Streambank Erosion Research Articles

The effect of piping stream channels on dissolved oxygen concentration and ecological health.

Sunlight plays a key role in the nutrient cycle within streams. Streams are often piped to accommodate urban residential or commercial development for buildings, roads, and parking. This results in altered exposure to sunlight, air, and soil, subsequently affecting the growth of aquatic vegetation, reducing reaeration, and thus impairing the water quality and ecological health of streams. While the effects of urbanization on urban streams, including changing flow regimes, stream bank and bed erosion, and degraded water quality, are well understood, the effects of piping streams on dissolved oxygen (DO) concentrations, fish habitats, reaeration, photosynthesis, and respiration rates are not. We addressed this research gap by assessing the effects of stream piping on DO concentrations before and after a 565-m piped section of Stroubles Creek in Blacksburg, VA, for several days during the summer of 2021. Results indicate that the DO level decreased by approximately 18.5% during daylight hours as water flowed through the piped section of the creek. Given the optimum DO level (9.0mg·L-1) for brook trout (Salvelinus sp.), which are native and present in a portion of Stroubles Creek, the resulting DO deficits were - 0.49 and - 1.24mg·L-1, for the inlet and outlet, respectively, indicating a possible adverse impact from piping the stream on trout habitat. Photosynthesis and respiration rates were reduced through the piped section, primarily due to the reduced solar radiation and the resultant reduction in oxygen production from aquatic vegetation; however, the reaeration rate increased. This study can inform watershed restoration efforts, particularly decisions regarding stream daylighting with respect to potential water quality and aquatic habitat benefits.

Climate change impacts on erosion and suspended sediment loads in New Zealand

Soil is a critical resource that provides many ecosystem services and is highly valued by indigenous cultures as key for supporting essential human needs. Land degradation processes such as erosion are depleting soil resources while increased sediment loads impact downstream receiving environments, with compounding effects due to land use and climate change. Models are required to estimate the magnitude and extent of climate impacts on soil erosion and sediment loads at national scale for policymakers and catchment managers to assess the future effectiveness and feasibility of policies and mitigation plans, and to prioritise mitigation efforts. Commonly used soil erosion and sediment load models are often unable to represent the diversity of erosion processes and the future trajectory of their hydroclimatic drivers at such scales. We present a modelling framework that estimates suspended sediment load contributions from three predominant erosion processes: mass movement, surficial erosion, and streambank erosion within their respective spatial erosion domains by differencing models of surficial erosion and total load within the domains. We estimate how catchment suspended sediment loads may change under future climate using change factors derived from the main hydroclimatic driver of each erosion process. Applying this framework at national scale for Aotearoa New Zealand, we demonstrate a disproportionate increase in mass movement erosion expected in soft-rock hill country, with <1–28 % of North Island watersheds and <1–8 % of South Island watersheds estimated to experience a 100 % increase in sediment yield by end-century, primarily driven by the impact of increasing storm magnitude-frequency on mass movement erosion. This results in regional increases in sediment load delivered to the coast ranging from 1 to 233 %. Our results highlight the need for policymakers and catchment managers to recognise spatial variations in the response of erosion processes and catchment loads to climate change when developing policy and prioritising mitigation efforts, as combating future erosion may require different methods to those used in contemporary management to achieve catchment objectives.

Streambank Erosion Phenomena and Understanding: Current Research and Future Directions

Highlights High rates of streambank erosion are detrimental to the stability and function of streams. This collection brings together six studies that represent key advances in streambank erosion research. Current research directions on streambank erosion, erodibility characterization, and sediment loading are presented. Future research directions and challenges related to high-frequency data collection and modeling are discussed. Abstract. Streams are in dynamic equilibrium with their environments, and as that environment is altered by human development and changing climate, streambank erosion is a common, but little understood, result. This article highlights the contributions of the special collection “Streambank Erosion, Sediment Dynamics, and Restoration (SER),” which assembled six studies that represent key advances in streambank erosion research, highlight current research in the field, and identify directions for future research. The studies in this special collection were grouped into three central themes: (1) streambank erosion monitoring, (2) streambank erodibility characterization, and (3) streambank erosion loading. In this article, key findings within each of these central themes are summarized, emphasizing the significant contributions of each study. Likewise, perspectives on future research directions are discussed, outlining important challenges that remain to be addressed. Overall, the studies in this special collection are unified in their overarching goal of improving quantitative and predictive understanding of streambank erosion phenomena. Keywords: Keywords., Erodibility Parameters, Jet Erosion Test, Monitoring, Sediment, Soil Erosion, Stabilization Practices, Streambank, Stream Restoration.

