The significance of ground water as an important source of water supply is no doubt to anyone in arid and semiarid areas. Therefore prediction of ground water level fluctuations seems as important parameters for planning conjunctive use in these areas. Neyshabour plain is selected for this research because of presence of 45 pizometerics that most of them have more than 12 years data. Therefore, at first preprocessing job is done on the row data using GIS for editing and generating requirement of data in month scale in 15 selective pisometeric wells and in its thiessen polygon. Then, the performance of different artificial neural networks (ANNs) such as multi layer perceptron (MLP), Generalized Feed Forward (GFF) and Recurrent Neural Network (RNN) in a groundwater level predicting is examined in order to identify an optimal ANN architecture that can simulate the variation of the groundwater level and provide acceptable predictions in during of months ahead. The different experiment results show that GFF neural network trained with the momentum algorithm has the best results for up to 6 months forecasts. The selected performance criteria indicators such as R2=.937 and NRMSE=.378 reveals the relevance of this method

Background and Objectives: The relation between water table depth and evaporation rate from bare soil is of great importance in arid and semi-arid areas. In this region, due to over irrigation, the water table is very close to the ground surface which leads to salinization of the soil. Evaporation from soil columns in the presence of a water table is of importance and has received great attention for many decades. The soil-drying process has been observed to occur in three recognizable stages. The first stage is evaporation with constant intensity. The second stage is evaporation in descending order. The third stage is the residual evaporation of low intensity, which begins after excessive drying of the surface layer of the soil and its effect on reducing the hydraulic conductivity of the soil. Given the importance of evaporation from the surface of the station in arid and semi-arid regions, it is necessary to measure this parameter accurately. The purpose of this study was to determine the effect of water table depth on the evaporation from soil surface, as well as the determination of different evaporation stages. Materials and Methods: The soil used in this experiment was loam with a bulk density of 1. 32 gr/cm3. The experiment was conducted in a greenhouse and the duration was 74 days. Soils were sived through a 2-mm mesh and then packed into the soil columns using soil funnel. PVC tubes with a diameter of 250 mm were used to provide test columns. water table was stabilized at depths of 400, 600 and 800 mm from the soil surface, and the experiment was repeated twice. For stabilizing the water table in different depths, each soil columns contained a pipe from the bottom, to supply water from bottles that maintained the water table constant. The water losses from the soil profile was measured at different depths and times using Delta-T Device Moisture Meter. Results: The results showed that water content between 0 and 160 mm in the soil column decreased during the experiment and the lower layers remained saturated. In the steady-state, the rate of water loss from bottle next to the soil column is equal to the rate of evaporation from the soil surface. In a non-steady-state, the evaporation rate from the soil surface is equal to the total loss of water from the water table and the water lost from the soil profile. The cumulative evaporation in the 74-day interval from the stopping surface, 400, 600 and 800 mm was 384. 6, 312. 3 and 293. 4 mm, respectively. The maximum evaporation from the water table was related to a depth of 400 mm and equal 384. 6 mm and the highest water loss from the soil profile was related to a depth of 800 mm and equal 51. 3 mm. By increasing the water table depth from 400 to 800 mm (increased 100%), the evaporation rate from the water table and the total evaporation from the soil surface decreased by 24 and 16. 5 percent, respectively. The length of the first stage of the evaporation for the water table depth 400 mm was 2 days and for 800 mm less than 1 day. Conclusion: The results of this study presented information for us regarding the flow of water above the shallow water table. water content changes in the soil surface soil are higher than close water table. Movement of water close water table is liquid and close the soil surface is in the form of vapor. The duration of the first stage of evaporation has decreased with increase water table depth. In general, it can be concluded that evaporation from the water table can provide a large portion of the water requirement by the plants.

