Photo-Electronic Erosion Pin Research Articles

Low amplitude of streambank erosion: distinguishing mass and surface fluvial erosions

The purposes of this manuscript are in two folds e.g.: first, to promote two novel techniques using field-laboratory protocols, each for quantifying surface and mass fluvial erosion, second, to capture and highlight the regime change in the mode of bank erosion from surface to mass fluvial erosion based on real monitoring and measurements on a streambank face. In this study, conduit erosion flume and Photo Electronic Erosion Pin (PEEP) sensor technique were used for monitoring and measuring surface and mass fluvial erosions, respectively. Using those techniques the τ c,sf and τ c,mf , two key parameters which determine the onset of surface and mass fluvial erosion, can be determined successfully. The PEEP sensor can measure the mass fluvial erosion occurred under water, even capture the quasi-continues nature of erosion. More importantly, using these two methods, the presence of two regimes in the low amplitude of bank erosion, e.g. surface fluvial erosion and mass fluvial erosion can be captured. Starting from low to high shear stress, the onset of surface fluvial erosion as well as the transition from surface to mass fluvial erosion can be depicted.

Understanding mass fluvial erosion along a bank profile: using PEEP technology for quantifying retreat lengths and identifying event timing

AbstractThis study provides fundamental examination of mass fluvial erosion along a stream bank by identifying event timing, quantifying retreat lengths, and providing ranges of incipient shear stress for hydraulically driven erosion. Mass fluvial erosion is defined here as the detachment of thin soil layers or conglomerates from the bank face under higher hydraulic shear stresses relative to surface fluvial erosion, or the entrainment of individual grains or aggregates under lower hydraulic shear stresses.We explore the relationship between the two regimes in a representative, US Midwestern stream with semi‐cohesive bank soils, namely Clear Creek, IA. Photo‐Electronic Erosion Pins (PEEPs) provide, for the first time, in situ measurements of mass fluvial erosion retreat lengths during a season. The PEEPs were installed at identical locations where surface fluvial erosion measurements exist for identifying the transition point between the two regimes. This transition is postulated to occur when the applied shear stress surpasses a second threshold, namely the critical shear stress for mass fluvial erosion.We hypothesize that the regimes are intricately related and surface fluvial erosion can facilitate mass fluvial erosion. Selective entrainment of unbound/exposed, mostly silt‐sized particles at low shear stresses over sand‐sized sediment can armor the bank surface, limiting the removal of the underlying soil. The armoring here is enhanced by cementation from the presence of optimal levels of sand and clay. Select studies show that fluvial erosion strength can increase several‐fold when appropriate amounts of sand and clay are mixed and cement together. Hence, soil layers or conglomerates are entrained with higher flows.The critical shear stress for mass fluvial erosion was found to be an order of magnitude higher than that of surface fluvial erosion, and proceeded with higher (approximately 2–4 times) erodibility. The results were well represented by a mechanistic detachment model that captures the two regimes. Copyright © 2017 John Wiley & Sons, Ltd.

Riparian land-use impacts on bank erosion and deposition of an incised stream in north-central Iowa, USA

