Journal of Irrigation Sciences and Engineering
Year:2010 | Volume:33 | Issue:1|Papers Count:8

Hydraulic calculations of the flow in channel and over bank areas of flood plains require an evaluation of roughness characteristics. The Manning roughness coefficient (n), Chesy coefficient (C) and Darsy-Weisbach coefficient (¦) are used to describe the flow resistance or relative roughness of a channel or over bank areas. Over the past decades many studies have been conducted to estimate the friction coefficient to the particle size but the effects of particle shapes are not clear so far. In this experimental research for determination of friction coefficient eleven types of particles; four angle rounded particles, four crushed particles and three spherical artificial particles have been tested under different hydraulic conditions in a flume of 10 meter long, 25 cm wide, 50 cm height and constant bed slope of 0.0005. The results show that in 11 mm sediment particles, the friction coefficient (¦) for crushed particles are larger than angle rounded particles. In 27 mm sediment particles, the friction coefficient (¦) in rounded and spherical artificial particles are equal nearly and values of friction coefficient (¦) for crushed particles shows little difference with aforesaid particles. In this study equation has been proposed for prediction of friction coefficient (¦).

one of the most important factors in trickle irrigation system is selecting the emitter, this is due to the fact that, the drip irrigation function depends on the emitter type and design method. In the present study, performance of 11 types of pressure compensating emitters available on the market, have been investigated regarding their uniformity of discharge. For this purpose, 18 samples of each kind of emitters with nominal discharges 2, 4, 8 and 24 L/hr, were chosen randomly and different discharges were examined in various operating pressures. The experiments were conducted according to ISO 9261, in the Water Sciences Engineering lab of Shahid Chamran University Ahwaz, Iran. The emitters were coded from A1 to M4 respectively. Ten operating pressure levels of 3, 4, 5, 6, 10, 15, 20, 30, 35 and 40 m were used in each sample. Emitters used in the study were classified based on the 3 indexes, emitter exponent (x) in the emitter function (q=khx), determination coefficient (R2) and relative error (Er). The emitter exponent (x) ranged from -0.0067 to -0.4969 which the minimum belongs to C2 and the maximum belongs to C1. The determination coefficient (R2), varied from 0.0007 to 0.609 where the lowest range belongs to M4 and the highest range belongs to D1. The variation of Er was between 0.1 and 34.6 corresponding to E2 and A2 respectively. The results indicated that, regarding pressure compensation, emitter J ranked the best while emitter D1 ranked last.

Nitrogen (N) loss from irrigated cropland, especially in rice paddies, results in low N-use efficiency and groundwater contamination. Soil conditions that increase ammonium and nitrate ion retention alleviate these problems. Clinoptilolite, a naturally occurring zeolite with high ion-exchange capacity, may be used to adsorb ammonium and retard excess leaching of nitrate. The objectives of this research were to determine the effects of different rates of Na-zeolite application (0, 2, 4, 8 and 16 g/kg soil) on pore water velocity and leaching of ammonium and nitrate applied as ammonium nitrate fertilizer to a silt loam soil at a rate of 350 kg N/ha under saturated conditions similar to that of a rice paddy. The results indicated that Na-zeolite applications of 2, 4 and 8 g/kg soil increase the pore water velocity by 5.0%, 19.9, 68.0 and 58.6% compared with the control treatment, respectively. The maximum relative concentration (c/c0) all treatments for the nitrate breakthrough curve (BTC) occurred at pore volume of about 0.5. When applying 39.1 cm of leaching water, leached nitrate by 86.9%, 66.00% and 48.5% of total applied nitrate at the soil surface with zeolite applications of 2, 4 and 8 g/kg soil, respectively. Although the ammonium discharged from all treatments was negligible (3.95, 3.48, 3.13 and 2.28 percent of total applied ammonium at the soil surface), the statistic analysis indicated significant differences among treatments that received zeolites. The relationship between the hydrodynamic dispersion coefficient (D) of nitrate and pore water velocity (v) was not linear and by increasing zeolite application to the soil, the value of D increased as well.

