivated land, were dug and studied. Important physical, chemical and biological soil quality indicators such as bulk density, mean weight diameter, organic carbon, cation exchange capacity, available P, biomass carbon and microbial respiration were compared in land uses. Description ِof soil profiles in study area revealed that Quercuse natural forest soils were classified as Calcic Argixerolls, cultivated soils as Typic Calcixerepts and pasture and Cuprecuse soils as Typic Calcixerolls. The results revealed that cultivation has led to decrease of studied soil quality. Organic matter, CEC and MWD in the forest and pasture area were significantly higher than that of cultivated land use. The mean weighted diameter of aggregates varied between 2. 36 mm in Quercuse natural forest and 0. 54 mm in cultivated land use. This investigation showed the efficiency of soil quality studies for the evaluation of present conditions of soil in agricultural and natural ecosystems.

Evaporation is one of the important problems in hydrology and water resources engineering, which is attracted by many researchers. The evaporation from water storage system causes the water loss, increases the concentration of salts and reduces the water quality. Use of heavy alcohols and floating coatings can reduces the evaporation, and salt concentration during dry seasons. In this study, octadecanol and hegzadecanol alcohols (C18H33OH and C16H37OH respectively) and mixture of alcohols equivalent to 20 and 40 gL-1 were used. These alcohols were dissolved in ethanol prior to application. The first step of the concentration of 20 gha-1 and the second phase, the concentration of 40 gha-1, were used. In this study in addition of alcohols polystyrene with two different thickness (1.5 and 5 cm) and magnetic water were used as physical approach for reducing the evaporation from water surface. The water level was measured in 2 stages within 38 days. Then the daily evaporation was measured and the statistical results were obtained using SPSS software. There are significant differences between treatments, in the 5% significant level, on the base of Duncan comparison test. Results showed that the physical and chemical methods, can reduce the amount of evaporation up to 30-55% and 40-55%, respectively.

In this paper, spinning rate of sediment particle during saltation in turbulent flow was measured by means of high speed photography technique. Experiments have been carried out for different hydraulic conditions, particle sizes and densities. Particle spin was measured in five stage of saltation step by analyzing and processing picture taken at 250 frame per seconds. The results showed that increasing turbulence parameter of flow will cause increase in angular velocity and under the same flow condition, particles with larger sizes and specific gravities spin more rapidly.

Tillage practices during several years will result in an unleveled soil surface on farms. At present, in most regions of Iran, land leveling operations on farms are performed by conventional levelers and this leveling method does not have high accuracy. In this study, for the first time in Ahwaz city in south west of Iran, Miskin laser leveler and conventional leveler (Deghat Kesht Shiraz Leveler) were compared from technical aspects. This study was conducted in agronomic year of 2008-2009 on a farm with soil texture of clay loam in Albaji village which is located 10 km north of Ahwaz in Khuzestan province. Measured factors were water consumption volume, leveling index (LI) and land leveling uniformity coefficient (LUC). Research in the field of land leveling methods needs plots with large area, because in large areas, the leveling accuracy of leveler machines can be measured and compared correctly. Thus, our experimental farm included 14 plots, each one hectare. Statistical method for analysis was T-Student with two treatments (leveling by laser and conventional levelers) and seven replications. Statistical analysis was done by SPSS software. Results of mean comparison indicated that there is a significant difference at 1% level between laser leveler and conventional leveler for water consumption volume. Laser leveler reduced irrigation time about 35% as compared with conventional leveler. Therefore, application of laser leveler decreased water consumption volume about 82 lit/s. Leveling index in laser leveler was closer to zero in comparison to conventional leveler. On the other hand, the value of this index for laser leveling was more acceptable and suitable than conventional leveling. Also, LUC value for laser leveling was closer to one in comparison with conventional leveling. Thus, LUC value of laser leveler was better and higher than conventional leveler. Generally, regarding the obtained results in this study, application of laser leveler instead of conventional leveler can be recommended for leveling agricultural lands in Ahwaz.

Great difference of flow depth and Manning's roughness coefficients in main channels and floodplains, generate a strong gradient of lateral velocity and hence, a lateral shear stress in the interface of the main channel and floodplain. This phenomenon increases the head loss in river system. Mathematical models which are currently used for water surface profile computations in rivers, e.g. HEC-RAS and MIKE11, neglect this mechanism. For taking into account this mechanism, the energy slope and energy correction factor should be modified in gradually varied flow computations. In this paper, using exchange discharge method, the current procedure of gradually varied flow computations were modified for compound channels. Comparison of this method and HEC-RAS results in an experimental flume with heterogeneous compound section in case of drawdown profile, M2, showed that the accuracy of these methods are 95 and 84.5%, respectively.

In this research, grazing effect on ecosystem function has been analyzed at different distances from water point to identify critical area. In 338 plots of the size 2×2 meter that were plotted in 8 main directions from 3 selected water points, 11 soil surface indices were estimated based on LFA method. Then soil stability, infiltration and nutrient cycle functional attributes have been evaluated by 11 soil surface indices. MANOVA and correlation analysis showed that functional attributes were not significant in 8 main directions (P<0/01) but they were significant with distance from water point (P<0/01) and ecosystem function increased with distance from water point. Duncan results showed that grazing intensity in close proximity to water point has been induced a critical area in 200 m from water point.

In order to investigate rangelands erodibility erodibility and sediment yield, a part of Segzi-Kuhpayeh subcatchment located in Zayandeh-Roud Drainage Basin was chosen. In this land use unit, field rainfall simulator for production of runoff and sediment and measuring sediment yield was used. Erodibility was estimated using K-factor in USLE model. For investigating effective factors in sediment production and erodibility, soils were sampled adjacent to each rainfall simulator plot and some of physical and chemical parameters of soils were measured and analyzed. According to the results, erodibility was relatively low in these lands (mean K value is 0.23 t.h/ MJ.mm) which can be related to coarse grained texture of the soils. According to the results of regression models and correlation coefficients, silt, very fine sand, silt+very fine sand, moisture and calcium carbonate parameters have the highest effect on sediment production and erodibility.