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Tahereh Gholami Estalkhi Kohi; Maryam Navabian; Mehdi Esmaeili Varaki
Abstract
Construction of drainage systems is inevitable in paddy fields to control the level of waterlogging during rice harvest and cultivation of the second crop. Finding the best design option of drainage is very important from the point of view of environmental and economic issues. This study was conducted ...
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Construction of drainage systems is inevitable in paddy fields to control the level of waterlogging during rice harvest and cultivation of the second crop. Finding the best design option of drainage is very important from the point of view of environmental and economic issues. This study was conducted with the aim of investigating the performance of open drains including pressure head and depletion flux in controlling the water level in the cultivation of rice plants and the second plant in paddy fields. In this regard, the performance of open drains during rice and the second crop growth period was simulated using HYDRUS-2D model. To calibrate and validate HYDRUS-2D model, the required information was collected from 130 hectares of paddy fields in Nodeh, Jirsar and Nupashan villages in Soumesara region, in 2019. Soil texture, bulk and specific density, porosity and infiltration rate were measured. Also, pressure head of water was measured monthly in the region by piezometers. After validation, different open drain design options (bottom width and depth of drain) were run in HYDRUS-2D and its results were compared. The simulation results showed that the HYDRUS-2D had a reasonable accuracy in simulating the changes in water pressure head. The statistical indexes including R2, RMSE, nRMSE and MAE in the calibration stage were 0.98, 4.39 cm, 1.6%, and 3.55 cm, respectively, and 0.98, 4.33 cm, 1.67%, and 3.37 cm in the validation stage, respectively. The results showed that the open drain with a depth and bottom width of, respectively, 200 and 170 cm had the best performance for controlling water table during rice and the second crop cultivation, with a discharge rate of 726440 and 169960 cm3 per unit of drain length, and the reaction coefficient of 0.293 and 0.583 per day, respectively.
Mahsa Hasanpour Nodehi; Maryam Navabian; Mehdi Esmaeili Varaki
Abstract
The purpose of this study was to evaluate WASP7.3 model in simulation of drainage water quality of paddy fields in Nodeh and Nopashan villages of Someh Sara township located in F4 unit of Sefidrood irrigation and drainage network. To evaluate the model, drainage discharge and drain water quality at nine ...
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The purpose of this study was to evaluate WASP7.3 model in simulation of drainage water quality of paddy fields in Nodeh and Nopashan villages of Someh Sara township located in F4 unit of Sefidrood irrigation and drainage network. To evaluate the model, drainage discharge and drain water quality at nine sections of drainage and nine drainage inlets and outlets were measured and introduced to the model. Model sensitivity analysis showed that in simulation of salinity and nitrate, drainage discharge was effective, while in simulation of orthophosphate and ammonium, in addition to drainage discharge and diffusion coefficient, phosphate dissociation coefficients in water column (orthophosphate), nitrification rate, and temperature coefficient of nitrification (ammonium) were more sensitive. Results showed that discharge, nitrate, orthophosphate, ammonium, biological oxygen demand, dissolved oxygen, and salinity were simulated with normalized root-mean-square error of, respectively, 0.166, 0.176, 0.143, 0.283, 0.148, 0.179 and 0.156. According to the results, the accuracy of the model simulation in the study area was classified as acceptable for all parameters, except for ammonium, and is recommended for simulating drain water quality. Due to the limitation of the model to obtain the number of discharge functions of the input and output sources to the drainage channel, application of the model in the main paddy field drainage canals that have fewer inputs than field drainage, can improve the simulation results.