Journal of Water and Soil Conservation
Year:2010 | Volume:17 | Issue:1|Papers Count:14

This paper presents the impact of different geometric and hydraulic factors on the water surface profile condition in a side channel carrying spatially varied flow with increasing discharge. Comparison between experimental observations and the results of the one dimensional spatially varied flow governing equation, which is the key tool for side channel design, indicated that relaying on such results could lead to insecure design. In this research, based on comprehensive experimental data, that reflect the influence of relevant factors and with the aid of suitable non-dimensional parameters such as a relative water surface irregularity, it is indicated that more than 97% of the mentioned parameter data fall within a arrange equal to the downstream critical depth and one-third of the mentioned depth. Accordingly, the proposed non-dimensional parameters provided a suitable collapse in the data based on which a design criterion was obtained that led to a systematic modification to the numerical results of the governing equation. The proposed modifications were based on an equation obtained for the envelope to the data, therefore, the results inherent a safety factor. The application of the proposed design criteria was presented and the generality of the drawn conclusion was supported by a relatively wide data range of the influencing factors. 

Selection of the suite subset of tracers, capable of discriminating sediment sources, is the first and the most important step in the sediment fingerprinting method. Selection of the suite subset is carried out by Discriminant function analysis. The presence of outliers affects the suite subset selection and prevents entering the important tracers into the model, hence reducing accurate classification percent of Discriminant function analysis. Therefore, the outliers must be detected and corrected or omitted, if enough evidences were present. In this study, different univariate and multivariate outlier detection methods were used to assess the presence of outliers in geochemical and organic elements and radionuclides of soil samples collected from Ghara aghaj watershed, Makoo township. According to four univariate outlier detection methods, no observations (samples) were outlier on a sufficient number of tracers. The [Median ± 3MAD] and box plot procedures showed better performance in outlier identification than the [Mean ± 3S] and Grubbs' test methods. Also, based on multivariate outlier detection methods, namely squared Mahalanobis distance, separate box plots of squared Mahalanobis distance for each of sediment sources, principal component analysis and plot of the squared Mahalanobis distances against the quantiles of the chi-square distribution, no observations were detected as outlier. From perspectives of each of the two group methods, there was no sufficient information and demonstrable proof about true outlierness of any observation. The advantages of the approach adopted in this study are the simplicity and computability of the selected outlier detection methods with commonly used statistical softwares, and the condition that an observation is regarded as outlier if its uniqueness is confirmed with several methods.

Choice of a design rainfall is a basic step in many commonly used methods for estimation of design floods. Determination of rainfall temporal pattern is of particular importance to estimate flood specially for urban and rural floods, design of runoff excrement systems, culverts and drains, and also soil erosion studies and estimation of storms flooding potential. In this research, 9 rain gauges’ graphs were used to determine rainfall temporal pattern in Sistan and Baluchestan province scattered throughout the province (From Meteorology organization and Energy ministry for scince 1968-2006 years). All intensive storms for each station were studied with 1-hour, 2-hour, 3-hour, 6-hour, 9-hour, 12-hour, 18-hour and 24-hour durations (1136 storms in addition). The method used was based on storms separation into four quarters and estimation of rainfall percentage for each quartile and quartile ranking, then ranks averaging in each quartile, specifying index rank and at last, obtaining final pattern for each duration.To statistically evaluate obtained patterns with durations of interest, Chi square test was used after establishing a contingency table. Results show that in all stations, maximum 1-hour and 2-hour precipitation occur in first and second quartiles and first quartile, respectively. In addition, in Sistan and Baluchestan province with hot and dry climate, almost 80 percent of short-term (1, 2, 3, 6-hour) precipitation takes place in first and second quartiles while long-term (9, 12, 18, 24-hour) precipitation occurs in third quartile.

Wind erosion is a major environmental problem affecting land resources and socio-economic settings in Iran. This paper outlines a study undertaken to provide a new tool to manage wind erosion from physical and economic perspectives. The southern part of the Varamin Plain in south of Tehran is used as a case study. The focus of this study is on exploring the economic and physical impacts of vegetation-based scenarios for wind erosion management as well as conducting a trade-off analysis using the multi-criteria-decision-making (MCDM) technique. This involves developing a modeling system to assist decision makers in formulating scenarios, analysing the impact of these scenarios on wind erosion, and interpreting and suggesting appropriate scenarios for implementation in the area. The Iran Research Institute of Forests and Ranges (IRIFR 1) model has been selected to create the wind erosion hazard maps. This was carried out for the present condition and also for the corresponding conditions of the scenarios. The IRIFR 1 considers having the ability to represent the model complex interactions between system variables in arid and semi-arid areas of Iran. Among 16 scenarios for wind erosion management, the most appropriate ones have been chosen considering the trade-offs associated with the outcomes.

In concern of the fast development of drip irrigation systems and knowing that this method has desirable ability in correct management and fertilize, study on application of fertilizer and chemical solution in micro irrigation systems is necessary. Water and fertilizer distribution uniformity are important considerations for designers and users of micro irrigation systems. In this study water and fertilizer distribution uniformity on the soil surface and in the soil profile were evaluated. Online dripper and tape line were used for distributing water and fertilizer. Injection pump, venturi, and fertilizer tank devices were installed in order to inject the fertilizer into the micro irrigation system. The results indicated that because of lower value of coefficient of manufacturing variability in the tape than online dripper, the operation of tape in water and fertilizer distribution uniformity on surface and in the soil profile was better than online dripper. Evaluation of variations of water and fertilizer application along the laterals and Christiansen's uniformity coefficients on the soil surface and in the soil profile indicated that venturi and injection pump had better operation in fertilizer distribution uniformity than fertilizer tank.

