Why small farm dams better than massive reservoirs
Dams provide massive benefits, with the most common being a great source of electricity and water for commercial and domestic needs. Despite these benefits, dams have proven to have negative environmental effects on the ecosystem.
Various strategies can be adopted to reduce the impact of dams on aquatic and terrestrial ecosystems. These mitigation measures can be classified into impact on water quality, impact on marine life, impact on land, vegetation, and air. There are specific measures that can be applied, such as:
- Construction of drainage systems to prevent water contamination which affects water quality
- The provision of containers that can dispose of chemical waste-reducing chemical pollution
Urbanization and the evolution of technology are other factors that have led to the deterioration of the environment and climate change. It is therefore essential to look into the environmental impacts of specific construction projects despite their economic benefits. The development of certain buildings and industrial plants does more harm than good and poses significant environmental risks.
Many controversies surround the impact of dams on the environment. Many environmentalists argue that dams pose great environmental and social threats such as people displacement and land degradation. On the other hand, those proposing the construction of dams look at its benefits, such as power generation adding a country’s economic value.
Environmental Impacts
The following are some of the environmental impacts of dams on the ecosystem, particularly during construction, at the reservoir area, and impact downstream.
Construction
The construction of dams poses a significant threat to the quality of water downstream. Activities during construction may release chemical compounds in water bodies interfering with water quality. Similarly, the release of excessive sediments in water moving downstream pollutes water bodies, thus water quality.
Sediment Release
The chances of the release of sediments during the construction of dams in water bodies are very high. Activities such as channel construction, exaction, and quarrying increase sediment load discharged into the surrounding water bodies. These activities done during construction become very detrimental to water flow due to the high sediment load disposed of in the water body.
Chemical Pollution
There are high chances of chemical pollution through chemical products such as gasoline, solvents, and paint used during dam construction. Accidents are inevitable, leading to chemical spillage on both land, water, and the air.
Effective mitigation strategies include the construction of a storage unit to store all chemical components used during construction and proper monitoring of all chemical products used to prevent spillage. The release of chemical effluents downstream interferes with water used for drinking, among other domestic functions.
Pollution from Domestic Water
Domestic wastewater from workers temporarily living in camps may be released downstream, interfering with water quality affecting the population leaving downstream.
Pollution from Solid Waste
Soil and water pollution are common during the construction of a dam. Solid waste arising from construction needs to be managed appropriately to prevent land and water pollution that adversely impacts the population and the environment at large. Workers working in the construction site need to follow appropriate disposal measures for disposing of domestic waste.
Impact during Reservoir Impound
The immediate closure of a dam poses adverse effects, particularly on the quality of the impounded water. The composition of organic matter surrounding the dam leads to oxygen depletion in the water impounded by the reservoir. The replacement of deoxygenated water becomes necessary to avoid toxins that can cause health effects to animals and neighboring populations.
This condition, commonly referred to as hypoxia, poses problems and future consequences in aquatic and human life due to the release of ammonia and metals such as iron from the reservoir. The release of such substances is harmful to marine life, leading to their extinction. Similarly, the release of nitrogen and phosphorus from vegetation contributes to water deoxygenation, thus interfering with water quality.
Flooded Biomass
Flooded biomass consists of both soft and hard biomasses. Soft biomass consists of grasses, leaves, and fruits, which decay very fast compared to complex biomass such as wood. Hard biomass during the first few years of water impoundment significantly contributes to water pollution.
There are two effective measures that can be used to clear biomass and clear fresh vegetation. These are:
- Burning of surrounding vegetation before water impoundment permanently avoids regrowth
- Physical clearing of wood and burning of collected wood and other hard biomass months before impoundment.
Impact on the Downstream Zone
There are chances of increased organic matter released downstream during filling activities. The likelihood that the water has toxins is also high, killing aquatic animals. Water flowing downstream cannot be used for domestic and animal use due to its high organic load, thus interfering with water quality. It is wise that the population nearby use an independent water source.
Impacts during Reservoir Operation
It can be quite difficult to assess these impacts during reservoir operation. However, other reservoir models can be used as a basis for the assessment of impacts during operation.
The commonly assessed features are the nutrient and projected potential for the surrounding water body. The standard criteria used in this assessment are comparisons made regarding the shape of the reservoir and the features adopted during the management of impounded water.
