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Streambank Erosion: Advances in Monitoring, Modeling and Management

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Streambank Erosion: Advances in Monitoring, Modeling and Management water Editorial Streambank Erosion: Advances in Monitoring, Modeling and Management Celso F. Castro-Bolinaga * and Garey A. Fox Biological and Agricultural Engineering, North Carolina State University, Raleigh, NC 27695, USA; [email protected] * Correspondence: [email protected]; Tel.: +1-919-515-6712 Received: 31 August 2018; Accepted: 26 September 2018; Published: 28 September 2018 Abstract: The special issue “Streambank Erosion: Monitoring, Modeling, and Management” presents recent progress and outlines new research directions through the compilation of 14 research articles that cover topics relevant to the monitoring, modeling, and management of this morphodynamic process. It contributes to our advancement and understanding of how monitoring campaigns can characterize the effect of external drivers, what the capabilities and limitations of numerical models are when predicting the response of the system, and what the effectiveness of different management practices is in order to prevent and mitigate streambank erosion and failure. The present editorial paper summarizes the main outcomes of the special issue, and further expands on some of the remaining challenges within the realm of monitoring, modeling, and managing streambank erosion and failure. First, it highlights the need to better understand the non-linear behavior of erosion rates with increasing applied boundary shear stress when predicting cohesive soil detachment, and accordingly, to adjust the computational procedures that are currently used to obtain erodibility parameters; and second, it emphasizes the need to incorporate process-based modeling of streambank erosion and failure in the design and assessment of stream restoration projects. Keywords: cohesive soil; fluvial erosion; erodibility parameters; jet erosion test; stabilization practices; stream restoration 1. Introduction Streambank erosion and failure is recognized as a significant source of sediment loading to streams (Figure1). In many Conservation Effects Assessment Project (CEAP) watersheds in the United States, for example, sediment eroded from banks is one of the primary sources of bed material [1], accounting in some cases for as much as 80% of the total load [2]. Likewise, degraded banks can be a major contributor to nutrient loading in streams as reported by Laubel et al. [3] and Mittelstet et al. [4], who estimated that eroded sediment can contribute up to 40% and 47% of the total phosphorus in small rural and agricultural watersheds, respectively, and [5] that reviewed a wide range of studies and noted that streambank phosphorus contributions can be significant. From a geomorphic perspective, streambank erosion and failure modify the channel planform and cross-sectional geometry, ultimately altering the flow and sediment transport dynamics of the reach. This leads to hydro-morphodynamic adjustments, such as changes in flow depth, bed-material composition, and transport capacity, that take place at various spatial and temporal scales [6]. Furthermore, the magnitude of such adjustments has been enhanced over the last several decades by land-use dynamics within watersheds. For example, Schottler et al. [7] reported that the use of artificial drainage has triggered an increase in annual flow from agricultural basins, resulting in streams with a higher erosion capacity and therefore subject to severe channel widening due to bank erosion and failure. Water 2018, 10, 1346; doi:10.3390/w10101346 www.mdpi.com/journal/water Water 2018, 10, x FOR PEER REVIEW 2 of 7 Water 2018, 10, x FOR PEER REVIEW 2 of 7 a higher erosion capacity and therefore subject to severe channel widening due to bank erosion and afailure.Water higher2018 erosion, 10, 1346 capacity and therefore subject to severe channel widening due to bank erosion and2 of 8 failure. (a) (b) (a) (b) Figure 1. Post-restoration streambank (a) erosion and (b) failure in Richland Creek, Wake County, FigureNC,Figure USA. 1. 