mitigating the downstream impacts of dams

8/8/2019 Mitigating the Downstream Impacts of Dams

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Mitigating the DownstreamMitigating the Downstream

Impacts of DamsImpacts of Dams

Jeff Opperman, The Nature Conservancy


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High productivityShallow, low velocity waterFloodplain vegetationHigh productivity

Time

Flo

w

1. Channel form

2. Connectivity

3. Water quality

4. Energy

5. Species

Rio Laguna


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Value of ecosystem services of

various habitat typesFloodplains have second highest

value per ha

Adapted from Costanza et al. 1997


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Mekong River Fisheries Provide Primary Source

of Protein for 55 million people


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Major Impacts from DamsMajor Impacts from DamsSeasonal flow patterns and flow eventsSeasonal flow patterns and flow events

Extreme daily flow fluctuations due to peakingExtreme daily flow fluctuations due to peaking

Barrier to migration of fish and other aquaticBarrier to migration of fish and other aquaticspeciesspecies

Captures sedimentCaptures sedimentWater quality including temperature, dissolvedWater quality including temperature, dissolvedoxygenoxygen


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Hydrologic Alteration


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High productivityShallow, low velocity waterFloodplain vegetationHigh productivity

Time

Flo

w

Flow regulation

by damsTime

Flo

w

High productivity area greatly reduced

Rio Laguna

Connectivity lost


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How to protect important ecosystemsHow to protect important ecosystems

downstream of dams?downstream of dams?


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Environmental Flows:

The flow of water in a river or lake thatsustains healthy ecosystems that canprovide benefits and services to people and

nature

Water for people, water for nature
http://fwp.mt.gov/fieldguide/mediaDisplay.aspx?id=2660&elcode=ABNMK01030


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Environmental Flow

Defined ecologically

For river communities and ecosystemsPatterns of flow
http://fwp.mt.gov/fieldguide/mediaDisplay.aspx?id=2660&elcode=ABNMK01030


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Dam Operations developing andDam Operations developing and

implementing environmental flowsimplementing environmental flows

Understanding hydrological alteration:Understanding hydrological alteration:

Indicators of Hydrologic Alteration (IHA)Indicators of Hydrologic Alteration (IHA)

free software from The Nature free software from The NatureConservancyConservancy

TNCs approach and experienceTNCs approach and experience

developing and implementingdeveloping and implementingenvironmental flowsenvironmental flows


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Analyzes hydrological characteristics and variations over time

Calculates 67 hydrological statistics that are ecologically relevant

using daily hydrological data Designed to be flexible and easy to use and applicable to various

river systems.


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TNC/Corps of Engineers Sustainable Rivers Project


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Mitigating Impacts from DamsMitigating Impacts from Dams

Dam operations are important, but

getting the design right is extremely important


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Analysis for dam designAnalysis for dam design1. How far downstream will alterations to dissolved oxygen

and temperature persist?2. How far will major fluctuations in amplitude persist (from

daily peaking)?

3. What are the implications for important resources at various

distances downstream?


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Mitigation at scale of a damMitigation at scale of a damCan potentially address:Can potentially address:

Seasonal patterns of flow and flow eventsSeasonal patterns of flow and flow events Impacts from peaking operationsImpacts from peaking operations

More difficult to address:More difficult to address:

Migratory fish and longitudinal connectivityMigratory fish and longitudinal connectivity

SedimentSediment

Temperature and water qualityTemperature and water quality

Loss of free-flowing riverLoss of free-flowing river

However, may be limited by operational constraintsHowever, may be limited by operational constraints


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Limits to sustainability at scale of dam

Floodplain fishery

Spawning habitat


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Our basic premise:Our basic premise:Sustainable hydropower must be defined and pursued

at large spatial scales, such as a river basin or region

Experimental flood on Colorado

River, Glen Canyon Dam

Conservation blueprint,

existing and proposed dams,

Upper Yangtze


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Basin-scale approaches to sustainability

Floodplain fishery

Spawning habitat

EnvironmentalFlows

mitigating the downstream impacts of dams

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