Anshun Dragon Palace Sample Area

Dragon Palace (formerly known as Longtan) is located in the southwest of Anshun City, Guizhou Province. It is the main outlet of the Dragon Palace underground river system. Longgong Water Cave and its surrounding areas are famous karst scenic tourist areas in Guizhou. Most of the water system originates from the Anshun Rongyuan watershed and flows from north to south into the Wanger River, a tributary of the Dabang River. The distribution of water systems is mainly controlled by NE-trending structures and has the basic characteristics of structural water systems. However, due to the Xijiang River Basin tilting and uplifting from north to south and from west to east in the recent geological period, smaller sub-basins have been rejuvenated one after another, and water systems have merged and annexed each other and changed frequently. The Longgong Underground River Basin is one of them, and in modern times Under the action of karst dynamics, surface flow continues to transfer underground, and the flowing valley evolves into a sloping valley in the landform transition zone, and further leaks into depressions, thus breaking the original water system pattern. From the analysis of its water system structure diagram (Figure 4-6), it has the following characteristics:

(1) The latest active NW and NNE-trending structures (Li Xingzhong, 1986) guide the old NE→SW-trending structures The water system develops underground. For example, the Longgong Water Cave is formed by the water flowing through a NW (310°) fault below Xuantang, and is exposed at the phase change line and drains into the Wanger River nearby.

(2) Since the rejuvenation information conveyed by the new discharge standard (Wang Er River) can reach the upper reaches of the water system faster, the upstream tributaries can adjust their response to the new standard. For example, the Shuixi River is changed from the original SW The flow direction changed to the current NE direction and became the "inverted river".

(3) Due to the formation of the main outlet of the Longgong water system, the original unified NE→SW structural water network was fragmented. It can be seen from Figure 4-6 that there is another underground river system to the south of the Longgong Water System, and its drainage base is also the Wanger River. Judging from the development trend, it may invade the upper reaches of the Longgong Water System. The lowest potential field map of the area was made (Figure 4-7), and it was found that the karst watershed in the flatter area in the northern part of the Longgong water system is not closed, and the watershed has a certain degree of openness, while the underground river system in the south has been continuously traced back to its source from the underground, and has been Push the underground watershed northward into the Longgong surface watershed (the north of the surface watershed line in the figure is the Longgong surface watershed).

The development of slope valleys in the Longgong water system, especially the large slope valleys, basically follows the NE-trending old structure, because they are originally part of the structural water system. Due to the recent changes in the water system and the re-adjustment of the watershed, the water flow and shape are not yet "suitable". This is reflected in the fact that the scale of the groundwater channel in the Poli Valley cannot allow the water to be discharged smoothly, that is, it has a certain flow restriction effect, thus producing a natural dam effect (Tan Ming, 1992), during the rainy season, the water in the basin is blocked in the slope valley for several days to several months, forming a seasonal karst lake. This seasonal accumulation of water increases lateral erosion and plays an important role in widening and rounding the lake basin. But on the other hand, because the Poli Valley is at the forefront of the depression process advancing toward the source, the development of draining further limits the expansion of the lake basin. Therefore, the development of uphill valleys in the geomorphic transition zone is simultaneously restricted by these two opposing dynamics.

Figure 4-6 Dragon Palace Water System Structure and Slope Valley Distribution

Analyzing the relationship between the shape and water flow of each slope valley in the Dragon Palace area, we can get the development model of this type of flowing karst slope valley. (Figure 4-8). The Rapeseed River slope valley in the picture is the longest. This slope valley is in the development stage when the Liushui Valley is divided by a new pass. The pass is 15m high. During the dry season, the upstream water flow can only pass through the pass underground and then be exposed in the downstream slope valley. However, during the flood period, the upstream water flow can still flow over the pass and enter the downstream slope valley section from the surface. There is a narrow dry water channel at the bottom of the Poli Valley basin, and the rest is covered by floodplains. The Rapeseed River model represents the early development stage when new passes grow out of the flowing valley, the valley is divided and begins to close, and the water in the sloped valley widens (Figure 4-8a). The length of the sloping valley in the Guantou River has become smaller, and the water-dissipation point in the dry season in the sloping valley has receded and is no longer at the front end. The basin bottom is deeply sunk, and the average pass is relatively high at 117m (while the sloping valley in the Rapeseed River is 94m). The Guantou River model represents the mid-term development stage in which the basin width further expands, but sinking causes the sloping valley to develop into a depression (Figure 4-8b). If the water dissipation point in the dry season eventually retreats to the upstream of the water outlet of the slope valley during the flood period (Figure 4-8c), then the original slope valley will completely lose the perennial surface water flow and become a depression, and the dry season water tank at the bottom of the basin will completely disappear and become a pool of water during the flood period. Puddles of water. This pattern represents a late-stage or extinct poli valley.

Figure 4-7 Minimum potential field diagram of the Longgong water system and adjacent areas

In fact, two opposite dynamic processes have always existed since the early stages of the development of the Poli Valley, such as the development of the Rapeseed River The water dissipation point also recedes during the dry season. The only difference lies in the comparison of the rates of these two processes at different development stages.

Figure 4-8 The development model of flowing water karst slope valleys

The flowing water karst slope valleys developed in the transition zone of high-speed flow fields are different from those abroad 5 summarized by I.Gams There are three types of sloping valleys, namely edge sloping valley, piedmont sloping valley, outer sloping valley, overflow sloping valley and base sloping valley (Gams, 1973). The latter is mainly caused by geology or hydrogeology, while the former is mainly caused by hydrogeomorphology. Causes (Tan Ming, 1992). However, it still meets the three basic morphological requirements defined by Polje, namely having a flat bottom, a closed basin periphery and a karst drainage channel (Gams, 1987).