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In hydrology
Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and drainage basin sustainability. A practitioner of hydrology is called a hydro ...
and geography
Geography (from Ancient Greek ; combining 'Earth' and 'write', literally 'Earth writing') is the study of the lands, features, inhabitants, and phenomena of Earth. Geography is an all-encompassing discipline that seeks an understanding o ...
, armor is the association of surface pebbles, rocks or boulder
In geology, a boulder (or rarely bowlder) is a rock fragment with size greater than in diameter. Smaller pieces are called cobbles and pebbles. While a boulder may be small enough to move or roll manually, others are extremely massive. In ...
s with stream bed
A streambed or stream bed is the bottom of a stream or river and is confined within a Stream channel, channel or the Bank (geography), banks of the waterway. Usually, the bed does not contain terrestrial (land) vegetation and instead supports d ...
s or beach
A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from Rock (geology), rock, such as sand, gravel, shingle beach, shingle, pebbles, etc., or biological s ...
es. Most commonly hydrological armor occurs naturally; however, a man-made form is usually called '' riprap'', when shoreline
A coast (coastline, shoreline, seashore) is the land next to the sea or the line that forms the boundary between the land and the ocean or a lake. Coasts are influenced by the topography of the surrounding landscape and by aquatic erosion, su ...
s or stream banks are fortified for erosion
Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...
protection with large boulders or sizable manufactured concrete objects. When armor is associated with beach
A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from Rock (geology), rock, such as sand, gravel, shingle beach, shingle, pebbles, etc., or biological s ...
es in the form of pebbles to medium-sized stones grading from two to 200 millimeters across, the resulting landform
A landform is a land feature on the solid surface of the Earth or other planetary body. They may be natural or may be anthropogenic (caused or influenced by human activity). Landforms together make up a given terrain, and their arrangement ...
is often termed a '' shingle beach''. Hydrological modeling indicates that stream armor typically persists in a flood stage environment.
Hjulstroms diagram
Bed armor is most often transported through entrainment, and more specifically suspension and saltation. Both of these processes involve moving the sediment both near and around the bed of a river. When a sediment is entrained it is being moved downstream through the forces between the layers of water around it, and once it settles it begins to create a layer on the bed of the river. This layer of sediment changes the hydrology of the river around it, as once this layer on the bottom is formed it affects the hydraulics of the river. This layer of sediments on the bed of the river can act as barrier to the incoming flow, and depending on the size and distribution of the grains, can change the river. The Hjulstroms diagram represents at what grain size and flow speed a particle is transported. The slope present at the top left of its graph is due to clay and silt cohesion.Particle size
The distribution and size of the sediments can sometimes help indicate the type of river, and the general flow direction. The grain distribution of the bed armor is essential to understanding the armor, and its function that is dependent on the size of the armor. For example, if there is a large piece of sediment that sits on the bed armor layer of the river it can change the threshold for critical flow. The change in critical flow at the bottom of the stream or river can change the turbidity of the flow, and create different types of river systems depending on the range of impact the change in flow has. This effect can create a positive loop, with the critical flow disrupting smaller sediments downstream which repeat the process.Stream power
Stream power expresses the amount of energy that a river is exerting on its bed. The equation is primarily used to understand the force in terms of the water doing work on the bed. Bed armor is directly involved with this equations, when the force on the stream increases the water acting on the sediments can also increase. This can lead to change and movement within the stream in reference to the sediments on the bottom layer.See also
* *References
{{DEFAULTSORT:Armor (Hydrology) Erosion landforms Geomorphology Sediments