5) Results:

3) Technical details of the small portable wind tunnel:

4) Investigated soil surface treatments:

Experimental investigation on soil erosion using a small portable wind tunnel

Contact: Dipl.-Geogr. Wolfgang Fister (Fach Physische Geographie, Universität Trier / D-54286 Trier Germany / phone: +49 (0)651 201 4512 / email: fist6c01@uni-trier.de)

1) Introduction:Water and wind erosion are the main driving factors for soil degradation and desertification in semi-arid landscapes. Although, in most areas, soil erosion by water is assumed to be more important than by wind, the exact ratio between both is mostly unknown. Especially with different soil surface conditions, for example physical soil crusts, trampling by grazing flocks, ploughing, harrowing, and rolling, this ratio can change significantly.

Fister, W.1 ; Ries, J. B.1 ; Wagner J.-F.2

1 University of Trier, Department of Physical Geography; 2 University of Trier, Department of Geology

a) Physical soil crusts:Due to the high silt content soil sealing and crusting occur frequently on abandoned fields in the Ebro-basin.

b) Sheep trampling / sheep hoof impacts:Grazing sheep can often be seen on abandoned fields in semi-arid areas. Through their trampling they cause the destruction of soil crusts and therefore increase its susceptibility against wind erosion.

c) Ploughed surface:Dry farming is the common agricultural land use in these areas. Farmers therefore often plough, harrow and roll their fields.

d) Harrowed surface:Crushing soil aggregates through harrowing causes a distinct reduction of the micro morphology.

e) Rolled surface:Rolling, the last process in the dry farming system, is used to seal the soil surface against evaporation loss.

b) Air straighter

0,7 m

0,7 m

c) Wind tunnel

1 m

0,7 m

3 m

a) Fan & transition section

2 m

0,7 m

d) Sediment catching area

1 m

5 m

1,5 m

3 m

2) Main objectives:• Development of a small and highly mobile wind tunnel for use in remote areas• Determination of the wind erosion risk of different soil surface conditions on silty soils in the

Central Ebro-basin, Spain.• Registration of the ratio change between wind and water erosion due to the different soil

surface conditions.

Wind erosion by grazing sheep

a) Fan & transition section:As wind source served a fan with 5.5 hp, 163 cm³ and a two wing propeller. Its wings can be variably adjusted in different angles to change the windpower.The turbulent rotating air stream is led through a 2 m transition section made of heavy PVC-foil (1 mm).

b) Air straighter:The air straighter is made of 1 cm thick PVC sheets. Its honeycomb structure is made of 289 PVC-tubes each 4 cm in diameter.

6) Conclusion:Even if this fairly simple device is not able to simulate all of the aerodynamic parameters which are necessary to represent exactly the natural wind conditions, the mobility together with the capability to produce verifiable data from different surface conditions recommend its utilisation.

c) Wind tunnel:The channel itself is made of three separate (1 m long) sections of aluminium and perspex sheets. The sheets are stabilized and connected by three aluminium frames. The open floor results in a 2 m² test area.

d) Sediment catching area:The sediment catching area is made of usual canvas cover (tarpaulin). For stabilization the wood poles were wired together.

1 2 3 5 6 74

• Sediment output on fallow land with developed physical soil crusts is almost negligible (see column 1).

• The destruction of soil crusts through sheep trampling doesn’t necessarily cause a significant increase in wind erosion (see column 2).

• But if sheep trampling is simulated during a wind erosion event, the sediment output increases significantly (see column 3).

• The total amount of sediment output by “sheep erosion” is comparable to that of agricultural treatments (see columns 4+5).

• Increase in sediment output from ploughing to harrowing and rolling is corresponding to the reduction of soil surface roughness (see columns 5+6+7).