Crystal lattice defects in nanocrystalline metacinnabar in contaminated streambank soils suggest a role for biogenic sulfides in the formation of mercury sulfide phases.

At mercury (Hg)-contaminated sites, streambank erosion can act as a main mobilizer of Hg into nearby waterbodies. Once deposited into the waters, mercury from these soils can be transformed to MeHg by microorganisms. It is therefore important to understand the solid-phase speciation of Hg in streambanks as differences in Hg speciation will have implications for Hg transport and bioavailability. In this study, we characterized Hg solid phases in Hg-contaminated soils (100-1100 mg per kg Hg) collected from the incised bank of the East Fork Poplar Creek (EFPC) in Oak Ridge, TN (USA). The analysis of the soil samples by scanning electron microscopy-energy dispersive spectroscopy indicated numerous microenvironments where Hg and sulfur (S) are co-located. According to bulk soil analyses by extended X-ray absorption fine structure spectroscopy (EXAFS), the near-neighbor Hg molecular coordination in the soils closely resembled freshly precipitated Hg sulfide (metacinnabar, HgS); however, EXAFS fits indicated the Hg in the HgS structure was undercoordinated with respect to crystalline metacinnabar. This undercoordination of Hg-S observed by spectroscopy is consistent with transmission electron microspy images showing the presence of nanocrystallites with structural defects (twinning, stacking faults, dislocations) in individual HgS-bearing particles. Although the soils were collected from exposed parts of the stream bank (i.e., open to the atmosphere), the presence of reduced forms of S and sulfate-reducing microbes suggests that biogenic sulfides promote the formation of HgS nanoparticles in these soils. Altogether, these data demonstrate the predominance of nanoparticulate HgS with crystal lattice defects in the bank soils of an industrially impacted stream. Efforts to predict the mobilization and bioavailability of Hg associated with nano-HgS forms should consider the impact of nanocrystalline lattice defects on particle surface reactivity, including Hg dissolution rates and bioavailability on Hg fate and transformations.

Stream corridor and upland sources of fluvial sediment and phosphorus from a mixed urban-agricultural tributary to the Great Lakes

Like many impaired Great Lakes tributaries, Apple Creek, Wisconsin (119 km2) has Total Maximum Daily Load (TMDL) targets for reducing suspended sediment and total phosphorus by 51.2 % and 64.2 %, respectively. From August 2017 - October 2018, a stream sediment budget and fingerprinting integrated study was conducted to quantify upland and stream corridor sources of suspended sediment and sediment-bound phosphorus. Phosphorus concentrations varied among source groups and fluvial sediments, with higher concentrations among suspended sediment and cropland soils. Eroding streambanks identified in the stream corridor sediment budget accounted for 100 % of the TMDL Soil and Water Assessment Tool (SWAT) suspended sediment load but only 20 % of the total phosphorus load. Fine-grained streambed sediment equated to approximately-three years of modeled suspended sediment load but only one third of total phosphorus load. The two primary sources of fine-grained streambed sediment were streambanks and cropland, with relative streambank contributions increasing with downstream direction and watershed area. The relative proportion of suspended sediment varied by season and streamflow; however, cropland and streambank erosion accounted for 54 % and 23 % of the suspended sediment when weighted by of the proportion for representative streamflow. Urban land was a source in the upper watershed, but the signature was sequestered by a mid-watershed detention basin. Contributions from construction sites were higher in the fall 2018, likely corresponding to increased activity following a wet spring. These integrated techniques helped describe sources, transport, and sinks of fluvial sediment and phosphorus throughout the watershed at a range of spatial and temporal scales.

