| The serious soil erosion in the Yellow River basin and its impact on the runoff and sediment of the Yellow River have always been a hot issue for related research.In recent decades,with the implementation of soil and runoff conservation measures in the central part of the Loess Plateau,the runoff and sediment amount has been significantly changed in the area,and characteristics of ruuoff and sediment in basin have been also changed significantly.The quantitative study of the sediment reduction contribution of various soil and ruuoff conservation measures in the Yanhe River basin and the investigation of whether there are synergistic sediment reduction benefits among the measures have important reference values for the future construction of soil and ruuoff conservation measures in the basin.The Yanhe River basin was been taken as the research object,which is located in the middle reaches of the Yellow River.Based on the long series of meteorological and hydrological data,statistical data of soil and ruuoff conservation measures,theoretical knowledge of interdisciplinary disciplines such as soil and ruuoff conservation,hydrology and ecology were applied.And hydrological analysis,statistical analysis,GAMLSS model and quantile attribution analysis were used to quantitatively analyze the influence of climate and human activities on the ruuoff and sediment changes in the Yanhe River basin.The author further calculated the sediment reduction amounts of check dams,terraces,forestry measures and the synergistic sediment reduction benefits among the measures,and discussed the differences among different methods.The main research results are as follows:(1)The trend and abrupt change points of annual precipitation from 1956 to 2015,and annual runoff and sediment transport from 1952 to 2018 in the Yanhe River basin were analyzed.The results show that there is no significant trend in annual precipitation;the annual runoff and the annual sediment transport have a significant decreasing trend.The year of abrupt change in runoff is 1996(p<0.05),and the year of abrupt change in sediment transport is 1996(p<0.05)and 2005(p<0.05).(2)The runoff modulus and sediment transport modulus of different hydrological control areas in the Yanhe River basin were calculated for different time periods.1980-2015,the average annual runoff modulus of the basin is 32500 m3/(km2.a)and the average annual sediment transport modulus is 5598 t/(km2.a).The time periods of strongest runoff and sediment production capacity is the 1980s and 1990s.In different research years,the average annual runoff modulus of Yanhe River basin above Ganguyi hydrology station show a spatial distribution pattern of higher in the northwest and lower in the southeast.The spatial distribution of the average annual sediment transport modulus changed from "higher in the upper reaches and lower in the middle reaches" before 2010 to"lower in the tributaries and higher in the main streams" from 2010 to 2015.(3)The effects of precipitation and human activities on runoff and sediment changes in the Yanhe River basin were classified by using the double cumulative curve method with taking 1982-1996 as the reference period.The results showed that the influence of human activities is the main reason for the runoff and sediment reduction in the Yanhe River basin.The reduction of runoff by human activities accounted for 66.27%of the measured runoff reduction in the reference period,while the sediment reduction by human activities accounted for 66.61%?100.76%of the measured sediment transport reduction in the reference period.(4)A backpropagation model of sediment interception by check dams was constructed to calculate the annual sediment interception by large and medium check dams in the Yanhe River basin from 1954 to 2011,and the sediment reduction amount of the terracing and forestry measures was calculated by using the existing terracing and forestry model,and the synergistic sediment reduction by three major soil and runoff conservation measures was further analyzed.The calculation results show that the sediment control amount of check dams are 6.46 million t/a and 5.66 million t/a,the sediment reduction amount of forest and grass are 22.95 million t/a and 38.07 million t/a,and the sediment reduction amount of terraces are 1.3 million t/a and 2.72 million t/a from 1997 to 2005 and 2006 to 2011,respectively;the sediment reduction amount of forest and grass>sediment reduction amount of check dam>sediment reduction amount of terraces.In addition,the sediment reduction amounts of the three major soil and ruuoff conservation measures in the Yanhe River Basin from 1982 to 1996,1997 to 2005,and from 2006 to 2011 are 7.89 million t/a,5.04 million t/a,and 9.97 million t/a,respectively.(5)Based on the GAMLSS model,the factors of annual precipitation and annual potential evapotranspiration which represent climate change,and the factors of dam-controlled area of check dam and terrace area and vegetation coverage which represent human activities were selected for the attribution analysis of annual sediment transport amount variation in the Yanhe River Basin.The results show that the contribution rate of annual precipitation to annual sediment transport amount in Yanhe River decreased from 7%to 1%in the periods of 1997 to 2005 and 2006 to 2011;the annual potential evapotranspiration basically had no effect on the annual sediment transport amount or indirectly affects the annual sediment transport amount by reducing the annual runoff;the contribution rate of check dam to the reduction of annual basin sediment transport amount decreased from 21%to 11%.The contribution rate of terraced fields to sediment reduction increased from 16%to 18%.The contribution of vegetation to sediment reduction increased from 37%to 46%?(6)The comparison results of different research methods show that the calculation results of the double accumulation curve method,the runoff conservation method and the GAMLSS model method are roughly the same,and the differences in the calculation results of different methods are mainly due to the different choices of parameters.The research results show that human activities are the main reason for the reduction of annual sendimet transport in the Yanhe River basin,and their contribution to sendiment reduction is increasing,among which forestry and grass measures are the main reason for sendiment reduction in the basin. |
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