Vt Flooding Project Validity

Final Project Validity

For my final project, I will be attempting to reproduce the Flood Hazard Vulnerability in Vermont’s Mobile Homes independent problem from GEOG 0261/GEOG 0120 at Middlebury. The assignment is for students to use fundamental spatial analysis tools in QGIS to identify the number of mobile homes at risk of flooding in Vermont. The analysis uses two approaches to idenfify flood risk: 1) FEMA 100yr Flood Zones and 2) Vermont River Corridors. The GEOG 0261/GEOG 0120 assignment seeks to compare the results of the two flood risk identification approaches. Anyways, I will be trying to reproduce this study using a code-based approach in R. I’m curious if I get the same results as when using the QGIS GUI workflow, and I also want to do this project to help refresh my spatial analysis skills.

Going into this study, I know that there is a boundary distortion along the eastern edge of the state along the Connecticut River error that compromises internal validity. Vermont River Corridors (the shapefile) does not include a river corridor model for the Connecticut River. This threatens the validity of the study, since there are many mobile homes along the banks of the river that get completely omitted when using the VT River Corridor approach to identify mobile homes at risk. I will attempt to estimate my own river corridor for the Connecticut River using satellite imagery and the 6x width of the meander belt rule of thumb for generating river corridors.

Also, I know going into this study that there are issues with small numbers of mobile homes in some towns that are used as denominators in calculating percentages, and this will lead to overly sensitive and overly inflated percentages in some towns. I do not plan to change this, as that would require calculating the area of towns and counties, which I did not have time for when completing this study. However, it does threaten the internal validity of the results when using percentages/proportions/rates.

Lastly, the original QGIS study utilizes an area weighted re-aggregation for determining a number of mobile homes at risk in the FEMA flood zones, based on ACS 2014-2018 survey data and assuming an even distribution of mobile homes across counties. However, the GEOG 0261 course has repeatedly demonstrated that this is an inaccurate approach to the research question, and thus I will not try to reproduce this part of the study. This is an issue of a modifiable areal unit problem.

Beyond these concerns, this should be a pretty straightforward study without too many sources of uncertainty or threats to geographic validity.