With some margin of error you can still get a contour or topographical/aerial maps from Google Map & Earth. You may have to pass the data through few other softwares. You can make topographical features from those for your preliminary map.
Use undrained strength for the clay and apply your pore pressures within your material types(if your using limit equilibrium analyses) ending with the phreatic surface at the dam water-level. You can build separate models for pressure depreciation effects, draw-down effects(time dep) if you...
I would say check your force diagrams to ensure they are complete and resolve well. Full water in tension cracks sometimes throw the assessment resulting in negative values. I would reduce the water in the crack to 80% full and see what you get...
