# Hydromorphological analysis on restored Alpine braided rivers

Lise Devreux, Margot Chapuis, Barbara Belletti

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Lise Devreux, Margot Chapuis, Barbara Belletti. Hydromorphological analysis on restored Alpine braided rivers. Geomorphology, 2022, 415, pp.108404. 10.1016/j geomorph.2022.108404. hal-03794714v2

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# Hydromorphological analysis on restored Alpine braided rivers.

L. Devreux<sup>a,*</sup>, M. Chapuis<sup>a</sup>, B. Belletti<sup>b</sup>

<sup>a</sup>Université Côte d'Azur, CNRS, ESPACE, 98 bd Edouard Herriot, 06 204 Nice Cedex 3, France

<sup>b</sup>Université de Lyon, CNRS, UMR 5600 EVS, France

## Abstract

Braided rivers have been exploited for decades by humans for the multiple resources they can provide (sediment and water sources for example). This frequently induces physical and biological dysfunctions and endangers ecosystem services, adjacent human infrastructures, and population. Restoration operations are being used increasingly to improve river status and function. However, monitoring post-restoration operations generally lasts a short time, and, in the case of braided rivers, monitoring methods are not adapted to their morphological specificities. This study evaluates restoration success by using morphometric indices on undisturbed and restored braided reaches before and after restoration using ortho-rectified aerial photographs and elevation data. The objectives of this study are (i) to evaluate the restoration operations effectiveness on the morphology of braided rivers, (ii) to test for the first time the application of morphometric indices specifically developed for braided rivers in a restoration context, and on braided rivers highly impacted by human pressures and (iii) to assess the impact of spatial scale and data type on the indices used. Two morphometric indices (normalised active channel width (Piégay et al., 2009) and bed relief index

<footnote>*Corresponding author</footnote>
(Liébault et al., 2013)) were applied on nine river reaches in south-east France and northern Italy, including four that have been restored or are still under restoration. Restoration operations were diverse but mainly process-based, from weir lowering to active channel widening and gravel augmentation. Operations date from 2008 to present. Active channel width and braiding morphological pattern improved after restoration (overall improvement of 79% and 67%, respectively for the two indices). Changes were supported by morphogenic floods occurrence on two out of the four restored reaches soon after the completion of restoration operations. This study shows that morphometric indices can be used to assess restoration effectiveness and spatial trajectories of braided rivers through time. It also demonstrates the significance of integrating restoration operations within a broader geomorphological context of the river catchment at the regional scale.

Keywords: Braided rivers, restoration, hydromorphology, functional braided morphology, morphometric indices, regional scale.

# 1. Introduction

Braided rivers are characterised by high sediment supply, limited transport capacity, and a large active channel where a multi-channel pattern develops with no or little vegetation (Ashmore, 2013). Braided river morphology changes frequently due to a dynamic hydrological regime, characterised by large floods as well as marked low flow periods.

Braided rivers form an important heritage in Europe, especially in south-east France where more than 600 km of braided rivers still remain (Piégay et al., 2009), but they are endangered significantly by climate change and human impacts notably over the last century. The significant sediment supply available in braided rivers was used intensively in the 1970s especially for building construction (Liébault and Piégay, 2002; Rinaldi et al., 2005), and
the need for farming and building land also drastically reduced their active channel areas. This reduction in area was accompanied by the construction of levees, groynes and weirs to protect claimed land. These perturbations caused vertical incision, active channel retraction, lateral instability, sediment and ecological disconnectivity (Liébault and Piégay, 2002; Piégay et al., 2006, 2009; Liébault et al., 2013; Surian, 2015).

Braided rivers are increasingly subject to restoration operations, especially with the implementation of the Water Framework Directive (WFD) in 2000 (European parliament and Council, 2000) and according to the increase of multiple pressures and freshwater uses (Schinegger et al., 2012). The aim of restoration operations ranges from restoration of the global ecosystem, to benefit a target species, or for a specific process (Friberg et al., 2016; Morandi et al., 2017). Restoration-objectives can hence be set against a reference state objective (to reach “good status”) or to achieve specific objectives in terms of river functioning (such as longitudinal continuity or bank erosion), and these directly influence restoration efficiency. If objectives are defined on the basis of a past state prior to human impacts, it is likely that the restoration efforts will result in failure (Dufour and Piégay, 2009; Morandi et al., 2014; Wohl et al., 2015). As well, the definition of a monitoring program with adapted indicators is a key condition which is not systematically met (Morandi et al., 2014; Kail et al., 2015; Friberg et al., 2016). In particular, adapted indicators to rank and quantify the restoration success are still missing.

Time and temporal scales are both essential parameters when restoration success is assessed. Restoration operations are usually carried out at reach or site scale, but larger scale factors (catchment scale context, knowledge on river trajectories as well as local and catchment pressures) should be known in order to identify catchment scale drivers and potential causes for restoration failure
(Trush et al., 2000; Beechie et al., 2010; Friberg et al., 2016, 2017; Cid et al., 2021). For example, a lack of sediment connectivity from upstream might prevent restoration success as restored braided morphology cannot be sustained in the long-term (Campana et al., 2014; Scorpio et al., 2020). Restoration success depends also on unpredictable events, such as morphogenic floods occurrences or morphological adjustments (Bond and Lake, 2003; Friberg et al., 2016).

In order to diagnose ecological status for the WFD, several methods and indicators have been produced for each "quality element" (Solimini et al., 2006; Belletti et al., 2015; Gurnell et al., 2016b; Poikane et al., 2020). Hydromorphological indices were developed across Europe, but few of these take into account the type of morphology, and they are usually based on physical habitat assessment (Belletti et al., 2015), or on a hydraulic approach which is not adapted to the high variability of flowing sections in braided rivers, such as the French index CarHyCE, (Gob et al., 2014; Tamisier et al., 2017). Other morphological indices have been designed (Piégay et al., 2009; Liébault et al., 2013; Belletti et al., 2013; Lallias-Tacon, 2015) to be specifically applied to braided rivers and their dynamic morphology trajectory: the W* index evaluates the active channel width related to upstream river catchment area (Piégay et al., 2009). A high W* indicates high sediment delivery, whereas a low W* shows a deficit in sediment supply. The Bed Relief Index (BRI*) is a dimensionless index that evaluates braiding intensity (Liébault et al., 2013). It is based on the standard deviation of elevation points along one or several cross-sections to assess bed macro-roughness. A high BRI* indicates high roughness, implying a limited sediment supply and therefore vertical incision towards a deep single channel morphology; a low BRI* indicates low roughness and limited sediment transport capacity,
indicating sediment aggradation, towards a shallow multi-channel morphology.
These indices have been developed and applied in near-natural braided rivers
and their application in more impacted hydrosystems is still missing.

We hypothesise that a braided functional pattern is resettled after
restoration and with time it remains present and is self-sustainable, in case the
system is still hydromorphologically functional and well-connected to its
upstream catchment. The objectives of the present study are (i) to evaluate
the restoration operations effectiveness on the morphology of braided rivers,
(ii) to test for the first time the application of morphometric indices
specifically developed for braided rivers in a restoration context, and on
braided rivers highly impacted by human pressures and (iii) to assess the
impact of spatial scale and data type on the indices used. We applied two
morphometric indices (W* and BRI*) on 9 braided river reaches, of which 4
have been restored or are under restoration at the time of writing. We then
discuss their application in a restoration context, compare results at the
regional scale, and discuss the effects of different spatial scales and the types of
data on the indices.

## 2. Study area

This study is based on five gravel-bed rivers in the Alpine region, spanning
different human-impacted and restored contexts and selected following several
criterions.

### 2.1. *Study site selection*

Three rivers are located in south-east France (Drac, Durance, Var), one in
north-east Italy (Mareta) and one flows through both France and Italy (Roya,
Figure 1). All rivers but the Roya had a reach that has undergone restoration
<figure><img src="image_2.png" /><figcaption>Figure 1: (A) General presentation of the studied reaches. Location of the studied reaches on the Drac (B), the Durance (C), the Var (D) catchments in France, and on the Roya (E) and on the Mareta (F) catchments in Italy.</figcaption></figure>

operations to restore sediment continuity, protect downstream area from floods, or re-establish braided morphology. River reach selection was based on the type of restoration operation (process-based restoration), the compatibility with the study duration and the fact that restoration operations were supervised by local river managers. The length of each restored reach was based on the restoration project length when it was defined. If this was not the case (single weir levelling for example), the length corresponds to about 20 times the active channel width, to be representative of the river morphology and to allow comparison between rivers (Belletti, 2012). As well, availability of high altimetric resolution DEM data (0.5 m or better) before and after restoration was considered. Finally, the presence of an upstream target reach displaying a well-developed, functioning braided pattern morphology was
<table><caption>Table 1: Main characteristics of the studied catchments.</caption><thead><tr><th>River</th><th>Drac</th><th>Durance</th><th>Var</th><th>Mareta</th><th>Roya</th></tr></thead><tbody><tr><td>Catchment (km²)</td><td>3,300</td><td>14,280</td><td>2,822</td><td>212</td><td>669</td></tr><tr><td>Lithology</td><td>sedimentary + metamorphic</td><td>sedimentary + crystalline (low portion)</td><td>sedimentary + metamorphic cristalline (low portion)</td><td>metamorphic</td><td>sedimentary + metamorphic</td></tr><tr><td>Climate</td><td>Mountainous, Mediterranean influence</td><td>Mediterranean</td><td>Mediterranean</td><td>Mountainous</td><td>Mediterranean</td></tr><tr><td>Hydrological regime</td><td>Nival-rain</td><td>Nival-rain</td><td>Nival-Mediterranean</td><td>Nivo-glacial</td><td>Mediterranean</td></tr><tr><td>Main river length (km)</td><td>43.2 (Upper Drac)</td><td>323</td><td>110</td><td>24</td><td>59</td></tr></tbody></table>

