O-LevelGeographyThe natural environment2217/22 · Oct/Nov 2018 · Q830 Marks

Students were planning fieldwork on a local river. They decided to investigate possible differences between a section where the river meandered and another section where the channel was straight.

(a)(i)First they visited the river and identified two sections about 100 m apart which were suitable for their fieldwork. These are shown in Fig. 8.1 below. [Figure 8.1] On Fig. 8.1 write the words EROSION and DEPOSITION in the two boxes to show where these processes occur.[1]
(a)(ii)State the feature which may be formed if a meander is cut off from the river by erosion and deposition.[1]
(b)(i)The students investigated the following hypotheses: Hypothesis 1: The pattern of velocity (speed of flow) across the river is different in a meander and a straight section. Hypothesis 2: Pebbles on the river bed (bedload) are larger where velocity is faster. To investigate Hypothesis 1 the students measured velocity using a flowmeter, as shown in Figs. 8.2 and 8.3 (Insert). Describe how the students used a flowmeter to measure velocity.[2]
(b)(ii)Give one advantage and one disadvantage of this method. Advantage Disadvantage[2]
(c)(i)The students measured velocity every 0.5m across a river meander and straight section. Their results are shown in Table 8.1 (Insert). Plot the result at the point 2.5 m from the bank on the straight section in Fig. 8.4 below. Use the key provided.[1]
(c)(ii)The students made the conclusion that Hypothesis 1: The pattern of velocity (speed of flow) across the river is different in a meander and a straight section is correct. Support this conclusion with evidence from Fig. 8.4 and Table 8.1.[3]
(c)(iii)One student compared the group's results with some previous fieldwork results collected at the same meander. Students who had done the earlier fieldwork used a different method to calculate the average velocity. They measured the average time taken by floats to move 10m along the river. The results of the previous fieldwork are shown in Fig. 8.5 below. Identify two main differences between the results for the meander shown in Figs. 8.4 and 8.5.[2]
(c)(iv)Suggest two reasons why the results from the two fieldwork investigations at the meander are different.[2]
(d)(i)To investigate Hypothesis 2: Pebbles on the river bed (bedload) are larger where velocity is faster, the students measured the size of five pebbles every 0.5m across the river channel on both the meander and straight section. Suggest a method the students could have used to measure each pebble.[2]
(d)(ii)The results of the students' measurements on both sections of the river are shown in Table 8.1 (Insert). To see if there was a relationship between velocity and pebble size the students plotted the results on scatter graphs shown in Fig. 8.6 below. Plot the results at 2.0m and 4.0m across the meander in Fig. 8.6.[2]
(d)(iii)Do the results shown in Fig. 8.6 and Table 8.1 support Hypothesis 2: Pebbles on the river bed (bedload) are larger where velocity is faster? Use data to support your answer. Refer to both the meander and the straight section.[4]
(e)(i)Having completed their fieldwork the students looked at the Bradshaw model, which states that bedload becomes smaller downstream. To test this model they measured the size of five pebbles every 0.5m across the river channel at another straight section of the river downstream. The results of the measurements at both sections are shown in Table 8.2 (Insert). The students plotted their results on histograms shown in Fig. 8.7 below. Use the results in Table 8.2 to complete the histogram for the section further downstream in Fig. 8.7.[2]
(e)(ii)Describe two pieces of evidence from Table 8.2 and Fig. 8.7 which show that bedload becomes smaller downstream.[2]
(e)(iii)Explain why bedload becomes smaller downstream.[2]
(f)Identify the two statements below which describe how river characteristics change downstream. Tick (✔) your choices. average velocity decreases downstream channel depth increases downstream channel width decreases downstream discharge increases downstream gradient increases downstream[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

