SLM-21306 Subsurface Solute Transport

Course

Credits 6.00

Language of instruction:

English

Assumed knowledge on:

SLM-20806 Water Quantity and Quality; MAQ-22806 Atmosphere-Vegetation-Soil Interactions.

Continuation courses:

SLM-32806 Ecohydrology.

Contents:

This course is about transport of chemicals by flowing water which affects soil and groundwater quality. During this course students will get acquainted with different aspects of solute transport in the subsoil. It contains lectures, a laboratory practical and a computer practical.
During the lectures, the physical and mathematical backgrounds of the convection-dispersion equation CDE for solute transport in soils and groundwater are discussed in detail, because the CDE is currently the basis of almost all scientific and commercially available solute transport software. The CDE is critically compared with stochastic-convective (SCM) or stream tube solute transport modelling to clarify the weak and strong points of either approach. SCM are very powerful and mathematically simple tools for addressing transport in heterogeneous soils and groundwater systems. Both ion exchange and adsorption/desorption effects on solute transport are shown. The soil hydraulic properties (retention curve, conductivity function) are discussed in relation with flow and (solute) transport. Different preferential flow mechanisms are outlined, together with their effects on solute movement, field observations methods to detect preferential flow, and modelling strategies at the local and at the regional scale.
As a computationally efficient and elegant alternative to solving the CDE, random walk simulations are discussed in class and demonstrated during the computer practical. The basic theory underlying the CDE and the stochastic-convective transport models is illustrated for a number of broadly relevant application areas, such as salinity and sodicity hazards in natural ecosystems and agro-ecosystems, pesticide and heavy metal leaching. Relatively simple mathematical tools such as moment theory are provided to give hands-on experience with applying the different transport concepts. Illustrations of complicated transport phenomena in case of spatiotemporal variability and for multicomponent transport processes are explained, giving a clear link with the laboratory and computer practicals.
The laboratory practical involves monitoring water flow and solute transport in a soil column by various sensors driven by a data logger, soil sampling in the field, various standard soil physical techniques (measurement of saturated hydraulic conductivity and the water retention curve), and several other methods and techniques.
During the computer practical emphasis is put on numerical techniques to simulate solute transport in saturated part of groundwater. First attention is paid to the different transport processes with the aid of ready maid models (applets) which are based on several analytical solutions. Next students need to derive different numerical approximations of the CDE which need to be implemented in a spreadsheet to develop numerical models. To clarify certain transport processes, an alternative to the CDE, the Random Walk method will be implemented in a spreadsheet as well. Finally commercial software will be used to setup a three dimensional groundwater and transport model including a heterogenic conductivity field. Mass moment calculations illustrate the effect of the heterogeneity on a contamination plume.

Learning outcomes:

After successful completion of this course students are expected to be able to:
- give examples of various (differential) equations and conceptual approaches for modelling solute transport;
- explain the processes involved in biochemically reactive solute transport and the concept of moment theory for interpreting transport behaviour;
- appraise the strengths and limitations of the convection-dispersion equation CDE, and judge the value of CDE and alternatives such as SCM and apply them for simple cases;
- install, connect and operate various soil sensors at an introductory level;
- critically evaluate the data the soil sensors generate to apply suitable (combinations of) instruments for observation/monitoring of solute transport in soils and groundwater;
- distinguish several numerical techniques to handle time and space scales of the CDE;
- derive numerical expressions for the CDE;
- perform model simulations of solute transport and groundwater flow.

Activities:

- attending lectures;
- laboratory and computer practicals;
- self study.

Examination:

- lab practical: assignments and report (pass/fail);
- computer practical: assignments and report (pass/fail);
- written examination (60% lectures, 40% computer practical).

Literature:

Lecture notes.