Supporting proactive planning for climate change adaptation and conservation using an attributed road-river structure dataset

Freshwater species and their habitats, and transportation networks are at heightened risk from changing climate and are priorities for adaptation, with the sheer abundance and individuality of road-river structures complicating mitigation efforts. We present a new spatial dataset of road-river structures attributed as culverts, bridges, or fords, and use this along with data on gradient and stream order to estimate structure sensitivity and exposure in and out of special areas of conservation (SAC) and built-up areas to determine vulnerability to damage across river catchments in Wales, UK. We then assess hazard of flooding likelihood at the most vulnerable structures to determine those posing high risk of impact on roads and river-obligate species (fishes and mussels) whose persistence depends on aquatic habitat connectivity. Over 5% (624/11,680) of structures are high vulnerability and located where flooding hazard is highest, posing high risk of impact to roads and river-obligate species. We assess reliability of our approach through an on-ground survey in a river catchment supporting an SAC and more than 40% (n = 255) of high-risk structures, and show that of the subset surveyed >50% had obvious physical degradation, streambank erosion, and scouring. Our findings help us to better understand which structures pose high-risk of impact to river-obligate species and humans with increased flooding likelihood.

An integrated assessment of land use impact, riparian vegetation and lithologic variation on streambank stability in a peri-urban watershed (Nigeria)

Bank erosion is an important source of sediment and phosphorus to inland fluvial systems and is generally responsible for more than half of the total watershed sediment export. Numerous studies have quantified bank erosion and the spatio-temporal variation of sediment flux in different watersheds. However, there is sparse research to date on the linkages between bank erosion/accretion and sediment export under different land uses, especially in rapidly evolving peri-urban watersheds. This research, therefore, integrated remote sensing techniques and repeated field survey of erosion pin plots to quantify bank erosion and sediment flux in the 80 km2 Nkisi River watershed (NRW), southeast Nigeria, over a three-year period. The impact of land use change on streambank erosion was evaluated by utilising remotely sensed Landsat datasets of 2003, 2010, 2016 and 2019. Geotechnical tests were used to characterise the lithologic properties of the banks, while the Bank Stability and Toe Erosion Model (BSTEM) was used to determine the stability of the banks under various hydrological conditions and mechanical properties of the riparian vegetation. Mean bank recession rates increased from 10.7 cm during the 2017–2018 monitoring period to 17.5 cm for the 2019–2020 monitoring period. The percentage of total watershed export ascribed to bank erosion in the three stream reaches varied from 6.6 to 44.9%. The high rates of bank erosion and accretion within the NRW were attributed to rapid changes in land use, which evolved from grassland and woodland to cropland, built-up and bare land. The BSTEM accurately predicted the high erosion rates of the streambanks and showed that riparian vegetation has a mechanical effect on bank stability. However, the mechanical effect diminishes as the depth to water table rises during high streamflow events.

Transaction costs for collaboration in the watershed management of the Cuyahoga River Area of Concern

This study examines the transaction costs of collaborative watershed management in the Cuyahoga River Area of Concern (AOC)—one of the 43 geographic areas designated by the U.S. and Canada Great Lakes Water Quality Agreement (GLWQA), where significant impairment of beneficial uses has occurred as a result of human activities. The Cuyahoga River is located in Northeast Ohio, the U. S. and flows through the City of Cleveland before draining into Lake Erie—one of the five Great Lakes of North America. The watershed is degraded due to municipal and agricultural discharges, streambank erosion, and contamination from urban and industrial sources. This research explores how a diverse group of stakeholders convened under the Cuyahoga River AOC Advisory Committee to share information, coordinate activities, agree on activities that restore beneficial uses, and support strategic management actions. In this study, 23 semi-structured interviews with members of the advisory committee were conducted between January 28, 2020 and April 20, 2020, with follow-up emails and phone calls as needed to corroborate information. A review of research articles and government documents supported the interviews, including United States Environmental Protection Agency (U.S. EPA) and Ohio Environment Production Agency (OEPA) reports on the GLWQA and Cuyahoga River Remedial Action Plans. A third source of data is from direct participant observation at quarterly meetings of the advisory committee during 2017–2020, binational AOC conferences in 2017 and 2019, and other professional events geared towards restoring the Cuyahoga River AOC in 2016–2020. Results help to explain the collaborative process within the advisory committee and measure the institutional performance of the advisory committee in terms of efficiency, equitability, accountability, and adaptability. Results of this study include a set of recommendations to help guide group structure and decision-making processes, including (1) employing best available technology to organize AOC events and disseminate information; (2) supporting new members with an orientation and/or mentor to clearly define formal and informal committee rules; (3) assuring equal access to detailed information on management action plans with a real time dashboard; (4) updating voting procedures and the prioritization of management actions; and (5) better incorporating underrepresented local communities and high-level decision makers from municipalities, government agencies, and nongovernmental organizations located within the Cuyahoga River AOC.

