What Are Headwaters ?
Think small watersheds. Headwaters are those areas that are comprised of small, ephemeral or intermittent streams as well as perennial streams. Generally, most streams you can jump across are headwater streams. Headwaters also refer to the terrestrial areas surrounding these streams. The composition of the upland will influence the chemistry, hydroperiod, and response to disturbances such as precipitation, changes in vegetative structure, and anthropogenic influences.
An excellent general resource on headwaters and their importance and function in the landscape is provided by Meyer and others. You can find it here.
Headwater streams comprise between 53 and 75% of the total length of all waterbodies in both Europe and North America. That is, when we measure the total length of all mapped waterbodies, we find that the vast majority of those are found in headwaters.
To further demonstrate this, at right is a diagram showing a small catchment (brown). This is a typical headwater catchment. If we draw a boundary (dotted line) around all headwater streams and their source areas, we see that they constitute the majority of the area in these catchments.
Now if we place this small headwater catchment in the context of a watershed (far right, in green), we can appreciate how many headwater regions exist within a single watershed (scale is relative here) and realize the extent of headwater regions that exist in the landscape.
What are the functions of Headwaters?
Headwaters provide many important ecological functions to downstream systems and can be broken down to three major categories: