JWSS - Journal of Water and Soil Science

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One of the most vital problems in the storage and utilization of surface waters for drinking, flood control, hydropower, and agricultural purposes is that of sedimentation in reservoirs and subsequent decline of dam lifetime. The useful lifetime of a dam is defined as the time necessary for approximately 80% of the volume of its initial capacity to be filled by sediments washed in by water. It is a function of the volume of the incoming sediments, specific weight of sediments, and reservoir trap efficiency. Trap efficiency depends on sediment characteristics, life, shape, and rule curves of the reservoir as well as on the capacity-inflow ratio. It is the purpose of the present study to calculate sediment trap efficiency of small dams and also to determine the relationship(s) among the effective parameters in the Chaharmahal and Bakhtiary region. For our purposes, 14 small earth dams (with heights of less than 15 m and capacities of about 1 MCM) were selected around Shahrekord and Borougen. Since no data were available on the erosion and sedimentation for these dams, the MPSIAC empirical model was used to estimate the incoming sediment to the dams' reservoirs. The model considers nine factors effective on erosion and sediment production in each watershed. These factors were analyzed for the watershed of each dam under study and the annual sediment yield was calculated. The amount of sediments retained in the reservoirs as a result of the working life of the dams was estimated by reservoir surveying. The trap efficiency was calculated for all the reservoirs under study. The results obtained revealed that the trap efficiencies for these small dams ranged from 10.4 to 68.9%. New curves were developed and suggested for the trap efficiency of small dams based on these results.

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Agricultural insurance is one of the appropriate ways to overcome the risk in agricultural production and to increase farmers’ income security. In this study, the influence of wheat insurance, as personal-free insurance, and sugar beet insurance, as group-forcible insurance, on farmers’ risk attitudes in Fars Province were investigated as a case study. Data were collected using stratified multi-stage cluster sampling method and interviews in the years 1375-1376. The sample included wheat and sugar beet farmers in three different climates including Mediterranean, warm sub-desert and cold mountainous in Fars Province. Results of estimating risk aversion coefficients of farmers, using Safety First Rule (SFR), showed that sugar beet forcible insurance along with giving inputs, mechanization services, lookout of farms by sugar plants led to continuous insurance purchase by farmers in consecutive years. Therefore, sugar beet farmers tended to welcome insurance and the effect of insurance on their risk aversion coefficients was positive. However, discontinuity of insurance purchase by wheat farmers in consecutive years and farmers’ lack of confidence in insurace system caused the influence of insurance on wheat farmers’ risk aversion coefficient to be insignificant. Thus, sugar beet insurance type is closer than wheat insurance type to one of the main aims of agricultural insurance system, which is increasing farmers’ tendency to take risks.

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To detect the rice paddis areas in Isfahan region, the IRS-1D data from PAN, LISS III and WiFS time series were used. Geometric, atmospheric, radiometric and topographic corrections were applied to various images from 2003 to 2004. Necessary preprocessing and various analyses as well as time series composite image analyses were applied and field sampling was done for appropriate times in 2003 and 2004. Image classification was applied using suitable training sites in various images. The SWIR band capabilities were useful for NDWI (Normalized Difference Water Index) to detect the rice paddies. On PAN and LISS III images, urban areas, roads, agricultural lands, non cultivated farms, rocks and brackish soils are detectable. The error matrix was calculated to assess the produced map accuracy using the ground truth data. The total classification accuracy was %91 and the Kappa index value was %89. The rice paddy areas was about 19500 ha in 2003, detected through LISS III data, and 20450 ha through WiFS data. The paddies were 21670 in 2004 through WiFS data. The results of this study confirmed that one can use the LISS III data to detect and determine the rice paddys areas with high accuracy, and WiFS data to estimate the paddies areas with acceptable accuracy.

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  A labyrinth spillway is an overflow spillway to regulate and control flow in canals, rivers and reservoirs. The main hypothesis for the development of such a spillway is to increase the discharge per unit width of structure for a given headwater. This type of structure is often an efficient alternative to a gated-spillway type where either the increase of the flood-passage capacity or the control of the water surface upstream is concerned. This study was aimed to investigate the hydraulic performance of labyrinth spillways of general trapezoidal planform with simple curved apexes. In the experimental work, twelve spillway models with double cycles were considered using three different curved apexes (R/w= 0.15, 0.2, 0.25), each with four different crest heights (w/P= 1.5, 2, 3, 4). Based on the cited recommendations, the length magnification was set to a constant ratio of (l/w= 3) the crest shape was to be of a semi-circular form with simple radius (r= 15 mm) and the spillway walls were vertical with the thickness of T= 2r. An intensive experiment was carried out over a wide range of flows, providing 720 flow data ranging from free flow to submerged flow conditions. 1D flow equation was presented using combined mathematical and dimensional analysis. A coefficient of discharge, C_d, was introduced to represent the influence of the effective geometric and hydraulic parameters on the flow capacity over the spillway. Modular limit was also controlled to see whether the flow over the spillway would be submerged. The results of the study indicate that the modified curved planform of the spillway apexes with consistent divergence in the downstream channel introduces a significant improvement in the flow efficiency over the labyrinth spillways. Spillways with narrower curved apexes (i.e. R/w≤ 0.2), and with the vertical-aspect ratio of (2≤w/P<3) provide more stable and higher hydraulic performance than any other labyrinth planforms over a wide range of flows (i.e. 0.10/P<0.6). In terms of the flow capacity, the proposed spillway model is shown to be more efficient than other zig-zag planforms (i.e. triangular and trapezoidal shapes) with an identical crest length.

