Check dams decrease the channel complexity of intermediate reaches in the Western Carpathians (Czech Republic)

Science of the Total Environment 662 (2019) 881–894

Contents lists available at ScienceDirect

Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv

Check dams decrease the channel complexity of intermediate reaches in the Western Carpathians (Czech Republic) Tomáš Galia ⁎, Václav Škarpich, Stanislav Ruman, Tereza Macurová Department of Physical Geography and Geoecology, University of Ostrava, Chittussiho 10, 710 00 Ostrava, Czech Republic

H I G H L I G H T S

G R A P H I C A L

A B S T R A C T

• The channel complexity of intermediate reaches between check dams was investigated. • Different adjustments were observed between steep mountain and foothill streams. • Decreased bed sediment heterogeneity was measured in the managed mountain stream. • Cross-sectional and longitudinal heterogeneity was degraded in the foothill stream. • Instream wood abundance was equal in the managed and unimpacted streams.

a r t i c l e

i n f o

Article history: Received 17 September 2018 Received in revised form 12 December 2018 Accepted 23 January 2019 Available online 24 January 2019 Keywords: Mountain stream Check dam Channel complexity Stream management Western Carpathians

⁎ Corresponding author. E-mail address: [email protected] (T. Galia).

https://doi.org/10.1016/j.scitotenv.2019.01.305 0048-9697/© 2019 Elsevier B.V. All rights reserved.

a b s t r a c t Check dams can modify local channel and sedimentological characteristics through sediment deposition in upstream sedimentary wedges and scour processes downstream of individual check dams. However, research focusing on the channel reaches between subsequent check dams (referred to here as intermediate reaches) is limited. We evaluated channel complexity and its selected dimensions (longitudinal and cross-section heterogeneity, sediment characteristics and the presence of instream wood) in 30-m long intermediate reaches (n = 10) between subsequent check dams in comparison with channel reaches that were not treated with check dams (n = 10) in both a stepped-bed stream in a steep confined valley and an originally pool-riffle stream in an unconfined foothill valley. Check dams altered the channel complexity of intermediate reaches when compared with reaches of undisturbed streams. However, in contrast to foothills streams, check dams did not heavily affect longitudinal or cross-sectional heterogeneity of the intermediate reaches in the steep streams. Despite an increase in sediment homogeneity in steep reaches treated with check dams, the presence of coarse bed sediments helped to preserve their stepped-bed morphology. In contrast, the longitudinal profile of the treated foothill stream completely lost its vertical oscillations because of the transformation of pool-riffles to a uniform plane bed morphology. Similarly, cross-sectional heterogeneity in the foothill stream was degraded in comparison with those of untreated reaches. We did not observe differences in instream wood abundance between treated and untreated streams. © 2019 Elsevier B.V. All rights reserved.

882

T. Galia et al. / Science of the Total Environment 662 (2019) 881–894

1. Introduction The spatial heterogeneity of a stream channel, which represents one important component of the geomorphic complexity in river corridors, can be understood as the patchiness of microhabitats and the irregularity of their connections within longitudinal and cross-sectional profiles (Wohl, 2016). This physical complexity (referred to here as channel complexity) drives downstream fluxes and retention of water and materials transported by flow (solutes, mineral sediment, and particulate organic matter) and reflects or influences processes in channels (Gooseff et al., 2007; Wohl, 2016). According to ecological theory, increases in habitat heterogeneity lead to greater biodiversity (Elosegi et al., 2010; Palmer et al., 2010). The individual metrics of channel complexity cannot be represented using averages or trends, such as median grain size for bed sediments or bankfull width for channel geometry. Instead, describing complexity involves separating the signal from the noise by quantifying the variability around the trend (Polvi et al., 2014). At the same time, channel complexity may include several dimensions, such as hydraulics, cross-section, longitudinal profile, bed sediment heterogeneity or planform geometry, which do not necessarily correlate (Laub et al., 2012; Polvi et al., 2014; Wohl, 2016). Moreover, the presence of large instream wood significantly contributes to higher channel complexity in forested basins (Dolloff and Warren, 2003; Livers and Wohl, 2016). Check dams (i.e., step-like transversal concrete or wooden gradecontrol structures from one to several meters high) modify longitudinal, cross-sectional and sedimentological characteristics of the original channel (Fig. 1). They represent a traditional approach to reducing sediment transport and stabilizing the channels of gravel- and boulder-bed steep streams draining European (Ballesteros-Cánovas et al., 2016; Bombino et al., 2009; Conesa-García et al., 2007; Galia et al., 2016; Lenzi and Comiti, 2003; Piton et al., 2017) and Japanese mountain ranges (Chanson, 2004; Kang and Kazama, 2014; Okamoto, 2007), and similar structures have been used to stabilize gullies in Loss Plateau (Jin et al., 2012; Xu et al., 2004) and semiarid environments elsewhere (Mongil-Manso et al., 2016; Navarro-Hevia et al., 2014; Nichols et al., 2016; Norman et al., 2016; Polyakov et al., 2014; Vaezi et al., 2017). From a European perspective, geomorphological research related to stream morphodynamics and channel complexity along check dam treated channels has primarily focused on sediment deposition in upstream sedimentary wedges and scour processes downstream of individual dam constructions (Conesa-García and García-Lorenzo, 2009; Lenzi et al., 2003; Marion et al., 2004; Ramos-Diez et al., 2016, 2017; Zema et al., 2014). However, few studies have systematically analyzed changes in channel morphology and the characteristics of bed sediments along whole longitudinal profiles affected by check dam series or in reaches between individual check dams, here referred to as ‘intermediate reaches’ (Fig. 1) (Boix-Fayos et al., 2007; Bombino et al., 2009;

Conesa-García et al., 2007; Fortugno et al., 2017; Galia et al., 2016; Martín-Vide and Andreatta, 2009). Sequences of check dams are able to decrease longitudinal sediment connectivity owing to sediment deposition and lowering of bed slopes by creating wedge structures upstream of individual check dams (Ramos-Diez et al., 2017; RomeroDíaz et al., 2007). Reduced sediment discharge in downstream sections leads to the selective scour of fine particles from stream beds and possible incision of intermediate reaches together with a clockwise rotation of the longitudinal profile between check dams (Boix-Fayos et al., 2007; Martín-Vide and Andreatta, 2009). These processes can transform an originally heterogeneous bed consisting of various channel forms (e.g., steps, pools, riffles) to homogenous armored plane-bed channels separated by vertical steps created by check dams (Galia and Škarpich, 2017). The degradation of overall channel complexity could be reinforced by the presence of artificial bank stabilization and channel straightening measures, which often accompany check dam management in inhabited mountain valleys and fans to prevent lateral shifting of watercourses (Piton et al., 2017). In general, human-altered river channels (e.g., by narrowing and straightening, bank reinforcement, removal of instream wood or large boulders) display overall degradation accompanied by lower values of complexity metrics than undisturbed channels within the same geomorphic settings (Elosegi and Sabater, 2013; Polvi et al., 2014; Wyżga et al., 2012). Such increased spatial homogeneity and ‘simplification’ is usually reflected by the presence of lower biodiversity in invertebrate or fish taxa (Beechie and Sibley, 1997; Hajdukiewicz et al., 2018; Kubín et al., 2018; Wyżga et al., 2014), although some compilation reports did not find a direct response between the increased complexity after river restoration and richness of stream biota (Louhi et al., 2011; Palmer et al., 2010; Turunen et al., 2016). Only a few scientific papers have focused on the consequences of check dams for aquatic and riparian ecosystems. Individual check dams reduce or stop upstream migration of lotic fish fauna (Comiti et al., 2009) and downstream transport of instream wood (Galia et al., 2018b; Shrestha et al., 2012). Significant differences in the composition and dynamics of vegetation were observed between upstream and downstream reaches adjacent to individual check dams, which were driven by sediment retention upstream and erosion downstream of these artificial structures (Bombino et al., 2008, 2009, 2014; Zema et al., 2018). This implies that the presence of check dams may contribute to the development of specific habitats in steep managed streams, which has consequent effect on species diversity within the aquatic and riparian zone. However, no comprehensive research on the local changes in abiotic conditions has been conducted so far in the intermediate reaches seemingly undisturbed by sequential check dams and related erosional or depositional processes. In order to accomplish this task, we focused on the potential alterations of channel complexity (including longitudinal and cross-sectional heterogeneity, as well as bed sediment heterogeneity, and the presence of instream wood) in 30-m long subreaches located within intermediate reaches. We expected overall homogenization of these reaches when compared with channel complexity of undisturbed streams. Particularly, we hypothesize the following adjustments in patterns and dimensions of channel complexity in managed streams: H1. Intermediate channel reaches in streams managed by check dams will have lower spatial heterogeneity in their longitudinal and crosssectional profiles than reaches of streams without check dams. This hypothesis implies higher stability of channel beds in streams managed by check dams and possible straightening of their watercourses. Intermediate reaches can have locally stabilized banks by artificial structures, which decrease the potential for bank erosion and simplify cross-sectional geometry.

