Iranian Journal of Irrigation and Drainage
Year:2010 | Volume:4 | Issue:1|Papers Count:20

The use of groundwater always in one of the main sources of the drinking water and agricultural demands in the arid and semiarid areas. Birjand aquifer is located in the arid region and ground water is the main sources of fresh water. The aim of this research study is the prediction of groundwater level by using of artificial neural networks. To reach such goal, the Birjand plain is divided to sixteen polygons (according to sixteen piezometric wells) by using Tisen's polygon approach. Then in each polygon the amount of recharge (due to precipitation) and discharge (due to pumping wells) were calculated and selected as input parameters in addition to groundwater level of previous month. The groundwater level in present time was selected as output parameter in artificial neural network. The innovation of this study is to account the precise value of discharge of each polygon by considering the volumetric flow meter and duration of pumping form wells. It must be noted that in previous studies, the evapotranspiration from the leaf area of reference plant was selected as an index of discharge from each polygon. From 130 months measuring data of each piezometric well, the 80 months were selected as a training data and the rest of them for verification and test of artificial neural network. The various artificial neural networks such as feed forward back propagation, cascade forward back propagation were tested and the best architectures of artificial neural networks for each piezometric well were found by trial and errors. The results show that artificial neural networks can simulate the decreasing trend of the groundwater level and provide acceptable predictions up to 12 months ahead (R2=0.99, MSE=0.032). The results also show that the accuracy of estimation for closer piezometric wells to weather station is more than the piezometric wells located far from it.

The analysis of the rainy season characteristics such as the rainfall onset, cessation and different length of dry spells between precipitation occurrences is one of the important issues in agricultural arenas. Daily rainfall data of Mashhad Station from 1961 up to 2008 have been used to determine these parameters. The onset date has been calculated by 7 different methods that some of them are based on cumulative rainfall amounts and the others are based on relations of rainfall and potential evapotranspiration. At last a hybrid method has been presented being qualified to determine this factor. Furthermore we have specified the occurrence of false starts by determining of false start definition. The cessation date was defined by 2 methods and after that the length of the growing season have been calculated by using hybrid method for determining onset date and second method of specifying cessation date. Based on these calculations the rainy season will start at 27th November in Mashhad and the length of rainy season will be 185 days. Finally the effects of climate change on characteristics of rainy season have been detected that it showed the climate change haven’t had any serious effect.

In this article the analytical solution has been presented for computing the unconfined steady state seepage from a curved canal with semi-elliptic cross section. The analytical solution of seepage from curved canals has not generalized because of the difficulty of conformal mapping of their cross sections. In the present study, velocity hodograph and Schwarz-Christoffel transformation have been used. Also the inverse method is used to obtain the mapping of canal cross section profile in which the profile boundary of actual canal cross section is mapped along a circle in the velocity hodograph plane. Computations are performed for the steady seepage from semi- elliptic canal in which a drainage layer has lied in limited depth below the bed of the canal. From this method, one could obtain the quantity of seepage discharge with the assumption of resting the drainage layer at infinite depth. From the presented solution also some of the items such as, seepage discharge, parametric equations for presenting the loci of phreatic line and the quantity of seepage width at drainage layer could be obtained. Moreover, the accuracy of inverse method in comparison to the analytical methods of other researchers such as Kozeny is acceptable and does not have the limitation of Kozeny's method, in other words, Kozeny's method is impracticable in canal cross sections with small ratio of free water surface width to depth.

Relatively little work has been done examining historical data of wind speed searching for evidence of climate change as compared to other parameters. The purpose of this study was to assess changes in mean wind speed over the period 1975-2005. in a network consisting of 40 synoptic stations of Iran. These stations represent different climates of the country based on extended- De Martonne climatic classification. All seasonal and annual series have been checked for normality with the Kolmogorov-Smirnov test. Time trends of this variable were analyzed using parametric and non-parametric techniques (Pearson correlation coefficient, least square linear regression, Mann-Kendall and rho-Spearman correlation coefficient). The results showed that based on the Mann-Kendall, rho Spearman and Pearson methods, 50%, 60% and 70% of the annual series had significant trend respectively. Besides, the most significant increasing trend was observed in winter and the least increasing trend in summer. The semi arid-temperate climates have experienced the most significant decreasing trend of mean wind speed, i.e. 0.045 m.s-1 .dec-1. In semi arid cold climates; most increasing trend of 0.145 m.s-1 .dec-1 was observed. In general, the decreasing trend of series was more than increasing trend which in turn, might change the evapotranspiration in arid and semi arid climates of Iran.

