Human activities are becoming the dominant factor that infect and change the natural
environment. Along with economic development and population growth, the intensity of the
basin exploitation was increased. At the same time, runoff and sediment loading of most
rivers in the world appeared significant changed, especially in Yellow River basin. From a
conventional viewpoint, human activities to alleviate flow conditions appear to be a growing
necessity. So that it is important to further study human’s role during the evolution process,
and it is meaning to understand the anthropogenic influence during the environmental changes
of the world. In addition it is useful to guide the ecological environment protection and carry
out economies and societies construction.
The Wuding River is one of the distributary of the Yellow River with heavy sediment
yield. The quantities of the sediment loading that entered into the Yellow river tremendous
influenced the sediment variation of the Yellow River. Since 1950’s, the Wuding River was
listed as the key area in which carried out soil and water conservation by the government。
Especially since 1983, massive soil and water conservation measures had implemented in the
catchment, the underlying surface was remarkably changed. The progress of the soil and
water conservation was rapidly, its’ conservation progress, quality as well as the survival rate
of the conservation measures were advanced at large. Therefore the soil erosion was
controlled at a certain extent, the ecological environment was also improved and the
characteristics of the water and sediment loading were changed. So we select Wuding River
basin as the research site.
In this study, we analyzed the historical causes of the soil and water loss in the study area
---- Wuding River basin where typical small watershed management was the basic means to
recover the eco-system. We analyzed the process of soil and water conservation and the land
use/cover change, and also their impact on the runoff of the basin on the inter-annual scale. Moreover, the periodic sediment of the runoff of Wuding River basin and the impact of
human activities were analyzed. The main research results are in the following:
(1) There were deeply historical causes for the severe soil and water loss in the Wuding
River basin. First, the continuously growing population in historical period was the root cause.
Second the destruction of forest vegetation is the direct cause. Agricultural civilization and
nomadic civilizations competition, war and the backward agricultural techniques had
important impact on the evolution of soil and water loss in the historical period in Wuding
(2) Government and the people were intensively and continuously invested in
management the ecosystem in Wuding River basin where carried out the harnessing of the
key small watershed. From 1984 to 2006, a total investment of 1.167 billion Yuan was
accumulated invested for the eco-system management of Wuding River basin in Shannxi
Provinc, of which the government invested 20.83% of total investment, public investment
accounted for 79.17%. The masses were the main investment account. During that time, 1.294
million hm2 new areas were built for soil and water conservation in the key small watershed.
During the measures the proportion of economic forest area increases every year. Significant
ecological, economic and social benefits were made from the soil and water conservation
measures in Wuding River basin. People’s income increased from 178 Yuan per capita in
1984 to 1656.25 Yuan in 2006. The ecosystem service value of the soil and water
conservation increased gradually.
(3) The land use change of the Wuding River basin was studied using remote sensing
technology. The results showed that the land use types changed a lot in this area in the past 30
years. The farmland increased during the earlier stage and decreased during the later stage
impacted by the policies and of human activity. Forest increased by 3.11% in the period. Land
use dynamical degree in the three periods of 1975-1986, 1986-1997, 1997-2006 were 2.03%,
1.94%, 2.22% respectively. The dynamical degree is gradually stabilizing with the gradual
adjustment of land use structure.
(4) We tested the runoff and sediment loading of the six hydrological stations in the
Wuding River basin used Mann-Kendall and Sperman method. The results showed that strong
downward trends were detected in the runoff and sediment loading series in the past 50 years.
The change points were detectd using Pettitt test mehod. Results showed that runoff and sediment loading of every hydrological station which we tested in the Wuding River basin
had significant changed point. The runoff of Baijiachuan hydrological station which controls
the whole basin had the changed point in 1973 and the sediment loading series in 1971. Then
we used the Flow-Duration Curve method analyzed the frequency characteristics of runoff
and sediment loading character. The results showed that runoff and sediment loading of all the
hydrological stations had significant decreasing trend at the same frequency. The runoff
discharge of the Baijiachuan hydrological station at the low, mean percentile and high
reduced by -35.3%, -35.0% and -36.0% respectively, the sediment loading reduced by 59.3%,
68.0% and 55.5%. Human activities especially the soil and water conservation measures were
the major reasons that casued the decrease of runoff and sediment loading. The different types
of soil and water conservation measures and control degree were the reasons that lead to the
different mutation time and variation degree.
(5) We used the wavelet analysis method analyzed the periodic variation and its
changing features of precipitation, runoff and sediment loading in Wuding River basin. The
roles of human activites were analyzed too. Rusults showed that precipitation, runoff and
sediment loading have significant periodicity and their sizes are approximate. The main
period of precipitation is about 15.5 years while the runoff and sediment loading is about 22
years. On the three-year scale, human activities played an important role in the periodic
variation of runoff and sediment loading. The phase of precipitation, runoff and sediment
loading is synchronous during 1950s, while the three hydrological sequences tend to disorder
from lata 1960s to 1970s, then its turned to synchronize again since 1980s. On the 12-year
scale, precipitation, runoff and sediment loading cycle phase were significantly different in
1960s and 1970s, while in 1980s, they tended to synchronize again. At the 23-year large scale,
the precipitation- runoff cycle phase was basic synchronization, but lag in sediment loading.
The impact of human activities on runoff and sediment loading weakened with the sacale
increased. The analysis of human activities showed that the water and soil conservation
projects and other large dam construction which were built in Wuding River basin in 1960s
and 1970s may direct reasons that lead to the changes in runoff, precipitation and sediment
loading cycle phases, while the corresponding factors of social policy was the driving factors
of the hydrological cycle changes.
(6) We estimated the influence of human activities on the annual runoff and sediment loading used precipatition-runoff and precipation-sediment loading statistical model. The
results showed the contribution rate of human activities were 75.00% and 79.58% for the
annual runoff and sediment loading changes compared with pre-treatment. The human
activities were being the major factor that caused the change of runoff and sediment loading.