A simulation study of the development of rillenkarren

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Abstract
Rillenkarren are patterns of tightly packed, small solution rills found upon bare, sloping surfaces of soluble rocks in all climates. They head at the crest of a slope and are replaced downslope by a planar solution surface, the ausgleichfläche. Development has been simulated successfully using a rainfall simulator and plaster of paris blocks. Ten principal experiments were completed with blocks at inclinations ranging 22½–60°, temperature and rainfall intensity being constant. Results suggest that rillenkarren develop within a hydrodynamic zone of rim effect where the depth of threads or sheets of runoff is insufficient to prevent direct raindrop impact upon the underlying soluble solid. Where depth of runoff becomes sufficient rills are replaced by the ausgleichfläche. Between upper and lower limits, rill length is proportional to slope in a log linear manner. Rill cross‐sections approximate the parabola, the most effective shape for focussing raindrop erosion in the axis of the trough: this explains the tight packing characteristic. Ausgleichfläche and rill troughs evolve by parallel retreat at the original slope angle, the erosion rate being greatest at about 45°.