MSI (morphometric slope index) for analyzing activation and evolution of calanchi in Italy

Geomorphology 191 (2013) 142–149

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MSI (morphometric slope index) for analyzing activation and evolution of calanchi in Italy Marcello Buccolini ⁎, Laura Coco Dipartimento di Ingegneria e Geologia, Università “G. d'Annunzio” Chieti-Pescara, Via dei Vestini 30, 66013 Chieti Scalo (CH), Italy

a r t i c l e

i n f o

Article history: Received 2 August 2012 Received in revised form 20 February 2013 Accepted 26 February 2013 Available online 6 March 2013 Keywords: Italian badlands Morphometry Morphogenesis Climatic control

a b s t r a c t The “calanchi” (singular calanco) are a typical example of Italian badlands, widespread in areas with hills of clay-rich sediments and rocks. They appear as a very dense and rapidly evolving drainage system characterized by an alternating pattern of narrow furrows and sharp crests. The calanchi can be considered as small hydrographical basins, characterized by two possible drainage patterns, parallel and dendritic. The two patterns show both linear and areal erosion processes. In this study, calanchi with dendritic drainage patterns were analyzed in three different areas representative of the Italian Peninsular: Atri in the Abruzzi region, Mount Ascensione in the Marche region, and Orcia Valley in the Tuscany region. For each calanchi, the pre-erosion topographic surface was reconstructed and the value of MSI (morphometric slope index) was calculated for the surface. The volume of eroded material was estimated by comparing the pre-calanchi and present surfaces. We assumed that slope morphometry influences the type of erosion processes, and the efficacy of these processes with respect to the amount of eroded material is a function of their duration. We deduced that calanchi inception was contemporaneous, because the duration of the processes was common to all landforms, and probably due to a common climate input. Moreover, the relations among MSI, eroded volume and erosion processes indicate that, over a long period, areally distributed surface processes contribute more to total sediment yields than channel flows. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Calanchi (singular calanco) (Fig. 1), a typical example of badlands widespread in hills of clay-rich sediments and rocks in Italy, are a type of the most spectacular forms of accelerated erosion. They can be defined as very dense and rapidly evolving drainage systems that affect clayey slopes. They are characterized by an alternating pattern of narrow furrows and sharp crests that have a height of several meters up to some decameters (Castiglioni, 1933; Vittorini, 1977; Alexander, 1980; Dramis et al., 1982; Clarke and Rendell, 2000; Moretti and Rodolfi, 2000). The main morphogenetic factors that affect calanchi formation are lithotype, geological structure, and climate (Castiglioni, 1933; Vittorini, 1977; Rodolfi and Frascati, 1979; Alexander, 1980; Bryan and Campbell, 1986; de Lugt and Campbell, 1992; Torri and Bryan, 1997; Regüés et al., 2000; Farifteh and Soeters, 2006; Della Seta et al., 2007). A required condition for calanchi formation is the presence of vegetation-free clay slopes with an appropriate inclination (Castiglioni, 1933; Guasparri, 1978; Dramis et al., 1982; Faulkner, 1990; Moretti and Rodolfi, 2000; Buccolini and Coco, 2010), in areas with strong seasonal humid/arid contrasts, often favored by microclimatic conditions

⁎ Corresponding author. Tel.: +39 871 3556424; fax: +39 871 3556454. E-mail address: [email protected] (M. Buccolini). 0169-555X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.geomorph.2013.02.025

that depend on slope aspect (Rodolfi and Frascati, 1979; Alexander, 1980; Torri and Bryan, 1997). The development and evolution of these landforms are also influenced by human activities, through clearance of vegetation cover, runoff diversion and mechanical modification of slopes (Dramis et al., 1982; Clarke and Rendell, 2000; Buccolini et al., 2007). Superficial runoff, and the consequent carving of a drainage network, is accelerated by particular slope morphology and low permeability due to clayey lithology. The drainage network develops with different patterns, depending on slope forms. Calanchi landforms originated from the evolution of drainage networks and some of them can be regarded as small hydrographical basins. Two calanchi typologies can be distinguished with regard to drainage network patterns: dendritic and parallel (Fig. 1). The first typology is similar to a miniature basin also in its evolution, while the latter evolves through parallel slope retreat (Della Seta et al., 2007). Calanchi basins, as in any catchment, are subject to both linear erosion (gullying, rilling and piping) and areal erosion (slide- or flow-type landslips and sheet erosion) (Mazzanti and Rodolfi, 1988; de Lugt and Campbell, 1992; Torri and Bryan, 1997; Moretti and Rodolfi, 2000). Depending on the initial slope features, one of the two processes can prevail (e.g., Schumm et al., 1987; Oguchi, 1996; Pelletier, 2003; Buccolini and Coco, 2010). In previous studies erosion rates within calanchi were measured, using direct and indirect methods (Benito et al., 1993; Sirvent et al., 1997; Clarke and Rendell, 2006; Della Seta et al., 2007; Ciccacci et al.,

