It was recently brought to my attention that the graphing tool in ArcGIS could be really useful if you had the right type of data (thanks to ND at UO). Well, I spent most of today trying to refine a longitudinal profile of the Owyhee River from my coveted LiDAR data set, and it occurred to me that I had some useful data.
My goal beyond just examining the profile was to indicate the locations of major landslide complexes along the river corridor to investigate how they may influence the river’s gradient. I actually extracted the profile data from the data using a tool in GlobalMapper which I like. I converted the data to an excel spreadsheet, opened the sheet in Arc and then exported it into my Geodatabase as a feature dataset. Once it was in there, I created a graph of the data (basically the profile) and began to select points on the profile along key reaches that I had mapped. Lo and behold, those points i selected on the map lit up in the profile graph. Sweet. This was huge. It goes both ways as well. Select points on the graph, and they light up on the map.
Restrict the displayed points on the graph to those selected on the map and you can export them as a subset of the data. This step comes in really handy for plotting the exact position of the landslide complex-reaches on the overall profile figure. Previously, I had stupidly brute-forced this process. Typical. The result is below:
Also very useful is to plot the profile data in the form of cumulative distance vs. slope of channel segment. This graph immediately indicates important trends and anomalies in the data. Turns out that the anomalously high slope values and negative slope values relate, in this case, mainly to inadvertently collected data from vegetated bars, extremely coarse gravel bars, and even wave trains at some of the rapids. Thus, an important and informed QA step can be taken to clean out the riff-raff. In general, though, you can see how useful this method is for zeroing-in on areas of key interest. For example, many of the points on the map below correspond to rapids
Posted via email from Fresh Geologic Froth