Development features of nine poljes and structural relationship of underground river system in the southwest area of Hubei

The carbonate rocks are exposed widely in the southwest area of Hubei province, forming a rich karst phenomenon. Particularly, it has been confirmed that the largest polje group has developed with typical underground river system in Hefeng county and nearby towns. Research on the development characteristics of nine poljes and structural relationship of underground rivers system is of great significance to reveal the formation process of karst in the area. The geological background and previous research has been reviewed and based on this, the karst phenomena in the scope of 92.53 km2 area in Yanzi village, Hefeng county was investigated. We have found a total of nine poljes, which are different in scales, patterns and evolution stages. However,the distribution of the slopes is roughly the same, and largely follows the regional structure in the area. In addition to the poljes, complex underground river system has also been formed with the strong karst processes. The development of the entrances and exits of these underground rivers are controlled by the regional tectonics.