Hydrodynamic dispersion is a measure for describing the process of solute transport in porous media.Characterizing the dispersion of water flow within gravel is essential for the prediction of solute transport especia...Hydrodynamic dispersion is a measure for describing the process of solute transport in porous media.Characterizing the dispersion of water flow within gravel is essential for the prediction of solute transport especially nonpoint source pollutants migration in alpine watersheds where the land surface is typically covered with gravel.In this study,an integrated model and experimental method using an electrolyte tracer is proposed for determination of the hydrodynamic dispersion coefficient.Two experimental scenarios were designed to measure electrolyte tracer transport processes in both free water flow and gravel layer flow under different slope gradients and transport distances.Subsequently,the measured data were used to simultaneously calculate both the hydrodynamic dispersion coefficient and flow velocity by fitting the experimental data with the mathematical model.Dispersivity,as a critical feature of hydrodynamic dispersion,was determined as well under the two specified scenarios.Finally,the impact mechanisms of the gravel layer and factors related to the dispersion processes were comprehensively analyzed.The results indicate that the presence of a gravel layer significantly reduces flow velocity and the hydrodynamic dispersion coefficient,but increases solute dispersivity.For the flow within gravel layers,with much lower velocity,the positive effect of the gravel layer on dispersivity may be neutralized or even surpassed by the negative effect of flow velocity.The results should be helpful in characterizing the dispersion processes of water flow within gravel layer and hence in predicting solute transport,especially in nonpoint source pollutants migration in alpine watersheds where the land surface is richly covered with gravel.展开更多
In order to satisfy the demand of land use, reclamation engineering has been undertaken in coastal cities for a long time. To study the contaminant transport in the reclamation districts, robust and accurate estimatio...In order to satisfy the demand of land use, reclamation engineering has been undertaken in coastal cities for a long time. To study the contaminant transport in the reclamation districts, robust and accurate estimation of dispersion coefficient is essential. In this study, the continuous sodium chloride （NaC1） solution with constant concentration was introduced into the column filled with the dredger fill to get the breakthrough curves （BTCs）. Inverse error function method （IEFM） and CXTFIT program were used for estimating dispersion coefficient. Results showed that the difference between the dispersion coefficients estimated by IEFM and CXTFIT program was slight. The main reason was that the BTC was not strictly linear. IEFM performed poorly in the nonlinear area, while the CXTFIT performed well over the entire BTCs. Moreover, the dispersion coefficient of dredger fill was small. The dispersion property of dredger fill would result in the slow migration of contaminants in the dredger fill.展开更多
基金This work was supported by the National Natural Science Foundation of China(Grant no.41571274 and 41230746)the Foundation of State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau under project(Grant no.10501-1209).
文摘Hydrodynamic dispersion is a measure for describing the process of solute transport in porous media.Characterizing the dispersion of water flow within gravel is essential for the prediction of solute transport especially nonpoint source pollutants migration in alpine watersheds where the land surface is typically covered with gravel.In this study,an integrated model and experimental method using an electrolyte tracer is proposed for determination of the hydrodynamic dispersion coefficient.Two experimental scenarios were designed to measure electrolyte tracer transport processes in both free water flow and gravel layer flow under different slope gradients and transport distances.Subsequently,the measured data were used to simultaneously calculate both the hydrodynamic dispersion coefficient and flow velocity by fitting the experimental data with the mathematical model.Dispersivity,as a critical feature of hydrodynamic dispersion,was determined as well under the two specified scenarios.Finally,the impact mechanisms of the gravel layer and factors related to the dispersion processes were comprehensively analyzed.The results indicate that the presence of a gravel layer significantly reduces flow velocity and the hydrodynamic dispersion coefficient,but increases solute dispersivity.For the flow within gravel layers,with much lower velocity,the positive effect of the gravel layer on dispersivity may be neutralized or even surpassed by the negative effect of flow velocity.The results should be helpful in characterizing the dispersion processes of water flow within gravel layer and hence in predicting solute transport,especially in nonpoint source pollutants migration in alpine watersheds where the land surface is richly covered with gravel.
基金Supported by the Tianjin Research Program of Application Foundation and Advanced Technology(No.10JCZDJC24700)
文摘In order to satisfy the demand of land use, reclamation engineering has been undertaken in coastal cities for a long time. To study the contaminant transport in the reclamation districts, robust and accurate estimation of dispersion coefficient is essential. In this study, the continuous sodium chloride （NaC1） solution with constant concentration was introduced into the column filled with the dredger fill to get the breakthrough curves （BTCs）. Inverse error function method （IEFM） and CXTFIT program were used for estimating dispersion coefficient. Results showed that the difference between the dispersion coefficients estimated by IEFM and CXTFIT program was slight. The main reason was that the BTC was not strictly linear. IEFM performed poorly in the nonlinear area, while the CXTFIT performed well over the entire BTCs. Moreover, the dispersion coefficient of dredger fill was small. The dispersion property of dredger fill would result in the slow migration of contaminants in the dredger fill.
