| 其他摘要 | Building terraces is an effective way to prevent soil and water loss of slope land and an important
measure to guarantee agricultural production and food security in the loess plateau. In view of the
problems of efficient agriculture multi-level terraces under rainstorm erosion in the Majiagou river
basin, such as fierce soil erosion, severe soil and water loss, terraces easy to be washed out and
insufficient corrosion prevention measures of terrace slope, this paper monitors the scour situation of the
multi-level terraces under the rainstorm, uses a new generation of water erosion prediction
model-WEPP model-to simulate the section erosion situation of the multi-level terraces, and get the
following main conclusions:
1. Spatial distribution rule of soil physical properties of the multi-level terraces. Analyze the soil
bulk density and soil moisture content of the multi-level terraces at different levels in Cao xinzhuang in
the Majiagou river basin, the results show that: the soil bulk density of the terraces of which the land
management measure is bare land is obviously higher than that of other terraces at different levels and
cultivation measures can reduce soil bulk density, playing an important role for improving the soil
structure and soil organic matter content. Suitable way of soil cultivation can not only improve the soil
properties, but also improve the efficiency of water use in the field, achieve the goal of water production.
Soil moisture content of the terrace section at different levels presents a trend of first increase, then
slowly decrease, and then increase with the increase of soil depth between 0-100cm soil depth; between
100-160cm soil depth, soil moisture content remains unchanged or a tiny change, soil moisture content
achieves the stability. Surface soil moisture content and 100cm soil moisture content gradually increase
with the increase of terrace levels from top to bottom, and soil moisture content of level 1-7 terraces
does not show an obvious increase, surface soil moisture content of the 8th level terrace reaches 52.7%
of saturated moisture content, soil moisture content of the 100cm soil depth reaches 80.7% of saturated
moisture content, close to saturation. 2. Rainstorm erosion rule of the multi-level terraces. Soil erosion of the multi-level terraces under
rainstorm scour in Cao xinzhuang in the Majiagou river basin is serious. Average erosion modulus is
20659.7 t/hm 2 , more than 47.6% of the average annual erosion modulus, is greater than the severe
erosion standard (15000 t/(km 2 •a)). The top level of the multi-level terraces is eroded slightly, and the
terraces erosion area percentage increases gradually and significantly from top to bottom according to
the elevation. The upper terraces mainly show surface erosion and only a slight gully erosion; the lower
terraces show both serious surface erosion and gully erosion. In particular, surface erosion and gully
erosion of the 7th, 8th level terraces reach a total area of more than 75%, most of the crops are covered
by the deposited sediment. Terraces erosion amount is related to such conditions as the terrace
catchment area and the surface runoff, the main factor influencing the terraces erosion disaster is the
surface runoff. Due to the increase of surface runoff, the lower terraces are eroded more severely than
the upper terraces.
3. Preliminary study on the simlation of multilevel terrace erosion under rainstorm scour using
WEPP model. For different length of slope, slope, management measures of terraces at different levels,
the simulation accuracy of the WEPP model to the amount of soil erosion and runoff is also different. In
general, WEPP model can well simulate the amount of soil erosion and runoff of multi-level terraces
under rainstorm in the Loess Plateau, the simulation accuracy of WEPP model has a tendency to reduce
with the increase of terrace levels from top to bottom, and simulation accuracy is higher to the amount
of runoff than to the amount of soil erosion. WEPP model well simulates the runoff of the multi-level
terraces under rainstorm, and because the groundwater is rich, the value calculated using the runoff
coefficient method is higher than that of simulation in general. The simulation accuracy of WEPP model
is lower to the lower terraces than to the upper terraces. So, when using WEPP model to simulate the
runoff in the region, we should be fully considered about the influence of recharge of groundwater to
surface runoff and the influence of soil moisture content. Because WEPP model is lack of blocking
measures module, without fully considering the role of terrace ridge in the sediment retention, when
simulating the amount of soil erosion, the simulation value is greater than the measured value on the
whole. As terrace levels increase, the relative error between the simulation value and the measured
value increase significantly, and in particular the relative error of the 8th level terrace reaches 169.01%.
Facing rainstorm scour, terrace ridge plays an important role in the corrosion prevention of multi-level
terraces.
4. Preliminary study on the water and sediment regulation measures of multi-level terraces. By
controlling the runoff coefficient in the region and catchment area or changing the micro top controlling the runoff coefficient in the region and catchment area or changing the micro topography
conditions, we can reduce surface runoff, thus achieve the goal of reducing the scour of runoff to terrace
slope, but only the forest-grass measures are not enough to withstand the scour of the worst torrential
rain, so we need to take engineering measures for water and sediment regulation design to layer upon
layer retain the slope runoff, in order to prevent the erosion of terraces. According to the actual situation
in the Loess Plateau, the main engineering measures are to build the back-slope terrace and terrace ridge
to regulate the water and sediment, the advisable slope of back-slope terrace is commonly 3°~5°,
construction of terrace ridge can refer to the terrace design specification and the erosion rule in the
region, according to the different terrace levels.
Key words: The Loess Plateau; Efficient Agriculture Multi-level Terraces; Erosion rule; WEPP model;
Corrosion prevention measures |
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