Fig. 1. Simplification of main channel processes along check dam sequences and localization of intermediate reach as the object of this study.

H2. Sediment trap efficiency of check dams will influence sediment distribution in intermediate channel reaches.

T. Galia et al. / Science of the Total Environment 662 (2019) 881–894

We suppose bed armoring processes with a coarsening of bed sediments in the intermediate reaches because of the possible effect of selective bed scouring on these reaches and preferential deposition of fine particles in sedimentary wedges upstream of check dams. H3. Intermediate reaches of impacted streams will have lower instream wood loads than reaches of streams without check dams. The presence of check dams leads to changes in the diversity and age structure of riparian vegetation, which supplies a stream with organic material, including instream wood. Additional artificial bank stabilization efforts prevent the recruitment of wood by lateral erosion. Moreover, individual check dams can be efficient in trapping transported wood in their sedimentary wedges, thus contributing to the decrease in instream wood loads in sub-reaches between check dams. H4. Finally, H1–H3 imply decreased channel complexity of intermediate reaches in streams managed by check dams in comparison with that in unimpacted streams. However, the size and form of the impact of check dams on channel complexity probably varies within the fluvial continuum owing to different patterns of channel-forming processes (e.g., character of sediment supply, stream transport capacity) and resulting reach morphologies (e.g., stepped-bed vs. pool-riffle channel) (Montgomery and Buffington, 1997). For example, an intensive supply of coarse particles from adjacent hillslopes likely leads to relatively higher crosssectional and sediment heterogeneity in steep confined channels despite the presence of check dams when compared with managed lowgradient streams with finer bed sediments. We test these hypotheses using field data collected from four streams draining flysch parts of the Western Carpathians in the Czech

883

Republic. We investigated two pairs of neighboring streams located in medium-high mountain relief and foothill areas: the first stream was affected by check dam constructions for a considerable length of time (N50 years), whereas the second control stream was never stabilized by check dams or other types of artificial structures. 2. Regional settings and studied basins We studied two pairs of neighboring streams that drain northern windward slopes of the Moravskoslezské Beskydy Mountains (the Malý Lipový and the Medvědí) and their foothills (the Baštice and the Bystrý) (Fig. 2 and Table 1). The first pair represents the steep (≥10%) confined mountain valley, whereas the second pair is the representative of the unconfined valley settings with milder slopes (ca. 2%). This medium-high mountain range peaking up to 1323 m asl is part of the flysch nappe structures of the Western Carpathians, which primarily consist of Mesozoic and Tertiary sandstones and shales. Such geologic structures lead to the frequent occurrence of deep and shallow landslide activity (Břežný et al., 2018; Pánek et al., 2009), which has consequences for the sediment supply from hillslopes into adjacent channels and human interventions in the watercourses. The annual precipitation varies between 800 mm in the foothills to 1400 mm in the mountain peaks (Tolasz et al., 2007). Morphologically important high flow events are connected to long-term intensive cyclonic precipitation or flash floods produced by convectional storms, whereas floods caused by snow melting are quite rare in this area (Šilhán, 2015). The hillslopes of all studied basins are covered by managed forests primarily consisting of Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica L.). The foothills are affected by significant agricultural activities at lower altitudes (Table 1), but riparian corridors

Fig. 2. Geographic context of the studied streams and reaches.

884

T. Galia et al. / Science of the Total Environment 662 (2019) 881–894

Table 1 Basic characteristics of the sampled streams. Characteristics

Management Basin area (km2)b Maximum altitude (m asl) Minimum altitude (m asl)a Mean basin slope (m/m)a Valley slope (m/m)b Length of main stream (km)a Mean channel slope (m/m)b Mean channel width (m)b Lithologya Present land usea Forest (%) Arable land (%) Grassland and pastures (%) Urbanised areas (%) a b

Streams of the mountain region

Streams of the foothill region

Malý Lipový

Medvědí

Bystrý

Baštice

Managed 0.90–1.53 902 479 0.45 0.10 1.1 0.060 2.6 Thick-bedded flysch

Unimpacted 0.65–1.04 950 541 0.43 0.11 1.3 0.104 2.6 Thick-bedded flysch

Managed 5.69–5.82 996 385 0.23 0.02 5.8 0.022 4.8 Mixture of thick- and thin-bedded flysch

Unimpacted 4.66–4.97 906 355 0.18 0.02 3.7 0.016 4.2 Mixture of thick- and thin-bedded flysch

92.0 4.1 0.0 3.9

90.6 9.0 0.0 0.4

46.1 36.8 9.0 8.1

33.7 47.6 10.1 8.6

Measured with respect to the last downstream sampled reach. Measured for the stream segment between the uppermost and the lowermost sampled reach.

consisting of mosaics of deciduous tree species are preserved along the studied streams. Intensive bedload transport and unstable geometry of river channels together with the development of settlements and industry in the Beskydian forefield from the second half of the ninetieth century on have led to systematic channelization of the majority of local gravel-bed rivers during the twentieth century (Škarpich et al., 2013, 2016). Similarly, many steep mountain streams acting as main sediment sources for gravel-bed rivers started to be managed by check dams in the early twentieth century. The first check dams in the Malý Lipový and its small tributaries were constructed in the 1920s to stabilize the stream's longitudinal profile and to decrease bedload transport rates from unstable landslide and gully-affected hillslopes. Currently, one retention check dam and five stabilization check dams up to 2.5–3 m high still operate along the main course of the Malý Lipový (Fig. 3a), while these structures are substituted by a sequence of tens of low bed sills (b1 m in height) at lower channel gradients downstream. We investigated the five uppermost intermediate reaches in this stream. In contrast, the reach of Bystrý passing through the foothills started to be systematically managed

with grade-control structures following the Second World War. Our sampling reaches were located in the downstream part of the Bystrý, with a sequence of eleven stabilization check dams with a mean height of 1.8 m (Fig. 3b). However, N30 bed sills up to 1 m high and several boulder ramps operate upstream. A large flood in 1997 (up to a 100-year recurrence interval event) caused notable damage to check dams and bed sills, and in contrast to the studied check dams in the downstream part, many bed sills were not repaired (Galia and Škarpich, 2017). A paved road runs along both streams managed by check dams and is connected to possible channel straightening and the occasional presence of additional ripraps to protect the road from bank erosion. The neighboring unimpacted streams, i.e., the Medvědí in the mountain region with stepped-bed morphology (Fig. 3c) and the Baštice in the foothill region with pool-riffle morphology (Fig. 3d), are likely the best examples that approximate premanagement conditions of the streams with check dams because of their similar basin areas, channel widths, valley slopes, geology and related sediment supply, and land use (Table 1). No notable changes in land use during past decades were detected by comparing aerial photos from 1955 and 2016 of the

Fig. 3. The features of the studied streams: a – check dam in the managed mountain stream (the Malý Lipový); b – intermediate reach in the managed foothill stream (the Bystrý); c – steppedbed channel of the unimpacted mountain stream (the Medvědí); d – pool-riffle channel of the unimpacted foothill stream (the Baštice) with indicated thalweg direction.