Stream bank erosion and deposition are complex phenomena because of the many factors that influence them. These factors can be spatial such as bank aspect, height and slope or temporal such as seasonal and yearly precipitation and streamflow events. Riparian land-use also has a major influence. This study investigated for two years, spatial and temporal patterns and dominant geomorphologic processes of stream bank erosion and deposition along a 10km reach of Bear Creek in north-central Iowa, USA. The channel sub-reaches used were adjacent to a riparian forest buffer, a perennial grass filter and a continuously grazed pasture. Two plots were placed in each sub-reach; one on a north-facing outside bank (north-bank) and the other on a south-facing outside bank (south-bank). Each plot had two photo-electronic erosion pins (PEEPs) placed at 1/3 of the bank height (bottom-bank) and the other at 2/3 of the bank height (top-bank). PEEP daily measurements were compared to daily precipitation and streamflow. The continuously grazed pasture banks had the highest erosion rates. The grass area banks had approximately equal rates of erosion and deposition. The riparian forest buffer banks had high erosion rates during the second year. In the continuously grazed pasture, fluvial entrainment was the dominant erosion process, although minor mass failures also caused erosion. In the riparian forest buffer most erosion was recorded after moderate streamflows removed the bank soil loosened by freeze–thaw cycling. This occurred in late winter/early spring, when trees provide primarily mechanical but not hydraulic reinforcement to stream banks and on the lower part of the banks that have less extensive root networks. Overall, stream bank erosion and deposition in each sub-reach occurred during different time periods and under different processes and conditions. This indicates the need for continuous erosion and deposition measurements along with continuous soil moisture, soil temperature and streamflow measurements to fully comprehend these erosion phenomena.

Using Photo-Electronic Erosion Pins for Measuring Bed Elevation Changes in the Swash Zone

Abstract Photo-Electronic Erosion Pins (PEEPs) can be used to measure short-term fluctuations in swash zone (foreshore) profiles. Because the sensors depend upon ambient light for the detection of bed elevation change, their signal indicates false changes during swash inundation. A method is presented to mitigate this source of noise and to allow a reconstruction of bed changes at swash frequencies. The protocol is illustrated with a sample data set.

Advances in the continuous monitoring of erosion and deposition dynamics: Developments and applications of the new PEEP-3T system

In most episodic erosion and deposition systems, knowledge of the timing of geomorphological change, in relation to fluctuations in the driving forces, is crucial to strong erosion process inference, and model building, validation and development. A challenge for geomorphology, however, is that few studies have focused on geomorphological event structure (timing, magnitude, frequency and duration of individual erosion and deposition events), in relation to applied stresses, because of the absence of key monitoring methodologies. This paper therefore (a) presents full details of a new erosion and deposition measurement system — PEEP-3T — developed from the Photo-Electronic Erosion Pin sensor in five key areas, including the addition of nocturnal monitoring through the integration of the Thermal Consonance Timing (TCT) concept, to produce a continuous sensing system; (b) presents novel high-resolution datasets from the redesigned PEEP-3T system for river bank system of the Rivers Nidd and Wharfe, northern England, UK; and (c) comments on their potential for wider application throughout geomorphology to address these key measurement challenges. Relative to manual methods of erosion and deposition quantification, continuous PEEP-3T methodologies increase the temporal resolution of erosion/deposition event detection by more than three orders of magnitude (better than 1-second resolution if required), and this facility can significantly enhance process inference. Results show that river banks are highly dynamic thermally and respond quickly to radiation inputs. Data on bank retreat timing, fixed with PEEP-3T TCT evidence, confirmed that they were significantly delayed up to 55 h after flood peaks. One event occurred 13 h after emergence from the flow. This suggests that mass failure processes rather than fluid entrainment dominated the system. It is also shown how, by integrating turbidity instrumentation with TCT ideas, linkages between sediment supply and sediment flux can be forged at event timescales, and a lack of sediment exhaustion was evident here. Five challenges for wider geomorphological process investigation are discussed. This event-based dynamics approach, based on continuous monitoring methodologies, appears to have considerable wider potential for stronger process inference and model testing and validation in many areas of geomorphology.

