This research investigated hillslope subsurface flow processes and the
mechanisms of runoff generation in a forested catchment in British Columbia in response
to rainfall and snowmelt events. Observations at a hillslope segment included subsurface
outflow from a soil pit, ground water levels, hydraulic conductivities, and snow water
equivalent. Stream discharge and meteorological data were monitored in the catchment.
Subsurface flow at the hillslope segment responded rapidly enough to inputs of
rain and snowmelt to contribute to stormflow at the catchment scale. On a contributing
area basis, outflow from the pit at the hillslope segment exceeded peak stream discharge
and total runoff, indicating that subsurface flow is able to contribute significantly to peak
stormflow and event runoff at the catchment scale.
Estimates of catchment-wide subsurface flow cannot be reliably estimated by
scaling up pit outflow using the ratio of pit length to the length of stream bank seepage
faces in the watershed. Estimates of effective contributing area to pit drainage at the
hillslope segment that were derived from runoff ratios, surface topography, and water-balances
varied. Contributing area estimates based on runoff ratio were much higher than
estimates based on topographic survey and water balance method. This lack of agreement
indicates that it is problematic measured pit outflow to extrapolate to the catchment scale
using contributing area ratios.
Peak rainfall intensity explained 79% of the variation in total subsurface flow
volume from mineral section 2 of the pit for 7 rainfall events in 1998-99 and total
precipitation and 7-day precipitation prior to storm were not significant. However, drier
antecedent soil moisture conditions have a major role in generating subsurface flow.
During the snowmelt season, outflow from the organic horizon was generated as
saturated throughflow and overland flow as a result of the rising water table. However,
during the autumn storms, outflow from the organic horizon occurred as a lateral
subsurface flow despite the fact that the mineral soil was unsaturated, possibly due to the
existence of hydrophobicity at the boundary between the organic horizon and mineral
soil.
The results of this study contradict assumptions of quasi-steady state,
topographically driven flow in models such as TOPMODEL and TOPOG. For the wet
soil moisture conditions, the fraction of outflow from the individual mineral sections
varied with time and with changes in total mineral horizon outflow throughout the melt
season. For dry soil moisture conditions, the fraction of outflow from the organic horizon
and individual mineral sections varied with changes in pit outflow. In addition, relations
between hillslope discharge and water table elevation measured from the well throughout
the melt season and during autumn storms showed marked hysteresis.
Saturated hydraulic conductivity back-calculated from Darcy's law was more than
an order of magnitude higher than the saturated hydraulic conductivity values derived
from slug tests. However, both methods generated values within the range of results of
other studies in forested areas. The larger estimated hydraulic conductivities are likely
due to existence of root channels as preferred pathways in forested hillslope.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/11775 |
| Date | 11 1900 |
| Creators | Kim, Hyeong Jeong |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Relation | UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/] |
Page generated in 0.0143 seconds