Indicators of Catchment Condition in the Intensive Land Use Zone of Australia – Impoundment density

\n\nIt should be noted that this data is now somwhat dated!\n\nNation-wide measures that would reflect the changes to flow regimes in rivers\nwere considered, for example changes in peakiness, and changes in volumes.\nHowever national long-term data sets approaching catchment scale detail were\nnot available or were of dubious quality. The regulation of river flows has\nchanged the natural flows regimes of rivers and this impacts on wetland\necosystems and aquatic biota. measure based on impoundments was considered\nto be the best available surrogate indicator for hydrological changes.\n\nThe Wild Rivers data set (Environment Australia, 1997) includes national data\non impoundments to river flow. The data set has four classes: major structures\n(dams, reservoirs); weirs; locks/sluice gates; and minor structures (banks,\nfarm dams on or immediately adjacent to stream). The Wild Rivers data set also\nincludes flow diversions data, but these are not used in the indicator here.\n\nThe maps show the location of major irrigation schemes and the major dams for\nurban water supply. The Wild Rivers impoundments data were obtained from state\npoint data sets, each of which were reclassified to a single four-class\nimpoundment rating system. Collection and derivation of data are not\nconsistent across the nation, and both point and polygon data have been\nincluded.\n\nThe polygon data has the effect of grossly inflating the number of\nimpoundments as it is possible to have 400 x 250 m grid cells within a 5 km\ngrid cell, all counted as individual impoundments. The data set is reliable at\nthe Topo250K drainage layer scale (AUSLIG, 2000).\n\nThe most modified rivers and streams are in Tasmania (Derwent, Gordon, King\nHenty, Pieman, Mersey, Forth, and Tamar Rivers). Other areas with significant\nimpacts on river flows are in the Mt Lofty Ranges around Adelaide (Fleurieu,\nMyponga, Onkaparinga, Torrens, and Gawler Rivers), the hinterland of Melbourne\n(Bunyip and Yarra Rivers) and in Queensland (Kolan, Ross, Barron and Tully\nRivers). In Western Australia the rivers with the highest impoundment values\nwere the Collie Harvey and Ord Rivers.\n\nData are available as:\n\n * continental maps at 5km (0.05 deg) cell resolution for the ILZ;\n * spatial averages over CRES defined catchments (CRES, 2000) in the ILZ;\n * spatial averages over the AWRC river basins in the ILZ.\n\nSee [further metadata](http://data.daff.gov.au/anrdl/metadata_files/pa_iccilr9ab\n__06821axx.xml) for more detail.\n\n