Non-point pollution modelling

by

Dr. Anders Refsgaard

DHI, Water and Environment

Denmark

The Problem

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Modelling environment

Decoupled simulation of: nitrogen leaching (DAISY -

code developed at the Royal Veterinary and Agricultural University);

integrated surface water and groundwater flow (MIKE SHE WM and MIKE 11 - code developed at DHI);

integrated nitrogen transport and degradation (MIKE SHE AD - code developed at DHI);

MIKE SHE

Physically based integrated hydrological modelling system for the entire land based hydrological cycle

Strong groundwater component with surface water interaction

MIKE 11 river model integrated

Solute transport modelling in all components of the hydrological cycle

Time-series editortools & statistics

Grid Editortools & statistics

Result Viewer

Water BudgetCalculations

Calibration tools• auto calibration

• statistics

MIKE SHE Dbases•Soils

•Vegetation

ExternalGIS tools

River EditorMIKE11

GUI Structure

Setup Editor - Core GUI

Core GUI surrounded by a suite of data handling tools, editors, result viewers etc.

Setup Editor (Core GUI)

Dynamic Model Browser and Data Tree

Graphical Data View and Input

Data checking and verification

• Context sensitive dialogs

• Depends on selections• No irrelevant user choices

• Setup data (unstructured / conceptual model)• Processed data (structured / numerical model)• Results (default/user defined HTML outputs)

MIKE MODFLOW

Setup Editor

Processed dataMODFLOW 96

MODFLOW Surfact

MODFLOW 2000

MIKE SHE

Result ViewerPlot ComposerHTML reporting

• MODFLOW fully integrated into GUI • Identical conceptual model for MODFLOW

and MIKE SHE (dynamic data tree)• Easily switch between MIKE SHE and

MODFLOW• Data tools for importing legacy MODFLOW

model data• First GUI designed for full functionality of

MODFLOW 2000

• Optional output formats (.HDS or .DFS)• Dynamic particle tracking with MODPATH

DAISY

Open and flexible, physically based agro-ecosystem modelling system (water, nitrogen and pesticides)

Changes in crop yield as a function of water and nitrogen availability under various agricultural management practices.

Irrigation optimisation Nitrate leaching from

agricultural areas Pesticide leaching from

agricultural areas User friendly DAISY GIS

interface available

DAISY GIS

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For each combination of soil type, management practice (e.g. crop or crop rotation) and climate region, which should be included in the simulation, data must be specified.

Model scales

Detailed

Local

Regional

All data on detailed or

local scale

Dynamic boundary

conditions extracted

from regional

models to local

sub-models.

Data level - Nitrogen load

Detailed data on local scale, i.e. information on farmers or field level on soils, crops, nutrients, farming practice etc.

Statistical data at regional scale, i.e. statistical information is dis-aggregated to produce realisations of likely distributions of “model” parameters

Case study: Karup, DK

Catchment characteristics: Area: 518 km2; Precipitation: 900 mm Pot. Evaporat.: 610 mm Run off: 451 mm; Mainly agricultural

areas; Alluvial sediments; Sandy, unconfined

regional aquifer; Little groundwater

exploitation; Large interaction

between river and aquifer system;

Karup: land use and crop rotation

NO3- leaching

-500

0

500

1000

1500

2000

2500

3000

3500

26-03-98 04-07-98 12-10-98 20-01-99 30-04-99 08-08-99

Dato

Nit

ratu

dva

skn

ing

[kg

N/h

a/år

]

NO3- leaching - validation

Nitrate measured and modelled at 57 locations in various depths;

graphs show mean

+/- one standard deviation of both measured and modelled results;

correspondence is impressive!

Infiltration

Water/pressure: the pressure

propagation from ground surface to water table takes about 4-5 months (depth to GW table 15 m);

Solutes: solute transport

through the unsaturated zone takes about 3-4 years;

Results: NO3- concentrations

NO3- :

large spatial variations both horizontally and vertically;

variations due to crop, fertilizer and agricultural management differences as well as hydrological and hydrogeological conditions;

Results: NO3- concentrations

NO3- :

large temporal variations with characteristic annual variation;

about 50% reduced before it reaches streams;

10-20 mg NO3-/l in

stream;

UZ depth

UZ depth

UZ depth

Cattle manure - upper groundwater

Mineral fertiliser

Pig manure

Pig manure -lower groundwater

Conclusions

Modelling environment developed for simulation of nitrogen load, leaching, balance and transport through the unsaturated zone and the groundwater;

model codes based on sound physical principles and equipped with user friendly GUI’s or GIS interfaces;

applicable for detailed analyses of soil processes and both local and regional scale analyses of impact from agriculture on water quality in groundwater and surface water;

methods extensively used in DK and abroad both for simulation of recharge to non-integrated groundwater models and for simulation of nitrogen balance;

THANK YOU FOR YOUR ATTENTION