NYJC Prelim H2 GEO 9751 P2 Answer

NYJC Preliminary Examination 2018 Paper 2 Mark Scheme 1. (a) With reference to Resources 1 and 2, suggest a suitable hypothesis for the group’s investigation. [1] • landuse changes has led to a heightening of flood risk and a reduction to the liveability of the area. • an area with a higher proportion of vegetation cover is less prone to flooding than one with a lower proportion. Point marked (b) What safety precautions should the team take when condu cting the stream investigation? [5] • do a visual check if there are dangerous animals in the river or along the river banks e.g. crocodiles, monitor lizards etc. • determine the best section for maki ng wading measurement s by noting the potential risk such as slippery rocks, deep segments, pot holes, quick sand etc. • always probe the stream bed ahead with a rod when mo ving from bank to bank. Keep your feet spread apart and alignment of legs paralle l to the flow for better stability. • wear a safety jacket when wading and conducting discharge measurements. Tie the tagline securely so that you may pull yourself out, if necessary. • always follow safety precautions when ent ering the stream. If the water is too deep or swift, select another site. Never venture out into the stream alone without another person available to assist you in case of emergency. • determine whether the river stage is rising or falling. Beware of rapid rises in river stage when wading and anticipate and allow fo r changes in flow conditions at the end of the measurement. It is a good idea to select an obj ect (rock, stump, mark along bank, etc.) that is just above water surface and keep watching it to determine if the river stage is rising or falling. • find out if there are dam s at the upper reaches of the stream. Notify dam, reservoir or gate operators before entering stream. Point marked (c) Calculate the mean velocity of the c hannel in Resource 3 and sketch one line graph to represent the cross- sectional velocity of the upstream segment of Stung Chrey Bak Stream. [4] Award 1 mark for the mean velocity of the channel • Mean velocity of the channel – 1.6 m/s For the sketching of line graph, 1 mark awarded for each of the following: • Title

2 Higher 2 Geography / 9751 / 02 • Relative accuracy of the line graph • Appropriate labels for both axes Line graph showing the cross-sectional velocity of the upstream segment of Stung Chrey Bak Stream Point marked (d) The team concluded that some of the data collected may not have been completely reliable and/or accurate. What improvements can be made in the planning and data collection process for this stream investigation? [6] Limitations: • data was done over two days in December during the dry season • only one measurement (at 10am for bot h days) were taken for each stream segment • measuring tape was unweighted. In addition, there were some boulders on the channel bed for the upper segment of the stream Improvements made to planning: • have a contingency plan to come back dur ing the wet season in June/July and if possible during the intermonsoonal mont hs of March and September to do stream measurements so that an average could be obtained across one year (annual Q) apart from noting the peak a nd low flow periods. Alternatively, students can also look for secondary data to find out about the level of discharge during the wet season to reduce the risk of having to collect primary data as discharge levels will be higher. Segments Velocity (m/s)

3 Higher 2 Geography / 9751 / 02 • to obtain more than one measurement per day instead of just at 10am. Afternoon measurements may record a different reading owing to greater surface evaporation or usage by farmers to irrigate their fields. Improvements made to the data collection process: • in improving the measurem ent of the wetted perimeter, it will be better to use a thicker rope so that it is more visible fr om the water surface and being heavier, it can sink to the bottom of the channel bed so that it hugs t he channel bed for a more accurate measurement. • as there are irregularities in the river bed on the upper segment, it will be good to make multiple measurements of the same si te or to move to another site just slightly further upstream or downstream to obtain a more accurate measurement of the cross-section. Level marked Level Marks Descriptors 3 5 – 6 Response shows accurate knowledge in articulating the limitations of the data collected and is able to provide a comprehensive list of suggestions towards how it can be improved during the planning and data collection stages. Response uses resource accurately. Response is clearly focused on the question throughout with a detailed explanation of the reasons. 2 3 – 4 Response shows adequate knowledge in articulating the limitations of the data collected and is able to provide some suggestions towards how it can be improved during the planning and data collection stages. Use of resource may be limited or lack accuracy at times. Response may lack detail and depth or lack a clear focus on the question. 1 1 – 2 Response shows limited knowledge in articulating the limitations of the data collected and is only able to provide limited appropriate suggestions towards how it can be improved during the planning and data collection stages. Little or no use of the resource. Use of resource where present will lack accuracy. Response lacks details and focus on the question. 0 0 No creditworthy response (e) Evaluate the usefulness of the river velocity data shown in Resource 3 in ascertaining the flood risk of Stung Chrey Bak Stream. [9] Indicative Content: Usefulness points could include the fact that the data gives some idea of river response to rainfall event. In general, higher velocity due to an increase in Q would increase the risk of flooding (direct relationship). Discharge level can be obtained by multiplying the mean channel velocity and cross-sectional area data obtained during the fieldwork.

4 Higher 2 Geography / 9751 / 02 However, as the measurements were taken during the dry season, it does not give a full picture of how high discharge can re ach during the wet summer monsoons in June/July. In addition, one should refer to other inform ation that would be useful in ascertaining flood risk. These could include the following: • climatic characteristics – precipitat ion amounts and type will determine input into the channel. Seasonality in c limate such as that of A m or A w may result in seasonal flooding i.e. flood risk increases during the wet monsoons (summer) with the convergence of trade winds at the ITCZ • drainage basin characteristics – size, geology (degree of permeability determines the generation of quick flow which in return increases flood risk), topography, vegetation cover, drainage density and bifu rcation ratio. Determines peak Q and lag time. • obtain secondary records such as the ann ual pattern of discharge levels. Enables the calculation of recurrence interval in order to predict flood frequency and magnitude. Floods with greater frequency will register a s horter RI. Greater care should be paid to floods with longer R.I as they may be low in frequency but when it happens, the magnitude is going to be devastating. • human disturbances within the drainage ba sin. Altered basins tend to lead to higher peak Q and a shorter lag time. Exam ples include channel modifications, deforestation, mining, agricultural practices, animal husbandry A higher response will present evaluati on of usefulness of resource and of knowledge of river velocity measurements. Response could also recognise that there are limitations related to the methods involv ed in the collection of velocity data. The improvised method is definitely less acc