Drainage basin and river vocabulary
The hydrological cycle moves water between sea, air and land via evaporation, precipitation, infiltration, run-off and river flow. A drainage basin is the area drained by a river and its tributaries, bounded by the watershed (the ridge between basins). Water enters at the source and leaves at the mouth. A tributary JOINS the main river at a confluence; a distributary BRANCHES AWAY near a delta. Rivers flow from source to mouth.
Erosion, transport and deposition processes
A river erodes, transports and deposits. Erosion: hydraulic action, abrasion (load scrapes bed/banks), attrition (particles knock together, rounding), solution (rock dissolved). Transport of the load: traction (boulders rolled), saltation (stones bounced), suspension (silt/clay), solution (dissolved). Deposition drops the load when the river loses energy (shallower water, gentler gradient, or the sea). Erosion dominates the upper course, deposition the lower.
2010 Pakistan (Indus) floods
The 2010 Indus River floods (Pakistan) are a reusable flood case study. Physical causes: heavy prolonged monsoon rain, already-saturated ground, rapid run-off from steep relief. Human causes: deforestation speeding run-off; weak embankments overtopped or breached. Impacts: ~2,000 killed, ~20 million affected, a fifth of Pakistan underwater, losses near 10 billion US dollars. Management: mass evacuation, the Tarbela and Mangla Dams regulating flow, then rebuilt defences.
Drawn from real examiner reports.
Erosion ≠ weathering
Erosion wears away AND removes material using a moving agent -- the river (hydraulic action, abrasion, attrition, solution). Weathering breaks rock down in situ, with no transport. Candidates often call any breakdown "erosion". Use erosion for the river wearing and carrying material; weathering for in-place breakdown of valley-side rock.
Tributary ≠ distributary; flow goes downhill
These terms are persistently mixed up. A tributary JOINS the main river at a confluence; a distributary BRANCHES AWAY near a delta. They are near-opposites, often reversed. A deeper error is believing rivers flow from coast inland -- they always flow downhill to the mouth. On a diagram, arrows point INTO the channel for tributaries, OUT for distributaries.
Digest (## 2.2): tributary/distributary/confluence are persistently confused, and candidates believe tributaries flow AWAY from the main river or that rivers flow from coast inland (s23 P21 Q1(d); w22 P22 Q1(d)).
V-shaped river valley ≠ U-shaped glacial
A sharp definition trap. A U-shaped valley is a GLACIAL landform -- NOT made by a river. A lower-course valley is wide and flat-floored (not a "U"), from lateral erosion and deposition. An upper-course valley IS a narrow, steep-sided V-shape, from vertical erosion. Examiners also flag describing the channel when asked about the valley (the wider landform).
Digest (## 2.2): the lower-course valley is frequently mislabelled U-shaped (a glacial feature), and candidates often describe the river channel rather than the valley when a valley cross-section is asked (w23 P12 Q3(a)(iii)).
Ox-bow lakes: link process to landform
An ox-bow lake needs two LINKED halves, but most give one. The process: the current is fastest outside (eroding the outer bank) and slowest inside (depositing a slip-off slope), narrowing the neck. The landform change: in a flood the river cuts through the neck, abandoning the loop; deposition then seals its ends into a crescent-shaped ox-bow lake. Link both.
Digest (## 2.2): oxbow-lake/meander explanations are commonly under-detailed -- answers address either the erosion/deposition process OR the resulting landform change, rarely linking both (w23 P12 Q3(c)).
Hydrograph: use the precise vocabulary
A storm (flood) hydrograph plots discharge against time after rain; vague "up and down" comments lose marks. Use precise terms: peak discharge (highest reached); lag time (gap between peak rainfall and peak discharge -- a SHORT lag means fast arrival); rising and falling limbs; base flow (between storms). Link a short lag or high peak to basin conditions.
Digest (## 2.2): hydrograph vocabulary (lag time, rising/falling limb, peak discharge) is weak even when the axes are correctly identified -- vague "more/less discharge" comments do not earn credit (s23 P21 Q4(b)).
River-velocity method under-specified
Describing how to measure river velocity, answers are under-specified -- "float it and time it" -- and lose marks. A full method states the float choice (an orange or cork, not blown by wind), a measured distance between marked start/finish points, and the sequence: distance, THEN time. The formula is velocity = distance / time, not time / distance. Give units (m/s).
Digest (## 2.2): river-velocity fieldwork descriptions are under-specified (float choice, measured distance, start/finish points, distance-then-time), and the velocity formula is sometimes inverted as time / distance (w23 P41 Q2d(i); s22 P42 Q1b(ii)).
Tributaries flow INTO the main river
A testable wrong belief: that tributaries flow AWAY from the main river, or a river flows from the sea inland. Water moves downhill from the source (high ground), through tributaries flowing INTO the main river, to the mouth. A channel flowing AWAY is a distributary (near a delta), not a tributary. Check flow runs high-to-low.
Digest (## 2.2): candidates believe tributaries flow AWAY from the main river, or that rivers flow from coast inland (s23 P21 Q1(d); w22 P22 Q1(d)).
Level 3 on the 7-mark flood case study
For the named-river flood 7-marker: name a real river (Indus, Pakistan, 2010) -- "a river in Asia" stays Level 1. Use figures (deaths, people affected, area flooded), not "a lot of damage". Cover physical and human causes, impacts and management, linking each point.
Measure along curves, then convert scale
Measuring a river's course, don't draw a straight ruler line -- a river curves, so its length is longer. Follow the channel with string, then apply the scale. Examiners flag straight-line measurement, and scale slips of a factor of ten (not converting cm to km).
Describe vs explain; quote data precisely
Watch the command word: "describe" means what a landform looks like, "explain" means the process that formed it -- the wrong one wastes the question. Quote data precisely: examiners mark down vague quantifiers ("about", "nearly", "a lot") in favour of exact figures with units.
Full notes, flashcards, Q&A and the topic quiz for every premium subject.
Premium plans are US$8.99/month or US$49.99/year — first month free.
Studying with a parent's blessing? Show them this.