T. Galia et al. / Science of the Total Environment 662 (2019) 881–894

pairs of mountain (the Malý Lipový and the Medvědí) and foothill (the Baštice and the Bystrý) basins. 3. Methods 3.1. Process of selection of the studied streams and reaches We sought two pairs of neighboring streams with similar basin areas, geology, and land use as much as possible in both studied regions (i.e., confined steep mountain valleys and unconfined foothill valleys), which differ only by the presence or absence of check dams (Fig. 3a– d). We chose this approach to minimize any additional effects of other basin-scale variables except the presence of check dams. For the second step, we selected 30-m long channel sub-reaches in five intermediate reaches between check dams in the managed stream with sufficient distance from individual check dam constructions. The geometry of the sub-reaches was not visually affected by augmented sediment deposition upstream of the check dam crest and by the presence of a scour pool downstream, and minimal or no riprap bank stabilization was present there. We also identified five related reaches in the neighboring unimpacted stream. These reaches had (i) channel widths and valley slopes similar to the related reaches of the stream managed by check dams, and (ii) the spacing among these reaches corresponded to the longitudinal distances among the sampled sub-reaches in the managed stream. The uniform length of an individual studied reach (30 m) was, in some cases, slightly less than is the common definition of channelreach length as an equivalent to 10–20 bankfull widths (Montgomery and Buffington, 1997). We were forced to use 30-m long reaches because of the relatively short spacing of check dams in the managed mountain stream, which did not allow us to systematically sample longer longitudinal transects. 3.2. Field measurements The studied streams were surveyed during baseflow conditions. We measured the longitudinal and cross-sectional profiles, bed grain sizes and dimensions of instream wood in each reach. We measured bankfull widths at 5-m intervals along the thalweg with a tape (±0.05 m accuracy). Topographic surveys of the longitudinal profile along the thalweg and four cross-sections (0, 10, 20 and 30 m downstream from the top of the reach) were conducted using a total station (Topcon GTS 212-2000). Points for the longitudinal profiles were taken at intervals of 0.5 m along the thalweg, and points for the cross-sections (between bankfull edges)

885

were taken at half intervals (0.25 m). Positions of water levels in the cross-sections were noted. A conventional 200-particle pebble count along equally spaced transects throughout the reach was conducted by a single operator to eliminate interobserver errors (Wohl et al., 1996). The intermediate b-axis was measured by a tape with an accuracy of ±1 mm for all bed particles except for boulders that cannot be picked from the stream bed (accuracy of ±5 mm). The minimum size of measured bed particles was set to 5 mm. We lowered the minimum criteria for included large instream wood (commonly 1 m in length and 0.1 m diameter (Wohl et al., 2010)) to 0.5 m in length and 0.05 m in diameter because of the presence of managed forests along the stream, which decreased the potential to supply the studied streams with large branches or trunks of mature trees. The length and diameter of every single piece within the bankfull channel were measured with a tape (±0.05 m accuracy for length and ± 0.005 m accuracy for diameter) for later calculation of instream wood volume in the reaches.

3.3. Selection of variables We used several variables describing basic channel geometry (width, depth and bed slope) and bed grain sizes (d16, d50 and d84) as well as the heterogeneity of longitudinal and cross-sectional profiles, bed sediments and instream wood (all complexity variables are summarized in Table 2) to assess differences between the intermediate reaches of streams managed by check dams and the control reaches of unimpacted streams. Then, we evaluated overall channel complexity based on these dimensions. The bed slope S was calculated from the difference in the elevations of boundary points of the geodetically measured thalweg. The reported bankfull width Wbf corresponded to the average of seven bankfull widths measured along the thalweg. The bankfull depth Dbf was set as the mean bed elevation calculated from four geodetically surveyed cross-profiles, and then a mean value for each individual reach was obtained. The bed grain-size percentiles d16, d50 and d84 were derived from grain-size curves, which were designed from pebble counts. The majority of complexity metrics used parameters of channel/ reach geometry, sediment distribution and instream wood, which were described previously in detail by papers dealing exclusively with geomorphic complexity of stream channels (Laub et al., 2012; Polvi et al., 2014; Wohl, 2016). We modified the parameter of longitudinal concavity Long_conc as the simple average difference of succeeding bed elevations along the thalweg, and it was not necessary to standardize the resulting value because of the uniform spacing (0.5 m) between

Table 2 Metrics variables calculated for sampled reaches. Complexity dimension

Variable

Abbreviation

Description

Longitudinal

Thalweg R-square Thalweg MSE Longitudinal roughness Longitudinal concavity Width/depth ratio Width standard deviation Average width concavity Depth standard deviation Bed standard deviation Sorting Gradation

Long_R2 Long_sqer Long_rough Long_conc CS_Wd CS_Wdev CS_conc CS_Ddev CS_Beddev Sed_sort Sed_grad

R2 value from linear regression of the longitudinal profile Mean squared error of linear regression Proportionally weighted deviations from predicted elevation Concavities between successive points along thalweg profile Average ratio between the channel width and mean depth Standard deviation of the channel width; scaled by the mean width and expressed in percent of the mean width Concavities between successive cross-sectional widths Standard deviation of the channel depth; scaled by the mean depth and expressed in percent of the mean depth Standard deviation of bed elevations of wetted cross-sections during base-flow conditions Standard deviation of distribution; calculated as (d84 − d16) / 2

Lower heterogeneity Upper heterogeneity Kurtosis

Sed_het1 Sed_het2 Sed_kurt

Spread in lower portion of sediment distribution; calculated as d10 / d60 Spread in sediment distribution above median size; calculated as d84 / d50

Frequency Total volume Volume per channel area Mean piece volume

LW_n LW_tot LW_volcha LW_volpiece

Number of measured instream wood pieces Total volume of instream wood Volume of instream wood per channel area; expressed as m3/ha tot Calculated as LW LW n

Cross-section

Bed sediment

Instream wood

Spread in sediment distribution; calculated as (dd84 þ dd50 Þ=2 50 16

d90 −d10 Peakedness of sediment distribution; calculated as 1:9ðd 75 −d15 Þ

886

T. Galia et al. / Science of the Total Environment 662 (2019) 881–894

the successive points (Table 2). Similarly, the cross-sectional concavity CS_conc was not standardized owing to uniform spacing between the measured cross-sections (5 m). We introduced the new metrics of bed deviation CS_Beddev as the standard deviation in bed elevations of wetted cross-sections during base-flow conditions (i.e., during our field measurements). The parameter CS_Beddev expresses spatial variations in flow depths during prevalent flow conditions in the stream. Therefore, this parameter better describes the habitat for aquatic biota during mean annual (or lower) flows than bankfull depth deviation CS_Ddev corresponding to low-frequent bankfull discharges. Moreover, we added the parameter of the width/depth ratio CS_Wd to our overall complexity analysis because it is believed that decreasing values of the width-depth ratio point to possible human-induced degradation of stream channels (Wolman, 1967; Wohl, 2015; Wyżga, 2001). We tested differences in large instream wood loads within the pairs of studied streams with the following variables: number of wood pieces LW_n, total wood volume within the reach LW_voltot and wood volume per hectare of channel area LW_volcha. Local streams with check dams are usually (to some extent) maintained by local authorities to prevent potential flood dangers from the clogging check dams or bridges with transported wood. Therefore, we added the variable mean volume of instream wood pieces LW_volpiece to assess the size of presented wood pieces, while we primarily assumed that long and thick wood pieces that are perceived to increase flood risk were artificially removed. However, LW_volpiece was not included in later assessments of the overall channel complexity. 3.4. Statistical analyses Differences in basic and complexity parameters between the managed and unimpacted streams were visualized by box plots and tested by nonparametric Mann-Whitney test (at the 0.05 statistical significance level) because of the low number of observations per group (n = 5). The centerlines of boxplots show the median, the edges of the box display the first and third quantiles, and the whiskers represent the interquartile range. To assess overall channel complexity for all reaches, we used principal component analysis (PCA) to plot reaches in a complexity-metric space. This statistical analysis effectively reduces the number of entered variables and allows us to determine the (potentially different) positions of unimpacted and managed reaches of individual regions in complexity-metric space. All complexity metrics were tested for normality and transformed using either log or power transformations if needed to meet this assumption for PCA variables. First, we ran separated PCAs for individual complexity dimensions (longitudinal, crosssectional, sediment distribution and instream wood) to obtain the representative variables for these four dimensions; all entered variables except for LW_volpiece are listed in Table 2. The resulting PCA components with eigenvalues N1 after the varimax rotation by the Kaiser (1960) rule were evaluated, and the variables with the highest communalities within the component were retained. The communality represents how well this variable is predicted by the retained components. Then, we ran the final PCA with the reduced number of variables selected by the initial PCAs to determine the location of the investigated reaches in complexity-metric space. We visualized the results for PCA components with eigenvalues N1 after the varimax rotation, and the reaches that plotted more closely to one another are more similar in terms of complexity metrics than those that plotted farther away. Additionally, we used MANOVA (a multivariate ANOVA) to test whether differences existed between managed and unimpacted reaches by using the reduced number of variables selected by the initial PCAs. We ran this analysis two times: (i) for the entire dataset of managed and unimpacted reaches and (ii) for both regions separately because of the contrasting morphological character of unimpacted streams (stepped-bed channel in the mountains vs. pool-riffle channel in the foothills). All statistical tests were performed using NCSS11 statistical software (NCSS, 2016).

