What is the lower limit of imperviousness that can lead to stream degradation?

The correct answer is 10%. Research has shown that stream degradation can begin at imperviousness levels as low as this. When land is developed and becomes impervious, such as through the installation of roads, parking lots, and buildings, it alters how water interacts with the landscape. At about 10% impervious cover, the natural flow and drainage patterns are significantly affected, leading to increased runoff, higher peak flows during storms, and reduced groundwater recharge.

This change in hydrology often results in erosion of stream banks, loss of habitat, and degradation of water quality, which can harm aquatic life and overall ecosystem health. Understanding this threshold is crucial for designing effective stormwater management practices to mitigate these impacts. The levels of imperviousness indicated by the other options are higher and typically reflect more severe degradation outcomes, reinforcing the importance of managing impervious surfaces early in the development process to protect water resources.