M. Buccolini, L. Coco / Geomorphology 191 (2013) 142–149

Fig. 1. Examples of calanchi with dendritic (a) and parallel (b) drainage in the Adriatic Central Apennines.

2008). Buccolini et al. (2012) highlighted the direct relation between the eroded volume for a single calanco front and morphometric features of pre-calanchi slope, introducing the morphometric slope index (MSI). Some authors related the inception of calanchi morphogenesis to climatic input (Moretti and Rodolfi, 2000), whereas others considered anthropogenic causes including deforestation (Dramis et al., 1982). Assuming that eroded volume per unit surface area is a function of soil clay content, precipitation characteristics, slope morphometric features, and the duration of erosion processes, this paper investigates whether or not the direct relationship between the eroded volume and MSI exists. If this relation is confirmed, using data from different areas, we can deduce that calanchi inception is contemporaneous, with the duration of the processes being common to all the areas; otherwise they activated in different periods. Furthermore, we assessed the relation between the eroded volume, erosion processes and the morphology of the initial slope. For these purposes, we considered calanchi having dendritic drainage patterns that are usually not subjected to parallel slope retreat. Eighty-one calanchi in three sample areas in central Italy were analyzed. Of these, 28 belong to the Atri area (TE) in the Abruzzi region, 29 to the Mount Ascensione area in the Marche region, and 24 to the Orcia River basin in the Tuscany region. 2. Regional settings Most Italian Plio-Pleistocene sedimentary successions are characterized by extensive formations predominantly consisting of clays and sands. These successions are widespread (Fig. 2) and characterize a type of landscape defined as “hilly landscapes of the Apennine piedmonts”. These lithotypes are mainly related to erosion of the Apennines during the Neogene–Quaternary uplift. The Mediterranean area underwent climatic changes during the Holocene, which led to “Mediterranean conditions” since 4500 yr BP (Magny et al., 2002; Jalut et al., 2009). These conditions developed through an alternation of dry and wet periods; specifically arid intervals occurred

