Effect of erosion control measures on sediment delivery ratio

Effect of the erosion control measures on the sediment delivery ratio is studied,based on the data from the Wuding River,a major sediment-supplying tributary of the middle Yellow River.The erosion control measures have greatly changed sediment erosion,transportation and deposition processes in the drainage basin,and thereby the previously established sediment budget has also been modified.In natural conditions without human disturbance,the sediment delivery ratio over the Wuding River basin approaches 1.0.However,when the sediment delivery ratio has rapidly declined to 0.4～0.3 due to the large-scale erosion control measures having been taken since the 1960s.The dramatic change of sediment delivery ratio is caused by the formation of artificial sediment sinks,i.e.,sediment-trapping check-dams and reservoirs.Large quantities of sediment has been trapped by them,only to decrease the sediment ratio.At present,the effect of the sediment interception of these artificial sinks is 2.4～6.3 times as high as that of the sediment reduction with the slope measures such as land terracing and tree-and grass-planting.This indicates that these direct erosion-reduction measures should be strengthened in the middle Yellow River basin.