Step 1: You will need one bulldozer and one cargo. Load the bulldozer into the cargo and position the cargo as shown in figure 1.2:
Step 2: Once you have done that, select the bulldozer while inside the cargo. You can do that by right-clicking on the cargo, where you will get a popup-menu with the list of units inside it. Select the bulldozer by left clicking on its name on the list (see figures 2.1 and 2.2). Once you have done that, the bulldozer icon should be flashing. Press the 'r' key (or select "build road" from the Actions menu). The resulting image should be something like this (the bulldozer icon if flashing on top of the cargo icon):
Step 3: Now, right click on the bulldozer to get the popup list again with the units that the cargo contains. This time, left click on the cargo to select it. Once the cargo icon is flashing, it means it has been selected. Move the cargo diagonally, bottom-right or bottom left - BOTH will work(!) - but for the purposes of this demonstration only one of the two will be shown. (see figure 3.2)
Step 4: Repeat the same actions as Step 2, in order to build a road and get the following result as demonstrated in figure 4.2. Notice that the square in which the Bulldozer is on, is a road surrounded by grass, whereas the road that is automatically built at the left-hand-side of the bulldozer is a road with water around it.
Step 5: If you seek further visual proof, then simply follow this last step, to illustrate clearly the two different tiles that have been created. Select the cargo and move it back to its original place as shown in figure 1 (see Step 1). While the cargo is still selected, press 'a' (or select "Attack" from the Actions menu). This will create a red crosshair, that you can move around with your mouse. Position the crosshair on top of the Grass-Bridge (figure 5.1). Left click with your mouse. You will be prompted with a verification asking you if you are sure you want to destroy that road. Click on "Yes". Notice that now the road has been destroyed and you are left with a Grass Tile. Repeat the steps above, only this time point the red cross-hair at the waterbridge as shown in figure 5.3. The end result is shown in figure 5.4.
Those tiles have been permanently changed. Bare in mind, you can do this in all four directions. It doesn't have to be facing north. However you can only do with with GRASS-waterside, NOT FOREST-waterside! See figures 6.1 - 6.4. Note that, the location of your BASE is insignificant. The only thing that matters is the sequence and location of the roads built as explained above from Steps 1 - 5.
If you have any questions or comments regarding this, don't hesitate to drop me a line.