Significant problems of water shortage are contributing to growing water crisis in Iran. This situation requires creative solutions to achieve efficient water resources management. Finding ways to meet irrigation demands with respect to available water, growing stages of crops, economical issues and interaction of the water system are the relevant strategy. However, such strategy requires aid of modeling tools and optimization models. This research work aims to presents an approach for optimizing these objectives by applying system dynamics optimization (SDO). To explore and evaluate the methodology, the Zayandeh Rud irrigation system was selected and the required models developed. The paper concludes that SDO is a useful tool to indicate irrigation water allocation and is a suitable to evaluate alternative irrigation system management scenarios. The results are also compared with non-linear optimization model using LINGO commercial package, which were very close together. However, the SDO has more advantages and can be applied as a decision support system (DSS), too.

Sediment controls in the inlet of network channels are very important. Usually inlet sediment settles in basin that causes to increase capacity of flow transportation. Also it causes increase in maintenance costs of networks. Thus, designers usually try to make fast and economical methods in order to control of sediments. One of the common methods for control of inlet sediments is using the Vortex tube which uses in network channels. This research is based on determination parameters which are effective on trap efficiency of Vortex Tube with two cases of controlled and uncontrolled outlet discharge. Researchers have been done with four t/d ratios 0.15, 0.2, 0.25, 0.3 and four outlet discharge ratios 2.5%, 5%, 7.5%, 10%. Results show that when t/d ratio is equal to 0.15, all of the parameters which effect on trap efficiency is in optimum condition for both controlled and uncontrolled outlet.

Development proper methods for performance assessment of pressurized networks to prevent their degradation and performance improvement is necessary. In this study a computer model for performance assessment of pressurized irrigation systems PAPIS has been developed. In this model irrigation systems could be evaluated from managerial, technical, economical, environmental and social points of view. Performance could be evaluated in two stages of rapid and comprehensive approaches. overall performance of the system, and reliability level of performance evaluation, are calculated as well. In this study the applicability of PAPIS model has been demonstrated on Akramabad unit of Aydoghmoush irrigation network. The performance evaluation results of Akram Abad project showed that the highest performance level were achieved in technical and managerial windows with performance level of about 87% and 81% with reliability level of about 82% and 92% respectively. The lowest performance level was archived in economical window with performance level of about 48% and 41% reliability level. The overall performance and the reliability level for rapid approach were about 88% and 87% and their values for comprehensive approach were about 80% and 88% respectively. The results showed that the PAPIS model is suitable tool for quantitative performance evaluation of pressurized irrigation systems.

Problems of water delivery scheduling are one of the reasons for poor performance of irrigation projects. These problems lead to high operational losses and miss-match of water delivery with water requirements. Traditional approach for water delivery planning is based on personal experiences, which is not necessarily satisfactory. The use of analytical and optimization methods could resolve some of these difficulties. For water delivery scheduling, in addition to delivery parameters (discharge, duration, and frequency), the number of intakes, their turn and order with which they receive water in irrigation blocks should be determined. Water delivery scheduling should provide several objectives such as minimization of water deficit and losses and canal capacity while satisfying several constraints such as canals' and structures' capacity and their operational limits. Therefore water delivery scheduling is a complex, multi-objective, multi-variable, and multi-constraint problem, which requires powerful optimization methods to be solved. Classical optimization methods are facing some limitations such as: being trapped in local optimum points, and difficulties in handling different variables. To overcome some of these limitations, new techniques which can solve complex problems could be used. The PSO method is derived from the swarm behavior of birds and fish. The community of birds and fish find their best position based on two elements which are the individual and the collective position of the group. In recent years this technique has been successfully applied on several engineering problems. In this study PSO algorithm is used for planning optimal water delivery in irrigation canals, and it is applied on amx canal of Varamin irrigation network. The objectives are to minimize canal capacity and to maximize the utility of irrigation frequency. Optimal discharge and delivery duration to 11 intakes, number of intakes grouped in 3 irrigation blocks, and their turn and order of receiving water are derived. The optimum canal capacity is derived to 1.64 cms, which is 320 lit/sec less than that derived using SA method on the same canal. The results show the capability of the PSO method for planning optimal water delivery in irrigation networks.

