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Water and Carbon Cycles

Catchment factors influencing storm hydrographs

  • 2 things to know
  • Component 2

Overview

Drainage density, porosity and permeability and rock that is porous but not very permeable.

What you need to know

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Key term

How does catchment size affect lag time?

Key term

How does catchment shape affect the hydrograph?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    How does catchment size affect lag time?

    Model answer

    A large catchment gives water further to travel before reaching the gauging point. Lag time lengthens and the peak is spread out and lowered.

  2. 2

    How does catchment shape affect the hydrograph?

    Model answer

    A circular catchment delivers water from all directions at once, giving a short lag and a high peak. An elongated catchment delivers water in sequence, giving a longer lag and a lower peak.

  3. 3

    Define drainage density.

    Model answer

    Drainage density is the total length of stream channel divided by the area of the catchment. Units are kilometres of channel per square kilometre.

  4. 4

    How does high drainage density affect the hydrograph?

    Model answer

    A dense channel network moves water into channels quickly rather than over slopes. Lag time shortens and peak discharge rises.

  5. 5

    How does rock permeability influence the hydrograph?

    Model answer

    Permeable rock such as chalk absorbs water and releases it slowly as baseflow. Impermeable rock forces water to travel overland, producing a flashy hydrograph.

  6. 6

    Distinguish between porosity and permeability.

    Model answer

    Porosity is the proportion of a rock's volume made up of pore space. Permeability is the ease with which water can actually pass through the rock.

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