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Modelling the rainfall-runoff process
Available Rainfall
Runoff (RR) models:
• UHM
• NAM
• SMAP
• URBAN
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Modelling the rainfall-runoff process (NAM)
RAINFALL
POTENTIAL EVAPORATION
MODEL
PARAMETERS
RUNOFF COMPONENTS
EVAPORATION
RECHARGE
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NAM : “nedbør-afstrømnings model”
Describes the land phase of the hydrological cycle
The NAM is a lumped, conceptual model:
• lumped
• conceptual
catchment regarded as one unit.
parameters are average values
based on considerations of the
physical processes
Similar models:
Stanford, SSARR, HBV, SMAR,..
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Types of Application
• General hydrological analysis
- runoff distribution
- estimates of infiltration / evaporation
• Flood Forecasting
- subcatchment inflow to river model
- links to meteorological models
• Extension of streamflow records
- advanced gap-filling
- improved basis for extreme value analysis etc.
• Prediction of low flow
- for irrigation management
- for water quality control
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The NAM Model
equations
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NAM, Initial conditions
Data to be specified:
• Initial Water Content of Surface and Root zone storages
• Initial values for Overland flow and Interflow
• Initial Groundwater Depth
Recommended to disregard the first half year or so of
the results to eliminate erroneous Initial Conditions!
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NAM, Model Calibration
Most NAM Parameters of empirical nature
=> values must be determined by Calibration:
• Water balance in system
• Runoff hydrographs, peak and shape
• Comparison of Runoff results with observations
Generally recommended to change only one
parameter between each run !
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NAM, Model Calibration
1. Manual Step-by-step procedure
(changing one variable at a time)
2. Autocalibration
Automatic optimisation routine using multi-objective
optimisation strategy.
4 objectives:
1) Overall Volume error (= water balance)
2) Overall root mean square error (= hydrograph shape)
3) average root mean square error of peak flow events
4) average root mean square error of low flow events
Easy to use - BUT EVALUATION OF VARIABLE VALUES
REQUIRED TO JUDGE HYDROLOGICAL SENSIBILITY
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NAM simulation, Liver creek
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RR Parameter editor
Editing of Model-specific parameters for Rural Catchments :
NAM Model-specific parameters comprise:
• Surface, Root-zone and Snow melt data
• Ground water data
• Initial Conditions
• Irrigated Area
Editor-file: *.rr11
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RR Parameter editor (NAM)
Example:
Surface-Rootzone
variables
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RR Input to HD Simulation
Inclusion of Runoff results in River model:
1) RR-simulation (produce RR Result-file)
2) Specify Catchment definitions in Network Editor
(input to single points or distributed along reach)
3) Specify RR Result-filename in Simulation Editor