Improving spatial representation of erosion sources using Sediment Fingerprinting with terrain data and sediment budget modelling

Sediment fingerprinting quantifies proportional contributions of catchment sediment sources to downstream sediment mixtures and deposits. While the sediment fingerprinting technique is well established it is still challenged by the coarse spatial resolution of sediment source discrimination which hinders understanding of catchment sediment dynamics and limits its usefulness for land management where finer resolution spatial information is required.

Here, two conventional sediment fingerprinting datasets from New Zealand are used to show how spatial modelling of source loads can improve 1) the usefulness of sediment fingerprinting approaches and 2) visualization of results for end-users by combining source apportionment with terrain information and sediment budget modelling. The two case studies involve unmixing sediment source contributions to 1) overbank deposits within the Oroua River catchment, where six sediment sources (Mountain Range, Mudstone, Hill Subsurface, Hill Surface, Unconsolidated Sandstone, and Channel Bank) across two size fractions (<63 µm and 125–300 µm) were characterized using bulk geochemical and radionuclide tracers and 2) suspended sediment in the Manawatu catchment, where a similar six sources were characterized using bulk geochemical tracers to determine changes in source contributions to hourly suspended sediment samples during a 53hr storm event.

The proportional source contributions for each case study are applied to modelled sediment loads and spatially distributed using terrain information for rock type, slope and channel network extent to produce specific sediment yield maps for both catchments and spatial visualization of sediment generation during the Manawatu catchment storm event. Integrating sediment fingerprinting results with spatial datasets and modelling can enhance interpretation of source apportionment results and improve the utility of this information for end-users focused on the spatial targeting of erosion sources for mitigation to reduce downstream sediment impacts.