Geography Final Ch 16

What is a flood plain? What are the different types of features found in the floodplain?

1. A floodplain is the most prominent depositional landscape, a low-lying, nearly flat alluvial valley floor that is periodically inundated with floodwaters. Frequently for where a meandering stream flows across a wide, nearly level valley floor. 2. Cutoff meanders and Natural Levees

What is an interfluve?

1. An interfluve (inter meaning "between," and fluvial, meaning "rivers") is the higher land above the valley walls that separates adjacent valleys. 2. Some interfluves consist of ridge tops or mountain crests, but others are simply board and flattish divides between drainage systems. 3. Conceptually, all parts of the terrain that are not in a valley are part of an interfluve. 4. We can envision unchanged overland flow until it reaches the lip of the interfluve. There, as water drops off the lip of the interfluve into the first small gullies of the valley system, stream flow begins.

What is the difference between competence and capacity? How are they each related to flow speed and volume?

1. Competence is a measure of the particles size a stream can transport, expressed by the diameter of the largest particles the stream can move. Competence depends mainly on the flow speed, with the power of the water generally increasing by the square of its speed. In other words, if the flow speed doubles, the size of the largest movable particles increases fourfold. If the flow speed triples, the source increases ninefold as stream speed increases even moderately, the largest moveable particles increases significantly. Thus, a stream that normally transports sand particles could potentially transport large boulders during a flood. 2. Capacity is a measure of the amount of solid material a stream has the potential to transport, normally expressed as the volume of material passing a given point in the stream channel during a given time interval. Capacity may vary tremendously over time, depending mostly on fluctuations in the volume and flow speed but also on the characteristics of the load (particularly the mix of coarse and fine sediments). It is difficult to overemphasize the significance of the greatly expanded capacity of a stream to transport material during floods.

What is a consequent stream? Subsequent stream? Antecedent stream? Superimposed stream?

1. Consequent stream is normally the first to develop on newly uplifted land, and many streams remain consequent throughout their evolutionary development. 2. Subsequent streams develop along zones of structural weakness and may erode their channels along an outcrop of weak bedrock or perhaps follow a fault zone or a master joint. They often trend at right angles to other drainage channels. 3. The antecedent stream predates the uplift 4. Superimposed stream existed when the landscape was higher, but this older, higher landscape has since largely or entirely eroded away. The original drainage pattern was incised into an underlying sequence of rocks of quite different structure. The result may be a drainage system that seems to bear no relation to the present surface structure.

What is downcutting? Base level? Graded streams?

1. Downcutting is more prevalent in the upper reaches of a stream, where the gradient is usually steep and the valley narrow. In general, downcutting produces a deep valley with steep sides and often a V-shaped cross section. 2. Base level is an imaginary surface extending beneath the continents from sea level at the coasts. Inland, it is gently inclined at a gradient that allows streams to maintain some flow. Sea level, then, is the absolute, or ultimate base level, or lower limit of downcutting for most streams. 3. Graded stream is a stream in which the gradient has adjusted to the point of allowing just the transportation of its load

What is a cut bank? Point bar?

1. Erosion on the outside of the curves is a cut bank, also where the water speed is greatest 2. Alluvium is deposited on the inside of the curves, forming a point bar, where the speed is slowest

What is a knickpoint and knickpoint migration? Why does knickpoint migration occur?

1. Knickpoints are commonly the result of abrupt changes in bedrock resistance. The more resistant material inhibits downcutting, and as the water plunges over the waterfall or rapids, the increased speed tends to scour the channel above and along the knickpoint and fill the channel immediately downstream. 2. Knickpoint migration is relatively rapid when the bedrock consists of soft sedimentary rocks but slower when the rock is resistant plutonic or metamorphic rock.

What is overland flow? How is it different from streamflow?

1. Overland flow moves downslope and its volume increases, the resulting turbulence tends to bead up the sheet flow into tiny channels called rills. 2. Once the gullies become larger they tend to become incorporated into the drainage system of the adjacent valley, and the flow changes from overland flow to stream flow.

What are the three stream types? How are they different?

1. Perennial streams 1. permanent. 2. Intermittent streams 1. Seasonal streams if they flow for only part of the year ( the wet season ) 3. Ephemeral streams 1. If they carry water only during and immediately after a rain. The term Intermittent is sometimes applied to both cases.

What are the three pieces of stream load? What are the differences between them? How do particles move along the stream bed?

1. Some minerals, mostly salts, are dissolved in the water and carried in solution as the dissolved load. 2. Very fine particles of clay and silt are carried in suspension, moving along with the water without ever touching the stream bed. These tiny particles, called the suspended load, have a very slow settling speed, even in still water. (Fine clay may require as much as a year to sink 30 meters {100 feet} in perfectly quiet water.) 3. Sand, gravel, and larger rock fragments constitute the bed load. The smaller particles are moved along with the general streamflow in a series of jumps or bounces collectively referred to as saltation. Coarser pieces are moved by traction, which is defined as rolling or sliding alone the streamed. The bedlam is normally moved spasmodically, especially during floods: debris, is transported some distance, dropped, and then picked up later and carried farther.