<table><caption>Table 2: Main characteristics of the studied reaches.</caption><thead><tr><th>Rivers</th><th>Drac</th><th>Durance</th><th>Var</th><th>Mareta</th><th>Roya</th></tr></thead><tbody><tr><td>Reach</td><td>Saint-Bonnet-en-Champsaur (R)<sup>1</sup></td><td>Chabottes (T)<sup>2</sup></td><td>La Brillanne (R)<sup>1</sup></td><td>Les Mées (T)<sup>2</sup></td><td>Low valley (R)<sup>1</sup></td><td>Vipiteno (R)<sup>1</sup></td><td>Ridanna/Ridnaun (T)<sup>2</sup></td><td>Low valley (I)<sup>3</sup></td></tr><tr><td>Geographic location</td><td>middle</td><td>middle</td><td>middle</td><td>middle</td><td>low</td><td>low</td><td>middle</td><td>low</td></tr><tr><td>Subatchment area (km2)</td><td>340</td><td>253</td><td>6,76</td><td>6,76</td><td>2,822</td><td>409</td><td>109</td><td>669</td></tr><tr><td>Reach length (km)</td><td>3.6</td><td>2.45</td><td>6.53</td><td>6.65</td><td>23</td><td>3.6</td><td>2</td><td>8.31</td></tr><tr><td>Type of ups. art. feat.<sup>4</sup></td><td>Weir of Pont-des-Fossé</td><td>Pont-des-Fossé weir</td><td>Escale Dam</td><td>Escale Dam</td><td>La Mescla Dam</td><td>Guillaumes weir</td><td>Weir</td><td>Weir</td><td>Airole weir</td></tr><tr><td>Distance (km) to ups. art. feat.<sup>4</sup></td><td>9.50</td><td>5</td><td>16</td><td>8.6</td><td>9</td><td>6.68</td><td>0.1</td><td>0.5</td><td>3</td></tr><tr><td>Type of restoration</td><td>Active channel widening, riverbed raising, equipment of fish pass</td><td></td><td>Lowering of La Brillanne weir</td><td></td><td>Weirs lowering (weirs n°9, n°10, n°8 and n°7)</td><td></td><td>16 weirs lowered, active channel widening</td><td></td><td>None</td></tr><tr><td>Restoration date</td><td>2013/2014</td><td></td><td>2019/2021</td><td></td><td>2009/on going</td><td></td><td>2008/2009</td><td></td><td>None</td></tr><tr><td>Distance between R¹and T²reach</td><td>3.9</td><td>3.9</td><td>0.8</td><td>0.8</td><td>58</td><td>58</td><td>6</td><td>6</td><td>NA</td></tr><tr><td>Slope after restoration on average (%)</td><td>1.05</td><td>NA</td><td>on going</td><td>NA</td><td>on going</td><td>NA</td><td>0.01<sup>5</sup></td><td>NA</td><td>NA</td></tr><tr><td>Active channel width (m) (after restoration)</td><td>105</td><td>NA</td><td>on going</td><td>NA</td><td>on going</td><td>NA</td><td>53</td><td>NA</td><td>NA</td></tr></tbody></table>

necessary to allow for Control/Impact comparison and "space for time" analysis (Looy et al., 2008; Dufour and Piégay, 2009). Indeed, elevation data on the former braided morphology, before degradation, on restored reaches were not available for before-after comparisons. The upstream, well-developed braided reach is then considered as the "target" or "control reach", the restored reach is then called "restored" and corresponds to the "impacted reach". The general characteristics of the catchments are presented in Table 1, the reaches and their restoration operations are summarised in Table 2. For more details on the nature and objectives of the restoration operations, see Appendix A.

<footnote n="1">¹ administrative management</footnote>

<footnote n="1">¹ restored ² target ³ impacted ⁴ upstream artificial feature ⁵ the values have been calculated in the context of the present study</footnote>
Daily discharge values for the French rivers were obtained from the "Banque Hydro" national database (MEDDE), from the Autonomous Province of Bolzano for the Mareta and from French electricity company (EDF) for the Roya (Table 3). Two gauging stations were selected on the Var valley (Var at Carros and Var at Nice) to cover the entire study period. Two gauging stations were also selected on the Durance (Durance at Oraison and Durance at Cadarache). For the Durance, the Oraison station represents natural flows, whereas the Cadarache station, located 28 km downstream, accounts for the impact of dams and flow diversion. Hydrological statistics (i.e. low flow discharge, 2, 5, 10, 20 and 50-years return periods discharges and mean annual discharge) are also reported in Table 3. In the case where one or more hydrological statistics were not available from the supplier, statistics were estimated using Gumbel's law (Gumbel, 1941) and then compared to existing literature and nearby hydrological stations. To compare reaches and rivers, exceedance flow frequencies were calculated with Hazen's formula (Hazen, 1914).

This study is based on morphometrics indices calculated from river landscape data extracted from remote sensing. Orthophotographies were obtained from local river managers, territorial organisations, the French National Geographic Institute (IGN) and the University of Florence, and were acquired between 2005 and 2018 at various resolutions (Table 4). Elevation data were extracted from DEMs, derived from LiDAR or photogrammetry, with high planimetric resolution between 0.1 and 5 m. Orthophotographies were selected to match
<table><caption>Table 3: General characteristics of the hydrological stations of the studied rivers. For French rivers, the low flow discharge corresponds to the average monthly dry discharge of 5 year-return period, values are from the Banque Hydro (MEDDE) for all the stations, except for the Durance. All discharges for the different return period are from the Banque Hydro, except for the Mareta which have been calculated with the Gumbel's law in the context of this study.</caption><thead><tr><th></th><th>Mareta</th><th>Drac</th><th>Durance</th><th>Durance</th><th>Var</th><th>Var</th><th>Var</th><th>Roya</th></tr></thead><tbody><tr><td>Gauging station</td><td>Mareta@Vipiteno</td><td>Drac@Chabottes</td><td>Durance@Oraison</td><td>Durance@Cadarache</td><td>Var@Entrevaux</td><td>Var@Nice</td><td>Var@Carros</td><td>Roya@Breil sur Roya</td></tr><tr><td>Reach <sup>1</sup></td><td>R &amp; T</td><td>R &amp; T</td><td>R &amp; T</td><td>R &amp; T</td><td>T</td><td>R</td><td>R</td><td>I</td></tr><tr><td>Restoration year</td><td>2009</td><td>2014</td><td>2013</td><td>2013</td><td>2009</td><td>2009</td><td>2009</td><td>NA</td></tr><tr><td>Area (km<sup>2</sup>)</td><td>212</td><td>253</td><td>6,760</td><td>11,700</td><td>676</td><td>2,820</td><td>2,770</td><td>461</td></tr><tr><td>Start year</td><td>1981</td><td>2007</td><td>1973</td><td>1918</td><td>1920</td><td>2016</td><td>2006</td><td>1969/2019</td></tr><tr><td>End year</td><td>2021</td><td>2021</td><td>2017</td><td>2018</td><td>2021</td><td>2021</td><td>2018</td><td>2017/2020</td></tr><tr><td>Accuracy of gauging station</td><td>Good</td><td>Good</td><td>Good</td><td>Good</td><td>Good</td><td>Good</td><td>Uncertain</td><td>Good</td></tr><tr><td>Mean annual discharge</td><td>7<sup>2</sup></td><td>6<sup>2</sup></td><td>115</td><td>175</td><td>16</td><td>50</td><td>51</td><td>12</td></tr><tr><td>Low flow discharge</td><td>NA</td><td>1</td><td>9<sup>3</sup></td><td>75</td><td>5</td><td>14</td><td>15</td><td>5</td></tr><tr><td>Q<sub>2</sub></td><td>45<sup>4</sup></td><td>35</td><td>610</td><td>870</td><td>86</td><td>440</td><td>500</td><td>100</td></tr><tr><td>Q<sub>5</sub></td><td>65<sup>4</sup></td><td>49</td><td>900</td><td>1300</td><td>120</td><td>700</td><td>660</td><td>170</td></tr><tr><td>Q<sub>10</sub></td><td>80<sup>4</sup></td><td>58</td><td>1100</td><td>1600</td><td>150</td><td>870</td><td>760</td><td>210</td></tr><tr><td>Q<sub>20</sub></td><td>90<sup>4</sup></td><td>NA</td><td>1300</td><td>1800</td><td>170</td><td>1000</td><td>860</td><td>250</td></tr><tr><td>Q<sub>50</sub></td><td>110<sup>4</sup></td><td>NA</td><td>1500</td><td>2200</td><td>200</td><td>1200</td><td>NA</td><td>300</td></tr><tr><td>Data producer</td><td>Aut. Prov. Bolz.<sup>5</sup></td><td>DREAL<sup>6</sup></td><td>EDF<sup>7</sup></td><td>EDF<sup>7</sup></td><td>DREAL<sup>6</sup></td><td>DREAL<sup>6</sup></td><td>DREAL<sup>6</sup></td><td>DREAL<sup>6</sup>/EDF<sup>7</sup></td></tr></tbody></table>

as closest as possible in time the DEM date. The overall survey period is set between 2004 and 2018 (Table 4).

