Hydrographs: components & controlling factors
Learn to read a hydrograph — the graph that shows how a river answers a storm. In this AS lesson we define a storm hydrograph and draw it fully labelled, with rainfall bars, a rising limb, the peak discharge, the all-important lag time, the recession limb and baseflow. Then we do the quantitative work examiners love: reading lag time straight off the graph as peak-time minus rainfall-centre time, and reading peak discharge. We compare a 'flashy' hydrograph that floods fast with a 'subdued', flat one, and work out exactly what controls the shape — precipitation type and intensity, temperature, evaporation, transpiration, evapotranspiration and antecedent soil moisture, plus porosity, permeability, slope, vegetation and land-use. Urbanisation around Windhoek and Namibia's flash-flooding ephemeral rivers bring it home.
By the end you should be able to (NSSCAS Geography (AS) 1.5):
- define a hydrograph
- identify and name the components of hydrographs
- describe how climate influences the shape of hydrographs with reference to types of precipitation and intensity, temperature, evaporation, transpiration, evapotranspiration, antecedent soil moisture
- explain how porosity and permeability of soil and rock, slopes, vegetation and land-use affect the shape of the hydrographs
Mr Robert and Mike talk through the whole topic — with the figure and working drawn live.