【Objective】The region of loess slopes covered with sporadic aeolian sand is the most
serious erosion-stricken area in the aeolian-water erosion interlaced zone of the Loess Plateau. This project
is oriented to study characteristics of the soil erosion in this region in an attempt to provide some principal
theory for prediction and control of soil erosion in the aeolian-water erosion interlaced zone. Observations in
this special region found that aeolian sand-covered loess slopes were different in runoff production pattern and
erosion process from ordinary loess slopes. So far，a little has been reported about studies on soil erosion on
this special type of slopes. 【Method】An indoor experiment with simulated rainfalls on soil erosion on
sand-covered loess slopes was carried out. The experiment was design ed to have only one rainfall intensity
（90 mm h-1），one slope gradient（15°），three levels of thickness for overlying aeolian sand（2 cm，
5 cm and 10 cm）and five patterns of particle size composition（100%＜0.25 mm，75%＜0.25 mm + 25%
＞0.25 mm，50%＜0.25 mm + 50%＞0.25 mm，original aeolian sand and 100%＞0.25 mm）. 【Result】
Results show that overlying aeolian sand layers delayed the initiation of runoff and reduced the generation rate
and volume of runoff，but increased the yielding rate and volume of sediment on loess slopes. The initiation
of runoff on slopes covered with 2 cm，5 cm and 10 cm thick of aeolian sand was 6～10 times，12～20 times
and 16～26 times later than that on the ordinary loess slope，respectively. Thickness of the aeolian sand
layer is the main factor affecting delayed runoff and sediment yield. The thicker the overlying sand layer，
the later the initiation of runoff，the lower the runoff rate and runoff volume and the higher the yielding rate
and volume of sediment yield. During the rainfall process，runoff and sediment fluctuated sharply in rate
and volume and the fluctuation intensified with the aeolian sand layer increasing in thickness. The effect of
particle size composition of the sand layer on runoff and sediment yield varied with thickness of the sand layer.
On slopes covered with a sand layer 2 cm in thickness，runoff and sediment yield tended to increase with the
sand layer increasing in particle size during the initial period of rainfall，but no such a tendency was observedduring the late period of rainfall. On slopes covered with a sand layer 5 cm in thickness，runoff increased in
rate with the sand layer increasing particle size. The slopes covered with coarse sand was higher in erosion
rate than the slopes covered with find sand during the initial period of rainfall，and it went reversely in the
late period of rainfall. On slopes covered with a sand layer 10 cm in thickness，runoff and sediment yield did
not vary much with particle size composition of the sand layer. There might be a reasonable range of aeolian
sand thickness in which the influence of particle size composition of the sand layer on runoff and sediment
yield existed. In short，thickness，particle size composition and their interaction significantly（p＜0.05）
influence the initiation of runoff，60 min runoff volume and 60-min sediment yield. 【Conclusion】 The
runoff production process on aeolian sand-covered loess slopes goes as vertical infiltration of rainwater-flow
at the interface between sand layer and loess layer-seepage at the toe of the sand layer-overland runoff，
while the erosion process goes as seepage erosion at the toe of the sand layer-retrogressive collapse caused by
gravity and flow-surface runoff transport，which are completely different from the pattern of runoff yield under
excessive infiltration and the erosion development process of splash erosion-sheet erosion-rill erosion on bare
loess slopes.
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