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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 catchment regarded as one unit.parameters are average values

• conceptual based on considerations of thephysical 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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equations

The NAM Model

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NAM, Initial conditions

• Initial Water Content of Surface and Root zone storages

• Initial values for Overland flow and Interflow

• Initial Groundwater Depth

Data to be specified:

Recommended to disregard the first half year or so of the results to eliminate erroneous Initial Conditions!

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NAM, Model Calibration

• Water balance in system

• Runoff hydrographs, peak and shape

• Comparison of Runoff results with observations

Most NAM Parameters of empirical nature=> values must be determined by Calibration:

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 events4) 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

Editor-file: *.rr11

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

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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