The U.S. has more than 87,000 dams greater than six feet high (and two million overall). While many dams continue to provide benefits such as flood control, irrigation, and water supply, for other dams the cost of maintenance or the negative effects on communities, fish, and tribes justifies their removal.
Dam owners and regulators decide whether to remove a dam by weighing many factors including: the cost of removal and the ability to replace any lost power generation against avoided long-term maintenance; safety concerns; benefits to endangered fish populations; increased recreational and commercial fishing; and restoration of cultural values of nearby tribes.
By 2020, roughly 70% of dams will be more than 50 years old, inviting us to reconsider the value to the public of long-term investments in this infrastructure.
Colombia, peru and bolivia are latin americas leading cocaine producers
<span> The himilayas are an example of an intervening obstacle, but that is an enviromental obstacle. You could have an economic obstacle such as a town along the way that may be in harsh poverty and you may not be able to continue migrating. Or a political obstacle: Migrating through a country that is ruled under a law that despises something about you like race, gender, culture, or personal status.</span>
3. As the sea-ice cover of the arctic and southern oceans shrinks, the albedo of the earth's surface decreases.
The coastal plains of south of the atacama desert.