Soil Amended With Organic Matter Increases Fluvial Erosion Resistance of Cohesive Streambank Soil

AbstractFluvial erosion of cohesive soil is mediated by interactions between soil physical, biological, and chemical characteristics such as soil aggregate stability and extracellular polymeric substances (EPS). While labile organic matter (OM) stimulates microbial EPS production and significantly improves soil aggregate stability in agricultural soils, these interactions remain unexplored in streambank soils. The study goal was to quantify the impact of OM on aggregate stability, EPS, and fluvial erosion rates of cohesive streambank soil. Increasing amounts of 1‐mm sieved dry grass were incorporated at rates of 0, 1, and 4 g per 100 g of 2‐mm sieved silt‐loam soil (treatments T0, T1, and T4, respectively). Samples (eight replicates per treatment) were matured in a greenhouse for 50 days prior to flume erosion testing. EPS carbohydrates were significantly (p &lt; 0.05) lower in T1 (324 ± 63 μg/g) compared to T0 (388 ± 37 μg/g) and T4 (376 ± 44 μg/g). EPS proteins were significantly higher in T1 (194 ± 15 μg/g) and T4 (223 ± 61 μg/g) compared to T0 (101 ± 20 μg/g) and positively correlated with mean weight diameter (MWD), a measure of soil stability against slaking. MWD was 16% and over 100% higher for T1 and T4, respectively, than for T0. Similarly, the average soil erodibility coefficient of T1 and T4 was 25% and 61% lower than the erodibility of T0; however, only the reduction for T4 was significant. The data presented here underscore the important role labile OM plays in improving soil physical stability and increasing the resistance of cohesive soil to fluvial erosion of streambanks.

Failure modes in cedar tree revetments: Observations on rivers and streams in eastern Kansas, USA

AbstractA cedar tree revetment is a bioengineering technique intended to stabilize eroding stream banks using longitudinally placed cedar trees. This technique, which has been implemented on many rivers and streams across the United States, has been proposed as a less expensive, ecologically compatible bank stabilization method. The limited documentation of these types of bioengineering techniques indicates high failure rates. River engineers need to understand the potential failure modes of cedar tree revetments, so they can take appropriate countermeasures when applying this technique. This article documents four common failure modes observed during post‐project site assessments on 12 streams in eastern Kansas, USA that took place in 2019 and 2020. These modes are (1) bed degradation with structure perching, (2) failure in flexion, (3) loose cables, and (4) lack of sediment infilling. Computed factors of safety for top of bank discharge range from 0.3 to 6.0 in flexion (bending stress vs. strength) and range from 1.7 to 40.1 for anchor forces vs. anchor strength. These factors of safety suggest that failure in flexion is an important failure mechanism that should be considered and mitigated during design of cedar tree revetments. Moreover, failure rate varies directly with project age. The authors hypothesize that progressive processes such as breaking of bankside branches may cause loose cables and cyclical loading and wetting/drying may lower the bending strength of the trees over time. Avoiding degrading streams, additional anchoring, and trimming the bank‐side branches of the cedar trees are suggested as means to reduce these types of failures.

