Geomorphology 277 (2017) 237–250

Contents lists available at ScienceDirect

Geomorphology

j ourna l homepage: www.e lsev ie r .com/ locate /geomorph

A conceptual connectivity framework for understanding geomorphicchange in human-impacted fluvial systems

Ronald E. Poeppl a,⁎, Saskia D. Keesstra b, Jerry Maroulis b,c

a Department of Geography and Regional Research, University of Vienna, Universitaetsstrasse 7, A-1010 Vienna, Austriab Soil Physics and Land Management Group, Wageningen University, Droevendaalsesteeg 4, 6708PB Wageningen, The Netherlandsc International Centre for Applied Climate Sciences, Institute for Agriculture and the Environment, University of Southern Queensland, Toowoomba, Queensland 4350, Australia

⁎ Corresponding author.E-mail addresses: ronald.poeppl@univie.ac.at (R.E. Poe

(S.D. Keesstra), Jerry.Maroulis@usq.edu.au (J. Maroulis).

http://dx.doi.org/10.1016/j.geomorph.2016.07.0330169-555X/© 2016 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 2 November 2015Received in revised form 21 July 2016Accepted 22 July 2016Available online 26 July 2016

Human-induced landscape change is difficult to predict due to the complexity inherent in both geomorphic andsocial systems aswell as due to the coupling relationships between them. To better understand system complex-ity and system response to changing inputs, “connectivity thinking” has become an important recent paradigmwithin various disciplines including ecology, hydrology and geomorphology.With the presented conceptual con-nectivity framework on geomorphic change in human-impacted fluvial systems a cautionary note is flagged re-garding the need (i) to include and to systematically conceptualise the role of different types of human agency inaltering connectivity relationships in geomorphic systems and (ii) to integrate notions of human-environmentinteractions to connectivity concepts in geomorphology to better explain causes and trajectories of landscapechange. Geomorphic response of fluvial systems to human disturbance is shown to be determined by system-specific boundary conditions (incl. system history, related legacy effects and lag times), vegetation dynamicsand human-induced functional relationships (i.e. feedback mechanisms) between the different spatial dimen-sions of connectivity. It is further demonstrated how changes in social systems can trigger a process-responsefeedback loop between social and geomorphic systems that further governs the trajectory of landscape changein coupled human-geomorphic systems.

© 2016 Elsevier B.V. All rights reserved.

Keywords:ComplexityResilienceCouplingHuman-landscape systemsRiver management

1. Introduction

“Connectivity thinking” and related concepts have a long history ingeographical research (e.g. in geomorphology (e.g. Chorley andKennedy, 1971; Brunsden and Thornes, 1979), or in terms of human-environment interactions (e.g. Barrows, 1923)). The earliest document-ed statement of connectivity in a geomorphological context can befound in Chorley and Kennedy (1971) where connectivity is definedas the transfer of energy and matter between two landscape compart-ments or within a system as a whole. Another precursor of present con-nectivity concepts in geomorphology is the coupling conceptwhichwasfirst introduced by Brunsden and Thornes (1979) and Brunsden (1993,2001) and extended by Harvey (1997, 2002) to explain landscape sen-sitivity and geomorphic change. Brunsden and Thornes (1979) statedthat landscape sensitivity ismainly controlled by the capacity of the var-ious components of the landscape to transmit an impulse; with capacitydependent on path density of the process and strength of the couplingbetween system components.

ppl), saskia.keesstra@wur.nl

Especially since the beginning of the 21st century, connectivity re-search experienced a surge within various disciplines including ecology(Kindlmann and Burel, 2008), hydrology and geomorphology (e.g.Brierley et al., 2006; Bracken et al., 2013, 2015), in developing new oradapting already existing concepts on connectivity to better understandsystem complexity and system response to change within their respec-tive discipline. Geomorphologists began to extend connectivity thinkingby incorporating connectivity concepts from other disciplines, especial-ly ecology and hydrology (cf. Bracken andCroke, 2007), to describe link-ages between sediment source areas and the corresponding sinks incatchment systems (e.g. Croke et al., 2005; Brierley et al., 2006; Fryirset al., 2007; Turnbull et al., 2008; Wainwright et al., 2011; Fryirs,2013; Bracken et al., 2015) which further resulted in a differentiationbetween three types of connectivity: “Sediment connectivity”, i.e. thepotential for sediments to move through geomorphic systems (Hooke,2003), being governed by the physical coupling of landforms (i.e. “land-scape connectivity”) and by the passage of the transporting mediumfrom one part of the landscape to another (e.g. via water, “hydrologicalconnectivity”).

Considerations of sediment connectivity in geomorphology aremainly based on thinking about sediment transfer between differentstores or zones within a given system placing an emphasis on the distri-bution of sediment stores and sinks reflecting and influencing the

238 R.E. Poeppl et al. / Geomorphology 277 (2017) 237–250

routes, travel distances and pathways of sediment movement withincatchment systems (e.g. between channel reaches (Hooke, 2003); orbetween hillslopes and channels (Harvey, 2012); see Bracken et al.(2015). Bracken et al. (2015) further pointed out that a shift from think-ing about sediment transfer between different stores to a continuum-based approach can be observed trying to understand pathways, routesand scales of movement of sediment that has been directly influencedby the progressive development of the concept of hydrological connec-tivity. Lexartza-Artza and Wainwright (2009, 2011), for example,underlined the importance of understanding the conditions for runoffgeneration and transmission to produce key information regarding sed-iment transfer in catchment systems.

Ecologists had already been using the concept of connectivity as acritical property in the persistence of spatially structured populations(Metzger and Décamps, 1997). In this context, hydrological connectivityhas been defined by Pringle (2001) as being thewater-mediated transferof matter, energy, and/or organisms within or between elements of thehydrologic cycle. This definition also reflects Chorley and Kennedy's(1971) definition of connectivity (see above). Furthermore, hydrologicalconnectivity, especially in the hydrological sciences, has been a dynamicarea of research in the last decade, resulting in a novel framework for un-derstanding runoff and run on (Bracken and Croke, 2007; Ali and Roy,2009), see Bracken et al. (2013), further influencing recent concepts onsediment connectivity in geomorphology (e.g. Lexartza-Artza andWainwright, 2009, 2011; Bracken et al., 2015).

Landscape connectivity has been defined in an ecological context asbeing ‘the degree to which a landscape facilitates or impedes the move-ment of individuals’ (Taylor et al., 1993). In this context, important land-scape characteristics include shape, size and location of different featuresin the landscape (Brooks, 2003). These considerations are also reflectedin the coupling concept within the sensitivity concept of Brunsden andThornes (1979; see above) which therefore can be seen as an early – ifnot the first – systematic consideration of landscape connectivity in ageomorphological context. At a later stage, Brierley et al. (2006) pro-posed a connectivity framework in which they characterized differentforms of landscape connectivity based on the position of geomorphicprocesses in a catchment. Based on Ward's (1989) conceptual modelon the four-dimensional nature of lotic ecosystems Brierley et al.(2006; p. 166) differentiated between longitudinal, lateral and verticallinkages within catchment systems to analyse “character and behaviourof landscape compartments, how they fit together (their assemblage andpattern) and the connectivity between them” to provide “a platform tointerpret the operation of geomorphic processes in any given system”.This framework has been further elaborated by Fryirs et al. (2007)resulting in a conceptual model on (dis)connectivity of catchment sedi-ment cascades in which catchment disconnectivity is defined as the de-gree to which any limiting factor (i.e. termed buffers, barriers andblankets) constrains the efficiency of sediment transfer relationships.

In the last two decades connectivity further gained increasing im-portance in river and catchment management (incl. river restoration).For example, evaluating the effects of river engineering on connectivityand geomorphic dynamics along European rivers has evolved as a legalrequirement under the European Water Framework Directive (EU,2000). As a consequence, engineered rivers and their floodplains are in-creasingly being restored (e.g. Constantinescu et al., 2015; Magilliganet al., 2016),while also a shift fromhard- to soft-engineering techniquescan be observed (e.g. Moss andMonstadt, 2008). However, many resto-ration projects have failed (Wohl et al., 2005) due to incomplete pre-assessments or basic concepts that neglect the role of complex geomor-phic system response to change (Schumm, 1973; Pizzuto, 2002). Thiscomplexity is mainly related to the system-specific landscape history(Brierley, 2010) and associated legacy effects (Doyle et al., 2005), self-regulatory system properties incl. feedback processes (cf. Bednarek,2001), interactions between processes and system components, andtime-dependent changes that progressively alter the balance betweenforces and resistance to geomorphic change (Brunsden, 2002).

Humans, over thousands of years, have significantly altered geomor-phic systems. These human impacts were mainly characterized byshort-lived changes to their micro-environment rather than occurringon larger scales (Werner and McNamara, 2007). However, the scale ofhuman impacts upon geomorphic systems such as fluvial systems isnow considerably larger than at any point in our history with a plenitudeof either direct (e.g. dam construction) or indirect (e.g. land cover chang-es) (Goudie, 2006) impacts on their structure and function (Gregory,2006). Simultaneously, increases in population and technology develop-ment have led to an increasing strength of interactions between humansand their natural environment resulting in regional or even global feed-back loops due to strong and complex interdependencies betweenhydro-geomorphological, ecological, and human processes and functions(Werner and McNamara, 2007; Harden et al., 2014; Chin et al., 2014).Moreover, the increasing strength of interactions betweenhuman agencyand landscape processesmeans that they “[…] can no longermeaningful-ly be treated separately, but rather only as an inter-weaved, coupled sys-tem” (Werner and McNamara, 2007; p. 394).

Research on coupled human-landscape systems hasmade good prog-ress over the last 15 years: in socio-ecological contexts, e.g. Holling, 2001;Alberti et al., 2003; Walker et al., 2004; Folke, 2006; Matthews andSelman, 2006; Dearing et al., 2006; Liu et al., 2007; Harden et al., 2014;(adaptive) water and river management, e.g. Kondolf et al., 2003;Pahl-Wostl, 2007; Pahl-Wostl et al., 2007; and geomorphology, e.g.Werner and McNamara, 2007; Dearing, 2008; Chin et al., 2014. In partic-ular, resilience has been increasingly used as a concept to understandsocial–ecological systems (e.g. Folke, 2006), further being applied to geo-morphic (Phillips, 2009) and eco-geomorphological (Collins et al., 2012)systems. These concepts, which are focussing on feedback characteristicsbetween open systems, are considered to provide valuable backgroundfor advancing research in coupled human–geomorphic systems (Chinet al., 2014). However, we are still facing a range of key challengeswhen investigating coupled human-landscape systems.

Although elaborated connectivity concepts, and approaches that useconnectivity to explain complex geomorphic systems and geomorphicresponse to change emerged in the last decade, a range of key challengesand gaps still persist. These include (i) to systematically conceptualise therole of different types of human agency/disturbance in altering connec-tivity relationships in geomorphic systems and (ii) to integrate notionsof human-environment interactions to connectivity concepts in geomor-phology to better explain causes and trajectories of landscape change.These key challenges and gaps, which are elaborated in more detail inSection 2, are further forming the basis of discourse on the developmentof a revised conceptual connectivity framework dealing with causes andtrajectories of geomorphic change in managed fluvial systems.

The aim of this paper is twofold. Firstly, we build upon earlier con-cepts and recent advances in geomorphology and landscape research(including notions of human-geomorphic interactions based on resil-ience theory) to develop a conceptual connectivity framework,underpinned by case study examples from literature to exemplify thecauses and trajectories of geomorphic change in human-impacted fluvi-al systems (Section 3). Secondly, an overview of existing key tools toquantify connectivity in geomorphic and coupled human-geomorphicsystems will be presented (Section 4), forming the second basis forSection 4 in which we will discuss the potential added value of ourframework in the context of human-impact, connectivity and complex-ity research in fluvial geomorphology, further deriving some generalimplications for river and catchment management.

2. Key challenges and gaps

2.1. Disturbance and the role of human agency in geomorphologicalconnectivity frameworks

Based on the frequency and magnitude concept of Wolman andMiller (1960); Brunsden and Thornes (1979) in their sensitivity concept

239R.E. Poeppl et al. / Geomorphology 277 (2017) 237–250

classified disturbance into pulsed and ramped types of inputs. Pulsed in-puts are typically extreme and episodic events that are spatially andtemporally restricted (e.g. low-frequency, high-magnitude floodevents), while ramped input changes are sustained, resulting in perma-nent shifts in the controlling variables or boundary conditions.Brunsden and Thornes (1979) also stated that changes and fluctuationsin environmental conditions, can be related to human activity such asland-use. In a revised version of the sensitivity concept, Brunsden(2001, p.99) stated that the likelihood of a given system to respond toany disturbance forces depends on “its structure, strength properties,transmission linkages, coupling efficiency, shock absorption capacity,complexity and resilience”. Similarly, Harvey (2001, p. 175) noted that“coupling behaviour conditions how the system responds to distur-bance, and is therefore important in determining the geomorphic re-sponse to human-induced, climatically-induced or tectonically-induced environmental change”. Similar notions on the importance oflandscape (dis)connectivity for the interpretation of landscape re-sponses to human disturbance including management applicationscan also be found in the work of Brierley et al. (2006). However, in allthese approaches no systematic information is provided on how differ-ent types of human activity induce and/or affect connectivity relation-ships and thus geomorphic sensitivity of geomorphic systems to(human-induced) change.

The first geomorphological landscape connectivity framework inwhich notions on different types of human disturbance on sedimentflux have been addressed explicitly can be found in Fryirs et al.(2007; see also Fryirs, 2013) in which the impact of humandisturbance upon sediment flux is framed in terms of alterations tothe operation of landforms that impede sediment transfer withincatchments. However, besides some general considerations aboutthe effects of human-induced land cover changes and the construc-tion of dams on lateral and longitudinal connectivity in catchmentsystems, no systematic conceptualisation on the role of differenthuman agencies in altering connectivity relationships in catchmentsystems, is evident. Considering the multiplicity of human impactsupon catchment systems, and assuming a complex relationship be-tween the different spheres of connectivity within these systems,yet a more systematic conceptualization of the role of human distur-bance in altering connectivity relationships in catchment systems isdeemed essential for understanding the role of human agency in al-tering catchment-scale sediment fluxes and geomorphic response tochange.

In their conceptual model on hydrological connectivity Bracken andCroke (2007) defined five components of hydrological connectivity af-fecting the conditions for runoff generation and transmission furtherinfluencing sediment connectivity in catchment systems: (1) climate,(2) hillslope runoff potential, (3) landscape position (4) delivery path-way and (5) lateral buffering. Within each of these components theynamed a number of factors which influence hydrological connectivityincluding the potential impacts of human agency such as landmanage-ment (e.g. ploughing, road construction) in altering hillslope runoff po-tential and delivery pathways. Lexartza-Artza and Wainwright (2009)presented practical guidelines for assessing connectivity in the field in-cluding anthropogenic influences such as water and catchmentmanagement. They further stressed the need to consider dynamic as-pects of connectivity that emerge from interactions and feedbackloops between structural and functional connectivity and the roleof self-regulation in providing a better understanding of system com-plexity (for hydrological connectivity: Bracken and Croke, 2007;Lexartza-Artza andWainwright, 2009;Wainwright et al., 2011; for sed-iment connectivity: Bracken et al., 2015). However, these frameworksdo not provide systematic information on the role of different types ofhuman agency in altering/inducing functional relationships betweendifferent spatial dimensions of connectivity in geomorphic systems,which are yet hypothesized to further influence the trajectory of geo-morphic change.

2.2. Human-environment interactions in geomorphology and the role ofconnectivity

In a socio-ecological context, research on human-environment in-teractions has received considerable attention in recent literature (e.g.Holling, 2001; Alberti et al., 2003; Walker et al., 2004; Folke, 2006;Matthews and Selman, 2006; Dearing et al., 2006; Liu et al., 2007).Many of these approaches are based on complex adaptive systems andresilience theory. According toHolling (2001) there are three propertiesthat shape the adaptive cycle and the future state of a system (whetherat the scale of the cell or the biosphere, the individual or the culture),which are wealth, controllability, and adaptive capacity. Holling (2001,p. 394) stated that the “internal controllability of a system; that is, thedegree of connectedness between internal controlling variables andprocesses, a measure that reflects the degree of flexibility or rigidity ofsuch controls, such as their sensitivity or not to perturbation”. In termsof human-environmental systems this implies that the sensitivity ofboth sub-systems, i.e. the environmental and human/social system,and the sensitivity of coupled human-environmental systems aregoverned by the strength of connectivity relationships.

Various approaches have been used to couple human behaviourwith geomorphic processes, ranging from conceptual frameworks (e.g.Urban, 2002; Kondolf et al., 2003; Chin et al., 2014) to field-based (e.g.Dearing, 2008) and modelling approaches (e.g. Werner andMcNamara, 2007; for a detailed review refer to Zvoleff and An, 2014).Yet, we are still facing enormous knowledge gaps in quantifying fullimpact-feedback loopswithin geomorphic systems involving significanthuman interactions, such as in the economic evaluation of changedlandscapes (Chin et al., 2014). General key problems are mainly relatedto the lack of effective communication and collaboration among multi-ple communities, integrative concepts, common metrics, integratingdisparate data types, and newways to synthesize and scale up researchresults from local case studies to broader large scale theories andmodels (Harden et al., 2014). For geomorphologists, Chin et al. (2014)identified general key questions and challenges in investigating coupledrelationships in human-landscape systems related to varying spatialand temporal scales for the processes involved, data gaps, linking im-pacts and responses, and a lack of integrative tools and interdisciplinarycollaboration. They mainly argue that development of new geomorphicprinciples and theoretical frameworks on potential feedbacks betweenphysical and human processeswithin a common conceptual frameworkfor human–landscape systems is required. It is further argued here, thatthe existing conceptual frameworks on coupled “human-geomorphicsystems” disregard the importance of type and location of human im-pact upon geomorphic systems, further neglecting the role of connectiv-ity relationships governing the systems' sensitivity and resilience tochange.

3. Conceptual connectivity framework for understanding geomorphicchange in managed fluvial systems

Building upon earlier connectivity concepts and recent advances ingeomorphology and landscape research,we intend to develop a concep-tual connectivity framework that helps to account for the causes andtrajectories of geomorphic change in human-impacted fluvial systems.To achieve this, initially, (1) a systematic outline of common human im-pacts on rivers (i.e. river engineering) and catchments (i.e. land coverchange and land management practices) considering their effects onon-site (!) longitudinal, lateral and vertical connectivity conditions ispresented in Section 3.1. In this context, connectivity in fluvial systemsis defined as being the potential for a sediment particle tomove throughcatchment systems (incl. all sub-systems) under the influence of water.Furthermore, according to the classification of different types of distur-bance (Brunsden and Thornes, 1979) differentiation is also made be-tween ramped and pulsed human disturbance (Table 1). (2) Therelationship between connectivity, sensitivity and resilience and the

240 R.E. Poeppl et al. / Geomorphology 277 (2017) 237–250

role of system-intrinsic self-regulatory processes in governing the tra-jectories of geomorphic response to different types of anthropogenicdisturbance (incl. their off-site effects) is conceptualized in Section 3.2.(3) A conceptual framework on coupled “human-geomorphic systems”will then be developed highlighting the importance of connectivity rela-tionships in governing systems' sensitivity and resilience to change(Section 3.3). In this context connectivity in social and coupledhuman-geomorphic systems is understood as being the general degreeof connectedness or interactions between system compartments, and/or factors and processes that influence them. The presented conceptualmodels will be additionally underpinned by case study examples fromliterature exemplifying human-induced connectivity changes andtheir geomorphic implications in human-impacted fluvial systems.

