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Improvements in riparian management, such as shrub/tree planting and livestock exclusion, are often assumed to result in reduced stream bank erosion and associated catchment sediment yield. Studies that quantify the effectiveness of riparian interventions aimed at reducing bank erosion and river sediment yields are, however, rare. This paper discusses how bank erosion processes can vary throughout catchments (with particular reference to their scale dependence) and hence how the effectiveness of different riparian interventions can be variable. The findings of known published accounts of the effectiveness of riparian management interventions for reducing stream bank erosion in New Zealand are also summarised. Only nine relevant studies were identified and most used qualitative or semi-quantitative analysis methods. Most studies compared stream banks in pasture catchments (with unlimited livestock access) with stream banks where livestock were excluded and riparian shrubs/trees were present. Many studies reported that managed stream banks were in better condition than unmanaged banks. The exclusion of livestock from riparian areas was generally reported as the principal factor in the measured improvements or differences. Only two studies specifically attributed reduced stream bank erosion to the presence of riparian vegetation. The dearth of research identified here highlights the need for further quantitative studies to determine the effectiveness of riparian management measures for reducing bank erosion. [ABSTRACT FROM AUTHOR]

Information on the effect of human-induced disturbances on sediment yields and sediment sources from New Zealand catchments is limited. This study analyses the sediment yields and event sediment dynamics for a 12-year period from two paired headwater catchments within the Waikato region. One catchment (Whakakai) was entirely vegetated in native forest, while the other (Mangaotama) was of mixed land use. Near the beginning of the study period, an integrated catchment management plan was implemented with the Mangaotama catchment. This plan included riparian planting, planting of degraded land in Pinus radiata and changes in stock management. Long-term in-stream turbidity data was calibrated with suspended sediment concentration (SSC) measurements and used to determine event and annual sediment yields. Hysteresis of the discharge (Q)–SSC relationship during events was used to infer differences in sediment sources. Event sediment yields within the Mangaotama catchment were similar to Whakakai catchment during small events (c. 1.01-year return period). For larger and less frequent events (>5-year return period), the event yields from Mangaotama exceeded Whakakai by about a factor of three, probably due to mass movement initiation. The specific sediment yield (±1σ) from Mangaotama (97±39 t/km2/year) was around 60% higher than Whakakai (60±22 t/km2/year). Clockwise hysteresis in the Q–SSC relationship dominated at Mangaotama, indicating the importance of near-channel sources. The persistence of near-channel source dominance throughout the study period (despite major land use changes) was attributed to switching of erosive mechanisms (i.e. from cattle-induced mechanical disturbance to subaerial processes). The prevalence of anti-clockwise hysteresis in the Q–SSC relationship of events at Whakakai suggests that hillslope sources are likely to be a principal source of eroded sediment. Such information provides valuable information that may help guide future decisions on the application of catchment rehabilitation measures. [ABSTRACT FROM AUTHOR]