According to the investigation and study of modern geologists, Jinan spring water comes from the mountainous area in the south of the city, and atmospheric precipitation seeps into the ground and flows northward along the inclined direction of rock strata until the city is blocked by intrusive rock mass, and confined water emerges from the surface to form spring water. The southern mountainous area of Jinan is the remnant vein of Mount Tai, with Zhongshan, low mountains and hills from south to north. The urban area has become the combination zone of the piedmont inclined plain and the Yellow River alluvial plain, with a height difference of more than 500 meters. This terrain is high in the south and low in the north, which is conducive to the collection of surface water and groundwater in the urban area. Geologically, the southern mountainous area belongs to the northern wing of Taishan uplift, which is a gentle monoclinal structure. Many small fault blocks have been formed by the cutting of faults on the north side, among which Qianfoshan fault block is the structural basis of urban springs. Pre-Sinian metamorphic rocks are the basement of mountainous areas, on which there are 1000 meters thick CAMBRIAN and Ordovician limestone. The dip angle of the strata is 3 ~ 15 degrees, and it is buried under the Quaternary sediments in the urban area. In the long geological age, these soluble limestones have developed karst landforms after many tectonic movements and long-term dissolution, and formed a large number of karst gullies, caves, underground rivers and so on. Together, they form a vein-like underground network, which can store and transport groundwater. The northern part of the city is Yanshanian gabbro body with fine texture, hard rock and good waterproof performance. There is a Qianfoshan fault passing through Wei Yi Road in the west of Qianfoshan fault block; Yangtouyu fault in the east passes through jiefang bridge and Laodongmen, forming a water-blocking rock mass in the east, west and north, and forming a closed drainage unit on three sides.
In the southern mountainous area, limestone is exposed, fractured karst is developed, and a large amount of atmospheric precipitation and surface runoff are absorbed and infiltrated into the ground, forming rich fractured karst water. These fissured karst waters, blocked by Archean metamorphic rocks, move horizontally to the north along the inclined direction of rock strata, forming an underground undercurrent. When the urban area is blocked by intrusive rocks and blocked by faults, underground undercurrents gather in large quantities, changing from horizontal movement to vertical upward movement, which promotes karst development and water level rise. Under the strong hydrostatic pressure, groundwater passes through karst fractures, grabs the ground in the contact zone between limestone and intrusive rocks and weak Quaternary sediments, and gushes out of the ground.
The amount and seasonal distribution of precipitation directly affect the change of spring water. Jinan has a warm temperate monsoon climate, with an average annual precipitation of 650 ~ 700 mm. Due to the influence of summer monsoon, the seasonal distribution of precipitation is uneven. Two thirds of the precipitation is concentrated in summer, less than 1/5 in autumn, and rarely in winter and spring. The specific situation of precipitation in four seasons is: 86.9 mm in spring (3 ~ 5), 448.2 mm in summer (6 ~ 8),11)124.9 mm in autumn and 25.2mm in winter. With the seasonal change of precipitation, the spring water level and flow rate also show seasonal changes of low-high-low and small-big-small, but the time is delayed relative to the seasonal change of precipitation. In general, the change process of spring water is from the beginning of the year, the flow gradually decreases, and the minimum amount and the lowest water level appear in June; In July, with the increase of precipitation, the flow began to increase, and the maximum flow and the highest water level appeared in August and September. The general rule is that the annual precipitation is more, the spring flow is larger and the water level is higher; The annual precipitation is less, the spring flow is also small, and the water level is low.
When the amount of artificial exploitation does not exceed the flow of spring water, it shows the leading role of atmospheric precipitation in the dynamic change of spring water. If the exploitation amount is greater than the spring flow, the rainfall factor is in a secondary position. The exploitation directly affects the dynamic change of spring water. 1972 65438+1At 6: 40 on October 20, the water pump system was shut down due to a large-scale power outage in the urban area for 4 hours and 50 minutes. During this period, the water level in the urban area rose by 40 cm. During the period of 1968, the exploitation amount is roughly equivalent to the spring flow, which is called the conversion year of the two. Prior to this, the exploitation amount was less than the spring flow, so the spring performance has been very good; After that, the spring flow became smaller because the exploitation exceeded the spring flow and increased continuously. On September 24th 1980, the underground water supply stopped for 8 hours, which was less than usual 13500 tons, and the underground water level in the urban area rose by 44 ~ 45 cm. According to the data of Shandong Hydrogeology Team, the urban water level dropped from 1973 to 1977, a decrease of 2.25 meters. Therefore, from 1976 to less than 1 month after the rainy season, the spring flow gradually decreases. Baotu Spring was cut off from early March to early September for three consecutive years from 198 1 and dried up for more than half a year. In recent years, by strengthening the protection of spring water, Baotu Spring continued to gush from September 6, 2003 to the end of September 2005, and the groundwater level reached more than 29.8 meters, the highest level in 38 years.