The answer to 'why is my drainage system bare spots' is that bare spots in your drainage system are typically caused by soil erosion or damage to the drainage pipes. This can lead to water pooling and the surrounding grass or landscaping dying off, creating bare patches.
Some common causes include damaged or clogged drainage pipes, high water flow overwhelming the system, and poor soil compaction around the pipes. Symptoms include standing water, soggy soil, and dying vegetation around the drainage area.
To solve the issue, you may need to inspect the drainage system, clear any blockages, repair damaged pipes, and potentially re-grade the soil to improve water flow. In some cases, you may need to call a professional landscaper or drainage specialist to fully diagnose and fix the problem, especially if it's a more complex system.