Armor (hydrology) on:
[Wikipedia]
[Google]
[Amazon]
In
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. Understanding the Hjulstroms diagram is important, as it represents at what grain size and flow speed a particle is transported. The slope present at the top left of the graph is due to clay and silt cohesion.
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 environmental watershed sustainability. A practitioner of hydrology is call ...
and geography
Geography (from Greek: , ''geographia''. Combination of Greek words ‘Geo’ (The Earth) and ‘Graphien’ (to describe), literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, an ...
, armor is the association of surface pebble
A pebble is a clast of rock with a particle size of based on the Udden-Wentworth scale of sedimentology. Pebbles are generally considered larger than granules ( in diameter) and smaller than cobbles ( in diameter). A rock made predomina ...
s, 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 stream bed or streambed is the bottom of a stream or river ( bathymetry) or the physical confine of the normal water flow ( channel). The lateral confines or channel margins are known as the stream banks or river banks, during all but fl ...
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, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc s ...
es. Most commonly hydrological armor occurs naturally; however, a man-made form is usually called riprap, when shoreline
A shore or a shoreline is the fringe of land at the edge of a large body of water, such as an ocean, sea, or lake. In physical oceanography, a shore is the wider fringe that is geologically modified by the action of the body of water past a ...
s or stream banks are fortified for erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is d ...
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, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc 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 natural or anthropogenic land feature on the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Landforms include hills, ...
is often termed a ''shingle beach
A shingle beach (also referred to as rocky beach or pebble beach) is a beach which is armoured with pebbles or small- to medium-sized cobbles (as opposed to fine sand). Typically, the stone composition may grade from characteristic sizes rangi ...
''. 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. Understanding the Hjulstroms diagram is important, as it represents at what grain size and flow speed a particle is transported. The slope present at the top left of the 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 forcritical flow
In continuum mechanics, the Froude number (, after William Froude, ) is a dimensionless number defined as the ratio of the flow inertia to the external field (the latter in many applications simply due to gravity). The Froude number is based on t ...
. 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