The river landscape (stricto sensu Carbonneau et al. (2012); Belletti (2012); Demarchi et al. (2016)) was classified by photointerpretation of aerial photographs and analysis of DEM data. This was executed on each reach at least for one date before and one after restoration, except for the target reach on the Var river and the reach on the Roya river where only one date was available. We delineated the active channel formed by water channels and sediment bars characterised by absence or little presence of pioneer vegetation, i.e. sparser, sharper and with smaller canopy compared to mature vegetation (Toone, 2009; Malavoi and Bravard, 2010; Toone et al., 2014; Surian et al., 2016). The active channel was digitised at a scale of 1 : 2000 to 1 : 5000. Pioneer vegetation and sediment bars areas under 10 m² were not considered and all water areas were taken into account. Then, cross sections were created along the reach, spaced 10 m each, to take into account the longitudinal variability of bedforms. According to DEM resolution, cross sections were then

<footnote n="1">¹ R, T and D: Restored (R), target (T) and impacted (I) reaches
² values calculated in the context of this study
³ SMAVD
⁴ calculated with the Gumbel's law</footnote>

<footnote n="5">⁵ Autonomous Province of Bolzano
⁶ Regional direction of environment, urban planning and housing
⁷ French electricity company</footnote>
discretised at regular spacing (Table 4). Elevation values and width values were then extracted at each point within GIS environment.

GIS operations were executed by the same operator on GIS softwares (ArcMap 10.6, QGIS 3.10.4 and QGIS 2.18.28; the tool boxes used are the Fluvial Toolbox on ArcMap and the Point Sampling Tool (0.5.3) on QGIS).

### 3.3. Morphometric indices

Two indices were selected: the W* (normalised active channel width, Piégay et al. (2009)) and the BRI* (normalised Bed Relief Index, Liébault et al. (2013)).

The extent and intensity of the braiding hydromorphological activity can be assessed by the W* which corresponds to the width of the active channel normalised by the catchment area (Eq.(1), Piégay et al. (2009)). The average active channel width was obtained from equidistant points on cross-sections. Catchment areas were extracted from the IGN Carthage® database.

$$W^* = \frac{\text{active channel width}}{\text{catchment area}^{0.44}} \qquad (1)$$

A W* value above the threshold value of 10 m/km⁰.⁴⁴ indicates a braiding activity. This threshold has been defined on a larger dataset from the same geographic area that includes braided rivers little impacted by human activities (Piégay et al., 2009; Terrier et al., 2019).

Braided pattern can also be assessed in terms of active channel macro-roughness through the normalized Bed Relief Index (BRI*) (Eq. (2), Figure 2) (Liébault et al., 2013). The BRI* corresponds to the ratio between the standard deviation of active channel elevations and the active channel width, measured between riverbank toes.
<figure><img src="image_3.png" /><figcaption>Figure 2: BRI* extracted from sub-cross section (green and top line, Z₁ and Z₂) and cross-section (orange and bottom line, Z₁) on active braided channel.</figcaption></figure>

$$BRI^* = \frac{\left[ \frac{1}{n-1} \sum_{i=1}^{n} (z_i - Z)^2 \right]^{0.5}}{x_n - x_1} \quad (2)$$

where zᵢ corresponds to the riverbed elevation at equidistant points along the cross-section, Z the mean elevation along the cross-section, xₙ - n₁ the active channel width where x identifies each measure along the cross-section.

Equation 2 is dimensionless and relies on measures at regular spacing along a cross-section. Terrier et al. (2019) indicates a regional threshold for this index at 0.004 from Liébault et al. (2013)'s study. Below this threshold, the reach is considered to be limited in transport capacity, showing a braided pattern that reflects a large sediment supply. Over this threshold the reach is considered sediment-supply limited.

The BRI* was applied at different transversal units: the cross-section and the sub-cross-section scales. Sub-cross-sections are created each time a mature vegetation island is present on the cross-section (Figure 2, top green dotted line) (Lallias-Tacon, 2015). The standard deviation is then applied for each sub-cross-section (Z₁ and Z₂ on the top green dotted line in Figure 2) and then summed to obtain a BRI value for the entire cross-section. At the cross-section scale,
standard deviation is applied to the whole length of the cross-section, i.e. the active channel width (Figure 2, bottom orange dotted line). In both cases, areas with mature vegetation islands are not included (Figure 2, vegetated islands).

The BRI* index was calculated from different datasets with various altimetric and planimetric resolutions. Altimetric resolution ranges between - 0.001 and 0.4 m (Table 4). The spacing between measurements along sub- and cross-sections used in the BRI* formula ($x_n$) was chosen according to the planimetric resolution (referred as planimetric resolution hereafter) of each DEM, ranging between 0.1 and 5 m (Table 4). As showed by Milan et al. (2011), morphological changes assessed from DEM data can lead to underestimation due to surface composition or topographic complexity amongst others. Therefore, to apprehend the spatially distributed uncertainty due to planimetric and altimetric accuracy, we calculated an error propagation on the BRI* for each dataset (Eq. 3).

$$EP = \frac{\sqrt{\frac{n}{n-1}} (2\delta Z)}{x_n - x_1} \quad (3)$$

where $n$ corresponds to the number of measures on a cross-section, $\delta Z$ the altimetric resolution of elevation data and $x$ the number of each measures.

In addition to the analysis of reach mean values, we also assessed the longitudinal evolution. We performed Before-After Control-Impacts (BACI) comparisons by means of pairwise tests on both indices on the following couples (Table 5): before and after restoration, after restoration and the corresponding target reach (recent date) and target reaches at both dates, except for the Var river target reach and the Roya river (impacted reference) where only one date was available. For each couple, the detailed longitudinal
<table><caption>Table 5: Pairwise tests performed on longitudinal evolution and standard deviation of the morphometrics indices. The notes “old date” and “recent date” for the restored reach correspond respectively to before and after restoration.</caption><thead><tr><th>Pair 1</th><th></th><th>Pair 2</th></tr></thead><tbody><tr><td>Restored old date</td><td>↔</td><td>Restored recent date</td></tr><tr><td>Restored recent date</td><td>↔</td><td>Target recent date</td></tr><tr><td>Target old date</td><td>↔</td><td>Target recent date</td></tr></tbody></table>

219 evolution and the standard deviation were used.

220 All calculations and analysis have been executed on R (4.0.3) and Rstudio (1.1.463), all packages used can be found in Appendix B.

221 The script used for BRI* and W* calculation is included in the package along with a tutorial for GIS data extraction (Devreux et al., 2021).

## 4. Results

### 4.1. Hydrological analysis

Figure 3 shows the daily discharges at the gauging stations between 2000 and 2020. The Durance (weir failure in 2013) displays, compared to 2000-2005, lower flow discharges with few floods since 2005 until 2013 and 2014 where two 10-year return period floods destroyed the weir. Since then, only an estimated 5 to 10-year return period flood occurred in 2016 (Dumoulin, 2018). The Drac (restored between 2013 and 2014) displays a significant active period before restoration (Figure 3, Brousse, 2020). After restoration, one 2-year and two 5-year floods occurred until 2021 when an estimated 10-year return period flood occurred (B. Breilh, river manager, pers. com.; not shown on Figure 3). The Mareta (restored between 2008 and 2009) underwent a low hydrological activity except an active period between 2000 and 2003 and an estimated 5-year flood in 2014. On the Var river, three gauging stations are analysed. The Var at Entrevaux corresponds to the target
reach station (Daluis), which shows six floods of 10-year return period floods between 2000 and 2020. On the lower Var valley (under restoration since 2009), several floods of 2-year return period occurred regularly, and two 10-year return period occurred in 2011 and 2016. Between 2000 and 2008, the few available information indicates a hydrological calm period with two 2-year-return period floods in 2009. The Roya (impacted reference) displays a very active hydrological time series except between 2004 and 2008. Several morphogenic floods occurred between 2000 and 2020, including one 50-year return period flood, one 20-year return period flood and several biennial and 3-year return period floods. An extreme hydrological event occurred late 2020 in the south-east France (rainfall return period > 1000 years on the Roya catchment and part of the Var catchment, CEREMA, 2021; not shown on Figure 3).

252

## 4.2. Braiding evolution following restoration

All river reaches positively responded to restoration operations, showing an increase in active channel width and an overall improvement in braiding pattern.

254

255

### 4.2.1. Normalised active channel width evolution following restoration

Figure 4 displays the W* values and standard deviations on all the studied reaches. On target reaches, the W* is always higher than the corresponding restored reach, ranging from 7.0 to 12.2 m/km⁰.⁴⁴ and are close to the 10 m/km⁰.⁴⁴ threshold indicating higher sediment delivery and channel dynamics, except for the Mareta. Here, the W* is very low and does not change through time (*p*-value = n.s.) because embankments limit further channel dynamics. On the Durance and Drac target reaches, W* remains constant for both dates (respectively from 7.0 to 7.9 and from 12.2 to 9.5

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<figure><img src="image_4.png" /><figcaption>Figure 3: Daily discharge normalised by the mean annual discharge on the gauging stations of the studied rivers. The normalised flood discharges with a return period of two years (purple and bottom line), five years (blue and middle line) and ten years (green and top line) are shown by dotted lines. The vertical red line corresponds to the restoration year. On the Durance at Oraison, the data gap corresponds to 2016.</figcaption></figure>

Daily discharge normalised by mean interannual discharge [m³/s]
m/km$^{0.44}$; *p*-value <0.001), due to little disturbance from morphogenic floods over the study period. The Var river target reach displays a W* equal to the 10 m/km$^{0.44}$ threshold in 2012 (10.2), no time comparison was possible on this reach. Finally, the lower Roya valley shows a similar value in 2018 to the lower Var valley in 2005 and in 2012 (respectively 5.1, 4.7 and 4.5 m/km$^{0.44}$), being both reaches embanked by artificial levees and bank protections, which constrain the hydromorphological activity within a relatively narrow active channel.

