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

The lower limit of imperviousness that could lead to stream degradation is typically recognized as around 10%. This level of impervious surface coverage can significantly alter the hydrology of a watershed. When impervious surfaces, such as roads and buildings, increase, the natural ability for rainwater to infiltrate into the ground decreases. Instead, more water is directed as surface runoff, which can lead to increased erosion, altered stream flows, and higher pollutant loads in nearby streams and rivers.

As imperviousness rises beyond this threshold, the negative impacts on stream quality and aquatic habitats often become more pronounced. Excessive runoff can lead to flash flooding, deteriorate water quality, and disrupt the natural ecosystems in those waterways. Thus, 10% serves as a critical limit for monitoring and managing land use to protect water resources effectively.