Worksheet on River and Coast ( Combination of River and Coasttopic)

1 a. Figure 1A is a graph showing surface runoff into a river channel from an urban area and a forested area.

a(i)Describe the differences in the surface runoff into the river channel from the urban and the forested areas. [4]

(ii)Explain why there is a difference in the surface runoff into the river channel. [6]

b. Account for the different characteristics of a river in its upper and lower course. [7]

Suggested Answers

a(i)Describe the differences in the surface runoff into the river channel from the urban and the forested areas. [4]

Urban area
Description of graph
· The graph shows that the surface runoff into river channel for urban areas is much higher than the runoff in forested areas. (1)
· The graph also shows a shorter time taken for the peak shown representing the discharge into the river channel (1) from the urban areas.

Forested area
Description of graph
· The graph shows that less water is discharged into the river channel from forested area(1)
· The graph also shows the rainwater takes a longer time to reach its peak in the river channel(1)


(ii)Explain why there is a difference in the surface runoff into the river channel. [6]

Urban Area

Explanation of graph

· In an urban area, there will be very high surface runoff and little infiltration into the asphalt and concrete surfaces

· Rain which falls immediately gets channelled into drains and from there into the river. (1)

· There is no interception or absorption because of asphalt and concrete ground (1).

· Rapid rise of water in river channel soon after the rain will likely cause floods.

Rural Area

· Less concrete and more natural vegetation to intercept rain resulting in less surface runoff immediately after the rain.(1)

· Percolation of rainwater into the ground which acts like a sponge would mean water will travel underground and fill up the water table before excess water finds its way back into the river channel somewhere further downstream.

This explains why the forested areas have less surface runoff that goes into the river channel which will cause flood.

b. Account for the different characteristics of a river in its upper and lower course. [7]









1 m for each pairing of description

1 m for each pairing of description

Explanation for the shape and other characteristics

Upper course
· In the upper section of the river, the river water is moving very fast because
· the gradient is steep.(1)
· The rocks that the river carries are very potent in eroding the bed of the river because they act as tools to help chisel the sides and bed of the river .
· More vertical erosion takes place resulting in (1)
· a steep-sided V shape valley and gorges and waterfalls

Lower course
· In the lower section of the river, the river valley acquires a wide V shape because

· the river is moving slowly due to loss of gradient, increase in load in channel and consequent loss of energy

· so more lateral erosion occurs resulting in a broad channel and

· deposition of fine river alluvium takes place resulting in formation of floodplains after several episodes of flooding.Max of 4m—any plausible explanation

Figure 1B shows one coastal management strategy.

Identify the coastal management strategy shown in Figure 1B.
Evaluate the effectiveness of several strategies in coastal protection.

Candidates may include the following :

Groynes
· Constructed at right angles to the coast to encourage deposition of materials transported by longshore drift

· Materials are deposited on the side of the groynes facing longshore drift

· However, groynes deprive the coast further down from receiving fresh supply of materials and hence aggravate erosion of the coast on the opposite side of the groyne that does not face the oncoming longshore drift i.e the downdrift side.

· Need to build a series of groynes to protect the entire stretch of the coast

· Short term protection.

Breakwaters
· Waves are made to break offshore at a distance from the coast causing destructive waves to lose energy

· Create a zone of quiet waters between the breakwaters and the coast

· Waves may deposit sediments to create a beach Over time, they serve to extend the coast seawards in the form of a beach.

· Breakwaters only encourage deposition along the part of the coast that is protected.

· The other parts of the coast that is left unprotected will
deprives the coast further down from receiving fresh
supply of materials

· Need to build a series of breakwaters to protect the entire stretch of coast

Seawalls.

· A seawall is usually made of concrete which absorbs the energy of the waves and protects the coast against strong waves.

· Does not guard against backwash, resulting in base of seawalls being eroded away. Seawalls can collapse over time.

· It is costly to build and maintain a seawall.

Soft engineering
· Plant mangroves along shore. Protect the coast against erosion by strong waves and winds. Roots of mangrove bind loose soil

· Prop roots trap sediments and reduce coastal erosion

· Increased sediment buildup may result in shallower coast – affect port activities

· However, coasts with destructive waves do not support mangroves.

· Planting of marran grass along the beach may help to trap sand .

· However all forms of soft engineering would still require human cooperation in the form of limiting human activities in order for nature to take root.

Candidates at each level will show the following characteristics:

Level 1 (0-3m)

May not refer to a measure or be vague in expression
No place reference or very general references to location
No mention of effectiveness, or simple statements only eg. “it worked”, “it was a lot better”

Level 2 (4-6m)

One or more measures considered

Allow assessment of measures
Brief statements of effectiveness, ‘it stopped erosion taking place,’ or ‘erosion occur less often’

Level 3 (7-8m)

Several measures considered in detail. Both hard and soft engineering methods discussed.

Clear statements of judgement such as ‘ high/ low degree of effectiveness ‘