Water Lecture 2- How Water Structures the British Landscape. Flashcards
Is there an East-West divide in rainfall?
Yes
How much rainfall does Durham have to Keswick?
Durham - 676 mm/yr
Keswick- 1575 mm/yr
What does evapotranspiration depend on?
Evaporation (local climate setting) - exposure and ventilation, albedo, seasonality
Transpiration (plant physiology) - stomatal cover, seasonal growth, growth stage, canopy health
Interception (plant architecture) - vegetation height, canopy depth, leaf area and shape, crop spacing
What is potential ET?
Et with unlimited water supply
What is actual et?
Amount of Et that actually takes place - limited by water availability
What is a mass balance equation involving rainfall?
Precipitation - evapotranspiration = effective rainfall
Who is thought of as the father of modern hydrology?
Robert Horton
What is the Hortonian or Infiltration-Excess overland flow equation?
Rate of overland flow production = rainfall intensity - infiltration rate
Discuss saturation overland flow.
During prolonged rainfall, you can still get overland flow, even if i is never greater than f (Hewlett and Hibbert, 1967)
Water-table rises during a storm to produce saturated areas (also called Dunne OF)
Also some water tables intersect with the hillslope (return flow)
Discuss Darcy’s Law.
Saturated zone!!!
Darcy’s Law
If saturated, the only thing in the soil that can
change is its flow rate or flux
DL says that flux is a function of the pressure
head (or gradient in potential energy) and
a parameter Ks the saturated hydraulic
conductivity
Q = Ks A H
Where Q = discharge, A = cross-sectional area,
and H = pressure head
Q= m3s-1
What is Ks in terms of Darcy’s Law?
Saturated hydraulic conductivity
What is Richards equation?
Unsaturated zone
If unsaturated, then the flux may change but so may the ‘porosity’, so Darcy’s law is
modified to allow for suction
But difficult to solve numerically
What three mechanisms are useful for understanding flow above ground?
- Hortonian overland flow
- saturated flow
- return flow (water tables intersecting with the hillslope)
What two mechanisms are useful for understanding flow below ground?
Darcy’s Law
Richards equation
What are variable source areas (VSAs)?
Runoff locations vary in time and space
Runoff areas can vary within and between
events due to changes in saturation and
infiltration rate
Use a topographic index to predict which areas
are likely to contribute runoff (slope & upstream area)
How can the effects of change be understood?
Paired catchment experiements (E.g. as seen with Severn and Wye -Plynlimon catchment experiments.
What happens to water yield when forest cover is removed?
Water yield increases when forest cover is removed but the amounts vary by forest type.
Name examples of sediment transport on hillslopes.
Creep (short distance and slow)
Splash (short distance but relatively fast)
Diffusion (short distance but quite fast)
Mass movement
Interrill erosions
Rill erosion
What equation is used to estimate changes in hillslope shapes?
Continuity equation
What depends on local slope?
Diffusion
What depends on upslope area?
Advection
What is advection?
Particles moving due to external force
What can we estimate if we can estimate what the transport rate is at a point on a slope?
What the changes in slope form should be through time
E.g. temperature forested landscape (creep, splash and tree throw and so all diffusive type processes and so convex slope) but temperature deforested landscape (splash, water eorion and ploughing so a mix of advective and diffusive processes)
What can show the importance of land use change from 14th century onwards?
Persistence of ridge and furrow
