Iranian Journal of Soil and Water Research
Year:2008 | Volume:39 | Issue:1|Papers Count:15

Numerous models have been developed in the past decades to explain the complicated earth dams' berach phenomena. These have included physical as well as mathematical and computer models. Among the more widely used dam breach computer models over decades is the BREACH model. It is based upon erosion and soil mechanics equations, hydraulic and sediment transport laws. The difficulty in gathering data motivates one to use other powerful methods. In this study a new method has been developed for prediction of peak breach outflow and breach time through Artificial Neural Networks (ANNs). Toward this end, synthetic breach parameters of about 115 dams were developed by BREACH model, and then employed to train and test the neural networks. The performance of the network model is investigated through a change of input parameters. A most efficient and global model for assessing a dam breach potential is presented. Later, the most significant input parameters affecting dam breach are investigated. Best results were found with back propagation neural network using multiple hidden layers. The most compatible structure for breach outflow prediction possesses the correlation coefficients of 0.992 and 0.909 for training and testing, respectively. As for breach time, a structure was obtained with the correlation coefficients of 0.993 and 0.884 for training and testing, respectively. A forecast study was performed for the case of Mollasadra Dam. Comparisons between the artificial neural network results and dam BREACH model were made, the results indicating that neural networks are appropriate for predicting dam breach parameters.

As a result of fast population growth, natural land covers, especially forests, are being degraded by humans because of getting dedicated to crop production. Release of large amounts of carbon and greenhouse gases is an unfavorable result of natural land use change. For a study of the changes in different soil quality attributes, loessial hillslope of eastern Golestan Province, Agh-Su Watershed, was selected. An estimate of about two hundred soil samples were taken from surface (0-30 cm) and subsurface (30-100 cm) layers of lands with two different kinds of land uses, namely forest and adjacent cultivated land. The study showed that long-term tillage practices had resulted in change of soil texture from silty clay loam to silty loam, the latter being very susceptible to further erosion. The change is related to a loss of clay particles as a result of the previous erosions. Severe changes in soil texture and an increase in the amount of silt particles in subsurface layers are also quite conspicuous. This change can indirectly affect such other soil quality parameters as organic matter. Mean weight diameter of aggregates decreased from 1.49 mm in forest to 0.88 mm in adjacent cultivated land areas. Bulk density is increased while infiltration rate reduced by about fifty percent due to a degradation of soil structure and the resulting compaction. A reduction in the amount of annual organic matter return into soil as a result of deforestation and its subsequent weak physical protection of organic matter were responsible for a decrease in the amount of organic carbon and total nitrogen by 70%.Consequently a microbial respiration decrease from 0.19 mg C02/g day to 0.1 0 in deforested areas. Changes in soil quality attributes were not observed to be significant in different slope positions of forested areas due to stability of the landscape. The effect of different slope positions on soil quality attributes is more significantly pronounced in cultivated areas than in forest lands.

The control of hydraulic jump through thin-crested sills in a trapezoidal channel was studied theoretically as well as experimentally. The experiments were conducted in a specially designed stilling basin for 1:1 side slope. The results show that for a given side slope, end sill increases the stability of the jump within the stilling basin. It also causes a 13-15 percent reduction in the length of jump and negligible changes of the sequent depth as compared with the jumps occurring in a trapezoidal section with no sill. Finally, a relationship has been proposed for the design of the height and for the location of the sill to control the jump for a wide range of conditions.

