The purpose of this paper is to use the application of the multilinear lag cascade model as a contaminant transport model through river networks. Monocacy River and Antietam Creek data, which were collected by USGS with different reach lengths and discharges conditions, have been used in the current study. It was found that multilinear discrete lag-cascade (MDLC) model is capable of reconstructing contaminant breakthrough curves. A complete study was performed to estimate the reach length for use in the accurate simulation, and it was concluded that by assuming a uniform flow through the reach, the length unit should be obtained by applying Pe = 12. Moreover, by using temporal moment matching, explicit relationships for MDLC model parameters (k, n, and τ) and based on conventional advection-dispersion equation (ADE) parameters (D, u, x) were extracted. MDLC parameters of the field breakthrough curves were extracted, and it was found that the increase of Pe number caused to increase of delay time and the number of cascades. However, the residence time was obtained to be fixed. Additionally, by assuming the dispersivity parameter (D/u) is constant, the changes in the MDLC parameters were investigated by velocity variation, and new relationships were proposed to estimate its parameters under different hydraulic conditions. Using presented equations provided in this study for residence time (k), cascade number (n), and delay time (τ), the sensitivity analysis was performed, and it was found that the parameters of velocity (u), dispersion coefficient (D), and velocity (u) have the most important effect in calculation of them, respectively.
Due to the entrance of pollutants in different branches of the river network, it is essential to study contaminant transport at the river confluences. In the present study, it was attempted to investigate the conservative pollution transport at channel confluence by operating a series of experiments in the laboratory flume. In the designed laboratory model, two branches, with different widths of 45, 25 cm, were intersected and a channel confluence was created. Five entrance discharges and three initial contaminant concentrations, introduced using a linear feeder, were chosen as experimental variables. Conservative tracer of sodium chloride solution was used, and the electrical conductivities were measured at eight locations of the main channel and upstream branches with 2 seconds interval. Junction zone was assumed as a control volume, and by applying mass equilibrium to it, a new mathematical model was extracted. It was observed that there is concentration fluctuation in the falling limbs of the experimental breakthrough curves of the junction zone; however, it was diminished by downstream motion. Moreover, the observed pollute graphs had double peak points which changed to a single point with an increase of distance from the confluence position. Operation of the presented model was investigated by variation of its parameters. It was found that the contaminant residence time parameters of the confluence zone have the most significant influence in the simulation of the analytical model. Additionally, it was observed that the values of Gaussian distribution of the upstream branches could displace the position of pulses of resultant breakthrough curves or can overlap them. Moreover, the model performance was examined using statistical goodness of fit parameters like Nash-Sutcliff, R2, and MAE. Their values were calculated as 0.88, 0.91, 66.88 (ppm), respectively.
The current study tried to investigate the hydrodynamic characteristics and the pollution mixing and dispersion from the sub-branch through the river confluence using the numerical model of Flow3D. A numerical model was used with length, width, and height of (7 × 1 × 1) m. Also, the nested mesh was used in the junction to refine the modeling and result depiction. It was observed that if there is a water level difference on both sides of the junction, the mixing will occur much faster, and only longitudinal mixing will prevail downstream of the junction. Therefore, it was concluded that to reduce the contamination effect through the river networks, the water level in the main channel should be higher than the subbranch. In the flow separation zone, several clockwise vortices were observed, which become weaker by moving towards the outer wall of the channel. Also, the most significant velocity vectors and also the highest contaminant concentration was observed in this region. Moreover, the vertical distribution of pollution concentration showed that the contaminant concentration would be higher at large distances above the channel bed. The highest values of turbulent intensity and turbulent Kinetic energy were also observed in flow recirculation zone. It was concluded that by increase of concentration gradient through the shear layers, the required mixing length for complete transvers pollution mixing would be decreased.
Considering the importance of rainfed agriculture in adaptation to nature and long-term sustainability in human food supply and livelihood of farmers, the main purpose of this study is to investigate the potential of rainfed agriculture in the Zarrinehroud basin as this basin is one of the most important sub-basins of Lake Urmia. For this study, the remote sensing data of surface soil moisture and evapotranspiration were combined with the SWAT model using the Data Assimilation method, Ensemble Kalman Filter (EnKF). Calibration of runoff flow rate in SWAT model showed the correlation coefficient ranging between 0.69 and 0.84 in the calibration period (2000–2009) and between 0.64 and 0.86 for the validation period (2010–2014). The assimilation of the remote sensing data with the calibrated SWAT model showed that the model simulations for both the variables of surface soil moisture and actual evapotranspiration improved by at least 25% in both 2010 and 2014. It has been determined that 10.5 and 25.4% of the region's lands have a Very Appropriate and Appropriate potential for rainfed wheat agriculture, respectively. Areas with Moderate and Inappropriate potential occupy 64.1% of the lands in the region.
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