How on earth do wells work?

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I don’t understand how do wells work. Like, I’ve seen a lot of wells made of stone, so, if you dig a huge hole in the ground, how does water come inside the well? Like, I’ve seen a lot of movies where someone gets stuck in a well or something, and there’s always a rock bottom. So, how does water get inside the well?

In: Engineering
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Groundwater. Picture like mini rivers under the land surface. When you dig deep enough, water will either come through and/or seep into the hole.

r/hydrology r/hydrogeology

In certain parts of the world, there is a layer of water saturating the ground under the surface. This is called the water table.

Pretend the water table is 9 meters below the surface. If you then dig a hole 10 meters deep, it will penetrate the water table. Water will flow into the hole, filling it to a depth of 1 meter. Water then can be removed from the hole, which is now called a well.

Most areas of land on earth have water in the soil. This water slowly flows towards a river or other body of water. This flowing water covers vast areas known as “aquifers”. If you drill down to the depth of your local aquifer (that depth is known as the water table) the hole you dug will begin filling with water from that aquifer. A well is that hole.

Modern wells use a solid well casing with a bottom made of gravel. The water will push up through the gravel in the bottom. and filter out any large contaminated like dirt and then it will be pumped to your house. Older style wells typically jusy line the wall with stones and no cement so the Ayer would flow in from the walls as well. However they would dig it deep enough that the dirt would settle out below the bucket. As cement was developed wells were reinforced on the sides and then the bottom was left as gravel much like a modern well.

The earth’s surface is 71% water. Some of that water ends up inside the top 2km of dry land to form a water table. The depth of the water table depends on the location. When they dig a well they are gaining access to that table. The table is pretty much a line that if you dig beneath it the water will start to pool in the hole.

Speaking of the water table filling the void of the well with water, would this not happen to coffins too?

Follow up question, how do you know where to dig a well? Are there signs of water being present 9 meter underground?

The rocks are just like sponge. Half of rocks volume or even higher is actually pores filled with water. These pores can be permeable so water easily flows through or can be impermeable so the rocks acts like a hydraulic barrier

Groundwater that you pump out of wells rarely occurs like an “underground river”. Sometimes solid rock is fractured and water moves through these fractures. But the most common groundwater is found between the the grains of sediment deposited by water or wind. This also can even occur between the grains of rock like sandstone. It is a bit like the water that has been sucked up by a sponge.

If you drill or dig a well down below the water table to where the space between the grains is completely filled by water, the water will flow into the well. But the trick is that you have to keep the sediment from collapsing in and filling the hole, unless the well is in solid rock. So you use something like a metal pipe or a wall of rocks to keep the hole open.

The trick is that you also need to let the water flow into the well. Leaving the hole open at the bottom isn’t usually good enough because there isn’t enough surface area for water to flow in and you won’t be able to pump much water. If you dig a well and line it with stone blocks the water can flow in through the cracks but it will still keep the dirt out (mostly). Modern drilled wells use a “well screen” – often a metal section with tiny slots to keep the sediments out but allow water to seep in. You can provide a lot more open area this way than by just leaving the hole open at the bottom.

Have you ever been at the beach and dug a hole until water started filling it?

Image this in bigger and not at the beach. Add some structure to make sure the hole doesnt collapse due to erosion, a nice bucket to get the water and you have a well.