The importance of high-resolution monitoring in erosion and deposition dynamics studies: examples from estuarine and fluvial systems

Erosion and deposition processes lie at the centre of geomorphological explanation, but progress in understanding has been limited by a lack of appropriate high-resolution monitoring methodologies which permit detection of erosion and deposition dynamics. This paper presents a case for monitoring erosion and deposition at high temporal resolutions, and uses hypothetical approaches supported by example erosion and deposition events and analyses drawn from estuarine and fluvial systems. The paper first presents testable hypotheses to demonstrate the complexity of possible event combinations, sequences and juxtapositions for the erosion driving forces which underpin the need for high-resolution monitoring. Second, it summarises recent improvements to the Photo-Electronic Erosion Pin (PEEP) automatic erosion and deposition monitoring system, including the novel concept of Thermal Consonance Timing (TCT), which is particularly promising because it helps to define the timing of nocturnal events and through the entire hydrograph. Third, example results are discussed from high-resolution monitoring of bank erosion at a tidal site at Burringham on the River Trent in northern England. Tidal banks are revealed to be much more dynamic than previous conventional monitoring has indicated. A key result is that, because the high-resolution approach allows erosional and depositional activity to be assigned to specific periods of tidal inundation, it becomes possible for the first time routinely to produce ‘event-based’ erosion (36 mm h −1) and deposition rates (4.5 and 8.4 mm h −1). Such rate determinations are potentially very useful in the field validation of sedimentological and geomorphological models, including grain settling and resuspension theory. Fourth, through a longer term of aggregated daily data, a striking 2-week cycle of deposition and erosion emerges which correlates most strongly with spring-neap tidal cycling, but is moderated by wind stress effects. Sediment was deposited on the bank relatively quickly, over 4–5 days, but then removed by erosion rather slowly, over 9–10 days. Fifth, the dangers of low-resolution monitoring are illustrated by comparing the daily PEEP data set with a series resampled at a lower (14-day) frequency, to simulate the information generated by conventional resurvey methodologies. The low-frequency series failed adequately to represent the cyclicity, mean, range, variability and trend of bank elevation changes, and without this dynamics information, rate and process definition is very difficult, largely because of self-concealing activity. Sixth, a useful advance is illustrated by the fluvial erosion sequence for the River Wharfe (N. England). This shows how TCT can generate rare and important results with the definition of the precise time of an erosion event within the hydrograph: bank retreat here occurred very quickly, after initial inundation, and within 4 h of the flow peak-information which can be used to define thresholds for entrainment (e.g. critical shear stresses). Such high-resolution monitoring helps to unravel some of the erosional effects of complex sequences, combinations and juxtapositions of similar or different forcing events. Finally, high-resolution approaches have been adopted worldwide for fluvial, estuarine, mudflat and canal systems, but considerable potential exists for their development and use in these and other contexts (e.g. gully, hillslope, beach and dune environments), to improve understanding and modelling of geomorphological processes more widely.

Measuring sediment exchange rates on an intertidal bank at Blacktoft, Humber Estuary, UK

Results from a suite of Photo Electronic Erosion Pins (PEEPs) and manual pins installed on an intertidal bank at Blacktoft, near the confluence of the Rivers Trent and (Yorkshire) Ouse, UK are presented for summer 1997 (1 May–28 September). These reveal a pattern of erosion and deposition, which can be related to variations in tidal range, freshwater flow and wind speed over the period. During spring tides, greater resuspension of bed sediment leads to a greater availability of sediment in the water column for deposition on the bank. High wind speeds cause greater erosion of material from the bank due to wind-induced wave action. These processes of sediment exchange are also modified by the effects of biological activity on the sediment and of consolidation. It was demonstrated that the mean daily change in elevation of the upper part of the bank at Blacktoft was approximately 11 mm, which is two–three-fold less than the equivalent figure measured by a similar method at Burringham on the River Trent. It is thought that this difference is due to the effects of a greater concentration of suspended sediment settling onto the banks at Burringham, which are also subject to greater erosion due to their steeper slope. Results from a longer and more widespread survey of eight other intertidal banks in the Trent–Ouse Estuary system suggest that deposition and erosion occur in phase on all intertidal banks within the study area. Intertidal banks towards the upstream end of the system show much less variation in bank level than those further downstream.

Application of a Novel Automatic Erosion and Deposition Monitoring System at a Channel Bank Site on the Tidal River Trent, U.K.