Modeling of water table depth fluctuations because of uncertainty in its parameters is rather complicated and was studied in the current work. For this purpose temporal variability of water table depth at 22 piezometric wells and precipitation data at 3 rainfall stations in the Malayer plain were evaluated from 1989 to 2007. Trends in data series of monthly, seasonally and annually with Sen's estimator nonparametric method was calculated and interpreted based on the defined constraints and trend start time by using Mann-Kendall test. The results showed that at monthly time scale 79.5% of the wells had significant positive slope. The remaining 16.3% had positive and 4.2% negative slope. At seasonal time scale 80.7% of trends had significant positive slope; 14.8% of the rest encountered with positive and the remaining 4.5% with negative slopes. At the annual time scale, analysis indicated that the trend in 81.8% of the wells was significant with positive slope. The trend in 13.6% was non-significant with positive slope and the 4.6% was negative. Over ally, the trends of piezometerc wells showed rapid decreasing in the water table depth at the sudied area and presenting unwise utilization of the ground water resources in the area.

A field study was conducted in Iran to evaluate the effects of water table management on quality of subsurface drain flows. Drain discharge volumes, N03-N concentrations, phosphorous concentrations and electric conductivity in drainage effluent were monitored during the growing seasons. Lysimetric site with drainage system and water table control system were prepared and annual alfalfa (Medicago Scatella) was cropped. The WTM treatments consisted of three subirrigation treatments with water table controls set at 0.3 m (CWT0.3), 0.5 m (CWT0.5), 0.7 m (CWT0.7) from the soil surface and a conventional free drainage (FD) treatment (water table more than 1.00 m below the soil surface). Drain flow volumes and N03-N concentrations were significantly reduced by WTM as compared with free drainage. Mean NO3-N concentrations in drainage water were reduced by 78.6%, 65.6% and 49.3% by the 0.3, 0.5 and 0.7 m controlled water table depths, respectively. Total drain flow was reduced by 49.6% and 41% by the 0.3 and 0.5 m controlled water table depths, respectively. Consequently, NO3-N loading was also reduced by 90% and 82% by the 0.3 and 0.5 controlled water table depths, respectively. Improvements in drainage water quality were attributed to both reduced drainage outflow and enhanced denitrification in the controlled water table treatments. Mean phosphorous concentrations in drainage water were reduced by 11.2% by the CWT treatments. Also mean electric conductivity in drainage water was lower than FD by the CWT treatments. In addition to significantly reduced NO3-N pollutions, economic benefits were achieved through fertilizer equivalent saving. Therefore, the practice of water table management in the region was demonstrated to be both environmentally and economically sustainable.

Scarcity of water resources in spite of burgeoning population makes them important and necessitates optimum use of these resources. Shallow groundwater is a resource that has been ignored in irrigation management, while it is an available free source of water which can provide at least part of plants water requirement. Therefore, a two-year experiment was conducted in 2009-2011 to find the effect of shallow groundwater tables, at 60, 80, and 110 em depth, on water requirement, water use efficiency (WUE) and yield of three wheat cultivars, namely, W33g, Cross Alborz, and Bahar. Experiments were performed at Razi University lysimeter research station No 1 as a randomized complete block factorial experiment with three replications. In these experiments, 45 tubular polyethylene lysimeters with 1.20m height and 0.30m diameter were fixed in the ground with 1m distance from each other. The highest utilization of groundwater was found for the water table depth of 60 em and the lowest was found for the 110 em depth. The 2-year average contribution to different cultivars by groundwater in depths of 60, 80, and 110 em was 63%, 55% and 45%, respectively. The results for Cross Alborz cultivar showed no significant difference (P<0.01) in WUE between the three water table depth treatments. Overall, the optimum WUE and yield was found at water table depth of 80 ern.

