GEOG 2051 Exam 3

Dendritic Drainage

"Tree like" pattern of stream network. Forms when you have rocks of uniform resistance to weathering & moderate slopes.

Increased Velocity

= Increased Slope

Decreased Velocity

= Increased roughness

Meandering Deposition

Along the inner bank-point bar. Low velocity-slowest on inner bank.

Meandering Erosion

Along the outer bank-pool and cut bank. High velocity-fastest on outer bank.

Arid Climate

Although limited vegetation cover, there is not enough runoff to carve extensive channel systems.

Channelization

An engineering technique to straighten, widen, deepen, or otherwise modify a natural stream channel.

Fluvial

Any process or landform related to streams/rivers. Move water and sediment from continents to oceans. Get their energy from insolation and gravity. Get their water from SURFACE RUNOFF (overland flow) and GROUNDWATER (base flow), making streams OPEN systems.

Open

Are rivers an open or closed system?

Single Cross-Section(s)

As discharge increases, the width WILL NOT CHANGE because the channel banks are somewhat steep. So water keeps getting deeper. The flow DEPTH is increasing. Increasing discharge at a _____ _____ _____ is accommodated by increasing depth and flow velocity.

Oxbow Lake

As the meander river bends and migrates, it eventually intersects to form a cutoff, which turns into _____ _____. When sediment fills the area that was cut off, then the lake forms.

Drainage Basin

Basic spatial geomorphic unit of a river system; the area of land that contributes water to a single point, where all water exits. Consists of a network of stream channels and slopes that drain into those channels. Also known as watersheds or catchments. Any _____ can be divided into several smaller ones.

Ripples, Dunes, Bars

Bed Forms

Strath Terraces

Bedrock terraces with little or NO deposition.

Dam, aggradation

Building a ___ on a river RAISES the LOCAL BASE LEVEL which results in ________

Flow Resistance

Caused by the roughness of the channel boundary. Affects the average velocity of the flow and can influence the 3D variations in velocity in a channel.

Form

Changes to channel _____ are caused by fluvial erosion, transport and deposition of sediment.

Straight, meandering, braided, anabranching/anastomosing

Channel Patterns

Deranged Drainage

Chaotic arrangement of channels connecting small lakes and marshes. Typical of landscapes following the retreat of ice sheets.

Bed Load

Coarser materials, such as pebbles, that move along the channel bed.

Vertical Accretion

Deposition of natural levee and flood deposits on the floodplain during periods of flood flow mainly silt and clay. Of fine sediment that falls out of the suspension during floods. Any time water spills out of a channel, that sediment is also going to spill out and then build a floodplain VERTICALLY. Common features are mud cracks, backwater, etc. EX: Pearl Bend, Wabash River

Floodplain

Depositional river landforms. Flat, low-lying areas of alluvium on either side of a stream channel and subject to recurrent flooding. Storage area for water during floods and for sediment over decades, centuries or even longer. Must be viewed as an ACTIVE part of the modern river and is not separate from river. Primarily developed through LATERAL ACCRETION. Form from lateral accretion and vertical accretion and a secondary process of filling OXBOW LAKES with sediment.

Natural Levees

Deposits of alluvium directly over channel banks that form a ridge that follows the channel bank lines. Deposition occurs here because the flow slows down as soon as it leaves the channel during flooding. As the levee builds up, it then takes progressively larger and larger floods to top them over.

Lag Time

Difference between the peak in precipitation and the peak in time.

Channel Patterns

Distinguished based on Sinuosity (curves) and Single vs. Multi-Thread Channels. Form under different slope, sediment load, and floodplain conditions.

Total length of all stream channels in the basin/area of the basin

Drainage density.

Insolation

Drives the hydrologic cycle making fluvial systems a part of the surface water reservoir.

Chute cutoff

During overbank flow (flooding) surface erosion cuts new channel across floodplain.

Humid Climate

Encourages vegetation cover, which REDUCES channel formation by holding surface sediment in place. Lowest drainage density.

