| Terraced apples are the pillar industries of the economic development in Loess Hilly and Gully Region.The terraced apple fields in Yan'an City have an area of nearly 2.5 million mu,with the output value exceeds 10 billion.It is an important manifestation of the development of "green water and green hills are Jinshan and Yinshan" in the eco-industry of Loess Plateau.In the context of global climate change,combined with the uneven spatial and temporal distribution of precipitation on the Loess Plateau,the frequency of extreme rainstorms in flood season has increased significantly in recent years,and the safe and efficient production of terraced orchards is seriously threatened.This study is aimed at the frequent occurrence of extreme rainstorms in Hilly and gully areas of the Loess Plateau,which seriously threatens the safety of terraced orchards.However,the studies about the effects of terraced orchards on different standards of extreme rainstorm erosion control are still weak.Therefore,field simulated rainfall experiment was carried out on Fangta terraced orchard in Yan'an,in order to studied the role of erosion control factors in terraced orchards during the process of raising the standard of rainstorm from once in a century to once in a thousand years.To provide scientific and technological support for the safe production of millions of Mu terraced orchards in Loess Hilly and gully areas.The results are as follows:(1)The process of runoff production in terraced orchards under different underlying surface conditions was studied,and clarified the effects of different regulatory factors on runoff production.Compared with terraces without regulating factors,when the rainstorm standard is raised from once in a hundred years to once in ten thousand years,it increases with the rainstorm standard:(1)The effect of fruit trees on runoff time was lagged,from 17% to 1.03%.The absolute reduction of runoff rate was relatively stable.And the total reduction rate of runoff was reduced from 17.76% to 4.87%.(2)The regulation effect of slope vegetation on runoff time was lagging effect.The lag time under different rain intensity is basically stable at about 140%;the reduction effect on runoff rate is increased from 21.11% to 28.26%;the total runoff yield reduction rate increased from 22.81% to 26.98%.(3)The effect of litter on runoff time was also lagged,from 119.05% to 43.3%.The effect of litter on runoff rate was increased from 39.35% to 55.9%.The reduction rate of total runoff yield was about 2 times that of slope vegetation,reaching 52.55%.The lagging effect of slope vegetation on runoff time is higher than that of fruit trees and litter,and the ability of litter to reduce runoff rate and total runoff is higher than that of slope vegetation and fruit trees.Overall,litter played a dominant role in the process of runoff control.(2)The regulation mechanism of different erosion control factors on erosion and sediment yield process in terraced orchards was revealed,and established the calculation relationship of sediment carrying capacity under different underlying surface conditions.Compared with terraces without regulating factors,when the rainstorm standard is raised from once in a hundred years to once in ten thousand years,it increases with the rainstorm standard:(1)The effect of fruit trees on sediment transport rate increased from 9.04% to 20.78%.(2)The effect of slope vegetation on sediment transport rate decreased from 18.26% to 14.21%.(3)The effect of litter on sediment transport rate decreased slightly with the increase of rainfall intensity,from 72.34% to 65.01%.Litter played a dominant role in controlling erosion and sediment yield.Based on the field test data of rainfall runoff and sediment under different underlying surface conditions,such as fruit trees,bare slope,vegetation and litter,the erosion and sediment transport laws under different underlying surface and rainfall intensity were studied.(3)The change trend of soil moisture under different regulatory factors was discussed,and the response of soil moisture under different standard rainstorms was clarified.Under rainstorm conditions,the runoff yield form of terraced orchards is Horton runoff,and runoff duration was the key factor affecting soil moisture.The effect of different regulators on soil infiltration capacity was different.Under fruit tree regulation,the improvement of soil infiltration capacity was weaker than that of litter and slope vegetation.The effect of slope vegetation and litter on soil infiltration capacity is similar,which can significantly increase soil infiltration capacity.Compared with the fruit tree,the soil moisture content of slope vegetation and litter increaseed by 17.23%~14.36%.(4)The benefits of water and sediment reduction under terraced orchard mode were given,and the criteria of rainstorm prevention for terraced orchard were obtained.The orchards in the terraced fields had good growth conditions.There are many kinds of vegetation on the terraced slopes with high coverage and abundant litter layers.They had strong ability to control rainfall and sediment.Compared with the non-regulated factors,the water and sediment reduction benefits were 84.68%~89.14% and 86.43%~92.56%,respectively.Under the condition of rainstorm every ten thousand years,the erosion modulus was 93.75t/km2,which was much lower than the allowable amount of soil erosion.The results showed that the current situation of Fangta orchard can withstand the once-in-ten-thousand-year rainstorm disaster,which was similar to the results of the study on the one-hundred-year rainstorm in 2013.Therefore,the comprehensive control model of Yan'an Fangta orchard can be used as a model for the terraced orchard in Hilly and gully areas of the Loess Plateau. |
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