In this study, the effect of time scales of measured meteorological variables on the estimation of the reference evapotranspiration (ETo) has been considered in an automatic weather station in Shahid Bahonar University of Kerman. At first, the effect of the time scales sampling on the estimation of the daily means of the shortwave solar radiation, wind speed, air temperature and relative humidity has been analyzed using a dataset measured 10 minutes interval (4318 data) during a period of one month (June 2007). Also using a sensitivity analysis of the Standardized Penman- Monteith ASCE model and combined the sensitivity coefficients with the errors due to the temporal sampling, the impact of the time scales sampling on the estimation of daily ETo for each variables has been quantified. The results showed that the solar radiation and wind speed are the most sensitive meteorological variables to bias induced by inadequate time scales sampling. Daily errors of 12.6% for the solar radiation and 13.6% for the wind speed may be obtained if these variables are inappropriately sampled. Moreover, the impact of inappropriate temporal sampling on the estimation of ETo can be significant with the maximum bias of 0.41 mmd-1 due to inappropriate solar radiation sampling.

This research was conducted to investigate potato cultivar Santeh yield and water use efficiency (WUE) responses to full and deficit irrigation. Results revealed that the highest (27.82 t) and lowest (24.95 t) yields were respectively produced by two-week delayed and full irrigation. These originated from insensitiveness of initial vegetative stage of potato to deficit irrigation and on the other hand, by full irrigation of 12803 m3 ha-1 water was applied to the experimental plots. While water requirement of potato is 6640 m3 ha-1 and it seems extra application of water caused a decrease in yield. Also, the highest (2.44 kg m-3) and lowest (1.96 kg m-3) WUE produced by two-week delayed and full irrigation. Since initial vegetative stage of potato is not sensitive to water deficit, accordingly deficit irrigation did not cause a decrease in yield but caused an increase in WUE relative to full irrigation condition. To relate crop yield to water applied, a water production function was worked out by multiple regressions analysis. Applying two-week delayed irrigation caused a yield increase as 11.44% and water saving as 10.33% relative to full irrigation condition. Therefore it is recommended that potato cv. Santeh should be irrigated with two week delay after third irrigation to achieve the optimum yield and WUE.

In order to study of the effect of cultivation method and water quantities in drip irrigation on yield of potato, an experiment was carried out using a split plot based on randomized complete block design with 4 replication in Firozkooh for two years (2003 and 2004). In this experiment there were 9 treatments. The main- plots were divided into 3 levels of irrigation: I1.=100, I2=80and, I3=60 percent of evapotranspiration. Sub-plots were 3 cultivation methods: B1.= distances between rows cultivation were 75 centimeter with one drip irrigation lateral, B2=two cultivation rows with the distance of 35 centimeter and a lateral between them. The distance between laterals was 135 centimeter and B3= two cultivation rows with the distance of 45 centimeter and a lateral between them. The distance between laterals was 150 centimeter. The results showed that the effect of cultivation method on wateruse efficiency (WUE) and the effect of irrigation levels on yield and economic yield was significant. I2 irrigation level had the most economic yield and WUE. The B2 treatment with 80% of the croRwater requirement had the highest yield (40249 kh/ ha), economic yield (36965 kglha), and WUE (11.69 kg/ m). Based on the obtaining in this research, treatment B2 with 80% of the crop water requirement is recommended for the cool and moderate weather condition such as Firozkooh region in Iran.

A problem that hinders the development of subsurface drip irrigation systems is the clogging of drippers as a result of sucking soil into drippers during pump turn-off. Using an envelope around the drippers may lessen the problem. However, the dripper envelope may also change the wetting pattern. The objective of this research was to investigate the effect of unwoven and woven geotextile dripper envelopes on the depth and width of wetting profile. Five 60-cm probes each containing 10-cm spaced moisture sensor were used for specifying the wetting profile. A factorial experiment with 9 treatment comprising the 3 levels of the dripper depth (0, 15 and 30 centimeters) and 3 levels of the envelope, (no envelope as control, unwoven envelope and woven envelope) in a complete randomized blocks structure with 3 replicates was carried out in the research greenhouse at University of Shahrekord. Results showed that the unwoven geotextile had more effect on the wetting pattern compared to woven geotextile. Unwoven geotextile increased the width of wetting profile from 27 to 37 centimeters after 30 minutes and from 37 to 45 centimeters after 60 minutes. Overall, using geotextile increased the width and decreased the depth of wetting significantly (P<0.01). Meanwhile the influence of unwove geotextile was more pronounced than that of the woven geotextile.

A semi empirical model has been developed to simulate the distribution pattern of a single sprinkler of center pivot irrigation system using Gamma and Normal distribution functions. A Nelson R-3000 sprayer with rotator pad and water application angle of 360o which is one of the most common types of center pivot sprinklers was selected. Several field experiments according to the ISO-8026 and ASAE-S398.1 standards were performed to assess the water distribution pattern in no-wind and windy conditions. Results of eighteen reliable experiments were used to validate the model. Minimum and maximum wind speeds recorded under the field conditions were 0.57 and 7.41 ms-1, respectively. In this range of wind speed variation the model using both distribution functions showed a proper capability to simulate the water distribution pattern. The average values of R2 and RMSE between observations and simulated values using Gamma distribution function were 0.86 and 0.35 and for Normal distribution function were 0.80 and 0.44, respectively. Then it was finally concluded that the model based on Gamma distribution function was more accurate than the other one with Normal distribution function. The best fitness between simulated values and observations was achieved using Gamma distribution function with R2=0.96 and the weakest obtained using Normal distribution function with R2=0.72.

