Introduction: Study of a Watershed Through 3D Modeling
I’m a Civil Engineering student and I’m currently developing a work for a subject named Fluvial Hydraulics. This work consists in characterizing a watershed - in short, this characterization is done by studying the surface of the watershed and the levels of rainfall that fall on it.
The study of the surface is the most complex part of this work, especially if it’s done by hand. So I made a research about the GIS software (Geographic Information System) so that it would be easier to do this part of the work. This ended up being great for me, since it allowed me to make this study in 3D and not in 2D, as it was supposed to.
Since I have some basic knowledge about Google SketchUp I was able to elaborate this work a little bit more by simulating the raised signage of the watershed through 3D modeling. Actually, what I really wanted was to create an animation of the rainfall falling into the watershed, through AutoDesk Maya software, but I would have to learn more about the Maya software, since I have very little knowledge about it!
So this work will focus on a region that frequently suffers from atmospheric phenomena, such as alluvia, and it’s known by its big raised signage – Madeira Island. I decided to study one of the watersheds responsible for the alluvia catastrophes registered in 2010, so that this work may be used in the future to prevent against catastrophes like those.
Step 1: Coordinates and Measurements - Google Earth
I found the coordinates of the place to study in Google Earth and also made a measurement from this place to the further away point of the island, so that I could insert them in Global Mapper. One must check if the coordinates are in the Geographic format (latitude/longitude).
1 - Pick the place to study.
2 - Google Earth → Insert → Point Indicator
3 - The coordinates obtained in this point will be used in Global Mapper. It was chosen a point in the center of the island and it was made a measurement to the further away point that will be inserted in Global Mapper.
Tip: the coordinates can be easily obtained if you place the mouse above the area and write down the coordinates that will appear.
4;5 - Check if the coordinates are in the format “Degree, Decimal”. To do so press: Cmd + Preferences.
Step 2: Insert Coordinates and Measurement - Global Mapper
In the Global Mapper will be inserted the coordinates and the measurement previously obtained, in order to generate the watershed and the contours.
Then, it will be chosen one of the watersheds created and model it in 3D, in Google SketchUp.
6 - Tools → Configure
7 - Check if the Projection is: Geographic (Latitude/Longitude)
8 - Download Free Maps (Elevation Data)
9 - Select Data Source: ASTER GDEM
- Select Area to Download: Within – the measurement made in Google Earth – and the coordinates Lat/Long.
Step 3: Generate the Watersheds and the Contours - Global Mapper
10 - Generate the watersheds
11 - Watershed Bounds → Draw a Box (to delimitate the area of analysis)
(since the area to study is about 1 square kilometer, I put 1)
12; 13 - Draw Box - OK
14 - View the generated watersheds.
15 - Tools -> Digitizer (alt+d) and select the wanted watershed.
Step 4: Save Workspace and the Watershed in Analysis - Global Mapper
After generating the watersheds I will choose only one to proceed to its characterization.
My work will be focused only on the selected watershed, everything else is irrelevant.
16 - Save workspace as
17 - Select - Export Bounds tab
18 - Select - Crop to Selected Area Feature
Open the saved file to generate the contours.
19 - Generate Contours
20 - Insert the Contour Interval
Step 5: Export and Visualize on Google Earth
Export the project in KML/KMZ format to visualize it on Google Earth, and also export the file in DXF format to later proceed to the 3D modeling on Google SketchUp.
21 - File -> Export Vector Format
22; 23 - Select KML/KMZ -> OK
24; 25 - Select DXF -> OK
Step 6: Visualize the Watershed on Google Earth
26; 27; 28; 29 - Visualize the Watershed on Google Earth
Step 7: Import and Create the 3D Watershed - SketchUp
In this section, I’ll import the DXF file into Google SketchUp.
30 - File -> Import
31 - Options - Don’t forget to work in the same unit used in Global Mapper (meters).
32 - Watershed visualization.
33 - Hide the 2D watershed
34 - Select all (cmd+a) -> Make Group
Step 8: Geo-Reference the Watershed - SketchUp
Now that we know which watershed we want to study, lets geo-reference it.
35 - File -> Geo-location -> Add Location
36 - In the search field put the region where the watershed is placed.
37 - Having the images of Google Earth as support, search the place that will be the focus of the study.
38 - In order to not overlap the Google Earth image above the watershed, move it away a little bit to the right:
select the watershed, cmd + 0 -> move it.
Repeat all the previous steps until all the area of study is covered.
39 - File -> Geo-location -> Add More Imagery
40; 41; 42; 43 - Move down the rectangle, to grab new area.
44 - File -> Geo-location -> Show Terrain
45 - The terrain by Google and the Global Mapper Watershed
Step 9: Add Some Solids and a Water Line to Watershed - SketchUp
In this section I'll add some solids that will represent the houses closest to the waterline, which are the first exposed to the water.
The solids will be modeled by simply pounce the Google layer's
46; 47 - Indicates where the open flow conduct begins.
48 - Solids and water line
49 - Overview of the Google Terrain
Step 10: From the Watershed Contours Generate the Terrain Model - SketchUp
50 - Select all - > Unlock
51 - Select all -> Explode
52 - Select the watershed -> Draw -> Sandbox -> From Contours
53 - Watershed Terrain
54 - To edit: select watershed -> Explode
55 - To make a base to the watershed, I will use the line tool (cmd+L) to simply draw some polygones
56 - Select all again (watershed) -> Explode
57 - Right click on watershed -> Soften/Smooth Edges
58 - Before the Soften/Smooth Edges
59 - After the Soften/Smooth Edges
Step 11: Transfer the Solids and the Water Line to the Watershed - SketchUp
Finally I will transfer the solids and the water line to the watershed
60 - Select the bottom part of Google Terrain and move it to the watershed.
After the selection -> cmd+0
61 - Adjust to be overlaped
62 - Hide the Google Terrain - in the Layers Box
63; 64; 65 - 3D Watershed
Step 12: Some Pictures From the Catastrophe
All this process to make the watershed terrain may not have been the most appropriate because I don't have a full knowledge about modeling this type of projects, I just followed some tutorials about Global Mapper and Google SketchUp in order to present this project.
When I showed this project to my teacher she was very excited about it! But our task for the subject was to characterize a watershed with just 1 square kilometer. So she proposed that I could use the whole watershed (which is about 16 square kilometers) in my masters thesis... Having the possibility of printing this watershed in 3D and simulate the 2010 catastrophe in a real model, as you can image, would be awesome!!!!!