when long records (greater than provides peak discharge estimates
25 years) are available. using annual peak stream
Statistical analysis flow data. Regional
equations based on used for calculating
the hydrologic parameters area flows at ungauged sites. These
and slope, are equations were
developed by the floods at ungauged
USGS in 1993 to estimate the magnitude and sites in six separate regions in Texas (Jennings et
frequency al., 1993).
EXTRACTING WATERSHED PARAMETERS FROM DIGITAL MODELS
Over the last twenty years, digital representations of topographic information have become increasingly available in the form of digital terrain models (DTMs). Using computers and extracting watershed data from digital terrain models is faster, and provides more reproducible measurements than traditional manual techniques using topographic maps (Garbrecht et al., 1999a).
GIS uses a DTM to describe the spatially distributed attributes of the terrain that are classified as topologic and topographic data. The topography of an area describes its elevation and land surface shape, while also important are the spatial distribution of terrain attributes other than elevation such as the land cover, soil type, and connectivity of the features. A DTM may be used to represent both topographic and/or physiographic features in the format of raster or grid data, triangulated irregular network (TIN) data or vector (point, line, and polygon) data (Olivera et al., 2000).
Using automated methods a surface may be analyzed so that drainage basin boundaries are defined, stream networks created, and drainage basin data