|dc.description.abstract||In recent years, the field of geotechnical engineering has identified the significance of the
surface mass flux boundary condition on the soil water flow conditions through the vadose
zone of the soil profile. This thesis investigates the soil surface flux which is directly a
result of the vegetative cover in the form of transpiration. Application of transpiration
theory may be extended to any geotechnical engineering problems which involves
vegetated surfaces. Typical applications include moisture redistribution evaluation for
volume change and stress analysis, contaminant transport and evaluation of the
performance of soil covers over hazardous waste sites.
Historical literature on the available methods to predict transpiration and root water
uptake were consulted. Methods available varied between highly empirical methods,
which lack accuracy, to physically based methods which are too complicated for practical
use. A semi-empirical method of evaluating the transpiration rate by the potential
evaporation rate, degree of vegetative cover and matric suction profiles through the root
zone was determined to be reasonable for use by geotechnical engineers. The method was
incorporated into an existing l-dimensional heat and mass transfer finite element computer
program by the name of ' SoilCover'.
A laboratory program was conducted to measure the evapotranspiration flux rate from a
vegetated soil surface and the moisture redistribution patterns through the soil profile.
The experiment consisted of a vegetated soil column system placed in an environmental
chamber. The surface of the soil column was allowed to evapotranspire at the prevailing
rates and the base of the soil column was subject to a hydraulic head boundary condition
for a period of 47 days followed by a zero flux boundary condition. In addition to the
base and surface flux rates of the soil column, the soil column profile was instrumented for
matric suction, temperature and manual water content determinations. Climatic variables
measured in the environmental chamber included pan evaporation rates, evaporating pan
and ambient temperature, and ambient relative humidity.
Data from the laboratory program were used to verify the proposed methodology to
predict transpiration. As well, a field data set from the Matador Site program, was used
to verify the predictive methodology using typical field data. In both cases, the analytical
solution provided by SoilCover was in agreement with the measured data trends. The
predictive methodology appears to be a simple method with variables which are relatively
easy to define and measure by geotechnical engineers. The most difficult factor in the
predictive methodology involves the definition of the boundaries of the active root zone.
In the laboratory program, the upper limit of the active root zone did not perform in a
reproducible fashion. Alternatively, the field data simulation results show the lower root
boundary to behave in a relatively unpredictable manner. However, the active root
boundaries could be calibrated using measured surface flux and water content profiles for
both the laboratory and field cases. Also, relatively minor changes to the definition of the
active root zone result in significantly modified results for both data sets. The
unpredictable behavior of the active root zone is of particular concern to predictive
modelling attempts, if a detailed data set is not available.
In summary, this thesis demonstrates the ability to incorporate knowledge and theories
which were developed by soil scientists. With this knowledge, geotechnical engineers can
be successful in providing analytical solutions to the problem of the surface flux
transpiration boundary condition.||en_US