(3) Xinzhou basin water system

1. The changeable water system in the basin

Today, the export of Xinzhou Basin is the Hutuo River on the east side. Hutuo River flows from northeast to southwest, flows through Xin kou, then makes a 90-degree bend, and then takes a 180 arc. At the throat of Jisheng Bridge on the west side of Dongye Town, it enters Zhoushan Gorge, winds southeast, crosses Yuxian County and flows to Pingshan (Hebei).

The water system on the south side of Xinzhou Basin has several peculiar features. First, the loess basin of Taiyuan water system is bounded in the south, and the river runs north and south. Second, the upstream water system here (Xinzhou side) can be connected with Taiyuan water system in a straight line except for the opposite flow direction; Third, the tributaries of the northern water system often flow in the opposite direction to the mainstream, such as the southern end of Niuweizhuang water system, Fujiazhuang water system and Taihe Station water system.

These facts reflect that the Muma River originally flowed smoothly to the Taiyuan River system, and later the attack on the upper reaches of the Hutuo River made the upper reaches of Taiyuan flow northward in the opposite direction and was incorporated into the Hutuo River. It is proved that the original outlet of Xinzhou Basin was Fenhe River system in the south, and now it turns to Hutuo River in the opposite direction, which was transformed by the later crustal movement. This transformation force caused the Shilingguan uplift, and at the same time, accompanied by the strong erosion of the Hutuo River system to the source, Taihang Mountain was cut in the southeast, and Jisheng Bridge was cut in the west of Dongye Basin, which made the original water system in Xinzhou become today's state. Therefore, the drainage of lake water in Xinzhou basin occurred after Shilingguan uplift.

At the northern end of Yuxian County, between Longhuakou and Wutai Dongye, the Hutuo River is a deep canyon, and the river meanders like a snake. It should be the channel formed when Hutuo River finally crossed Taihang Mountain. This river has two terraces, and the second terrace was formed 6,543,800 years ago. It can be explained that Xinzhou basin was drained in the late Pleistocene. Because Xinzhou basin itself has two terraces, which can correspond to the second terraces in the canyon.

Diversion schemes of Xinzhou River, Muma River and Yunzhong River

There is a canyon at the upper end of Xinzhou basin, which is the famous Xinkou, the upper mouth of the basin, and the Hutuo River valley basin above it. In the southwest of this canyon, Jinshan is more than 400 meters higher than it. Jinshan is an isolated mountain located in the basin. Its west and northwest are also flat, and it is an elevated basin inclined to the east. On the north and south sides of the strange village in the northwest, there are two parallel rivers flowing from the northwest, and the water system bends into a knee when it meets Jinshan. On the south is Yunzhong River (named after Yunzhong Mountain), and on the north is Hutuo River and its tributaries. This peculiar water system composition tells us that the recent uplift of Jinshan forced these two rivers to divert. Before the uplift, the main stream of Hutuo River was enclosed in a long lake basin on the west side of Yuanping City.

The Yuanping-Fan Shi Hutuo River Basin was originally closed and almost opened at the same time as Xinzhou Basin. Like Xinzhou basin, there are two terraces. Judging from today's topographic map, the last basin bottom of Xinzhou Lake Basin reaches the boundary source at the foot of Jinshan, then turns to the edge of Xinzhou City, and then follows the foot of Zhoushan Mountain to Jisheng Bridge. The eastern part of the area is a very flat small plain, and there is a circle of loess hills between its outer side and bedrock hills, including isolated bedrock hills such as Jinshan, Tuoluo Mountain, Douluo Mountain and Guanmao Mountain, which stand in the loess hills like islands in the sea. There is no definite evidence to prove that this loess hilly area was originally Xinzhou Lake or a hillside by the lake. We guess it's the slope by the lake, the accumulation area of aeolian loess hillside, and the bedrock mountain is above it.

Looking at Xinzhou Basin, it was originally composed of Yuanping-Fan Shi Valley Basin and Xinzhou Basin. In the early days, the lake can be flooded to an altitude of 1000 meters. Later, the erosion of the lower reaches of the Hutuo River cut off the estuary of Jishengqiao Lake and the estuary of Xinkou, opening up two basins. After the lake was drained, the uplift of Jinshan and Shilingguan-Guanmao Mountain finally captured the NW-trending water system flowing into the southwest corner of Xinzhou Basin in Taiyuan Basin, resulting in numerous loess basins, backward flowing rivers and broken valleys.