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at 9500–9000, 7500–7000, 4500–4000, 3700–3300, 2600–1900 and 1300–1000 yr BP (Jalut et al., 2009). The second half of the Holocene, after 6500 yr BP, is characterized by a general trend towards drier conditions, with a consequent decrease in sediment deposition and increase in floodplain incision (Magny et al., 2002). The Roman Empire (500 BC– 500 AD) developed during a relatively wet climate phase and its decline (3rd to 5th centuries AD) could be correlated with a long and continuous trend towards drier conditions (Reale and Dirmeyer, 2000). In the Middle Ages, between 1300 and 1850 AD, a cold-humid climate phase occurred, the so-called Little Ice Age that coincided with a glacier advance in the northern Alps and an increase in fluvial activity (Le Roy Ladurie, 1971; Lamb, 1982; Magny et al., 2002). Since the Roman age, the combinations of various factors triggered soil erosion. These factors include deforestation to improve agriculture, first on the Tyrrhenian side of Italy and then on the Adriatic side (Panini, 1983); the steep topography of most Italian piedmonts (Reale and Dirmeyer, 2000); and the rainy winter season, typical of the Mediterranean climate (Reale and Dirmeyer, 2000). During the Middle Ages, the development of pastoral rather than agricultural economy and the lack of land management strategies led to a continuous occurrence of these erosion processes (Reale and Dirmeyer, 2000). Deforestation became particularly significant since the 16th Century, although it did not occur simultaneously through the Italian regions (Panini, 1983). The most common morphotypes developed under these conditions are those from mass movement processes (roto-translational landsliding and mudflow) and those from intense soil erosion by runoff such as deep valleys and badlands (calanchi and biancane) (Castiglioni, 1933; Alexander, 1980; Farifteh and Soeters, 2006; Della Seta et al., 2007; Ciccacci et al., 2008). Del Monte et al. (2002) discussed the tectonic and sedimentological history, geomorphological features and their recent transformation in the Orcia Valley area. They refer to the landform evolution of the Tyrrhenian side of the Central Apennines that started around the late-Pliocene to Pleistocene transition. In particular, silt–clayey sediments, locally fossiliferous, of the Zanclean–Piacentian (lower to middle Pliocene) outcrop in the typical hilly landscape of the Orcia Valley area, whose elevation does not exceed 1000 m a.s.l. (Fig. 3). Locally, resedimented conglomerates or sand–clay alternations, some decimeter to meter-thick, are present and form these remnants of ancient pediments. The climate regime in the Orcia Valley area is temperate sub-littoral (Fazzini and Giuffrida, 2005), with an annual rainfall of 970 mm, generally below the national average, and temperatures characterized by strong seasonal contrasts. The data collected at the two meteorological stations (Radicofani and Pienza) have been available since the 1960s and reported in the Annali Idrologici (Yearly Hydrological Books), and show higher precipitation values and rainfall events in autumn and winter. During the summer season (July to September), the stations recorded lower precipitation values and higher thermometric values. This condition, indicative of strong summer drought followed by intense winter precipitations, favors the activation of intense erosion on clay substrates. In the mid-Adriatic Apennine section, in which the Mount Ascensione and Atri areas are located, the outcropping deposits consist of a PlioPleistocene succession (Fig. 4), composed of clayey sediments, overlying Messinian turbidities that often interbed with clastic deposits (sands and conglomerates with lenticular geometry, sometimes very thick) at various stratigraphic heights. In the Adriatic coast the sedimentary cycle ends with a thick deposit of sands, gravels and conglomerates of the fluvial–deltaic and coastal environment, Sicilian–Crotonian in age (Bigi et al., 1995; D'Agostino et al., 2001; Cantalamessa and Di Celma, 2004; Crescenti et al., 2004). On the basis of data referring to the period 1921–2003, the climatic pattern of the area that includes the Mount Ascensione and Atri areas is relatively homogeneous as expected in a sub-temperate littoral regime (Fazzini and Giuffrida, 2005). The annual number of rain days varies from 60 to 75 with mean daily totals of 10 to 12 mm. The total monthly maximum is registered in autumn,

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Fig. 2. Distribution of Plio-Pleistocene formations in Italy and location of the study areas.

secondary in spring. Summers are rather dry, especially near the coast, where periods without rain exceeded 40 days in a year. Mean annual temperatures vary between 12.5 and 15.5 °C; annual temperature range is about 17–19 °C. As in the Orcia Valley, climatic conditions favor intense erosion. 3. Methodology In the study areas, we sampled the 81 calanchi basins with dendritic drainage patterns, selecting the active and vegetation-free basins, in which drainage networks were well developed. The landforms of the basins were analyzed using orthophotos and the 1:10,000 numerical topographic basis (CTR; contour interval is 10 m), both provided by the Regions Abruzzi, Marche and Tuscany. From the latter dataset, a 10 m resolution DTM for each area was constructed, using the Topoto-Raster interpolation tool within ArcGIS 9.3 (ESRI). For each drainage basin, the total area and the calanco area were delimited (Fig. 5a) and their plan surface areas were measured: A2D (m 2) represents the two-dimensional surface area of the basin, and Ac (m 2) represents the two-dimensional surface area of calanchi. For each basin, the circularity ratio (Rc) was also obtained (Miller, 1953): 2