On restored reaches, the W* shows low values before restoration in all studied rivers (Figure 4), ranging between 2.8 and 5.1 m/km$^{0.44}$, indicating a deficit in sediment supply (i.e. below the 10 m/km$^{0.44}$ threshold). After restoration, the W* increases about 79% in average on restored reaches, with values ranging between 5.0 and 9.5 m/km$^{0.44}$ as a consequence of restoration operations and probably also linked to an increase in hydrological activity and sediment transport. Values are still under the 10 m/km$^{0.44}$ but suggest an improvement in braiding dynamics.

For the Drac and Mareta restored reaches, channel widening operations improved W* from 3.2 to 8.1 m/km$^{0.44}$ and from 2.8 to 5.0 m/km$^{0.44}$, respectively (*p*-values <0.001 for both reaches). The standard deviation increased on both reaches, from 0.9 to 3.3 and from 0.7 to 1.2 respectively, indicating higher heterogeneity due to the presence of localised vegetated islands and sections with lower active channel width. Even if restoration operations enabled a wider active channel with sediment bars and several channels, no significant morphogenic floods occurred after restoration until recently (Figure 3), thus the system was not able to readjust accordingly to the new restored morphology immediately after restoration operations (Scorpio et al., 2020). Moreover, right upstream the restored reach, the
Mareta river is still fragmented by a series of weirs that impact sediment connectivity and might impede further morphological adjustments. On the Var restored reach, W* and its standard deviation increased from 4.7 to 9.5 m/km⁰.⁴⁴ (p-value ≤0.001) and from 1.7 to 3.3 respectively, showing a higher heterogeneity as restoration operations progress. This is due to the progressive weir levellings along the reach, combined with two morphological floods (2011 and 2016) as well as the reach length and its spatial configuration. The Durance restored reach shows a similar trend but slightly less marked, from 5.1 m/km⁰.⁴⁴ before the weir failure, to 5.7 m/km⁰.⁴⁴ after (p-value <0.001). The standard deviation decreased on this reach from 1.9 to 1.6, suggesting a more homogeneous active channel width.

<figure><img src="image_5.png" /><figcaption>Figure 4: Normalised width of the active channel (W*) on target and restored reaches before and after restoration. The vertical dotted line shows the restoration year. The horizontal dotted line shows the index threshold (10 m/km⁰.⁴⁴, Terrier et al. (2019); Piégay et al. (2009)). For the Durance river, the restoration started in 2019 and is still on-going, the year 2013 corresponds to the weir failure due to a 10-year return period flood; for the Var river, the restoration started in 2009 and is also on-going.</figcaption></figure>
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4.2.2. Normalised bed relief index evolution following restoration

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Figure 5 displays for each BRI* values, the standard deviation and the error propagation, which accounts for the regular spacing between measures and the altimetric resolution of data. The BRI* on target reaches are always under the threshold for the Drac and the Durance (ranging between 0.002 and 0.004; *p* - value <0.001 and <0.01 respectively), showing a braiding pattern. On the other hand, the BRI* on the Mareta and the Var on their respective target reach are always higher than the 0.004 threshold value (ranging between 0.005 and 0.008, *p*-value ≤0.005 for the Mareta) suggesting a degraded braiding pattern. As for the W*, the BRI* on the Mareta is impacted by the presence of embankments and the lack of large floods. On the upstream Var, the configuration of the valley might influence the BRI* as for the lower Roya valley.

All reaches show pre-restoration BRI* values above the BRI* threshold (0.004), which indicates a limited sediment supply and a higher bed macro-roughness with values ranging between 0.003 and 0.018 (Figure 5). After restoration, BRI* values decrease about 67% in average and are lower or equal to the 0.004 threshold, ranging from 0.002 to 0.004 and indicating a limitation in transport capacity (Terrier et al., 2019). All restored reaches show a decrease in their standard deviation after restoration operations (*p*-value ≤0.05), which suggests success in restoration operations through a reduction in bed roughness variability along reaches.

The restored reaches on the Drac and the Var show major improvements of their BRI* (*p*-value <0.001) and standard deviations after restoration which suggests a reorganisation of the channel pattern towards a more homogeneous braiding. On the Drac river, the restored reach before restoration shows the
<figure><img src="image_6.png" /><figcaption>Figure 5: Normalised bed relief index (BRI\*) on target and restored reaches before and after restoration. The horizontal dotted line shows the index threshold (0.004, Terrier et al. (2019); Liébault et al. (2013)) indicating braiding below the line. The vertical dotted line shows the restoration year for each river. For the Durance river, the restoration started in 2019 and is still on-going, the year 2013 corresponds to the weir failure due to a 10-year return period flood; for the Var river, the restoration started in 2009 and is also on-going.</figcaption></figure>

highest BRI\* value amongst all reaches (0.018 and a standard deviation of 0.010), which, after restoration, decreases to a value below the 0.004 threshold (0.003, *p*-value <0.001 and 0.002 respectively). Since no morphogenic floods occurred until 2019, we can then hypothesise that the BRI\* decrease is the effect of the restoration only. On the lower Var valley, the BRI\* (*p*-value <0.001) and its standard deviation progressively decreases from 2005 (0.010 and 0.009 respectively) to 2012 (0.004 and 0.003 respectively) and to 2018 (0.002 for both), as consequence of restoration operations along the reach. It is worth mentioning that sediment transport on the lower Var valley was already active before the first restoration operations, thanks to the cessation of gravel mining upstream and to the major flood of 1994 (which caused the destruction of weirs n°2 and n°3 in the downstream section, see Appendix A). After the levelling of the first weir (weir n°9, in 2009) and the occurrence of several morphogenic floods (Figure 3), the BRI\* met the 0.004 threshold in 2012. As for the W\*, the lower Roya valley (Figure 5) shows a BRI\* value equal to the lower Var valley in
344 2005, before restoration (0.01 for both). Despite the similarities between the
345 two rivers (see Appendix A), the vertical incision on the lower Roya valley is
346 not as important as on the lower Var valley, resources uses within the river
347 catchment were indeed different on the Roya compared to the Var catchment.
348 On the Durance river, the BRI* shows a slight decrease after the failure of the
349 weir (- 0.0005, p-value <0.001) and a constant standard deviation through time
350 (Figure 5).

351 On the Drac and the Var rivers, the error propagation is equal or lower
352 than the corresponding standard deviation, indicating that BRI* results are
353 meaningful. However, the error propagation increases with time (i.e. 0.002 for
354 the Drac and, 0.003 and 0.004 for the Var) suggesting that even if restoration
355 improves the braided morphology (reduction of standard deviation), altimetric
356 and planimetric resolutions as well as the morphological pattern heterogeneity
357 impact the BRI* calculation. On the Durance, the error propagation remains
358 equal or lower than the standard deviation for both dates (both ranging between
359 0.0005 and 0.002), indicating that BRI* results are reliable.

360 The BRI* on the Mareta restored reach shows a slight decrease after
361 restoration (from 0.005 to 0.004, p-value <0.01). The Mareta did not undergo
362 any significant morphogenic floods since the restoration operations in 2009,
363 and vegetation started to encroach on the new, restored channel. The
364 estimated 5-year return period flood which occurred in 2014 was not sufficient
365 to reverse the vegetation encroachment (Scorpio et al., 2020). The error
366 propagation values displayed on the Mareta reaches before and after
367 restoration are the highest (ranging between 0.004 and 0.02 on both reaches
368 and at both dates), higher than standard deviation (ranging between 0.002
369 and 0.005), confirming that the index is sensitive to the river morphology and
370 hence poorly reliable when the channel pattern is not truly braiding and
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decrease the uncertainty that however remains high (0.004 and 0.007 after
restoration on restored and target reaches).

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4.3. *Spatial scale analysis*

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4.3.1. W* and BRI* longitudinal pattern in restored reaches

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The analysis of the longitudinal variation of the active channel width (W) and the BRI* demonstrates that the morphometric indices are able to catch restoration effects and existing human pressures locally. This analysis is focused on the Durance and Var restored reaches. For the Drac and Mareta restored reaches, no specific longitudinal pattern can be distinguished (see appendices C and D), probably due to their smaller size.

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Figures 6 and 7 display respectively the active channel width evolution and the BRI* variation along the lower Var valley before (2005) and during restoration (2012 and 2018). Five sub-reaches can be distinguished from the indices evolutions and based on the progression of restoration operations along the reach. Local variations are similar between the three years but the increase in the active channel width is clear with a net difference between 2012 and 2018, for example for weir n°10, levelled in 2012, to which corresponds an average width increase of 190%, fostered by the 2012 morphogenic floods. The BRI* longitudinal pattern displays peaks of higher values corresponding to weirs locations (e.g.: n°16, n°9 or n°5 with BRI* values of 0.086, 0.037 and 0.040 respectively in 2005), demonstrating BRI* ability in capturing the weir proximal morphological effects. Throughout time and restoration operations, the BRI* decreases, as well as its variability within and between sub-reaches (e.g. the peak for weir n°9 in 2005 versus 2012 and 2018; respectively 0.037, 0.003 and 0.001).
<figure><img src="image_7.png" /><figcaption>Figure 6: Longitudinal evolution of the active channel width on the lower Var valley. The five sections have been delimited based on the braiding pattern and the indices evolution. The horizontal pink dotted lines display the overall mean for each section. Weir n°9 has been lowered in 2009, weir n°10 in 2012 but after the orthophotography collection date (therefore not taken into account by the W in 2012) and weir n°8 has been lowered in 2018 before the orthophotography collection. Weirs n°2 and 3 were destroyed during the major 1994 flood.</figcaption></figure>

Figures 8 and 9 display respectively the active channel width evolution (W) and the BRI* variation on the Durance restored reach before (2012) and after (2017) the weir failure (2013). Two sub-reaches are distinguished. A first sub-reach is displaying BRI* values below the 0.004 threshold and an overall large active channel for both years (353 m in average). A second sub-reach, including the weir and an embanked section, shows higher BRI* values (0.004 in average) and an overall narrower active channel for both years (239 m in average). In this sub-reach, the decrease in BRI* value is well visible downstream the weir and at the embankment location. This is probably due to the reactivation of sediment transport from upstream of the weir and the creation of a new water channel. Locally, small variations of the active channel width occurred and are due to re-vegetation of the channel and lateral erosion.

