At my previous place of employment with an civil engineering consultancy we used 3D mapping (DEM) to help a city manage stormwater issues. They continually had a stormwater basin overflowing, and the water pooling on the roads (i.e. not reaching the basin). Through 3D mapping we were able to demonstrate where flooding will occur, helped them determine any changes in their network required to drain the land better and size their basin for them (or suggest alternatives to transport the stormwater).
It could however also be used to benefit general stormwater infrastructure across a city (in Australia many cities are retro-fitting their urban areas with WSUD/bioretention gardens which replace traditional pits). The 3D mapping helps pick the location and flows for these.
Another project I was involved in required viewsheds and building shadows to be determined (this was in relation to tourism, property rights etc.) Also that same city used the 3D mapping to determine a height restriction on buildings within the CBD, and also to determine height based on the predominant wind direction (as poor planning in the past created a wind tunnel through the main street).