3.1. Human impact on connectivity in fluvial systems (1)

Connectivity in fluvial systems is operating at longitudinal, lateral,and vertical spatial dimensions (Ward, 1989; Fryirs et al., 2007),governed by a complex interplay of “natural” factors such as climate,tectonics, geology, topography, soils and vegetation (for an extensivereview see Bracken and Croke, 2007; Fig. 1). Human activities directlyaffect connectivity by land cover changes and different land use prac-tices altering sediment delivery from hillslopes and floodplains to thechannel system (i.e. lateral connectivity), or by actions in the riverchannels influencing sediment exchange between the channel and thechannel subsurface (i.e. vertical connectivity) or sediment transport(i.e. longitudinal connectivity; see Fig. 1).

Different types of river engineering have been shown to affect longi-tudinal connectivity. Dams represent one of the most dominant featuresdisrupting longitudinal connectivity as they interrupt the transfer ofwater and sediments from headwater source areas (Petts and Gurnell,2005). Although, dam constructionworks had been reported to increasesediment yields by N50% (Nilsson, 1976), once closed dams and thereservoirs they impound had been shown to act as effective sedimentsinks (Grimshaw and Lewin, 1980). The degree of longitudinal dis-connectivity is determined by the trap efficiency of the dam. For exam-ple, research on three reservoirs in central Missouri (USA) has shownthat dam trap efficiency ranges from 33% to 99% during individual

Table 1Common ramped (R) and pulsed (P) type human impacts on river channels and catch-ments and their on-site effects (X) on the different spatial dimensions of connectivity(adapted from Poeppl, 2012). According to Brunsden and Thornes (1979) pulsed inputsare typically extreme and episodic events that are spatially and temporally restricted(e.g. low-frequency, high-magnitude flood events), while ramped input changes aresustained, resulting in permanent shifts in the controlling variables or boundaryconditions.

Location and type of humanimpact

Ramped(R)/pulsed(P)

Longitudinal Vertical Lateral

River channelDam construction/removal R XFlow diversion and abstraction R XClearing P XChannelization(incl. bed protection)

R X X

Embankment and leveeconstruction

R X

Sediment (incl. bed armour)removal

P X

Sediment addition(sediment slugs, clogging)

P X X

CatchmentLand cover change(clearing, afforestation etc.)

P X

Land use (agriculture, urbanization,roads etc.)

R X

Land management (tillage,drainage, levelling etc.)

R/P X

storms, further being governed by the detention time of storm runoff,dam characteristics and by factors governing particle size (Raush andHeinemann, 1975). Results of Poeppl (2012) who analysed suspendedsediment samples directly up- and downstream of a 6 m high overflowdam in a smallmixed-load river in Austria, for example revealed a grain-size-selective reduction of longitudinal connectivity (Fig. 2): nearly allsilt is retained, while clay is transported through the impoundmentand across the dam crest. Similarly, flow diversion and abstraction atdam locations can also lead to a significant decrease of flow magnitudeand hence longitudinal connectivity (cf. Kingsford, 2000). Contrarily,when dams are removed or reservoirs are flushed (e.g. Wen Shen,1999) or when river channels are cleared of woody debris (e.g. Piégayand Gurnell, 1997; Brooks et al., 2004) longitudinal connectivity andsediment flux is increased (cf. Hart et al., 2002).

Channelization and meander cut-offs associated with the installa-tion of bed and bank protection structures involves channel straighten-ing which may further affect longitudinal connectivity. If channelstraightening results in an increase in channel slope (e.g. Brooker,1985) and/or there is the presence of channel bed and bank protectionmeasures, which reduce hydraulic roughness (Arcement and Schneider,1989), then stream power and thus longitudinal connectivity is locallyincreased. Bed protection structures further cause a decline of verticalconnectivity (Boulton et al., 1993; for an extensive review on exchangeprocesses between rivers and groundwater see Brunke and Gonser,1997).

Anthropogenic sediment addition or removal in river channels mayalso affect longitudinal and/or vertical connectivity. For example, sedi-ment addition to river channels can lead to a clogging of the river bedwhich reduces vertical connectivity (Schälchli, 1992) or to the develop-ment of sediment slugs reducing longitudinal connectivity (Nicholaset al., 1995). Contrarily, sediment removal from gravel bed channelsmay locally increase vertical connectivity due to bed armour removalwhich – if present – has been shown to reduce the exchange of matterbetween the water body and the bed subsurface (Prudic et al., 2007).

Channel embankments (including road embankments) and leveesare permanent features that locally disrupt lateral connectivity as theyprevent sediments from entering the channel system (Poeppl et al.,2012; Marchmalo et al., 2015). Furthermore, a variety of human activi-ties in catchments, mainly related to land cover changes and land man-agement, can significantly affect lateral connectivity. For instance,deforestation may lead to an increase of surface runoff and the genera-tion of new overland flow pathways such as rills and gullies (Piersonet al., 2001; Li et al., 2007) and thus enhances lateral connectivity,while afforestation has been shown to reduce lateral connectivity(Sorriso-Valvo et al., 1995; Keesstra, 2007).

Land management activities such as contour ploughing decrease lat-eral connectivity by preventing the input of eroded soils fromagriculturalfield to the channel systems, while perpendicular ploughing has beenshown to enhance lateral connectivity (Kirkby et al., 2002; Poeppl et al.,2012). Land levelling (filling), in response to rill and gully formation, de-creases overland flow, water erosion (Liu et al., 2013) and thus lateralconnectivity, while the construction of ditches in agricultural areas(Dunn and Mackay, 1996) as well as subsurface drainage (Skaggs et al.,1994) have been shown to have the opposite effects. Furthermore, roadconstruction and urbanization also increase lateral connectivity as theyact as efficient overland flow pathways collecting and routing storm run-off to the river channel systems (Booth and Jackson, 1997; Croke andMockler, 2001; Wemple and Jones, 2003).

3.2. Geomorphic response to human disturbance: connectivity, sensitivity,resilience and self-regulation (2)

Geomorphic response to human disturbance depends on a multiplic-ity of factors including type, location and duration of impact (e.g. pulsedvs. ramped), system-specific boundary conditions, connectivity andself-regulatory system properties (incl. system-intrinsic feedback

Fig. 1. Human impact on connectivity in fluvial systems at the three spatial dimensions.(Adapted from Poeppl, 2012)

241R.E. Poeppl et al. / Geomorphology 277 (2017) 237–250

processes; cf. Brunsden, 2002). Connectivity relationships in geomorphicsystems further determine sensitivity and resilience of the system tochange (cf. Brunsden and Thornes, 1979; Harvey, 2007; Lexartza-ArtzaandWainwright, 2009; Fig. 3). Geomorphic systemswith low connectiv-ity are less sensitive and thus more resilient to disturbance as the propa-gation of the effects of change is limited. This relationship, for examplehas been shown in the work of Fryirs and Brierley (1999) and Harvey(2001) where in some settings, slopes and channels are disconnectedwith materials mobilised on slopes re-stored onslope or in fans at thebase of slopes. An example of channel-hillslope (dis-)connectivity isshown in Fig. 4. The temporal characteristics of connectivity relationshipsare further governed by the magnitude and frequency of threshold-exceeding disturbance events required to breach or create (dis-)connecting landscape features switching on and off certain parts of catch-ments over certain timeframes (Harvey, 2001; Fryirs et al., 2007). As aconsequence, connectivity in geomorphic systems changes over time –either due to natural processes and/or anthropogenic factors – alteringor inducing process-form relationships (e.g. via feedback processes)that determine geomorphic change (Turnbull et al., 2008; Wainwrightet al., 2011; Bracken et al., 2015).

Dams, for example can be seen as ramped human disturbancespermanently decreasing longitudinal connectivity until the dam is

Fig. 2. Grain-size-selective reduction of longitudinal suspended sediment connectivity cause(adapted from Poeppl, 2012): nearly all silt is retained, while clay is transported through the im

removed which further results in channel erosion in the downstreamriver reaches due to a lack of sediments (Kondolf, 1997). However, geo-morphic response to dam construction has been shown to be complexin space and time as being determined by the system-specific boundaryconditions (incl. system history) and self-regulatory system propertiesrelated to feedback processes. As shown by Williams and Wolman(1984) geomorphic changes following dam construction can be rapidin semi-arid regions (i.e. up to 1 m of bed erosion per year), while else-where (e.g. along the Peace River below the Bennett Dam, Canada)mor-phological adjustment has been shown to be of the order ofmillennia asa result of the small magnitude of bed material transport (Church,1995). Contrarily, stable bars of coarse sediments had been observedat major tributary confluences along regulated rivers (Graf, 1980).Moreover, accelerated rates of sedimentation had been describedwhere regulation had reduced tributary base-levels during floods, caus-ing tributary degradation at the junctions (e.g. Makkaveyev, 1972;Kellerhals and Grill, 1973; see Petts and Gurnell (2005) as a conse-quence of emerging feedback processes between the main river andits downstream tributaries. Additionally, geomorphic response to damconstruction as well as their removal have been shown to be influencedby emerging feedback processes in multi-dam systems (Skalak et al.,2013), further being governed by the proximity of other dams, channel

d by a 6 m high overflow dam located in a mixed-load section of the Kaja River, Austriapoundment and across the dam crest.

Fig. 3. Conceptual model on the relationship between connectivity, sensitivity andresilience in geomorphic systems (right) as further being influenced system-intrinsicself-regulatory mechanisms and different types of human disturbance (pulsed/ramped;exemplified left).

