Non-point pollution modelling by Dr. Anders Refsgaard DHI, Water and Environment Denmark

The Problem 29

Modelling environment Decoupled simulation of: lnitrogen leaching (DAISY - code developed at the Royal Veterinary and Agricultural University); lintegrated surface water and groundwater flow (MIKE SHE WM and MIKE 11 - code developed at DHI); lintegrated nitrogen transport and degradation (MIKE SHE AD - code developed at DHI);

MIKE SHE lPhysically based integrated hydrological modelling system for the entire land based hydrological cycle lStrong groundwater component with surface water interaction lMIKE 11 river model integrated lSolute transport modelling in all components of the hydrological cycle

Time-series editor tools & statistics Grid Editor tools & statistics Result Viewer Water Budget Calculations Calibration tools auto calibration statistics MIKE SHE Dbases Soils Vegetation External GIS tools River Editor MIKE11 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 data MODFLOW 96 MODFLOW Surfact MODFLOW 2000 MIKE SHE Result Viewer Plot Composer HTML 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 lOpen and flexible, physically based agro-ecosystem modelling system (water, nitrogen and pesticides) lChanges in crop yield as a function of water and nitrogen availability under various agricultural management practices. lIrrigation optimisation lNitrate leaching from agricultural areas lPesticide leaching from agricultural areas lUser friendly DAISY GIS interface available

DAISY GIS 29 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 lDetailed data on local scale, i.e. information on farmers or field level on soils, crops, nutrients, farming practice etc. lStatistical 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: lArea: 518 km 2 ; lPrecipitation: 900 mm lPot. Evaporat.: 610 mm lRun off: 451 mm; lMainly agricultural areas; lAlluvial sediments; lSandy, unconfined regional aquifer; lLittle groundwater exploitation; lLarge interaction between river and aquifer system;

Karup: land use and crop rotation

NO 3 - leaching

NO 3 - leaching - validation lNitrate measured and modelled at 57 locations in various depths; lgraphs show mean +/- one standard deviation of both measured and modelled results; lcorrespondence is impressive!

Infiltration Water/pressure: lthe pressure propagation from ground surface to water table takes about 4-5 months (depth to GW table 15 m); Solutes: lsolute transport through the unsaturated zone takes about 3-4 years;

Results: NO 3 - concentrations NO 3 - : llarge spatial variations both horizontally and vertically; lvariations due to crop, fertilizer and agricultural management differences as well as hydrological and hydrogeological conditions;

Results: NO 3 - concentrations NO 3 - : llarge temporal variations with characteristic annual variation; labout 50% reduced before it reaches streams; l10-20 mg NO 3 - /l in stream; UZ depth Cattle manure - upper groundwater Mineral fertiliser Pig manure Pig manure -lower groundwater

Conclusions lModelling environment developed for simulation of nitrogen load, leaching, balance and transport through the unsaturated zone and the groundwater; lmodel codes based on sound physical principles and equipped with user friendly GUI’s or GIS interfaces; lapplicable 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; lmethods extensively used in DK and abroad both for simulation of recharge to non-integrated groundwater models and for simulation of nitrogen balance;

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