4. Results 4.1. Variables of channel geometry Visual inspection of the longitudinal profiles shows clear differences in bed morphology, especially for the pair of foothill streams (Fig. 4). Whereas sequences of pools and riffles were captured in the unimpacted stream, plane bed morphology without large bed oscillations was typical for intermediate reaches in the stream with check dams (Fig. 4b). The intermediate reaches of the managed mountain stream displayed significantly lower bed slopes (Fig. 5a). We observed much higher differences between the mean values of the valley slope and the bed slope in comparison with the unimpacted stream (Table 1). We found significant differences for all longitudinal heterogeneity metrics between unimpacted and managed streams in at least one of the assessed regions, but only Long_sqer was different in both regions (Fig. 5c). The parameters Long_R2 and Long_rough showed significant differences in only the foothills (Fig. 5b and d), which likely resulted from the bed-oscillating pool-riffle character of the unimpacted stream (see Fig. 4b). The unimpacted mountain stream expressed higher values of Long_sqer and Long_conc in comparison with intermediate reaches of the stream managed by check dams (Fig. 5e), which stemmed from the distinct stepped-bed character with higher bed amplitudes in the unmanaged stream. The intermediate reaches of managed streams were significantly deeper than the reaches of unimpacted streams in both regions (Fig. 6b), but we did not observe such a difference in the parameter bankfull width (Fig. 6a) or in the ratio between bankfull width and depth (Fig. 6c). In contrast to the tested pair of mountain streams with no evident differences, three metrics of cross-sectional heterogeneity (CS_Wdev, CS_conc and CS_Ddev) were significantly different in the foothill streams (Fig. 6d–f). In this case, significantly lower values of concavity or deviations in widths and depths were recorded for managed streams, which pointed to the effect of check dams on the simplification of channel geometry in unconfined foothill streams. Nevertheless, the parameter of bed deviation during base flow conditions (CS_Beddev) was not significantly different in either examined region (Fig. 6g). 4.2. Variables of sediment distribution We observed significant differences in bed sediment distribution within only the pair of mountain streams, whereas the pair of foothill streams expressed similar bed sediment characteristics (Fig. 7). Significant differences were found for d16 (Fig. 7a) and for three of five sediment heterogeneity metrics: Sed_sort, Sed_grad and Sed_het2 (Fig. 7d, e and g). The managed foothill stream had a tendency to contain coarser bed sediments than the unimpacted stream of the same region, but the difference was never significant for d16, d50 or d84 at the 0.05 p-level (Fig. 7a–c). Note the quite uniform grain-size medians (ca. 60 mm) observed in intermediate reaches of the managed streams in both examined regions, whereas the unimpacted streams produced a wider range of d50 values (Fig. 7b). 4.3. Large wood loadings We found no differences in the frequency or volume of large instream wood within the pairs of tested streams (Fig. 8a–c). The mountain stream with check dams indicated the largest scatter in the observed number of instream wood pieces: one reach was absolutely devoid of wood, whereas the uppermost investigated intermediate reach contained 19 instream wood pieces. These values corresponded to the lowest and the highest frequency of observed wood pieces in all studied streams. We additionally looked for differences in the mean size of wood pieces in the streams, but again we found no significant

T. Galia et al. / Science of the Total Environment 662 (2019) 881–894

887

Fig. 4. Comparisons of measured longitudinal profiles of streams (a) in the mountain region and (b) in the foothill region.

difference between mean volumes of instream wood pieces within the pairs of tested streams (Fig. 8d). Note the low instream wood volumes per channel area measured in the unimpacted streams; these volumes varied between 2.2 and 16.5 m3/ha and 0.5–18.8 m3/ha in the unimpacted mountain and foothill streams, respectively. 4.4. Differences in the overall channel complexity Seven variables were selected as the most representative variables of individual complexity metrics by initial PCAs (Table 3 and Supplementary Table 1). The first two components exceeded the threshold eigenvalue for longitudinal profile heterogeneity, explaining 90.6% of the variance, and the variables Long_R2 and Long_sqer showed the best communalities with these two components. For cross-sectional heterogeneity, three variables (CS_Wd, CS_Beddev and CS_Wdev) explaining 90.5% of the variance were selected by retaining three components with sufficient eigenvalues. In contrast, Sed_sort and LW_volcha were the only representatives of sediment heterogeneity and large wood metrics; the first individual components explained 91.8% and 72.1% of the variance, respectively. The final PCA retained three components with eigenvalues N1 after varimax rotation, explaining 85.0% of the variance. Therefore, the

locations of unimpacted and managed reaches of individual regions in complexity-metric space were plotted by three individual plot diagrams instead of a single diagram with two main components, which is regularly used (Fig. 9). The first component represented mainly Long_R2 and CS_Wd (31.1% of the total variance), the second component represented Long_sqer and CS_Wdev (29.6% of the total variance), and the third component mostly represented LW_volcha and CS_Beddev (24.3% of the total variance). The retained parameter sediment heterogeneity (Sed_sort) was partially included in the first (42.8% communality) and the second component (33.7% communality) (see Table 3 and factor loadings in Fig. 9). The overall complexity differed between the managed and unimpacted streams, but these variations were much more accentuated in the foothill region. The positions of the intermediate reaches of the managed and unimpacted foothill streams did not overlap by plotting any pairs of the resulting factors (Fig. 9). This finding implies that the presence of check dams notably transformed overall complexity metrics from undisturbed (premanaged) conditions. Nevertheless, the values of the third component did not differ by the criteria of management in the foothill region, which also indicated some similarity in wood loadings and bed deviations explained by this component. The partial overlap of the positions of the managed reaches and the unimpacted reaches

888

T. Galia et al. / Science of the Total Environment 662 (2019) 881–894

Fig. 5. Boxplots of the bed slope and longitudinal heterogeneity metrics with calculated p-values for managed and unimpacted streams within the individual regions. Significant differences are bolded.

of the mountain region occurred most notably for the second component (Long_sqer and CS_Wdev). For the first and the third components, the complexity gradient between managed and unimpacted reaches

was suggested by comparing the negative values of these components of the managed reaches to the positive values of the reaches without check dams.

Fig. 6. Boxplots of the channel width and depth and cross-sectional heterogeneity metrics with calculated p-values for managed and unimpacted streams within the individual regions. Significant differences are bolded.

T. Galia et al. / Science of the Total Environment 662 (2019) 881–894

889

Fig. 7. Boxplots of the main grain-size characteristics (d16, d50 and d84) and sediment heterogeneity metrics with calculated p-values for managed and unimpacted streams within the individual regions. Significant differences are bolded.

Fig. 8. Boxplots of the instream wood with calculated p-values for managed and unimpacted streams within the individual regions.

890

T. Galia et al. / Science of the Total Environment 662 (2019) 881–894

Table 3 Communalities of variables selected for the final PCA; only components that reached eigenvalue 1 within individual dimensions are displayed. See Table 2 for a description of abbreviations. Dimension

