River VL 11 ?? Flashcards
What are pre-dams for?
Pre-dams are smaller reservoirs constructed upstream of the main dam.
They can greatly improve the water quality of the main dam, since sediments and turbidity gets trapped in the predam and the clear water on top enters the main dam.
It also reduces nutrient content downstream through algae growth and creates litoral zones to create stabel water levels.
What is a spillway? What is a bottom-outlet for?
A spillway is a structure built into a dam to provide a controlled pathway for excess water to flow out of the reservoir and
downstream.
* main function of a spillway is to prevent the reservoir from overflowing, which could potentially damage the dam or
cause uncontrolled flooding.
Bottom outlets serve several functions
* water regulation for downstream use,
* maintenance of environmental flow requirements,
* sediment management,
* reservoir drawdown for inspection or repairs
Functions of reservoirs (Stauseen):
- Flood protection: Stores excess water during high rainfall.
- Drinking water supply: Provides clean, nutrient-poor water.
- **Service water supply: **For industrial use, such as cooling water.
- Irrigation: Supplies water for agriculture.
- Hydropower: Uses water flow to generate electricity.
- Low water elevation: Maintains water levels during droughts.
- Fishing and recreation: Supports biodiversity and leisure activities.
- Conflicts: Not all functions are compatible. For example, drinking water requires nutrient-poor conditions, while fisheries benefit from nutrient-rich water for fish growth.
What is defined a “large reservoir”? ICOLD criteria:
- Height > 15m from the deepest point to top of dam wall
- Height > 5m and < 15m and volume > 3 million m³
- ICOLD is an international NGO
What are ecological and physical/structural consequences of strong surface level fluctuations in a reservoir/artificial lake?
Ecological Consequences:
1) Habitat Disruption:
* Aquatic Life: Rapid changes in water levels can harm fish and other aquatic organisms by altering
their habitats, aecting spawning grounds, and reducing available shelter.
* Vegetation: Fluctuations can damage shoreline vegetation and wetlands, which are crucial for
biodiversity and serve as buers against erosion.
* No typical littoral zone (ufernahe zone oft mit Schilf)!
2) Water Quality:
* Sedimentation: Lower water levels can expose and disturb sediments, increasing turbidity and
releasing trapped pollutants.
* Nutrient Cycling: Fluctuations can disrupt the natural cycling of nutrients, leading to issues like algal blooms during low water periods and oxygen depletion when water levels rise rapidly.
3) Wildlife Impact:
* Migration Patterns: Fluctuations can interfere with the migration and reproductive cycles ofaquatic and semi-aquatic species.
Physical and Structural Consequences
1) Erosion:
* Shoreline Erosion: Varying water levels can increase erosion rates along the shorelines, leading to
loss of land and destabilization of structures near the water’s edge.
2) Infrastructure Stress:
* Dam Structures: Repeated fluctuations can place additional stress on the dam and associated infrastructure, necessitating more frequent inspections and maintenance.
* Recreational Facilities: Docks, boat ramps, and other recreational facilities can be damaged.
Name Ecological impacts of dams
- Disruption of the river continuum -> up- and downstream barriers for migrating species; barriers for dead wood
- Extinction of migrating fish species
- Destruction of terrestrial habitats -> Loss of top predators -> Increased herbivore populations -> Substantial reduction of seedlings and saplings; loss of floodplains
- Reduced flow dynamics
- Water scarcity downstream
- Greenhouse gas emissions
Environmental problems of hydropower plants:
- Tropical reservoirs emit more carbon than temperate or boreal ones (CO2 + CH4).
- Stronger climate forcing of methane (CH4) is considered.
- Gas or coal as alternative would yield similar numbers.
Impacts of Controlled Sediment Flushing
- Downstream Sediment Load: Sudden increase in sediment load can smother (verkleben) aquatic habitats (called
colmation), reduce water quality, and affect fish and other aquatic organisms. - Water Quality: The sediment released during flushing can carry pollutants such as heavy metals, nutrients, and organic matter. This can lead to downstream water quality issues.
- River Morphology: The sudden influx of sediment can alter the riverbed and banks downstream, potentially causing
erosion, changes in channel structure, and impacts on floodplain ecosystems. - Ecosystem Disruption: Aquatic organisms, particularly those that are not mobile, can be severely impacted by the rapid changes in sediment load and water quality. Fish spawning grounds can be disrupted or destroyed.
Name four differences between dams and natural lakes and their hydrological and/or ecological consequences
1) Water Flow Regulation:
* Dams: Regulate water flow for flood control, irrigation, and hydropower, often leading to reduced/altered
downstream flow variability.
* Natural Lakes: Exhibit natural flow patterns with seasonal variations, supporting native aquatic ecosystems
adapted to these conditions.
2) Sediment Transport:
* Dams: Trap sediments, reducing downstream sediment transport, which can lead to erosion and loss of habitat
downstream.
* Natural Lakes: Allow natural sediment transport, maintaining downstream habitats.
3) Water Temperature:
* Dams: Release water from dierent depths, often causing unnatural thermal stratification in downstream rivers.
* Natural Lakes: Typically have more uniform temperature distribution, supporting stable thermal conditions for aquatic life.
4) Nutrient Dynamics:
* Dams: Can alter nutrient flow by trapping organic matter, potentially leading to nutrient depletion downstream.
* Natural Lakes: Maintain natural nutrient cycles, supporting balanced aquatic ecosystems and nutrient
distribution downstream.