Streambank and floodplain geomorphic change and contribution to watershed material budgets

Stream geomorphic change is highly spatially variable but critical to landform evolution, human infrastructure, habitat, and watershed pollutant transport. However, measurements and process models of streambank erosion and floodplain deposition and resulting sediment fluxes are currently insufficient to predict these rates in all perennial streams over large regions. Here we measured long-term lateral streambank and vertical floodplain change and sediment fluxes using dendrogeomorphology in streams around the U.S. Mid-Atlantic, and then statistically modeled and extrapolated these rates to all 74 133 perennial, nontidal streams in the region using watershed- and reach-scale predictors. Measured long-term rates of streambank erosion and floodplain deposition were highly spatially variable across the landscape from the mountains to the coast. Random Forest regression identified that geomorphic change and resulting fluxes of sediment and nutrients, for both streambank and floodplain, were most influenced by urban and agricultural land use and the drainage area of the upstream watershed. Modeled rates for headwater streams were net erosional whereas downstream reaches were on average net depositional, leading to regional cumulative sediment loads from streambank erosion (−5.1 Tg yr−1) being nearly balanced by floodplain deposition (+5.3 Tg yr−1). Geomorphic changes in stream valleys had substantial influence on watershed sediment, phosphorus, carbon, and nitrogen budgets in comparison to existing predictions of upland erosion and delivery to streams and of downstream sediment loading. The unprecedented scale of these novel findings provides important insights into the balance of erosion and deposition in streams within disturbed landscapes and the importance of geomorphic change to stream water quality and carbon sequestration, and provides vital understanding for targeting management actions to restore watersheds.

Extreme precipitation-based vulnerability assessment of road-crossing drainage structures in forested watersheds using an integrated environmental modeling approach

The goal of this study is to develop geospatial-hydrology models incorporating design rainfall intensities and land morphologic features to identify erosion hazards and vulnerability risks to road culverts/stream crossings in three watersheds at USDA Forest Service long-term experimental forests: i) Coweeta Hydrologic Laboratory, NC, ii) Santee Experimental Forest, SC, and iii) Alum Creek Experimental Forest, AR. These models developed in an ArcGIS ModelBuilder platform were: i) Streambank Erosion Vulnerability Assessment (SBEVA) and ii) Modified Revised Universal Soil Loss Equation (MODIFIED-RUSLE) for potential erosion and streambank vulnerability estimation. The SBEVA model, developed using a Delphi-based weighted-probability scale, and MODIFIED-RUSLE were integrated to identify locations of culverts/stream-crossings morphologically vulnerable to erosion and scouring, which were ground-truthed for the SC site only. As the MODIFIED-RUSLE model does not assess streambank erosion, its integration with the SBEVA helps to develop a better decision-support tool for relevant agencies for safeguarding these road culverts/stream crossings.

History of slope instability in the Oldina plantation, Tasmania

Background: This paper describes a landslide swarm generated by exceptionally high two-day rainfall (c. 300 mm) associated with a stationary cut-off low pressure system over northern Tasmania in early June 2016 and investigates evidence for previous slope instability. The landslide swarm occurred in a recently harvested plantation in the Inglis River catchment at Oldina, south of Wynyard in north-west Tasmania. Within a relatively small area of plantation underlain by weathered Permian tillite and minor siltstones more than thirty rapid earthflows, rotational and translational landslides occurred. Many landslides also occurred in the nearby Forth and Mersey River catchments. Methods: Field observations combined with a digital elevation model produced from high-resolution drone imagery were used to describe the morphology of the Oldina landslides, and to calculate the mass of soil, sediment, and woody debris displaced. Radiocarbon dating of charcoal exposed in landslide backwalls enabled palaeo-landslides and periglacial activity at Oldina to be dated. Results: An estimated 48,400–72,310 t of soil, sediment and woody debris was carried downslope by the major landslides but has been retained within the plantation area. The total sediment loss from the affected upper catchments is likely to be greater than the above estimate as the contribution from small riparian landslides, sheet, gully, and rill erosion has not been accounted for, nor has streambank erosion and sediment transported off the study site been measured. Radiocarbon dating of charcoal in sediments indicated that two landslides had evidence of previous instability in the Holocene. Most ages indicated that previous instability dated to 35–15 cal ka BP, i.e., to a time when the climate was cold and dry and freeze-thaw processes in a sparsely vegetated landscape were active. Conclusions: During planning for harvest the soils developed on Permian tillite were correctly described as having a low to moderate risk of landslide erosion. This study concludes that the landslides initiated in June 2016 resulted from exceptionally heavy rain falling on harvested steep and hilly land coupled with the decline in root strength of the harvested trees. The frequency of such a combination of circumstances may increase if high-intensity rainfall increases in Tasmania as the result of climate change. To improve the long-term stability of this terrain and the overall sustainability of plantation forestry it is recommended that landslides and riparian areas are seeded with native vegetation, and that the current assessment of landslide risk for this terrain is re-evaluated.

