Introduction to the TOPMODEL

1
Introduction to the TOPMODEL

• Venkatesh Merwade

2
Brief History

• Development Initiated by Prof. Mike Kirkby,
  School of Geography, University of Leeds in 1974.
• First version programmed by Keith Beven in
  Fortran IV (Who is currently the head of group
  working on the model at Lancaster University)
• Since 1994 many versions of TOPMODEL have been
  developed at Leeds, Lancaster and some other
  places.
• Not intended to be a traditional model package
  but is more a collection of concepts that can be
  used where appropriate.
• The present version will be best suited to
  catchments with shallow soils and moderate
  topography which do not suffer from excessively
  dry periods.

3
Description

• . the problem is what to route and how to
  route. (Cordova and Rodriguez-Iturbe, 1983)
•  
• Two components 
• Water Balance at the soil surface (run off
  prediction )
• Routing (transfer of runoff to the basin outlet)

4
Description Contd.

• The water balance at the soil level is the
  component which characterizes the model and
  constitutes the most important part.
• The transfer component is divided into two
  phases, the first representing transfer along the
  slopes towards the drainage network and the
  second representing transfer along the drainage
  network to the basin outlet.
• In the TOPMODEL, by its very nature
  (distributed!), both the surface component and
  the flow in the soil are made available directly
  along the drainage network at each time interval.

5
Parameters

• Five parameters
• M the parameter of the exponential
  transmissivity function or recession curve (m).
• Ln (To) the natural logarithm of the effective
  transmissivity of the soil when just saturated. A
  homogenous soil throughout the catchment is
  assumed (m2/h).
• SRmax the soil profile storage available for
  transpiration, i.e. an available water capacity
  (m).
• SRint the initial storage deficit in the root
  zone (m).
• ChVel routing velocity for scaling the distance
  over area also called network width function.
  Linear routing is assumed (m/h).

6
Physical Processes

• Vegetation interception Capacity
• represented by a reservoir with a capacity of
  SRmax. The water is extracted from the reservoir
  at potential evapotranspiration rate the net
  precipitation in excess of the capacity SRmax
  reaches the soil and forms the input for the
  subsequent model components.

7
Physical Processes Contd.

• Surface runoff from saturation excess
• In the TOPMODEL the saturated hydraulic
  conductivity of the soil follows a negative
  exponential law vs. depth.
• It is also assumed that the water table is
  parallel to the soil surface so that downslope
  flow beneath water table at a depth zi is given
  for any point i by
• Series of calculations gives the value of zi. The
  value of zi is determined only by the parameter
  f and the topographic index.

8
Physical Processes Contd.

• Surface runoff from infiltration excess
• In the TOPMODEL, the infiltration excess
  computation is based on the Philip equation.
• Calculation of flow in the saturated zone and the
  sequence of calculation in the TOPMODEL
• The value of permits the estimation of the
  saturated basin fraction. The value of is
  updated at every time step by using the equation
• which is basically a continuity equation.

9
Initial Conditions

• Initial Conditions
• The continuity equation is initialized by
  assuming that the simulation begins after a long
  dry period in other words, the unsaturated zone
  is held to be totally dry and the flow observed
  at the basin outlet is deemed to have been
  generated only by the subsurface flow
  contribution

10
Project Files

• Input Data File
• The input data file provides the rainfall,
  potential evapotranspiration and observed
  discharge data required for a particular
  application of TOPMODEL.
• Topographic Index Map Data File
• This file should be the map of the topographic
  index values from which the distribution input as
  part of the catchment data files can be derived.
• Catchment Data File
• It provides the distributions for the catchment
  or for each subcatchment

11
Output Options

• The Hydrograph Prediction Option
• This option allows the model to be run and
  hydrographs displayed. Parameter values can be
  changed on screen. After each run four indices of
  goodness of fit are given for evaluation, viz.,
  The Nash and Sutcliffe Efficiency Criterion, SSE,
  SLE and SAE.
• Sensitivity Analysis Option
• The allows to observe the sensitivity of the
  objective functions to changes of one or more of
  the parameters to be explored.
•  
• The Monte Carlo Analysis Option
• In this option a large number of runs of the
  model can be made using uniform random samples of
  the parameters chosen for inclusion in the
  analysis. 

12
(No Transcript)
13
(No Transcript)