My parent's basement floods every time they get a heavy rain. My father has tried just about everything he could do without major construction being done to try and resolve the issue, but nothing has worked. The sump pump is the largest he could find and runs almost constantly every day. Some other issues; because of the high volume of water being removed from the basement it pools up in the back yard. And (I think) the slab is poured below the water table. The hydrostatic pressure has cracked the slab in various places and there's always seepage.
There's one sump and drain tile all around the inside of the foundation. The gutters drain at least 6' from the foundation. The grade is flat but there is a lake about 200 yards south of the house. So I'm assuming the water would run towards the lake. And there's no city storm drain around.

We've been trying to think of a solution to the problem, but we're just not positive what to do. Add another sump pit? Break up the slab, add fill, and re-pour the slab so that its above the water table? Dig a curtain drain? But where would the water go? Just not sure what to do here.

 

All you have to do is read all the "water in my basement" threads. It's a common problem and there is no magic solution to keep water outside. You parents basement is a boat. You can either bite the bullet and waterproof the hull and keep the water away on the outside or add more bilge pumps (sump pits and pumps) and remove the water after it's gotten in.

 

At least 90% of the time the issue needs to be addressed outside not inside.
No mulch against the foundation.
No flower beds forming ponds.
Outside of foundation should have been water proofed, grade needs to run away from the foundation.
May even need a french drain.

 

Discharging the gutters only 6' from the foundation could be a problem since the water could easily be a problem.

Where does the sump pump discharge relative to the house? Distance away horizontally and height above the basement floor and grade around the house.

You may be creating high water table near your house especially if you have a flat lot.

The bullet-proof method would involve adding a second sump tied into the interior drain tile on an opposite wall and another pump (to drain the immediate basement bottom area) and extend the pump discharge below the yard level well away from the house (a screed pipe or a pop-up). The pump discharge should be in a solid wall pipe that has proper drainage.

Not cheap, but it can work. The buried sump pump discharge can be problematic in a some climates (depending on the snow depth or if the ground freezes deep before snow since the snow can be a great insulator).

Dick

 

The sump pump discharges about 30' out and above grade into the back yard.

What you suggested would be bullet-proof, is actually what my father and I were last thinking about doing. When we built the house the city made us dig a 40' trench in the front yard and fill it with gravel then dirt. We were thinking of putting in a second sump pit and pump and draining it into the front above that trench. And also drain all downspouts into it as well. That trench is about 20' to 25' from the house.

 

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What is the topography like around the house? The front yard with the gravel filled trench. Is that uphill from the house? Why were you required to dig a trench filled with gravel? Was any drain pipe installed in that trench?