Little Panola is a
scale model of a hillslope in Panola Mountain State Park, near Atlanta Georgia.
The Panola hillslope has been the site of extensive research into subsurface flow paths,
chemical and nutrient fluxes and the interactions
between vegetation, soils and hydrology (Peters et al 2000, Hooper 2001). One of the findings of the
Panola experiments was the profound impact of subsurface topography on flow,
despite the fact that 80% of inputs are lost to deep seepage into the permeable granitic bedrock (Tromp-van Meerveld and McDonnell, 2006)! The bedrock was found to control
routing of subsurface flow (Freer et al 2002) (which in turn controlled the chemical
weathering of the subsoil (Burns et al 2001)) as well as creating a threshold before lateral subsurface flow would occur (Tromp-van
Meerveld and McDonnell, 2006).
The observation of the importance of the bedrock topography lead to the creation
of Little Panola, a 11:1 scale model of the Panola hillslope.
Little Panola was built by Martin Frey, in the Fall of 2004,
while he was visiting the Jeff McDonnell watershed lab at Oregon State
University from Switzerland. The bedrock is stacked plywood overlain with
cement and waterproof paint. The bedrock and surface topographies are based on a survey
of Panola by Freer et al (2002). The soil
used in the laboratory model is coarse
laboratory sand (12/20 grade Accusand), which was chosen to scale the capillary
fringe of the Panola soil, a sandy loam. Rain is supplied with a sprinkler
system 3 meters above the table sprinkling at a constant rate of 20 ± 7 mm/hr.
Recent experiments include tracer experiments on both clothed
(with soil) and naked Little Panola (soil removed, see link above). Dyed salt
solutions were injected at various sites on the hillslope (see labeled sites in
figure to right), as well as in 3 line injections to help determine the
importance of bedrock and surface topography on flow paths, as expressed in the
mean residence time (MRT) and the dispersion coefficient of hillslope subsurface
flow. The breakthrough of the tracer was measured at the base
of the hillslope (YSI EC Probe), integrated across the base. The
concentration was normalized by dividing by the total salt discharged. All
injections were during steady state conditions, based on hillslope discharge,
and measurements were made until the EC returned to pre injection levels,
generally less than 1 hour. Experiments were repeated at 5 slopes, 6o, 8o, 14o,
18o & 24o. 14o is the slope of Real
Panola.
By clicking on the index below, you can see the salt breakthrough
curve from the trench at the hillslope base for each of the labeled sites,
or selected summaries of the experiments.