Semi-Arid Climate

Enough rain to produce RUNOFF, but not enough to sustain much vegetation. Highest drainage density.

Ultimate Base Level

Ex: Sea Level-water can't be driven any further. Surface that EXTENDS INLAND from sea level, sloping gently UPWARD. A drop in sea levels would affect rivers near the coast because rivers would start to ERODE deeper down to decrease the elevation of the river bottom (degradation).

Channel slope, Channel roughness

Factors in flow velocity.

Highly erodible rocks, impermeable rocks, steep slopes, minimal vegetation

Factors of high drainage density.

Less erodible rocks, permeable rocks, gentle slopes, dense vegetation

Factors of low drainage density.

Sinuosity, single channel vs multi-thread channel

Factors that determine channel pattern.

Alluvial Fans

Fan-shaped deposits of sediment where stream emerges from a mountain front. As the water and sediment rush out and hit the flat belly bottom, it loses energy so it dumps it at the base of the slope. Combination of mudflows or debris flows and alluvial deposits. Coarse grained. Catchment area in mountains. Confined, steep valley. Abrupt drop in energy, leads to deposition. Fan shape due to avulsion process. Deposition of the _______ ___ is caused by a RAPID decrease in SLOPE.

Aggradation

Filling in of the channel via fluvial EROSION. Balancing the amount of water and the SLOPE. If water is increased, it will scour out all the sediment within. If the slope of a river is too gentle to transport the grain size of the sediment that is entering the channel from upstream, the channel bed will experience _______ until it reaches a steep enough slope to transport the grains. The process by which a Stream's gradient steepens due to increased Deposition of sediment. Ex: Building a dam on a river will raise the local base level of that river channel. You'll no longer have energy to pull it, so you just dump the sediment there.

Suspended Load

Fine-grained clasts (fragments of rock) that are suspended in water, held up by turbulence.

Rectangular Drainage

Forms in a FAULTED and jointed landscape which directs stream courses in patterns of RIGHT-ANGLED turns. A flow pattern in which streams consist mainly of straight line segments with right angle bends and tributaries join larger streams at right angles.

River channels, floodplains, deltas

Forms of Fluvial Systems

Anabranching/Anastomosing

Fully vegetated, multi-threaded channels. Islands are large compared to the channel. Separated by STABLE and VEGETATED floodplains (islands). Multiple channels and stable islands both LARGE relative to the channels. LOW energy. Low gradients, cohesive banks, high organic content, vertical deposition. Avulsions are common- During overbank flows (flooding), rapid development (abandonment) of a new channel through the floodplain.

Fluvial Valleys

Fundamental features of fluvial erosion. Generally V-shaped. Deep and narrow bedrock valleys. Valley widening is because of rivers moving laterally. It starts to migrate side to side and starts to widen the valley bottom (floodplain).

By changing the amount of resistance (friction) to water movement.

How do channel morphology and sediment transport influence flow?

Longitudinal Profile

How the slope of a stream varies over its length. Generally, concave up, steeper at headwaters, gentler at mouth. It happens through degradation and aggradation.

Slope, mouth

If we increase our _____, we can move sediment downstream. As more water is collected, we get down near the ______.

Channel bed

If we measured the elevation along the _________ _____, we would see a concave slope upwards and a steeper headwater (source) due to degradation and aggradation.

Urbanization

If you put pavement in, water rushes quicker across the landscape. Results in increased discharge and a decrease in lag time.

Entrenched Meanders

Incised river meanders excavated deeply into the landscape, rejuvenation. Forms due to a sudden DROP in base level relative to the river bed (usually due to tectonic uplift) causing the river to rapidly cut down into the bedrock. We either lower the water level or LIFT the land level due to tectonic plates. Lateral migration is restricted by resistant bedrock and rapid uplift, so the original platform of the river is maintained as it cuts down. Can sometimes form bedrock terraces.

Flow

Influences channel morphology through sediment erosion and deposition.