What are the four different types of overland flow erosion? How do they work?

1. Splash Erosion 1. Raindrops collide with the surface that create the splash erosion 2. Sheet Erosion 1. Run off of water causing a sheet of water flowing down hill forming a sheet erosion 3. Rill Erosion 1. Water is starting to cut channels 4. Gully Erosion 1. Grows into a channel

What is stream discharge? What do you use to measure it?

1. Stream discharge is the volume of flow per unit time. 2. Q = wdv 3. Q is the discharge of a stream, w is the width of the channel, d is the depth of the channel, and v is the stream velocity. 4. Usually described in cubic meters per second or cubic feet per second

What is a drainage basin? What is the other name for it?

1. The drainage basin, of a stream is all of the area that contributes overland flow, streamflow, and groundwater into the stream. In other words, the drainage basin consists of a stream's valley bottom, valley sides, and those portions of the surrounding interfluves that drain towards the valley. 2. Watershed

What is alluvium?

1. The general term for stream-deposited sediment is alluvium. Such deposits may include all sizes of rock debris, but smaller particles constitute by car the bulk of the total.

What is a recurrence interval?

1. The probability of a given-size flood occurring is usually described as a recurrence internal or return period.

What are the five drainage patterns? What do they look like? What is the difference between them?

1. dendritic * tree branch * tributaries are joining acute streams at less than 90* * fairly erosion resistant 2. trellis * very common in oachitah mountains * parallel lines 3. Radial * streams radiating out from a central point 4. centripetal * streams are converging towards a central point 5. annular * complicated * ring shape pattern of streams

How does headward erosion work to lengthen a stream?

1. lateral erosion * causes valley to become wider 2. headward erosion * causes valley to become longer 3. stream capture * captor stream * beheaded stream * elbow capture 4. delta formation * mouth of the river

Be able to describe the four channel patterns discussed in class

1. straight * short and straight * geology is controlling the surface 1. sinuous * gentle winding pattern * every topography can have something like this * as the land becomes flatter the more severe the curves become 1. meandering * much more intricate pattern of curves * ox bone 1. braided * cimarron river * interwoven channels within a larger stream bed * high capacity for flooding * rapid increase in discharge

What is a valley?

A valley is that portion of the terrain in which a drainage system is clearly established. It includes the valley bottom , which is partially or totally occupied by the channel of a stream, as well as the valley walls that rise above the valley bottom on both sides. The upper limit of a valley is not always readily apparent, but it can be clearly conceptualized as a lip or rim at the top of the valley walls above which drainage channels are indistinct or absent.

How does flow speed relate to erosion? How do you increase flow speed?

Flow speed is governed by the gradient (slope angle) of the stream-bed (the steeper the gradient, the faster the flow), by the shape of the channel (generally the narrower the channel, the faster the flow), and by the volume of flow (more water normally means higher speed.)

How/why does a delta form?

Flowing water slows down whenever it enters the quiet water of a lake or ocean and deposits its load. Most of this debris is dropped right at the mouth of the river in a landform called a delta, after a fancied resemblance to the greek letter delta. The classic triangular shape is maintained in some deltas, but it is severely modified in others because of variations in sediment load or the removal of those sediments by ocean waves.

What is the process of stream capture? What is the other name for it?

Headward erosion is illustrated dramatically when a portion of the drainage basin of one stream is diverted into the basin of another stream by natural processes. This event, called stream capture or stream piracy, is relatively uncommon in nature, but evidence indicates that is does occur.

What are the three theories of landform development discussed in class? How do each of them describe how the landscape forms?

Theories of Landform Development Davis's Geomorphic Cycle * Youth * Maturity * closer to the theoretical stream * Old Age * base level * much larger flood plain * Penenilin plain * Rejuvenation * Stream Terrace * Entrenched Meanders * Peck's Theory of Crustal Change and Slope Development * Uplift stimulates erosion immediately and that slope form is significantly influenced by the rate of uplift. He argues that slopes tend to maintain a constant angle as they erode, retaining their steepness as they retreat rather than being worn down at a continuously lower sold angle. In this way, the shape of many initial surfaces is retained long after they would have been worn away in Davis's concept. Many of Penck's ideas in his theory of crustal change and slope development have been substantiated by subsequent workers. * Equilibrium Theory

How does turbulence influence erosion capability?

Turbulence flow creates a great deal of frictional stress. This stress dissipates much of the stream's energy, decreasing the amount of energy available to erode the channel and transport sediment. Yet, turbulence contributes to erosion by creating flow patterns that pry and lift rock materials from the stream bed