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  Organic fertilization has been practiced in Iran due to the shortage of soil organic matter. In recent years, attention has been payed to the organic fertilizers because their commercial production has recently started and demands for their application have increased. The objectives of this study were to investigate the effects of organic fertilizer type, rates and times of application on the N mineralization potential (NMP) in a calcareous soil (fine loamy, mixed, thermic, Typic Haplargid) in Isfahan region. The soil samples were collected from a previousely established field experiment. The experiment design was split plot with three replications. Each main plot was split into subplots receiving 1, 2 and 3 annual consecutive applications of cow manure and sewage sludge at the rates of 0, 25 and 100 Mg ha^-1. The soil samples were taken from 0-15 cm depth, 6 months after the third application of the organic fertilizers. Nitrogen mineralization potential was measured by a long-term leaching-incubation procedure. Results indicated that NMP was similarly affected by cow manure and sewage sludge. Nitrogen mineralization potential in the treatments which received 100 Mg ha^-1 organic fertilizers, was 4 and 1.7 times greater than that of control and 25 Mg ha^-1 treatments, respectively. A significant increase was also observed in NMP in the treatments which received different times of application. The NMP in the three-year applied treatments was 5, 2.5 and 2.1 times greater than that of control, two- and one-year applied soils. Significant correlations were observed between NMP and corn yield (r=0.531**) and corn N uptake (r=0.568***). The product of NMP and N mineralization rate constant was also significantly correlated with corn yield (r=0.710***) and corn N uptake (r=0.734***). Different patterns were observed between the responses of total N and NMP in the treated soils.

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Dates of start and end of frost based on minimum shelter temperature equal to or less than 0°C were studied in Zanjan, Ghazvin and Tehran during 1961-2000. The cause of these frosts was determined by weather parameter values at observation hours and the aid of synoptic maps. Frost series based upon last spring or first fall advection are defined and found to be random and normally distributed. The "potential growing season", defined as the interval between spring last and first fall advection frosts, is found to be 29 days in Zanjan, 23 days in Ghazvin and 10 days in Tehran longer than the "growing season" defined by the interval from last spring to first fall occurrences of minimum shelter temperature of 0°C or less. The numbers of radiation frosts in the interval between first radiation frosts in fall or last radiation frost in spring and related advection frost were counted and found that this parameter is greater in Zanjan. Frostless days between the first two fall frosts and last two spring frosts show that the lengthening of spring season with one night protection is possible for 4 days in Zanjan, 6 in Gazvin and 4 in Tehran, providing that first fall and spring last frost is radiation. Results of this study permit estimating the practicality of frost protection for specialized crops in the area of study.

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Remote sensing has been considered as an appropriate tool for temporal monitoring of some natural phenomena. Ardestan Region is prone to land degradation and masked by sand sheets, sand dunes, clay flats, desert pavement and different kinds of salt crust due to dry climate. To study the trends of land degradation in last three decades, four satellite data sets of Landsat MSS, Landsat TM, Landsat ETM+ and IRS acquired in 1976, 1990, 2001 and 2008, respectively were analyzed. The time series analysis revealed that the bare clayflats have decreased and clayflats with vegetation cover have expanded over 32 years. During this period, the areas which are covered by gravel have decreased 13 percent and both the area covered by salt crusts and aeolians have extended 2 percent. Puffy grounds have developed by 2001 but their magnitudes have decreased between 2001 and 2008 as they have been masked by the moving sand ripples. Reduction of 13 percent of sand sheets between 1990 and 2008 indicates that soil conservation practices have efficiently controlled land degradation and desertification in the area.

