Related Links: ENR's Top 200 Environmental Firms of 2011 The 2011 Top 200 Environment Firms Rankings The green tide seems to be turning in 2011 for the Top 200 Environmental Firms, with overall revenue for list participants rebounding 6.2% to $51.3 billion from last year's recession-driven falloff. In international work, there were strong gains fueled by the needs of growing economies and environmental requirements of natural-resource development projects. Top 200 firms also climbed in the rankings by acquisition, which added significant girth to some list participants.Based on revenue reported in 2010, there was growth in nearly all the markets. Even
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.