Significant Topographic Changes in the United States
Because they are a natural partitioning of the land surface, watersheds have been used extensively to study and report on environmental conditions. As such, they provide another useful way to view and present the extent of topographic changes. The connectivity of watersheds may be an important condition when assessing the impacts of land surface transformations. For instance, an important consideration might involve determining which watersheds are immediately downstream of the watersheds that contain topographic change polygons.
The figure below shows the watersheds in the conterminous United States that contain topographic change polygons. In this case, the watersheds are the hydrologic cataloging units that are widely used in water resources studies. These watersheds are commonly referred to as 8-digit cataloging units because of the unique code assigned to each unit. The 8-digit cataloging units have the detail, accuracy, and information content equivalent of a 1:250,000-scale topographic map. The average size of the 8-digit units is slightly less than 4,000 square kilometers. Not all the cataloging units are watersheds according to the strict definition, as some units have an administrative or political boundary rather than a drainage divide.
Summary Statistics and Rankings:
Top Ranked Watersheds (by Area) Containing Topographic Change Polygons