Theme 6: River systems Flashcards
What is an alluvium deposit?
Material deposited by running water. The
deposits are young and un
consolidated.
What is the normal sequence of processes in landscape development?
Weathering, erosion, transport, deposition
Briefly describe the hydrological cycle
Water from precipitation reaches ground and either becomes runoff or infiltrates ground and percolates down and becomes groundwater. Base flow eventually causes these previous water sources to become inputs into streams (discharge). This water then slowly makes it way towards the ocean. Water from streams and lakes is evaporated, evapotranspiration from soil and plants becomes water vapour, and transpiration from plants.
Waterbalance in a drainage basin
P = Q + E + Δ (I, M, G, S)
P: precipitation
Q: discharge (river runoff)
E: evaporation/evapotranspiration
I: Interception, storage
M: Soil water storage
G: Groundwater storage
S: Channel storage
What are the recurrence intervals of precipitation?
Extreme events: are high intensity and duration, they do lots of work but are rare
Low magnitude events: low intensity and duration, common, and do small amounts of work repeatedly
What are drainage basins?
It is a water/sediment drainage system that is defined by ridges and highlands (drainage divides). It conveys sediment from steep uplands to less steep lowlands and then
onto an outlet called a basin outlet. Drainage basins contain streams of various sizes as well as smaller tributary drainage basins
Define stream order
(important)
A classification/ranking of streams based on the number tributaries that flow into them. A stream with no tributary is a first order stream. When and only when two streams of the same rank join up together does stream order increase (eg. two 1st order streams join up to make a 2nd order stream).
Name the different type of streams depending on their permanence
(IMPORTANT)
Intermittent: runs dry for part or most of the year
Permanent stream: flows yr round
Ephemeral stream: common in arid environments, if only present for a couple of hours or days after heavy rainstorms
Describe drainage patterns and name the types
Drainage patterns are the arrangement of streams in an area. They are affected by relief, steepness, resistance of framework, climate, and hydrology.
Dendritic: like branches on a tree
Trellis: develops in valleys or ridges where rocks of different resistance to erosion are folded into anticlines or synclines
Rectangular: form on strongly jointed terrain and follow those joints
Radial: develops on singular, high peaks
Discharge is…
a stream’s volume per time. It is affected by climate, stream order, surface permeability, season
Q = wvd
w: channel width
v: stream velocity
d: channel depth
LOOK AT HYDROGRAPH
see notes
Compare flood conditions in a river to that of normal flow conditions
Flood conditions: flow in a river channel (Q) exceeds the capacity of the channel. This higher energy causes increased erosion. Maximum erosion occurs when the entire channel is filled (bankful). Eventually, if the discharge is high enough, the flow will spill over the banks and onto the flood plain where now the energy is spread over a wider area and erosion is lessened.
Normal conditions: river is close to equilibrium, and there is a balance between the volume of water and the sediments entering and leaving a river
Describe the longitudinal profile of a river and define stream gradient and base level
Longitudinal profile: Steep at headwaters, so more erosion, and progressively gets gentler at a river’s mouth. As a stream flows downslope, its potential energy falls and reaches zero as it meets the sea. Its discharge increases, its velocity decreases, and its cross-section increases.
Stream gradient: refers to the steepness/the drop in elevation of the stream channel in as it progresses in the downstream direction
Base level: the level below which a stream can no longer erode its valley. So, it can only erode above it. The higher the stream is above its base level, the more energy it has to erode the land surface. Usually lakes or larger rivers act as local base levels (other than the ocean).
What are the different channel types? (IMPORTANT)
Single
Straight: occur in bedrock areas with steep gradients, in alluvial channels (sed filled) where channel is +/- straight the main zone of flow
Meandering:common in chanbels with fine grained seds and gentle gradients, over time they cut across the floodplain, they erode along the cutbank (Thalweg here) and deposit material on the point bar (low velocity), can form oxbow lake after cut off.
Multiple
Braided: braided pattern, multiple unvegetated and shifting channels that converge and diverge within a larger channelway, characterized by rapidly migrating channels, separated by gravel bars, variable discharge in each stream, and high sed load
Anastamosing: multiple channels separated by vegetated semi permanent islands, splits are permanent, composed of 2 or more interconnected channels enclosing floodplains, they have low energy near base level.
What are the controls on form and processes in rivers? What is incision and aggravation? (IMPORTANT)
The substrate (the resisting framework): It will determine how much incision occurs. In rivers, this framework is mainly affected by sediment size; the bigger the sediment and the more of it, the more incision will occurs (unlike fine seds).
The discharge (hydraulic driving forces): it will determine how much aggradation will occur. The discharge in rivers is mainly determined by the stream slope. The steeper the slope, the more agggradation will occurs (unlike a flat area).
Incision is the natural process of erosion where a river cuts downwards into it riverbed deepening the active channel.
Aggradation is the increase in land elevation due to deposition of segment. It occurs when the supply of sediments is greater than what can be transported.
