lab 8 stream processes

Delta

A landform made of sediment that is deposited where a river flows into an ocean or lake

oxbow lake

A meander that has been cut off from the river

braided stream

A stream or river that is composed of multiple channels that divide and rejoin around sediment bars

alluvial fan

A wide, sloping deposit of sediment formed where a stream leaves a mountain range

yazoo tributary

If a tributary cannot breach a river's levee, then it will become a yazoo tributary that flows parallel to the river

head

In the uplands, a stream's (tributary's) point of origin

differential erosion

Rocks composed of soft and more easily weathered minerals are generally less resistant to erosion and form valleys

drainage basin

The entire area of land that is drained by one stream, or an entire stream drainage system

divides

The linear boundaries that separate one drainage basin from another

natural levees

The more abundant minor flooding events deposit sediment only where the water barely overflows the river's banks. Over time, this creates natural levees that are higher than the rest of the floodplain

uplands

The smallest valleys in a drainage basin occur at its highest elevations

escarpments

The steep slopes or cliffs separating the relatively horizontal stream terraces

meandering

Winding back and forth

Sinuosity

a measure of how much a stream meanders side-to-side, the way a snake crawls

stream order

a measure of the relative size of streams. The smallest tributaries are referred to as first-order streams, while the largest river in the world, the Amazon, is a twelfth-order waterway. First- through third-order streams are called headwater streams.

Rectangular pattern

a network of channels with right-angle bends that form a pattern of interconnected rectangles and squares. This pattern often develops over rocks that are fractured or faulted in two main directions that are perpendicular (at nearly right angles) and break the bedrock into rectangular or square blocks. The streams erode channels along the perpendicular fractures and faults.

Deranged pattern

a random pattern of stream channels that seem to have no relationship to underlying rock types or geologic structures.

Annular pattern

a set of incomplete, concentric rings of streams connected by short radial channels. This pattern commonly develops on eroding structural domes and folds that contain alternating folded layers of resistant and nonresistant rock types.

Radial pattern

channel flow outward from a central area, resembling the spokes of a wheel. Water drains from the inside of the pattern, where the "spokes" nearly meet, to the outside of the pattern (where the "spokes" are farthest apart). This pattern develops on conical hills, such as volcanoes and some structural domes.

Centripetal pattern

channels converge on a central point, often a lake or playa (dry lake bed), at the center of a closed basin (a basin from which surface water cannot drain because there is no outlet valley).

point bar

deposit of sediment build up by a river on the inside bend of a meander

Floodplains

develop when alluvium accumulates landward of the river banks, during floods

sinuosity can be calculated by

dividing the length of a stream channel (along the winding path of water flow) by the straight-line distance from start to end of the stream segment

stream drainage system

drainage network including upland tributaries and main stream

how to calculate gradient

elevation over distance

Perennial streams

flow continuously throughout the year and are represented on topographic maps as blue lines

Intermittent streams

flow only at certain times of the year, such as rainy seasons or when snow melts in the spring. They are represented on topographic maps as blue line segments separated by blue dots (three blue dots between each line segment)

cutbanks

form at the outer edge of meanders and experience erosion

Alluvium consists of

gravel, sand, silt, and clay deposited in floodplains, point bars, channel bars, deltas, and alluvial fans

Load

he amount of material (mostly alluvium, but also plants, trash, and dissolved material) that is transported by a stream. In the uplands, most streams have relatively steep gradients, so the streams cut narrow, V-shaped valleys. Near their heads, tributaries are quick to transport their load downstream, where it combines with the loads of other tributaries.

stream drainage pattern

is the arrangement of stream channels and tributaries that forms on a landscape as a result of its underlying geology and relief.

stream terraces

old floodplain deposits left high as streams downcut through their own floodplains

Trellis pattern—

resembles a vine or climbing rose bush growing on a trellis, where the main stream is long and intersected at nearly right angles by its tributaries. This pattern commonly develops where alternating layers of resistant and nonresistant rocks have been tilted and eroded to form a series of parallel ridges and valleys. The main stream channel cuts through the ridges, and the main tributaries flow perpendicular to the main stream and along the valleys (parallel to and between the ridges).

Dendritic pattern

resembles the branching of a tree. Water flow is from the branch-like tributaries to the trunk-like main stream or river. This pattern is common where a stream cuts into flat lying layers of rock or sediment. It also develops where a stream cuts into homogeneous rock (crystalline igneous rock) or sediment (sand).

headward erosion

stream channels deepen and erode their V-shaped channels uphill through time

mouth

the end of a river valley

what happens to the gradient of a stream as order increases

the gradient decreases as order increases

Base level

the lowest level to which a stream can theoretically erode. For example, base level is achieved where a stream enters a lake or ocean. At that point, the erosional (cutting) power of the stream is zero and depositional (sediment accumulation) processes occur.

fluvial processes

the processes of erosion, transport and deposition associated with rivers and streams

Discharge

the rate of stream flow at a given time and location. Discharge is measured in water volume per unit of time, commonly cubic feet per second (ft3/sec).

channel bars

underwater sandbars

sheet flow

water that flows across paved surfaces.