Seep

Seep

—a wetland area located on gently to steeply sloping land and dominated by colluvial (i.e. gravity-driven), unidirectional movement of water and material down-slope.

Seeps are often located on the side-slopes of a valley but they do not, typically, extend onto a valley floor.
Water inputs are primarily via subsurface flows from an up-slope direction. Water movement through the seep is mainly in the form of interflow, with diffuse overland flow (known as sheetwash) often being significant during and after rainfall events.

Seeps are characterised by their association with geological formations (lithologies) and topographic positions that either cause groundwater to discharge to the land surface or rain-derived water to ‘seep’ down-slope as subsurface interflow. Examples of places where these conditions occur are
(1) on slopes where the water table intersects the land surface, resulting in groundwater discharge directly to the land surface;
(2) land that is down-slope of a break in slope of the groundwater table;
(3) where subsurface discontinuities in geological units (e.g. faults) cause upward movement of roundwater; or
(4) on slopes where a relatively impervious subsoil layer impedes the infiltration of rainderived water into the ground.

It is important to bear in mind that seeps can occur in relatively flat or very gently-sloping landscapes, as long as there is sufficient slope for there to be a unidirectional subsurface flow of water.

As for depressions, you can further classify seeps according to their outflow drainage characteristics at Level 4B.

Posted on February 8, 2023 09:15 PM by tonyrebelo