Erosion Pin Data Research Articles

The invasive alien plant, Impatiens glandulifera (Himalayan Balsam), and increased soil erosion: causation or association? Case studies from a river system in Switzerland and the UK

A monitoring investigation undertaken along the River Ibach, northwest Switzerland over the winter 2012/2013, found that riparian areas recently supporting the invasive plant Himalayan Balsam (HB) recorded significantly higher erosion rates than nearby uninvaded areas. This communication sythesises the latest findings about the influence of HB on sedimentation processes, again, from the Ibach, but also from a second river system in southwest UK. Erosion pins, a micro-profile bridge and a digital caliper were used to measure changes in soil surface profile (SSP) at selected riparian areas supporting HB plants along both rivers. Values were statistically compared against equivalent data recorded from nearby reference areas supporting mixed perennial vegetation. A comparison of source and sediment geochemistry was also undertaken on soil from HB-invaded and uninvaded floodplain areas along the Ibach, to assess the potential for identifying the extent to which either group acts as a sediment source. Erosion pin data indicate that soil loss from HB-colonised areas was significantly greater than soil loss from reference areas in two out of the four periods at the River Ibach site, and in two out of three measurement periods at the River Taw site. Colonisation of new HB sites may initially occur by hydrochorous processes, but HB plants may increase colonisation potential by trapping additional fine sediment and organic matter, including viable HB seeds. Geochemical results from the Ibach suggest that high inputs of suspended sediment originate from sources close to the river channel, but HB-invaded floodplain sources have geochemical properties that are most similar to suspended river sediment. The findings from both rivers led us to rethink our original hypothesis; that HB promotes soil erosion, to an amended hypothesis in which HB may be associated with areas where high erosion is sometimes recorded. Whilst initial colonisation may be due to hydrochorous processes, as HB becomes increasingly established, the displacement of perennial vegetation increases the risk of erosion during the winter period when live HB plants are absent. Preliminary geochemical findings of floodplain soils supporting different vegetation types along the Ibach tentatively suggest that at least some material originating from HB sites may enter the watercourse.

A 13‐year record of erosion on badland sites in the Karoo, South Africa

AbstractLand degradation in South Africa has been of concern for more than 100 years with both climate change and inappropriate land management (overgrazing) being proposed as primary drivers. However, there are few quantitative studies of degradation and, in particular, few of erosion by water. Badlands, taken here to be the landform which results from extreme erosion, have been notably neglected. We report on 13 consecutive years of erosion pin measurements of badland erosion on 10 study sites in the Sneeuberg uplands of the eastern Karoo in South Africa. The study sites are on Holocene colluvium which mantles footslopes. They have been subject to overgrazing for at least 100 years, c. 1850–1950. Currently they are lightly grazed by sheep. The area receives about 500 mm rainfall per year. The sites are remote, with only informal, farmer‐operated, daily raingauges nearby. The nearest sub‐daily raingauge is c. 55 km distant. Also we report on an analysis of the erosion pin data which focuses on establishing the origins and context of the badlands, including the relationship between study sites and adjacent valley‐bottom gully systems; compare erosion rates on our study sites with rates determined by erosion pins on other badland sites; and discuss the implications of these erosion rates for landscape development and off‐site impacts. Net erosion rates on the study sites are relatively high compared with global badland rates and range from 3.1 to 8.5 mm yr‐1 which may be extrapolated to 53 to 145 t ha yr‐1 (using a measured bulk density of 1.7 g cm‐3). However, comparisons with badland sites elsewhere are difficult because of different measuring methodologies, lithologies, climate and dominant processes. Erosion rates on the study sites are strongly influenced by rainfall amounts and, in particular, by daily rainfall events which exceed ~10 mm: this is the threshold intensity at which runoff has been observed to commence on badlands. Of significance, but of lesser influence, is weathering, mainly by wetting and drying: this prepares bare surfaces for erosion. However, questions remain regarding the role of site characteristics, and of processes at each site, in determining between‐site differences in erosion rate. Crude extrapolation of current rates of erosion, in conjunction with depths of incision into the badlands, suggests that badland development started around 200 years ago, probably as a response to the introduction of European‐style stock farming which resulted in overgrazing. We assume, but cannot quantify, the additional influence of periods of drought and burning in the erosional history of the area. Intermittent connection of these badlands to valley‐bottom gullies and therefore to small farm dams and ultimately to large water storage reservoirs increases their impact on local water resources. Copyright © 2015 John Wiley & Sons, Ltd.

