(1) The newly active NW-trending and NNE-trending structures (Li Xingzhong, 1986) lead the old NE→SW-trending structural water system to develop underground. For example, the Longgong Water Cave is formed by water flowing through a NW (3 10) fault below Xuantang, exposed at the phase transition line and discharged into the nearby Wanger River.
(2) Because the rejuvenation information transmitted by the new drainage benchmark (Wangerhe River) can reach the upper reaches of the water system faster, the upstream tributaries, such as the Xihe River, respond to the new benchmark, changing from the original SW flow direction to the current NE flow direction, and become "inverted rivers".
(3) The original unified NE→SW structural water network was separated due to the formation of the general outlet of Longgong water system. As can be seen from Figure 4-6, there is another underground river system south of the Longgong River system, and its discharge basis is also Wang Er River. From the development trend, it may attack the upper reaches of Longgong River system. The lowest potential map in this area (Figure 4-7) shows that the karst basin in the gentle area in the north of the Longgong River system is not closed, and the basin is open to a certain extent, while the underground river system in the south has been traced back to the ground and has pushed the underground basin northward to the Longgong surface basin (the Longgong surface basin is north of the surface basin in the figure).
The valleys in Longgong River system, especially Dapo Valley, basically follow the old NE-oriented structure, because they are originally a part of the structural water system. Due to the recent changes in the water system and the readjustment of the river basin, the water flow and morphology can not be "properly balanced", which shows that the scale of sewers in the slope valley can not make the water flow discharge smoothly, that is, it has a certain flow restriction effect, thus producing a natural dam effect (Tan Ming, 1992), which blocks the catchment of the slope valley for days to months in the rainy season and becomes a seasonal karst lake. This seasonal water accumulation enhances lateral erosion and plays an important role in expanding and surrounding the lake basin. On the other hand, because the valley is at the front of the depression process, the development of leakage depression further limits the expansion of the lake basin. Therefore, the development of the vertical valley on the uphill slope in the geomorphologic transition zone is restricted by these two opposite dynamic actions.
Figure 4-6 Longgong Water System Structure and Distribution of Slope and Valley
By analyzing the relationship between the shape of each valley and water flow in Longgong area, we can get the development model of karst valley with running water (Figure 4-8). In the picture, the standing valley of rape river slope is the longest, and it is in the development stage that the flowing valley is divided by Xinyakou. Pass height 15m. In the dry season, the upstream water can only be exposed to the downstream valleys after passing through the pass underground, but in the flood season, the upstream water can still overflow the pass and enter the downstream valleys from the surface. There is a narrow low tide trough at the bottom of the basin, and the rest is covered by floodplain. The rape river model represents the early development stage, that is, a new pass grows from the flowing valley, the valley is divided and closed, and the accumulated water in the inclined valley is widened (Figure 4-8a). The length of the valley on the broken river slope becomes smaller, and the drainage point in the valley on the slope in dry season recedes from the front end, and the basin bottom sinks deeply, with an average passing height of 1 17m (the valley on the rape river slope is 94m). The Duantou River model represents the medium-term development stage, in which the width of the basin is further expanded, but the leakage makes the valley develop into a depression (Figure 4-8b). If the drainage point in the dry season finally retreats to the upstream of the outlet of the valley in the flood season (Figure 4-8c), the original valley will completely lose the perennial surface water flow and become a depression, while the trough at the bottom of the basin will completely disappear in the dry season and become a waterlogged depression in the flood season. This model represents a valley with late development or decline.
Figure 4-7 Lowest Potential Field Map of Longgong Water System and Its Adjacent Areas
In fact, two opposite dynamic processes have existed since the early development of slopes and valleys. For example, the water dissipation point of rape river is also retreating in the dry season. The only difference is that the two processes have different speed comparisons in different development stages.
Figure 4-8 Development Model of Karst Flowing Water Slope and Valley
The flowing karst valleys developed in the geomorphic transition zone of high-speed flow field are different from the five types summarized by I.Gams, namely, marginal valleys, piedmont valleys, outer marginal valleys, overflow valleys and reference valleys (Gams, 1973). The latter is mainly caused by geology or hydrogeology, while the former is mainly caused by hydrogeology (Tan Ming, 65438+). However, it still meets the three basic morphological requirements of wave train definition, namely, it has a flat bottom, a closed basin and a karst drainage channel (Gams, 1987).