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GIS and Remote Sensing Technologies for Efficient Agricultural Water Use


Standard procedure in the development of a 3D conceptual model includes spatial data acquisition, data processing in ArcGIS, and model building in ArcScene.

A vast quantity of data/information from different data sources goes into the construction of a conceptual model. ArcGIS serves as a tool that enables multiple types of data to be integrated for both analytical and visual analysis. ArcGIS’s 3D Analyst adds functionality to ArcMap to provide three-dimensional visualization, topographical analysis, and surface creation capabilities. ArcScene also allows advanced spatial data visualization and interaction in a 3D environment.

Following major spatial data/datasets have been collected:

  • DEMs
  • Remotely sensed images
  • Rivers
  • Channels
  • Localities
  • Irrigation area boundaries
  • Watertable levels
  • Geological formations
Original data available for use in the 3D conceptual model are of widely varying spatial reference, scales and accuracy. They are all processed to a geographic coordinate system (WGS84) in ArcGIS. Colour composite of Landsat 7 ETM+ images (RGB 742) are used to drape onto the DEM (250m resolution) for representing the ground level surface (e.g. landscape and crops). Model domain and other boundary conditions are defined by irrigation boundaries, channel and stream network and major localities. Geological framework is formed by the top elevation of geological formations. The structural contours of them are firstly digitised from the hydrogeological maps of Australian Geological Survey, and then interpolated into representative geologic surfaces. Groundwater depth data are incorporated to show the subsurface watertable level. All the above data layers are then overlayed in ArcScene. The hydrologic characteristics and properties are assigned to each layer to illustrate/reflect system losses and gains, regional groundwater flow, vertical interactions between the formations, recharge due to irrigation and rainfall, leakage to and from the drainage channels, surface-groundwater, agriculture and environment interactions, and so on. A vertical exaggeration is applied for presentation emphasis. Interactive perspective viewing can be performed to the model. The final 3D conceptual model can also be animated fly-throughs, and exported for presentation and analysis.

4. Evaluation of Land and Water Management Options
The conceptual models are used to develop calibrated surface and groundwater models which enable integration of biophysical processes with crop production and economics components for different management scenarios. These scenarios can be modelled in consultation with local groups to enable ready adoption of modelling results. The models and framework are capable of simulating following scenarios at the farm and irrigation area levels:

  • the do nothing case (i.e. no change);
  • change in agricultural enterprise;
  • change in irrigation water quality;
  • change in volume and quality of drainage water;
  • change in water allocation; and
  • change in commodity pricing, water pricing and other costs including environmental costs.
The integrated decision support system allows identification of rice areas, areas of higher recharge and leaky channel and river reaches. Overlaying the surfacegroundwater interaction model results with the GIS model grid and channel network layers can help identify groundwater hotspots in the irrigation areas (Fig-5).


Figure-4 Conceptual Model of the a Rice Growing Irrigation System



Figure-5 Surface network features overlaid on model grid


Groundwater model simulations give predictions of watertable heights under different scenarios. Spatial distribution of watertable heights combined with the aquifer hydraulic properties can be used to derive groundwater flow vectors. The groundwater flow vectors can be used to identify groundwater recharge and discharge zones to understand how management actions at farm level affect watertables in other areas (Khan et al, 2000 a & b). Therefore groundwater models coupled with GIS databases provide a powerful tool for the environmental management of irrigation areas.

5. Conclusions
The following conclusions are drawn from this work:

  • Using GIS for rice monitoring has improved the efficiency of crop measurement and the associated administrative processes, e.g., customer inquiries, information searches, approval for growing crops, crop statistics and information presentation.
  • GIS has enabled other doors to open as new technology arises. The adoption of EM survey for soil suitability in rice bays has been possible by importing surveys directly into GIS and overlaying them on image data to pinpoint approved and unsuitable rice growing areas.
  • Integration of GIS databases with conceptual and dyanmic models is helping identify on farm and regional impacts of irrigation management practices.
  • Visualisation capabilities of GIS helps community interaction with the modelling scenario outcomes and therefore provides a useful mechanism for acceptance of complex modelling results by the farmer groups.
Acknowledgements

The author is grateful to CRC for Sustainable Rice Production, CRC for Irrigation Futures, CSIRO Water for a Healthy Country Flagship and Murray Irrigation Limited for providing assistance with the various aspects of this work. Technical inputs from a number of colleagues including Dr Yun Chen, Dr Akhtar Abbas and Tariq Rana are acknowledged.

References

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