Two-dimensional Water Flow Model Research Articles

Use of environmental isotopes to define the capture zone of a drinking water supply situated near a dredge lake

Summary Lake–ground water interactions in the vicinity of a dredge lake (Lake Leis; SW Germany) were studied by means of the stable isotopes ( 18 O, 2 H) mainly to determine the capture zone of a pumping well for the drinking water supply to the nearby town of Baden-Baden. The water supply is situated in a Quaternary gravel aquifer of the Rhine Valley. Numerical simulation performed using a two-dimensional water flow model was not able to characterise the capture zone uniquely. Several best fit options were possible by applying the values of hydraulic conductivities obtained from the pumping tests. As a result it was not possible to define whether Lake Leis is situated either completely inside or fully outside of the capture zone. To overcome this problem and to define the shape of the catchment area of the water supply precisely, a two-dimensional water flow and tracer transport model was established using both hydraulic heads and isotope data. The isotope data were applied to determine the proportion of lake water in down-gradient pumping and observation wells. Additionally, the isotope compositions of lake water and those in observation wells, measured as a function of time, were used to determine the mean water velocity ( v = 0.6 m/d) along some selected 200 m long flow-paths. Based on known porosity and hydraulic gradient values, a hydraulic conductivity of about k = 6 × 10 −4 m/s was determined for the central area down-gradient of the lake. This hydraulic conductivity and the proportion of lake water in the groundwater were used to calibrate a numerical two-dimensional regional scale transport model. The study demonstrates that it is possible to calibrate a water flow model in the vicinity of a dredge lake uniquely, only when stable isotope signals measured in a time series in both the lake and groundwater are taken into consideration. The calibrated model finally enables the capture zone of the production well to be precisely defined.

Fluid and Solids Flow Affecting the Solids Circulation Rate in Spouted Beds with a Draft-Tube

In a spouted bed, the gas flow rates cannot be changed independently in either the spout or the annulus. In this study, an experimental spouted bed equipped with a draft-tube was made in such a way that each of the gas flow rates can be changed independently. The effect of the gas flow rate in the spout or in the annulus on the circulation rate of solids was examined for the three types of spouted bed. The relation between the solids circulation rate and the average gas velocity in the annulus differs among these three types of spouted beds. In the spouted bed with a gas inlet nozzle, the solids circulation rate initially sharply decreased with the average gas velocity in the annulus. It was found that an eddy motion of solid particles caused this sharp decrease in the solids circulation rate. The fluid flow that caused this eddy motion in the solids was confirmed by using a two-dimensional water flow model.

MEASURING AND MODELLING OF SOIL WATER DYNAMICS AND RUNOFF GENERATION IN AN AGRICULTURAL LOESSIAL HILLSLOPE

Surface runoff may be generated when the rainfall intensity exceeds the infiltration capacity, or when the soil profile is saturated with water. Indications exist that both types of overland flow may occur in hilly agricultural loess regions. Here, for a loessial hillslope under maize in the southern part of The Netherlands, it was shown, with pressure head and runoff measurements, that Hortonian overland flow occurs during typical summer rain events. Surface runoff was initiated after saturation of the top 5–10 cm of the soil. Deeper in the soil, unsaturated conditions prevailed while runoff took place. Peak runoff discharges at the outlet of the subcatchment occurred a few minutes after peak rainfall intensities were measured. It appeared that SWMS_2D, a two-dimensional water flow model, was capable in simulating observed pressure head changes and runoff. Simulated potential runoff for the transect studied was higher by a magnitude of three than the measured areal average. This indicates effects of surface ponding, and the probable location of this particular transect in a region with high runoff production.

MEASURING AND MODELLING OF SOIL WATER DYNAMICS AND RUNOFF GENERATION IN AN AGRICULTURAL LOESSIAL HILLSLOPE

Surface run-off may be generated when rainfall intensity exceeds infiltration capacity, or when the soil profile is saturated. Both types of overland flow may occur in hilly agricultural loess regions. It was shown with pressure head and run-off measurements that Hortonian overland flow occurs during summer rain events. A two-dimensional water flow model could simulate pressure head changes and run-off. Simulated potential run-off for the transect studied was three times as high. This indicates effects of surface ponding and the probable location of this particular transect in a region with high run-off production.