242 R.E. Poeppl et al. / Geomorphology 277 (2017) 237–250

engineering and related legacy effects (Poeppl et al., 2015). The latterexamples clearly show how dam-induced changes of longitudinal con-nectivity trigger off-site geomorphic feedback processes that further de-termine the trajectories of geomorphic response to human disturbance.

Feedback processes are system-intrinsic self-regulatory properties:a negative feedback brings about an adjustment that counters or limitsthe initial change, while positive feedbacks are self-enhancing mecha-nisms that tend to cause instability within systems (for an overviewon feedback relationships in geomorphology, see King, 1970; Murrayet al., 2008; Chin et al., 2014). A simple scenario exemplifying dam-induced functional linkages between the different spatial dimensionsof connectivity via positive and negative feedback processes and relatedgeomorphic off-site effects is presented in Fig. 5. Dams decrease longitu-dinal connectivity which often further results in channel erosion in thedownstream river reaches due to a lack of sediments (Kondolf, 1997). Acommon consequence of channel erosion is bank undercutting followed

Fig. 4. Hillslope-channel (dis-)connectivity in the Ghandaki valley near Jharkot, Nepal. Low hiltivity in the centre of the picture.Photo: R. Pöppl, 2016

by bank or slope failure (e.g. Lawler and Leeks, 1992; cf. Brunsden, 2001;Fig. 6) locally increasing lateral connectivity (Fig. 5A). Positive feedbackcan be observed when large quantities of bank or hillslope sedimententer the channel system, further causing channel blockage (e.g. dueto landslide dams; Korup, 2005; Fig. 7) and a decline of longitudinalconnectivity (Pearce andWatson, 1983; see Fig. 5A). A similar, yet relat-ed to different spatial dimensions of connectivity and type of feedbackmechanism is shown in Fig. 5B. Dam-induced channel bed degradationin the downstream reaches often causes channel bed armouring (e.g.Vericat et al., 2006)which significantly decreases vertical sediment con-nectivity (Prudic et al., 2007). Bed armouring in turn increases hydraulicroughness andwith this streampower and thus longitudinal connectiv-ity (Gomez, 1994), representing a negative feedback mechanism.

Pulsed human disturbances such as extensive deforestation can leadto an abrupt increase in lateral connectivity which is followed by a re-covery phase (see also Fig. 3). Duration and type of recovery and relatedgeomorphic effects further depend on system-specific boundary condi-tions (e.g. climate) and self-regulatory system properties related to veg-etation dynamics. Vegetation and vegetation change significantly affectssurface runoff and sediment dynamics on the hillslopes themselves fur-ther governing lateral sediment input rates to the channel systems (fora comprehensive review on vegetation-geomorphology linkages seeMarsten, 2010). To underpin the complex relationship between vegeta-tion dynamics, recovery of lateral connectivity and the trajectories ofgeomorphic change in channel systems we present a simple example,however quite common for temperate climates, showing the effects ofcatchment deforestation followed by natural vegetation recovery dueto land abandonment on lateral connectivity and channel morphologyin the Dragonja catchment, Slovenia.

The Dragonja catchment has seen an increase in forest cover of N60%from1954 to2002most evident on the steep slopes adjacent to the riverchannel which were previously cultivated on small terraces beforebeing abandoned in the 1950s–1960s. Abandoned fields initiallyreverted to grassland before returning to a fully forested state over30 years. Due to natural reforestation, distinct nonlinear changes wereobserved in both the hydrological and sediment dynamics in the catch-ment (Fig. 8). The dense vegetation cover on the slopes between thesource area, the fields on hill crests, and the river, decreased channelsediment influx by N90% (Keesstra, 2007). Furthermore, water influxdecreased due to the trees' higher water demand compared to

lslope-channel connectivity can be seen in the lower right, high hillslope-channel connec-

Fig. 5. Conceptual model on positive (+) and negative (−) feedback processes between the different spatial dimensions of connectivity in fluvial systems as being triggered by damconstruction (i.e. ramped human disturbance): the different spatial dimensions are shown to be functionally linked by feedback mechanisms that further govern the trajectory ofgeomorphic response to human disturbance. Dam construction generally decreases (−) longitudinal connectivity which further induces geomorphic channel changes upstream (US)and downstream (DS), i.e. increasing (+) lateral connectivity (A) and decreasing (−) vertical connectivity (B), in turn affecting longitudinal connectivity (i.e. feedback processes).

243R.E. Poeppl et al. / Geomorphology 277 (2017) 237–250

agricultural fields. However, relative changes in water discharge werenot as large as sediment influx resulting in a nonlinear decrease of hy-drological and sediment connectivity (see Fig. 8). As a consequence,river water was depleted of sediment causing channel incision(Keesstra, 2007). Channel incision occurred in two phases: firstly, inci-sion occurred immediately post large-scale abandonment of agricultur-al fields. Bare fields, previously susceptible to erosion, were quicklyinvaded by pioneer species of herbs and grasses exhibiting a relativelylow water demand (Keesstra et al., 2009). In this phase, the percentageof discharged rainfall (the rainfall-runoff ratio) and the resulting riverdischarge had not changed significantly, but sediment flux had, causingmajor channel incision of ~2m (Fig. 9),while the secondphase occurred~30 years after initial land abandonment. Since 1975, a 30–35 year oldstand of forest developed on the former fields. These forests have highwater demand and therefore generate less runoff in all periods of theyear (Keesstra, 2007), with both peak and base flows decreasing. Thelower peak flow results from higher interception and infiltration dueto the higher leaf area of the forest, improved soil structure, higher or-ganic matter content, higher root density and thicker litter layers inthe forest compared to the former cropped fields. Due to lower peakflows, gravel bars in the river have stabilized and are currently over-grown by pioneer vegetation that has further stabilized the bars (seeFig. 9). These bars function as the floodplain area – currently used for

Fig. 6. Slope undercutting inPhoto: R. Pöppl, 2016.

grazing – throughwhich the undersized river meanders within the cur-rently oversized channel bed, incising an additional 0.5 m since 1975(Keesstra, 2007).

3.3. Connectivity in coupled human-geomorphic systems (3)

The causalities of management decisions and thus of type, localityand duration of human disturbance are strongly related to the sensitiv-ity and resilience of social systems which is further governed by the de-gree of connectedness (incl. feedback processes) between internalcontrolling variables and processes (Holling, 2001). Social systemswith low connectivity have weak control and thus low resilience/highsensitivity (i.e. high vulnerability) to disturbance (cf. Holling, 2001). Innatural hazard research, resilience and vulnerability of populations todifferent types of natural (incl. hydro-geomorphic) hazards have beenstrongly influenced by different controlling variables that are furthersubject to spatial and temporal change (cf. Cutter and Finch, 2008).

Controlling variables of social systems include knowledge, technolo-gy, social organisation, population (e.g. density and locality) and values(e.g. economic) which are interrelated via feedback processes that fur-ther influence human behaviour and the repertoire of human actions(Marten, 2001; Urban, 2002; Fig. 10). The degree of connectivity be-tween geomorphic and social systems (i.e. the strength of “human-

the Lupra valley, Nepal.

Fig. 7. Breached landslide dam in the Kali Ghandaki River near Beni, Nepal.Photo: R. Pöppl, 2016.

244 R.E. Poeppl et al. / Geomorphology 277 (2017) 237–250

geomorphic connectivity”) is therefore also strongly dependent on thestrength of connectivity within both sub-systems (Fig. 11). Connectivitybetween geomorphic and social systems is characterized by thepresence of process-response feedback loopswhich are triggered by dif-ferent types of human disturbance (e.g. different types of river andcatchmentmanagement) or (human-induced) geomorphic disturbanceaffecting the social system (see Fig. 11; for an overview on feedback re-lationships between social and geomorphic systems see Chin et al.,2014). Different types of river and catchment management decisionsare governed by human needs (e.g. increasing food demand due to pop-ulation increase) or technological changes (e.g. during industrialisation;see Fig. 10). Referring to fluvial systems, in the following we use twosimple examples to demonstrate how changes in social systems cantrigger a process-response feedback loop between social and geomor-phic systems that further governs the trajectory of landscape changein coupled human-geomorphic systems.

Dams, for example, areman-made features constructed for differentpurposes to fulfil human needs such as hydropower generation, floodcontrol or fish farming. Besides the direct effects of large reservoirs

Fig. 8. Comparison of the yearly sediment outflow and yearly average discharge of theDragonja River from 1960 to 2002 (Keesstra, 2006).

upon individuals and families who are forced to resettle or otherwisealter their livelihood patterns (McCully, 2001; Sneddon and Fox,2008), dam construction induces geomorphic processes such as up-stream channel aggradation and downstream erosion due to a changein longitudinal connectivity (cf. Kondolf, 1997). These geomorphic re-sponses may also compromise values of the social system, e.g. reservoirsedimentation reduces dam efficiency while downstream erosion mayreduce bank and slope stability further affecting infrastructure locatedin the vicinity of the river. As a consequence, further intervention suchas dam excavation or removal or channel bank and/or bed protectionmeasures may become necessary which in turn again induces furthergeomorphic responses. Dam removal, for example induces upstreamerosion further affecting bank and slope stability (Williams andWolman, 1984) where the installation of channel protection measuresmay become necessary. However, a major problem for river manage-ment is that the time scales relevant to human processes and institu-tions and related management decisions are often short compared tothe time frames of geomorphic processes (Kondolf and Podolak, 2014)and lag times between forcing factors (e.g. dam removal) and systemresponses (Chin et al., 2014). Furthermore, legacy effects of past distur-bances condition modern morphodynamics and alter the trajectories ofgeomorphic system responses (Liu et al., 2007; see Fig. 10).