Variable

PC1

PC2

PC3

Total communality

Longitudinal

Long_R2 Long_sqer CS_Wd CS_Wdev CS_Beddev Sed_sort LW_volcha

0.942 0.001 0.708 0.031 0.046 0.428 0.020

0.004 0.779 0.063 0.794 0.013 0.337 0.078

0.008 0.129 0.007 0.037 0.718 0.076 0.729

0.954 0.909 0.778 0.861 0.777 0.840 0.827

Cross-section

Sediments Instream wood

We did not find differences between the entire datasets of managed reaches and the unimpacted reaches by running MANOVA (Wilks' Lambda 0.0159 N p-value 0.0001) and by using the reduced set of complexity metrics (CS_Beddev, CS_Wd, CS_Wdev, Long_R2, Long_sqer, LW_volcha, Sed_sort). However, significant differences between the managed and unimpacted reaches existed in individual tests of the mountain streams (Wilks' Lambda 0.0344 b p-value 0.1156) and the foothill streams (Wilks' Lambda 0.0419 b p-value 0.1392). 5. Discussion 5.1. Channel geometry Our results support H1, namely, that the presence of check dams with occasional bank stabilization and channel straightening activity decreased spatial heterogeneity in longitudinal and cross-sectional profiles of the intermediate reaches in both regions. This implies that spatial heterogeneity of the reaches located between check dams was still impacted by this management despite sufficient distance from sites directly altered by individual constructions (i.e., deposition upstream and erosion downstream a check dam). We observed different forms of these adjustments. In the managed mountain stream, the clockwise ‘rotation’ of the longitudinal profile sensu Martín-Vide and Andreatta (2009) took place between check dams owing to their relatively close spacing and related channelforming processes impacted by individual check dams. This led to the systematic lowering of the bed slope of the intermediate reaches, which likely contributed to the decrease in bed amplitudes in stepped-bed morphology channels (also represented by Long_sqer and Long_conc). The longitudinal profile of the managed foothill stream lost vertical oscillations because of the transformation of pool-riffles to a more uniform plane bed morphology as a consequence of channel straightening and installation of check dams (Fig. 4). This channel degradation was underscored by the significant difference in three of four related heterogeneity metrics (Fig. 5). Similar channel simplification and degradation were previously confirmed for wider nonperennial streams managed by grade-control structures in Spain (Martín-Vide and Andreatta, 2009). The loss of cross-sectional heterogeneity in the managed foothill stream (Fig. 5) was likely enhanced by previous channel straightening and the occasional presence of bank stabilizations. Such channelization efforts usually lead to a loss of cross-sectional heterogeneity (Hajdukiewicz et al., 2018; Laub et al., 2012; Polvi et al., 2014).

Fig. 9. The positions of the unimpacted and managed reaches from individual regions in complexity-metric space; the first three components, together with related factor loadings, were plotted. The polygons were created by connecting the outermost reaches of a given region and type of management.

5.2. Bed sediments We did not find significant differences in the sediment heterogeneity of the foothill streams; thus, H2 was fully confirmed for only the managed mountain stream. The occurrence of coarse sedimentary fractions as large as boulders in the intermediate reaches of the mountain stream managed by check dams helped to sustain a certain degree of bed and bank heterogeneity, although this stream displayed lower heterogeneity for bed sediments in three metrics when compared to the

neighboring unimpacted stream (Fig. 7). The decreased sediment heterogeneity likely resulted from the trap efficiency of check dams and the related scour of fine particles in the intermediate reaches (BoixFayos et al., 2007; Galia and Škarpich, 2017), which was reflected by the significantly coarser d16 in the managed stream (Fig. 7a). Common flood events are not able to transport large boulders from upstream sediment sources due to lowered bed slopes (and decreased stream transport capacity) produced by check dams. Piton and Recking (2017)

T. Galia et al. / Science of the Total Environment 662 (2019) 881–894

demonstrated by their laboratory experiments that bedload fluxes in steep streams with check dams can remain unchanged in the long term. However our results suggested that changes can be produced in the grain-size and sorting characteristics of bed sediment in reaches between consecutive check dams. The unaltered sediment heterogeneity in the foothill managed stream is likely related to the less effective bed scouring processes in transport-limited channel morphologies such as pool-riffles, where high but relatively frequent flow events are able to move all present particle-sizes as bedload. Once the sedimentary wedge is formed upstream from the check dam, the normal sediment transport is reestablished (after previous unsaturated flow conditions) in streams with milder channel gradients S b 0.04 m/m (Conesa-García et al., 2007). These findings reflect the typical function of check dams at this position of fluvial continuum (i.e., unconfined valley settings and mild bed slopes), which are built here for the longitudinal and planimetric bed stabilization rather than to control intensive bedload transport (Piton et al., 2017). 5.3. Instream wood We did not observe a higher instream wood frequency or volume in unimpacted streams, which contradicts H3. The main reason could be the presence of managed forests (including riparian buffers) along all studied streams, which decreased the potential for lateral recruitment of large wood into channels. The removal of wood by local people was also possible owing to the relatively short proximity of all studied reaches to settlements and to the presence of paved roads in the valleys with managed streams. These conditions resulted in very low observed instream wood volumes per channel area even in the unimpacted streams, which never exceeded 20 m3/ha (Fig. 8c). This was up to an order of magnitude lower than instream wood volumes reported from steep headwater streams, which drained the protected second-growth forests ca. 10 km south of the studied streams (Galia et al., 2018a). Instream wood is perceived to have an important effect on geomorphic processes in stream channels, and Livers and Wohl (2016) concluded that the management history of riparian forests exerts the strongest control on reduced channel complexity in the Rocky Mountains, USA. We interpret the lack of instream wood in the studied streams managed by check dams likely contributed to a decreased heterogeneity in their longitudinal and cross-sectional profiles. Similarly, increasing spatial homogeneity of intermediate reaches can be expected in all check dam managed streams draining forested basins, where systematic removal of instream wood or silviculture practices limits the supply of large wood into channels. 5.4. Overall channel complexity Spatial heterogeneity can be used in different ways depending on the scale of interest (Li and Reynolds, 1995). Previous investigations demonstrated that the construction of check dams not only changes bed slope and channel shape, but also alters habitat form and structure, impacting river ecology (Bombino et al., 2008, 2009, 2014; Shieh et al., 2007; Conesa-García et al., 2018; Zema et al., 2018). As a result, the presence of check dams is able to increase habitat heterogeneity at larger scales by considering overall longitudinal profiles of mountain streams. These papers also suggested that alterations induced by check dams became larger the closer to the check dam's crest. Nevertheless, at more detailed reach scale, our results showed that check dams increase channel homogeneity in the intermediate reaches when compared with premanagement conditions. Multivariate analyses (MANOVA) showed sufficient segregation of reaches affected by check dams from unimpacted reaches only when testing the regions (i.e., mountain and foothill streams) separately. This finding suggests confirmation of H4, namely, that managed streams indicate different overall channel complexity from unimpacted streams

891

but that the effect of check dams on intermediate reaches will vary with respect to the character of fluvial processes along the fluvial continuum. It also implies that there is no single channel complexity gradient for both studied regions but that mountain and foothill streams should be assessed separately. Note that no single complexity metric was clearly representative for all evaluated reaches, which is in agreement with previous research on overall channel complexity (Laub et al., 2012; Polvi et al., 2014). Based on our field observations and the results of statistical analysis, we propose empirical models of the change in channel complexity for the studied mountain and foothill intermediate reaches managed by check dams (Fig. 10). Although the models were developed by using a limited regional set of the studied streams, they can be transferred to other environments by considering specifics of sediment supply and transport capacity conditions of steep confined streams and unconfined channels with lower bed slopes. The grouping and separation of reaches by the region and management along the three final components indicated somewhat higher degradation of intermediate reaches in the foothill region than for the mountain streams (Fig. 9). The majority of longitudinal and cross-sectional complexity metrics showed notable alterations in the intermediate foothill streams, reflecting the simplification of the channel geometry. This finding is in agreement with the complexity gradient observed in streams draining northern Sweden, where much lower bank and bed heterogeneity was observed in historically channelized streams in comparison with restored or unimpacted streams (Polvi et al., 2014). Check dams in steep mountain streams did not heavily affect longitudinal or cross-sectional metrics of the intermediate reaches as it did in foothill streams. According to the results of PCA, one exception could be the variable of CS_Beddev despite the lack of a statistically significant difference between the managed and unimpacted streams (Fig. 6g). Therefore, the different clustering along the third component (Fig. 9) likely corresponded to the combination of lower observed instream wood loads (LW_volcha) and lower values of CS_Beddev in the managed steep stream. Milder bed slopes together with better sediment sorting (or lower sediment gradation) in the intermediate reaches (Fig. 7d, e) likely had a direct effect on lower values of CS_Beddev and significantly lower values of Long_sqer and Long_conc (Fig. 5c, e). 5.5. Implications for management The intermediate reaches between check dams were transformed in both studied regions but in different ways. Check dams often achieve several functions (e.g., longitudinal and planimetric stabilization, sediment transport retention) and their complete removal is usually not possible in terms of risk mitigation (Piton et al., 2017). Therefore, sustainable management leading to process-based stream restorations should take into consideration the location of reaches on the fluvial continuum. For steep mountain reaches between individual check dams, we found decreased sediment heterogeneity, which likely resulted in the degradation of some parameters of longitudinal heterogeneity (Long_sqer, Long_conc). However, the presence of high longitudinal heterogeneity in steep headwater streams increases transient storage or retention of organic matter in the channel (Gooseff et al., 2007; Wohl, 2016) and plays a positive role in the abundance of local endangered fish and amphibian species as Alpine bullheads or Alpine newts (Kubín et al., 2018; Vojar et al., 2010). Moreover, the lacks of fine particles near the channel banks owing to the reduced sediment heterogeneity may influence the original structure of riparian vegetation (e.g., BoixFayos et al., 2007; Bombino et al., 2009; Zema et al., 2018). Therefore, restoration efforts can target the issue of sediment connectivity through the sequence of check dams if the reason for check dam installation was not the control/blocking of augmented bedload transport but rather the stabilization of the longitudinal profile. This can be achieved by using modern open check dams or through the installation of large stabilized boulders into a channel bed, mimicking natural step-pool morphology

892

T. Galia et al. / Science of the Total Environment 662 (2019) 881–894

Fig. 10. Empirical model of the effect of check dams on the intermediate channel reaches in the foothill and mountain region.

