Describe how the debris basins need to be maintained in order to remain effective.

After a debris basin fills up, it needs to be cleared to make room for more debris. The debris basins throughout Los Angeles County have trapped more than twenty million tons of materials that slide down the mountains. Continuous cleaning out of these basins is needed, otherwise they will overflow and debris will simply fall into houses downstream. It is very expensive to keep these basins clear. Some of the mountain sand trapped in the basins is purchased by Los Angeles and shipped to the county's beaches.