[1] 8(a)(i) NOTE: both need to be correct for ONE mark
[1] 8(a)(i) Erosion in top box
[1] 8(a)(i) Deposition in bottom box
[1] 8(a)(ii) Oxbow lake
[2] 8(b)(i) Examples: Hold pole of flowmeter at top (1)
[2] 8(b)(i) Put propeller / flowmeter below surface of water / into the river / in the water / submerged (1)
[2] 8(b)(i) Propeller must be facing upstream (1)
[2] 8(b)(i) Allow propeller to rotate / turn (1)
[2] 8(b)(i) Read number of turns in fixed period / 1 minute (1)
[2] 8(b)(i) Read digital screen / velocity display (1)
[2] 8(b)(ii) Advantage - accurate / reliable reading / instant reading / quick / no calculating / can save readings (1)
[2] 8(b)(ii) Disadvantage – inaccurate in low flow conditions / battery may go flat / may break / cannot use in deep water / obstacles get in way (1)
[1] 8(c)(i) Plotting of correct criss-cross shading for 0.53 at 2.5 m on cross section
[3] 8(c)(ii) NOTE: Candidates are told decision re hypothesis is correct. So no need to credit any decision they give.
[3] 8(c)(ii) Evidence: Velocity is highest near to outside bend / by concave bank / at 4 m on meander and highest in centre on straight section / at 2.5 m (1)
[3] 8(c)(ii) Stats: 0.63 / more than 0.6 m close to outside bend on meander but 0.53/0.51-0.6 / below 0.6 m near centre of straight section (1)
[3] 8(c)(ii) Velocity increases more across the meander than across straight section (1)
[3] 8(c)(ii) Stats: Range 0.28 to 0.58 /0.3 m across meander but only 0.3 to 0.37/0.07 m across straight section (1)
[3] 8(c)(ii) Velocity increases across meander but straight section rises and falls around the middle (1)
[3] 8(c)(ii) Stats: Range 0.28 to 0.58 /0.3 across meander but rises 0.3 to 0.53 and falls to 0.37 m/s in straight section (1)
[3] 8(c)(ii) Credit 1 mark MAX/RESERVE for paired data to compare velocity on meander & straight section
[2] 8(c)(iii) Examples: TWO differences required; can be statement or stats.
[2] 8(c)(iii) NOTE Fig 2.4 = now; Fig 2.5 = previous. Accept use of Figs.
[2] 8(c)(iii) Do NOT credit comparing individual sites/distances as stats.
[2] 8(c)(iii) Higher velocity recorded in students' results now OR more than 0.6/0.63 now compared to 0.41–0.5 range before (1)
[2] 8(c)(iii) Greater range of velocity in students' results now OR 0.21–0.3/0.28 to more than 0.6/0.63 compared to 0.21–0.3 to 0.41–0.5 before (1)
[2] 8(c)(iv) Examples: TWO separate suggestions needed
[2] 8(c)(iv) More measurements in students fieldwork / 9 now compared to 5 before / different intervals used (1)
[2] 8(c)(iv) More rainfall before fieldwork now / less rainfall or drier conditions before (1)
[2] 8(c)(iv) Higher discharge before fieldwork now / lower discharge before(1)
[2] 8(c)(iv) Measuring errors (1)
[2] 8(c)(iv) Floats may become stuck before (1)
[2] 8(c)(iv) Different instruments / flowmeter now instead of float / different methods (1)
[2] 8(d)(i) Examples: No mark for just stating callipers / pebbleometer.
[2] 8(d)(i) Put pebble into callipers or pebbleometer / adjust callipers to hold pebble (1)
[2] 8(d)(i) Measured length on scale / measure long axis with ruler or tape measure (1)
[2] 8(d)(ii) Plot crosses at 2 m and 4 m as follows.
[2] 8(d)(ii) 2 m: 0.42/12 (1)
[2] 8(d)(ii) 4 m: 0.63/17 (1)
[4] 8(d)(iii) Meander: Hypothesis is TRUE / results support hypothesis – 1 mark reserve
[4] 8(d)(iii) Credit 1 mark for supporting data – need 2 sets of velocity and pebble length measurements
[4] 8(d)(iii) e.g. at 0.28 m / s size is 4 cm but at 0.58 m / s size is 15 cm. (1)
[4] 8(d)(iii) Straight section: Hypothesis is NOT TRUE/FALSE results do not support hypothesis – 1 mark reserve
[4] 8(d)(iii) Credit 1 mark for supporting data – need 2 sets of velocity and pebble length measurements
[4] 8(d)(iii) e.g. at 0.30 m / s size is 8 cm but at 0.40 m/s size is 5 cm (1)
[4] 8(d)(iii) If say FALSE for meander mark X HA = 0 and do not mark evidence.
[4] 8(d)(iii) If say TRUE for straight section mark X HA = 0 and do not mark evidence.
[4] 8(d)(iii) If say PARTLY TRUE for either mark X HA =0 and do not mark evidence.
[2] 8(e)(i) Completion of histogram; credit plots ignore shading.
[2] 8(e)(i) 21 at 6-10 cm (1)
[2] 8(e)(i) 8 at 11-15 cm (1)
[2] 8(e)(ii) Examples: More pebbles between 1–5 cm downstream OR 9 downstream at 1–5 cm but 4 upstream / 5 more downstream (1)
[2] 8(e)(ii) More pebbles between 6–10 cm downstream OR 21 at 6–10 cm downstream but 14 upstream / 7 more downstream(1)
[2] 8(e)(ii) Less pebbles between 11–15 cm downstream OR 8 downstream at 11-15 cm but 17 upstream / 9 less downstream (1)
[2] 8(e)(ii) Less pebbles between 16-20 cm downstream OR 2 downstream at 16-20 cm but 5 upstream / 3 less downstream (1)
[2] 8(e)(iii) Examples: terms must be defined correctly for credit. Eroded by water for longer time (1)
[2] 8(e)(iii) Corrosion or solution – dissolves pebbles (1)
[2] 8(e)(iii) Attrition - pebbles crash into each other (1)
[2] 8(e)(iii) Abrasion or corrasion – pebbles rub against bed and banks (1)
[2] 8(e)(iii) Pebbles are moved further downstream because they are lighter to transport / heavier pebbles were deposited upstream (1)
[2] 8(f) channel depth increases downstream
[2] 8(f) discharge increases downstream
[2] 8(f) Rows 2 and 4 are correct.