Evaluation of soil erosion risk for watershed management in Shenmu watershed, central Taiwan using USLE model parameters

This study compiles the latest regional topographic data from field investigation and remote-sensing images to recalculate parameters of the universal soil loss equation (USLE) model of the Shenmu watershed; also to compensate for reduced accuracy of this model on small-scale slopes, this study incorporates soil erosion pin data which were collected periodically to measure the extent of soil erosion. Firstly, this study utilized the USLE model and soil erosion pin data to compare the soil erosion potential of the Chushui and Aiyuzi subwatersheds and concluded that soil erosion drastically increased if accumulated rainfall exceeded 200 mm; also, erosion depths were greater in the Aiyuzi subwatershed while estimated total erosion volume was higher in the Chushui subwatershed; this was attributed to the larger area of Chushui subwatershed and based on field measurements which supported the results of the USLE model. Secondly, this study utilized modified USLE model to compare the extreme event erosion resulting from typhoon Morakot which revealed that high rainfall intensity and long-duration rainfall events can generate large volume non-point sources of sediment that is estimated to far exceed 7–10 times of the annual soil erosion. Thirdly, this study related the C parameter of the USLE model to the existing land use in the Shenmu watershed using current, real data. Finally, this study established a post-typhoon Morakot soil erosion risk map composed of five categories of risk which was compared with post-event land cover to suggest high-erosion risk zones that may require further monitoring, remediation, and engineering measures to limit soil loss.

Identifying causes and controls of river bank erosion in a British upland catchment

Abstract Spatial and temporal variation in river bank erosion rates in a British upland catchment was quantified over a 2 year period using a network of erosion pins. Potential causal mechanisms and site-specific controls of this erosion were examined through bivariate analyses and significance testing. Problems with existing process-inference methodologies were identified and addressed through the application of a novel technique involving the disaggregation of erosion pin data using a combination of morphodynamic behaviour descriptors and hierarchical cluster analysis. Observed mean bank erosion rates were comparable with those reported from similar-sized upland catchments in temperate environments elsewhere but considerable spatial and temporal variation was detected. Site-specific parameters, including bank material properties and the presence or absence of livestock grazing, could not explain the observed variation in bank erosion rates. Fluvial processes were identified as the dominant driver of morphological activity in the study area, contesting the notion that subaerial processes are more significant in the headwater reaches of river catchments. The disturbed morphological status of streams in the study area may explain the findings and the results indicate that the existence and spatial organisation of “process-intensity domains” may be influenced by extreme geomorphological events and/or wider catchment-scale changes that have affected hydrology and sediment supply processes.

Bank erosion and channel width change in a tropical catchment

AbstractCatchment sediment budget models are used to predict the location and rates of bank erosion in tropical catchments draining to the Great Barrier Reef lagoon, yet the reliability of these predictions has not been tested due to a lack of measured bank erosion data. This paper presents the results of a 3 year field study examining bank erosion and channel change on the Daintree River, Australia. Three different methods were employed: (1) erosion pins were used to assess the influence of riparian vegetation on bank erosion, (2) bench‐marked cross‐sections were used to evaluate annual changes in channel width and (3) historical aerial photos were used to place the short term data into a longer temporal perspective of channel change (1972–2000). The erosion pin data suggest that the mean erosion rate of banks with riparian vegetation is 6·5 times (or 85%) lower than that of banks without riparian vegetation. The changes measured from cross‐section surveys suggest that channel width has increased by an average of 0·74 (±0·47) m a−1 over the study period (or ∼0·8% yr−1). The aerial photo results suggest that over the last 30 years the Daintree River has undergone channel contraction of the order of 0·25 m a−1. The cross‐section data were compared against modelled SedNet bank erosion rates, and it was found that the model underestimated bank erosion and was unable to represent the variable erosion and accretion processes that were observed in the field data. The reach averaged bank erosion rates were improved by the inclusion of locally derived bed slope and discharge estimates; however, the results suggest that it will be difficult for catchment scale sediment budget models to ever accurately predict the location and rate of bank erosion due to the variation in bank erosion rates in both space and time. Copyright © 2008 John Wiley & Sons, Ltd.

Improving precision in sediment source and erosion process distinction in an upland catchment, south-eastern Australia

Abstract Analysis of sediment sources is an important component in the development of catchment sediment budgets and in determining links between erosion from sources and sediment delivery to catchment outlets. In this study 137Cs and 210Pbex were used to determine surface and sub-surface source contributions of fine sediment in a small upland headwater catchment (1.6 km2) in south-eastern Australia. The findings from this analysis are employed in an adjustment procedure to better differentiate sediment source erosion processes by utilising channel survey and erosion pin data. This improved the precision of estimates of sediment-source erosion-process contributions from hillslopes and channel/gully walls. A mean of 74% of in-channel deposits and suspended sediment exiting the study catchment was derived from sub-surface sources and when adjusted for erosion process this increased to 81%, which may be attributed to channel and gully wall erosion alone. Net erosion of the channel floor was low and constitutes only a small part of the total channel source input to sediment flux. Variability in sediment source contributions within the catchment was high, with rapid transition from hillslope to channel source dominance of sediment flux with distance downstream in the study catchment.

