Answer: Drainage and runoff problems are very complex -- basically, the water has to go somewhere and it will naturally run down hill. If it is following an undesirable path, then either it has to be redirected to a place where it can soak into the ground, or be directed into a ditch (swale) or a drain to continue flowing until it can safely soak into the ground or run into a waterway.
Based on your description this sounds like a fairly serious problem, and erosion issues generally worsen over time as the water cuts its trail deeper each time it runs. The spring rainy season for instance can cause real issues.
It is possible that a relatively simple solution such as a swale would solve the problem, or it might require something more complex such as installing a drain to move that water to a more suitable area. I would strongly suggest you consult on site with a professional such as a degreed landscape architect or engineer with experience in grading/drainage issues. They will be able to evaluate the drainage pattern not just on your property but the surrounding area to see what needs to be done to redirect the water and protect the foundation of your home.
If this is a new subdivision type situation, I would also suggest you consult with your local authorities as to the overall drainage plan for the development. Generally, water should not be flooding your home from a neighboring property. I'm sorry I can't be more specific for you long distance.
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