## 2 Proposed Methodology
### The Purpose of New Indicators
#### 2.1.2 The Indicators  
Figure 5 shows the workflow for the calculation of the three indicators. _(i) Indicator 1: Distance from Active Channel to Stakes or Floodplain Margins._ This first indicator calculates the distance between any points of the active channel and any point within the floodplain. In order to quantify the temporal river dynamics, it is possible to calculate the distance between any points of the active channel and the floodplain boundaries. Thanks to this indicator, we can follow and quantify the lateral migrations of the active channels through time. The first step to build this indicator is to generate a raster proximity map indicating the distance from the center of each pixel to the floodplain boundaries. This may be completed by using the GDAL tool 'gdal_proximity.py' [45] interfaced in QGIS in the Raster menu 'Proximity (Raster Distance'). The spatial resolution of this raster should be high. We recommend setting it to 1 m in order to be consistent with the points we have previously extracted along the active channel. Moreover, 1 m is an acceptable resolution because the active channels widen during floods and contract in between by much more, often by several tens of meters. This is what has been shown,  
Figure 5: Workflow for the calculation of the indicator 1 (**A**), 2 (**B**) and 3 (**C**). for example, by the diachronic analysis of active channels in the French Southern Alps (Guil River) and on the foothills of the Montagne Noire (rivers Argentt Double, Ognon and Clamoux; [46]). On this raster, the pixel values correspond to the distance between the pixel and the margins of the floodplain. For instance, a pixel with a value of 10 means that this pixel is 10 m away from the closest margin of the floodplain. The second step is to sample the value of this raster proximity map for each extracted point of the streams. In QGIS, we may use the'sample raster values' tool. By performing this action, we know how far each point of the active channel is to the closest margin of the floodplain. In the case that we have the position of the river at different dates, we can quantify the lateral migration of the active channel. From a perspective of risk management, we should now generate a raster proximity map indicating the distance from the center of each pixel to the infrastructure we want to protect in the floodplain. In this raster, the pixel values correspond to the distance between the pixel and the closest edge of the infrastructure to be protected. For instance, a pixel with a value of 10 means that this pixel is 10 m away from the closest edge of the infrastructure. Thanks to this indicator, it is possible to precisely identify the portions of the river which are less than a certain distance to the infrastructure. This indicator may help the river manager to identify the places where the building of embankments along the active channel can be relevant. _(ii) Indicator 2: Distance from Stakes to Active Channel._ This indicator aims to calculate the distance between any points of the edges of any infrastructure and the active channel. It may help the river manager to precisely identify the places where it can be relevant to build a protection wall, for instance. The first step is to generate a raster proximity map indicating the distance from the center of each pixel to the channel. On this raster, the pixel values correspond to the distance between the pixel and the channel. For instance, a pixel with a value of 10 means that this pixel is 10 m away from the river. The second step is to sample the value of this raster proximity map for each point of the edges of the infrastructure. This indicator may help the manager to precisely identify which parts of the infrastructure should be protected. In the case that the position of the active channel is known for different dates, it is possible to follow the evolution of the vulnerability of the infrastructure through time.