نشریه دانش آب و خاک
سال بیست و یکم شماره 4 (زمستان 1390)

In order to use overland and stream flows of watersheds, flood control is a basic water resources management step especially in arid and semi-arid areas. Selecting suitable areas for flood spreading is one of the most important parameter in the success of the concerned projects. The aim of this study was to evaluate the accuracy of index of overlay maps, Boolean and fuzzy methods to identify the flood spreading areas, using GIS techniques. For this purpose, five geographical information layers including slope, land use, surface infiltration, quaternary units and aquifer depth were interpolated based on the three presented approaches. The results (as the output maps) were evaluated and compared with the field control sites. The results showed that the method of Multi class maps, because of its maximum overlaying surface with the control sites, comparing to the other models was the best method for the selection of flood spreading sites in the Poshtkoh Basin, Iran.

Appropriate and successful design of an adsorbing column needs to predict dynamic changes in outflow concentration of the substance (i.e. breakthrough curve), which is possible by modeling of the adsorption process. In this study, dynamic experiments were carried out by passing two aqueous solutions of 75 and 150 mg-NO-3 L-1, and a polluted groundwater from Guilan province through a packed bed column of anionic resin, Purolite A-400. Outflow solution was sampled at different time intervals, and the samples were analyzed for nitrate concentration. Dynamic behavior of adsorption was evaluated by modeling of breakthrough curves using Thomas, Bohart-Adams, Lin-Wang and Wolborska models. Comparison and evaluation of the models showed that though the first three models were structurally different and their parameters provided useful information about adsorption process, the data simulated by them were almost the same, and thus parameters of each model could be predicted from the parameters of the two other models without refitting. The predicted curves by the models of Thomas, Bohart-Adams and Lin-Wang were in more agreement with the measured curves than the Wolborska model in all parts of the breakthrough curves, and the dynamic parameters of adsorption process were determined by them more accurately. In the experiment with the polluted groundwater, Thomas model (and other two similar models) deviated from the experimental data at the end of the adsorption process which seemed to be due to the presence of sulfate and phosphate ions in the inflow water.

This research study was conducted in Tabriz plain with the aim of assessing the spatial variability and frequency distribution of some biological properties within and between landforms. For this purpose, a total of 98 surface soil samples (top soil) were collected according to a grid sampling design with spacing of 1000 meters between sampling points and then some biological properties (carbon biomass, microbial respiration, microbial and metabolic quotient) together with organic carbon and soil pH were analyzed. Soil variables frequency distribution showed that soil biological properties had abnormal distribution and the logarithmic transformation caused their normal distribution. Samples separation according to landform units caused their normal distribution and these properties became normal except at plain. Organic carbon and microbial respiration were moderately spatial dependent where as soil pH was strongly dependent and metabolic and microbial quotient showed no spatial dependence. Results indicated that spatial dependence of soil biological properties were much affected by non intrinsic and management factors such as land use type, tillage and irrigation. These biological variables were also strongly affected by scale and showed stronger spatial dependence by becoming larger scale. Therefore these soil properties variations could be due to changes in depositional environments or variance of pedogenic or hydrological processes in different kinds of landforms.

Water scarcity for agricultural productions increases steadily and development of new water resources incurs heavy cost. Study on the reaction of different crops to deficit irrigation is an important step for improving management and optimal use of water. To evaluate the response of two soybean cultivars to different irrigation regimes, the current research was conducted in the crop year 2006 in Gorgan research station. The experiment was arranged in a randomized complete block design as split-plot with three replications. Irrigation treatments of 100 (I100), 75 (I75) and 50 (I50) percent of the irrigation requirement comprised main plots and the subplots were two soybean cultivars: DPX (semi determinate and late maturity) and SEPIDEH (indeterminate and early maturity). Results showed that drought stress (I50) had negative significant effec on: node number, plant height, pod number and yield. Furthermore, there was no significant difference between I100 and I75. DPX cultivar by producing higher number of branches, pods and seed weight led to an increase in yield compared to the SEPIDEH. Moreover DPX cultivar with greater water use efficiency (0.88 kgm-3) than to SEPIDEH cultivar (0.66 kgm-3) would consume less irrigation water for the same yield and might be more tolerant to water deficit.

