Reducing Runoff/Soil Erosion by Afforestation in a Semiarid Area
Investigators (most current known information)
The undertaken research project addresses increased sustainability of semiarid lands by afforestation, expressed herein by a decrease in runoff and soil erosion and particularly in decrease in gullying from a previously overgrazed and presently savannized semiarid area in the Northern Negev. This has been undertaken in the Bikhra Basin. Automatic monitoring of rainfall, runoff and sediment was undertaken in large (0.6 and 1.6 km2) basins as well as in 2 pairs of 1st order basins (7-12 ha), of which one each is gullied and the other ungullied with considerable bank vegetation. This study also included monitoring of bedload particles moved from hillslopes and in 1st order channels.
- Rainfall and runoff increase water content in alluvium underlying the channels by about 5% to a depth of 1-1.5 m, but we could not determine whether the downward seepage reaches the jointed chalks underlying the alluvium. This, it is uncertain whether and to what extent runoff increases deeper-lying groundwater storage. Runoff events occurs 20% more often in the unforested area than in the afforested (savannized) area.
- Event unit runoff is higher (1.4 mm vs 1.0 mm) in the unforested basin. The runoff from the afforested area is higher than expected, likely due to areas which have not been treated or where mechanical devices moved over the soil.
- Runoff occurs earlier in the gullied basins (in comparison with the vegetated, ungullied basins).
- The suspended sediment concentration was on average higher (20,000 mg/l) in the gullied basins than in the ungullied basins (15,900 mg/l during hydrograph rise and 9,300 mg/l during recession).
- Bedload yield is high and includes coarse particles in the gullied channels. The source of the coarse-texture sediment was found to be gully walls as well as sediment mobilized in steep hillslopes.
- The lower runoff in the savannized area contributes altogether lower erosion (133 T/km2 ) than the afforested area (268 T/km2).
In summary, it has been found that similar to afforestation, savanization decreases runoff and therefore sediment transport, thereby increasing soil moisture and decreasing soil erosion.
No outcomes reported