Soil quality has been defined as "the capacity of a soil to function within ecosystem and land use boundaries, to sustain biological productivity, maintain environmental quality, and promote plant as well as animal health". Its assessment is needed to improve sustainable soil management. Since soil quality can't be measured directly, it must be inferred from quality related indicators, which are measurable soil properties. The objectives of this research are: I) to identify a factor of quantitative assessment of soil quality, namely soil physical quality index (S) and II) to predict the S index by using, Pedo-transfer functions along with some conveniently measurable soil properties. Some physical and chemical properties of 84 soil samples (27 samples saline and 57 ones calcareous), such as particle size distribution, organic matter, bulk density, carbonates (CaC03), Electrical Conductivity (EC), and Sodium Adsorption Ratio (SAR) were assessed. Also soils' moisture retention curves were plotted at 0, 2.5, 5.5, 10, 20, 30, 50, 100, 200, 300, 500, 1000 kpa pressure heads. The parameters of Van Genuchten equation (1980), through a use of ROSSET A software, as well as the slope of moisture retention curve, at the inflection point, were determined. The slope of the curve was considered as soil physical quality index (S). Regression was established between this index and the conveniently measurable soil properties through a use of Pedo-transfer functions and an employment of SPSS software. The results showed that there is a significant correlation existing S index and the percentage of clay, silt and carbonates in saline, calcareous as well as in all data set (p=0.01). Also a significant correlation existed between S index and bulk density in saline and calcareous soils shown at 5 and 1% level, respectively. The results finally indicated a strong regression relationship between calculated S obtained from moisture retention curve and S predicted from conveniently measurable properties. Correlation coefficients between the two were 0.855, 0.920, and 0.919 in saline, calcareous, and all data set, respectively.

Finding the meteorological parameters' and drought indices' relationship with barley yield through an employment of Artificial Neural Network was the main objective of the present research work. To achieve the objective, such meteorological parameters as: precipitation; averages of maximum and minimum temperatures; mean average temperature; sumation of temperature recordings exceeding 10oc; evaporation; water vapor pressure; average wind speed, as well as sunshine were taken into account. Such drought indices as: Percent Normal Index, Standard Index of Annual Precipitation, Hydrothermal Index, Nguyen Index, Transeau Index, Standardized Precipitation Index, Shashko Moisture Drought Index and Rainfall Anormaly Index obtained from Tabriz and Miane meteorological stations were evaluated in terms of normality as well as their mutual influences. Optimum ANN models between barely yield and the above mentioned climatic parameters and drought indexes were obtained. Among the proposed models, the one with five input parameters (Rainfall Anomaly Index, Transeau Index, SP124, Sunshine, and the average of minimum temperatures) for Tabriz station with 30 years of data was found out to be the most suitable model. The results of the study indicated that drought indexes, Nguyen Index, Transeau Index, Rainfall Anomaly Index, and Standardized Precipitation Index (SPI24) bear the highest correlation with barely yield. Due to a high determination coefficient of. the optimum model concluded in this research, ANN model is recommended for monitoring and predicting agricultural drought.

Accumulation of secondary calcium carbonates in arid and semiarid regions is a valuable tool in evaluating the degree of soil evolution, soil age, paleoenvironmental reconstruction, soil classification as well as land use. In addition, laminated pedogenic calcium carbonate coatings can provide some evidence regarding local environmental and climatic changes. In this study, pedogenic calcium carbonate coatings from southern Alborz mountains were investigated. Based on a reconnaissance survey, previous field observations and topographic maps, a transect of 10 soil profiles was selected to demonstrate the variation in physiography, land use and parent material in Takestan region, Iran. These profiles were sampled using standard techniques and then described and classified according to norms in soil taxonomy. Disturbed samples were analysed physico-chemically while undisturbed and oriented ones used for making thin sections. According to micromorphic studies, pedogenic calcium carbonate coatings were classified in the four following categories: 1) Typic Coatings, being formed as a result of super saturation of soil solution with carbonates, mostly occuring in the underside of skeletal grains, peds and void faces. Typic coatings were subdivided into three types. The first type is limpid, light monolayer calcitic coatings, composed of micritic calcite that thoroughly covers skeletal grains, like the first type, and additionally has sequences of light and dark colored lamina. Another type namely the 3rd occurs on the underside of coarse fragments, where the downward growth of calcium carbonate appears restricted by contact with the soil matrix. These coatings are either two or multilayered too. 2) The second form is carbonatic pendants; occurs as mammillary to botryoidally stalactite-like masses (segregations), which either emanate from the bottom of carbonate coats or occur on the bottoms of coarse fragments. Pendants are multi layered and composed of two to five light and dark colored layers, indicating the differences in conditions of calcite precipitation. 3) Needle-fiber calcite is the third form of coatings, which occurs in some depths near the soil surface or in upper layers of calcic horizons. This shape probably forms as a result of decomposition of in voids plant residues and of settlement of the Ca-containing components of cell walls, and also of the calcification of dead plant roots. 4) Finally, the forth form is Cappings which have the same morphology as pendants, but in contrast to pendants, occur in the upper side of coarse fragments. Pendants and Typic coatings composed of sequences of light and dark colored lamminea can represent probable climatic changes. Light colored lamminea with relatively pure calcite, have been precipitated in dry periods when climatic conditions heve not been favorable for biological activities, whereas, the dark colored lamina, composed of calcite and some organic mixed materials have been formed in relatively wet periods when climatic conditions have been fit for biological activities. Thus, the sequence of light and dark colored lamminea can bee employed as a useful tool for paleoclimatic and paleoenvironmental studies.