Land evaluation is an important step in soil surveying and developing the sustainable agriculture. In this research three Storie, Square root and Almagra model were used to evaluate the qualitative suitability of wheat, maize, potato and soybean for 9000 ha in Ahar area located in the East Azerbaijan province. The study was conducted using a factorial experiment based on completely randomized design to assess the efficiency of each of the mentioned procedures for the studied land-use types. The results showed that the area was more suitable for wheat, maize, potato and soybean, respectively. Also, suitability classes suggested by the Almagra model were higher as compared with parametric methods. Assessing the interaction effect between land-use type and different approaches revealed that Almagra model had the best suitability in comparison with square root and that than storie. Furthermore, the cause can be due to both the nature of Almagra model that acts based on simple limitation and number and no impact of climate on classification. Therefore, it is clear that Almagra model application is only possible for soil suitability evaluation while for land suitability evaluation must be used after Terraza and Cervatana models usage. However, in the case of no climatic limitation soil evaluation results will be equal with land suitability evaluation. Interaction of land-use and soil type also indicated that above mentioned methods may have different different efficiencies in various soils. The cause of higher range for the land suitability by Almagra can be attributed to the effect of soil matrix properties on limitation types. Integrating the Almagra model and the output from parametric methods with using GIS can produce geo-referenced thematic maps with high accuracy which will increase understanding and interpretation of land suitability for different crops.

In order to evaluate the effects of deficit irrigation on yield and water productivity of seven soybean cultivars, an experiment was conducted as split plots based on randomized complete block design with three replications at agricultural research farm, Faculty of Agriculture, Guilan University. Main factors of the experiment were four irrigation levels based on soil moisture potential, 30-35 (I1, full irrigation), 50-55 (I2), 70-75 (I3) centibars (measured using tensiometer) and without irrigation (I4). Sub plot factors were included seven soybean cultivars: 033, 032, Sahar (maturity group IV), L.17, Zan, Clark and Madari (maturity group III). Water productivity was calculated based on seed and biological yield. The results showed that deficit irrigation significantly reduced seed yield. The highest and lowest values of the seed yield were obtained in I1 and I4, respectively. But irrigation water productivity significantly increased with application of deficit irrigation treatments (13% and 33% increment in I2 and I3, respectively). During the growing season, treatment I1 received the highest amount of irrigation (2457.14 m3/ha) and also the highest frequency of irrigations (8). According to the ratio of dry matter production to water consumption, water productivity of this treatment (I1) was low. Among all of the irrigation treatments, I3 showed the highest water productivity and there was no significant difference between I2 and I3 for the seed yield. It seemed that I3 had the best water productivity index. Among the studied cultivars, cultivar 033 showed the highest irrigation water productivity (this cultivar had the highest seed yield, as well). According to the results of the present experiment, in Rasht region, combination of treatment I3 and cultivar 033, not only economizes water consumption, increases irrigation efficiency and optimum use of water resources but also produces satisfactory soybean seed yield.

Sediment transport phenomenon in rivers, which has been under the consideration of specialists and water engineers, is one of the complicated problems in river engineering studies. Usually sediment transport and storage that threaten hydraulic structures in rivers are important problems. So presenting new and efficient approaches for accurate estimation of suspended sediment load at different scales will play very important role in river engineering studies. As in most of the sediment gauging stations of the country, sediment sampling is carried out daily and irregularly, if it is needed to know the suspended sediment load in a particular of river, it is necessary to utilize suitable temporal and spacial models. In this study, geostatistics and artificial neural network were used in order to combine time and space series analyses together to present a comprehensive model to estimate monthly suspended sediment load in Aji-chay river. Therefore, rational data has been produced with the aid of artificial neural network at monthly scale, then by both uni and multi-parametric estimators namely kriging and cokriging (in addition to suspended sediment load, water discharge is also used as a secondary variable) methods, monthly suspended sediment load was estimated along the Aji-chay river. Results showed that while both models were valuable in restricted area, the cokriging model in comparison with kriging model was more accurate.

Cation exchange capacity (CEC) is one of the most important soil properties. Its direct measurement is difficult, costly and time-consuming. In spite of large number of researches done to predict CEC, its prediction improvement by adding new input variables, however, remains a challenging issue. To our knowledge no one has used the auxiliary variable of specific surface to predict CEC. In the present work, 1662 disturbed soil samples were collected from different parts of Guilan province. Soil properties including pH, sand, silt, clay, organic carbon, and CEC were measured. The entire particle size distribution (PSD) curve was extended from limited soil texture data. Using Skaggs et al moded. Then, total specific surface (TSS) and the product of the specific surface of clay fraction and its mass fraction (SS1) were calculated from the extended PSD curve to predict CEC by artificial neural networks. Strong nonlinear correlation was found between CEC, TSS and SS1. CEC predictions were improved by using TSS and SS1 in the PTFs. SS1 was the most important variable in the prediction of CEC. Partitioning the whole data into eight groups improved significantly the performance of the PTFs and increased the effect of TSS and SS1 in improving the CEC prediction. Using these PTFs is an easy and economical method and it would be a great step forward in improving the estimation of soil CEC.

