Construction of Glen Canyon Dam in 1963 impounded nearly 300km of the Colorado River and its tributaries, creating Lake Powell in the US state of Utah. Researchers are now taking advantage of the opportunity to study exposed areas of sediment that have been revealed in the lake due to recurrent droughts since the year 2000.
A collaborative study published in The Sedimentary Record by the United States Geological Survey and Utah universities looks at how sedimentary formations were established, and how they might impact the future of the shrinking lake.
As the lake surface area has now receded to a third of its maximum extent, a completely new ecosystem is emerging out of that area with vegetation growing where it has never grown before.
USGS scientists are trying to learn more about the nutrients and metals present in the sediments. These are likely to be redistributed by the wind and water, and it will be useful to understand the potential impacts of this.
Looking to the future, the authors say that increasingly sophisticated sediment management will be required in large reservoirs as infrastructure ages. Regardless of management strategy, the authors add that reservoir sediment will become “a long-lived archive of recent earth history” and has the potential to be a focal point for scientific and societal discussions regarding human impacts on earth surface processes.
Godavari River
India’s Godavari River has experienced a significant decline in streamflow and sediment discharge since 1965, with a sharp fall after 1990.
A new study published in Catenna has documented such changes based on the analysis of a database of daily streamflow from 57 gauging stations, and sediment discharge from 25 stations, during the period from 1965 to 2015 in the Godavari basin.
Many stations recorded a decline in sediment discharge (up to 90%) after 1990. Such a critical drop has been equated with high sediment entrapment caused by extensive dam construction. The authors say that this resulted in a substantial decrease in sediment supply, contrasting to increasing sea levels which are further implicating significant coastal erosion in the near future.
Toxicity
A study has been carried out to analyse the toxicity of accumulated sediment accumulated in the vicinity of hydropower plants on the Ślęza and Bystrzyca rivers in Poland, as well as investigating the possibility of using these sediments for soil enrichment purposes.
According to the authors of the research published in Land Degradation & Development, to date “there has been little comprehensive research related to the analysis of the impact of hydropower plants on the properties of sediments”.
The research found that after passing through plants, the granulometric composition of the sediment changed and more coarse-grained formations (mainly sands) dominated, while upstream, there were more fine-grained clays and silts. Fine-grained materials have a greater tendency to absorb various substances, and in most samples upstream of hydropower plants, the concentration of pollutants is higher than downstream
The authors believe that more in depth analysis, especially from a practical and interdisciplinary point of view, is required to further understand the properties of bottom sediments within hydropower plants.
Hydropower management
Research in Hydroecologie Applique has studied how hydropower management can have an impact on the sediment composition of a lake. The study focused on the Alpine Corne Lake which has been utilised for hydroelectric production since 1976.
The aim was to document the ecological changes occurring in a lake managed as a reservoir. The management of Alpine lakes as reservoirs can induce long-term ecological changes in relation to water level fluctuations and degradation of littoral habitats. Objectives included measuring the temporal variation of sediment composition in relation to soil and sediment erosion, and describing the ecological evolution through algae conserved in the sediment which can typically be used as indicators of the current and past ecological status of water bodies.
Moroccan mud
The silting up of reservoirs in Morocco has led to the loss of capacity of nearly 73 Mm³/year. While de-silting remains as the best solution to the problems, it also leads to the production of enormous volumes of mud that can cause potential environmental pollution and occupy vast areas of land.
This has instigated research into identifying variety of possible uses for sediments in civil engineering, agriculture, craftsmanship, and the environment.
Research by Mohafid et al looks at ways sediment could be used in:
- Road works – the mud extracted from reservoirs can be valued as a top layer in the construction of roadways.
- Aggregates for concrete – dredged sediments are considered as fillers because of their grain size.
- Brick Manufacturing – due to its clay nature, sediments can be used as a raw material in red brick manufacturing.
- Agriculture – spreading sediments on arable land can provide more material for fertilisation and improving soil properties.
- Waterproof layer for lagoon basins or landfills
- Soil amendment – sediments can be used as a material for making landforms for landscaping or reshaping and for recharging old quarries and ballast pits as part of site restoration. It can help create spaces for industrialists, for leisure parks, for railway or road developments, or even for the creation of artificial islands
- Craft – in the manufacture of ceramics and glass if certain conditions are met.
The authors conclude that dam managers and operators can compensate part of the cost of desilting by targeting the different users according to the quality of the sediment extracted.
REFERENCES:
Sedimentary record of annual-decadal timescale reservoir dynamics: Anthropogenic stratigraphy of Lake Powell, Utah, U.S.A. by Cari L. Johnson, Jonathan Casey Root, Scott A. Hynek and John (Jack) C. Schmidt. The Sedimentary Record, Vol. 20, No. 1, p. 15–29, March 2022 DOI: 10.2110/sedred.2022.1.3
Toxicity studies on sediments near hydropower plants on the Ślęza and Bystrzyca rivers, Poland, to establish their potential for use for soil enrichment by PawełTomczy, Bernard Gałka, Mirosław Wiatkowski, Aleksandra Wdowczy and Łukasz Gruss. Land Degradation & Development, 33 (5) 2022, 756– 770. https://doi.org/10.1002/ldr.4210
Recent decline in streamflow and sediment discharge in the Godavari basin, India (1965–2015) by Sumit Das, Satish J.Sangode, Avinash M.Kandekar. CATENA Volume 206, November 2021, 105537 https://doi.org/10.1016/j.catena.2021.105537
Effects of hydropower management on the sediment composition and metabolism of a small Alpine lake by J. Félix-Faure, M. Ramon, C. Hatté, F. Rimet, J. Gaillard, V. Chanudet, A.-L. Develle, J. Garcia-Orellana, E. Dambrine. Hydroécol. Appl. (2022) Tome 22, 1 © EDF, hosted by EDP Sciences, 2022. https://doi.org/10.1051/hydro/2021003
Guide for valuing mud extracted from dam reservoirs in Morocco by Said Mohafid, Laila Stour, Ali Agoumi , Manar Ouassil, E3S Web of Conferences 314, 01001 (2021) https://doi.org/10.1051/e3sconf/202131401001
