Abstract:

Nabkha is a common kind of biological wind deposition geomorphy in arid and semi-humid desert, and sandy coast.The nabkha's form is a kind of dynamical balanced shape made by the interaction of regional plant, wind and sand in the specific developmental stage of nabkha. It can reflect eco-environmental characteristics and regularity of change in the region. In this paper, the change regularity and characteristics of nabkha's shape in different developmental stages have been discussed on the basis of statistical analysis on morphological data of nabkha surveyed in the basin of Hotan River, Xinjiang. Results indicate that there exist better correlations among length, width and altitude of all kinds of nabkhas, but there is difference in different developmental stages of the same typical nabkha and different typical nabkhas, and according to analysis on mathematical model of nabkha's morphological data, regional eco-environmental features and aeolian characteristics, the development of nabkha can be divided into the growing stage with all shape data covariation, the stabilizing stage with higher gradient, synergistic growth of length and width and plant being the main factor, and the declining stage with nabkha's length shortening and more complex relations among all morphological data. The long axis and short axis of all kinds of nabkhas are in synergic growth. The horizontal scale and height of nebkha show significant correlation. The geometric shape of nabkha is approximately semi-ellipsoid which has few difference in slope-length and slope-gradient between upward and leeward sides in the basin of Hotan River. At the growth stage, Tamarix nabkha mainly appears approximately conical, and at the mature and stable stage, it is approximately hemispherical. The shape of Phragmite nabkha is approximately semi-ellipsoid which has shorter and steeper upward slope and longer and lower gradient leeward slope. The shape of Alaghi nabkha presents approximately semi-ellipsoid which has longer and lower gradient upward slope and shorter and steeper leeward slope. The result can be a quantizing index for monitoring regional desertification or oasis enlarging.

Key words: nabkha, morphological change, growth stage, Hotan River basin