Surface Runoff

Is a term used to describe when soil is infiltrated to full capacity and excess water, from rain, snowmelt, or other sources flow over the land. This is a major component of the water cycle or the hydrological cycle. A land area that produces runoff draining to a common point is called a watershed. Water flowing off the land into bodies of surface water.

Mouth

Is the part of a river that flows into a lake, reservoir or ocean.

Closed

Is the water cycle an open or closed system?

Bars

Largest scale channel deposits that are most often composed of sand and gravel.

Sinuosity

Length of a river DIVIDED BY the straight valley line. How much the channel platform deviates from a straight path.

Alluvial Terraces

Level areas that appear as topographic steps above a stream. Form when a change in environmental conditions isolates the floodplain from the river channel. When finished cutting down/eroding, a balance point is reached where the river just wants to cut side to side. That floodplain begins to erode into "perched floodplains above the river." Level areas of alluvium that "step down inwards and toward a river channel. Caused by river degradation due to episodic drops in base level relative to the river bed (due to uplift or drop in sea level). Flooding no longer occurs or rarely occurs. ALL TYPES ARE EROSIONAL FEATURES.

Base Level

Lowest point where water is being pulled downslope. It is just barely enough slope (potential energy) to sustain the flow of water. Theoretical level below which a stream cannot erode (denude) its valley. Lowest level to which running water can flow.

Alluvium

Material (sediment) deposited by stream water.

Bajadas

Merging of separate alluvial fans into ONE blanket covering.

Traction

Mode of bed load transport. Rolling, sliding.

Saltation

Moving along the bed in short hops. Bouncing. Mode of bed load transport.

Multiple Cross-Sections

Moving downstream-discharge increases due to tributaries and greater drainage area. Most of the change and increasing is in CHANNEL WIDTH. Velocity also increases with increasing discharge, but at a slower rate than channel size.

Braided

Multi threaded channels separated by two or more UNVEGETATED bars contained within a dominant pair of floodplain banks. Steep drainage basin with an abundant bed load and lots of sediment. LOW sinuosity. HIGH energy, HIGH sediment loads, variations in discharge, and lack of vegetation. Common in arid and glacial environments. Seasons where water is all tied up, but then summer comes and it melts and releases a lot of water that can flush sediment through. Channels/bars constantly changing-over time-generally unstable. TD;LR: Steep slopes, variable discharge, lots of sediment-abudant bed load, Erodible/non-cohesive banks.

Graded Streams

Mutual balance between slope, size and shape of channel so that the _______ has enough energy to transport the sediment load WITHOUT degradation or aggradation.

Neck Cutoff

Narrow floodplain, then cuts off and there is a relatively small path that the water can follow. Progressive migration of TWO meander limbs together. Distance is <1 channel width.

Local Base Level

Point to which is the lowest part of that water can flow. Can control the lower limit of local smaller streams for a region. Often referred to as the mouth of the river. Can be a river, lake, hard rock layer, or man-made reservoir.

Knickpoints

Point where there is a sharp change in channel slope. Something that controls the local elevation of the river channel. Undercut and work their way UPSTREAM. Ex: Waterfalls, rapids, etc. In order to create waterfall or _____ you need a resistant layer. As water falls over the edge and erodes out the rock/material the resistant rock collapses over the top of it.: Waterfalls, river, lake, hard rock layer, man-made reservoir.

Headlands

Points of high land that stick out into a body of water.

Annular Drainage

Produced by STRUCTURAL DOMES ( domes formed by folding of rocks in 2D), with concentric patterns of rock strata guiding stream courses.

Radial Drainage

Produced when stream flow off a central peak or dome, such as a volcanic mountain. A flow pattern where streams flow outward and downward from a central elevated point.

Larger Particles

Require greater velocity.

Degradation

Scouring out of the channel via fluvial TRANSPORT. Balancing the amount of sediment being moved and how big the sediment is. The process by which a Stream's gradient becomes less steep, due to the Erosion of sediment from the Stream bed. Generally follows a sharp reduction in the amount of sediment entering the Stream

Dissolved Load

Sediment that is dissolved into the water and transported within the current of the stream. Usually calcite or salts.