These examples demonstrate that the chosen temporal and spatial scales, i.e. hydromorphological analysis few years after the restoration operations executed at the reach scale, are adapted to evaluate restoration success and morphological
<figure><img src="image_8.png" /></figure>

Figure 7: Longitudinal evolution of the BRI* on the lower Var valley. The horizontal black line displays the index threshold (0.004, Terrier et al. (2019); Liébault et al. (2013)) indicating braiding below the line. The five sections have been delimited based on the braiding pattern and the index evolution. The pink dotted lines display the overall mean for each section. Weir n°9 has been levelled in 2009, weir n°10 in 2012 but after the orthophotography collection date (therefore not taken into account by the BRI* in 2012) and weir n°8 has been levelled in 2018 before the orthophotography collection. Weirs n°2 and 3 were destroyed during the major 1994 flood.

412 changes.

413 4.3.2. *Cross-sections and sub-cross-sections BRI* \* calculation

414 The BRI* index was applied at the cross-section and sub-cross-section scales
415 to apprehend the influence of both the transversal units used for calculation.
416 Figure 10 shows a marked difference between the two formulas for some reaches,
417 notably for the Drac target reach or the Roya river in 2018 (difference of 0.002
418 in both cases). Attention should be paid to the transversal scale for the BRI*
419 calculation as it impacts results, the BRI* should therefore be applied at the
420 cross-section scale.
<figure><img src="image_9.png" /></figure>

Figure 8: Longitudinal variation of the active channel width on the restored reach (La Brillanne) on the Durance river. The two sections have been delimited according to the braiding pattern and the evolution of the indices, the pink dotted lines display the overall mean for each section.

# 5. Discussion

## 5.1. Restoration success can be captured by the spatio-temporal evolution of the morphological indices BRI\* and W\*

This study documented the overall success of a range of restoration operations on different braided rivers measured by morphometric indices commonly applied to natural braided rivers (Piégay et al., 2009; Liébault et al., 2013; Lallias-Tacon, 2015) or to physical models (Hoey and Sutherland, 1991). We show an improvement on all studied reaches approximately three years after the restoration operations and the improvement is still progressing along the Var reach nine years after the restoration started, confirming our initial hypothesis. Notably, when coupled with a period of dynamic hydrology, the braided pattern seems to re-establish better and more rapidly, especially if a morphogenic flood occurs soon after the operation (e.g. the lower Var valley). On the contrary, where no morphogenic hydrological event occurs for several years (e.g. the Mareta), the vegetation starts to encroach the active
<figure><img src="image_10.png" /></figure>

Figure 9: Longitudinal variation of the BRI* on the restored reach (La Brillanne) on the Durance river. The horizontal line shows the index threshold (0.004, Terrier et al. (2019); Liébault et al. (2013)) indicating braiding below the line. The two sections have been delimited according to the braiding pattern and the evolution of the indices, the pink dotted lines display the overall mean for each section.

channel, making it more difficult for next floods to uproot growing vegetation (Gurnell et al., 2012, 2016a, 2018). The braided pattern is then less able to readjust after restoration, and as time passes, a stronger hydrological event is needed to mobilise sediments and thus trigger a morphogenic evolution of the bed. Two cases can then be distinguished: a first case includes the Drac and Mareta where no major morphogenic floods occurred after restoration and where the improvement is mainly due, for now, to the restoration effect. These two operations were more extensive and also included significant modification of the channel bed forms. The second case comprises the Durance and the Var where operations were focused mainly on the restoration of sediment transport and that were initiated and further supported by the occurrence of morphogenic floods.

Along the Drac reach, the improvement due to the restoration corresponds mainly to the active channel width increase (61%), which allowed to pass from a single-thread incised channel to a braiding pattern with the presence of
<figure><img src="image_11.png" /><figcaption>Figure 10: Application of the two transversal unit calculation modes on the BRI* index. The horizontal line shows the index threshold (0.004, Terrier et al. (2019); Liébault et al. (2013)) indicating braiding below the line.</figcaption></figure>

several water channels and sparsely vegetated sediment bars. Because no morphogenic flood occurred after restoration operations, the braiding pattern is not self-sustaining: it concerns only a shallow part of the alluvial bed (field observations and B. Breilh, river manager, pers. comm.) and displays limited groundwater interactions (Marteau et al., submitted). As a consequence, the W* increases significantly due to restoration operations before reducing again, approximately 7%, and could be due to the lack of morphogenic floods during this period (see also Brousse et al. (2020)). In 2019, (i.e. after our 2018 post-restoration observation), several biennial floods occurred (B. Breilh, river manager, perso. comm.), and caused a regressive erosion in two areas of the restored reach and incision into lacustrine deposits, similar to pre-restoration conditions (ETRM, 2019). This required the river managers to make two additional operations of sediment augmentation of 2,600 m³ in 2020 (Communauté Locale de l’Eau du Drac Amont, 2020). A further morphogenic flood (estimated between a 5 and 10-year return period) occurred in May 2021, 13 years after the last similar event, which generated a significant sediment reorganisation and transport (B. Breilh, river manager, pers.
comm.). It will be interesting to study the evolution of the Drac restored reach after these hydrological events and the new gravel augmentation operations. Along the Mareta river, despite the slight improvement of the bed macro-roughness measured in 2013 (i.e. three years after the restoration), the braided pattern did not re-establish nine years after the restoration (field observations on summer 2019). Since last flood in 2014, the vegetation encroachment induced active channel narrowing. As for the Drac, the improvements on the Mareta are only due to the restoration operations. Thus, vegetated islands increased in number and size due to the coalescence of former pioneer islands and the creation of new sediment bars, as described by Scorpio et al. (2020), who analysed the mosaic of geomorphic units between 2014 and 2018. Two floods occurred in late summer and autumn 2020 and triggered noticeable sediment transport (K. Blaas, Autonomous Province of Bolzano, pers. comm.). Monitoring should therefore continue on the Mareta to assess and monitor morphological evolutions due to the last events. The weir failure on the Durance reach due to two morphogenic floods allowed to reshape a near-natural (although embanked) channel and thus to re-establish the sediment transport continuity as demonstrated by a 0.0005 reduction of BRI*, which indicates improved macro-roughness. The W* did not particularly increase overall (i.e. localised lateral erosion and revegetalisation is observed) which seems consistent with hydrologic records (Figure 3). Weir levellings on the Var restored reach induced several improvements in the braided pattern. W* and BRI* have both improved towards their threshold values (respectively from 4.73 to 9.54 m/km⁰.⁴⁴ and from 0.011 to 0.002). Restoration operations and recent floods (especially in 2011 and 2016) allowed lateral erosion of recent terraces located within embankments, the simplification of the macro-roughness on former weir sections as well as the
re-establishment of the longitudinal sediment continuity, notably the migration of the sediment bedload sheet (Chapuis and Collomb, 2012; Devreux and Larraun, 2018; Chapuis et al., 2018), which was located at weir n°8 in 2005, then at weir n°7 in 2018, with migration distance of 1.2 km approximately. This favoured the recreation of a braided pattern (i.e. BRI* further reduced and W* increased in 2018), but downstream a single-thread and narrow channel pattern persists locally, where the propagation of the sediment wave has not reached yet, which explains the increase in W* standard deviation in 2018. Five weirs are still in place in the lower Var valley, of which three should be lowered in the future (two are key knickpoints which will not be lowered). The morphological pattern will continue to evolve on the reach due to future restoration operations.

Together with the reduction in BRI* values with the restoration and throughout the years, the standard deviation also diminishes, for example on Var or Drac restored reaches (Figures 5, 7, D.1). This is due to the fact that the bed macro-roughness becomes more homogeneous along the reach as a consequence of the channel widening and the re-establishment of the braiding pattern. On the contrary, the W* standard deviation varies greatly between reaches, with an increase after restoration compared to pre-restoration standard deviation on some reaches (see the restored reaches on the Drac or the Var). The width values actually depend on each specific spatio-temporal context, suggested by the longitudinal analysis (see also section 5.4): the existence of human infrastructures such as embankments and localised vegetated islands (e.g. on the Drac), or the local occurrence of single-channel morphology constrained by high vegetated terraces (e.g. on the Var) (Figure 7) contribute to increase the variability of the active channel along a reach. As well, the low W*, such as on the Durance or the Mareta, can
indicate a sediment deficit at catchment scale but also a calm hydrological
period, allowing for vegetation encroachment. Therefore, the W* application
should be contextualised within an analysis of the flood regime (see also
section 5.3).