Rc ¼ 4πA2D =p

ð1Þ

where p is the drainage basin perimeter. Longitudinal topographic profiles were constructed from the highest to the lowest points (Fig. 5a) from which the average profile slope (S in

degrees) and plan length (L in m) were computed. Initial slope topography, prior to the development of the calanchi hydrographical network, was also reconstructed based on the height distribution of each watershed (Buccolini et al., 2012). New straight contour lines were traced through the connection of points with the same height on the watershed divide (Fig. 5b). From these reconstructed contour lines, a DTM with a resolution of 10 m (the same as the original DTM) was constructed using the Topo-to-Raster. From this DTM, the reconstructed three-dimensional surface area (Ar in m2) of each watershed was calculated to indicate the extent of the watershed before the present-day calanchi development (Fig. 6). MSI (in m) was calculated using the formula of Buccolini et al. (2012):

MSI ¼

Ar  L  Rc : A2D

ð2Þ

It summarizes the morphometric features of the slope on which the calanchi developed, combining surface area, plan area, length, form, and also the general inclination, through the ratio Ar/A2D, and width in terms of the product of L and Rc. Depending on the scale, MSI was regarded as significant when Ar − A2D is larger than 2500 m 2. In the calanchi areas, we mapped drainage networks based on the CTR topography and checked them using the orthophotos, taking into account furrows with a minimum length of 10 m. It was hierarchized using Strahler's (1957) method (Fig. 5a). Drainage density (D in m −1) and drainage frequency (F in m −2) (Horton, 1945) based on Ac were calculated for each calanco network.

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Fig. 3. Geological sketch of the Orcia Valley area. 1) Undifferentiated Quaternary deposits; 2) undifferentiated Pliocene-Quaternary volcanic rocks; 3) Plio-Pleistocene marine deposits and Messinian evaporites; 4) undifferentiated sedimentary–metamorphic unit (Palaeozoic to Miocene); 5) main normal faults.

The amount of eroded volume in each calanchi area was estimated by reconstructing the original topography based on the procedure used for the reconstructed DTM: the topography was filled using straight contour

lines over the calanchi (Fig. 5c). The comparison between the resultant topography and the present topography permits the estimation of eroded volume (V, m3) and mean erosion depth (V/Ac, m).

Fig. 4. Geological sketch of the Mount Ascensione and Atri areas. 1) Undifferentiated Quaternary deposits; 2) Plio-Pleistocene marine deposits and Messinian evaporites; and 3) undifferentiated sedimentary–metamorphic unit (Palaeozoic to Miocene); 4) Main thrusts.

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Fig. 5. Methods of morphometric measurements. (a) Drainage network hierarchization, delimitation of a calanco and tributary areas and the trace of the slope profile. (b) Reconstruction of the initial slope. (c) Filling of the calanco for reconstructing topography before calanchi erosion and calculating eroded volume.

With statistical correlation and regression analyses, the relations between global characteristics of the initial slope (MSI), drainage network organization (D and F) and the erosion depth (V/Ac) were investigated.

(r = − 0.246, p b 0.01; Fig. 8) and between F and V/Ac (r = − 0.208, p b 0.05). However, these correlations are weaker, suggesting that linear erosion processes have not markedly influenced the magnitude of total erosion.

4. Results and discussion 5. Conclusions Table 1 shows the data derived from the morphometric analyses, and Table 2 shows the Pearson's correlation matrix for all data from the three areas. MSI eventually depends on the parameters that constitute Eq. (2) (with Ar/A2D, r = − 0.453, p b 0.01; with Rc, r = 0.233, p b 0.05; and with L, r = 0.856, p b 0.01). Moreover, MSI depends on S (r = −0.614, p b 0.01). These results indicate that MSI is a good combined indicator of the morphometry of the slope prior to calanchi erosion, effectively summarizing slope characteristics. The correlation between MSI and eroded volume is statistically significant, and it has the best correlations with both V (r = 0.869, p b 0.01) and V/Ac (r = 0.649, p b 0.01; Fig. 7). This means that the amount of erosion in the calanchi depends on the form of the initial slope. There are inverse correlations between D and MSI (r = − 0.256, p b 0.01) and between F and MSI (r = − 0.207, p b 0.05), showing that drainage networks with lower D or F occur on slopes with greater MSI. Likewise there are negative correlations between D and V/Ac

