The answer to 'drainage system thin grass' is that a poorly functioning drainage system is a common cause of thin, patchy grass. Excess moisture from poor drainage can lead to soil compaction, root rot, and nutrient deficiencies that prevent healthy grass growth. Symptoms include waterlogged soil, moss growth, and yellowing or thinning of the lawn.
To fix the problem, start by inspecting your drainage system for blockages, damage, or inadequate slope. Consider adding drainage pipes, improving grading, or installing a French drain to divert water away from the problem area. In some cases, you may need to aerate the soil or overseed the lawn to help it recover. If the issue persists or requires major excavation, it's best to call in a professional landscaper for further assessment and repairs.