1. Post-restoration Post-restorationPictures courtesy streambank of the NCSU ((aa)) BAE-DMS erosionerosion and and stream ( b()b failure) failure restoration in in Richland Richland team. Creek, Creek, Wake Wake County, County, NC, NC,USA. USA. Pictures Pictures courtesy courtesy of the of NCSUthe NCSU BAE-DMS BAE-DMS stream stream restoration restoration team. team. The breadth of research being published on streambanks is rapidly expanding, especially since the earlyTheThe breadth breadth1990s as of illustrated research beingbeing in Figure publishedpublished 2. The on on purp streambanks streoseambanks of this is is rapidly special rapidly expanding, issue expanding, was especiallyto especiallycompile since recent since the theprogressearly early 1990s and1990s as highlight illustrated as illustrated new in Figure researchin Figure2. The directions 2. purpose The purp ofrelevant thisose specialof tothis streambank issuespecial was issue to er compileosionwas to and recentcompile failure. progress recent The progressspecialand highlight issue and contains highlight new research 14 newresearch directionsresearch articles directions relevant that: (i) tospan re streambanklevant across to the streambank erosion realm of and monitoring, er failure.osion and The modeling, specialfailure. issue Theand specialmanagement,contains issue 14 research contains with the articles 14 ultimate research that: goal articles (i) span of advancing that: across (i) the span realmour across understanding of monitoring,the realm of of modeling,monitoring, the processes and modeling, management,that govern and management,thesewith thecomplex ultimate with and goal the dynamic ofultimate advancing phenomena; goal ourof advancing understanding and (ii) our build understanding of theupon processes the rapidlyof thatthe processes govern expanding these that research complex govern theseliteratureand dynamic complex (Figure phenomena; and 2). dynamic and phenomena; (ii) build upon and the (ii) rapidly build expanding upon the research rapidly literature expanding (Figure research2). literature (Figure 2). FigureFigure 2. 2. NumberNumber of of publications publications on on the the topic topic of of “str “streambank”.eambank”. Data Data are are extracted extracted from from the the Institute Institute Figureforfor Scientific Scientific 2. Number Information’s Information’s of publications (ISI) (ISI) Web Web on theof of Science Sciencetopic of database. database.“streambank”. A A total total Data of of 541 541are publications publicationsextracted from were were the identified identified Institute forunderunder Scientific the the topic topic Information’s of of “streambank” “streambank” (ISI) Web as as of of of August August Science 2018. database. A total of 541 publications were identified under the topic of “streambank” as of August 2018. 2.2. Main Main Outcomes Outcomes of of the the Special Special Issue Issue 2. Main Outcomes of the Special Issue TheThe research research articles included inin thisthis specialspecial issueissue specifically specifically targeted targeted three three areas areas that that are are key key to tobetter betterThe understanding understandingresearch articles streambank streambank included erosion inerosion this special and and failure,fa ilure,issue namely,namely,specifically monitoringmonitoring targeted [[8–11], 8three–11], areasmodeling that [12–17],are [12 –key17], toandand better management management understanding [[18–21].18–21 streambank]. As anan ensemble,ensemble, erosion the theand articlesarti failure,cles highlight highlightnamely, themonitoring the value value of of [8–11], monitoring monitoring modeling campaigns campaigns [12–17], to andtocharacterize characterize management the the effect [18–21]. effect of of external As external an ensemble, drivers drivers (e.g., the (e.g., arti hydrologic hydrologiccles highlight events), events), the the value the capabilities ca ofpabilities monitoring and and limitations campaignslimitations of toofnumerical characterizenumerical models models the effect for for predicting predictingof external the thedrivers response response (e.g., of theofhydrologic th systeme system (e.g.,events), (e.g., stream streamthe ca restorationpabilities restoration design),and design), limitations and and the oftheeffectiveness numerical effectiveness models of managementof management for predicting practices practices the response to to prevent preven of andtth ande system mitigate mitigate (e.g., the the stream impactsimpacts restoration ofof streambank design), erosion erosion and theandand effectiveness failure. failure. of management practices to prevent and mitigate the impacts of streambank erosion and failure. Water 2018, 10, 1346 3 of 8 2.1. Monitoring Arnold and Toran [8] monitored erosion rates and turbidity levels in an urban stream to examine the effect of commonly found invasive species on bank retreat. Their results highlight the impact of different types of bank vegetation on erosion rates and their implications for calculating sediment supply. Dragi´cevi´cet al. [9] reconstructed the lateral migration of a 15-km reach of a meandering river using 87 years of observations from cadastral maps and aerial photographs. This study is a relevant example of the use of historical data to characterize long-term trends of bank erosion relative to the hydrologic regimes that triggered them. Karimov and Sheshukov [10] monitored an ephemeral gully over a period of two years to identify the main factors responsible for soil detachment. They developed a critical shear stress function
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