18- Elevation Map Analysis
On the project lot (approx. 23 Ac) and its surroundings (108 Ac), 131 Ac in total, we carried out a survey to determine the elevations and characterize the surrounding land, and to understand the actual flow lines, dry areas, and interventions.
To complete the study, we tied into the DOT geodetic network, set two benchmarks on the site, and complied with all the protocol for a boundary survey of the lots under study, adjacent roads, and other areas we considered necessary. Additionally, all the procedures for a topographic survey were completed. Due to the vegetation density, in order to obtain greater point density and better clarity of the terrain, we used LIDAR technology mounted on an RTK drone connected to an RTK placed on one of the existing benchmarks in the field.
This LIDAR captured about 200,000 points/second, which gives us a redundancy of information well above what is necessary, but which allows us to build an elevation map that is quite revealing. The first thing we did was calibrate the colors of the model, that is, assign blue colors to the flooded areas; for this, we verified from an aerial photogrammetric image (taken the same day as the LIDAR) the existing water bodies and verified their elevation with an accuracy of 1/10”. In the same way, we assigned the color brown to the swampy wet areas, not flooded. From there, the colors from orange to dark green represent the dry areas, orange for the dry perimeter and then towards green for the higher areas.
The next thing we did after processing the information was to compare our elevation map with the definition of the dry areas for the PD project on the lot to the west, a project already submitted by another company and already approved. Our information, which covered that adjoining lot, perfectly matches the information of this mentioned existing project. Based on the above and the elevation plan and table presented, we show that the perimeter of the dry area is between elevations 115.5–115.9. And although the area is classified as wetlands, we can say that actually 45.5% of the area is dry, although some part of it, which is in the perimeter, presents wetland-type vegetation that will be identified in the environmental report presented with our study.
From this image processed with GIS software, an infinite number of analyses can be obtained, such as knowing areas intervened by humans, dry areas by each Parcel ID, etc. This information can be provided digitally to local authorities so that it becomes part of the review of their studies, the procedures used, and serves as a reference. In lands with wetlands or difficult for the surveyor to walk, in the company of the environmental specialist engineer, it is customary to walk the site and define wetland points by marking them with a handheld GPS. This is useful, but the procedure used in this case is more precise than the usual practice; nevertheless, the environmental engineer walked the site to verify the information presented in the images and its match with his research.
