RVHS Prelim_H2_GEO_P1_Soln

1 RVHS H2 GEOGRAPHY PAPER 1 PRELIMS 2018 1 (a) Explain how channel morphology changes downstream in a humid tropical drainage basin. [12] Indicative Content: A humid tropical drainage basin is characterised by abundant total annual precipitation, yet there might be seasonality of rainfall in the Am climate or negligible seasonality in Af climates. In any case, this signals the conditions enabling the work of perpetual streams due to a sufficiently shallow water table that constantly feeds streams through baseflow. In such a context, Bradshaw’s model and Schumm’s model would be suitable for explaining how channel morphology changes downstream in tande m with parallel changes to discharge and velocity. To account for these changes, it is helpful to analyse the interactions between channel form, channel energy and the contextual hydrological environment at different parts of the river’s long profile. (b) Using examples, discuss the factors contributing to the variation in channel patterns in a tropical drainage basin. [20] Indicative Content: Some of the largest drainage basins in the worl d occur in the tropical latitudes: the Mekong, Amazon and Nile river basins are obvious examples. Yet, they span a range of climatic, altitudinal and geological regions and hence display a vari ety of channel forms and patterns (even within different parts of the drainage basin. This essay discusses the interplay between these factors and contends that in view of a longer time scale in geological time, the current channel patterns and forms cannot be attributed to a dominant factor alone. Climate as a factor is central for the prima ry role of rainfall amount and seasonality in determining river regime. Most saliently hum id hydrology differs significantly from arid hydrology and both are characterized by distinct channel pattern and forms. Topographical factors like altitude and slope changes, as well as geological factors like jointing and rock type should be discussed through exampl es like braided channels and karst hydrology that demonstrate the influence of these factors together with tropical climates. Attempts to make synoptic links to human actions like deforestation and engineering are possible but should always relate clearly to the hydrological concepts directly altering channel pattern. 2 (a) Explain the role of water in the development of soils in the semi-arid and arid tropics. [12] Indicative Content: Soil development begins with the physical and chemical weathering of rocks and regolith exposed to the atmosphere and to the action of water percolating down from the earth surface. Even though the semi-arid and arid tropics experiences general moisture deficit, there can still be the occurrence of rainfall when the ITCZ is overhead. Processes of calcification and salinization should be discussed to explain the role water plays in the development of soils in the semi-arid and ar