Walter and Merritts (2008), for example exhibited that gravel-bedstreams in the mid-Atlantic piedmont region of the eastern US are ac-tively incising into legacy sediment left when thousands of milldamswere abandoned during the nineteenth century due to the adoption ofsteam engines (i.e. a change in technology; see Fig. 10). Increased sedi-ment yields to downstream nearshore environments called forsediment-control efforts in river corridors thereby further influencingmodern system response to dam removal. A similar example can befound in Poeppl et al. (2015) who investigated the geomorphic legacyeffects of medieval dams in the Bohemian Massif, Austria. Along the11.7 km long Kaja River, a small mixed-load low mountain rangestream, 14 dams and reservoirs existed which had been built for exten-sive fish farming purposes. Due to reservoir sedimentation combinedwith a rapid loss in the importance of fish farming economy the major-ity of these dams had been removed whichwas followed by active inci-sion into legacy reservoir sediments. Incision and lateral erosion furtheraffected newly acquired agricultural fields in the vicinity of the river

Fig. 9. Channel changes in theDragonja River since the 1950s: a) channel narrowing through time (1954, 1975, 1985 and 1994) from aerial photographs just upstream from the confluenceof theDragonja and itsmajor tributary, the Rokava. Arrows indicate locations of channel narrowing; b) schematic diagram of channel planformchanges in the Dragonja River from 1945 to2002. Before reforestation (1945), the river was braided. However, from 1945 to 1975, the river incised and formed a terrace 1.5 m above the current river. From 1975 to 2002, incisioncontinued,while the river started tomeanderwithin the confines of the older riverbed (cf. Keesstra et al., 2005). Darker grey areas represent the highest terrace at 2.5m above the currentriverbed; light grey areas represent the terrace at 1.5 m, and white areas are 0.5 m above the current riverbed.

245R.E. Poeppl et al. / Geomorphology 277 (2017) 237–250

which called for the installation of channel protection measures(Fig. 12).

As shown in the examples above there is a need to integrate notionsof connectivity in both, conceptual frameworks and empirical (includ-ing quantitative) approaches in order to better understand resilience/sensitivity and thus causes and trajectories of human-geomorphic sys-tems to change. However, quantification of connectivity – either withingeomorphic or social systems or between them – is a difficult task dueto the complexity inherent in these systems. As quantification of con-nectivity in these systems strongly depends on the specific researchquestion and thus the respective temporal and spatial scale of study,the applied techniques and therefore also the respective key tools arehighly variable (see Section 4).

4. Key tools to quantify connectivity in geomorphic and coupledhuman-geomorphic systems: an overview

In a geomorphological context, techniques to measure connectivitycan range from single-event small-scale measurements (cf. Cerdanet al., 2010) to multi-annual large-scale monitoring (e.g. Verstraetenet al., 2003). Besides deriving connectivity from measuring structureand fluxes in the field, advances in index development (e.g. Cavalliet al., 2013) and modelling approaches (e.g. Baartman et al., 2013)have been made over the past years. Connectivity indices mainly use acombination of topography and vegetation characteristics to determineconnectivity (e.g. Borselli et al., 2008; Cavalli et al., 2013). Indices arestatic representations of structural connectivity, which are useful for

Fig. 10. Conceptual model of human-geomorphic connectivity determined by the presence of process-response feedback loops (bold black arrows) between fluvial and social systemswhich are triggered byhumandisturbances (e.g. different types of river and catchmentmanagement) or (human-induced) geomorphic disturbances/responses affecting the social system.

246 R.E. Poeppl et al. / Geomorphology 277 (2017) 237–250

determining areas of high and low structural connectivity within thestudy areas. Based on GIS analyses, Borselli et al. (2008) developed aconnectivity index (IC) reflecting the potential for each cell within acatchment system to receive sediments from other parts of the

Fig. 11. Conceptual model on the relationships between connectivity, sensitivity and resilienregulatory properties associated to positive and negative feedback processes as well as being c

landscape and governed by catchment surface, slope gradient andtype of land use. However, because indices are static, they do not pro-vide information about fluxes and thus functional connectivity. Differ-ent types of models (e.g. cellular automata, statistical models), on the

ce in social and geomorphic systems as further being governed by system-intrinsic self-onnected via human and geomorphic disturbance.

Fig. 12. Dam section along the Kaja River, Austria (flow direction from South to North;adapted from Poeppl et al., 2015). “r”= removed dams, “a”= active dam. Note: Channelerosion at lowermost removed dam (no channel engineering) vs. no channel erosion at re-moved dams upstream (engineered); former reservoir area upstream of the uppermostremoved dam is still clearly visible (dashed line).

247R.E. Poeppl et al. / Geomorphology 277 (2017) 237–250

other hand, do provide information on (potential) fluxes and can bepowerful tools in determining how structural connectivity relates tosediment transport (e.g. Mueller et al., 2007; Poeppl et al., 2012;Heckmann and Schwanghart, 2013; Baartman et al., 2013). Baartmanet al. (2013), for example, used a landscape evolution model calledLAPSUS to simulate sediment connectivity of different landscapetypes, relating feedback mechanisms between erosion and depositionto landscape complexity.

Integrative modelling tools for linking and quantifying geomorphicand human processes are also available (for an overview see Zvoleffand An (2014) or Chin et al. (2014)). These include agent-based andspatial simulation models such as provided by Werner and McNamara(2007) in which they used a cellular agent-based modelling approachto investigate the dynamics of coupled human-landscape systemsalong a single reach of the Mississippi River in New Orleans involvingand linking the following factors (Fig. 13): 1. The state of the landscapewith variables defined on a one-dimensional array of cells (for problemsinvolving coastlines) or a two-dimensional array covering a tightlycoupled landmass (as in a river floodplain), i.e. the landscape model;2. The state of the economy within that landmass using variables asso-ciated with those cells that specify supply, demand and price of productaswell as revenues and profits for economic actors and their predictionsfor the future, i.e. the economic and political model; 3. The impact of thelandscape on the economy through the effect of repeated fast-scaledamage events and slowly varying changes to the landscape, i.e. thehazard model; 4. The impact of the economy on the landscape through

the effect of economically driven alterations to the landscape tomitigatedamage, i.e. the hazard mitigation model.

Although the approach of Werner and McNamara (2007) is seen as amajor leap forward inmodelling complex coupling relationships betweengeomorphic and social systems, it is arguedhere that the landscapemodelthey useddoes not integrate notions of connectivity as: a) being restrictedto a single part of a catchment system, and b)widely neglecting aspects oflandscape evolution that govern the spatio-temporal dynamics of connec-tivity. Note that a) could be overcome by adding static information onconnectivity to each cell of the array as being provided by the calculationof connectivity indices across catchment systems (e.g. Borselli et al., 2008;Cavalli et al., 2013),while b) could be addressed byusing a landscape evo-lutionmodel (e.g. LAPSUS or CAESAR-Lisflood) instead of static represen-tations of the landscape.

5. Discussion and conclusions

5.1. Human impact on connectivity in fluvial systems (1)

The proposed framework on human impact on connectivity in fluvialsystems conceptualizes the on-site effects of common human impacts(i.e. pulsed or ramped types; Brunsden and Thornes, 1979) on differentspatial dimensions of connectivity in fluvial systems (Ward, 1989;Brierley et al., 2006; Fryirs et al., 2007). With this, a systematic basis fora more detailed conceptualization of complex geomorphic response tohuman disturbance is provided. Complex geomorphic response is con-ceptualized as being governed by connectivity relationships and thussensitivity, resilience as well as by system-intrinsic self-regulatory pro-cesses (2). Furthermore, such a systematic representation on the effectsof different types of human disturbances and knowledge on where andhow disturbance interrupts or enhances connectivity in fluvial systemsis deemed necessary to better understand the role of human agency inaltering catchment-scale sediment fluxes and thus geomorphic responseto change. These considerations are also in line with Gregory (1987,2006) in which he posed important key questions in relation to researchon human impact upon river channels, i.e. what causes/will change, howmuch change occurs/how longwill it take/howdoes it occur,whenwill itstart and finish, where will it occur, and why will it change hazards andrisks/why will it increase costs? Our conceptual framework on humanimpact on connectivity in fluvial systems (1), addresses the key ques-tions on what causes change, where initial changes occur and providesbasic information on which dimensions of connectivity are directly af-fected by which type of human disturbance, further forming the basisfor (2).

5.2. Geomorphic response to human disturbance: connectivity, sensitivity,resilience and self-regulation (2)

Considerations on the sensitivity and resilience of geomorphic sys-tems to change (Brunsden and Thornes, 1979; Brunsden, 2001; Harvey,2001) and recent advances in hydrological and sediment connectivity re-search (e.g. Bracken and Croke, 2007; Lexartza-Artza and Wainwright,2009; Wainwright et al., 2011; Bracken et al., 2015), have led to the de-velopment of a conceptual model in which we provide information onthe role of different types of human agency in altering/inducing function-al relationships between the different spatial dimensions of connectivityin fluvial systems. These relationships and self-regulatory system prop-erties associated with feedback processes and vegetation dynamics arefurther conceptualized to determine the spatio-temporal trajectories ofgeomorphic response (incl. off-site effects) to different types of humandisturbance.

It has been shown that the geomorphic response to ramped distur-bance (dam construction) is being governed by strong functional link-ages between the different spatial dimensions of connectivity andemerging feedback mechanisms. Furthermore, geomorphic responseto dam construction and removal has been shown to be complex in

Fig. 13. Conceptualization ofWerner and McNamara's cellular agent-basedmodelling approach to investigate the dynamics of coupled human-landscape systems (adapted fromWernerand McNamara, 2007): landscape processes (left) dominated by water, sediment or biological routing and transformation, with morphology, vegetation, river channel, ocean, fire andsurface water flow (“landscape model”); human processes (right) dominated by economic and political dynamics, showing homes and businesses (“economic and political model”);landscapes impact humans (top) through damage (to buildings shown here) from natural disasters and slowly varying changes to landscape (“damage model”); humans impactlandscape (bottom) through effects of economically driven landscape modifications to mitigate damage, with a levee and a water drop on a fire (“hazard mitigation model”).

