The answer to 'why is my drainage system brown patches' is that the brown patches are likely caused by excess moisture, poor drainage, or a buildup of organic matter in the system. This can lead to the growth of algae, moss, or other organisms that discolor the drainage area.
Common symptoms include standing water, mushy or spongy soil, and a foul odor. Solutions may include clearing debris, improving drainage, or adjusting the slope of the system. In some cases, you may need to repair or replace damaged drainage pipes or components. If the issue persists, it's best to call in a professional landscaper or drainage specialist to diagnose and resolve the problem.