| 其他摘要 | The severe soil erosion in the Loess Plateau and its influence on the sediment discharge
of the Yellow River has always been a hot issue in the related research field. In recent years,
a rapid decrease of sediment discharge in the Yellow River. The annual average sediment
discharge at Tongguan station was decreased sharply from 1.6 billion t before the 1970s to
0.26 billion t in 2000-2015, which has changed people's understanding significantly in the
past for the sediment of the Yellow River. The simultaneous development of forest-grass
measures and check-dams construction since the implementation of the “Grain for Green”
project in 1999, have already improved the natural ecological environment greatly due to
vegetation restoration after more than and 10 years. However, it is still not clear that what is
the contribution of the actual sediment retention amount by check-dams to the reduction of
sediment discharge in the Yellow River? As well as how is the deposition rate and
interception potential of the existing check-dams? These are important links to understand
the sharp decline of sediment discharge recently in the Yellow River. Therefore, the 2
check-dam systems and 5 check-dams were selected by field investigation in the typical
tributaries of the middle Yellow River. According to the drilling samples, the deposition
couplet identification and erosive rainfall events correspondence, the capacity curves of
check-dams were established to estimate the sediment deposition by combining with
1:10000 topographic map and the Total station measurement, and then the characteristics of
sediment yield of dam-controlled watershed were deducted. Combined with the existing
research data, the sediment retention amount by check-dams in different decades of the typical tributaries were estimated, and the effect of sediment retention by check-dams on the
contribution of sediment discharge variation in tributaries were analyzed. The main results
are as follows:
(1) The capacity curve method could better fit the gully form before check-dam
construction, its application and promotion could more accurately calculate sediment
deposition of check-dams. The difference was distinct in sediment deposition of check-dam
couplets in Yanhe and Huangfuchuan River Basin, which was related to the construction
time and dams-controlled area.
(2) The difference of specific sediment yield variation was significant in dams-
controlled area at the runoff event and annual scale of the Yanhe and Huangfuchaun River
basin. The maximum specific sediment yields at the runoff event scale were 6~23 times and
9~13 times of the minimum value in the Fangta dam-controlled watershed of Yanhe River
Basin and Manhonggou dam-controlled watershed of Huangfuchaun River Basin,
respectively. The largest specific sediment yields in the Fangta watershed at the runoff event
and annual scale appeared in Fangta No.1 dam, which was mainly due to this dam running
time early and poor watershed management so that the specific sediment yield was large.
While in the Manhonggou watershed, the largest specific sediment yields at the runoff event
and annual scale appeared in Mahaogou dam. In addition to this check-dam construction
time early, also associated with the dam-controlled area was small.
(3) The specific sediment yield at the annual scale of the small watersheds decreased
significantly with time. Since the 21 st century, the annual average specific sediment yield
was 2094.3 t/(km 2 ·a) in the Fangta watershed of Yanhe River Basin and was 12305.7
t/(km 2 ·a) in the Manhonggou watershed of Huangfuchaun River Basin, which was far
beyond the tolerable erosion rate of these region.
(4) Due to the great differences in the underlying surface in different dam-controlled
watersheds, there were differences in the minimum erosive rainfall in two basins. The
minimum erosive rainfall of dam system and single dam in the Yanhe River Basin were
greater than in Huangfuchuan River Basin. The erosive rainfall for sediment deposited in the
dams was greater than 30 mm in the Fangta dam system-controlled watershed and 20 mm in
the Majiagou single dam-controlled watershed of Yanhe River Basin, respectively. In the Huangfuchuan River Basin, the erosive rainfall for sediment deposited in the dams was
greater than 20 mm in the Manhonggou dam system-controlled watershed and about 10 mm
in the Telagou single dam-controlled watershed, respectively. And there was a significant
correlation between the specific sediment yield and erosive rainfall at the runoff event and
annual scales in different dam-controlled watersheds and small watersheds.
(5) The sediment retention amounts by check-dams decreased gradually in the Yanhe
and Huangfuchuan River Basin due to the effective soil and water conservation measures. In
the rainstorm year of 2010-2015, the annual average sediment retention amounts by
check-dams increased more than two times compared to 2000-2009. As a result, the
contribution of sediment retention by check-dams was still significant in the rainstorm year.
(6) The influence of precipitation on sediment discharge reduction was weakened after
abrupt change, and the effect of human activities was enhanced gradually, while the
contribution of sediment retention amount by check-dams was on the contrary. After 2000,
the sediment discharge decreased was more than 85% in the Yanhe and Huangfuchuan
tributaries, while the contribution of sediment retained amount by check-dams was less than
10% and 20%, respectively. It showed that the effect of sediment retention by check-dams
was weakened, while the effect of sediment reduction by vegetation was enhanced. Due to
the differences of soil erosion environment, especially the effect of vegetation restoration,
the contribution of check-dams on sediment discharge reduction in the Huangfuchuan River
Basin was greater than the Yanhe River Basin.
(7) Soil erosion was still a major ecological problem in the Loess Plateau, especially in
the basin with the weathered sandstone dominated (pisha rock). More efforts should be made
to strengthen soil and water conservation management in the future.
Keywords: Check dams; Deposition couplet; Watershed sediment yield; Sediment discharge;
Yanhe River Basin; Huangfuchuan River Basin; Soil erosion |
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