(Chin et al., 2009; Lenzi, 2002; Piton and Recking, 2016; Yu et al., 2010). Furthermore, such structures can also lead to an increase in connectivity for fish species or other aquatic biota (Comiti et al., 2009). In the other case, bed heterogeneity can be increased by supplementing intermediate reaches with boulders and wood structures, and the issue of their stability should be carefully evaluated to avoid increasing flood risk. The reaches of streams with check dams in foothills showed overall channel degradation, which led to decreased longitudinal and crosssectional heterogeneity. Although some pool habitats are usually developed by scour holes downstream of individual check dams, there is much more frequent pool spacing (5–7 multiplies of bankfull widths) in natural pool-riffle reaches (Montgomery and Buffington, 1997). Note that fully developed slow-water habitats are crucial for many aquatic species (e.g., salmonids) occupying relatively narrow poolriffle streams (e.g., Ayllón et al., 2010; Rosenfeld et al., 2000). The installation of wood structures may help in the development of scour or dammed pools in the intermediate reaches, while instream wood is also able to increase bank heterogeneity (Wohl, 2013). Moreover, the presence of artificial bank stabilization (e.g., rip rap embankments) that decreases bed heterogeneity is not always necessary, and its contribution to preventing flood damage should be assessed. 6. Conclusions We evaluated the channel complexity of intermediate reaches of streams managed by check dams and made comparisons to streams without check dams at the two positions on the fluvial continuum: a steep confined channel with stepped-bed morphology and an originally pool-riffle channel in a foothill unconfined-valley setting. Stream

channels under direct human impact (e.g., channelization) usually exhibit decreased values of metrics of channel complexity. Check dam management with additional interventions (straightening of channels, occasional bank stabilization) was not an exception. Overall, the presence of check dams affected channel complexity of reaches which were not directly disturbed by individual dam constructions and related erosional or depositional processes. We observed a decrease primarily in the heterogeneity of bed sediments in the intermediate reaches of the steep managed channel and degraded complexity metrics of longitudinal and cross-sectional profiles in the unconfined foothill stream managed by check dams. The different adjustment of channel complexity to the presence of check dams in the intermediate channel reaches corresponds to the position of a particular reach on the fluvial continuum. The presence of coarse bed sediments in the steep reaches helped to sustain some degree of ‘undisturbed’ heterogeneity for channel cross-sections and longitudinal profiles. However, lowering the channel slope and increasing sediment homogeneity in comparison with the steep unimpacted stream likely degraded some aspects of longitudinal heterogeneity, which was well reflected by the presence of lower bed amplitudes in the intermediate reaches. This finding implies that any restoration effort should be primarily targeted at the increase in bed heterogeneity, e.g., by restoring longitudinal sediment connectivity or installation of roughness elements into channel beds. In contrast, foothill streams managed by check dams indicated overall degradation of their crosssectional and longitudinal metrics primarily by the complete loss of natural pool-riffle morphology. Therefore, process-based restorations of intermediate foothill reaches should take into consideration an approach that will approximate the alteration of slow and fast flows within

T. Galia et al. / Science of the Total Environment 662 (2019) 881–894

stream longitudinal profiles. The supplementation of instream wood (after careful consideration of flood risk) will be helpful to restore overall channel complexity in both mountain and foothill settings. Further research is needed on the potential degradation of channel complexity in check dam managed streams under different hydrologic and sedimentological regime as well as for comprehensive evaluation of the effect of check dams on aquatic and riparian biota in order to fully understand links between this widespread management practice in mountain streams and its consequences on stream hydromorphology. Supplementary data to this article can be found online at https://doi. org/10.1016/j.scitotenv.2019.01.305. Acknowledgements The authors sincerely appreciate the comments and suggestions of the two anonymous reviewers and the Guest Editor Manuel Esteban Lucas-Borja, which led to a significant improvement of the manuscript. The study was supported by an internal grant of the University of Ostrava (SGS05/PřF/2017-2018). The English language was reviewed by American Journal Experts. References Ayllón, D., Amodóvar, A., Nicola, G.G., Elvira, B., 2010. Ontogenetic and spatial variations in brown trout habitat selection. Ecol. Freshw. Fish 19, 420–432. https://doi.org/ 10.1111/j.1600-0633.2010.00426.x. Ballesteros-Cánovas, J.A., Stoffel, M., Corona, C., Schraml, K., Gobiet, A., Tani, S., Sinabell, F., Fuchs, S., Kaitna, R., 2016. Debris-flow risk analysis in a managed torrent based on a stochastic life-cycle performance. Sci. Total Environ. 557–558, 142–153. https://doi. org/10.1016/j.scitotenv.2016.03.036. Beechie, T.J., Sibley, T.H., 1997. Relationships between channel characteristics, woody debris, and fish habitat in northwestern Washington streams. Trans. Am. Fish. Soc. 126, 217–229. https://doi.org/10.1577/1548-8659(1997)126b0217:RBCCWDN2.3.CO;2. Boix-Fayos, C., Barberá, G.G., López-Bermúdez, F., Castillo, V.M., 2007. Effects of check dams, reforestation and land-use changes on river channel morphology: case study of the Rogativa catchment (Murcia, Spain). Geomorphology 91, 103–123. https:// doi.org/10.1016/j.geomorph.2007.02.003. Bombino, G., Gurnell, A.M., Tamburino, V., Zema, D.A., Zimbone, S.M., 2008. Sediment size variation in torrents with check dams: effects on riparian vegetation. Ecol. Eng. 32, 166–177. https://doi.org/10.1016/j.ecoleng.2007.10.011. Bombino, G., Gurnell, A.M., Tamburino, V., Zema, D.A., Zimbone, S.M., 2009. Adjustments in channel form, sediment calibre and vegetation around check-dams in the headwater reaches of mountain torrents, Calabria, Italy. Earth Surf. Process. Landf. 34, 1011–1021. https://doi.org/10.1002/esp.1791. Bombino, G., Boix-Fayos, C., Gurnell, A.M., Tamburino, V., Zema, D.A., Zimbone, S.M., 2014. Check dam influence on vegetation species diversity in mountain torrents of the Mediterranean environment. Ecohydrology 7, 678–691. https://doi.org/10.1002/ eco.1389. Břežný, M., Pánek, T., Lenart, J., Zondervan, A., Braucher, R., 2018. 10 Be dating reveals pronounced Mid-to Late Holocene activity of deep-seated landslides in the highest part of the Czech Flysch Carpathians. Quat. Sci. Rev. 195, 180–194. https://doi.org/ 10.1016/j.quascirev.2018.07.030. Chanson, H., 2004. Sabo check-dams - mountain protection systems in Japan. Int. J. River Basin Manag. 2, 301–307. Chin, A., Anderson, S., Collison, A., Ellis-Sugai, B.J., Haltiner, J.P., Hogervorst, J.B., Kondolf, G.M., O'Hirok, L.S., Purcell, A.H., Riley, A.L., Wohl, E., 2009. Linking theory and practice for restoration of step-pool streams. Environ. Manag. 43, 645–661. https://doi.org/ 10.1007/s00267-008-9171-x. Comiti, F., Mao, L., Lenzi, M.A., Siligardi, M., 2009. Artificial steps to stabilize mountain rivers: a post-project ecological assessment. River Res. Appl. 25, 639–659. https://doi. org/10.1002/rra.1234. Conesa-García, C., García-Lorenzo, R., 2009. Local scour estimation at check dams in torrential streams in south east Spain. Geogr. Ann. Ser. B 91, 159–177. https://doi.org/ 10.1111/j.1468-0459.2009.00361.x. Conesa-García, C., López-Bermúdez, F., García-Lorenzo, R., 2007. Bed stability variations after check dam construction in torrential channels (South-East Spain). Earth Surf. Process. Landf. 32, 2165–2184. https://doi.org/10.1002/esp.1521. Conesa-García, C., Sánchez-Tudela, J.L., Pérez-Cutillas, P., Martínez-Capel, F., 2018. Spatial variation of the vegetative roughness in Mediterranean torrential streams affected by check dams. Hydrol. Sci. J. 63, 114–135. https://doi.org/10.1080/02626667.2017.1414384. Dolloff, C.A., Warren, M.L., 2003. Fish relationships with large wood in small streams. In: Gregory, S.V., Boyer, K.L., Gurnell, A.M. (Eds.), American Fisheries Society Symposium, pp. 179–193. Elosegi, A., Sabater, S., 2013. Effects of hydromorphological impacts on river ecosystem functioning: a review and suggestions for assessing ecological impacts. Hydrobiologia 712, 129–143. https://doi.org/10.1007/s10750-012-1226-6. Elosegi, A., Díez, J., Mutz, M., 2010. Effects of hydromorphological integrity on biodiversity and functioning of river ecosystems. Hydrobiologia 657, 199–215. https://doi.org/ 10.1007/s10750-009-0083-4.

