Topographic Change Detection

Purpose of Project

We want to be able to detect topographic change within a river system and understand the processes behind the changes. Here, we used data provided to us to analyze topographic changes of the River Feshie in Scotland, UK. We learn to use Geomorphic Change Detection software in conjunction with ArcGIS as a tool in topographic change detection.

Analysis of the River Feshie

Topographical changes between 2003 and 2004 were analyzed and a GCD was used to determine whether deposition or erosion occurred.

Figure 1. Screen capture of the mask process done in the GCD software.

As seen on the left (Figure 1), DEMs from 2003 and 2004 were our main inputs. I used additional provided surface change data for each year, which was used to determine change detection. This created a Mask that I was able to input into GIS. The Mask was used as a visual guide to determine where topographic changes occurred.

Figure 2. DEMs for 2003 and 2004 added to ArcGIS Pro, along with the Mask layer which is labeled as tresh.tif.

In Figure 2, I used the added Mask layer (tresh.tif) to aid in analysis of where deposition and erosion occurred. We see erosion in red and deposition in blue. .

What I needed to do next was determine what type of erosion or deposition the Mask was presenting. To do this, I used the base map and toggled between DEM layers.

I drew polygons around each area of interest and made sure to label them in the attribute table (Figure 3). This allowed me to add the polygon shapefile into the GCD software and run more analysis.

Figure 3. Polygons drawn around each area of interest.

Bank Erosion

In the two figures above, I outlined what I determined to be bank erosion. I chose these spots as they were on the banks of the braided channels and were presented in red. They also appear to be on outside bends next to areas of deposition. Likely, creating in-channel bar development.

Channel Bed Lowering

I had difficulty finding strong examples of bed lowering, it wasn't a very strong topographic change between 2003 and 2004. I determined these two as bed lowering due to their location within the river channel and not having occurred near the banks.

Channel Bed Rising

Determining channel bed rising can be difficult since the occurrence can be confused with bar development. I chose these two areas as the rising area was channel spanning and the total amount of rising was relatively similar across the entire area, telling me there was an even distribution of new sediment being deposited in these areas. Likewise, there wasn't much bed or bank erosion happening around them that would suggest the creation of a bar.

Bar Development

Here are my two examples of bar development. Determining these areas were the easiest for me as they occurred mid channel and were next to areas of bank or bed erosion. They also present a variety of deposition as can be seen by the varied intensity of blue.

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