Option A: Freshwater - Part 1: The Drainage Basin Flashcards
5 factors that affect the drainage basin. (G,L,P,L,T)
Geology Land use Precipitation Land relief Time
4 Types of Erosion + 1 describing word.
Hydraulic Action - pressure
Corrasion - sandpaper
Corrosion - dissolving
Attrition - collision
4 Types of Transportation + 1 describing word.
Deposition - 1 describing word.
Traction - rolling Saltation - bouncing Suspension - floating Solution - dissolving Deposition - dropping
River Velocity: channel shape, bed roughness and slope.
Higher hydraulic radius = quicker river flow
Higher roughness = slower river flow
Steeper slope = quicker river flow
8 River Landform Features (V, W, F, L, D, M, O, P)
V-Shaped Valleys Waterfalls Floodplains Levees Deltas Meanders Oxbow lakes Point bars
7 Factors affecting flood risk and defintions (S, D, C, S, V, H)
Shape: Circular = shorter lag time, higher peak flow. Elongated = longer time for water to reach gauging station from extremities.
Density: Higher in impermeable rocks = more flash floods + higher peak flow.
Lower density = rocks and sands.
Climate: Prolonged rainfall = more flooding, ground is saturated, infiltration replaced by overland flow.
Soil: Sandy soils with large pore spaces = rapid infiltration = less flooding.
Vegetation: Encourages interception = decreases flooding.
Human impact: Urbanisation - tarmac,concrete = impermeable. Gutters + drains carry water to river more quickly. Deforestation decreases infiltration + increases surface runoff.
How Hydrographs Predict Floods.
Peak discharge, magnitude, falling limb, lag time
PEAK DISCHARGE used to predict MAGNITUDE.
Historical records of FALLING LIMB used to predict duration.
LAG TIME needed in order to know the arrival time downstream.
Flood Hydrograph definition and 8 components
A way of showing the discharge of a river at a given point over a short period of time.
Approach Segment: The amt. of discharge before the storm.
Rising Limb: The river’s response to the rainfall period.
Peak Discharge: When the river reaches its highest level.
Lag Time: The period between maximum precipitation and peak discharge.
Falling Limb: Where discharge is decreasing and river levels are falling.
Stormflow: The discharge attributed to a single storm.
Baseflow: By continually releasing groundwater it maintains the rivers flow during low precipitation.
Bankfull Discharge: Water level = top of its channel, further increase = flooding.
River discharge definition and equation
The volume of water that passes through a stream’s cross section in a given period of time.
Discharge = velocity x cross sectional area
DB Examples of Inputs
Precipitation: rain, snow, etc.
DB Examples of Outputs
Evaporation and transpiration
DB Examples of Flows
Infiltration, through-flow, overland flow and base flow.
DB Examples of Stores
Vegetation, soil, aquifers, the hydrosphere and cryosphere
Drainage Basin Definition. Open or closed sysstem?
Open system as there are inputs and outputs. All the area that gets drained by a river and its tributaries divided by a watershed.
What is the hydrological cycle? Closed or open system?
Closed system as there are no inputs or outputs. The cycle of water between the biosphere, atmosphere, lithosphere and hydrosphere.
Stores (4) of the Hydrological cycle.
Clouds, sea, lakes, vegetation
Flows (4) of the Hydrological cycle.
Evapo-transpiration, precipitation, surface run off and groundwater flow.
Describe the 2 types of flow in a river (L and T)
Laminar: straight horizontal
Turbulent: helicoidal flow of horizontal eddies and verticle eddies
Outline waterfall formation in 6 steps.
- Softer, less resistant rock is easily eroded.
- Harder rock on top (cap rock) is undercut by the erosion of softer rock.
- Eventually, the overhang collapses due to lack of support.
- As water falls over the tip, more of the rock is eroded by Hydraulic Action and Corrasion.
- A plunge pool is formed by continued erosion.
- Over time, the waterfall retreats upstream, leaving a steep-sided gorge.
Outline levees formation in 3 steps.
- Before a flood, river surrounded by floodplain.
- During a flood, water level increases. The thickest and coarsest sediments are deposited on channel edges. Thin and fine sediments deposited over outer parts of floodplain.
- After many floods, natural levees build up sediment.
Outline meander and oxbow lake formation in 5 steps.
- River erodes laterally, forming bends and then loops called meanders.
- Force of water erodes the bank on the outside where water flow has most energy due to less friction.
On inside of the bend, flow is slower, material is deposited, more friction. - Over time the horseshoe becomes tighter, until the ends become very close together.
- As the river breaks through, e.g. during flood when there is higher discharge + more energy, the ends join together.
- The cut-off loop is called an oxbow lake.
Outline Deltas + 3 types with examples.
Deltas = at mouth of large rivers - formed when river deposits material faster than the sea can remove it.
Arcuate/fan-shaped - land arches out into sea and river splits many times. E.G. Niger Delta
Cuspate - the land juts out arrow-like into the sea. E.G. Ebro Delta
Bird’s foot - river splits, each part juts out into the sea, rather like a bird’s foot. E.G Mississippi Delta
Outline V-Shaped Valley Formation in 3 steps.
- River has the greatest gravitational potential energy = greatest potential to erode vertically.
- High discharge = transports large bedload by traction, eroding river bed and valley by corrasion, deepening it.
- Not much lateral erosion = so the channel and valley remains narrow.
Outline what Floodplains are in 3 bullet points.
- The large, flat area of land that a river floods onto when it’s experiencing high discharge.
- During flood - efficiency decreases as friction increases, reducing velocity = deposition = alluvium.
- The alluvium is very fertile so floodplains are often used as farmland.