A recognition of appropriate soil erosion control methods along with the use of convenient alternatives in erosion control are necessary for a proper management of natural resources. Run off control through polymers is one of the new methods employed in reducing soil erosion. This research was conducted to evaluate the effects of a polymer, called anionic polyacrylamide, on soil infiltarion rate. A factorial experiment based on a compelelty randomised design including the treatments of polymer at 0, 5, 10, and 15 mg/kg, and the final soil infilatration rates (in field and in the laboratory) in five replications was adopted. Data were ana lysed for an evaluation of the main and interaction effects in homogenous agricultural soils, using SPSS. The resutls indicated that using polyacrylamide at a concetration of 10 mg/kg has an optimal effect on increasing the final infiltartion rate in both field and laboratory conditions. In addition, in an evaluation of the initial infiltration rate, while employing the double ring method in the field along with polyacrylamide containing water, indicated that the polymer at a 10 mg/kg concentration has an optimal effect on enahncing the initial infiltration rate.

Chromium is among the metals that, due to its particular specifications, has numerous applications in various fields of industries and its use in industry is steadily on the increas. Widspread use of this metal has been accompanied by its increased release into environment, entailing numerous environmental hazards. In this research the effect of organic adsorbents was investigated on hexavalent chromium adsorption from soils cotaminated through leather tanning industries. A factorial design with three replications was employed. Treatments consisted of three types of adsorbents (wool, sawdust and peat moss), three concentrations of adsorbents namely 2, 5 and 10%; along with three contact times of 2, 15 and 30 days. The results indicated that use of organic adsorbents is effective among them wool being the most suitable and the most applicable one. Different concentrations of adsorbents had different significant effects on chromium adsorption. Different application times also had different significant effects on chromium adsorption. Wool and sawdust had their maximum adsorption effect in 15 and 2 day, treatments respectively, but peat moss, adsorption of chromium contaminant was the same for the different application times.

Many plant growth promoting rhizobacteria (PGPR) contain 1-aminocyclopropane-1-carboxylate (ACC) deaminase enzyme that can convert the ACC, the immediate precursor of ethylene in plants, to ammonia and a-ketobutyrate and cause a decrease in stress emanted ethylene. Wheat is a strategic crop and the people's main staple in Iran. On the other hand salinity stress prevails in many soils as well as in many water resources in Iran. Therefore it is essential to find and offer the operational measures for increasing wheat yield in these conditions. In this greenhouse research work, the effect of two strains of Sinorhizobium meliloti namely KYA40 and KYA71 that contain ACC deaminase enzyme and S. meliloti KY A95 (non ACC deaminase enzyme containing, as control) on growth and on nutrients uptake of wheat in salinities of 7 and 10 dS.m-1 and SAR=10 mmol.l-1 in a complete factorial randomized block design was investigated. The results indicated that inoculation with strain KY A40 significantly increased the shoot length, shoot weight, root length, as well as Fe, Mn and Cu uptake. This strain increased shoot and root lengths by 13% and 34% respectively in 7 ds.m-1. Strain KY A40 increased the shoot dry weight by 9% in 10 dS.m-1 compared to non-inoculated. This strain increased Fe, Cu and Mn uptake by 47, 45 and 37% (in 10 dS.m-1)respectively. Inoculation was not observed to have any significant effect on length and weight of ears, leaf area index, flag leaf lengh, flag leaf area, N, P, K and Zn uptake.

