| Summary: | Four artificial tracers were applied to a small headwater catchment in south western
British Columbia to study runoff generated from topographically distinct landscape units.
The seven hectare catchment is located in the University of British Columbia Malcolm
Knapp Research Forest at low elevation (190-280 masl). A weir, multiple tipping bucket
rain gauges and several piezometers were used to collect hydrological data. Three
separate landscape units were identified based on topography, soil properties and
proximity to the stream. The units included an area of shallow slope and deep soil, a
riparian area along the intermittent stream channel and an area of very shallow soil with
bedrock outcrops on a steep slope. Tracers used included rhodamine-WT, uranine,
sodium chloride and potassium bromide. A suite of ion selective and fluorometric probes
were used along with automated water sampling to monitor tracer breakthrough. The
collected samples were analysed in the lab to validate the field measurements. Tracers
were dissolved in solution and applied aerially with a backpack sprayer at the onset of
forecasted precipitation events to facilitate rapid infiltration into the soil. The first
application took place January 4th, 2006. Measurements were then taken continuously
until March 20th, 2006, when a second round of tracers was applied to the landscape
units. During the first measurement period, 532 mm of precipitation fell below the forest
canopy over 75 days. During the second 78 day measurement period, 290 mm of rain fell.
It was found that the overall wetness of the catchment affected travel times significantly.
Large storms during the first, significantly wetter, application period exhibited similar lag
times from peak event discharge to tracer arrival between the different landscape units.
During small precipitation events and under dryer conditions, travel times were greatest in the area of shallow slope and deep soils. These lag times are indicative of longer
pathways and perhaps the non-initiation of preferential flow below certain thresholds. In
general, it was concluded that delineating catchments into groups of similar landscape
units based on physical characteristics may be a promising new approach to explaining
catchment runoff response.
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