past paper questions

Question 1

define stemflow

Answer 1

Any precipitation that has been intercepted by vegetation (1) then passes down the branches and stems of vegetation (1).

Question 2

define overland flow

Answer 2

Water from precipitation that runs over the ground surface (1) as it is unable to be absorbed into the ground (1).

Question 3

Briefly explain what is meant by a water table

Answer 3

• defines the top of the saturated zone / layer (1).
• Subsurface feature (1)
• in permeable rock (1).
• May rise or fall depending on inputs and outputs of the hydrological cycle (1).

Question 4

Explain how the shape of a storm hydrograph is influenced by precipitation type and intensity

Answer 4

• intense: more overland flow: steep rising limb and higher peak flow
• low intensity: infiltration, percolation: higher lag time and lower peak flow
• type: snow: melt delay: how quickly it melts: gradual: broader hydrograph

Question 5

Explain why catchment flows change after urbanisation

Answer 5

• Decrease in vegetation means less evapotranspiration, and more water is stored on the ground
• Less interception leads to more water reaching the surface and possibly more overland flow.
• Reduction in roots, as a result of less vegetation, leads to decrease in infiltration as fewer pathways for water to go, less time to reach saturation
• Impermeable surfaces, a result of urbanisation, reduces infiltration, increasing overland flow and directing flows of water through artificial drainage, percolation, through-flow and base flow reduced.
• Human impacts on flows – abstraction of groundwater reducing groundwater flow, dam building/drainage systems, associated with urbanisation

Question 6

define cavitation

Answer 6

explosion of air bubbles (1) trapped in river banks by water action (1).

Question 7

define suspension

Answer 7

the transport of fine particles/sediment (1) within/on the
water/not in contact with bed or banks (1).

Question 8

Describe the formation of a point bar within a river

Answer 8

• Related to deposition in meandering river channels.
• Eroded material from the outside bend is carried across the channel and deposited on the inside bend.
• Where velocity is slower, thus leading to build up of sediment into a point bar or slip off slope.

Question 9

Explain how a river flood can impact people

Answer 9

The impact of a river flood will be dependent on the size and location as well as the management of the flood event. There are a variety of impacts, and the answers may discuss economic and social impacts as well as refer to case study examples. Short term and long term impacts may be contrasted. Emphasis is on people rather than the environment in general. Impacts can also be beneficial, e.g. cultivation on flood plains.

Question 10

‘The intensity of precipitation is the most significant influence on the shape of a storm hydrograph.’

Answer 10

consider a range of factors which influence a storm
hydrograph, including drainage basin characteristics, type of precipitation, soil type, and land use. Candidates should evaluate the significance of the intensity of precipitation against other factors. Emphasis should be on intensity but amount will be a valid discussion point. Characteristics of the storm hydrograph (lag, peak discharge, rising and falling limbs) need description and explanation.

Question 11

Briefly explain the formation of the features of a delta

Answer 11

Comments relating to the formation of the features can include:
* the volume of the sediment from the river – including the proportion of the bedload to suspended load (1)
* the different densities of the river and sea water (1)
* the relatively little strength of the tide and wave action and longshore drift resulting in a more elongated shape (1)
* flocculation of clays (1)
* the stability of the coastal zone, and factors which affect this (1)
* the high bedload resulting in braiding of the distributary channels (1)

Question 12

suggest how the delta may change shape over time

Answer 12

• There are three ways that the delta may change shape: internal changes, reduction in size or increase in extent
• changes are related to changes in sediment supply, discharge of the main river and strength of marine processes (longshore drift, strength of the waves etc.)
• Distance from the shoreline or by lateral movement
• the change of the beds building out over time (1) – especially as there is a lot of sediment shown within the photograph
• following deposition, the number of distributaries may change (1) and new channels may be built (1)
• reduction in size by increased marine erosion (1)
• avulsion may occur between distributaries (1)

Question 13

Describe how drainage density is measured

Answer 13

Total length of all the streams (1) and area of drainage basin (1) , Drainage density is total length divided by area of the basin (1)

Question 14

Briefly explain how velocity affects erosion in a river

Answer 14

• the Hjülstrom curve (HC)
• higher velocities mean that the rate of erosion increases
• The HC shows that for particles which are the size of sand and above, the higher the velocity, the more likely it is that larger particles are being entrained and eroded
• cohesive nature of clay

Question 15

Explain how catchment flows and stores are affected by urbanisation.

Answer 15

• Reference to throughflow, infiltration, percolation, surface storage
• demand for water which means flows and stores are affected beyond the urban area.
• change of land use (e.g. deforestation) as the urban area increases

Question 16

‘River flooding impacts people more than it impacts the environment.’
With the aid of examples, how far do you agree?

Answer 16

• go through the different impacts (economic / social / environmental) and attempt to quantify them in order for a comparison to be made
• emphasis will be on negative impacts, the recognition that some environmental impacts could be positive (addition of nutrients, alluvium, creation of diverse habitats such as wetlands, marshes) might indicate a higher level response

Question 17

features of a braided channel and how they form

Answer 17

features:
* wide channel
* multiple channels
* unvegetated and vegetated channel bars
* slight meander
* channel opening out and becoming wider
formation:
* High river loads
* Fluctuating discharge and velocity
* The erodible nature of river banks, enabling the channel to widen

Question 18

throughflow

Answer 18

downslope movement of water (1) within the soil towards the river channel (1)

Question 19

soil water

Answer 19

water present in the soil (1) after infiltration (1)

Question 20

Briefly explain how drainage density affects the shape of a storm hydrograph

Answer 20

A high drainage density will lead to a more flashy hydrograph because:
* the distance water has to flow (either as overland flow or throughflow) to reach a river channel is reduced
* there is less chance that water flow will be impeded or evaporated if flowing on the surface.

Question 21

Explain the effects of land use change on catchment flows and catchment stores

Answer 21

• Deforestation and urbanisation: increased surface runoff
• reduced infiltration and percolation for urbanisation and reduced interception and reduced evapotranspiration for deforestation
• Water abstraction, building of dams and increased channel flow because of hard engineering
• Change in agricultural land use

Question 22

With the aid of examples, assess the extent to which river floods can be prevented.

Answer 22

• various hard and soft engineering procedures to prevent river flooding
• comprehensive evaluation of the effectiveness of these techniques
• difficult to prevent floods but that their effects can be minimised