Speed and direction of wind greatly influence the water distribution pattern in a sprinkler irrigation system. Based on an acceptable water distribution uniformity range, distribution pattern of any single sprinkler, under different wind conditions, is needed for determinae the most suitable sprinkler arrangement. In this study water distribution of a spray sprinkler was assumed to be a function of the Beta probability distribution. Then influences of wind speed and direction on the distribution pattern was studied. Similar to Sprinkler situation on the center pivot irrigation system, a spray sprinkler PROS-04 with wetting radius of 9 m and application angle of 180o was set in 3m height from land surface. In match with the application pressure adopted in center pivot system, a 29 psi pressure was aplied during the carried out experiments. In total 17 experiments were recorded in different conditions of wind speed within a range of 0-6 m/s. Initially the Beta distibution function parameters were evaluated on the basis of measured water distribution pattern under controlled (no wind) condition. Then the change of distribution pattern to different wind conditions as well as the relevant suitable probability function parameters for each condition were determined. The water distribution pattern uniformity was observed as fair. A good proximity between the calculated and observated data was also resulted in the wind speed range of 0-3 m/s, the relative error being less than 4% in this case. In wind speeds of 3-6 m/s the distribution pattern uniformity was poor with the relative error being raised up to 7%. In wind speed greater than 6 m/s the relative error between the calculated and measured pattern was about 10%, because of wind drift and evaporation losses and also due to the diverse effect of wind on water uniformity distribution pattern.

The application of fertilizer through irrigation water (fertigation) is an efficient and cost-effective method in which crop yield increases while potential environmental problems related to conventional application methods reduced. In this study, distribution uniformity of fertigation in different furrow irrigation regimes is evaluated, a numerical fertigation model established, calibrated and validated. Conducted experiments includ: injection of fertilizer only during the first half of the irrigation event (FH), injection during the second half (SH) and injection during the entire irrigation event (T). These options were conducted under free draining as well as under blocked-end conditions with two replications. All the experiments were conducted through cutback method. Potassium nitrate was used as fertilizer in the experiments. Distribution uniformity of low half (DULH) and low quarter (DULQ) of water and fertilizer was assessed to evaluate different fertigation scenarios. A sensitivity analysis approach was also performed to assess the effects of longitudinal dispersivity parameter on overland solute transport. The results show that DULH has significantly differs within the three application times (FH, SH, T). That shows injection in the second half of the irrigation event is more appropriate than injection in the first half and during the entire irrigation event as based on the results. The best case is injection in the second half of the irrigation event preferably starting before completion of the advance phase and in blocked-end conditions. Because in this case, solute losses due to runoff from the outlet is zero and also distribution uniformity is somewhat higher whereas in free-draining conditions fertilizer application during the first half of irrigation provide acceptable fertilizer uniformity and least losses due to runoff. Results of the model show that the best case would be injection in the second half of the irrigation event with blocked-end conditions. No significant difference was observed between distribution uniformity of free-draining and blocked-end experiments. It was found that dispersivity parameter doesn't affect the fertigation uniformity. A value of 5 ern for dispersivity provided a reasonable fit to the experimental data.

For preventing groundwater and soil from heavy metal contamination and/or to decrease contamination, and to clean up the former disposal sites from these metals, one must be beforehand able to predict the movement of these pollutants in soils. In this research in order to describe Cadmium [Cd (II)] transport in soils, we incorporated an equilibrium-kinetic two-site model into the convection-dispersion equation for reactive solutes under steady state water flow conditions in uniform soils. Also the irreversible retention of Cd (II) was described as a first-order kinetic process. For an assessment of Cd (II) movement in soils, five samples with different physical and chemical properties were collected and taken to the laboratory. Miscible displacement experiments were conducted with disturbed soil columns. Model parameters were obtained by fitting model to the experimental data resulting from miscible displacement experiments using a nonlinear least squares (best fit) parameter optimization scheme. The model was applicable in predicting Cd (II) BTCs for different soils representing a broad array of soil properties. By putting these parameters into the model, concentration and retention of Cd (II) with time and depth were calculated for different soils.