Erosion processes in the calanchi include both linear erosion (gully erosion) and areal erosion (sheet erosion and flow-type landsliding). In this work, these two types of processes were analyzed using two parameters: for linear erosion we mainly used D (specifically representing deep gully erosion), and for total erosion (both linear and areal) we mainly used V/Ac. The results indicate that the development of erosion processes depends on MSI. This agrees with the negative correlation between D and MSI and the positive correlation between V/Ac and MSI. The low correlation between D and V/Ac indicates that areal processes induce a greater amount of erosion (Lin and Oguchi, 2004; Descroix et al., 2008; Buccolini et al., 2012). Assuming that slope morphometry influences the processes of erosion and that the efficacy of these processes with respect to the amount of eroded material is a function of their duration, we consider that the positive correlation between V/Ac and MSI indicates that the analyzed calanchi are contemporaneous and the calanchi process was activated around the same moment in the three areas. One of the presumable causes for this activation is deforestation, but this did not occur at the same time across Italy. Although a more probable cause is climate change, it is difficult to indicate a specific period of the change from the current knowledge of past climate. However, it is reasonable to state that the calanchi process in Italy initiated at least after the onset of the typical Mediterranean climate about 4500 yr BP (Jalut et al., 2009). Acknowledgments

Fig. 6. Parameters used for calculating MSI. A2D = plane tributary area, Ar = reconstructed surface area, L = plane length, and p = drainage basin perimeter and circle circumference (equal to basin perimeter). Modified from Buccolini et al. (2012).

This study was supported by the University “G. d'Annunzio” funding to M. Buccolini (named ex 60%). The authors thank Prof. Francesco Dramis (University of Roma Tre) for his suggestions for the draft of this article, and the two

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Table 1 Dataset used. Id = calanchi identification number; Ac = calanchi surface area; D = drainage density; F = drainage frequency; A2D = plane tributary area; Ar = reconstructed surface area; Rc = circularity ratio; L = plane slope length; S = slope inclination; MSI = morphometric slope index; V = eroded volume. Id

Ac (104 m2)

D (m−1)

F (m−2)

A2D (104 m2)

Ar (104 m2)

Ar/A2D

Rc

L (m)

S (°)

MSI (m)

V (104 m3)

V/Ac (m)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73

7.11 6.45 3.16 2.18 9.44 3.69 3.14 8.31 28.40 16.28 4.32 4.16 7.92 13.01 8.96 4.59 24.37 6.74 32.80 33.34 29.89 27.94 7.32 10.90 2.62 4.96 3.30 2.03 13.47 6.58 13.49 6.61 36.67 5.29 3.60 8.66 7.79 5.84 16.79 6.74 9.18 10.29 5.48 5.77 15.49 8.67 7.91 3.97 11.75 22.67 4.36 15.68 3.24 3.18 4.60 2.97 3.53 7.04 28.76 7.01 26.19 36.66 37.87 27.17 14.95 12.67 73.31 17.18 7.64 8.52 3.89 4.13 6.13

0.036 0.046 0.063 0.062 0.032 0.019 0.033 0.034 0.036 0.042 0.043 0.022 0.026 0.023 0.029 0.018 0.016 0.054 0.038 0.032 0.041 0.036 0.048 0.046 0.048 0.039 0.058 0.042 0.026 0.025 0.027 0.024 0.021 0.022 0.027 0.029 0.029 0.025 0.025 0.021 0.023 0.024 0.025 0.029 0.023 0.025 0.021 0.022 0.019 0.018 0.022 0.025 0.026 0.038 0.039 0.036 0.019 0.028 0.018 0.027 0.021 0.022 0.018 0.015 0.022 0.024 0.017 0.017 0.035 0.034 0.047 0.018 0.018

0.00053 0.00087 0.0013 0.00147 0.00051 0.00016 0.00041 0.00053 0.00058 0.00078 0.00074 0.00022 0.00037 0.0003 0.00037 0.00015 0.00016 0.00122 0.00063 0.0005 0.0007 0.0006 0.00093 0.00083 0.0008 0.00061 0.00097 0.00069 0.0003 0.0003 0.00034 0.00026 0.00025 0.00021 0.00028 0.00035 0.00044 0.00029 0.00033 0.00018 0.00027 0.0003 0.00027 0.00045 0.00027 0.00023 0.00019 0.00015 0.00016 0.00014 0.00027 0.00027 0.00025 0.00057 0.00057 0.00061 0.00017 0.00035 0.00018 0.00033 0.00026 0.00026 0.00018 0.0001 0.00021 0.00029 0.00012 0.00016 0.00059 0.00054 0.00095 0.00012 0.00013