There is a well-defined need to improve understanding of the dynamics of sediment erosion and deposition on intertidal channel banks, given their importance to channel stability, sediment budgets, depth maintenance, pollutant and nutrient transport, and ecological processes in estuarine systems. Conventional, manual methods for field monitoring of erosion and deposition, however, normally deliver information of low temporal resolution conditioned by infrequent field resurveys. To address this problem, this paper discusses a recently developed and improved automatic erosion and deposition monitoring technique, the Photo-Electronic Erosion Pin (PEEP) system, and its application to a tidal channel bank site at Burringham on the River Trent, U.K. The PEEP system allows the magnitude, frequency and timing of individual erosion and deposition events to be monitored much more precisely than with conventional manual methods. PEEP sensors also monitor light intensity and sediment temperature, variables which can influence bank stabilizing and destabilizing processes. Example results at both the event and spring-neap timescales are presented from a short PEEP system deployment between March and May 1997 at Burringham. These establish that discrete erosion events of >60mm and 100mm can occur in response to individual tidal cycles, events which are readily monitored automatically and quasicontinuously by the PEEP system. The capability of the PEEP approach to enhance temporal resolution of monitoring is demonstrated by the determination of the timing of the 100-mm bank erosion incident to an ‘event window’ of 2·75h: this converts to mean bank erosion rate of 36mm h−1over the period of inundation. In addition, the PEEP system defines the magnitude and date of two example deposition events of 47 and 92mm on the lower bank during a sequence of rising spring tides. These represent mean deposition rates of 4·5 and 8·4mm h−1respectively over the periods of inundation. The Burringham site is shown to be highly active, with regular and dynamic erosion and deposition cycles. Upper bank surface elevation oscillations, driven by this sediment cycling, were characterized by a strong 14-day cycle which clearly reflected the spring-neap cycling of tidal range. Sediment was deposited on the bank relatively quickly, but removed by erosion rather slowly, giving an asymmetric sediment cycling profile. Higher bank elevations were strongly correlated with high tidal ranges, and especially to water level peaks 2 days previously. Incorporation of a simple Wind Stress Index further improved the statistical explanation of tidal bank elevation, and suggested that high on-shore wind speeds were associated with increased bank erosion. Such vigorous sediment cycling means that many erosion-deposition sequences on tidal banks can be self-concealing and therefore may not be recorded by infrequent manual resurveys which will inevitably underestimate total activity. This reinforces the need for an automated method such as the PEEP system to determine these typically cyclic sequences of self-cancelling accretion and removal activity if site dynamism is to be correctly quantified. The ability of the PEEP approach to generate such detailed and high-resolution information on the temporal distribution of erosion and deposition events in tidal environments should significantly enhance future process and applied studies, especially of entrainment thresholds, sediment recycling, estuarine sediment supply and sediment fluxes, the operation of biomediation mechanisms, bank erodibility changes, storage and residence times of contaminants and site management options.

Bank erosion of an incised upland channel by subaerial processes: Tasmania, Australia

The headwaters of many rivers are characterized by gullies and incised streams that generate significant volumes of sediment and degrade downstream water quality. These systems are characterized by harsh climates, ephemeral flows that do not reach bank top, and bare cohesive banks of clay and weathered bedrock. We investigated the rates and processes of bank erosion in an incised canal that has such characteristics. Detailed measurements of bank position were made over two years with a purpose-built groundprofiler and photo-electronic erosion pins (PEEPs). Stage height and turbidity were also monitored. The bare banks eroded at 13 ± 2 mm a−1. Erosion is controlled by subaerial processes that loosen bank material. Observations show that needle-ice growth is important in winter and desiccation of clays predominates in summer. Flows are unable to erode firm cohesive clays from the banks, and erosion is generally limited by the availability of loosened material. This produces strong hysteresis in turbidity during events. Peak turbidity is related to the number of days with low flow between events, and not peak stage. Rehabilitation with a moderate cover of grass is able to prevent bank erosion by limiting the subaerial erosion processes. Projections of current erosion suggest that without vegetation cover the banks are unlikely to stabilize for many years. Copyright © 2000 John Wiley & Sons, Ltd.

