3D Modelling the Effects of Climate Change on the Coast of NSW

                                                                                                                                                                              

                                                                                                                                                                                 Ben Bartlett - October 2007

                          

                        Abstract                   Method                   Results               Conclusion                   Future Study                 Contact

Method

Creation of DEM

The following procedure was used to create three the DEMs, Area 1, Area 2 and Area 3 (see map below) encompassing Windang and Primbee. The ArcGIS (version 9.2) software package was used for this purpose.

  1. Change all “.non” files into “.txt” files by simply replacing “.non” with “.txt” in the names of the files.

  2. Import “.txt” files containing ALS data into ArcMap.

  3. The data will not be shown visually, so using the function “Add X-Y Data” specify the coordinate system that the data is to be displayed in, i.e. GDA94.

  4. Create “shape files” from the point data (.txt files) so that different functions can be performed on them by using the “export data” function. Specify file name and location.

  5. Merge the shape files for the area which is being modelled by utilising the “Merge” function. The Windang area is quite large so three separate, smaller DEMs were created to enhance the speed of model generation and lower the memory requirements for the computer. Therefore, all the shape files that contained information for Area 1 were merged, separately to those of Area 2, and similarly to Area 3. The result is one individual, larger shape file for each specific area.

  6. Create a TIN from the merged shape file using the “create TIN” function in the “3D Analyst Toolbar.”

  7. Open ArcScene and import the TIN. ArcScene allows 3D visualisation so the TIN can now be viewed. Adjust the horizontal exaggeration such that the shape of the topography can be easily observed and appears suitable for analysis.

  8. Drape the corresponding orthorectified aerial photos over the TIN. This is achieved by importing the photos that correspond to the DEM. Then select the DEM as the model which will dictate the heights at which the photos will be exhibited in the orthophoto’s properties, under the “Base Heights” tab. This is now the draped DEM of the subject topography which is the basis of the three-dimensional analysis.

This entire process was repeated to generate three draped DEMs

Figure: Map of subject areas.

 

 

Simulating Three Dimensional Sea Level Rise

The following procedure was used to simulate sea level rise in the areas surrounding the aforementioned DEMs. Several flat (that is, with constant height) TINs were created which represent the height of the water surface at different heights. Hence as each new TIN is displayed, a new sea level height is represented. Thus, combining this with the draped DEM, the image of rising sea level is displayed, and this becomes the basis for inundation analyses.

The first set of sea level rises was created with six individual TINs with ascending height increments of 0.2m, starting from 0m AHD and finishing at 1.0m AHD. This set represents sea level rise due to climate change and is displayed in the table below.

 

Increment

Sea Level TIN (m AHD)

Colour

1

0.0

Dark Blue

2

0.2

Dark Blue

3

0.4

Dark Blue

4

0.6

Dark Blue

5

0.8

Dark Blue

6

1.0

Dark Blue

Table: The first set of sea level rise’s. This set represents sea level rise due to climate change.

 

The second set of sea level rises, displayed in increments of 0.2m starting from 1.54m AHD and finishing at 2.54 AHD, represents the combination of rises in water level due to climate change and the flood events that occurred in March 1975 and February 1984. Both of these flood events reached a height of 1.54m AHD in the local area. This set of sea level rises is displayed in the table below.

 

Increment

Water level (m AHD)

Flood Event Height (m AHD)

Total Water Level (m AHD)

Colour

1

0

1.54

1.54

Dark Blue w/ White Spots

2

0.2

1.54

1.74

Dark Blue w/ White Spots

3

0.4

1.54

1.94

Dark Blue w/ White Spots

4

0.6

1.54

2.14

Dark Blue w/ White Spots

5

0.8

1.54

2.34

Dark Blue w/ White Spots

6

1.0

1.54

2.54

Dark Blue w/ White Spots

Table: The second set of sea level rise’s.

 

The third set of sea level rises, displayed in increments of 0.2m starting from 1.84m AHD and finishing at 2.84m AHD, represents the combination of rises in sea level due to climate change and the flood events that occurred in August 1998 and March 1978. Both of these flood events reached a height of 1.84m AHD in the local area. This set of sea level rises is displayed in the table below.

Increment Number

Water level

(m AHD)

Flood Event Height 

(m AHD)

Total Water Level

(m AHD)

Colour

1

0

1.84

1.84

Light Blue w/ Dark Blue Spots

2

0.2

1.84

2.04

Light Blue w/ Dark Blue Spots

3

0.4  

1.84

2.24

Light Blue w/ Dark Blue Spots

4

0.6  

1.84

2.44

Light Blue w/ Dark Blue Spots

5

0.8

1.84

2.64

Light Blue w/ Dark Blue Spots

6

1.0

1.84

2.84

Light Blue w/ Dark Blue Spots

Table: The third set of sea level rise’s.

  1. Create a point shape file with four points that border the extent of the original TIN and have Z-values of 0m. To do this, a “.txt” file must be created with the X, Y and Z data of each four points, like that of the ALS data. The Schema file must then be modified in accordance with the new file, so that the software will read it.

  2. Import the new data file into ArcGIS and display the data. Export the data such that a point shape file is generated.

  3. Create a new TIN from the point shape file by the same means as above.

  4. Importing the TIN into the same ArcScene files as each of the 3D models will simulate water level, statically, at MHWM or 0m on AHD. Repeat all steps for the remaining aforementioned heights to simulate their respective rises in water level.

 

 

 

Creating Animations of Sea Level Rise

The following method was used to create animations of sea level rise and subsequent inundation in the suburbs of Windang and Primbee. A DEM and several TINs representing sea levels of incremental heights were generated.

  1. Open ArcScene and import a draped DEM and all the sea level TINs which will be included in the animation.

  2. Using the animation toolbar, select “create key frame” and then select the “camera” type key frame. This is the tool by which the flight path of the camera is selected for the duration of the animation.

  3. Using the tools in the standard view screen, move the screen to the view and angle that is desired for the opening of the animation. Select “create key frame.” This saves a “snapshot” of the view that will be used for the opening of the animation.

  4. Now, move the view to the next desired “snapshot” or key frame for the path of the camera in the animation. Select “create key frame.” The program automatically interpolates the flight path from key frame to key frame, hence the difference in angle and distance between key frames will determine the speed and movement of the camera.

  5. Continue creating key frames at the desired angles around the scene until satisfied that the path of the camera will effectively exhibit the desired features of the combination of the DEM and sea level rise TINs.

  6. Playback the camera path which has just been created by using the play button in the animation toolbar. Properties such as looping and time length can be altered here too.

  7. Now select the “group layer” type key frame from the Animation toolbar. In the group layer dialogue box do not make any selections under “Layer Visibility,” but select “Blend Layers When Fading” under the “Transitions” heading. This creates an animation such that each layer is shown consecutively according to the order of layers in the Layers box on the left of the normal screen view. Make sure the order of the layers is such that the draped DEM appears first and then the sea level TINs in ascending order of height, running down the screen.

  8. Playback the animation using the play button and an animation will play which shows each layer successively, using the camera flight path that was generated earlier. Each water level TIN will appear one after the other, in order of ascending height, giving the illusion of the sea level rising.

  9. Once satisfied with the animation, using the drop down menu, use the export function and save it in “.avi” format to create a movie file.

 

 

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