21.73 13.59 11.62 7.29 21.68 10.98 11.07 21.84 74.30 29.93 7.74 9.06 13.61 23.58 14.82 26.45 67.55 15.58 51.36 72.10 66.40 30.81 9.02 20.75 7.17 12.63 11.05 3.83 18.78 9.82 22.76 15.60 39.49 8.72 5.21 10.41 12.48 6.18 22.98 12.53 11.04 12.11 5.63 6.34 16.22 12.55 8.37 4.46 14.79 32.32 7.36 29.26 9.82 3.44 5.76 2.97 9.90 12.55 33.34 16.23 38.47 51.51 49.53 42.79 26.29 18.55 106.28 30.87 15.78 22.44 11.13 8.27 9.01

22.20 14.26 12.26 7.65 22.16 11.39 11.49 22.47 75.60 30.85 8.25 9.44 14.13 24.25 15.47 27.09 69.36 16.30 53.15 74.25 67.71 32.28 9.55 21.57 7.44 13.28 11.62 4.09 19.32 10.20 23.27 16.06 40.77 9.80 5.78 11.25 13.09 6.71 24.25 13.21 11.57 12.72 6.07 6.91 17.11 13.73 9.21 4.92 16.36 34.22 7.66 30.17 10.08 3.81 6.22 3.26 10.17 12.93 34.20 16.59 39.06 52.26 50.59 43.38 26.77 18.99 107.48 31.34 16.48 23.45 11.58 8.54 9.35

1.02 1.05 1.05 1.05 1.02 1.04 1.04 1.03 1.02 1.03 1.07 1.04 1.04 1.03 1.04 1.02 1.03 1.05 1.03 1.03 1.02 1.05 1.06 1.04 1.04 1.05 1.05 1.07 1.03 1.04 1.02 1.03 1.03 1.12 1.11 1.08 1.05 1.09 1.06 1.05 1.05 1.05 1.08 1.09 1.05 1.09 1.1 1.1 1.11 1.06 1.04 1.03 1.03 1.11 1.08 1.1 1.03 1.03 1.03 1.02 1.02 1.01 1.02 1.01 1.02 1.02 1.01 1.02 1.04 1.05 1.04 1.03 1.04

0.65 0.59 0.54 0.33 0.51 0.39 0.36 0.6 0.71 0.63 0.59 0.59 0.66 0.67 0.52 0.45 0.46 0.55 0.69 0.65 0.39 0.68 0.5 0.54 0.59 0.72 0.66 0.41 0.65 0.54 0.63 0.54 0.74 0.52 0.42 0.71 0.76 0.56 0.75 0.73 0.59 0.67 0.69 0.58 0.77 0.46 0.6 0.44 0.63 0.53 0.64 0.7 0.7 0.75 0.68 0.72 0.81 0.68 0.67 0.53 0.66 0.7 0.76 0.69 0.63 0.65 0.6 0.59 0.44 0.62 0.41 0.52 0.41

747 708 724 705 734 842 869 860 1155 987 502 596 662 584 711 1036 1590 801 1118 934 1882 838 673 889 547 495 558 512 701 676 730 858 917 617 573 524 470 520 694 582 647 589 395 452 680 780 588 507 692 1168 472 816 527 295 430 295 491 546 914 823 796 1126 864 1087 825 827 1955 928 957 877 820 623 759

17 17 18 18 17 15 14 14 12 14 18 16 16 16 16 13 12 18 16 18 9 19 17 17 14 20 17 19 14 14 13 11 15 25 23 23 19 22 21 18 16 16 21 20 18 24 23 21 25 18 16 15 11 23 20 24 13 14 12 12 12 9 11 9 10 11 7 10 16 17 15 14 14

496 436 411 246 385 342 328 529 836 641 316 364 455 404 387 479 753 460 802 627 744 597 353 496 336 376 388 225 470 375 473 475 697 363 265 402 372 318 551 449 401 416 295 286 549 391 389 246 479 657 316 591 379 245 318 232 408 381 631 442 536 800 671 757 529 551 1188 557 440 572 349 333 321