248 R.E. Poeppl et al. / Geomorphology 277 (2017) 237–250

space and time as being determined by the system-specific boundaryconditions (incl. system history, related legacy effects and lag times;Walter and Merritts, 2008; Brierley, 2010; Poeppl et al., 2015). More-over, it has been further demonstrated that geomorphic response toland abandonment is complex in space and time and governed by therecovery time of the system after disturbance. This is itself strongly re-lated to vegetation dynamics in influencing hydrological and sedimentconnectivity in a nonlinear way (Keesstra et al., 2009). These observa-tions are further comparablewith observations on the effects of refores-tation on catchment systems as presented in Harden and Mathews(2002), Liebault et al. (2002) and Marston et al. (2003).

Returning to the key questions raised by Gregory (2006), our concep-tual models (2) and (3) provide useful information to address questionsabout how and why causes and trajectories of change in fluvial systemsoccur. Ourmodel (2) is in linewith conceptual frameworks on connectiv-ity in which system complexity and thus system response to change isconceptualized as being governed by structural and functional interde-pendencies (e.g. Lexartza-Artza and Wainwright, 2009; Wainwrightet al., 2011; Bracken et al., 2015) and system-intrinsic self-regulatorymechanisms (e.g. King, 1970; Murray et al., 2008; Phillips, 2009; Chinet al., 2014). The proposed conceptual models (1) and (2) are consideredto involve innovative potential in the context of human-impact researchin fluvial geomorphology, in putting forward existing connectivity con-cepts and providing potentially valuable information for river and catch-ment management by: a) systematically addressing the role of differenthuman agencies (i.e. external disturbance) in altering/inducing function-al connectivity relationships, and b) further relating these to system-intrinsic mechanisms that govern the propagation (incl. off-site effects)and spatio-temporal trajectories of geomorphic change.

The proposed framework is not capable of providing generalized in-formation on how much change occurs/how long will it take/how doesit occur, whenwill it start and finish, andwhere will it occur as these pa-rameters have been shown to be highly system-specific. Instead a cau-tionary note is flagged regarding the need to attain “catchment-specificknowledge of landscape character and behaviour, connectivity and evo-lution to provide a physical platform with which to engender effectiveriver and catchment engagement (e.g. Brierley et al., 2002)” (Brierleyet al., 2006; p. 166).

5.3. Connectivity in coupled “human-geomorphic systems” (3)

Based on fundamental concepts on resilience (e.g. Holling, 2001) andfeedback relationships (e.g. Chin et al., 2014) in the context of coupledhuman-landscape systems research as well as based on our consider-ations as presented in (1) and (2), we developed a theoretical modelconceptualizing connectivity between geomorphic and social systems.Connectivity between geomorphic and social systems is considered asbeing dependent on the connectivity, sensitivity and thus resilience ofthese systems to (human-induced) change. Connectivity between geo-morphic and social systems has been further shown to be characterizedby the presence of process-response feedback loops which are triggeredby different types of human disturbance (e.g. different types of river andcatchment management) or (human-induced) geomorphic disturbanceaffecting the social system. We used different examples from the litera-ture to underpin our model assumptions and to further address the im-portance and surplus value of integrating notions of connectivity inboth, conceptual frameworks and empirical (including quantitative) ap-proaches in order to better understand resilience/sensitivity and thus

249R.E. Poeppl et al. / Geomorphology 277 (2017) 237–250

causes and trajectories of human-geomorphic systems to change. More-over, we indicated potential options to integrate representations of con-nectivity in fluvial systems to existing modelling frameworks (e.g.Werner and McNamara, 2007) including the integration of connectivityindices (e.g. Borselli et al., 2008) and/or landscape evolution models(e.g. LAPSUS or CAESAR-Lisflood). However, to date these options andthus their potential additional value to better reflect the complexity ofhuman-geomorphic systems as well as their applicability – either inthe context of geomorphological research or adaptive river and catch-ment management – remain untested and are subject to further inquiry.

References

Alberti, M., Marzluff, J.M., Shulenberger, E., Bradley, G., Ryan, C., Zumbrunnen, C., 2003. In-tegrating humans into ecology: opportunities and challenges for studying urban eco-systems. Bioscience 53 (12), 1169–1179.

Ali, G.A., Roy, A.G., 2009. Revisiting hydrologic sampling strategies for an accurate assess-ment of hydrologic connectivity in humid temperate systems. Geogr. Compass 3 (1),350–374.

Arcement, G.J., Schneider, V.R., 1989. Guide for selecting Manning's roughness coefficientsfor natural channels and floodplains. USGS Water-Supply Paper 2339.

Baartman, J.E., Masselink, R., Keesstra, S.D., Temme, A.J., 2013. Linking landscape morpho-logical complexity and sediment connectivity. Earth Surf. Process. Landf. 38 (12),1457–1471.

Barrows, H.H., 1923. Geography as human ecology. Ann. Assoc. Am. Geogr. 13 (1), 1–14.Bednarek, A.T., 2001. Undamming rivers: a review of the ecological impacts of dam re-

moval. Environ. Manag 27 (6), 803–814.Booth, D.B., Jackson, C.R., 1997. Urbanization of aquatic systems: degradation thresholds,

stormwater detection, and the limits of mitigation. J. Am.Water Resour. Assoc. 33 (5),1077–1090.

Borselli, L., Cassi, P., Torri, D., 2008. Prolegomena to sediment and flow connectivity in thelandscape: a GIS and field numerical assessment. Catena 75, 268–277.

Boulton, A.J., Findlay, S., Marmonier, P., Stanley, E.H., Valett, H.M., 1993. The functional sig-nificance of the hyporheic zone in streams and rivers. Annu. Rev. Ecol. Syst. 29,59–81.

Bracken, L.J., Croke, J., 2007. The concept of hydrological connectivity and its contributionto understanding runoff-dominated geomorphic systems. Hydrol. Process. 21 (13),1749–1763.

Bracken, L.J., Wainwright, J., Ali, G.A., Tetzlaff, D., Smith, M.W., Reaney, S.M., Roy, A.G.,2013. Concepts of hydrological connectivity: research approaches, pathways and fu-ture agendas. Earth-Sci. Rev. 119, 17–34.

Bracken, L.J., Turnbull, L., Wainwright, J., Bogaart, P., 2015. Sediment connectivity: aframework for understanding sediment transfer at multiple scales. Earth Surf. Pro-cess. Landf. 40, 177–188.

Brierley, G.J., 2010. Landscape memory: the imprint of the past on contemporary land-scape forms and processes. Area 42 (1), 76–85.

Brierley, G.J., Fryirs, K., Outhet, D., Massey, C., 2002. Application of the river styles frame-work as a basis for river management in New SouthWales, Australia. Appl. Geogr. 22,91–122.

Brierley, G., Fryirs, K., Jain, V., 2006. Landscape connectivity: the geographic basis of geo-morphic applications. Area 38 (2), 165–174.

Brooker, M.P., 1985. The ecological effects of channelization. Geogr. J. 151 (1), 63–69.Brooks, C.P., 2003. A scalar analysis of landscape connectivity. Oikos 433–439.Brooks, A.P., Gehrke, P.C., Jansen, J.D., Abbe, T.B., 2004. Experimental reintroduction of

woody debris on the Williams River, NSW: geomorphic and ecological responses.River Res. Appl. 20 (5), 513–536.

Brunke, M., Gonser, T., 1997. The ecological significance of exchange processes betweenrivers and groundwater. Freshw. Biol. 37, 1–33.

Brunsden, D., 1993. The persistence of landforms. Z. Geomorphol. Suppl. 93, 13–28.Brunsden, D., 2001. A critical assessment of the sensitivity concept in geomorphology. Ca-

tena 42, 99–123.Brunsden, D., 2002. Geomorphological roulette for engineers and planners: some insights

into an old game. Q. J. Eng. Geol. Hydrogeol. 35, 101–140.Brunsden, D., Thornes, J.B., 1979. Landscape sensitivity and change. Trans. Inst. Br. Geogr.

NS 4, 463–484.Cavalli, M., Trevisani, S., Comiti, F., Marchi, L., 2013. Geomorphometric assessment of spa-

tial sediment connectivity in small Alpine catchments. Geomorphology 188, 31–41.Cerdan, O., Govers, G., Le Bissonnais, Y., Van Oost, K., Poesen, J., Saby, N., Gobin, A., Vacca,

A., Quinton, J., Auerswald, K., Klik, A., Kwaad, F.J.P.M., Raclot, D., Ionita, I., Rejman, J.,Rousseva, S., Muxart, T., Roxo, M.J., Dostal, T., 2010. Rates and spatial variations ofsoil erosion in Europe: a study based on erosion plot data. Geomorphology 122(1–2), 167–177.

Chin, A., Florsheim, J.L., Wohl, E., Collins, B.D., 2014. Feedbacks in human-landscape sys-tems. Environ. Manag. 53 (1), 28–41.

Chorley, R.J., Kennedy, B.A., 1971. Physical Geography: A Systems Approach. Prentice-HallInternational.

Church, M., 1995. Geomorphic response to river flow regulation: case studies and time-scales. Regul. Rivers Res. Manag. 11 (1), 3–22.

Collins, B.D., Montgomery, D.R., Fetherston, K.L., Abbe, T.B., 2012. The floodplain large-wood cycle hypothesis: a mechanism for the physical and biotic structuring of tem-perate forested alluvial valleys in the North Pacific coastal ecoregion. Geomorphology139–140, 460–470.

