Galvanized pans and a garden water bucket are used to create a small rainfall simulator.
Different soil conditions are used to demonstrate the effects of soil cover and management practices on water erosion.
Have the students form hypotheses about
- time to intiation of runoff;
- amount of runoff; and
- runoff water quality (amount of sediments in water)
Return to Dr. Dirt's K-12 Activities
Return to Erosion
The
galvanized pans are bent slightly to give a lip on one side to direct
water flow (visible in larger image), and filled with
the same soil. Surface conditions effects on soil loss may be shown
using turf (living grass), bare soil, and a mulch (straw. grass
clippings, wood chips, etc.). A silt fence used to limit sediment loss
from construction sites is simulated here.
Prop
the pans to provide uniform slopes, and to catch runoff in the cups.
Use glass cups for best qualitative visual results. A garden watering
can is used to simulate rainfall. Three cans used simultaneously
provide instant comparisons. Note time until runoff begins on each pan,
and clarity of runoff (amount of sediments in the water). Slope can be
varied to observe its impact on runoff and erosion.
Observe
the difference in clarity of the runoff and amount of sediments in each
cup. Vegetation on the surface greatly limits soil loss. The silt fence
(or mulch) limit soil loss relative to the bare surface.
This
closeup shows the color of the runoff, and the amount of sediments in
the bottom of the cups. The cups are in the same order, so the silt
fence is on the left, bare surface in the middle, and vegetated surface
on the right. When the turf is fresh, the runoff is usually clear.- Measure quantities of water added and time (for rate of precipitation).
- Measure quantites of runoff, time to initiate runoff, and time to completion of runoff.
- Measure the slope (rise over run, report in per cent)
- Quantity of sediments may be determined by pouring runoff through preweighed filter paper, then oven-drying the paper.
- Erosion rate may be determined by calculating the area of the pan (the area of a circle will be close enough), and dividing the mass of the eroded soil by the area of the pan, e.g., grams per square centimeter.
- Use multiple replications. Multiple runs on the same pans is a reasonable estimate, though if the pans are dry at the beginning, the amount of runoff will vary due to differences in infiltration.
- Vary the treatments, e.g., evaluate the effect of slope (0 to 10%), alter the amount of surface cover, etc.
Copyright, Clay Robinson, PhD, CPSS, PG, 2009.