section_path: Creation/Impact assessment/Dam removal
section_name: Dam removal
paragraph_text: Dam removal
  
  Water and sediment flows can be re-established by removing dams from a river. Dam removal is considered appropriate when the dam is old and maintenance costs exceed the expense of its removal. Some effects of dam removal include erosion of sediment in the reservoir, increased sediment supply downstream, increased river width and braiding, re-establishment of natural water temperatures and recolonisation of habitats that were previously unavailable due to dams.
  
  The world's largest dam removal occurred on the Elwha river in the U.S. state of Washington (see Restoration of the Elwha River). Two dams, the Elwha and Glynes Canyon dams, were removed between 2011 and 2014 that together stored approximately 30 Mt of sediment. As a result, the delivery of sediment and wood to the downstream river and delta were re-established. Approximately 65% of the sediment stored in the reservoirs eroded, of which ~10% was deposited in the riverbed. The remaining ~90% was transported to the coast. In total, renewed sediment delivery caused approximately 60 ha of delta growth, and also resulted in increased river braiding.