5.2. *The influence of the catchment on restoration success*

Since river systems are hierarchically organised, to guarantee the success in
the long term, restoration must be planned in accordance with the reach and
catchment scale context, which support the proper river processes and
functioning such as no further human intervention nor management is required
(Beechie et al., 2010; Friberg et al., 2016). At reach scale, sediment
connectivity must be guaranteed (e.g. the river has the possibility to migrate
laterally through banks or terraces erosion and to ensure longitudinal sediment
continuity (Piégay et al., 2005; Surian and Cisotto, 2007; Rinaldi et al., 2011;
Liébault et al., 2013)). At catchment scale, connection with the upstream
network and hillslopes must be active (e.g. presence of sediment production
areas well connected to the river network that will guarantee long term
sediment supply to the restored reach) (Liébault and Piégay, 2002; Hooke,
2003; Habersack and Piégay, 2007; Liébault et al., 2010; Blanpied et al., 2018).

This relates to the hydrosystem resilience and the sensitivity of braided
rivers to changes in control factors. Hydrosystem sensitivity can be defined as
the reactivity to a disturbance or an event (Fryirs, 2017). Braided rivers are
sensitive systems as they react quickly to floods, especially morphogenic floods
where the braided pattern and riverscape mosaic can be completely reset.
Hydrosystem resilience, on the other hand, can be defined as the ability of the
system to recover from a disturbance (Phillips, 2009). Piégay et al. (2018)
make a difference between pulse disturbance (event-based, such as a flood) and
press disturbance (long term and continuous, such as a dam construction).
They conclude that braided rivers are sensitive and resilient to pulse
disturbances (Tockner et al., 2003), which rejuvenate the mosaic, but not to
press disturbances, which can generate significant and irreversible changes in
the system. In this context, restoration acts often as an attempt for the
reinstatement of the capacity for the hydrosystem to be functional for pulse
disturbances. This is why the understanding of the catchment context and of
the spatial and temporal trajectories are essential to the restoration success, in
order to also account for existing, irreversible press disturbances.

Our Control/Impact comparison between target and restored reaches
through time confirms that accounting for the catchment scale context might
increase restoration success and allows us to support our interpretations. The
Drac for example has undergone a major restoration operation coupling active
channel widening by 61% and sediment augmentation. The sediment sources
identified in the pre-restoration studies were located close upstream (CLEDA,
2010; BURGEAP, 2013): the Chabottes reach, the target reach in this study;
the Ancelle mountain stream, which is joining the Drac downstream of the
Chabottes reach; and further upstream with the two mountain streams that
form the Drac river, the Drac noir and the Drac blanc. The bedload transfer
of 1 km a⁻¹ within the main channel estimated by Brousse et al. (2020) shows
a strong connectivity between the target and restored reach. Therefore,
sediment supply is available but the low hydrologic activity after the
restoration did not allow the hydrosystem to adjust the restored braiding
morphology. As a confirmation, the target reach also displays a tendency
towards narrowing between 2011 and 2018, with some oscillation through
time. However, it is expected that the additional gravel augmentations in 2020
combined with the recent floods in May 2021, have reactivated the
morphological processes and the reach might possibly recover a functional
braiding morphology as demonstrated by the longer term trajectory of the
target reach (Brousse et al., 2020).

Where catchment scale context is not favourable, restoration success might
be compromised. For example, the Mareta has undergone an extensive
restoration in 2008-2009, but the braided pattern did not resettle after
restoration. Beyond the unfavorable hydrological conditions (i.e. only few
significant hydrological events occurred in the 21st century compared to the
late 1980s and the 1990s), the presence of a proglacial lake since the 1970s
(0.06 km²) is acting as a sink, trapping sediments coming from the glacier
(Scorpio et al., 2020). In addition, the high number of check dams on
tributaries, the 99 weirs and two filtering dams along the main channel
upstream, intercept sediments from the catchment and prevent sediment
transport downstream in the reach. The presence of embankments along the
main stem also prevents lateral erosion and local sediment supply entering into
the channel (lateral sediment discontinuity). Beyond the catchment scale, the
installation of very large blocks during restoration operations created lateral
and vertical constraints, partly fixing the bed and thus stopping natural
geomorphic processes. The last 2020 floods still need to be expertised (at least
10 year-return period according to our first assessment) and will provide
further insights on sediment transport processes and the effects of restoration
operations 11 years later. However, due to the lack of connectivity with
sediment production areas, it can be expected that the braided pattern will
not resettle, an incision process could even establish locally as it is seen in
low-flow channels (Scorpio et al., 2020).

In summary, beyond internal system drivers (e.g. active sediment sources at
reach and catchment scales), external anthropogenic drivers act on the system
processes on a long term scale and might impact on the success and durability of
the restoration (Peiry et al., 1994; Wohl et al., 2005; Piégay et al., 2006; Beechie
et al., 2010; Kondolf and Podolak, 2014).

5.3. *Braided reaches restoration within the context of the regional French Alpine braided rivers*

As presented by Piégay et al. (2009), Liébault et al. (2013) and Belletti et al. (2014), a regional context of braided rivers in the south east France exists, with rivers displaying different patterns and functioning according to their geographic location (within their catchment and at a regional scale) or within their temporal trajectory. We compared the studied reaches and their evolution before/after restoration with this French regional context. Figure 11 displays the BRI* applied to the studied reaches and to other braided rivers from Liébault et al. (2013) related to their active channel width (W).

A general trend can be noticed with higher BRI* values (between 0.003 and 0.018) for small active channel widths (value ranging between 40 and 80 m), and as the active channel width increases, the BRI* value decreases and gets below the 0.004 threshold value. Most reaches before restoration are far from the trend except the Mareta reach. After restoration, the active channel width increases and the bed macro-roughness decreases, confirming an improvement in the braiding pattern and morphology despite anthropogenic features.

Figure 12 shows the relationship between the active channel width (W) and the upstream catchment area within the regional context from Piégay et al. (2009), Belletti et al. (2013) and Bizzi et al. (2019), which was used to calculate the W*.

The restored reaches analysed in this study are located below the regional threshold (Terrier et al., 2019) and towards the bottom of the regional dataset
<figure><img src="image_12.png" /></figure>

Figure 11: BRI* relative to their active channel width on the studied reaches presented with braided rivers from the south east of France. The data is from Liébault et al. (2013) and has been calculated with Hoey and Sutherland's formula (Hoey and Sutherland, 1991) on 43 cross sections distributed on 26 rivers. A power law has been fitted to the regional data based on Lallias-Tacon (2015)'s work. Two reaches are in common between the two datasets: the target reach on the Drac and the target reach on the Var (both in green with label 2009 on the figure), both from field measurements in 2009.

before restoration. As restoration is occurring, the W value is increasing and shows a better relation with their upstream catchment area, such as the Drac. Opposite to this trend, some reaches display an overall long-term decrease, such as the Drôme, which indicates a deficit in sediment supply and rather a wandering pattern (Piégay et al., 2009). Target reaches show a temporal trend that is consistent with the regional context. Figure 12 also shows further observations (dates) for the Var and Drac target reaches that were analysed before by Piégay et al. (2009) and Belletti et al. (2013). The close values observed between previous observations and the present study indicate a stable pattern but cyclic variability in active channel width over time according with flood regime, as observed by Belletti et al. (2014). This confirms that active channel width measures need to be interpreted within a temporal evolutional context.
<figure><img src="image_13.png" /><figcaption>Figure 12: Active channel width relative to the upstream catchment area on the studied reaches presented with braided rivers from the south east of France. Data are from Piégay et al. (2009), Belletti et al. (2013) and Bizzi et al. (2019) on 94 reaches. Pink arrows show the changes before and after restoration, purple arrows show the changes on target reaches between the old and the recent dates and black arrows show the changes through time on regional data. Two reaches are in common between the two datasets: the target reach on the Drac (2003, purple square with green contour) and the target reach on the Var (2000 and 2004, purple circles with green contours).</figcaption></figure>

5.4. *Effects of spatial scale, data resolution and type*

Rivers are hierarchical and (dis)connected systems where local scale processes and forms are embedded into and controlled by upper scales processes and forms (Brierley et al., 2006; Fryirs, 2015; Gurnell et al., 2016b; Fryirs and Brierley, 2018). As a consequence, each spatial element within the system needs to be assessed at the appropriate spatial scale (e.g. river bedforms are usually assessed at reach scale, sensu Gurnell et al. (2016b)). In riverscapes impacted by human pressures, expected spatio-temporal relationships might be altered or divergent, thus a critical assessment and the choice of the proper spatial scale is key, notably to assess the effect of restoration operations. Sensitive indices able to detect such effects are needed. Our detailed analysis of BRI* and W* allowed us, beyond the assessment of restoration success, to discuss and clarify the index sensitivity to local scale morphological variability, spatial scale effects, errors and data type effects,
which are important operational elements for the application of such indices in
a restoration context.

5.4.1. *Longitudinal scale*

Human infrastructures, such as weirs for bed stabilisation commonly present in our study reaches, are longitudinal discontinuities causing hydraulic and sediment transport disturbances (Petts and Gurnell, 2005; Fuller et al., 2015; Bizzi et al., 2015). These are usually used to delimit reaches or sub-reaches given that they determine discontinuities in river bedforms, processes and functioning (Rinaldi et al., 2013; Gurnell et al., 2016b)).

