Hydrology BC ENV 3025
Dams
- the earliest recorded dam is believed to be a masonry
structure
49 ft (15 m) high built across the Nile River in Egypt c.
2900 BC
- very large (>60m?) dams all over the world (Fig)
- a summary of issues related to dams is given in the talk given
by
Marc
Reisner
- Dams have a whole range of positive and negative effects
- positive:
- reduced risk of floods
- more reliable water
supply
- hydro power generation, by region (table),
by
country (table)
- fishing
- tourism
- negative effects
- changes in channel morphology
- reduced beaches
- debris jams in tributaries
- lower temperature of the downstream water
- lower sediment load -> clearer water
- increased sediment storage
- altered riparian vegetation,
- displacement of people
- Three gorges:
- location (fig)
- statistics (fig)
- changes in fish population
- declining numbers and quality of spawning grounds for
native
fish
- NW US: loss of most of the salmon fishery in the regional
ocean waters & within the river itself, due to
obstruction of fish
spawning migration by dams, as well as other perturbations.
(Fisheries
is 7% now from what it was)
- mercury contamination of fish in the new reservoirs (James
Bay)
- large production of methane gas from the flooded forest
areas
(addition source of greenhouse gas)
- dam construction
rates
have gone down in the US dramatically, because the best sites
have been
built up and also because of increasing opposition
- global construction of dams (Fig)
Resources
