| As new soil and water conservation biological measures, sea-buckthorn plant flexible dams have shown good performance in controlling water and soil erosion in soft rock area. Sea-buckthorn plant flexible dams can effectively intercept sediment within ditches, improve soil water redistributing, and enhance soil fertility. Therefore, the measures can not only radically reduce sediment discharge to Yellow river, but also greatly improve the local ecological environment. The capabilities of sea-buckthorn plant flexible dams in soil and water conservancy all attribute to the function of regulating velocity field through weakening water flow energy, which is in favor of depositing sediment and smoothing flood peak in gullies. Field investigations and laboratorial experiments are combined in this study. Field investigations are carried out both in Xi'zhao watershed in Ordos of Inner Mongolia and in experimental base of sea-buckthorn plant flexible dams in Hua County of Shaan'xi province. The main achievements are summarized as follows:(1) It is revealed that the vertical distribution of organic matter is closely related to soil water transmission process as well as soil's development process and layered construction; The sea-buckthorn plant flexible dams with different ages can improve soil organic matter contents in different extent; with the extension of research scope, the soil spatial heterogeneity is increasing obviously.(2) The sediment becomes finer in the sea-buckthorn valley especially in the upper cross section; there is no obvious regularity of sediment deposition along a single sea-buckthorn dam; it is observed that the sea-buckthorn plant flexible dam can diminish the sediment particle size from the upper reach to the lower reach along the valley, and also can effectively filtrate the sediment grain with particle size bigger than 0.25mm. (3) The sea-buckthorn intensity imposes an determinative impact on water flow pattern, and further influence the variation of micro-terrain; Increasing the number of sea-buckthorn planting rows appropriately can weaken the erosion of land surface by water flow behind the rows; The maximal sunk depth scoured out by flow often comes behind the first row; It's easier to form smooth river bed as the number of sea-buckthorn rows becomes more, and then lower level of erosion is achieved.(4) It is preliminarily discussed that sea-buckthorn is not suitable to grow in relative wet soil because of its root feature, and sea-buckthorn intensity is very important for colony's stability and development. The height of trunk, basal-stem and canopy of sea-buckthorn are simulated using Logistic model and cubic polynomial function.(5) If sea-buckthorn plants are too discrete to keep dam body's continuity, its capability of weakening water flow energy will be impaired greatly; In virtue of stream experiencing a process of firstly increasing, later lessening, and subsequently gradually increasing from the inlet to the outlet of the flow bed, the experimental flow bed is divided into inlet segment, backwater segment in front of the dam and dam inner segment; Sea-buckthorn plant flexible dam plays less role in inlet segment, while having great effect on backwater segment in front of the dam; Through contrastive analysis in aspect of accuracy, feasibility and efficiency, it is validated that PIV method is more practical than Stain Tracer Method.(6) In small watershed, the method of layout designing of sea-buckthorn plant flexible dams is presented. Such hydrological characteristics as rainfall,underlaying surface features and the area of basin as well as the laws of runoff generating and converging processes should be considered. Firstly, design flood is ascertained according to the design storm, and then planting parameters of sea-buckthorn plant flexible dams are defined according to design flood combined with gully figures. Moreover, a theoretical analysis is performed in this paper.
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