Students in Portugal went to six sites along a local river to do a fieldwork investigation on changes in the river channel downstream. The river which they studied flows 13km from the Sintra Hills to the Atlantic Ocean. The students investigated the following hypotheses: Hypothesis 1: The area of the cross section of the river channel increases downstream. Hypothesis 2: Average velocity of river flow increases downstream.

1. (a)From the alternatives below choose the correct terms to complete the following sentences. confluence mouth source tributary valley • A river begins at its ................................................................................................................. • A river enters the sea at its .....................................................................................................[2]
2. (b)(i)The students selected six sites along the river approximately 2 kilometres apart to do their fieldwork. In pairs they measured the width of the river channel at each site using a tape measure. Suggest two things the students could have done to make sure that their results were reliable. 1 ................................................................................................................................................... 2 ...................................................................................................................................................[2]
3. (b)(ii)The results of their measurements at each site are shown in Table 4 (Insert). Plot the result for site 6 on Fig. 7 below, which shows how the width of the river channel varies downstream. [Figure 7][1]
4. (b)(iii)Next they measured the depth of the river. In the space below draw an annotated (labelled) diagram to explain how they would do this.[4]
5. (b)(iv)At each site the students measured the depth at five points across the channel. The results of their measurements at each site are shown in Table 4 (Insert). The students drew cross sections of the channel at each site. These are shown in Fig. 8 opposite. Use the information in Table 4 to complete the cross section and shade in the river channel at site 4. [Figure 8][3]
6. (b)(v)The method used to calculate the area of the cross section at each site is shown below. Insert the correct figures from Table 4 in the calculation for site 1 below. Calculation of the area of the cross section at site 1 Area of the cross section = width of river (metres) × average depth of river (metres) = = 0.65 sq metres[1]
7. (b)(vi)The results of the students' calculations of the area of the cross sections are shown in Table 5 (Insert). To what extent do the results support Hypothesis 1: The area of the cross section of the river channel increases downstream? Circle your decision below and support your decision with evidence from Table 5 and Fig. 8. completely partially not at all[3]
8. (c)(i)To investigate Hypothesis 2: Average velocity of river flow increases downstream, the students measured the velocity at each site using the equipment shown in Fig. 9 (Insert). Describe how they measured velocity.[4]
9. (c)(ii)The students calculated the average velocity of flow at each site. Their results are shown in Table 5 (Insert). Plot the result for site 6 on Fig. 10 below. [Figure 10][1]
10. (c)(iii)The students' conclusion was that their results did not support Hypothesis 2: Average velocity of flow increases downstream. Use evidence from Table 5 and Fig. 10 to explain why they reached this conclusion.[3]
11. (d)(i)One student wondered if there was any relationship (correlation) between the area of the river channel cross section and average velocity at the six sites. These results are shown in Table 5 (Insert). The student plotted these results on a scatter graph, Fig. 11 below. Use the data in Table 5 to plot the results of site 6 on Fig. 11 below. [Figure 11][1]
12. (d)(ii)The student decided that there was a partial relationship (correlation) between the area of the river channel cross section and average velocity. Support this decision with evidence from Table 5 and Fig. 11.[3]
13. (d)(iii)Explain why the area of the river channel cross section may affect average velocity.[2]

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