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1. groundwater type

according to different underground burial conditions, groundwater can be divided into two categories: phreatic water and confined water.

submersible water is groundwater buried on the first stable aquiclude layer below the earth's surface. most of the groundwater we usually see is phreatic water. springs are formed when groundwater flows out of the ground.

confined water (artesian water) is deeply buried groundwater that exists between two aquiclude layers. this kind of groundwater often has large water pressure, especially when the upper and lower aquifers are inclined, the soil in the interlayers has to bear greater water pressure. when a well or borehole penetrates the upper roof, strong water pressure causes the water to gush out, forming artesian water. in modern engineering, the pressure of confined water has a great influence on the safety and stability of foundation pits. in deep and ultra-deep foundation pits, measures are often required to reduce the height of the confined water head.

the burial conditions for the formation of confined water are:

① there are water-proof layers up and down; ② there is a water-permeable layer in the middle; ③ water must fill the entire water-permeable layer.

the following rock formation combinations can all form confined water: clay covers sand; shale covers sandstone; shale covers dissolved limestone; dense and impure limestone covers limestone with cracks and dissolved gaps. on rock; dense lava covers porous lava.

the formation of confined water is closely related to geological structures. as long as there is a suitable geological structure, whether it is loose sediment or bedrock, confined water can be formed. the most suitable geological structures for the formation of confined water are syncline structures and monoclinic structures.

2. interpretation of isodiving line diagrams

1. the size of the reading value can be used to determine the depth of diving burial, the height of the terrain, and the direction of the river.

①read the value to find the burial depth of the dive

burial depth of diving = surface altitude - diving level

② read the value to determine the terrain fluctuation and river flow direction

the phreatic level is consistent with the terrain fluctuations. the phreatic level is high in high terrain and low in low terrain.

2. read the density and density conditions to determine the diving flow rate.

where the phreatic potential lines are denser, the slope of the phreatic surface is steeper and the phreatic flow velocity is faster; comprehensively compiled by teacher tan’s geography studio

where the phreatic lines are sparser, the slope of the phreatic surface is gentler and the phreatic flow velocity is slower.

where the distance between the water potential lines is large, the flow velocity is slow, and where the distance between the water potential lines is small, the flow velocity is fast.

3. read the bending direction to determine the diving flow direction and the supply relationship between diving and the river.

the flow direction of diving is always perpendicular to the phreatic line from high water level to low water level.

3. selection of location of water wells and drainage ditches

1. the location of the water well should be selected in a location with shallow underground water.

2. the location of the water well should be selected in the diving collection area.

3. the location of the water well should be selected in a location with a large diving catchment area.

4. generally, water wells and drainage ditches are arranged along the water level line.

when solving this problem, we must first determine the burial depth of the dive, and then mark the flow direction of the dive to determine the diving collection area and the size of the water catchment area at each location, and finally determine the best location of the water intake point (i.e., the well).

5. use diving contours to rationally arrange wells and drainage ditches. in order to maximize the flow of phreatic water into wells and drainage ditches, wells and drainage ditches should generally be arranged along isohydrogen lines.

as shown in the figure below, it is obvious that the arrangement of water wells 1 and 3 is reasonable, but there is a "conflict" in water intake between 1 and 2, which is unreasonable: in the same way, drainage ditch 5 is reasonable, but 4 is unreasonable.

4. the impact of human activities on diving

diving updates quickly, the replacement cycle is short, and updates can be restored within a short period of time after use. it is a renewable resource. as long as people mine it reasonably, they can ensure sustainable utilization. however, if humans mine unreasonably, it will cause some environmental problems, such as over-exploitation of underground phreatic water, and the mining speed exceeds the natural recharge and recovery speed of the phreatic water, which will cause the water level to drop and form a groundwater funnel area.

the groundwater funnel area refers to the area where the groundwater level is significantly lower than the surrounding areas and the phreatic surface presents a funnel-shaped surface, as shown in the figure. what's more serious is that overexploitation of groundwater will also cause ground subsidence, tilting or collapse of buildings. if it is in coastal areas, it will also cause seawater intrusion and groundwater become salty.

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note: this article is compiled by teacher tan’s geography studio from we all love geography, middle school geography research, middle school geography class, ingenious geography, learning geography easily, college entrance examination geography, talking about land and reasoning, lao ding talking about geography, planet geography, and so on learn geography and other geographical public accounts like this orwatermark in textwait, herethanks also! if the quotation is inappropriate, you can alwaysleave a message at the end of the articlecontact us to indicate the source or delete it.

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