JWSS - Journal of Water and Soil Science

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Numerous methods are used in the investigation of floods in catchments such as regional flood frequency analysis. Regional flood frequency analysis relies on physical, climatic and ecological characteristics of catchments and applies statistical methods to study flow records. Hosking and Wallis developed Probability Weighted Moments and presented L-moments statistics as a new tool for flood frequency analysis. In this paper, the theory of L-moments was used to study the flood frequency of central catchments of Iran. A number of 27 sites each with more than 5 years of observed data were studied. In the first step, the diagram of L-kurtosis versus L-skewness was used and proper distributions for each site were applied. In order to eliminate the heterogeneous sites, homogeneous tests based on D, H₁, H₂ and H₃ criteria were performed indicating that two sites appeared to be heterogenous. Next, using Goodness of Fit Test, the best regional distributions were determined which are GL, GEV, GN, PE3 and GPA, respectively. Finally, quantile estimates for distributions accepted at a 90% level were presented.

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An approach for regional low flow frequency analysis is to use multiple regression techniques for obtaining relationships between low flows with specific return periods and catchments characteristics. In this paper, this method has been used. After single-site frequency analysis for 20 stream gauging stations, homogeneity test was performed. Regional relationships between low flows with return periods 2 , 5 , 10, and 20 years and catchments characteristics were derived. For this purpose, catchment area, mean elevation, minimum elevation, shape factor, main channel length, length of main chanel from catchment centroid to outlet, forest area, mean annual rainfall, and mean catchment slope as model inputs were examined and cachment area, mean elevation, and mean catchment slope entered to the models. Finally, the mean relative error of models for different return period, 2, 5, 10, and 20 years, was computed 41.1, 41.3, 45.0, 47.2 percent, respectively that in comparison with other studies, it displays smaller errors.

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Channel lining is essential to increase resistance against scour, reducing water losses and as a result increase water conveyance efficiency. Since the canal lining has significant costs, selection of type of lining must be made with great care and with considering engineering properties. One of the conventional lining for water conveyance cannel is concrete lining. Because of advantages of concrete lining including durability (about 40 years) and low maintenance costs, this type of lining is the best option in many regions, however the construction expenses is high. So far many researches have been published about the types and the durability of concretes containing synthetic pozzolans. Due to high production of wheat in our country, nano particles of wheat ash sheath (NPWAS) were used. In this study the mechanical properties of concrete (compressive strength, tensile strength and durability) incorporating nano-particles of wheat ash sheath were investigated. The results showed that the compressive and tensile strength of samples incorporating 20 percent of NPWAS has not statistically significant difference (P<0.05) with the values of tensile and compressive strength of control samples. Therefore, the optimum replacement percentage of NPWAS was 20 percent by weight of cement. Moreover, results of durability of concrete samples showed that concrete containing 20 percent NPWAS were more durable than control samples in the magnesium sulfate solution. NPWAS with having 90.56 percent of silicon dioxide, high pozzolanic activity and ability to perform substantial chemical reaction with calcium hydroxide would decrease porosity and increase resistance of concrete.

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In this study, in order to determe low flow conditions in Karkhe watershed, 5 indices of Q7,10, Q7,20, Q30,10, Q4,3 and Q95 were used for analyzing 12 hydrometric station data in the years of 1345-46 to 1380-81. Discharge data homogeneity was performed by Run Test. The Q95 index was determined by flow duration curve (FDC) and other indices were determined using 4, 7 and 30-day low flow frequency analysis. After calculating the indices, periods of low flows were determined. The indices were regionalized by Kriging method. The results showed that for the most stations, low stream flows happened in the years of 1345-46, 1377-78, 1378-79, 1379-80 and 1380-81 and the percentages of stations having low flows in these years were 68, 92, 84, 75 and 59, respectively. According to the regional maps of low flows in Karkhe watershed, maximum low flows are located in central and southern areas and all of the mentioned indices decrease from south to the north of this watershed.

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Crisis of quality and quantity of water resources is one of the most important problems in arid and semi-arid areas such as Iran. Wastewater treatment and reuse as a potential source of water can not only compensate for the water scarcity but also can prevent the hazardous pollutants from entering the groundwater and surface water resources. There are various methods to improve water quality, among which method of filtration is an effective and efficient method to remove elements. The most important issue for filter system is the selection of adsorbent materials. In this work, the tire chips were used as adsorbent. Column adsorption tests in a pilot system were conducted in two distinct steps using two types of water, including salt water and industrial effluents. Each test was conducted as a factorial experiment with three factors based on a completely randomized design with three replications. Three factors were studied including particle size (2-5 mm and 3-5 cm), filter thickness (10, 30 and 50 cm) and sorbent contact time with solution. The results showed that adsorption rate increased by increasing the thickness of the filter and sorbent contact time with solution. The best performance of reducing the salinity was observed in the treatment with 50 centimeter thickness and 24 contact hours. The salinity of this treatment was reduced by 20.3 percent (in the test with salt water) and 11.2 percent (in the test with industrial effluents). This filter reduced the heavy metals of lead, zinc and manganese up to 99, 72.1 and 41.4 percent, respectively. Also, the performance of millimeter and centimeter particles did not show a significant difference. Generally, the tire chips showed a proper performance to improve the water quality especially for industrial wastewater.

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Nitrogen (N) loss from irrigated cropland, particularly sandy soils, significantly contributes to nitrate contamination in surface and groundwater and increases N applications to crops. This is because negatively charged nitrate normally does not have much affinity to soil particles. To retard the movement of nitrate, materials should have high affinity for anions, which most naturally occurring minerals do not have. The cation-exchange properties of natural zeolites can be exploited to modify their surface chemistries so that other classes of compounds, particularly anions and non-polar organics are retained. In this study, the ability to remove nitrate from aqueous solutions with different Cl- concentrations using Iranian zeolite (Semnan) modified by hexadecyltrimethylammonium bromide in millimeter and nanometer particle sizes was determined and the equilibrium isotherms were characterized. The nitrate release as affected by time and ionic strength was also evaluated. It was demonstrated that SMZ is capable of adsorbing more than 60 mmol kg-1 and 80 mmol kg-1 nitrate in millimeter and nanometer sizes, respectively, and adsorbed nitrate can be easily released under different ionic strengths. The millimeter and nanometer-sized SMZ showed 26.7% to 82.3% and 37.8% to 85.5% nitrate removal efficiency, respectively. The average of nitrate released by millimeter-sized SMZ was 6.92 mmol kg-1 in deionized water while it was 14.68, 22.71, and 34.91 mmol kg-1 in releasing solutions with ionic strengths of 0.03, 0.1, and 0.3 M, respectively