Numerical models are frequently used for simulation of water movement in soils. Soil water flow simulation models require a description of root water uptake as a sink term. In this study, two water flow models including the proposed SWMRUM model and the HYDRUS software were compared based on the field measurement in an apple orchard. Probe-type time domain reflectometry (TDR) was used to measure soil volumetric water content within radial (R) and depth (Z) vectors. Root water uptake model includes root density distribution function, potential transpiration and soil water stress-modified factor. A root water uptake sink term was developed, and entered into a soil water dynamic model to enable simulation of water flow in soil via numerical solution of Richards equation. The outputs from the two models were compared against the measured water content data. Simulated and measured water contents were in excellent agreement. Analysis of residual errors, differences between the measured and simulated values, was performed to evaluate the model performance, based on the maximum error (ME), root mean square error (RMSE), coefficient of determination (CD), modeling efficiency (EF), and coefficient of residual mass (CRM). Results showed that maximum root water uptake was 0.04 m3m-3d-1 at 25-30 cm depth and the minimum was 0.005 m3m-3d-1 at 80 cm depth.

Study of effective factors on morphometric characteristics of bed sediments may lead to better understanding of sediment transportation and deposition processes and finally, their efficient control or optimal utilization. The present study was aimed to evaluate the effects of erosion sensitivity of formations, land use and sand and gravel mining on morphometric characteristics of bed sediments at a 30 km reach of Vazrood River in Mazandaran Province, Iran. To achieve the study purposes, 9 sampling sections were selected so that the desired effects could be assessed. The bed sediments were then sampled using combining technique and the morphometric characteristics viz. mean, sorting, skewness, kurtosis, d10, d50,, d90, texture, sphericity and roundness were determined using sieving and GRADISTAT software. The results of the study revealed that erosion sensitivity of the formations, residential use and sand and gravel mining in the river all affected the natural trends of the sediments size parameters (mean, d10, d50 and d90 and sediment texture) as well as roundness, and reversed the trend in some sections.

Stepped gabion spillways have many applications in dam structure, river engineering and soil conservation works. These types of weirs have more flexibility in respect to rigid (impervious) type and are more stable against water pressure. Energy dissipation through this weir is high due to over flow and inflow from steps, so the cost of stilling basin construction can be reduced. Flowing water through the body of weir is one of its important characteristics that make flow condition more complex. Most of the researches until now were on rigid stepped weir in large dams and there are a few studies on gabion stepped spillways. The purpose of this study is to investigate flow over and through the gabion stepped spillway body and determine energy dissipation rate. For this purpose 8 physical gabion stepped spillways with 3 different porosities 38 to 42 percent and two slopes 1:1 & 1:2 (V:H) were made and iron plate on each horizontal or vertical step was used to study the effect of step pervious on energy dissipation. Results show that at higher discharge, energy dissipation is more in pervious (gabion) spillway. In fact at higher discharge or skimming flow regime, energy dissipation divided in to over flow and inflow through the spillway body. In this situation energy dissipation through the spillway body have more effect on total energy dissipation. Thus in skimming flow regime, gabion stepped spillway will have greaterenergy dissipation. At lower discharge, energy dissipation is more in impervious stepped spillway. In this condition other rank belongs to gabion, step with vertical plate and step with horizontal plate respectively. Gabion with higher porosity had bigger energy dissipation and with increasing in discharge, their differences tend to zero. Slope decreasing from 1:1 to 1:2 causes more energy dissipation.

Study of changes in groundwater resources in any region is important from the view point of planning and sustainable water management. Scientific management of water resources needs to know the relationship of drought and groundwater level. In the present study trend analysis was conducted on groundwater level of 32 piezometeric stations located in Ardebil plain for the observation period of 1367-1387 using Mann-Kendall non-parametric test. Trend line slope was estimated by Sen’ s estimator for each time series. Homogeneity of trends was tested using the Van Belle and Hughes method. Results showed that trends of groundwater level for all stations (except Niare-Madrase, Yengjeh-Molla-Mohammd Reza, Agche-kandi and Darvazeh Astara) were negative. Significant negative trends were detected for more than 72 percent of the stations. Results of trend line slopes revealed that in average the groundwater level of Ardebil plain declined about 18 cm/year. The strongest decline belonged to Khalife-loo-sheikh station, which had negative trend of 1.93 m/year. Results of homogeneity test of trends showed that trends were homogeneous for different months and heterogeneous for various stations.