When talking about sediment issues at hydropower plants or other hydro facilities operators usually face millions of dollars removing or even reducing their problems. Only when economic and/or ecologic pressure starts to force action companies usually drag the sediment or try to flush it out by the dam’s main valve. A prominent example is the great rinse of the Colorado River in 2008 which is going to be repeated at least every two years, probably more frequently. Here each flush comes with the transport of some hundred thousand tons of sediment, but unfortunately also with the loss of some million cubic meters of water and therefore some million dollars in power generation revenues. Dragging the sediment comes with the shutdown of a concerned facility for several months causing the same or even bigger economical effect.A hydro storage power plant in Germany almost inoperable due to sedimentation turned out to be the start for a complete different approach. A combination of wet dredging, new equipment operation techniques and plant operation allows for low cost and no negative effect on plant performance. Once implemented, three years later the plant and combined reservoir is going to be free from sediment problems permanently. The new technical approach is transferable on almost any range of plants, small to large and run-of-river to pump storage. It also restores river morphology almost back to its natural situation improving often criticized ecological matters. Best of all: It fully suits European Water Framework Directive and U.S. sediment acts at no extra cost.
Greenhouse gas (GHG) emissions from hydroelectric dams are often portrayed as nonexistent by the hydropower industry and have been largely ignored in global comparisons of different sources of electricity. However, the life cycle assessment (LCA)of any hydroelectric plant shows that GHG emissions occur at different phases of the power plant's life. This work examines the role of decommissioning hydroelectric dams in greenhouse gas emissions. Accumulated sediments in reservoirs contain noticeable levels of carbon, which may be released to the atmosphere upon decommissioning of the dam. The rate of sediment accumulation and the sediment volume for six of the ten largest United States hydroelectric power plants is surveyed. The amount of sediments and the respective carbon content at the moment of dam decommissioning (100 years after construction) was estimated. The released carbon is partitioned into CO2 and CH4 emissions and converted toCO2 equivalent emissions using the global warming potential (GWP) method. The global warming effect (GWE) due to dam decommissioning is normalized to the total electricityproduced over the lifetime of each power plant. The estimated GWE of the power plants range from 128-380 g of CO2eq./kWh when 11% of the total available sediment organic carbon (SOC) is mineralized and between 35 and 104 g of CO2eq./kWh when 3% of the total SOC is mineralized. Though these values are below emission factors for coal power plants (890 g of CO2eq./kWh), the amount of greenhouse gases emitted by the sediments upon dam decommissioning is a notable amount that should not be ignored and must be taken into account when considering construction and relicensing of hydroelectric dams
The flow regime of the gravel-bedded river North Tyne has been regulated by the Kielder reservoir for the past 12 years; for the past nine years, regulation has been dominated by hydropower generation. Diurnal stage fluctuations of up to 0.6m are experienced during periods of peak hydropower flows. The main morphological and sedimentological impacts of this regulation are identified and physical explanations provided for the observed adjustments. The main morphological adjustments are identified as the degradation of riffle spawning grounds, the development of fine ssediment berms along channel margins, the aggradation of pools, vegetation of former gravel shoals and the growth of tributary confluence bars. Sedimentological adjustments are subtle and are characterized by higher percentages of fines within spawning gravels, coarsening of surface gravels and the development of a stable, strong bed fabric. The physical explanations for these adjustments relate to changes in the sediment transport regime controlled by the hydraulics associated with the pool-riffle swquence during hydropower generation
Threats to imperiled freshwater fauna in the U.S. were assessed through an experts survey addressing anthropogenic stressors and their sources. Specifically, cause of historic declines and current limits to recovery were identified for 135 imperiled freshwater species of fishes, crayfishes, dragonflies and damselflies, mussels, and amphibians. The survey was designed to identify threats with sufficient specificity to inform resource managers and regulators faced with translating information about predominant biological threats into specific, responsive actions. The findings point to altered sediment loads and nutrient inputs from agricultural nonpoint pollution; interference from exotic species; and altered hydrologic regimes associated with impoundment operations as the three leading threats nationwide, accompanied by many lesser but still significant threats. Variations in threats among regions and among taxa were also evident. Eastern species are most commonly affected by altered sediment loads from agricultural activities, whereas exotic species, habitat removal/damage, and altered hydrologic regimes predominate in the West. Altered sediment loading from agricultural activities and exotic species are dominant problems for both eastern mussels and fishes. However, whereas eastern mussels appear to be more severely affected by altered nutrient impacts from hydroelectric impoundments and agricultural runoff. Our findings suggest that control of nonpoint source pollution associated with agriculture activities should be a very high priority for agricultural producers and governmental support programs. Additionally, the large number of hydropower dams in the U.S. subject to federal relicensing in coming years suggests a significant opportunity to restore natural hydrologic regimes in the affected rivers.
The Nature Conservancy, FWI