Because the water receives no treatment, it is important that sediment and debris are absent from the water. Many times the changes are made to develop an area. Construction typically removes plant life at the development site. When it rains, there is nothing on the site to keep the soil in place. The soil is carried to surface waters via storm water runoff.
Soil erosion continues even after the development is completed.
Now the storm water does not have a place to seep into the ground. Again storm water runoff is formed, following any path it can find. Eventually the runoff will find a stream or creek, but the force of the flowing water is much greater than before, thus eroding the streambank. The material picked up by the runoff will now be deposited in the larger surface waters. The erosion caused by the runoff destroys animal and plant habitats along the streambank.