The Rainfall Depth-Duration-Frequency (DDF) relationship is an important concept in hydrology, which is of important in engineering projects as well as in water structures. In this study twenty four recording rain gage stations (from Ministry of Energy) in Khorasan provinces were considered. The region was divided in two homogeneous sections (A and B with 8 and 16 stations, respectively), by considering different parameters of mean annual precipitation (MAP), longitude, and latitude by using cluster analysis. The homogeneity of these regions were confirmed by linear moment theories. Generalized Extreme Value (GEV) were fitted to the short duration rainfalls, regional depth- duration, and depth- frequency, which were established for each region. The equations were combined to assign regional DDF relationships. The derived equations are functions of duration, frequency, and a key parameter; 10- year, 60-minute rainfall were showed a maximum error of 19%. which are able to determine the depth of rainfall in the duration of 5 to 60 minute and the frequency of 2 to 100 years. The differences of these results were negligible, as compared with the Gumble distribution.

Decision makers' objective in selecting different cropping activities usually isn't a specific object and they must establish a balance between outcomes of conflicting and competing objectives. This paper introduces a method for driving a multi-objectives cropping pattern in water resources management of Zayandeh Rud Basin by using researches, statistical and survey data. The framework of this method was fuzzy compromise non-linear programming (FCNLP) in which optimal irrigation depth was obtained by SWAP model at different salinity conditions. Results showed that although the economic benefit of this model was set at current crop pattern, but this model also release 99.2 and 39.1 percent of two objectives' ideal levels including water use minimization and gross margin constancy maximization, respectively, at zero salinity condition. It will release 76.6, 14.8 and 98.8 percent at 4 dS m-1 salinity level and 97.7, 14.3 and 2.2 percent at 7 dS m-1 salinity level, respectively for minimizing risk, maximizing employment and minimizing urea fertilizer objectives' ideal levels. These levels have been obtained by changing areas of crops including wheat, alfalfa, sugar beet, rice and vegetables and change in irrigation depth and fertilizer use. As a result of these changes, Fuzzy composite distance would be maximized and 47.5, 41.2 and 41.1 percent of total ideal levels, respectively at zero, 4 and 7 dS m-1 salinity levels would be released by considering the objectives' related weight of studied decision makers. This approach was diagnosed as superior strategy compared to other ones which followed individual goals including maximum production efficiency and profits, with or without change in the crop pattern and suggested to test at the farms level of basin.

Effects of various calculation methods of aerodynamic and canopy resistances on estimates of reference evapotranspiration (ETo) by Penman-Monteith (PM) equation for 70 days of lysimeter- weather data was evaluated. Canopy resistance (rc) was computed according to PM, FAO PM, ASCE PM and Todorovic (1999) methods and as a function of net radiation. Aerodynamic resistance (ra) was computed and modified based on atmospheric stratification according to eight methods including PM, FAO PM, Thom (1975), Verma et al. (1976), Hatfield et al. (1983), Mahrt and Ek (1984), Chouhury et al. (1986) and Choudhury and Monteith (1988). Daily ETo was computed using daily climatological data and from the sum of hourly computed ETo values. Considering the combinations of various methodologies for computation of rc and ra in PM equation, hourly ETo was computed from 40 methods and compared with lysimeter data. Three methods namely PM, FAO PM, and Todorovic (1999) were used to compute daily ETo. Computing rc according to ASCE method gave the highest r2 value for calculation of daily ETo as the sum of hourly values. Todorovic(1999) method gave r2 value close to the ASCE method and was ranked as second method based on r2 values. But, Todorovic (1999) method when compared with ASCE method improved slope and theY-intercept of the regression line. ETo estimates were improved when ra was corrected for stability by Mahrt and Ek (1984) and Chouhury et al. (1986) methods as compared to other stability correction methods. In regard to daily methods, Todorovic (1999) method had r2, slope and Y- intercept values equal to 0.92, 0.74 and 0.21 respectively and had the best performance. Todorovic (1999) method when compared with PM and ASCE methods improved r2, slope and Y- intercept of the regression line. The performances of sum of hourly methods were generally better than computations from average daily data.