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In this paper, velocity profiles were analyzed under different conditions such as bed slope, discharge and concentration of density current, and water entrainment. Experiments were carried out in a tilting flume with the density currents being provided using salt and water solution. Results showed that the above mentioned factors have significant effects on the velocity profile characteristics. Dimensionless velocity profiles were also provided and compared for sub-critical, critical and supercritical flow conditions and the results showed that for supper critical conditions the velocity profiles are generally thicker due to the more ambient water entrainment. The coefficients of velocity profile equations were also derived for the jet and wall zones, which showed good agreements with the experimental measurements. Relative values of the velocity profile characteristics were also calculated in order to have a better understanding about the velocity profile structure.

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LISS IV sensor's data from IRS-P6 satellite was used to produce land use map of eastern region of Isfahan, the studied part of which has an area of 22121 hectares. Its three band data, namely band 2 (Green), band 3 (Red) and band 4 (Near infra red) of LISS-IV sensor images with 5.8 m ground resolution were georeferenced by nearest neighbor method and first-order polynomial model to the DEM map of 1:25000, where the RMSE was equal to 0.3 pixel. To analyze the satellite data, various image processing methods such as supervised and unsupervised classification methods, principal component analysis, NDVI vegetation index and filtering were applied to the satellite data. Finally, the land use map was produced with hybrid method. The final map detected 6 land uses very clearly, which are: Agricultural lands, barren lands, disturbed lands, cultivated Haloxylon amodendron, roads, residential areas and industrial locations. The kappa of land use map is 0.89 and the overall precision is 0.92. The barren lands have a very poor natural vegetation and are considered as natural deserts. Disturbed lands have been formed because of brick kiln activities, and the vegetation cover of these areas has disappeared completely The LISS IV data has a high ability to detect the various studied land-uses especially to digitize the roads. They can be used to update the 1:25000 topographic maps, as well.

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Cylindrical and semi-cylindrical weirs are used in water distribution systems for flow measurement in open channels and for control of water surface. Review of literature shows that cylindrical and semi-cylindrical weirs are not widely used in practice. Because of their low construction cost and simplicity, an investigation was done to study cylindrical and semi-cylindrical weirs in terms of their hydraulic characteristics such as discharge coefficient, energy loss and flow depth over the spillway crest. The research was done for 128 models in the hydraulic laboratory of water engineering department, Shiraz University. According to the results, due to flow separation from body of the weirs, flow coefficient increases in the cylindrical and semi cylindrical weirs by 57%. It was found that discharge coefficient increases by increasing the total head of upstream. Therefore, construction of cylindrical and semi-cylindrical weirs and side weir is recommended due to reduction in weir length, increased hydraulic efficiency, and reduced administrative costs compared to other wide edge side weirs.

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Side weir is the structure to evacuate extra water from a canal when level of water rises. This structure is mounted on the wall of canal. It is used predominantly to set flow in irrigation and drainage systems or urban wastewater harvesting systems. Implementing guide vanes is a simple way to increase side weir efficiency. In this study, the effect of using guide vanes on discharge and discharge coefficient of rectangular sharp-crested side weirs was investigated. ADV instrument was applied for recording vertical velocity over the crest of side weir. Local discharge was calculated by vertical velocity data for both conditions of presence and no presence of guide vanes. Results showed that in both cases, increasing the Froude number results in the decrease of passing discharge and discharge coefficient of the rectangular sharp-crested side weir. Data analysis also showed that by increasing the Froude number, guide vanes have more effect on increasing discharge coefficient and local discharge. The local discharge increased along the crest and the most passing local discharge occurred near the end of the side weir.  Analysis indicates that using guide vanes leads to the increase of discharge coefficient by about 32%.

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Changing the date of the first fall frost and the last spring frost is an important phenomenon in agriculture that can be one of the consequences of global warming. Using general circulation models (GCMs) is a way to study future climate. In this study, observations of temperature and precipitation were weighted by using Mean Observed Temperature-Precipitation (MOTP) method. This method considers the ability of each model in simulating the difference between the mean simulated temperature and mean precipitation in each month in the baseline period and the corresponding observed values. The model that had more weight, selected as the optimum model because it is expected that the model will be valid for the future. But, these models are not indicative of stationary climate change due to their low spatial resolution. Therefore, in this research, the outputs of GCM models are based on the three emission scenarios A₂ and B₁ and A₁B, downscaled by LARS-WG for Isfahan station. The data were analyzed by SPSS software at a 95% confidence level (P<0.05). The results indicated that in the Isfahan in the future period 2020-2049 based on the three scenarios, as compared with baseline period 1971-2000, the first fall frost will occur later and the last spring frost will occur earlier. The first fall frost will occur later for 2 days (based on the A₁B emission scenario) to 5 days (based on the A₂ emission scenario) and the last spring frost will occur earlier for 2 days (based on the and B₁ emission scenario) to 4 days (based on the A₂ emission scenario). Finally, the best distribution functions for the first fall frost and the last spring frost for the baseline period and under climate change were selected and compared using the EasyFit software.

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