Bank erosion of an incised upland channel by subaerial processes: Tasmania, Australia

The headwaters of many rivers are characterized by gullies and incised streams that generate significant volumes of sediment and degrade downstream water quality. These systems are characterized by harsh climates, ephemeral flows that do not reach bank top, and bare cohesive banks of clay and weathered bedrock. We investigated the rates and processes of bank erosion in an incised canal that has such characteristics. Detailed measurements of bank position were made over two years with a purpose-built groundprofiler and photo-electronic erosion pins (PEEPs). Stage height and turbidity were also monitored. The bare banks eroded at 13 ± 2 mm a-1. Erosion is controlled by subaerial processes that loosen bank material. Observations show that needle-ice growth is important in winter and desiccation of clays predominates in summer. Flows are unable to erode firm cohesive clays from the banks, and erosion is generally limited by the availability of loosened material. This produces strong hysteresis in turbidity during events. Peak turbidity is related to the number of days with low flow between events, and not peak stage. Rehabilitation with a moderate cover of grass is able to prevent bank erosion by limiting the subaerial erosion processes. Projections of current erosion suggest that without vegetation cover the banks are unlikely to stabilize for many years. Copyright (C) 2000 John Wiley and Sons, Ltd.

Dynamics of erosion and deposition events on an intertidal mudbank at Burringham, River Trent, UK

Measurements using an automatic bank level monitoring technique [the photoelectronic erosion pin (PEEP) system] over a 70-day period between 16 March and 27 May 1997 have revealed a complex pattern of erosion and deposition on an intertidal mudbank on the River Trent at Burringham. Comparison of mean daily changes in bank elevation at upper and lower bank positions suggest that wave activity induced by high wind speeds causes erosion, while high tidal range leads to deposition as a result of higher suspended solids concentrations. A greater variability in mean daily erosion and deposition events at the lower bank compared with the upper bank appears to indicate that higher bed shear stresses, as well as a greater availability of sediment for settling, owing to higher concentrations and a greater depth of water, lead to a more dynamic exchange of material at this position. The PEEP data also show longer term trends in sedimentation, with the mean deposition for the period exceeding mean erosion. Manual erosion pin measurements at a lower frequency over a longer, seven-month period confirm this, and also highlight the advantage of the PEEP system in monitoring events at a finer temporal resolution. Copyright © 1999 John Wiley & Sons, Ltd.

Cohesive Sediment Dynamics on an Inter-tidal Bank on the Tidal Trent, UK

This paper uses Photo-Electronic Erosion Pin (PEEP) data and measurements of sediment dynamics on an active inter-tidal bank to determine the significance of changes in tidal range, sediment availability and meteorological conditions on sediment accretion and erosion. The results show how sediment accumulates on the upper bank at a rate of up to 50 mm per tide in response to increased suspended sediment concentrations during spring tides. However, sedimentary processes differ on the lower bank as deposition occurs approaching spring tides, only to be eroded by high boundary shear stresses generated by the flow as tidal range increases to a maximum. Erosion from the upper bank appears to be dominated by wind-induced wave activity which destabilises the transient, active sediment layer. These results have implications for evaluating the behaviour and residence times of sediment and pollutants within the estuarine system, the impact of the turbidity maximum on the recirculation of sedimentary deposits, and the significance of wave activity on erosion processes in inter-tidal zones.

