Spatial scale impact on daily surface water and sediment fluxes in Thukela river, South Africa uri icon

abstract

  • The on- and off-site effects of soil erosion in many environments are well known, but there is still limitedunderstanding of the fluxes in downstream direction due, among other factors, to scarce and poorquality. A four year study to (i) evaluate water and sediment fluxes at different spatio-temporal scalesand (ii) interpret the results in terms of processes involved and the controlling factors, was conducted inThukela basin, South Africa. Five hierarchically nested catchments; namely microcatchment (0.23 km2),subcatchment (1.20 km2), catchment (9.75 km2), sub-basin (253 km2) and basin (29,038 km2), were usedin addition to fifteen (1 m2) microplots and ten (10 m2) plots on five locations within the microcatchment.The results showed 19% decrease of unit-area runoff (q) from 3.1 L m2 day 1 at microplot to2.5 L m2 day1 at plot scale followed by steeper (56%) decrease at microcatchment scale. The qdecreased in downstream direction to very low level (q 0.26 L m2 day1). The changes in q wereaccompanied by initial 1% increase of soil loss (SL) from 18.8 g m2 day1 at microplot to19.1 g m2 day1 at plot scale. The SL also decreased sharply (by 39 fold) to 0.50 g m2 day1 atmicrocatchment scale, followed by further decrease in downstream direction. The decrease of q withspatial scale was attributed to infiltration losses, while initial increase of SL signified greater competenceof sheet than splash erosion. The decrease of SL beyond the plot scale was attributed to redistribution ofthe soil on the hillslope and deposition on the stream channel upstream of the microcatchment outlet.Therefore, erosion control strategies focussing on the recovery of vegetation on the slope and stabilisationof gullies are recommended

publication date

  • 2016
  • 2016