133.06 131.81 40.97 23.63 186.14 50.57 33.70 160.75 798.78 471.21 67.90 59.90 138.58 375.42 248.54 56.56 641.07 119.59 1253.42 886.61 829.76 1065.95 158.79 255.98 28.89 75.54 52.52 18.35 472.17 167.04 440.64 146.27 1588.48 96.83 41.79 146.54 191.56 76.16 508.93 102.40 235.32 300.02 121.09 144.67 509.26 221.92 167.55 51.03 295.92 748.63 83.79 402.95 63.80 64.22 93.96 42.39 48.29 99.29 583.22 99.39 717.33 1210.66 1011.90 708.03 281.67 202.59 2573.10 297.65 126.91 158.91 53.77 33.83 66.32

19 20 13 11 20 14 11 19 28 29 16 14 17 29 28 12 26 18 38 27 28 38 22 23 11 15 16 9 35 25 33 22 43 18 12 17 25 13 30 15 26 29 22 25 33 26 21 13 25 33 19 26 20 20 20 14 14 14 20 14 27 33 27 26 19 16 35 17 17 19 14 8 11

(continued on next page)

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Table 1 (continued) Id

Ac (104 m2)

D (m−1)

F (m−2)

74 75 76 77 78 79 80 81

3.79 13.26 14.82 26.86 13.35 38.00 17.48 4.90

0.025 0.019 0.018 0.019 0.023 0.022 0.023 0.027

0.00024 0.00021 0.00014 0.0002 0.0003 0.00023 0.00028 0.00039

A2D (104 m2) 5.50 21.04 32.11 31.50 18.92 82.97 30.67 15.18

Ar (104 m2) 5.77 21.66 37.54 32.81 19.62 84.06 31.54 15.56

Ar/A2D

Rc

L (m)

S (°)

1.05 1.03 1.17 1.04 1.04 1.01 1.03 1.03

0.7 0.66 0.65 0.72 0.64 0.59 0.71 0.77

354 732 797 694 694 1534 742 543

18 13 11 14 14 8 11 14

MSI (m) 261 495 608 517 458 923 541 427

V (104 m3)

V/Ac (m)

63.29 250.05 372.01 920.19 406.92 1189.33 505.16 83.82

17 19 25 34 30 31 29 17

Table 2 Pearson's correlation matrix. D = drainage density; F = drainage frequency; A2D = plane tributary area; Ar = reconstructed surface area; Rc = circularity ratio; L = plane slope length; S = slope inclination; MSI = morphometric slope index; V = eroded volume.

−1

D (m ) F (m−2) Ar/A2D Rc L (m) P (°) MSI (m) V (m3) V/Ac (m)

D (m−1)

F (m−2)

Ar/A2D

1.000 0.980⁎⁎ 0.062 −0.230⁎ −0.128 0.264⁎⁎ −0.256⁎⁎ −0.261⁎⁎ −0.246⁎⁎

1.000 0.017 −0.238⁎ −0.079 0.214⁎⁎ −0.207⁎ −0.217⁎ −0.208⁎

1.000 −0.089 −0.456⁎⁎ 0.735⁎⁎ −0.453⁎⁎ −0.337⁎⁎ −0.183

Rc

L (m)

P (°)

MSI (m)

V (m3)

V/Ac (m)

1.000 −0.260⁎ −0.056 0.233⁎ 0.248⁎⁎ 0.401⁎⁎

1.000 −0.604⁎⁎ 0.856⁎⁎ 0.707⁎⁎ 0.422⁎⁎

1.000 −0.614⁎⁎ −0.448⁎⁎ −0.233

1.000 0.869⁎⁎ 0.649⁎⁎

1.000 0.767⁎⁎

1.000

⁎⁎ Significant correlation at the 0.01 level. ⁎ Significant correlation at the 0.05 level.

50

r2 = 0.422

V/Ac

40 30 20 10 0 0

200

400

600

800

100

1200

1400

MSI Fig. 7. Linear regression between MSI and V/Ac.

50

r2 = 0.057

V/Ac

40 30 20 10 0 0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

D Fig. 8. Linear regression between D and V/Ac.

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