Meandering

Single sinuous channel. Common in HUMID TEMPERATE and TROPICAL environments. Occur where there are moderate slopes, mixed bed and suspended load and more resistant/cohesive banks. Curving path of highest velocities-FASTEST on the outer bank (cut bank) and SLOWEST on the inner bank (point bar). As bends migrate they eventually intersect to form cutoffs, which turn into oxbow lakes.

Rate of elevation decline/Horizontal distance downstream

Slope.

Ripples

Smallest beach ridges parallel to the shoreline created by wave action

Flow Velocity

Speed and direction of water movement.

Silt and clay

Stick together (cohesion) and require higher velocity to move those substances.

Gentler

Streams that have HIGHER discharge and finer sediment can transport sediment at a ______ slope.

Lateral Accretion

The lateral migration of bar deposits (mainly sands and gravels). Of sediment on point bars as the river migrates across the valley bottom. Not only depositing sediment but also mobilizing the sediment. A dominant way to build floodplains-it sets the foundation. As the channel migrates laterally, all of the coarse sediment is as well moved.

Drainage Divides

The outer boundary of a drainage basin, also the boundary between it and adjacent basins; follows the crest of the interfluve between two adjacent drainage basins. Separates one basin from a neighboring basin. Ridges and highlands mark the limits of the catchment area/drainage basin.

Channel morphology

The shapes of river channels and how they are altered in shape & direction over time. Causes the flow velocity to spatially vary in 3D throughout the channel.

Fluvial Geomorphology

The study of the INTERACTION between streams/rivers and forms (within a hydrologic and geologic context).

Base Flow

The sustained low flow of a stream, usually ground-water. Water that reaches the channel largely through slow through-flow and from permeable rock below the water table. Known as groundwater.

Confluence

Two channels come TOGETHER. Merging flows, more energy.

Trellis Drainage

Typical of dipping (monocline) or folded topography with differential weathering. Forms where there are folded landscapes, and the river has to follow long and straight valleys. Where you have folds, ridges and valleys- you get those ridges and valleys because of different resistance in rocks. The rectangular drainage pattern created if rivers flow through alternating bands of hard and soft rock.

Surface

Velocity is GREATEST at the ______ of the stream, where there is less frictional resistance.

Middle

Velocity is GREATEST in the ______ and away from the bed and the banks.

Outer Bank

Velocity is high on the _______ ______ because of the curving path. Water is being pushed side to side because of the centripetal force (turning left, but you feel like you're pulled right). The water can be turning right, but will have momentum going left.

Inner Bank

Velocity is slowest on the _______ _______.

Straight Channels

Very rare in nature and most channels of this type are man-made. Only occur over short distances. LOW sediment load. LOW slope. Highest velocity is in the MIDDLE of the channel at the TOP of the water surface. Ex: >90% of headwater streams in Illinois are channelized, bayous in Louisiana.

Discharge

Volume of flow per unit time (m^3/s or cfs) "Q". Increases in Q must be accommodated by a combination of increases in width, depth, and velocity. ______ in river can vary because of precipitation events (short periods), spring snow-melt, and seasonal variations in the level of the water table (long periods).

Example of Fluvial System

Water flowing downslope under the force of gravity, erosion, transportation and deposition by that flowing water.

Gravitational

Water flows from high to low elevation converting ______ potential energy to kinetic energy of moving water.

Fluvial

Water moving over a sediment bed will result in ______ erosion, transport and deposition of sediment.

Diffluence

Where ONE channel splits into TWO. Diverging flows, less energy.

Because it is not losing mass.

Why is the water cycle closed?

Dunes

Windblown accumulations of sand. Larger scale.

Point Bars

Zone of decreased velocity on the insides of meanders where debris acquired by the stream at the cut bank moves downstream with the coarser material is deposited.

Anastomosing

______ Rivers are an endmember of anabranching type.