River discharge and hydrographs
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Question
Define river discharge.
Answer
The **volume of water passing a point per second**, measured in cumecs (m³/s).
Question
What is a storm hydrograph?
Answer
A graph showing how a river's **discharge responds to a storm** over time (rainfall bars above, discharge curve below).
Question
Define peak discharge.
Answer
The **highest discharge** the river reaches after a storm.
Question
Define lag time.
Answer
The gap between **peak rainfall** and **peak discharge** — how fast the basin responds.
Question
Rising limb vs falling limb?
Answer
**Rising limb** = the steep climb as run-off reaches the river; **falling (recession) limb** = the gentler fall as it drains.
Question
What is base flow?
Answer
The steady background discharge from **groundwater** between storms.
Question
What makes a basin 'flashy'?
Answer
A **short lag time + high peak** — impermeable, steep, urban, sparse vegetation; water reaches the river fast.
Question
What makes a basin 'subdued'?
Answer
A **long lag time + lower peak** — permeable, gentle, vegetated, rural; water reaches the river slowly.
Question
Why does urbanisation raise discharge?
Answer
Impermeable surfaces stop infiltration and drains speed run-off → higher peak, shorter lag time.
Question
How do discharge and hydraulic radius change downstream?
Answer
Both **increase** — tributaries add water and the larger, smoother channel is more efficient (Bradshaw model).
Question
Two physical factors that shape a hydrograph?
Answer
Geology/permeability and relief/slope (also soil, vegetation, rainfall intensity, basin shape).
Question
What does a top [10] Examine answer need?
Answer
Two+ developed factors (peak + lag), an example, a weighing of their relative importance, and a clear judgement.
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Full study notes for River discharge and hydrographs
Topic 7.1 hub
Drainage basin hydrology and geomorphology
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