2. It is the fault rise in Zhoushan.

Zhoushan, on the east side of Xinzhou basin, is a mountain range with fault uplift, and its northern plate is a broken plate. When there is no absolute standard body, the meaning of enumeration is relative. We can call it a fault in Zhoushan or a fault in the northern plate.

People take a bus from Xinzhou to Wutai Mountain and have to cross a canyon to climb Wutai Basin. To the east, you have to cross Geziling to enter Rucun Basin, and finally you have to cross a loess canyon to climb the higher Zhijiazhuang Basin, and then quickly descend to Doucun Basin, and reach Jinggeling eastward along Panshan Highway to enter Taihuai Town, a Buddhist holy place.

From the map, from Xinzhou to Wutai Mountain, it has experienced five basins: Xinzhou Basin, Dongye Basin, Wutai Basin, Rucun Basin and Zhijiazhuang Basin. In fact, between Xinzhou and Dongye, there is also a Tongchuan basin famous for producing pears. This series of five basins arranged from west to east are distributed from low to high in topography. This height variation law is not only reflected in the elevation of the top surface of five basins, but also in the elevation of the watershed between basins, reflecting the characteristics of the north plate of Zhoushan fault.

If the original elevation of Zhoushan is kept unchanged, the northern plate is a plate with its rotation axis in the northwest, with its western plate falling and its eastern plate rising. When this rotating shaft rotates downward at the same angle to the west, the greater its vertical drop, the more it goes to the west. This shows the movement characteristics of the northern plate, that is, it controls the gradual upward movement of the basin to the east. And one basin after another, it turned out to be a valley, and the river was blocked by weirs. Due to the relative uplift of the lower reaches of Zhoushan, five rivers flowing from northwest to southeast are blocked: Tongchuan River, Xiaoying River, Hutuo River, Unknown Rucun River and Zhijia River from west to east. So today's basin, when the river weir has become five natural reservoirs. The loess in the original loess hills quickly silted up into the reservoir and was slowly filled up, forming a loess basin. Due to the slow and continuous rise of Zhoushan, four downstream rivers of these five rivers often cross the dam to keep the intermittent water bodies downstream, so that the downward cutting of the river can continue. So until today, these five rivers still maintain their original flow direction.

As the northern plate keeps falling westward, the southernmost Tongchuan River has never crossed the watershed near the lake, silting up the original undulating bedrock ridge into a loess watershed that occasionally exposes the top of the mountain. The last two small rivers in the east, because the basin area is too small and the catchment is too small, the river water can't rush through the blocked mountain downstream. When the water is full, they will change their course and turn west along the front edge of Zhoushan body, forming a knee-shaped turn attack and seizing the valley. The lower reaches became Tuwei River with the original river breach as the watershed.

Tuwei river

There is also a long and narrow river between Xiaoying River and Hutuo River. After the collapse of the fault, water quickly overflowed the river channel, causing the Loess Canyon to attack and capture the valley on the fault. Tianchi Village attacked and captured the valley on the back, cutting a long valley into three sections, and the downstream section became a reverse river that went upstream and flowed eastward from Hongyacun Canyon, forming the only valley that was captured eastward.

Among these five basins, Rucun Basin was still a lake in the early years of the Republic of China, and there were many aquatic plants along the lake, belonging to the "Ruhu Wild Goose", one of the five scenic spots. In the early years of the Republic of China, Ruhu River finally cut into the basin and drained the lake, forming a small basin with a mirror-like surface of 7 square kilometers today. Among them, all the villages were distributed on the sloping land by the lake. Today's building in the center of the lake was built in the 1980s.

Except that the middle part of Rucun basin is not eroded by river water, the other five basins have two terraces. The first terrace is 2 ~ 4 meters high, with long and narrow terraces, and the whole country is irrigated. The second terrace is the original lake bottom, so it is very wide. It is about 20 meters above the water. At that time, Wutai City was built on the secondary terrace, and Wutai Middle School in the city center also had an artesian well, and groundwater gushed from the terraces on both sides of the slope (cut off in the 1970s).

It is a fault mountain in Zhoushan, which blocked the flowing water in the south and formed loess accumulation, so we know that its fault occurred before the late Pleistocene (654.38+ 10,000 years ago). Ostrich eggs and large ivory (2 meters long) were found in loess, which shows that the climate here was subtropical at that time, in order to adapt to the living environment of elephants and ostriches today.