The importance of drought monitoring in a near real-time manner makes the use of remote sensing systems indispensable. In this study, a comparison between SPI and EDI climatic indices (in two time scales of 1 and 3 months) with satellite indices of NDVI, VCI and DEV is made for Tehran province. For this, satellite images of AVHRR on NOAA satellite for 6 years (from 1996 to 2001) are prepared and processed. Furthermore, the simple linear regression and dummy variables regression are applied to correlate climatic and satellite indices. The selection of variables is based on examining all possible equations and the Step by Step method. Results of regression analysis for the study area showed a more significant correlation between NDVI and SPI (3 months), while using dummy variables. Also, the correlation between the indices in regions equipped with more meteorological stations was found to be higher.

Time domain reflectometry (TDR) is increasingly employed in soil science for measuring soil water content as well as soil bulk electrical conductivity (ECa). However, TDR calibration especially for solute measurements at large field scales is not an easy task. A series of calibrations might be required for TDR probes used in solute transport measurements to ristly relate the impedance (Z) to ECa and then the latter to electrical conductivity of soil solution (ECw). In this paper, these TDR calibration steps are discussed for measuring solute concentrations in large undisturbed soil monoliths. Six undisturbed soil experimental monoliths, each having roughly 0.5 m3, were collected from two different fields, being loamy and sandy loam in texture. The monoliths were subsequently equipped. with such measuring devices as TDR probes for measuring both water content and as well bulk electrical conductivity, temperature sensors intended for soil temperature measurements, suction cups (corresponding in depths and position to the TDR probes) for extracting soil water solution from different depths, as well as tipping buckets equipped with EC metres at the outlet. One tracer experiment was conducted on each monolith. Automated TDR measurements were made during the experiments whereas soil solutions (ECw) were manually collected fallowing the pulse application. The TDR measurements were subsequently transformed into ECa using obtained probe properties in known solutions. The ECa-ECw relationships were characterized by hysteresis. This behaviour was clearly observed in both of the soils studied as well as for nearly all probes. To calibrate the relationship between ECa-ECw, a linear model was fitted to the selected data close to equilibrium conditions. The accuracy of the calibration was verified at a few points on the breakthrough curves (BTCs) of known ECw.

Heavy metals, due to their inhibitive effects on growth and development of plants and microorganisms are among environmental contaminants. An increase in the heavy metals use and application in industry has lead to adverse effects on agricultural production and human health. Phytoremediation is the technology of exploitation of plants for extraction, fixation and detoxification of pollutants. In this research, a study was carried out on the Shazand Lead and Zinc Mine located in Arak, Iran. The heavy metal pollution and transferring capacity from root to aerial organ in the flora of the area were determined and an identification of heavy metal -absorbent indigenous species was made. From the studied species Achillea wilhelmsii carried the highest level of heavy metal in its aerial organs. There was a significant difference (P<0.01) observed between this species and the others as to the Pb, Zn, and Cd content (110.1, 387.6, 3 mgkg-1 respectively) based upon Dunken's Test. Nickel content of the root in wheat crop, cultivated in the area around the location of the mine was on average 29.5 mgkg-1 which was the highest among all plants studied. Results indicate that wheat is a suitable plant for phytoremediation and can be effective in absorbing Ni which in fixed in the roots. In a study of the Translocation Factor (TF) of heavy metals in plants, maximum TFs of 5.9, 4.4, and 4.3 were respectively recorded for Pb, Zn and Cd in Aconthophyllum microcephallam, whereas a maximum Ni TF of 3 was recorded for Achillea wilhelmsii. Results obtained also indicate that heavy metals' level in soils of the area under study is beyond the permissible, for remedy of which proper measures have to be taken. During the course of the study seven species of heavy metal resistant bacteria were isolated from rhizosphere as well as from soil, inoculums of which could be effectively used inphytoremediation of the heavy metal contaminated soils of the area.