Morphodynamics and climate controls of two aeolian blowouts on the northern Great Plains, Canada

AbstractBlowouts are the most regionally pervasive active aeolian landform on the northern Great Plains of North America. This study reports a long‐term investigation into the morphological development of two adjacent blowouts in a continental dune field. The blowouts were monitored for a decade in the Bigstick Sand Hills of southwestern Saskatchewan, Canada. Topographic changes were determined from dense arrays of erosion pins in each blowout (1 per 4 m2, n = 171; and 1 per 16 m2, n = 150). Pin measurements were made 16 times between May 1994 and May 2004. Over the decade both blowouts expanded and more than doubled in volume. Differences in form–flow interactions have caused the larger of the two blowouts to deposit more than a metre of sediment within the deflation basin, and the smaller blowout to erode by more than a metre. A negative feedback effect was triggered when the larger blowout reached a critical size around 1994 (60 m × 36 m × 8·1 m, length × width × height) when sediment was no longer eroded from the deflation basin. A positive feedback in the smaller blowout continues to facilitate erosion from the deflation basin. Monthly observations since 2002 indicate that aspect plays an important role in the development of these blowouts by creating a spatial asymmetry in sediment availability. Sediment is more readily available throughout the year on south‐facing slopes, which receive greater insolation than north‐facing slopes and are often drier and more frequently thawed in this cold‐climate environment. Comparisons between climate data from a remote meteorological station 45 km to the southwest and sediment transport indices developed from the erosion pin data produced very few correlations significant at the 95 per cent confidence level. Nevertheless, the signs of the correlation coefficients indicate that sediment erosion and deposition in both blowouts respond similarly to the following climate variables recorded at the remote station: (i) the amount of precipitation, (ii) the transport capacity of the wind and (iii) transporting winds from a directional wedge between 180 and 330°. Taken altogether, the results from this study highlight the importance of climate and feedback effects in blowout development that may be extended to other blowouts in continental and coastal settings. Copyright © 2006 John Wiley & Sons, Ltd.

Process–form relationships in Southern Italian badlands: erosion rates and implications for landform evolution

AbstractCharacteristic badlands are incised into Plio‐Pleistocene clays in Basilicata, southern Italy, creating steep, scarp slopes with knife‐edge ridges (calanchi) and small dome‐shaped forms (biancane). Erosion pin data for the period 1997–2003 give mean annual erosion rates for dome‐shaped biancane in the range 9–19 mm a−1, while rates for the calanchi scarps are lower, at 7–10 mm a−1. The erosion pin data also show a non‐linear relationship with slope angle. Maximum erosion rates coincide with a slope angle of 35°, within an envelope defined by combining the theoretical effects of both rainsplash and surface weathering. Monitoring of surface changes and erosion rates for two 0·5 m2 cleared swathes on biancane forms reveals a complex relationship between weathering and erosion. Characteristic forms can develop from large blocks of intact clay bedrock over a time period of less than 30 a. The implications of the measured erosion rates for the landform association of mountain front/pediment/domed inselberg are explored. Copyright © 2005 John Wiley & Sons, Ltd.

Seasonal sand transport through a trough blowout at Pinery Provincial Park, Ontario

Trough blowouts represent transport pathways for sediment through coastal dune systems. This paper documents seasonal differences in sand transport through a trough blowout. Measurements were made by trapping sand in Rosen-style traps installed at the mouth and crest of the parabolic dune and with erosion pins in the throat. Erosion-pin data indicated that the surface of the dune was generally accreting in late summer and eroding in winter, suggesting that the major loss of sediment from the dune was occurring in winter. The traps were emptied every 2–4 weeks and showed that, in general, more sand left the dune system than entered it. The amount of sand transported past the traps at the mouth of the dune varied seasonally, with smaller amounts during the summer months than in winter. The upper traps showed greater variability, but had more sediment transported in all months when compared with the lower traps. Amounts of sand transported during winter were greater than in summer.

Estimating rates of ground retreat on mining spoils using caesium-137

The potential for using the artificial radionuclide caesium-137 to estimate rates of ground retreat on mining spoils is introduced. The 137Cs contents of cores from slope transects on a regraded opencast infill at Waunafon, Gwent are compared with long-term erosion pin measurements from adjacent slopes. The data suggest an inverse relationship between 137Cs inventory and measured ground retreat. Additional measurements from an unvegetated slope indicate that 137Cs depletion is partially explained by topographic factors, particularly slope curvature. Anomalies between the 137Cs measurements, erosion pin data and erosion estimates from a mass balance procedure are discussed. The results suggest that 137Cs measurements may provide an efficient means of obtaining data on erosion rates in mining spoil environments but a number of uncertainties remain to be resolved.