What is the easiest way to get past or mine out aquifers?

[Dyemoon]

I selected a kinda -bleh- starting point where there is lots of trees and food but the ground has quite a bit of sand and sandy clay in the first few layers and the layers beyond the sandy clay area are challenging to get through due to the hung sections of damp walls that are impossible to dig through without creating a new underground river.

I tried brute force mining through the some damp walls in order to drain the aquifers only to find out that they are an infinite water source unless you mine out the source block.

I then brute force mined my way down by mining a bunch of channels instead of stairs and quickly found myself with a new never ending waterfall in the bottom layers of my base.

at this point i really wish i could pump out the lower layers of my base

[Diarmuhnd]

I build a walled / smoothed stairwell straight down. That's the easiest for me. I use stone blocks, not raw stone or wood. I keep it 5x5 tiles wide all the way down, with a 3x3 , X design stair wells.

I also find 3 to 5 wide ramps going down another easy way. Just have to make sure flow is not heavy down the ramp, and that wide tunnel seems to work most times. Then drain it off the map edge by smoothing and fortifying the stone at the map edge. Slowing the flow of water is easy once you hit a layer with no leak, just widen it a little and water will spread before going down more.

You could pump that water out and engineer the area to divert the water flow if you wish. You can use mine carts to destroy massive amounts of water with arcane dwarf magics so you can get some work done. Twisted Logic Gaming on youTube has some video's if you want to learn how.

[harlequin_corps]

So, aquifers are.. well. LIGHT aquifers are helpful, just finicky. Heavy aquifers are to be avoided.
The good thing about Light aquifers is that they are a solid block. No movement in/out of your base. They are a constant source of water. Light aquifers with the right touch will provide a constant consistant flow of a BIT of water that you can adjust to fit your needs by digging out or walling in. Dorfs get happy thoughts from being in a mist, they get happy thoughts from seeing a Waterfall. You will.. may want to have Wells inside your base that don't compromise your perimeter. Your dorfs will want to bathe at a water point, provide Drink to wounded Dorfs in the hospital. All in all, water management is part of the game.
So I do have some tricks that you can use that will seem obvious after you do them.
First, digging a main vertical staircase through aquifers. Each level, immediately smooth over the walls. Aquifers put water down into an space that isn't a wall. Ramps/Stairs/Open spaces. Edit: Caveat... Aquifers will drip down from above as well BUT the making of the stairs above turns the aquifer block into a non aquifer block. to prevent water in other areas from dripping down you need to dig out the area above and Smooth the Floor down. Since this usually means having to dig out .. well everything it has a tendency to make the entire multiple Z levels of the aquifer level and the floor immediately below of little to no value. Edit complete. At each level, Smoothing it over prevents THAT level from dripping into the space occupied by the Up/down Stairs. Smoothing is part of the Smoothing/Engraving/Track Laying/Fortification tab at the bottom of the screen with the Mining/Woodcutting/Plant Gathering. Edit: If one or more of the aquifer levels is of some other material than smoothable stone, i/e Sand, you will need to dig out the walls around the area and put constructed walls in. Edit complete. Edit continues: Sand however is VERY fast to dig, so having a layer of sand above your farming area is GREAT for building a Trade Depot level/Inn Level if that strikes your fancy because that's a LOT of digging. Edit complete. Again.
The Stairs themselves, after you get down as far as you are comfortable, BECOME the Waterfall space. Dorfs moving up/down the stairs will get happy thoughts. To do that though you will need to dig out a bit of the aquifer around one of the Z levels of the stairs until you get the right level of flow that your fortress is comfortable to accommodate.
So at some point though, you will get to the point where your dorfs won't be able to dig the Stairs down any further because water is filling the stairwell.
You won't be blindsided by this, it will be obvious that your stairwell is filling gradually with water. So..
On one of the floors below the aquifer build a temporary water sump. This is a room that is dug out from above by digging a couple open spaces away from the stairs, putting down stairs 1 z level and digging out a room that is isolated at that level from the stairs, i/e the only access is from above. Then dig a channel down into this room and designate the open space above the channel as a Pit/Pond and to Fill with Water.
Then at the Z-level above where the water is filling that you have already dug stairs to, dig out a channel directly adjacent to the stairs so that the Z-level below becomes 2 blocks instead of 1 (or whatever your stairs are 1x1/1x2/2x2 what have you.) Then designate the stair space next to the open channel as a water source and have buckets available.
Your dorfs will then take the water from the level below, take it to the floor above the Water Sump room and dump it in. This will remove as much of the water as they can get to and you can continue to dig Stairs further down. You shouldn't have to repeat this if you have already dug through the entire aquifer and everything is smoothed over.
If you hit Heavy Aquifer.. just.. retire and re-embark. The process for dealing with it is definitely Master level dorf fortress and rivals the process for draining the Caverns.
To identify and discriminate Aquifers during the Embark phase you select the Find Embark Location thing and you can put in parameters for your embarkation. It will then search out for locations that fit your parameters so you don't have to go through the entire map. Then you can look at each one of the ones the search function found and pick which one you want.