Option A: Freshwater - Part 1: The Drainage Basin

Question 1

5 factors that affect the drainage basin. (G,L,P,L,T)

Answer 1

Geology
Land use
Precipitation
Land relief
Time

Question 2

4 Types of Erosion + 1 describing word.

Answer 2

Hydraulic Action - pressure
Corrasion - sandpaper
Corrosion - dissolving
Attrition - collision

Question 3

4 Types of Transportation + 1 describing word.

Deposition - 1 describing word.

Answer 3

Traction - rolling 
Saltation - bouncing
Suspension - floating
Solution - dissolving
Deposition - dropping

Question 4

River Velocity: channel shape, bed roughness and slope.

Answer 4

Higher hydraulic radius = quicker river flow
Higher roughness = slower river flow
Steeper slope = quicker river flow

Question 5

8 River Landform Features (V, W, F, L, D, M, O, P)

Answer 5

V-Shaped Valleys
Waterfalls
Floodplains
Levees
Deltas
Meanders
Oxbow lakes
Point bars

Question 6

7 Factors affecting flood risk and defintions (S, D, C, S, V, H)

Answer 6

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.

Question 7

How Hydrographs Predict Floods.

Peak discharge, magnitude, falling limb, lag time

Answer 7

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.

Question 8

Flood Hydrograph definition and 8 components

Answer 8

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.

Question 9

River discharge definition and equation

Answer 9

The volume of water that passes through a stream’s cross section in a given period of time.
Discharge = velocity x cross sectional area

Question 10

DB Examples of Inputs

Answer 10

Precipitation: rain, snow, etc.

Question 11

DB Examples of Outputs

Answer 11

Evaporation and transpiration

Question 12

DB Examples of Flows

Answer 12

Infiltration, through-flow, overland flow and base flow.

Question 13

DB Examples of Stores

Answer 13

Vegetation, soil, aquifers, the hydrosphere and cryosphere

Question 14

Drainage Basin Definition. Open or closed sysstem?

Answer 14

Open system as there are inputs and outputs. All the area that gets drained by a river and its tributaries divided by a watershed.

Question 15

What is the hydrological cycle? Closed or open system?

Answer 15

Closed system as there are no inputs or outputs. The cycle of water between the biosphere, atmosphere, lithosphere and hydrosphere.

Question 16

Stores (4) of the Hydrological cycle.

Answer 16

Clouds, sea, lakes, vegetation

Question 17

Flows (4) of the Hydrological cycle.

Answer 17

Evapo-transpiration, precipitation, surface run off and groundwater flow.

Question 18

Describe the 2 types of flow in a river (L and T)

Answer 18

Laminar: straight horizontal
Turbulent: helicoidal flow of horizontal eddies and verticle eddies

Question 19

Outline waterfall formation in 6 steps.

Answer 19

1. Softer, less resistant rock is easily eroded.
2. Harder rock on top (cap rock) is undercut by the erosion of softer rock.
3. Eventually, the overhang collapses due to lack of support.
4. As water falls over the tip, more of the rock is eroded by Hydraulic Action and Corrasion.
5. A plunge pool is formed by continued erosion.
6. Over time, the waterfall retreats upstream, leaving a steep-sided gorge.

Question 20

Outline levees formation in 3 steps.

Answer 20

1. Before a flood, river surrounded by floodplain.
2. 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.
3. After many floods, natural levees build up sediment.

Question 21

Outline meander and oxbow lake formation in 5 steps.

Answer 21

1. River erodes laterally, forming bends and then loops called meanders.
2. 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.
3. Over time the horseshoe becomes tighter, until the ends become very close together.
4. As the river breaks through, e.g. during flood when there is higher discharge + more energy, the ends join together.
5. The cut-off loop is called an oxbow lake.

Question 22

Outline Deltas + 3 types with examples.

Answer 22

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

Question 23

Outline V-Shaped Valley Formation in 3 steps.

Answer 23

1. River has the greatest gravitational potential energy = greatest potential to erode vertically.
2. High discharge = transports large bedload by traction, eroding river bed and valley by corrasion, deepening it.
3. Not much lateral erosion = so the channel and valley remains narrow.

Question 24

Outline what Floodplains are in 3 bullet points.

Answer 24

1. The large, flat area of land that a river floods onto when it’s experiencing high discharge.
2. During flood - efficiency decreases as friction increases, reducing velocity = deposition = alluvium.
3. The alluvium is very fertile so floodplains are often used as farmland.