GIS and Remote Sensing Technologies for Efficient Agricultural Water UseNDVI=(Red-Near Infrared)/(Red+Near Infrared) Because vegetation has a low visible reflectance and high near infrared reflectance, by using this index water bodies appear black and high vegetation areas appear brighter than lower vegetation areas. Results of NDVI are given in Fig-1. On a farm scale, it appears that after classification of rice areas, the data could still require a considerable amount of manual editing. Errors of commission can occur in the classification process with the inclusion of other water bodies such as storage dams and waterways. On Screen Digitising of SPOT Panchromatic Imagery The climate in MIL area and timing of imagery acquisition results in a large contrast between irrigated and non-irrigated areas making visual identification of rice crops very easy from the SPOT panchromatic data. (Fig-2) ESRI’s Arcview software was selected and scripts were written, in house, to streamline the digitising process. The operator is able to type in a landholding reference number and the program zooms to that area of interest. The rice area is identified visually and digitised on screen. The program then writes that area to the landholding selected. Identical areas measured in previous years do not have to be re-digitised; they can be added to the current year by clicking on a button then clicking on that area. This function has greatly reduced the time taken to measure crops each year. MIL now has five seasons of rice growing captured digitally. (Fig-3) The rice growing areas can be overlaid on soils maps and electro-magnetic surveys to identify leaky paddocks, which can help reduce groundwater recharge to shallow watertables. Other uses of digital rice area data are to provide ready crop statistics, crop approval and environmental reporting. The spatial distribution of rice areas provides input to the spatially distributed hydrologic models, which are described in the next section.  Figure-1 Normalised Vegetation Index Image  Figure-2 On Screen Digitising of Spot Panchromatic Imagery  Figure-3 ArcView GIS database of Rice Growing Areas 3. Conceptual Models of Irrigation Systems Applications of GIS and hydrological models for natural resource management have been described by several authors including Bradley (1993), Alaric (1994), Lilburne et al. (1998) and Belmonte et al. (1999). This section describes how GIS, remote sensing and hydrology are being integrated for the environmental management of rice growing areas. A conceptual model is developed to explain the hydrogeology of the irrigated regions. It illustrates the geologic formations, hydrological flows in and out the region and the capacity of the aquifers. The structural contours of geologic formations based on hydrogeological maps of Australian Geological Survey (Hennessy, et al., 1994) are digitised in the GIS environment. The spatial reference for this spatial database is Zone 54, Zone 55 and Datum is Australian Geodetic 1984. |