Ebinur Watershed Development And Evolution Of Parabolic Dunes

Parabolic dunes is a developmental fixed and semi-fixed sand dune landform type in good soil, water, vegetation conditions inland desert areas and coastal zones. Study on parabolic dunes has great significance in aeolian landform, land desertification monitoring and evaluation, regional environmental evolution and so on.This paper took Ebinur Lake basin typical parabolic dunes as the research project, regarded sand geomorphology, sand physics, plant ecology and sedimentology disciplines theory as a guide, measured morphological parameters of22parabolic dunes in Haloxylon desert in southeast of the basin by using the technology of "3S" and RTK.220sediment samples were collected from the dunes in various dune surface,110sediment samples were collected from surface among the dunes; The paper also analyzed wind conditions data of6Stations of7years in the study area, experimented on dune source characteristic and investigated on Dunes wind power mechanism, all of these aimed to clarify the development and evolution of parabolic dunes in the Ebinur Lake basin. After a comprehensive analysis, the main conclusions are as follows:Aeolian landforms of the Ebinur lake basin can be divided into two categories: Aeolian geomorphology and Wind erosion. Nebkhas and parabolic dunes are the most typical Aeolian landforms. Parabolic dunes in the Ebinur Lake are divided into five types of semi-circular, parabola of the V-shaped, U-shaped parabolic, hook and composite according to their complexity and spatial combination conditions. Parabolic dunes of the study area showed characteristics of dense distribution, semi-circular, parabola of the V-shaped, U-shaped parabolic line are mainly distributed in the southeast of the basin, the Haloxylon sand in the south of State Road312, hook parabolic dunes are mainly distributed partial East in the middle of the basin, shrub sand in the north of State Road312and the compound parabolic dunes are distributed in both places.The morphology of parabolic dunes in the Ebinur lake basin showed the parabolic shape opening to the northwest, towards the northwest-southeast direction. The arc sand beam on the top of the parabola dunes showed the northwestern slopes were long and gentle recessed, the southwest slopes were short and steep and showed arc-shaped protrusion and a parabola-shaped from the top plan view. The relative height of Dunes was between2.1-15.48m and the length of the two wing angles was approximately range of45.7-290.5m, the width between the two wings was among54-162m, the length of the central axis was between56.59-330.35m and the ratio of the length and the width of the dunes was between0.8-2.11.The wind direction of the rising sand wind of the Ebinur lake basin was mainly the NW and NNW wind. The frequency of the NW wind accounted for54.98%and the NNW wind direction frequency accounted for18.31%of the annual rising sand wind frequency. The Ebinur Lake Basin belongs to a high wind environment and the annual drift potential is between679.88-1203.38VU. The direction variability index each year is more than0.9, which can be classified the characteristics of single-peak wind conditions. The synthetic sediment transport direction is126.15°that is between the ESE-SE. There is a big space difference in terms of the drift potential strength in the basin and the high value point appears in lashankou. Due to the characteristics of the topography and landforms of the basin, Alashankou strong wind is the main reason for the formation of aeolian landforms.The underlying substances of the Ebinur Lake basin are mainly Quaternary unconsolidated sediments and lake sediments, which were re-transformed and transported by the role of water and wind, and provided rich sand source material for the development of parabolic dunes. Mountain rocks, weathered by water and wind and transported by glaciers and rivers to the piedmont zone, were included in the composition of the substance of the sand, so the source material particles of the parabolic sand dunes in the basin were coarse. The surface sediment grain size of the parabolic dunes in Ebinur Lake basin was between0.399um-2116.54um, the fraction, average particle size, sorting coefficient, skewness and kurtosis of the sediment in different landforms parts were all showing regular changes, these were the combined result of the sand flow, the dunes, vegetation and sediments.The vegetation formed parabolic dunes in Ebinur Lake basin was Haloxylon vegetation communities for constructive species, and Haloxylon coverage differed greatly in different geomorphologic parts of parabolic sand dunes. The coverage between the two wings was the maximum, and followed by that of the two wing angles and hilltop came the third, the windward slope vegetation coverage was the minimum. The key to the formation of parabolic dunes was the fixation of greater vegetation coverage to two wing angles. Vegetation would not only lead to the deposition pattern changes of sand dunes, but also directly affect the dune morphological changes. Vegetation can weaken the strength of the wind and sand activities and slowed down its mitigation of surface wind erosion. The presence of vegetation could intercept suspended particles in the sand flow and then form the settlement, thus causing the dunes morphology changes. There was a significant positive correlation between ground vegetation cover and dune height between the two wings. Vegetation had played a key role in the formation and development of parabolic dunes.Parabolic dunes in the Ebinur Lake basin originated from the wind erosion depressions. The formations of sand dunes were divided into the following five stages of development and evolution:wind erosion depression stage, semi-circular dune stage, the initial parabola-shaped stage, the mature parabolic stage, longitudinal dunes stage or hook-shaped-linear dunes phase. They could also be divided into Embryonic Period (0.4<L/W<0.8), the growing season (0.8<L/W<1), mature (1<L/W<3) and decline (L/W>3) according to the aspect ratio of a dune.The developmental pattern of parabolic dunes can be summed up as follows. Mode1:the barchan----transverse dunes----parabolic dunes----hairpin-shaped dunes; mode2:wind erosion depression----curved sand Beam----parabolic dunes----longitudinal dunes or hairpin-shaped dunes. The parabolic dunes in study area formed by wind erosion depressions, the model can be summarized asfollows:wind erosion depressions----semi-circular dunes----parabolic dunes----longitudinal dunes or hook-shaped dunes----linear dunes. The parabolic dunes can be transformed into two types. One can be evolved into longitudinal dunes from parabolic dunes; another can be evolved into hook-shaped dunes from parabolic dunes, gradually transformed into linear dunes.