Detecting the Planform Changes Due to the Seasonal Flow Fluctuation and 2012 Severe Flood in the Amazon River near Iquitos City, Peru Based on Remote Sensing Image Analysis

The Upper Amazon River forms an anabranching planform, which has been found to have significant changes in migration rate and river morphology. Previous studies have elaborated long-term evolution of the anabranching systems; however, research on the influence of the water level on temporal changes in anabranching is absent. According to the theory of river hydraulics, fluvial scour usually occurs when the shear force possessed by the high flow exceeds the resistance of the streambank. In contrast, deposition occurs when the tractive force of the low flow is insufficient to overcome the forces of gravity and friction. This study investigated the Muyuy anabranching planform change of the Upper Peruvian Amazon River due to the seasonal flow fluctuations and a severe flood in 2012. The Muyuy anabranching area is located 20 km upstream of Iquitos City, Peru. Landsat images from the wet and dry seasons in 2008, 2009, 2012, and 2013 were collected. The images were classified into three land cover classes (water, bare soil, vegetation and others) based on NDVI analysis. Quantitative analysis of the erosion/deposition shows that deposition is more noticeable than erosion in the Muyuy anabranching area. Considerable deposition can be found on the island of the anabranching system, and the streambank erosion occurred in the outer (concave) side of the main channel. This phenomenon of river erosion and deposition consistently occurred in 2008 and 2009 because of the periodical variation among the wet and dry seasons. However, prominent erosion was observed in 2012 and it was recognized to be caused by the severe flood. Furthermore, the extensive island was formed in 2013, which means substantial depositions accumulated in the recession of the 2012 flood.

Integrating Streambank Erosion with Overland and Ephemeral Gully Models Improves Stream Sediment Yield Simulation

HighlightsSimulation of overland (AnnAGNPS) and ephemeral gully (REGEM) erosion underestimated watershed sediment yield.Three methods were used to disaggregate contribution of streambank sediment loads to daily streamflow events.A rainfall-based method, with scaling factor and threshold term, had good performance and low bias in all watersheds.Calibrated model results indicated that most sediment yield was from streambank sources (78% to 93%).Abstract. Models used to guide watershed management must account for sediment from all erosion sources (interrill and rill, ephemeral gully (EG), and streambank), each of which operates at different spatial and temporal scales. Our hypothesis was that the use of separate models to explicitly simulate sediment yield contributions for each of these three sources would improve model agreement with measured watershed sediment yield data. We tested this hypothesis using AnnAGNPS (overland flow/erosion model), REGEM (EG erosion model), and field-measured streambank erosion disaggregated to an event basis using three methods in three watersheds (North Fork, Main Stem, and Irish Creek, Kansas). AnnAGNPS alone and in combination with REGEM underestimated sediment yields and had a poorly calibrated performance in all three watersheds, which reinforced the need to include sediment loads from stream sources. The three streambank sediment disaggregation methods each included two calibration terms: a scaling factor and a threshold term, which disaggregated 2-year-total streambank erosion measurements into event-based values based on rainfall, streamflow, or stream power. All three methods gave “very good” sediment-yield calibration results (event-based Ef = 0.6, PBIAS near 0%) for Main Stem and Irish Creek but gave “satisfactory” results only for the rainfall-based streambank disaggregation method in the evaluation watershed (North Fork). Calibrated model results indicated that most of the measured outlet sediment yields in the study watersheds were from streambank sources (78% to 93%), with less from overland erosion (7% to 22%) and little from EG erosion (0% to 7%). These methods could be equally effective in scaling and disaggregating stream-based sediment contributions without measured streambank erosion, but the calibration terms would lose physical meaning in reference to measured streambank values. The skill demonstrated by all three streambank disaggregation thresholds may provide a foundation for building simple, process-based streambank sediment yield simulation models. Keywords: Ephemeral gully erosion, Interrill and rill erosion, Modeling, Streambank erosion, Watershed.