893

Fortugno, D., Boix-Fayos, C., Bombino, G., Denisi, P., Quiñonero Rubio, J.M., Tamburino, V., Zema, D.A., 2017. Adjustments in channel morphology due to land-use changes and check dam installation in mountain torrents of Calabria (southern Italy). Earth Surf. Process. Landf. 42, 2469–2483. https://doi.org/10.1002/esp.4197. Galia, T., Škarpich, V., 2017. Response of bed sediments on the grade-control structure management of a small piedmont stream. River Res. Appl. 33, 483–494. https://doi. org/10.1002/rra.3111. Galia, T., Škarpich, V., Hradecký, J., Přibyla, Z., 2016. Effect of grade-control structures at various stages of their destruction on bed sediments and local channel parameters. Geomorphology 253, 305–317. https://doi.org/10.1016/j.geomorph.2015.10.033. Galia, T., Ruiz-Villanueva, V., Tichavský, R., Šilhán, K., Horáček, M., Stoffel, M., 2018a. Characteristics and abundance of large and small instream wood in a Carpathian mixedforest headwater basin. For. Ecol. Manag. 424, 468–482. https://doi.org/10.1016/j. foreco.2018.05.031. Galia, T., Tichavský, R., Škarpich, V., Šilhán, K., 2018b. Characteristics of large wood in a headwater channel after an extraordinary event: the roles of transport agents and check dams. Catena 165, 537–550. https://doi.org/10.1016/j.catena.2018.03.010. Gooseff, M.N., Hall, R.O., Tank, J.L., 2007. Relating transient storage to channel complexity in streams of varying land use in Jackson Hole, Wyoming. Water Resour. Res. 43, 1–10. https://doi.org/10.1029/2005WR004626. Hajdukiewicz, H., Wyżga, B., Amirowicz, A., Oglęcki, P., Radecki-Pawlik, A., Zawiejska, J., Mikuś, P., 2018. Ecological state of a mountain river before and after a large flood: implications for river status assessment. Sci. Total Environ. 610–611, 244–257. https:// doi.org/10.1016/j.scitotenv.2017.07.162. Jin, Z., Cui, B., Song, Y., Shi, W., Wang, K., Wang, Y., Liang, J., 2012. How many check dams do we need to build on the Loess Plateau? Environ. Sci. Technol. 46, 8527–8528. https://doi.org/10.1021/es302835r. Kaiser, H.F., 1960. The application of electronic computers to factor analysis. Educ. Psychol. Meas. 20, 141–151. Kang, J.H., Kazama, S., 2014. Development and application of hydrological and geomorphic diversity measures for mountain streams with check and slit-check dams. J. Hydro Environ. Res. 8, 32–42. https://doi.org/10.1016/j.jher.2013.05.002. Kubín, M., Rulík, M., Lusk, S., Závorka, L., 2018. Habitat degradation and trout stocking can reinforce the impact of flash floods on headwater specialist Alpine bullhead Cottus poecilopus - a case study from the Carpathian Mountains. J. Appl. Ichthyol. 34, 825–833. https://doi.org/10.1111/jai.13682. Laub, B.G., Baker, D.W., Bledsoe, B.P., Palmer, M.A., 2012. Range of variability of channel complexity in urban, restored and forested reference streams. Freshw. Biol. 57, 1076–1095. https://doi.org/10.1111/j.1365-2427.2012.02763.x. Lenzi, M.A., 2002. Stream bed stabilization using boulder check dams that mimic steppool morphology features in Northern Italy. Geomorphology 45, 243–260. https:// doi.org/10.1016/S0169-555X(01)00157-X. Lenzi, M.A., Comiti, F., 2003. Local scouring and morphological adjustments in steep channels with check-dam sequences. Geomorphology 55, 97–109. https://doi.org/ 10.1016/S0169-555X(03)00134-X. Lenzi, M.A., Marion, A., Comiti, F., 2003. Local scouring at grade-control structures in alluvial mountain rivers. Water Resour. Res. 39. https://doi.org/10.1029/ 2002WR001815. Li, H., Reynolds, J.F., 1995. On definition and quantification of heterogeneity. Oikos 73, 280–284. Livers, B., Wohl, E., 2016. Sources and interpretation of channel complexity in forested subalpine streams of the Southern Rocky Mountains. Water Resour. Res. 52, 3910–3929. https://doi.org/10.1002/2015WR018306. Louhi, P., Mykrä, H., Paavola, R., Huusko, A., Vehanen, T., Mäki-Petäys, A., Muotka, T., 2011. Twenty years of stream restoration in Finland: little response by benthic macroinvertebrate communities. Ecol. Appl. https://doi.org/10.1890/10-0591.1. Marion, A., Lenzi, M.A., Comiti, F., 2004. Effect of sill spacing and sediment size grading on scouring at grade-control structures. Earth Surf. Process. Landf. 29, 983–993. https:// doi.org/10.1002/esp.1081. Martín-Vide, J.P., Andreatta, A., 2009. Channel degradation and slope adjustment in steep streams controlled through bed sills. Earth Surf. Process. Landf. 34, 38–47. https://doi. org/10.1002/esp.1687. Mongil-Manso, J., Navarro-Hevia, J., Díaz-Gutiérrez, V., Cruz, V., Ramos-Díez, I., 2016. Badlands forest restoration in Central Spain after 50 years under a Mediterraneancontinental climate. Ecol. Eng. 97, 313–326. https://doi.org/10.1016/j. ecoleng.2016.10.020. Montgomery, D.R., Buffington, J.M., 1997. Channel-reach morphology in mountain drainage basins. Bull. Geol. Soc. Am. 109, 596–611. https://doi.org/10.1130/0016-7606 (1997)109b0596:CRMIMDN2.3.CO. Navarro-Hevia, J., de Araújo, J.C., Mongil-Manso, J., 2014. Assessment of 80 years of ancient-badlands restoration in Saldana, Spain. Earth Surf. Process. Landf. 39, 1563–1575. https://doi.org/10.1002/esp.3541. NCSS, 2016. Statistical Software NCSS Ver. 11. Nichols, M.H., Polyakov, V., Nearing, M.A., Hernandez, M., 2016. Semiarid watershed response to low-tech porous rock check dams. Soil Sci. 181 (7), 275–282. https://doi. org/10.1097/SS.0000000000000160. Norman, L.M., Brinkerhoff, F., Gwilliam, E., Guertin, D.P., Callegary, J., Goodrich, D.C., Nagler, P.L., Gray, F., 2016. Hydrologic response of streams restored with check dams in the Chiricahua Mountains, Arizona. River Res. Appl. 32, 519–527. https:// doi.org/10.1002/rra.2895. Okamoto, M., 2007. The Structure of Sabo Administration. International Sabo Network. Palmer, M.A., Menninger, H.L., Bernhardt, E., 2010. River restoration, habitat heterogeneity and biodiversity: a failure of theory or practice? Freshw. Biol. 55, 205–222. https:// doi.org/10.1111/j.1365-2427.2009.02372.x. Pánek, T., Hradecký, J., Šilhán, K., 2009. Geomorphic evidence of ancient catastrophic flow type landslides in the mid-mountain ridges of the Western Flysch Carpathian