Magnitude and variation in the contribution of bank erosion to the suspended sediment load of the River Severn, UK

The wide range of studies describing the role of bank erosion in fluvial sediment supply have mostly lumped amounts of bank erosion into coarse temporal units, such as years. This paper investigates sediment yields from individual bank erosion events within the upper River Severn, UK (basin area 380 km2). Manual erosion pins and photo-electronic erosion pins were used to estimate bank erosion, and turbidity meters were used to determine suspended sediment transport. At the annual time-scale, the silt-clay fraction of bank-derived sediment accounted for an equivalent of 17 per cent of the suspended load, increasing to an average of 38 per cent at the monthly timescale, and then to an average of 64 per cent at the event timescale. This research highlighted that for an upland catchment, bank erosion was an important supply of suspended sediment, and that for some flood events bank erosion can supply more sediment than is transported. © 1997 John Wiley & Sons, Ltd.

Bank erosion events and processes in the Upper Severn basin

Abstract. This paper examines river bank retreat rates, individual erosion events, and the processes that drive them in the Upper Severn basin, mid-Wales, UK. Traditional erosion pin networks were used to deliver information on patterns of downstream change in erosion rates. In addition, the novel automatic Photo-Electronic Erosion Pin (PEEP) monitoring system was deployed to generate near-continuous data on the temporal distribution of bank erosion and accretion: this allowed focus on the magnitude and timing of individual erosional and depositional events in relation to specific flow episodes. Erosion dynamics data from throughout the Upper Severn basin are combined with detailed information on bank material properties and spatial change in channel hydraulics derived from direct field survey, to assess the relationships between flow properties and bank erosion rates. Results show that bank erosion rates generally increase downstream, but relate more strongly to discharge than to reach-mean shear stress, which peaks near the basin head. Downstream changes in erosion mechanisms and boundary materials, across the upland/lowland transition (especially the degree of development of composite bank material profiles), are especially significant. Examples of sequences of bank erosion events show how the PEEP system can (a) quantify the impact of individual, rather than aggregated, forcing events, (b) reveal the full complexity of bank response to given driving agents, including delayed erosion events, and (c) establish hypotheses of process-control in bank erosion systems. These findings have important implications for the way in which bank erosion problems are researched and managed. The complex responses demonstrated have special significance for the way in which bank processes and channel-margin sediment injections should be handled in river dynamics models.

Design and installation of a novel automatic erosion monitoring system

AbstractProcess inference in geomorphology is hindered by a lack of information on the true temporal distribution of contemporary erosional and depositional activity. To tackle this problem a low‐cost, automatic monitoring system based on the photo‐electronic erosion pin (PEEP) sensor has been developed. The PEEP is essentially an array of photosensitive cells enclosed within a transparent tube and connected by cable to a datalogger. When inserted into an eroding landform, subsequent retreat of the face exposes more photosensitive cells to light which increases PEEP voltage output. Deposition decreases sensor outputs. The logged signals thus reveal the magnitude, timing and frequency of erosion and deposition events with much greater precision than has hitherto been possible. Measurement principles, electronic and physical design, calibration, field installation, problems and prospects and pilot results from a river bank erosion site are discussed. The PEEP system appears to have great potential for disentangling competing hypotheses in geomorphological process studies, and in building and testing erosion and sediment transport models of high temporal resolution.

A New Technique for the Automatic Monitoring of Erosion and Deposition Rates

The rates and processes of erosion and deposition of soils and sediments are subjects of widespread and increasing concern in the Earth and environmental sciences. Process inference from field studies, however, has been hampered by a lack of information on the precise magnitude, frequency and timing of erosional and depositional activity, because noautomaticmonitoring technique has hitherto been available. I describe here an automatic Photo‐Electronic Erosion Pin (PEEP) system which, apparently for the first time, allows quasi‐continuous time series of erosion and deposition data to be collected. Example results from a river bank site show how the PEEP system helps to define the true temporal distribution of geomorphological change, quantify the erosional impact of individual forcing events, and discriminate between competing hypotheses of process control in erosional and depositional contexts. The system should thus allow more effective testing of erosion models of high temporal resolution and facilitate a more rigorous linking of catchment sediment output to supply dynamics.