Our observations confirm, for some of the analysed reaches, the existence of hydromorphologically different sub-reaches delimited by weirs such as on the Var and the Durance restored reaches (see section 4.3.1). The definition of the spatial scale of analysis is key in applied geomorphology, especially within the context of river management. Restoration operations can be implemented at local scale (weir levelling, habitat improvement) or at reach scale (active channel widening, sediment reintroduction) but in case of process-based operations, as those analysed in the present study, the effects can propagate several hundred of meters downstream (Beechie et al., 2010; Kondolf and Podolak, 2014; Grabowski et al., 2014; Poeppl et al., 2017). Therefore, analyses at the reach scale are more suitable to capture morphological pattern evolutions after restoration, nevertheless local scale considerations are useful to understand variations from the average behaviour. Notably, we demonstrated that the presence of artificial elements and the consequent dynamics affected the standard deviation values of the analysed morphological indices. Beyond the values of BRI* and W* indices, the reach scale analysis of standard deviation values thus bring additional informations that can help further qualify the restoration success.
5.4.2. *Cross-section and sub-cross-section scales effects on bed macro-roughness*

Our results show that the choice of the lateral spatial scale can have an effect on the BRI* calculation. We tested in this study the application of the BRI* on the sub-cross-section (Lallias-Tacon, 2015) and the cross-section scales. Results show that the different calculation method can lead to values up to 65% different within a same cross-section (Figure 10), where the sub-cross-section method systematically displays higher value than the cross-section method (except the Drac restored reach in 2011 and the Mareta target reach in 2005, where the sub-cross-section values are approximately 2% lower than the cross-section values). The BRI* represents the bed macro-roughness on a cross-section calculated as the standard deviation of the elevation (Hoey and Sutherland, 1991; Liébault et al., 2013). Therefore applying the BRI* over sub-cross-sections seems inadequate to assess the cross-sectional roughness. The practical recommendation from this study is to take into account the complete cross-section of the active channel, excluding areas where mature vegetation is present (Figure 5).

5.4.3. *Error propagation and elevation data type effects on bed macro-roughness*

Our analysis of the error propagation demonstrates that the results and the interpretation of the BRI* depend on reach morphology and also on the altimetric and planimetric (represented as the interval between measuring points) resolutions of the dataset.

Elevation data used in this study had diverse planimetric and altimetric resolutions (Table 4). An error propagation value is displayed when altimetric resolution is very high, for example on both reaches on the Drac river in 2011 (- 0.001) or the restored reach on the Var river in 2005 (0.115), even though the planimetric resolution is low (i.e. 5 m on the Var in 2005, Table 4). However, even when altimetric and planimetric resolutions are high as in the case of the
Mareta, the morphological pattern (e.g. a single-thread, narrow and straight active channel for the target reach and the restored reach before restoration) seems the most important parameter playing a role on the error of the BRI* calculation (Table 4). After restoration, the BRI* decreased slightly but the uncertainty is still higher than the standard deviation because the reach has not completely regained a functional braided pattern (see section 5.1). Similarly, on the Var after restoration, the uncertainty is slightly higher than the standard deviation, because the braided morphology has not been re-established on the whole reach length yet, and some sub-reaches still display a single-thread and narrow channel. The calculation of the bed macro-roughness through the BRI* seems unsuitable to this kind of impacted and not truly-braided morphology.

We can then conclude that the BRI* result reliability depends in first order on the reach morphology, and then on altimetric and planimetric resolutions, which are influenced by bed micro-roughness. We also make the hypothesis that in case of data collected on the field, uncertainty can be higher due to the irregularity of measures which can impact BRI* results more than planimetric resolution.

Elevation data used in this study are DEMs extracted from LiDAR and, to author's knowledge for the first time, from photogrammetry techniques. These type of data can be biased as these techniques do not penetrate water, the submerged section is then ignored and can cause underestimation in the BRI*, especially if the water section is large and the discharge is high (Lallias-Tacon, 2015). However, our results on the Drac restored reach are in good agreement with the ones from Brousse et al. (2020) who used bathymetric data. As well, the photogrammetry data used on the lower Var valley allowed us to calculate a BRI* value that seems realistic and consistent with other studies on the same reach (unpublished data), thus confirming the relevance of such remote
sensing datasets to implement BRI* calculation. This is a useful result as
photogrammetry are cheaper to implement, thus potentially enabling to
increase the frequency of such monitoring for river managers compared to
LiDAR datasets.

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5.4.4. Timescale of the datasets

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Morphometric indices used in this study are based on the active channel
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area which was delimited using orthophotographies and elevation data. Such
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datasets are usually collected during a time period at a regional or county
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scale (Carbonneau and Piégay, 2012; Bizzi et al., 2016) and are not always
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available at the same date for a specific study site. In this study, most of the
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data used were taken on a single date by river managers but in some cases the
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dates differed between the orthophotography and the elevation data (Table 4;
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the Mareta river in 2005 and 2013, the Durance in 2012 or the Drac river in
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2018) or were even collected during several years (Table 4; DEM on the lower
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Var valley in 2012). This is particularly relevant for the data extraction since
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braided morphology can change along with hydrological conditions, thus
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orthophotography and elevation data could no longer match. In order to assess
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consistency between elevation and planimetric data, we checked for flood
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occurrence between the two data collection dates. Secondly, we carried out an
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expert-based check to ensure that channels location did not change between
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the orthophotography and elevation data. This two-step assessment was
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performed on all the reaches and dates mentioned above. We thus recommend
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to collect LiDAR and orthophotography data at the same date to ensure the
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BRI* application conditions and to save time and resources.
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# 6. Conclusion

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This study provides new insights on the morphological evolution of restored braided reaches within the Alpine context and discusses the application of morphometric indices and the effects of different factors (including spatial and temporal scales and anthropic context) on the analysis and evaluation of restoration success. This was achieved by comparing restored and braided-functional reaches, using orthophotographies and elevation data, extracted from LiDAR or photogrammetry sources.

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The study highlights that in all cases, restoration operations allowed an improvement in the braided pattern. Nevertheless, hydrological activity is a determining driver for the sustainability of restoration operations and supports system resilience. We highlighted that for the cases where a long time lag is occurring between the restoration and the next morphogenic flood, restoration might be considered as failed. Moreover, connectivity to sediment production areas and longitudinal sediment continuity from upstream as well as to internal sediment stocks within the erodible corridor (Piégay et al., 2005) are key drivers for the durability of the restoration, and should be carefully assessed before restoration.

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The study also demonstrated a good performance of the morphometric indices (W* and BRI*, Piégay et al. (2009), Liébault et al. (2013)) on restored braided rivers and on rivers highly impacted by human pressures. The W* is influenced by the restoration itself, especially in case of active channel widening operation, and by morphogenic floods, according to braided rivers cyclic pattern (Belletti et al., 2013, 2014). Analyses should therefore continue to assess the W* behaviour several years after restoration. This recommendation implies only to collect orthophotographies, which can usually be considered of limited cost for river managers and is rather easy to
implement on a routine mode. The BRI* is less impacted by the type of
restoration and results presented here showed that this index can be used in
an anthropogenic context, provided the braided morphology is developed.
Both indices should be applied with an analysis of the hydrological regime
within a proper spatio-temporal framework (e.g. one index value after
restoration is not sufficient to characterise the restoration effectiveness). These
indices can be used by river managers to monitor braided rivers evolution and
to evaluate the effects of management actions.

To conclude, some technical recommendations for the application of the
BRI* are:

(i) to use elevation data and orthophotographies that have the same collection date. If this is not possible, the operator must ensure that no major hydrologic events nor major channel changes occurred between the data collection dates;

(ii) elevation data extracted from LiDAR and photogrammetry can both be used for the BRI* application. We recommend here a planimetric resolution of 5 m maximum and an assessment of the data resolution compared to the active channel width (i.e. if the active channel width is too small, a low resolution will generate few measuring points and thus an overestimation of the BRI*);

(iii) to make sure that the morphology on the studied reach is braided or slightly wandering for the BRI* application (see section 5.4.3). If not, the index detects aberrations and human infrastructures and values might not be meaningful, error propagation and standard deviation calculations are therefore essential to assess if the values obtained are reliable;

(iv) to apply the BRI* at cross-section scale, therefore to take into account the
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whole cross-section except where mature vegetation is present (see section 3.3).

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*Acknowledgements*. We thank the University Côte d'Azur, the Agence de l'Eau Rhone-Méditerranée-Corse, the region Provence-Alpes-Côte d'Azur, the program UCA Jedi and the ZABR for supporting this study. B. Belletti was supported by EUR H2O'Lyon (ANR-17-EURE-0018) at University of Lyon. We also thank river managers and public organisations for data sharing and discussions: the Communauté Locale de l'Eau du Drac Amont (CLEDA), the Syndicat Mixte d'Aménagement de la Vallée de la Durance (SMAVD), the Syndicat Mixte Inondations, Aménagement et Gestion de l'Eau Maralpin (SMIAGE) and the Civil Protection Agency of the Autonomous Province of Bolzano, the Conseil Départemental des Hautes-Alpes and the INTERREG Alpine Space HyMoCARES project, the Métropole Nice Côte d'Azur, the INTERREG ALCOTRA Concert-Eaux program and the University of Florence. We also thank EDF for the share of hydrologic data on the Roya river. We thank F. Liébault and S. Lallias-Tacon for useful and precious discussions as well as F. Liébault, H. Piégay and S. Bizzi for the regional data on braided rivers.

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1185

# Appendix A: Sites' description

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The Drac river was heavily impacted by gravel mining between the late 1960s and 2012, (CLEDA, 2010) with a total volume of extracted sediments around 93,000 m³ yr⁻¹ on the total Upper Drac basin (Vivian and Thomas, 1982 cited by Brousse et al. (2020)). Other human pressures are embankments and groynes built since the 19th century to protect human infrastructures (CLEDA, 2010), which contributed to sediment supply reduction. As a consequence, riverbed incision reached between 2 m to 5 m (BURGEAP, 2013; Breilh and Bourdin, 2018), and the active channel narrowed and shifted towards a single-thread channel pattern. Flood events of the late 2000s led to irreversible incision in the lacustrine clay deposits along several kilometres.