Evaluating Causal Factors That Influence the Spatial and Temporal Variability of Streambank Erosion in Iowa

Highlights Critical shear stress and erodibility were quantified for Iowa streambanks at regional and seasonal scales. Variations in critical shear stress and erodibility were apparent across landform areas. Values of critical shear stress in northern Iowa were less than those in southern Iowa. Seasonal variations in critical shear stress and erodibility are due to soil moisture and freeze-thaw cycles. Abstract. Streambank erosion exhibits high variability both spatially and temporally, and few studies have attempted to characterize the causal factors of the variability at regional and seasonal scales. This study combines geotechnical field measurements with historical trends of soil moisture and temperature to quantify the spatial and temporal variability of critical shear stress and erodibility in streambanks of the Major Land Resource Areas of Iowa (MLRAs). The data suggest that till-derived soils in north-central and northeast Iowa lack cohesion compared to loess-derived soils in southern Iowa. Thus, critical shear stress values from the northern parts of the state were significantly less than those from western and southern Iowa. A multivariate regression equation was developed using properties of texture and bulk density to quantify critical shear stress values for all stream bank soil series in the state. The cumulative distribution functions of these values visually reflect the separation between the critical shear stress values of the different MLRAs, with the loess-derived soils in western and southern Iowa having similar, overlapping patterns, in contrast to MLRAs in north central and northeast Iowa with the till-derived soils. Temporally, the critical shear stress reaches minimum values during March when soil moisture is high and there are several freeze-thaw events. This is most apparent with bank soils in eastern Iowa. Keywords: Cohesion, Critical shear stress, Erodibility, Sediment, Streambank erosion.

Fine-Grained Sediment and Phosphorus Storage in a Suspended-Load-Dominated, Alluvial Channel

HighlightsIn-channel sediment and TP storage were quantified along 13.5 km of a stream.TP and sediment masses were 1 and 3 times greater than their respective annual watershed load.Colluvial material at streambank toe represented the dominant storage pool.Sinuous stream reaches exhibited significantly greater storage versus channelized reaches.Abstract. In-channel storage of both fine sediment and sediment-bound phosphorus has been recognized as potentially large contributors to respective watershed loads, yet they are rarely quantified in the field. In this field-based study, we quantified and characterized in-channel fine sediment and total phosphorus (TP) storage within a third-order stream. We hypothesized storage to be significant within the context of watershed-scale sediment and TP loads and that storage trends are influenced by channel characteristics and hydraulics. In May 2015, the volume of stored in-channel sediment was estimated within a 13.5 km stretch of Walnut Creek, an alluvial stream draining an agriculturally dominated watershed in Jasper County, Iowa, USA. Storage volume was estimated in-field through a series of 240 transects which were stratified across reaches of the varying channel and hydraulic conditions (e.g., sinuosity, stream power). Overall storage volume was broken down into feature classes (e.g., point bars) based on in-channel depositional processes. Following in-field quantification, feature class sediment samples were collected and analyzed for physical properties (e.g., bulk density) and TP concentration. Physical and chemical analyses, coupled with in-field volume estimation, allowed for watershed-scale masses of in-channel sediment and TP to be calculated and then placed within the context of respective annual loads. Sediment and TP were estimated to be stored at ~2.7 Mg m-1 and 0.7 kg m-1, respectively. Sinuous reaches exhibited significantly greater sediment storage volume (p &amp;lt; 0.001) and depth (p &amp;lt; 0.001) versus straight reaches. Reach sinuosity exhibited a significant positive correlation (p = 0.03) with storage mass and represented the most effective storage predictor. The majority of storage mass (72%) was represented by colluvial material accumulations at the streambank toe. Loose bed sediment was the second greatest contributor to storage mass (18%), with the remaining feature classes (e.g., bars) representing a combined ~10%. Sediment storage mass was ~3.25 times greater than the watershed suspended sediment load for 2015. The TP mass was found to be nearly equal to the respective watershed load for 2015. In-channel sediment and TP storage masses within Walnut Creek were found to be significant in comparison to respective annual loads, and thus storage is expected to play a significant role in respective watershed routing, loading, and the overall budgets of these parameters. Though challenging, quantification of in-channel fine sediment and TP storage is necessary to relate source contributions (e.g., streambank erosion) to watershed loads and is critical to account for interannual sediment and TP export. Keywords: Channel evolution, Channel morphology, Iowa, Sinuosity, Stream power, Water quality, Watershed export.

