The answer to 'why is my drainage system erosion' is that there are several common causes of drainage system erosion, including poor installation, excessive water flow, and lack of maintenance. Symptoms can include standing water, muddy areas, and visible erosion around the drainage pipes or outlets. Solutions may involve repairing or replacing damaged components, improving the drainage system design, and implementing erosion control measures.
If the erosion is severe or the cause is unclear, it's best to consult a professional landscaper or drainage specialist. They can assess the situation, identify the root cause, and recommend the most effective solution to prevent further damage and ensure proper drainage.