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The restoration reach is characterised by a decommissioned gravel-mining pit transformed into a leisure lake in the 1990s on the right bank and is protected from floods and bank erosion by a longitudinal dike with shallow foundations. Restoration operations consisted of active channel widening and gravel augmentation (280,000 m³ from adjacent alluvial terraces plus 80,000 m³ from other additional sources). Restoration operations buried the upstream weir and raised the downstream weir to control the restored longitudinal profile around 1% slope. The reach was also equipped with a fish pass and a canoe pass.

1205

1206

The target reach, located 3.9 km upstream, displays a well-developed braided pattern and is locally exposed to little human pressures.

1207

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1209

1210

On the Durance river, sediment transport is altered by significant flow diversion for hydroelectricity production, approximately 10% of the mean annual flow is left in the riverbed, and by the presence of several dams located on the main channel upstream of the two reaches.

1211

Restoration operations consist in the removal of a weir located on the reach
impacted by flow diversion. It started in 2019 and still ongoing at the time
of writing to improve sediment and fish continuity, release sediment stocks and
increase the upstream slope and aggradation in the incised areas (SMAVD,
2016)). The weir already broke in 2013 in its middle part and then the failure
kept on evolving due to two 10-year return period floods in 2014 (approximately
1000 m³/s, reconstituted discharge, Artelia (2015)).

The target reach is located 0.8 km upstream and displays a braided stable
pattern, little impacted by human pressures despite partial embankment on
both sides.

The Var restored reach is located in the lower valley, downstream of gorges.
All the lower Var valley is embanked on both sides and gravel mining was
significant between 1946 and 1983; the extracted sediments volume is
estimated of 50 Mm³ corresponding to about 150 years of sediment transport
(Commission Locale de l'Eau nappe et basse vallée du Var, 2015). This caused
a major incision up to 8 m (SMEBVV, 2003), a disconnection with the
groundwater table and a destabilisation of the longitudinal profile. In the
1970s and 1980s, 11 weirs were built to raise and maintain the water table
level. In 1994, an estimated 50 to 100-year return period flood occurred
(MEDDE ; SMEBVV, 2003), which reactivated sediment transport (Devreux
and Larraun, 2018). Restoration operations consist of weir levelling in order to
re-establish sediment and biological continuity and a braided morphology
(SMEBVV and SOGREAH, 2006). Four weirs have been lowered between
2009 and 2019 (Figure 6).

The target reach is located 58 km upstream in the middle Var section,
exiting the Daluis gorges. This reach is located in a different hydroecoregion,
is naturally confined on both sides by hillslopes and is partially influenced by
mountainous climate. This site was chosen for the near-natural braided
1239

1240

pattern and also for the similar topographical configuration compared to the
restored reach (i.e. downstream of a gorge).

1241

1242

1243

1244

1245

1246

Gravel was also intensely extracted from the Mareta in the 1970s causing channel incision between 4 m and 9 m (Scorpio et al., 2020). Channelisation and massive weir and check-dam constructions (126 weirs only on the main channel) were carried out in the catchment in order to claim agricultural lands and to mitigate the impacts of gravel mining. Two dams (partially permeable, (in.ge.na., 2015)) were built in order to reduce flooding risk.

1247

1248

1249

1250

1251

1252

1253

Restoration operations consisted in active channel widening and the levelling of 18 weirs, to improve flood peak attenuation and the overall environmental conditions. Former abandoned levees were also removed and sediment materials from adjacent terraces were reinjected into the active channel (130 000 m³, (Hecher and Blaas, 2018)). Large blocks of a few meters in diameter were buried in the active channel to prevent incision and lateral erosion. Bank protections were built at the toe of recent terraces to mitigate lateral erosion during floods.

1254

1255

The target reach is located 6 km upstream and its morphology is wandering/braided but influenced by artificial embankments on both sides.

1256

1257

1258

1259

1260

1261

1262

1263

1264

1265

The reach of the lower Roya valley was selected for its geographic similarities and proximity to the lower Var valley. Their hydrologic regimes are similar with Mediterranean influence downstream and a mountainous influence in their upper catchment, and their topographic lithologic and geologic contexts are also analogous. Their stream network is also comparable with a major tributary joining the main channel right after exiting gorges and close to the mouth: the Bevera tributary flows in the Roya few kilometres before the sea, alike to the Esteron river for the Var. The lower Roya valley shows a wandering pattern and is impacted by human modifications with artificial embankment on both sides, though vertical incision is not as developed as in the lower Var valley. It is used
in this study as an “impacted reference”, for comparison to the lower restored
Var valley. It is to note that a major flood (estimated 100 years to 500 years
return-period flood) occurred in oct. 2020 on the Roya catchment, inducing a
fluvial metamorphosis on most of the main branch. The Roya could now be
considered as a "fully functional braided river" in its lower valley, but this new
morphological state could not be analysed within the timeframe of this study.
1272 Appendix B: List of packages used

<table><caption>Table B.1: Packages used for this study with references.</caption><thead><tr><td>Packagename</td><td>Version</td><td>Maintainer</td><td>References</td></tr></thead><tbody><tr><td>knitr</td><td>1.33</td><td>Yihui Xie xie@yihui.name</td><td>Xie (2021)</td></tr><tr><td>pacman</td><td>0.5.1</td><td>Tyler Rinker tyler.rinker@gmail.com</td><td>Rinker and Kurkiewicz (2019)</td></tr><tr><td>forcats</td><td>0.5.1</td><td>Hadley Wickham hadley@rstudio.com</td><td>Wickham (2021a)</td></tr><tr><td>stringr</td><td>1.4.0</td><td>Hadley Wickham hadley@rstudio.com</td><td>Wickham (2019)</td></tr><tr><td>purr</td><td>0.3.4</td><td>Lionel Henry lionel@rstudio.com</td><td>Henry and Wickham (2020)</td></tr><tr><td>readr</td><td>1.4.0</td><td>Jim Hester james.hester@rstudio.com</td><td>Wickham and Hester (2020)</td></tr><tr><td>tibble</td><td>3.1.1</td><td>Kirill Müller krlmlr+r@mailbox.org</td><td>Müller and Wickham (2021)</td></tr><tr><td>tidyverse</td><td>1.3.1</td><td>Hadley Wickham hadley@rstudio.com</td><td>Wickham (2021c)</td></tr><tr><td>RColorBrewer</td><td>1.1.2</td><td>Erich Neuwirth erich.neuwirth@univie.ac.at</td><td>Neuwirth (2014)</td></tr><tr><td>scico</td><td>1.2.0</td><td>Thomas Lin Pedersen thomasp85@gmail.com</td><td>Pedersen and Crameri (2020)</td></tr><tr><td>scales</td><td>1.1.1</td><td>Hadley Wickham hadley@rstudio.com</td><td>Wickham and Seidel (2020)</td></tr><tr><td>ggnewscale</td><td>0.4.5</td><td>Elio Campitelli elio.campitelli@cima.fcen.uba.ar</td><td>Campitelli (2021)</td></tr><tr><td>cowplot</td><td>1.1.1</td><td>Claus O. Wilke wilke@austin.utexas.edu</td><td>Wilke (2020)</td></tr><tr><td>infer</td><td>0.5.4</td><td>Andrew Bray abray@reed.edu</td><td>Bray et al. (2021)</td></tr><tr><td>rstatix</td><td>0.7.0</td><td>Alboukadel Kassambara alboukadel.kassambara@gmail.com</td><td>Kassambara (2021)</td></tr><tr><td>gridExtra</td><td>2.3</td><td>Baptiste Auguie baptiste.auguie@gmail.com</td><td>Auguie (2017)</td></tr><tr><td>tidyr</td><td>1.1.3</td><td>Hadley Wickham hadley@rstudio.com</td><td>Wickham (2021b)</td></tr><tr><td>ggplot2</td><td>3.3.3</td><td>Thomas Lin Pedersen thomas.pedersen@rstudio.com</td><td>Wickham et al. (2020)</td></tr><tr><td>lubridate</td><td>1.7.10</td><td>Vitalie Spinu spinuvit@gmail.com</td><td>Spinu et al. (2021)</td></tr><tr><td>dplyr</td><td>1.0.6</td><td>Hadley Wickham hadley@rstudio.com</td><td>Wickham et al. (2021)</td></tr><tr><td>readxl</td><td>1.3.1</td><td>Jennifer Bryan jenny@rstudio.com</td><td>Wickham and Bryan (2019)</td></tr><tr><td>openxlsx</td><td>4.2.3</td><td>Philipp Schauberger philipp.schauberger.co.at</td><td>Schauberger and Walker (2020)</td></tr><tr><td>here</td><td>1.0.1</td><td>Kirill Müller krlmlr+r@mailbox.org</td><td>Müller (2020)</td></tr></tbody></table>
1273

1274

Appendix C: Longitudinal variation of the active channel width on
the Drac and Mareta rivers restored reaches

<figure><img src="image_40.png" /><figcaption>Figure C.1: Longitudinal variation of the active channel width on the Drac river restored reach before (2011) and after (2018) restoration.</figcaption></figure>
<figure><img src="image_41.png" /><figcaption>Figure C.2: Longitudinal variation of the active channel width on the Mareta river restored reach before (2005) and after (2013) restoration.</figcaption></figure>
1275

1276

Appendix D: Longitudinal variation of the BRI* on the Drac and
Mareta rivers restored reaches

<figure><img src="image_42.png" /><figcaption>Figure D.1: Longitudinal variation of the BRI* on the Drac river restored reach before (2011) and after (2018) restoration.</figcaption></figure>
<figure><img src="image_43.png" /><figcaption>Figure D.2: Longitudinal variation of the BRI* on the Mareta river restored reach before (2005) and after (2013) restoration.</figcaption></figure>