In many hydrologic and agricultural researches, the amount of water requirement to raise a shallow water table to the soil surface, i.e., soil water storage capacity (SWSC), is important. In this research, the amount of SWSC was measured and estimated. Then, relationship between SWSC and groundwater depth were obtained as a polynomial function for Kuye-Asatid soil (silty loam) using theoretical and experimental methods. Also the effect of encapsulated air on SWSC is investigated in both methods. Four water table depths of 30, 60, 90 and 120 cm were simulated in laboratory, and soil water contents at different depths were measured and the amount of SWSC was calculated under different water table depths. Regression analysis was used to obtain the relationships between SWSC and water table depth for the experimental data. The amounts of soil water storage capacity in both experimental and theoretical methods are compared using linear regression. The values of the coefficient of determination R2 for cases encapsulated and without encapsulated air were 0.96 and 0.99, respectively. Further, the values of slope and intercept of linear relationship indicated that the data obtained with encapsulated air are close to the results of theoretical approach. The results show the amount of encapsulated air in soil water storage capacity is about 21% of soil porosity. Therefore, it should be considered in SWSC calculation. The proposed equation accommodates the reduction effect of the capillary fringe on SWSC. By statistical comparison the proposed function for case of encapsulated air is similar to theoretical equation, but in case of without encapsulated air condition, they are not similar.

In humid regions, water table control during growing season is a common irrigation method for efficient use of water and optimum crop production. However application of this method in arid and semi arid region is doubtful because of high evaporation rate and salt movement toward the root zone limitations. This research was conducted to examine the possibility of using water table control techniques (i.e., controlled drainage and sub irrigation) in an arid region (e.g., Iran) with special attention to its salinity management. Three water table control treatments including: free drainage (FD), controlled drainage (CD), and sub irrigation (SI) were considered. Treatments were applied in 12 lycimeters (90 cm height, 57 cm diameter). The experimental setup included three treatments and four replications. water table was set at depth 55 cm from soil surface. The electrical conductivity (EC) of water was 1.5 dS/m. The crop cultivated in lycimeters was tomato. The soil leaching considered to be conducted when EC reached to the plant threshold level (EC = 3 dS/m). The results indicated that SI and CD methods can be used in arid and semi arid conditions. In all the treatments the soil EC was not reach to the crop threshold level. However the EC of soil surface layer in SI treatment was high, but it had not any significant effect on crop yield. The evidence was the higher yield of SI treatment than FD treatment. The total yield of CD was 73% more than FD and 12% more than SI. However the number of tomato fruits in CD treatment was more than the other two treatments (FD, SI). water consumption in SI was half of CD and FD treatments, and consequently its water productivity (1.4 Kg/m3) was higher than the water productivity for FD (0.57 Kg/m3), and CD (0.97 Kg/m3).

Today the main function of drainage, is not only out excess water, but its main purpose has changed to manage the water table. Controlled drainage is one of the procedures that can fulfill this goal. In this study, controlled drainage system in the lands of the Maghan plain was implemented to reduce the volume of drainage water, water table management, increase efficiency and productivity of water use efficiency in corn and wheat. This study was implemented in 40 hectares' area in three treatments and three repeated included free drainage (FD), controlled drainage with fixed control depth 70 cm (CD70) and controlled drainage with variable depth during plant growth (CDch). The collected information includes the discharge from drains, temporal and spatial changes in water table levels and production of corn and wheat crops in two consecutive seasons. The results showed that volume of laterals drainage in CDch and the CD70 treatment 51. 2 and 43. 8 percent in corn and 46. 6 and 33. 1 percentage for wheat declines into significant related to free drainage (FD). Investigation on water table fluctuation revealed that the free drainage has more frequency than the controlled drainage treatments. The wet forage in maize in the treatment of CD70 and CDch was to the 24. 9 and 19. 1 percent and in grain wheat increased 41. 3 and 26. 6% percent compared to the treatment of FD. Finally, the results showed that the water use productivity in controlled drainage treatments and especially is the CDch treatment was more than free drainage treatment. By implementing controlled drainage system in addition to reducing drainage water, it will be reduced the environmental damage caused by the drainage for downstream farms.