An Appraisal of Soil Erosion in Dehradun Valley

In the recent past, there has been a very rapid increase in the developmental activities in the Himalayas in general and Dehradun Valley in particular. These comprise large-scale construction, roads, mining activity, overgrazing, and deforestation etc. leading to the land degradation. A near exponential population growth has placed a further heavy demand on already limited natural resources. High rainfall coupled with fragile rocks and good relief provides a dense network of stream system. The debris from landslides and mine waste cause inequilibrium in flow regime causing meandering in both mountain and valley streams. These problems pose serious threat to environmental and ecological balance in an already fragile eco-system. Landslide, river sedimentation, disruption to communication lines and depletion of water sources are some of the direct consequences of mass erosion problem. The effect of majority of casualties and other natural hazards due to mass erosion often disrupts economic and social fabric over a much wider area than the hazard site and prompt action is required in order to minimize these losses. There are several mass erosion problems but landslides, mine spoil stabilization and stream bank erosion problems are dominant and therefore selected for the present study.

FARMERS PERCEPTIONS ON SOIL EROSION IN SEBEYA CATCHMENT, RWANDA

Soil erosion is one of the major causes of land degradation which result in low agriculture productivity. Especially, western part of Rwanda including Sebeya catchment has high susceptibility to erosion leading to huge amounts of soil loss. This study held to explore the actual status of soil erosion in Sebeya catchment. Global Information System data were used for catchment delineation. Qualitative and quantitative data were collected and analyzed. Specifically, 75 farmers living and having farm lands in the catchment were interviewed in terms of knowledge on soil erosion, causes and control measures. The results showed that streambank erosion is due to the erosive power of runoff from uplands areas with (18.7%). The main natural causes of soil erosion in Sebeya catchment are heavy rainfall (69.33%) and the slope steepness (28%). Public and private land conservation agencies should be more involved in soil management centred on farmer’s awareness and capacity building.

Investigation of Local Scour around L-Shape Submerged Groynes in Clearwater Conditions

Submerged Groynes are low profile linear structures that are generally located on the outside bank to form Groynes fields and prevent the erosion of stream banks by redirecting high-velocity flow away from the bank. This research was studied in detail through two major stages. The first stage of the study is based on laboratory experiments to measure the development of local scour around L-shape submerged Groyne with the time, and special attention is given to the effects of different hydraulic and geometric parameters on local scour. Also; maps were drawn showing contour lines that represented the bed levels for maximum scour depth after reaching the equilibrium case. The result showed that a decrease in the scour depth ratio due to the increasing submerged ratio, and the number of Groynes. While the scour hole geometry will increase with the Froude number, flow intensity, and the spacing between Groynes, the decreasing percentage in the scour hole was measured to be about (4.3) % and (4.4) % for decreasing the spacing between Groynes from (2Lg) to (1.5Lg). Besides, it was range about (11.1) % and (14.0) % when reducing the spacing from (1.5Lg) to (Lg) under the same value of maximum Froude number. The second stage of the study is based on experimental results. A new formula was developed by using statistical analysis and it was found that a good determination coefficient.