Geology - Chapter 12

Equation for discharge

(channel width)(channel depth)(velocity)/ area component

What are some ways in which flooding can be controlled?

1. Dam 2. Artificial levees 3. Floodwall 4. bypass channel

What are the four types of drainage patterns? How would you describe them? What each pattern indicate about the rock beneath it?

1. Dendric - indicates a uniform rock type of collection of rocks that all weather at the same rate (branch like) 2. radial - indicates a conical-shaped feature (volcano) 3 Rectangular - exposed fractured bedrock 4. Trellis - form in region where tilted layers of resistant rock such as sandstone alternate with non resistant rock such as shale

What are the three modes of transport for stream sediment and what characteristic of sediment determines its mode of transport?

1. Dissolved Load - minerals, ions, and elements 2. Suspended load - silt and clay 3. Bed load - gravel and sand (traction and saltation)

Factors that control stream velocity (stream velocity is the key factor in stream erosion, transportation, and deposition)

1. Gradient: MOST IMPORTANT - increases and increase velocity 2. Channel roughness - decreases velocity 3. Channel shape - narrow and deep decrease friction, increase stream velocity. Wide and shallow, increase friction and decrease stream velocity

parts of a stream

1. Headwaters: upper part of the stream near its source in the mountains 2. Mouth: where the stream enters a body of water 3. Flood plains: surrounding a stream from deposited sediment from the stream

What are the three types of erosion by which a stream erodes rock and sediment?

1. Hydraulic acid - ability of flowing water to pick up and move rock and sediment 2. Abrasion - the gridding of stream channel by the friction and impact of the sediment load 3. Solution - a slow process by which rock is dissolved in water

Describe streams not at base level, nearing base level, and at base level

1. Not at base level = straight path, contour lines are close together, high gradient, dominate process is erosion by downcutting (v-shape and no flood plains) 2. Nearing base level = deposition is more dominate, moderate gradient, lateral erosion, narrow flood plains. 3. At base level = wide floodplain, extreme meandering

What are some examples of stream features created in response to changes in base level?

1. Stream terraces - step like landforms found above a dream and its flood plain 2. Incised meanders -> downcutting into existing meanders in response to change in base level

Three types of marine deltas

1. Wave dominated: shape of delta and its depositional features are shaped by wave action, depositional features are parallel to the shoreline, features = barrier island, spits, and badmouth bars 2. tide dominated: depositional features are perpendicular to shoreline, tidal sandbars 2. Stream dominated: Network of distributaries

What type of feature results when a stream drains into an internal drainage basin?

Alluvial fan

Ungraded stream

As a stream begins downcutting into the land, its longitudinal profile is usually irregular with rapids and waterfalls along its course

Graded stream

As a stream smoothes out its longitudinal profile to a characteristics concave-upward shape (balance between transporting capacity and sediment load) - through erosion and deposition

What does a Braided stream indicate about its sediment load?

Choked with too much sediment than it can efficiently transport (more bedlam, coarser grained, decreasing stability, high variability, and high slope)

Why is fine-grained silt and clay harder to erode off the bottom than sand once it has been deposited on the stream bed?

Clay has high cohesion and compaction of clay particles which makes it harder to erode of the bottom when its in deposition

How stream velocity effects erosion, transportation, and sediment deposition

Erosion and transportation = high velocity Sediment deposition = low velocity

Why are floodplains conducive for agricultural purposes but not for urbanization?

Floodplains are natualled tilled by migrated channels and supplied nutrients and fresh sediment during floods making it highly conducive for argricultual purposes bc of flooding, these areas are not conducive for urbanization.

What feature of the terrain or landscape has the greatest impact on stream characteristics? Explain.

Gradient controls stream velocity, which determines the dominate process - erosion, transport, or deposition

Stream gradient nearing head of stream and nearing mouth

Head = increase Mouth = decrease

How is sediment load and grain size affected by stream gradient?

Increased stream gradient = increase bed load = increased grain size

Greatest water velocity location on a meandering stream?

Outer portion

How are floods classified?

Reacurrance interval - avg. time between floods of a particular magnitude (eg. 25 year flood and 100 yr flood)

How is base level calculated for most streams in coastal regions?

Sea level is the base level for streams draining into costal areas

Stream

a body of running water that is confined in a channel and moves downhill under the influence of gravity

Stream Channel

a long, narrow depression eroded by a stream into rock or sediment

Sheet flow

a thin layer of unchannel water flowing downhill

Equation for gradient of a stream

highest elevation - lowest elevation / distance between two elevations

How can base level change?

increase in tectonic uplift = change in base level and changes in sea level

How does urbanization effect flooding?

increase urbanization = decrease in vegetation = increase artificial surfaces = decrease water infilltration = increase discharge = increase flooding

Meanders

rivers that carry fine grained silt and clay in suspension tend to be narrow and to develop pronounced sinuous curves

What is a pointer and what occurs there?

the deposit on the opposite side of the channel and is where the deposition occurs

Lateral Erosion

the erosion and undercutting of a stream's bank and valley walls as the stream swings from side to side across its valley floor

What is a cutback and what takes place there?

the outer bank of a meander in a meandering stream and erosion takes place

Downcutting

the process of deepening a valley by erosion of the stream bed

Baselevel

the theoretical limit to downcutting by a stream

What is a drainage basin and how are their boundaries defined?

the total area drained by a stream and its tributaries boundaries are defined by high relief features (ie/ called divides)

Discharge and why is it important

volume of water that flows past a given point in a unit of time and helps us plan and prepare for floods (humid climates = increase going downstream, arid = decrease going downstream)