Shallow water table is an important problem in arid and semi-arid regions. Since it causes reduction of agricultural yield; therefore, water table fluctuation is necessary to be monitored in irrigation and drainage fields. These conditions are intensified for arid and semi-arid countries, such as Iran, where saline groundwater is the main water resource. These problems were increased in sugarcane industrial farm that covered large area in Khuzistan province, Iran. Therefore, it is necessary to determine water table in sugarcane field during growing season. Regarding the purpose, it is important to evaluate water table fluctuations in each farm continuously. There are some problems to achieve this purpose like spending time and financial supports. So, computer models are developed to solve the problems. In the other hand, water table can be simulated under different farm conditions, even before designing an agricultural unit, using the models. In order to achieve the mentioned goal, this research was conducted to evaluate three models: DRAINMOD, SWAP and Endrain, to simulate water table levels in Amirkabir Agro-industry farms. The studied area is located at latitude between 31˚ 15’ and 31˚ 40’ and longitude between 48˚ 12’ and 48˚ 30’ , southwest of Iran. Regarding this aim, water table data were collected from a 25 ha farm. Each model use different equations to simulate water table. Nevertheless, Richards’ s equation is the main formula to determine water movement in saturated and unsaturated soils. SWAP uses this formula as following: Where: θ is volume of water content (cm3. cm-3); t, time (hr); z, increasing in depth to soil surface (cm); K(θ ), hydraulic conductivity (cm. h-1) and h is hydraulic pressure (cm). In order to estimate all of those parameters, sample data were collected from the farm. In addition, RETC model was used to determine some of mentioned data. Upper boundary conditions like irrigation and rainfall were measured from local sensors. For simulating evapotranspiration, meteorological data were collected from the nearest metrological station. SWAP uses FAO Penman Monteith equation and Drainmod applies Thornthwaite formula. Lower boundary conditions were also determined based on soil and drains conditions. Before simulation, all data were randomly sorted out. Then, 70% of them were used to calibrate those models and the 30% of remained data were used for validation. Four statistics criteria root mean square error (RMSE), modeling efficiency (EF), coefficient of residual mass (CRM) and coefficient of determination (R2) were used for evaluating the results. The calibration results of soil physics parameters for SWAP and DRAINMOD revealed that in both models, the parameters n and Alpha had the most variations compared with the other parameters. Similar results were cited by other researchers. In calibration stage, the amount of R2 for DRAINMOD model was 87. This result showed that there was a good correlation between field and simulated data. The result of R2 for SWAP and ENDRAIN models were 83 and 93, respectively. RMSE values for DRAINMOD, SWAP and ENDRAIN were 12. 42, 10. 46 and 11. 63 cm, respectively. So, in the calibration stage, SWAP had more accuracy, compared with the other models, to determine water table. The CRM values were obtained as-0. 028,-0. 022 and-0. 061 cm for DRAIMOD, SWAP and ENDRAIN, respectively. Then, all three models lead to overestimate of water table. The results of EF were 0. 83, 0. 85 and 0. 88 for mentioned models, respectively. Validation results of DRAINMOD model revealed that RMSE, CRM and R2 were 13. 19 (cm),-0. 008 and 0. 85, respectively. These statistical criteria were found to be 17. 00 (cm), 0. 020 and 0. 82 for SWAP. These parameters were obtained as 28. 10 (cm), 0. 603 and 0. 82 for ENDRAIN model. Therefore, all the models had acceptable error to estimate water table depth. The results of EF were 0. 84, 0. 75 and-2. 80 for DRAINMOD, SWAP and ENDRAIN models, respectively. These results showed that ENDRAIN was inefficient to determine water table. It is due to lack of using parameters to simulate all boundary conditions in soil. However, since DRAINMOD simulates evapotranspiration and downside boundary conditions well, the mentioned results were better rather than two other models. Although DRAINMOD had a better accuracy compared with SWAP, both of those models had good efficiency to simulate water table. Thus, DRAINMOD had overestimate error and SWAP and ENDRAIN had underestimate error. DRAINMOD is recommended as a better model according to the higher coefficient of determination and lower error value.