The GIS structural components, which are known as Arc Objects, are structures composed of functions, methods and different properties which are used in software environments in form of encapsulated entities and nowadays have important role in creating GIS software's. Despite the important role of these objects in implementation of required concepts and algorithms in GIS software's, unfortunately the usage of them have been less noticed while the facilities built in GIS software are limited too. On the other hand, the extent of using this technology, in natural resources sciences, agriculture and etc, increases day to day.In this research, using mentioned objects, a software including 12293 lines of code in form of 275 procedures has been designed and created. The software is capable of managing spatial, non-spatial and time series data (in scale of 1: 250000) of gauging station and stream networks. The software provides possibilities to store, edit, query, and display data and also prepares output data.One of the software individual characteristics, which is not available in other current GIS software's, is the execution of multiple spatial searches and quary on Geodatabase without any need to load and to display data layers into map display. The other software benefits are the production of figurative data layers resulted from spatial queries that can be displayed and used without any physical origins on hard disk.

Few rivers running on straight paths are seen in nature; most of them have meandrous form. For meandering rivers, the flow pattern is highly complex and flow mechanics has specific characteristics at bends, which not observed on straight paths. Numerical models can be used as an effective tool for predicting such flow fields. Since all river bends do not have a uniform with, the numerical model SSIIM 3-D was used to simulate 1800 bends, one with a uniform (0.6 m) width and other with a divergent (0.6 m to 0.75 m) width. Flow characteristics such as stream wise and vertical velocity profiles, primary and secondary flows, stream wise and span wise slopes of water surface, bed shear stress distribution and helical flow strengths were compared. Verification using experimental measurements on a uniform bend showed that the numerical model can successfully simulate flow fields in bends. Results indicate that in a divergent bend, the path of maximum velocities at plane near water surface crosses the channel's center line at about 50o, while in uniform bend  this occurs at about 55o Also the path of maximum velocity tangent to outer wall of uniform bend at about 90o-100o, while in divergent bend occurs at about 80o. The range of changes in height of water surface has increasing trend in the divergent channel in adverse of uniform bend and the maximum strength of helical flow is 10.55% larger than the uniform bend. Also, an additional secondary circulation cell at 135o is present in the divergent and uniform bends.

Laboratory experiments were conducted in smooth trapezoidal channel with side slope 1: 1 to measure boundary force and shear stress. Preston tube is used to estimate contribution of wall and bed shear stresses. Available formulas for estimation of boundary shear were evaluated and new formulas were presented. The effect of aspect ratio on wall and bed shear stresses was determined. Results showed that ratio of wall shear force to total shear force decreases as aspect ratio increases.

The probable maximum precipitation (PMP) is the maximum possible depth of precipitation, which could occurs in a region. The PMP has so many influences on designing of dam weirs and storage constructions and water distribution. Therefore, the storage constructions and water distribution must design like they can stand maximum flood without any impairment. The synoptical (convergence) and statistical analysis are two general methods for the PMP estimation. The statistical or Hershfield method is used when rainfall quantities are available and sufficient. There is worth exactness in convergence method because of using more parameters for PMP estimation. In this' paper, by using of Meteorology Organization research which has estimated PMP for Khaf and Khalshour basins by convergence method and concerning 24h PMP in rainguage stations basin, k; was estimated for whole of the area. The 24h PMP data were received from synoptic and climatology stations in Khorasan Razavi province. Then PMP was estimated by first and second Hershfield methods. The results show that there are many differences between them and the Hershfield's second method estimates PMP close to the. convergence estimations.

Regarding the bottom outlet gates, the optimal hydraulic design to ensure non-occurrence of destructive vibrations is very important. Forces inserted into the gates due to the flow with high hydrostatic pressure under the gates may cause creation of damage on the lower edge of gates. Compressive hydrostatic force along with the gate weight and friction forces determine the required powers for down-pull (or uplift) of the gates which is also affected by the geometric shape and flow passing under the gates. The existence of high pressure flow in the upstream of bottom outlet gates, as well as the small quantities of gate opening compared to the head water, may cause using common theoretical methods result in significant errors in the determination of different involved parameters. Therefore there is a need for accurate laboratory studies. In this paper, the results of the study on the physical model of bottom channel and service and emergency gates of Narmasheer Dam is presented. Also the results of measurements of exerted forces gate and vibrations into the gates are provided. The necessary tests have been made, so that using the measured pressure distribution on the gates, vertical forces and maximum damage in both normal head tank and various gate openings, were determined respectively. The exerted forces were calculated based on the use of pressure distribution obtained by piezometers installed above and under the gates. In this study, the maximum horizontal force appears on the 2 percent gate opening and is equivalent to 2410 (KN). The maximum horizontal force into the emergency gate has also occurred in the initial gate opening situation with a value of 2507 (KN). The experimental results also indicated that the maximum operation frequency of vibration due to the high pressure flow in the bottom outlet channel is 80 per second. The tests showed that by increasing the diameter of gate lift arm, the frequency of vibration can be controlled.