Studying temporal variation of suspended sedimentgraph is an important tool in soil and water resources management of a watershed. At present, most of estimates and studies for sediment generation are accomplished by sediment rating curves, while their accuracy has ever been questionable. Therefore, sedimentgraph analysis has great importance in sediment studies in watersheds. Hence, the present study was conducted in educational watershed of Tarbiat Modares University located in Mazandaran Province, Iran, with an area of some 50000 ha to analyze sedimentgraph and rating loops of seven observed storm events from 24 October 2007 to 21 July 2008. Individual analysis of sedimentgraphs and hydrographs ascertained complexities governing the aforesaid forest watershed. The results of studying sedimentgraphs with duration of 6 to 13h verified an average sediment yield of 15.830±3.756 tons. It also showed that most of the sedimentgraphs are in advance with an average interval of +2.600±2.881 h. The developed rating loops were also recognized as clockwise type. However, this behavior varied in corresponding with sand and gravel mining and storm coverage area. The results owing to providing appropriate elementary data needed for watershed management approved the necessity of further detailed studies in storm scale and different time bases.

CEC can be measured directly but its measurement is especially difficult and expensive in the Aridisols of Iran because of the large amounts of carbonates and gypsum in these soils. Pedotransfer functions (PTFs) provide an alternative to direct CEC measurement by estimating CEC from more readily available soil data. Estimation of costly measured properties from widely available or more easily measured basic soil properties by means of regression equations is referred to pedotransfer functions. To develop pedotransfer functions, we can use regression PTFs and neural networks. In the present study for estimating CEC, 60 surface soil samples (0-30 cm) were collected in 250´250 m grid from calcareous and gypsiferous soils of Yazd-Ardakan plain. Input parameters for estimating CEC in both mentioned models were: soil texture class and soil organic carbon content. Finally, result of prediction of CEC by regression PTFs and neural networks compare with empiric pedotransfer functions. In general, the neural network-based models were provided more reliable predictions (RMSE=1.04 and coefficient of determination=0.97) than the regression-based PTFs. Higher accuracy of ANN is because of non-linear correlation between dependent and independent variables.

Variable rate water application can be achieved along the length of centre pivot by variable-rate control systems. But to attain a satisfactory level of irrigation efficiency, high water application uniformity over area with same irrigation rate is required. In this research, the water distribution uniformity was evaluated with a modified centre pivot irrigation system that was able to vary the amount of water along the length of centre pivot and vertical to movement direction. Uniformities along the length of centre pivot and vertical to movement direction were calculated at three movement speeds and seven solenoid valve pulsing levels. Results showed that modified centre pivot is able to apply water with acceptable uniformity coefficient (82 to 96%) under different pulsing level and movement speed. Uniformity was increased by increasing pulsing level and decreasing movement speed.

In order to evaluate the impacts of climatic factors during the periods of the occurrence of wet and dry years, using a model is one of the best solutions. In this paper, drought severity was determined by using Scalogram model based on 3 climatic factors (annual precipitation, number of rainy days and amount of potential evapotranspiration) for Zabol region over 16-years period (1991-2006). The results showed that the most severe drought had not always occured in a year with the least precipitation. This is due to the role of other climatic factors. It is concluded that the occurrence of the most severe drought and the wettest year has been in 2001 and 1992, respectively. In addition, potential evapotranspiration is the most important factor affecting on occurrence of drought in the study area.

Existence of many effective parameters and the variation range of suspended sediment load cause low accuracy of sediment rating curve. So the novel approaches such as artificial neural networks since it consider many independent variables are suitable. In this study, three various cases were used for estimation of suspended sediment load. In the first case, as compared with sediment rating curve, the suspended sediment discharge was considered as a function of flow discharge. In second cases the suspended sediment discharge was considered as a function of water discharge in mentioned time and water discharge occurred one day before. In third case the suspended sediment discharge was considered as a function of water discharge in mentioned time and water discharge occurred respectively one, two days before. The results showed that the artificial neural networks with (R2=0.979, MSE=0.0011) can be used for estimation of suspended sediment load in comparison with sediment rating curve approach with (R2=0.778, MSE=0.043).

The first step in many commonly used methods for estimation of design floods is choice of a design rainfall. Design rain has some characteristics such as time distribution of rainfall in rain period. In this research, the data of nine rain gauge stations in Sistan & Baluchestan province has been used. In this method, in every time duration based on this fact that in which quarter the maximum rain has happened the first, second, third and fourth rainstorms were defined and the related charts with 10 to 90% probability were prepared. The results show that: the maximum abundance of rainstorms in short-term duration is related to first quarter rainstorms and in all stations except Khash, Kahir and Sarbaz stations the 1, 2, 3 and 6 hours durations are the main first quarter rainstorms. In 9, 12, and 18 durations the rainstorms in each four quarters is distributed and in 24 hours duration except Kahir station, the others are in second quarter rainstorms. In Sistan and Baluchestan province about 80% of rain happens in short-term durations, in first and second rain quarter and in long-term durations it happens in third quarter.

The necessity of drought preparedness can be verified by assembling drought mitigation scheme. In this study, the severity, duration and extent of drought during 1986 to 2005 have been studied using monthly precipitation data of all IRIMO stations over Northern Khorasan province. For all stations, meteorological drought indices including Standard Precipitation Index (SPI), Deciles Index (DI), Percent of Normal Index (PNI) have been used in order to assess and compare their capability for drought severity and duration in annual scale. Finally, for the purpose of study on the drought extent, the zoning maps have been prepared by IDW method. The consequences resulting from the zoning of drought severity, have illustrated that the most extensive drought occurred in 1990 and 2001 respectively. The most durable drought, Based on SPI capability has occurred during 1994-1997.