894

T. Galia et al. / Science of the Total Environment 662 (2019) 881–894

Mountains (Czech Republic). Int. J. Sediment Res. 24, 88–98. https://doi.org/10.1016/ S1001-6279(09)60018-4. Piton, G., Recking, A., 2016. Design of sediment traps with open check dams. I: hydraulic and deposition processes. J. Hydraul. Eng. 142, 04015045. https://doi.org/10.1061/ (ASCE)HY.1943-7900.0001048. Piton, G., Recking, A., 2017. Effects of check dams on bed-load transport and steep-slope stream morphodynamics. Geomorphology 291, 94–105. https://doi.org/10.1016/j. geomorph.2016.03.001. Piton, G., Carladous, S., Recking, A., Tacnet, J.M., Liébault, F., Kuss, D., Quefféléan, Y., Marco, O., 2017. Why do we build check dams in Alpine streams? An historical perspective from the French experience. Earth Surf. Process. Landf. 42, 91–108. https://doi.org/ 10.1002/esp.3967. Polvi, L.E., Nilsson, C., Hasselquist, E.M., 2014. Potential and actual geomorphic complexity of restored headwater streams in northern Sweden. Geomorphology 210, 98–118. https://doi.org/10.1016/j.geomorph.2013.12.025. Polyakov, V., Nichols, M., McClaran, M., Nearing, M.A., 2014. Effect of check dams on runoff, sediment yield and retention on small semi-arid watersheds. J. Soil Water Conserv. 69, 414–421. https://doi.org/10.2489/jswc.69.5.414. Ramos-Diez, I., Navarro-Hevia, J., San Martín Fernández, R., Díaz-Gutiérrez, V., MongilManso, J., 2016. Geometric models for measuring sediment wedge volume in retention check dams. Water Environ. J. 30, 119–127. https://doi.org/10.1111/wej.12165. Ramos-Diez, I., Navarro-Hevia, J., San Martín, R., Mongil-Manso, J., 2017. Final analysis of the accuracy and precision of methods to calculate the sediment retained by check dams. Land Degrad. Dev. 28, 2446–2456. https://doi.org/10.1002/ldr.2778. Romero-Díaz, A., Alonso-Sarriá, F., Martínez-Lloris, M., 2007. Erosion rates obtained from check-dam sedimentation (SE Spain). A multi-method comparison. Catena 71, 172–178. https://doi.org/10.1016/j.catena.2006.05.011. Rosenfeld, J., Porter, M., Parkinson, E., 2000. Habitat factors affecting the abundance and distribution of juvenile cutthroat trout (Oncorhynchus clarki) and coho salmon (Oncorhynchus kisutch). Can. J. Fish. Aquat. Sci. 57, 766–774. https://doi.org/10.1139/ f00-010. Shieh, C.L., Guh, Y.R., Wang, S.Q., 2007. The application of range of variability approach to the assessment of a check dam on riverine habitat alteration. Environ. Geol. 52 (3), 427–435. Shrestha, B.B., Nakagawa, H., Kawaike, K., Baba, Y., Zhang, H., 2012. Driftwood deposition from debris flows at slit-check dams and fans. Nat. Hazards 61, 577–602. https://doi. org/10.1007/s11069-011-9939-9. Šilhán, K., 2015. Frequency, predisposition, and triggers of floods in flysch Carpathians: regional study using dendrogeomorphic methods. Geomorphology 234, 243–253. https://doi.org/10.1016/j.geomorph.2014.12.041. Škarpich, V., Hradecký, J., Dušek, R., 2013. Complex transformation of the geomorphic regime of channels in the forefield of the Moravskoslezské Beskydy Mts.: case study of the Morávka River (Czech Republic). Catena 111, 25–40. https://doi.org/10.1016/j. catena.2013.06.028. Škarpich, V., Kašpárek, Z., Galia, T., Hradecký, J., 2016. Anthropogenic impact and morphology channel response of beskydian gravel-bed rivers: A case study of the Ostravice River, Czechia. Geografie 121. Tolasz, R., Míková, T., Valeriánová, A., Voženílek, V., 2007. Climate Atlas of Czechia. Český Hydrometeorologický Ústav, Palackého Univerzita, Praha, Olomouc. Turunen, J., Muotka, T., Vuori, K.M., Karjalainen, S.M., Rääpysjärvi, J., Sutela, T., Aroviita, J., 2016. Disentangling the responses of boreal stream assemblages to low stressor

levels of diffuse pollution and altered channel morphology. Sci. Total Environ. 544, 954–962. https://doi.org/10.1016/j.scitotenv.2015.12.031. Vaezi, A.R., Abbasi, M., Keesstra, S., Cerdà, A., 2017. Assessment of soil particle erodibility and sediment trapping using check dams in small semi-arid catchments. Catena 157, 227–240. https://doi.org/10.1016/j.catena.2017.05.021. Vojar, J., Denoël, M., Kopecký, O., 2010. Movements of Alpine newts (Mesotriton alpestris) between small aquatic habitats (ruts) during the breeding season. Amphibia-Reptilia 31, 109–116. https://doi.org/10.1163/156853810790457821. Wohl, E., 2013. Floodplains and wood. Earth Sci. Rev. 123, 194–212. https://doi.org/ 10.1016/j.earscirev.2013.04.009. Wohl, E., 2015. Legacy effects on sediments in river corridors. Earth Sci. Rev. 147, 30–53. https://doi.org/10.1016/j.earscirev.2015.05.001. Wohl, E., 2016. Spatial heterogeneity as a component of river geomorphic complexity. Prog. Phys. Geogr. 40, 598–615. https://doi.org/10.1177/0309133316658615. Wohl, E.E., Anthony, D.J., Madsen, S.W., Thompson, D.M., 1996. A comparison of surface sampling methods for coarse fluvial sediments. Water Resour. Res. 32, 3219–3226. Wohl, E., Cenderelli, D.A., Dwire, K.A., Ryan-Burkett, S.E., Young, M.K., Fausch, K.D., 2010. Large in-stream wood studies: a call for common metrics. Earth Surf. Process. Landf. 35, 618–625. https://doi.org/10.1002/esp.1966. Wolman, M.G., 1967. A cycle of sedimentation and erosion in urban river channels. Geogr. Ann. Ser. B 49, 385–395. Wyżga, B., 2001. Impact of the channelization-induced incision of the Skawa and Wisloka Rivers, southern Poland, on the conditions of overbank deposition. Regul. Rivers Res. Manag. 17, 85–100. https://doi.org/10.1002/1099-1646(200101/02)17:1b85::AIDRRR605N3.0.CO;2-U. Wyżga, B., Zawiejska, J., Radecki-Pawlik, A., Hajdukiewicz, H., 2012. Environmental change, hydromorphological reference conditions and the restoration of Polish Carpathian rivers. Earth Surf. Process. Landf. 37, 1213–1226. https://doi.org/ 10.1002/esp.3273. Wyżga, B., Amirowicz, A., Oglecki, P., Hajdukiewicz, H., Radecki-Pawlik, A., Zawiejska, J., Mikuś, P., 2014. Response of fish and benthic invertebrate communities to constrained channel conditions in a mountain river: case study of the Biała, Polish Carpathians. Limnologica 46, 58–69. https://doi.org/10.1016/j.limno.2013.12.002. Xu, X.Z., Zhang, H.W., Zhang, O., 2004. Development of check-dam systems in gullies on the Loess Plateau, China. Environ. Sci. Pol. 7, 79–86. https://doi.org/10.1016/j. envsci.2003.12.002. Yu, G.A., Wang, Z.Y., Zhang, K., Duan, X., Chang, T.C., 2010. Restoration of an incised mountain stream using artificial step-pool system. J. Hydraul. Res. 48, 178–187. https://doi. org/10.1080/00221681003704186. Zema, D.A., Bombino, G., Boix-Fayos, C., Tamburino, V., Zimbone, S.M., Fortugno, D., 2014. Evaluation and modeling of scouring and sedimentation around check dams in a Mediterranean torrent in Calabria, Italy. J. Soil Water Conserv. 69, 316–329. https:// doi.org/10.2489/jswc.69.4.316. Zema, D.A., Bombino, G., Denisi, P., Lucas-Borja, M.E., Zimbone, S.M., 2018. Evaluating the effects of check dams on channel geometry, bed sediment size and riparian vegetation in Mediterranean mountain torrents. Sci. Total Environ. 642, 327–340. https:// doi.org/10.1016/j.scitotenv.2018.06.035.