Rivers

Seven Common Drainage Patterns

1) Dendritic drainage 2) Trellis drainage 3) Radial drainage 4) Parallel drainage 5) Rectangular drainage 6) Annular drainage 7) Deranged drainage

Channel Patterns

A number of factors, including the sediment load, affect the channel pattern. Multiple-thread channels, either braided or anabranching, tend to occur in areas with abundant sediment or in the lowest reaches of large river systems. Single-thread channels are either straight or meandering. Straight channels tend to occur in headwater areas where gradient is high. In lower-gradient areas with finer sediments, meandering is more common.

Parallel Drainage

A parallel drainage is associated with steep slopes.

Annular Drainage

A pattern of stream flow in which the stream tends to form a circular path around the hill. It happens when there is a layer of less resistant rock in the hill.

Radial Drainage

A radial drainage pattern results when streams flow off a central peak of dome.

Rectangular Drainage

A rectangular pattern is formed by a faulted and jointed landscape, which directs stream courses in patterns of right-angle turns.

Single-Thread Channels

Although perfectly straight channels are rare or nonexistent in nature, many streams in steep mountain regions or in bedrock-controlled channels have a relatively straight channel pattern. Where channel slope is gradual, streams develop a more sinuous (snakelike) form, weaving back and forth across the landscape in a meandering stream pattern.

Dendritic Drainage

Dendron means "tree." Energy expanded by this drainage system is efficient because the overall length of the branches is minimized.

Deranged Drainage

Deranged drainage patterns are often in the areas with disrupted surface patterns, such as the glaciated shield regions of Canada. A deranged pattern is associated with no clear geometry and no true stream valley pattern.

Stream Discharge (Q)

Discharge (or runoff) is the streamflow volume passing a point (e.g., outlet of a watershed) in a given unit of time. Discharge is calculated as: Q = w * d * v where w is width and d is depth for a specific cross section of the channel, and v is the velocity. What is the unit of discharge? Cubic volume/Time (e.g., m3/s, cfs (cubic feet per second)) Length × Length × Length/Time = Cubic Length/Time

Erosion

Erosion in fluvial systems is the process by which water dislodges, dissolves, or removes weathered surface material. This material is then transported to new locations (fluvial transport), where it is laid down in the process of deposition. Erosion, transport, and deposition are affected by discharge and channel gradient.

Drainage Density and Patterns

Generally, a humid climate is associated with a high drainage density and a typical desert has a very low drainage density. The drainage pattern is the arrangement of channels in an area, which is influenced by climatic and geologic conditions.

Alluvial Fans

In arid and semiarid climates, alluvial fans are prominent cone-shaped, or fan-shaped, deposits of fluvial sediments. They commonly occur at the mouth of a canyon where an ephemeral stream channel exits the mountains into a flatter valley. Alluvial fans are produced when flowing water (such as a flash flood) abruptly loses velocity as it leaves the constricted channel of a canyon and therefore drops layer upon layer of sediment along the base of the mountain block. Water then flows over the surface of the fan and produces a braided drainage pattern, sometimes shifting from channel to channel.

Basic Fluvial Concepts

Streams, a mixture of water and solids, provide resources and shape landforms. They create fluvial landscapes through the ongoing erosion, transport, and deposition of materials in a downstream direction. The energy of a stream to accomplish this geomorphic work depends on a number of factors, including gradient, base level, and volume of flow (discharge). The gradient of a stream is defined as the drop in elevation per unit distance. Characteristically, a river has a steeper slope nearer the headwaters and a more gradual slope downstream. The level below which a stream cannot erode its valley is base level. In general, the ultimate base level is sea level.

Depositional Landforms

The general term for the unconsolidated clay, silt, sand, gravel, and mineral fragments deposited by running water is alluvium. The processes of fluvial deposition occur when a stream deposits alluvium, thereby creating depositional landforms, such as bars, floodplains, terraces, and deltas.

River Deltas

The mouth of a river is where the river reaches a base level. There, the river's velocity rapidly decelerates as it enters a larger, standing body of water. The reduced stream energy causes deposition of the sediment load. Coarse sand is deposited closest to the river's mouth. Finer materials, such as silty mud and clays, are carried farther and form the extreme end of the deposit. The level or nearly level depositional plain that forms at the mouth of a river is a delta, named for its characteristic triangular shape, after the Greek letter delta (Δ).

Fluvial Processes and Landforms

The ongoing interaction between erosion, transportation, and deposition in a river system produces fluvial landscapes.

Trellis Drainage

The trellis drainage pattern is characteristic of dipping or folded topography

Fluvial Transport

Three types of load in streams: 1) Dissolved load (solution): chemical solution 2) Suspended load: fine-grained particles 3) Bed load: coarser materials

Multiple-Thread Channels

With excess sediment, a stream might become a maze of interconnected channels that form a braided stream pattern. In large river systems, an anabranching channel pattern sometimes occurs, in which multiple large channels are present across a vast floodplain.