Okay here's one that I'm not exactly sure where to turn for help. My front porch has a large cavity underneath where the ground appears to have eroded away. The cavity runs the entire length of the porch (about 20 feet) with the deepest spot probably close to 4 feet -- possibly more. My question is who should I have take a look at this to fix/assess? I'm not sure if it posses a structural hazard or if it is the reason water is entering my basement during heavy rains. Regardless, it really should be looked at. Would this be something for a landscape architect? Any suggestions?

Yes you do need to have the issue looked at. It sounds as if your perimeter drainage has failed.
Most general building contractors would know how to resolve the problem as they are required in most areas for site and perimeter drainage when building new structures.
It will most likely be a combinations of run off, swales, roof drainage and perimeter drains.



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