Constantinescu, Ş., Achim, D., Rus, I., Giosan, L., 2015. Embanking the lower Danube: fromnatural to engineered floodplains and back. In: Hudson, P.F., Middelkoop (Eds.), Geo-morphic Approaches to Integrated Floodplain Management of Lowland Fluvial Sys-tems in North America and Europe. Springer, New York, pp. 265–288.

Croke, J., Mockler, S., 2001. Gully initiation and road-to-stream linkage in a forested catch-ment, Southeastern Australia. Earth Surf. Process. Landf. 26, 205–217.

Croke, J., Mockler, S., Fogarty, P., Takken, I., 2005. Sediment concentration changes in run-off pathways from a forest road network and the resultant spatial pattern of catch-ment connectivity. Geomorphology 68, 257–268.

Cutter, S.L., Finch, C., 2008. Temporal and spatial changes in social vulnerability to naturalhazards. Proc. Natl. Acad. Sci. 105 (7), 2301–2306.

Dearing, J.A., 2008. Landscape change and resilience theory: a palaeoenvironmental as-sessment from Yunnan, SW China. The Holocene 18 (1), 117–127.

Dearing, J.A., Battarbee, R.W., Dikau, R., Larocque, I., Oldfield, F., 2006. Human–environment interactions: learning from the past. Reg. Environ. Chang. 6 (1-2), 1–16.

Doyle, M.W., Stanley, E.H., Orr, C.H., Selle, A.R., Sethi, S.A., Harbor, J.M., 2005. Stream eco-system response to small dam removal: lessons from the Heartland. Geomorphology71 (1), 227–244.

Dunn, S.M., Mackay, R., 1996. Modelling the hydrological impacts of open ditch drainage.J. Hydrol. 179, 37–66.

European Union (EU) Water Framework Directive, 2000. Directive 2000/60/EC of theEuropean Parliament and of the Council of 23 October 2000 Establishing a Frame-work for Community Action in the Field of Water Policy.

Folke, C., 2006. Resilience: the emergence of a perspective for social–ecological systemsanalyses. Glob. Environ. Chang. 16 (3), 253–267.

Fryirs, K.A., 2013. (Dis)connectivity in catchment sediment cascades: a fresh look at thesediment delivery problem. Earth Surf. Process. Landf. 38 (1), 30–46.

Fryirs, K., Brierley, G.J., 1999. Slope–channel decoupling in Wolumla catchment, NewSouth Wales, Australia: the changing nature of sediment sources followingEuropean settlement. Catena 35, 41–63.

Fryirs, K.A., Brierley, G.J., Preston, N.J., Kasai, M., 2007. Buffers, barriers and blankets: the(dis)connectivity of catchment-scale sediment cascades. Catena 70 (1), 49–67.

Gomez, B., 1994. Effects of particle shape and mobility on stable armor development.Water Resour. Res. 30 (7), 2229–2239.

Goudie, A.S., 2006. Global warming and fluvial geomorphology. Geomorphology 79 (3),384–394.

Graf, W.L., 1980. The effect of dam closure on downstream rapids. Water Resour. Res 16,129–363.

Gregory, K.J., 1987. River channels. In: Gregory, K.J., Walling, D.E. (Eds.), Human Activityand Environmental Processes. Wiley, Chichester, pp. 207–235.

Gregory, K.J., 2006. The human role in changing river channels. Geomorphology 79,172–191.

Grimshaw, D.L., Lewin, J., 1980. Reservoir effects on sediment yield. J. Hydrol 47, 163–171.Harden, C.P., Mathews, L.E., 2002. Hillslope runoff and soil erosion following reforestation

in the Copper Basin, Tennessee, USA. Aust. Geogr. Stud. 40 (2), 130–142.Harden, C.P., Chin, A., English, M.R., Fu, R., Galvin, K.A., Gerlak, A.K., McDowell, P.F.,

McNamara, D.E., Peterson, J.M., Poff, N.L., Rosa, E.A., Solecki, W.D., Wohl, E.E., 2014.Understanding human-landscape interactions in the ‘Anthropocene’. Environ.Manag. 53 (4), 4–13.

Hart, D.D., Johnson, T.E., Bushaw-Newton, K.L., Horwitz, R.J., Bednarek, A.T., Charles, D.F.,Kreeger, D.A., Velinsky, D.J., 2002. Dam removal: challenges and opportunities forecological research and river restoration We develop a risk assessment frameworkfor understanding how potential responses to dam removal vary with dam and wa-tershed characteristics, which can lead tomore effective use of this restoration meth-od. Bioscience 52 (8), 669–682.

Harvey, A.M., 1997. Coupling between hillslope gully systems and stream channels in theHowgill Fells, northwest England: temporal implications. Geomorphol. Relief Process.Environ. 1, 3–20.

Harvey, A.M., 2001. Coupling between hillslopes and channels in upland fluvial systems:implications for landscape sensitivity, illustrated from the Howgill Fells, northwestEngland. Catena 42, 225–250.

Harvey, A.M., 2002. Effective timescales of coupling within fluvial systems. Geomorphol-ogy 44, 175–201.

Harvey, A.M., 2007. Differential recovery from the effects of a 100-year storm: signifi-cance of long-term hillslope-channel coupling; Howgill Fells, northwest England.Geomorphology 84, 192–208.

Harvey, A.M., 2012. The coupling status of alluvial fans and debris cones: a review andsynthesis. Earth Surf. Process. Landf. 37 (1), 64–76.

Heckmann, T., Schwanghart, W., 2013. Geomorphic coupling and sediment connectivityin an alpine catchment — exploring sediment cascades using graph theory. Geomor-phology 182, 89–103.

Holling, C.S., 2001. Understanding the complexity of economic, ecological, and social sys-tems. Ecosystems 4, 390–405.

Hooke, J.M., 2003. Coarse sediment connectivity in river channel systems: a conceptualframework and methodology. Geomorphology 56, 79–94.

Keesstra, S.D., 2006. Impact of Natural Reforestation on the Hydrology, Geomorphologyand Sediment Budget of the Dragonja River, SW Slovenia (PhD Thesis) VrijeUniversiteit, Amsterdam (188 pp.).

Keesstra, S.D., 2007. Impact of natural reforestation on floodplain sedimentation in theDragonja basin, SW Slovenia. Earth Surf. Process. Land. 32 (1), 49–65.

Keesstra, S.D., van Huissteden, J., Vandenberghe, J., Van Dam, O., de Gier, J., Pleizier, I.D.,2005. Evolution of the morphology of the river Dragonja (SW Slovenia) due toland-use changes. Geomorphology 69, 191–207.

Keesstra, S.D., van Dam, O., Verstraeten, G., van Huissteden, J., 2009. Changing sedimentgeneration due to natural reforestation in the Dragonja catchment, SW Slovenia. Ca-tena 78, 60–71.

250 R.E. Poeppl et al. / Geomorphology 277 (2017) 237–250

Kellerhals, R., Gill, D., 1973. Observations and potential downstream effects of large stor-age projects in Northern Canada. Trans. 11th Int. Congr, on Large Dams, Madrid,Spain. ICOLD, Paris, pp. 731–754.

Kindlmann, P., Burel, F., 2008. Connectivity measures: a review. Landsc. Ecol. 23 (8),879–890.

King, C.A.M., 1970. Feedback relationships in geomorphology. Geogr. Ann. Ser. A Phys.Geogr. 52 (3/4), 147–159.

Kingsford, R.T., 2000. Ecological impacts of dams, water diversions and river managementon floodplain wetlands in Australia. Aust. Ecol. 25, 109–127.

Kirkby, M.J., Bracken, L.J., Reaney, S., 2002. The influence of landuse, soils and topographyon the delivery of hillslope runoff to channels in SE Spain. Earth Surf. Process. Landf.27, 1459–1473.

Kondolf, G.M., 1997. PROFILE: hungry water: effects of dams and gravel mining on riverchannels. Environ. Manag. 21 (4), 533–551.

Kondolf, G.M., Podolak, K., 2014. Space and time scales in human-landscape systems. En-viron. Manag. 53 (1), 76–87.

Kondolf, G.M., Piégay, H., Sear, D., 2003. Integrating geomorphological tools in ecologicaland management studies. Tools in Fluvial Geomorphology, pp. 633–660.

Korup, O., 2005. Geomorphic imprint of landslides on alpine river systems, southwestNew Zealand. Earth Surf. Process. Landf. 30, 783–800.

Lawler, D.M., Leeks, G.J.L., 1992. River bank erosion events on the Upper Severn detectedby the Photo-Electronic Erosion Pin (PEEP) system. Erosion and Sediment TransportMonitoring Programmes in River Basins: Proceedings of the Oslo Symposium, August1992. International Association for Hydrological Sciences, Wallingford, UK,pp. 95–105.

Lexartza-Artza, I., Wainwright, J., 2009. Hydrological connectivity: linking concepts withpractical implications. Catena 79 (2), 146–152.

Lexartza-Artza, I., Wainwright, J., 2011. Making connections: changing sediment sourcesand sinks in an upland catchment. Earth Surf. Process. Landf. 36, 1090–1104.

Li, K.Y., Coe, M.T., Ramankutty, N., De Jong, R., 2007. Modeling the hydrological impact ofland-use change in West Africa. J. Hydrol. 337, 258–268.

Liebault, F., Clement, P., Piegay, H., Rogers, C.F., Kondolf, G.M., Landon, N., 2002. Contem-porary channel changes in the Eygues basin, southern French Prealps: the relation-ship between sub-basin variability and watershed characteristics. Geomorphology45, 53–66.

Liu, J., Dietz, T., Carpenter, S.R., Alberti, M., Folke, C., Moran, E., Pell, A.N., Deadman, P.,Kratz, T., Lubchenco, J., Ostrom, E., Ouyang, Z., Provencher, W., Redman, C.,Schneider, S.H., Taylor, W.W., 2007. Complexity of coupled human and natural sys-tems. Science 317 (5844), 1513–1516.

