geography final #1

alluvial streams

1. alluvial river is a river in which the bed and banks are made up of mobile sediment. 2. they are self-formed. their channels are shaped by the magnitude and frequency of the floods that they experience, and the ability of these floods to erode, deposit, and transport sediment. 3. tectonic setting generally stable or very low rates of uplift

floodplains are critical to water quality by

1. filtering nutrient and impurities from runoff 2. processing organic wastes 3. moderating temperature fluctuations 4. enhancing GW recharge

fluvial process

1. flow initiation begins as laminar sheetflow when the infiltration capacity is exceeded 2. as water mass increases, flow become turbulent streamflow (or concentrated flow)

alluvial valleys result from:

1. long term lateral stream migration that widens valleys by erosion of bluffs 2. storage of alluvium on valley floors

two functions of streams

1. move water as part of hydrologic cycle 2. move sediment as part of rock cycle

floodplains are critical to flooding by

1. store floodwaters 2. reduce flood velocities - giving us more time to react to floods 3. reduce flood peaks 4. reduce sedimentation

alluvial streams characteristics

1. valleys have widened through lateral migration that eroded uplands. 2. sediment storage in flood plain is reworked by stream meandering 3. channel forms may be braided, meandering, or straight.

dendritic

A dendritic drainage pattern occurs when the tributary systems subdivides headway like the limbs of a tree. These patterns usually form in horizontal sedimentary or in intrusive igneous rocks where the rock mass is reasonably homogeneous.

parrallel

A parallel drainage system is a pattern of rivers caused by steep slopes with some relief. Because of the steep slopes, the streams are swift and straight, with very few tributaries, and all flow in the same direction. ... All forms of transitions can occur between parallel, dendritic, and trellis patterns.

radial

A radial drainage pattern occurs when the tributaries flow radially outward and downward from a central topographic high. This type of pattern is typical of volcanic cones, isolated hills, and elevated domes.

trellis

A trellis drainage pattern occurs where subparallel streams erode a valley along the strike of less resistant formations. These beds are usually steeply dipping and may be part of a fold system. The tributaries often intersect at right angles where a notch called a water gap cuts through a harder formation.

SE WI drainage density

SE WI has deranged drainage pattern because of glaciation that filled valleys. low density, irregular patterns, lakes, and wetlands.

SW WI drainage density

SW WI has dendritic & rectangular drainage pattern because old landscape eroded for 100s of millennia. high density, very little glacial fill in valleys.

floodplain

an area of low-lying ground adjacent to a river, formed mainly of river sediments and subject to flooding.

loval

beaver ponds, reservoirs, rock ledges

stream sediment transport - 3 types of loads

bedload suspended load dissolved load

alluvial fans

best observed in arid environments

fluvial landforms

both erosional and depositional

stream ordering

classification system to quantitatively order the hierarchy of stream segments in drainage basins

meandering

deeper than it is wide. suspended sediment dominated, low gradients. lateral migration constructs floodplain

ganges river delta

deltas result from rivers reaching the sea and thus losing the potential energy to transport sediment, thus depositing and prograding into the sea

capacity

describes amount of sediment transported, which varies with velocity and gradient

competence

describes size of sediment transported, which varies with velocity

streamflow characteristics

discharge - volume of water flowing past a point of unit in time.

pediments

erosional landforms that have been cut into bedrock or other sediments by long-term weathering and stream erosion

depositional (constructional) landforms:

floodplains, natural levees, point bars, deltas, & alluvial fans

stream gradient

gradient is change in elevation over distance. longitudinal profile of many rivers is steepest in headwaters, w/ decreasing gradient downstream. gradients may adjust either spatially or temporally in response to the water and sediment supply to a channel

late glacial WI

high sediment loads & variable discharges streams connected to ice sheet were braided sand and gravel streams result was aggradation

erosion mechanisms in a channel include

hydraulic action due to turbulence abrasion

holocene transition

ice sheets retreating reduced sed loads caused stream to shift from braided to meandering massive floods from drainage of Lake Agassiz caused incision (erosion) of Mississippi river, tributaries follow terraces form from incision of older floodplains

dissolved load

ions

bedrock (entrenched) streams

little to no alluvium mantling the bedrock over which it flows. formed by incision into bedrock via abrasion of the channel bed and "quarrying" or "plucking" of large blocks. rock falls from valleys sides is common. tectonic uplift rates are greater than stream incision

base level of streams

lowest level to which a stream will erode its valley and transport sediment

suspended load

maintained in suspension by turbulence (inc boils & eddys)

hydrologic alterations by ditching

many areas are ditched to lower the water table for agriculture and development

bedload

moved by tractional forces, rolling & saltating

alluvium

regolith transported and deposited by running water

drainage patterns

result from long term erosion in various geologic structures

ultimate

sea level

streams purpose in geomorphology process

shaping the landscape through erosion and deposition

stream erosion

stream incision and lateral erosion is likely the most pervasive land forming process in nature.

drainage density

sum of the lengths of channels divided by drainage area. generally a fixation of time

alluvial terraces

terraces are former floodplains abandoned due to incision (erosion) caused by lowering base level or reduced sediment load

drainage basin

the area contributing water and sediment load to a stream. it is a fundamental unit of study in hydrology and fluvial geomorphology. divide is the boundary

erosional landforms:

valleys, hillslopes, pediment, bluffs, cut banks, oxbow lakes, entrenched meanders & terraces

braided

wider than it is deep. coarse bedload dominated, steep gradients, multiple mid-channel bars