Automatic delineation of drainage networks and catchments using DEM data and GIS capabilities : a case study

Catchment and drainage network delineation is an important step of hydrologic model development that represents hydrologic boundary. Due to spatial and temporal variations of the characteristics of a watershed, it is often necessary to delineate a watershed into smaller-sized model areas where variables can be considered homogeneous. Catchments are scale independent delineations to capture surface water in an area of interest. Generally there are two types of delineation; manual and automatic. The traditional manual catchment delineation method for large-scale watersheds is time consuming. Using an elevation raster or digital elevation model (DEM) as input, it is possible to automatically delineate a drainage system and quantify the characteristics of the system. With the development of computer and information technology, automatic catchment delineation becomes widely popular. For accurate delineation, the quality of grid based DEM is vital. The DEM quality depends on two important aspects i.e. horizontal resolution and vertical accuracy. In this paper catchment and drainage network have been delineated for a case study area ‘Rockhampton Golf Course’. A rainfall runoff model was needed to develop in the study area and catchment delineation is a prerequisite to get the model boundary. In this study 3sec DEM data and 1sec DEM data were used for automatic delineation along with hydrologic analysis tools in ArcGIS Spatial Analyst. The hydrologic analysis tools described the physical components of a surface through some major functions like flow direction, flow accumulation and determining watersheds from a given source. Moreover the channel shape file generated by Geoscience Australia was also used as reference data of delineation to fix up the flow accumulation threshold area value. The delineated catchment and drainage networks using the two DEM data and their comparison are plotted and discussed in this paper. Besides consideration regarding automatic catchment or drainage network delineation found in this study are discussed here.