Students from Santiago, Chile, were studying how the characteristics of a river change downstream. They wanted to investigate possible changes in velocity (speed of flow) downstream. They decided to test the following hypotheses: Hypothesis 1: Velocity increases downstream. Hypothesis 2: Velocity increases as the hydraulic radius of the river channel increases. Hydraulic radius is a measurement which indicates how much friction there is between the river channel and the flow of the river.

1. (a)(i)The students carried out their fieldwork at five sites along the river. Suggest three factors the students should have considered in choosing their fieldwork sites.[3]
2. (a)(ii)Suggest why it was important that they made all of their measurements on one day.[1]
3. (a)(iii)In preparation for their fieldwork the students visited a local stream to do a trial (pilot) study. Give two advantages of doing a trial (pilot) study.[2]
4. (b)(i)Fig. 8 (Insert) is a student sketch which shows their method of measuring velocity. Describe the method shown.[3]
5. (b)(ii)Another way to measure velocity is by using a flowmeter. Describe how this is done.[3]
6. (b)(iii)The results which the students obtained at the five sampling sites are shown in Table 3 (Insert). Use these results to complete Fig. 9, below, to show how average velocity changes downstream.[2]
7. (b)(iv)What conclusion could the students make about Hypothesis 1: Velocity increases downstream? Support the conclusion with evidence from Fig. 9 and Table 3.[2]
8. (c)(i)In order to calculate the cross-sectional area the students measured the width of the river channel and the depth of the river at points across the channel. What equipment would the students use and how would they make their measurements?[4]
9. (c)(ii)The results of sample measurements made at site 3 are shown in Table 4, below. Table 4 Sample measurements made at site 3 Distance across channel (m) | 0.5 | 1.0 | 1.5 | 2.0 | 2.5 | 3.0 | 3.5 --- | --- | --- | --- | --- | --- | --- | --- Depth of river (m) | 0.15 | 0.21 | 0.29 | 0.26 | 0.24 | 0.20 | 0.19 Calculate the average depth of the sample measurements at this site. Average depth = ..............................................m[1]
10. (c)(iii)The students measured the width of the river at site 4 as 8.2 m. They calculated that the average depth at site 4 was 0.31 m. Using this data calculate the cross-sectional area at site 4 below. Cross-sectional area = width of river (m) × average depth of river (m) Answer ..............................................sq.m.[1]
11. (c)(iv)Next the students measured the wetted perimeter. The wetted perimeter is the part of the channel cross-section which the river touches. Photograph C (Insert) shows a way to measure the wetted perimeter. This method is described in Fig. 10, below, which is part of a student's fieldwork notebook. Fieldwork notebook Measuring the wetted perimeter The tape was placed across the bed of the river, starting and finishing at water level on both banks. To make the method more accurate a student walked along the tape across the river. Suggest two disadvantages of this method in a large river.[2]
12. (d)(i)The students then calculated the hydraulic radius of each site using the following formula: cross-sectional area wetted perimeter The results of their calculations are shown in Table 3 (Insert). Complete the scatter graph, Fig. 11, below, by plotting the data for Site 5.[1]
13. (d)(ii)The students reached the conclusion that Hypothesis 2: Velocity increases as the hydraulic radius of the river channel increases was correct. What evidence from Fig. 11 and Table 3 supports their conclusion?[2]
14. (e)Whilst doing the fieldwork one student noticed how the river valley was different at the five sites. How could the student record these differences during fieldwork?[3]

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