It happens to the best of us. Heavy rainfall was expected to come, you thought nothing of it, you checked your basement and the whole thing was absolutely flooded. What now? Do you salvage your possessions first? Do you just drain the water first? How do you even do that?
First of all, make sure exterior floodwater has dissipated. With exterior floodwater present, it’s not yet possible to drain the basement, as it’ll fill right up again.
Then, once the floodwater is gone, it’s time to acquire a dab water pump, or any other kind of pump capable of removing this body of water. Make sure that the pump is waterproof. To use the pump, you’ll also need a generator and an extension cord that won’t break down once submerged in water. If the water runs very deep, it’s worth considering getting a sturdy rope to attach your water pump to and lowering the pump into the water. Attach the pump to a hose of some sorts and make sure that the pump’s connection to the water is not near water. Also make sure the hose points in a direction that has a gutter or a storm sewer as to not cause another flood.
Once this is done, it’s time to position the pump correctly. Try to lower it as far as possible.
Once the actual pumping is done, it’s time to evaluate the damage that has been done. Water damage is nothing to scoff at. It might be worth getting everything in your basement checked, as leaving your basement unchecked might lead to fungi, algae and mold growing literally everywhere. No carpentry is safe, no drywall is safe, anything slightly porous within a few inches of anything that might be biodegradable is a heaven for mold and the like. Also check with any local health department about the mold risk, as mold carries many safety hazards with it.