Liu, H., Zhang, T., Liu, B., Liu, G., Wilson, G.V., 2013. Effects of gully erosion and gully fillingon soil depth and crop production in the black soil region, northeast China. Environ.Earth Sci. 68, 1723–1732.

Magilligan, F.J., Graber, B.E., Nislow, K.H., Chipman, J.W., Sneddon, C.S., Fox, C.A., 2016.River restoration by dam removal: enhancing connectivity at watershed scales.Elementa 4 (1), 000108.

Makkaveyev, N.I., 1972. The impact of large water engineering projects on geomorphicprocesses in stream valleys. Geomorphologia 2, 28–34.

Marchmalo, M., Hooke, J.M., Sandercock, P.J., 2015. Flow and sediment connectivity insemi-arid landscapes in SE Spain: patterns and controls. Land Degrad. Dev. http://dx.doi.org/10.1002/ldr.2352.

Marston, R.A., Bravard, J.P., Green, T., 2003. Impacts of reforestation and gravel mining onthe Malnant River, Haute-Savoie, French Alps. Geomorphology 55 (1), 65–74.

Marsten, R.A., 2010. Geomorphology and vegetation on hillslopes: interactions, depen-dencies, and feedback loops. Geomorphology 116, 206–217.

Marten, G.G., 2001. Human ecology: Basic concepts for sustainable development.Earthscan.

Matthews, R., Selman, P., 2006. Landscape as a focus for integrating human and environ-mental processes. J. Agric. Econ. 57 (2), 199–212.

McCully, P., 2001. Silenced Rivers: The Ecology and Politics of Large Dams: Enlarged andUpdated Perspective. Zed Books, London.

Metzger, J.P., Décamps, H., 1997. The structural connectivity threshold: an hypothesis inconservation biology at the landscape scale. Acta Oecol. 18 (1), 1–12.

Moss, T., Monstadt, J. (Eds.), 2008. Restoring Floodplains in Europe: Policy Contexts andProject Experiences. IWA Publishing, London.

Mueller, E.N.,Wainwright, J., Parsons, A.J., 2007. Impact of connectivity on themodeling ofoverland flow within semiarid shrubland environments. Water Resour. Res. 43 (9).

Murray, A.B., Knaapen, M.A.F., Tal, M., Kirwan, M.L., 2008. Biomorphodynamics: physical–biological feedbacks that shape landscapes. Water Resour. Res. 44, W11301.

Nicholas, A.P., Ashworth, P.J., Kirkby, M.J., Macklin, M.G., Murray, T., 1995. Sediment slugs:large-scale fluctuations in fluvial sediment transport rates and storage volumes. Prog.Phys. Geogr. 19 (4), 500–519.

Nilsson, B., 1976. The influence of man's activities in rivers on sediment transport. Nord.Hydrol 7, 145–160.

Pahl-Wostl, C., 2007. Transitions towards adaptive management of water facing climateand global change. Water Resour. Manag. 21, 49–62.

Pahl-Wostl, C., Sendzimir, J., Jeffrey, P., Aerts, J., Berkamp, G., Cross, K., 2007. Managingchange toward adaptive water management through social learning. Ecol. Soc. 12(2), 30.

Pearce, A.J., Watson, A., 1983. Medium-term effects of two landsliding episodes on chan-nel storage of sediment. Earth Surf. Process. Landf. 8, 29–39.

Petts, G., Gurnell, A.M., 2005. Dams and geomorphology: research progress and future di-rections. Geomorphology 71, 27–47.

Phillips, J.D., 2009. Changes, perturbations, and responses in geomorphic systems. Prog.Phys. Geogr. 33 (1), 17–30.

Piégay, H., Gurnell, A.M., 1997. Large woody debris and river geomorphological pattern:examples from S.E. France and S. England. Geomorphology 19, 99–116.

Pierson, F.B., Robichaud, P.R., Spaeth, K.E., 2001. Spatial and temporal effects of wildfire onthe hydrology of a steep rangeland watershed. Hydrol. Process. 15, 2905–2916.

Pizzuto, J., 2002. Effects of dam removal on river form and process. Bioscience 52 (8),683–691.

Poeppl, R.E., Keiler, M., Elverfeldt, K.v., Zweimueller, I., Glade, T., 2012. The influence of ri-parian vegetation cover on diffuse lateral connectivity and biogeomorphic processesin amedium-sized agricultural catchment, Austria. Geogr. Ann. Ser. A Phys. Geogr. 94,511–529.

Poeppl, R.E., 2012. Investigating the Role of Humans as (Dis)connecting Agents in FluvialSystems—New Concepts and Applications for Fluvial Geomorphology and LandscapeResearch. Unpublished PhD thesis (typescript), Department of Geography and Re-gional Research, University of Vienna, Austria; 233 pp.

Poeppl, R.E., Keesstra, S.D., Hein, T., 2015. The geomorphic legacy of small dams — anAustrian study. Anthropocene 10, 43–55.

Pringle, C.M., 2001. Hydrologic connectivity and themanagement of biological reserves: aglobal perspective. Ecol. Appl. 11, 981–998.

Prudic, D.E., Niswonger, R.G., Harrill, J.R., Wood, J.L., 2007. Streambed infiltration andgroundwater flow from the Trout Creek drainage, an intermittent tributary to theHumboldt River, North-Central Nevada. USGS Professional Paper 1709 — Ground-Water Recharge in the Arid and Semiarid Southwestern United States (Chapter K).

Raush, D.L., Heinemann, H.G., 1975. Controlling trap efficiency. Trans. Am. Soc. Agric. Eng18, 1105–1113.

Schälchli, U., 1992. The clogging of coarse gravel beds by fine sediment. Hydrobiologia235 (236), 189–197.

Schumm, S.A., 1973. Geomorphic thresholds and complex response of drainage systems.In: Morisawa, M. (Ed.), Fluvial Geomorphology. SUNY Binghamton Publication inGeomorphology, pp. 299–310.

Skaggs, R.W., Brevé, M.A., Gilliam, J.W., 1994. Hydrology and water quality impacts of ag-ricultural drainage. Crit. Rev. Environ. Sci. Technol. 24 (1), 1–32.

Skalak, K.J., Benthem, A.J., Schenk, E.R., Hupp, C.R., Galloway, J.M., Nustad, R.A., Wiche, G.J.,2013. Large dams and alluvial rivers in the Anthropocene: the impacts of the Garrisonand Oahe Dams on the Upper Missouri River. Anthropocene 2, 51–64.

Sneddon, C., Fox, C., 2008. Struggles over dams as struggles for justice: the World Com-mission on Dams (WCD) and anti-dam campaigns in Thailand and Mozambique.Soc. Nat. Resour. 21 (7), 625–640.

Sorriso-Valvo, M., Bryan, R.B., Yair, A., Antronico, L., 1995. Impact of afforestation on hy-drological response and sediment production in a small Calabrian catchment. Catena25 (1-4), 89–104.

Taylor, P.D., Fahrig, L., Henein, K., Merriam, G., 1993. Connectivity is a vital element oflandscape structure. Oikos 571–573.

Turnbull, L., Wainwright, J., Brazier, R.E., 2008. A conceptual framework for understandingsemi-arid land degradation: ecohydrological interactions across multiple-space andtime scales. Ecohydrology 1, 23–34.

Urban, M.A., 2002. Conceptualizing anthropogenic change in fluvial systems: drainage de-velopment on the upper Embarras River, Illinois. Prof. Geogr. 54 (2), 204–217.

Vericat, D., Batalla, R.J., Garcia, C., 2006. Breakup and reestablishment of the armour layerin a large gravel-bed river below dams: the lower Ebro. Geomorphology 76, 122–136.

Verstraeten, G., Poesen, J., de Vente, J., Koninckx, X., 2003. Sediment yield variability inSpain: a quantitative and semiqualitative analysis using reservoir sedimentationrates. Geomorphology 50 (4), 327–348.

Wainwright, J., Turnbull, L., Ibrahim, T.G., Lexartza-Artza, I., Thornton, S.F., Brazier, R.E.,2011. Linking environmental regimes, space and time: interpretations of structuraland functional connectivity. Geomorphology 126, 387–404.

Walker, B., Holling, C.S., Carpenter, S.R., Kinzig, A., 2004. Resilience, adaptability andtransformability in social–ecological systems. Ecol. Soc. 9 (2), 5.

Walter, R.C., Merritts, D.J., 2008. Natural streams and the legacy of water-powered mills.Science 319, 299–304.

Ward, J.V., 1989. The four-dimensional nature of lotic ecosystems. J. N. Am. Benthol. Soc. 8(1), 2–8.

Wemple, B.C., Jones, J.A., 2003. Runoff production on forest roads in a steep, mountaincatchment. Water Resour. Res. 39, 1–17.

Wen Shen, H., 1999. Flushing sediment through reservoirs. J. Hydraul. Res. 37 (6),743–757.

Werner, B.T., McNamara, D.E., 2007. Dynamics of coupled human-landscape systems.Geomorphology 91 (3-4), 393–407.

Williams, G.P., Wolman, M.G., 1984. Downstream effects of dams on alluvial rivers. Geo-logical Survey Professional Paper 1286.

Wohl, E., Angermeier, P.L., Bledsoe, B., Kondolf, G.M., MacDonnell, L., Merritt, D.M., Palmer,M.A., Poff, N.L., Tarboton, D., 2005. Water Resour. Res. 41, W10301 (Riverrestoration).

Wolman, M.G., Miller, J.P., 1960. Magnitude and frequency of forces in geomorphic pro-cesses. J. Hydrol. 69, 54–74.

Zvoleff, A., An, L., 2014. Analyzing human–landscape interactions: tools that integrate. En-viron. Manag. 53 (1), 94–111.