A few questions....

The next option is a little more complicated.After the borad is cut and the edges are painted use wide masking tape to make a raised border arond the base.Mix some plaster to an oatmeal like consistency and spread in into the taped area.You have to play with the plaster to find the right time to work it.When it holds the shapes you want you can work it into any shape you want.I used a sponge to texture it as in the photos.Push the sponge down to create rocky areas and drag it along the surfaces to create the runway appearence.When the plaster is dry remove the tape and sand the edges to match the edge of the base.I left the plaster unpainted to simulate a coral airstrip.I dry-brushed some brown over it.I used paint to color the revetment areas with some scenic materials as described above.The palm tree was made from a wooden dowel.I cut it into small sections and them glued them together without sanding to make the trunk.After I painted it I added the leaves using materilas from a craft shop.You can find some pretty convincing ferns to do this.Add the plane and some figures and you're done.The oily patches are just some dirty thinner dripped onto the surfaces.

Here is the most complicated one.After preparing the base as above use the masking tape again to seal the edges.Make it really tight.Mix the plaster to a soupy consistency and pour it onto the base.It must be very liquidy so it will be smooth when finished.This can be used to make any concrete surface.Use a lenght of balsa to define the edges of the runway.Any grassy area around it can be done as shown above.As the plaster dries use a straightedge to impress lines in the "cement".Paint the concrete ares with Floquil "concrete".I find this is the pefect color.I did this diorama in two steps to give the concrete a slope down into the water.Just add edges to a section and put the plaster down as real concrete is layed.When the plaster was dry I sanded it into a slope for the concrete apron.After painting the concrete use a fine line permanent marker to show some cracks.Now for the water.I paint the water area with colors until it looks right.Now it is colored but not yet wet.Now retape the edges realy tight.I used testors glosscote in the bottle and poured it over the water painted areas making sure some of it went over onto the painted concrete surface.This simulates the very shallow water.When dry you won't believe the results.There are newer ways to ake water but I find for small areas nothing beats this technique.If you want a figure in the water make sure you put him in before you pour the water.This particular diorama has been used at various shows with different models as can any you make.