| Building terraces is an effective way to prevent soil and water loss of slope land and an importantmeasure to guarantee agricultural production and food security in the loess plateau. In view of theproblems of efficient agriculture multi-level terraces under rainstorm erosion in the Majiagou riverbasin, such as fierce soil erosion, severe soil and water loss, terraces easy to be washed out andinsufficient corrosion prevention measures of terrace slope, this paper monitors the scour situation of themulti-level terraces under the rainstorm, uses a new generation of water erosion predictionmodel-WEPP model-to simulate the section erosion situation of the multi-level terraces, and get thefollowing main conclusions:1. Spatial distribution rule of soil physical properties of the multi-level terraces. Analyze the soilbulk density and soil moisture content of the multi-level terraces at different levels in Cao xinzhuang inthe Majiagou river basin, the results show that: the soil bulk density of the terraces of which the landmanagement measure is bare land is obviously higher than that of other terraces at different levels andcultivation measures can reduce soil bulk density, playing an important role for improving the soilstructure and soil organic matter content. Suitable way of soil cultivation can not only improve the soilproperties, 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, thenslowly decrease, and then increase with the increase of soil depth between0-100cm soil depth; between100-160cm soil depth, soil moisture content remains unchanged or a tiny change, soil moisture contentachieves the stability. Surface soil moisture content and100cm soil moisture content gradually increasewith the increase of terrace levels from top to bottom, and soil moisture content of level1-7terracesdoes not show an obvious increase, surface soil moisture content of the8th level terrace reaches52.7%of saturated moisture content, soil moisture content of the100cm soil depth reaches80.7%of saturatedmoisture content, close to saturation. 2. Rainstorm erosion rule of the multi-level terraces. Soil erosion of the multi-level terraces underrainstorm scour in Cao xinzhuang in the Majiagou river basin is serious. Average erosion modulus is20659.7t/hm2, more than47.6%of the average annual erosion modulus, is greater than the severeerosion standard (15000t/(km2a)). The top level of the multi-level terraces is eroded slightly, and theterraces erosion area percentage increases gradually and significantly from top to bottom according tothe elevation. The upper terraces mainly show surface erosion and only a slight gully erosion; the lowerterraces show both serious surface erosion and gully erosion. In particular, surface erosion and gullyerosion of the7th,8th level terraces reach a total area of more than75%, most of the crops are coveredby the deposited sediment. Terraces erosion amount is related to such conditions as the terracecatchment area and the surface runoff, the main factor influencing the terraces erosion disaster is thesurface runoff. Due to the increase of surface runoff, the lower terraces are eroded more severely thanthe upper terraces.3. Preliminary study on the simlation of multilevel terrace erosion under rainstorm scour usingWEPP 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. Ingeneral, WEPP model can well simulate the amount of soil erosion and runoff of multi-level terracesunder rainstorm in the Loess Plateau, the simulation accuracy of WEPP model has a tendency to reducewith the increase of terrace levels from top to bottom, and simulation accuracy is higher to the amountof runoff than to the amount of soil erosion. WEPP model well simulates the runoff of the multi-levelterraces under rainstorm, and because the groundwater is rich, the value calculated using the runoffcoefficient method is higher than that of simulation in general. The simulation accuracy of WEPP modelis lower to the lower terraces than to the upper terraces. So, when using WEPP model to simulate therunoff in the region, we should be fully considered about the influence of recharge of groundwater tosurface runoff and the influence of soil moisture content. Because WEPP model is lack of blockingmeasures module, without fully considering the role of terrace ridge in the sediment retention, whensimulating the amount of soil erosion, the simulation value is greater than the measured value on thewhole. As terrace levels increase, the relative error between the simulation value and the measuredvalue increase significantly, and in particular the relative error of the8th level terrace reaches169.01%.Facing rainstorm scour, terrace ridge plays an important role in the corrosion prevention of multi-levelterraces.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 topographyconditions, we can reduce surface runoff, thus achieve the goal of reducing the scour of runoff to terraceslope, but only the forest-grass measures are not enough to withstand the scour of the worst torrentialrain, so we need to take engineering measures for water and sediment regulation design to layer uponlayer retain the slope runoff, in order to prevent the erosion of terraces. According to the actual situationin the Loess Plateau, the main engineering measures are to build the back-slope terrace and terrace ridgeto regulate the water and sediment, the advisable slope of back-slope terrace is commonly3°~5°,construction of terrace ridge can refer to the terrace design specification and the erosion rule in theregion, according to the different terrace levels. |
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