Contributing Area - Multiple Flow Direction (Partial) derived from 1" SRTM DEM-H

Brief description

CA_MFD_PARTIAL is contributing area in m2 computed using multiple flow directions on hillslopes and ANUDEM-derived flow directions in channels. The contributing area was computed on 1 degree tiles with 200 cell (about 5 km) overlaps so the areas in channels do not account for catchments beyond that size (hence the use of PARTIAL in the name). The primary purpose of this product was to calculate topographic wetness index (TWI; Gallant and Wilson, 2000) for which full contributing areas in channels are not necessary. Do not use this product to represent contributing areas of catchments larger than 5 km across.

The CA_MFD_PARTIAL product was derived from the Hydrologically enforced Digital Elevation Model (DEM-H; ANZCW0703014615), which was derived from the 1 arc-second resolution SRTM data acquired by NASA in February 2000.

This data is available in tiled format at 1 arc-second and 3 arc-second resolution.

The 3 arc-second resolution product was generated from the 1 arc-second CA_MFD (partial) product and masked by the 3” water and ocean mask datasets.

Lineage: Source data

1.\t1 arc-second SRTM-derived Hydrologically Enforced Digital Elevation Model (DEM-H; ANZCW0703014615).
2.\tDEM-H Flow direction grid
3.\t1 arc-second CA_MFD (partial) product
4.\t3 arc-second resolution SRTM water body and ocean mask datasets


CA_MFD_PARTIAL calculation
CA_MFD_PARTIAL was calculated from DEM-H to provide the contributing area for the calculation of TWI, following the methods described in Gallant and Wilson (2000). It is derived from a slope-weighted multiple flow algorithm for flow accumulation, but uses the flow directions derived from the interpolation (ANUDEM) where they exist. In this case, they are the ANUDEM-derived flow directions only on the enforced stream lines, so the flow accumulation will follow the streams.

The varying area of grid cells with latitude due to the geographic projection of the data was accounted for in the calculation of contributing area.

The CA_MFD_PARTIAL calculation was performed on 1° x 1° tiles, with 200 cell (about 5 km) overlaps at tile edges. This overlap ensures that contributing area for channels with catchments up to 5 km across is correctly captured, but the area of larger catchments will not be included. This product is therefore not suitable for use where the contributing areas for larger catchments are needed. The primary purpose of this product was to support calculation of Topographic Wetness Index (TWI), which is designed to represent patterns on hillslopes and does not need full catchment contributing area in channels.

A full contributing area product will be developed in the future.

The 3 arc-second resolution version was generated from the 1 arc-second CA_MFD (partial) product. This was done by aggregating the 1” data over a 3 x 3 grid cell window and taking the maximum of the nine values that contributed to each 3” output grid cell. The 3” CA_MFD data were then masked using the SRTM 3” ocean and water body datasets.


References
Gallant, J.C. and Wilson, J.P. (2000) Primary topographic attributes, chapter 3 in Wilson, J.P. and Gallant, J.C. Terrain Analysis: Principles and Applications, John Wiley and Sons, New York.