Residence Time
Residence time is identified as the period allowed for the impounded water in the reservoir. The longer the water impoundment, the higher risk of water deoxygenation leading to an increased level of minerals leading to algal blooms that are toxic, thus a process identified as eutrophication.
Shoreline Development
There is a need for a reservoir to be less dendritic to prevent the eutrophication process and the development of vegetation that interferes with water quality.
Temperature and Reservoir Stratification
Meteorological weather conditions predict water temperatures in the reservoir. Thermal stratification changes with different depths of the reservoir. Shallow waters of the reservoir are likely to show a higher temperature.
Electrical Conductivity and Salinity
Processes such as evaporation are likely to increase water salinity, and thus its electrical conductivity interfering with irrigation.
Nutrient Loading and Primary Productivity
A critical nutrient that contributes to the eutrophication process is Phosphor (P). Phosphor is a common macronutrient; however, high levels of the nutrient promotes algae which produce toxins that contaminate the water due to the presence of phytoplankton that floats on the surface of the water.
Reservoir Sedimentation
The formation of a river is characterized by deltas, lakes, dikes, coastal beaches, among other banks that form as a result of sediments carried away. Dams, however, interfere with the formation of these river banks leading to phenomena such as erosion where sediments in the dams tend to increase. Alternatively, rivers prevent water storage replaced by residues leading to reduced water for power generation, irrigation and eventually a decline in the benefits of the dam.
Impacts on Aquatic Ecology
The construction of dams has detrimental impacts on aquatic life, which interfere with their habitat. The flooding permanently interferes with aquatic life and the surrounding ecology, such as forests and wetlands.
Dams prevent the growth of some species due to suppressed sediments altering the ecosystem. In general, the construction of dams reduces the diversity of wildlife, the generation of new species, and the loss of animal habitats.
Impacts on Fish Biodiversity
Dam construction affects the habitat of aquatic animals such as fish. Alternatively, when dams close, the fish decreases due to the dam’s interference with the spawning process. There is a need for an environmental impact post-assessment which involves:
- Assessment of the effect of the dam project on both planktonic animals and plants, fishes among other aquatic organisms
- Evaluating these impacts on species that are rare
- Analyzing spawning impacts on aquatic life
- Having meaningful discussions on ways to conserve all aquatic species
Aquatic species find it difficult to thrive in artificial habitats. Alternatively, activities that lead to changes in river patterns and water contamination kill aquatic species, particularly benthic organisms.
Permanent Land Occupation
Dams are permanent features that occupy land, and in most cases, they have an impact on climate change. Reservoirs in hot climates contribute to the formation of greenhouse gases such as Methane, causing unpredictable climatic conditions. Methane contributes to biomass deterioration affecting surrounding vegetation. Similarly, Methane is an air pollutant thus affects the environment.
Access Roads
The construction of a dam leads to the formation of roads in a forested area. Deforestation poses its threats, such as soil erosion, climatic changes, and loss of environmental species.
Impact on Vegetation
Vegetation is greatly affected by the construction of a dam affecting vegetation that grows laterally to rivers and streams. The natural process of the river may change due to changes in the riparian vegetation. The construction of a dam thus interferes with riparian vegetation.
Floating and Aquatic Vegetation
Weeds and floating vegetation cause risks such as;
- Death of fish and other aquatic organisms
- Increase in mosquitoes and diseases
- Clogging of dams
- Reduced water in dams
Impacts during Operation Period
The operation of dams consists of water fluctuations. During the operation of the reservoir, the level of water is likely to drop, and in some instances, plans can grow. This area is commonly identified as the landing zone, thus affecting the quality of water.
Drowning of Animals
During activities such as biomass clearance and clearing of forested areas, animals may be trapped in the area and may fall victim to drowning due to their inability to swim. Animals are also bound to be injured, leading to their death.
Reservoir Areas
Wildlife is likely to be affected due to the presence of a reservoir. Rivers tend to be dry for some months of the year, which eventually affects wildlife.
Greenhouse Gas Emissions and Contribution to Global Warming
Gases such as Methane and carbon dioxide, also identified as greenhouse gases and may be released from dams contributing to global warming. Other activities such as the burning of the surrounding environment and clearing forests contribute to global warming, thus negatively impacting the environment.
Impacts on Micro-Climate
The presence of a dam in an area may interfere with the local climate. Activities such as the evaporation of water in the reservoir change the humidity and temperature conditions of the area.