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