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- Conventional Hydro
A Stratigraphic Approach to Characterize the Deposition and Storage of Organic Matter in Reservoir Sediments
Lead Companies
Oregon State University
Lead Researcher (s)
- Laurel Stratton
The relationship between carbon burial and sedimentation in reservoirs is unknown, exposing gaps in our fundamental understanding of the transport, processing, and deposition of sediment and organic matter in fluvial and lacustrine systems and contributing to uncertainty in our understanding of the net impact of dams to the global carbon budget. The 2011-2014 removal of two large dams on the Elwha River, Washington State, the largest dam removal yet completed globally, created extensive cutbank exposures of reservoir sediments, allowing the first characterization of the facies architecture of sediments through direct observation in reservoirs worldwide and providing an unparalleled opportunity to 1) assess the relationship between environmental influences, such as and changes in sediment supply, and their expression in the stratigraphic record, 2) assess the relationship between sedimentation processes and detrital organic carbon deposition and storage, and the importance of coarse-grained organic matter and woody debris to the total carbon budget of a reservoir, and 3) apply the insight gained from these reservoirs to evaluate current global estimates of carbon storage in reservoirs and develop a conceptual model of carbon burial in reservoirs to guide further research, as defined by characteristic stratigraphic “types”. Former Lake Mills, the younger, upstream reservoir, was characterized by a tripartite, subaerial Gilbert-style delta which prograded >1 km into the main reservoir from 1927 to 2011. Sediments were composed of coarse-grained topset beds, steeply dipping foreset beds, and a fine-grained, gently dipping prodelta. While individual event horizons were discernible in fine-grained sediments of former Lake Mills, their number and spacing did not correspond to known drawdown or flood events. Former Lake Aldwell, impounded from 1913 to 2011, was initially defined by the rapid progradation of a Gilbert-style, subaerial delta prior to the upstream completion of Glines Canyon Dam. However, the 1927 closure of Glines Canyon Dam upstream caused the delta to evolve to a fine-grained, mouth-bar type delta indicative of low, finer-grained sediment. This evolution, combined with a previously-unrecognized landslide deposit into the upper delta plain, suggests that understanding the exogenic influences on reservoir sedimentation is critical to interpretation and prediction of the sedimentation within individual systems. Former Lake Mills accumulated ~330 Gg of, with depositional-zone average accumulation rates from 229 to 9262 gCm-2 yr-1 , while Former Lake Aldwell accumulated ~ 91 Gg (263 to 2414 gCm-2 yr-1). Carbon storage in both reservoirs was dominated by heterogeneous, coarse organic matter and woody debris in the coarse-grained delta slope and relatively coarse-grained prodelta regions of the reservoirs, with little storage in the gravel-dominated, subaerial delta plains. Carbon accumulation in fine-grained lacustrine and prodelta sediments was relatively homogeneous, but turbidity flows from the Gilbertstyle delta slope in former Lake Mills delivered significantly more carbon to the prodelta than the mouth-bar style delta of former Lake Aldwell. C:N ratios support interpretation of most organic matter in both reservoirs as allochthonous. Sampling schemes based only on lacustrine and/or prodelta would underestimate of total carbon accumulation by up to 30% in former Lake Aldwell, but the overestimate by up to 47% in former Lake Mills. Global estimates of carbon sequestration rates in reservoir sediments vary by three orders of magnitude, while individual-reservoir estimates vary by four orders of magnitude and over only 37 reservoirs and a literature review of predictive variables suggests weak or contradictory relationships. A conceptual stratigraphic framework of four unique reservoir types suggests that organic matter deposition is intrinsically tied to sedimentation processes and that patterns of carbon storage vary systematically with the stratigraphy of reservoir sediments. Deltaically-dominated reservoirs (whether Gilbert style or shoalwater) appear to store most carbon in their deltaic and prodelta regions, while thalweg-style reservoirs exhibit a bimodal distribution, with allochthonous carbon preferentially routed along the former river thalweg and autochthonous deposited on the former floodplain. Lacustrine-style reservoirs are dominated by suspended sediment deposition and thus relatively homogeneous, but literature suggests these reservoirs are more variable than typically measured. Current methods of reservoir sampling fail to account for this systematic variation and tend to be biased toward fine sediment, suggesting that global reservoir carbon storage is underestimated.
Technology Application
Conventional Hydro
Research Category
Environmental and Sustainability
Research Sub-Category
Sediment Transport
Status
complete
Completion Date
2018
- Conventional Hydro
Baseline sediment budget for the Klamath River
Lead Companies
U.S. Geological Survey
Lead Researcher (s)
- Chauncey Anderson (ORWSC)
- Scott Wright (CAWSC)
USGS is working with PacifiCorp, Klamath River Renewal Corporation (KRRC), Tribes, States of OR and CA, and others to understand the effects of the Klamath Hydroelectric Project (KHP) on sediment transport and water quality in the Klamath River. In anticipation of a the potential removal of the lowermost 4 dams of the KHP, the USGS is working with the Tribes to help conduct monitoring required of KRRC under the Section 401 permits for the dam removal, currently scheduled for 2023, and at a larger scale to generate a baseline sediment budget for the river. Similar work is anticipated during and after the drawdown and dam removal process. Sub-studies, such as evaluating the bed mobility and effects of reservoir flushing on sediment resuspension, with application to mitigation of fish disease, are also ongoing. The study uses a mix of sediment flux, geomorphic assessments, and sediment tracer effects to estimate the overall effects of sediment releases from the reservoirs on downstream processes and place it in context with historical sediment transport in the basin.
Technology Application
Conventional Hydro
Research Category
Environmental and Sustainability
Research Sub-Category
Sediment Transport
Status
ongoing
Completion Date
TBD
- Conventional Hydro
Condit Dam Removal
Lead Companies
U.S. Geological Survey
Lead Researcher (s)
- Jon Major, Cascades Volcano Observatory
Immediate sediment response to removal of Condit Dam on the White Salmon River.
Technology Application
Conventional Hydro
Research Category
Environmental and Sustainability
Research Sub-Category
Sediment Transport
Status
complete
Completion Date
2014
- Conventional Hydro
Fall Creek Reservoir Drawdowns
Lead Companies
U.S. Geological Survey
Lead Researcher (s)
- Mackenzie Keith, Liam Schenk, Oregon Water Science Center
Geomorphic and sediment response to annual drawdowns at Fall Creek Reservoir, Oregon, for fish passage purposes
Technology Application
Conventional Hydro
Research Category
Environmental and Sustainability
Research Sub-Category
Sediment Transport
Status
ongoing
Completion Date
2021
- Conventional Hydro
Investigation of flow and sediment transport over RoR dams, and potential effects on upstream and downstream geomorphology, sedimentation, and aquatic habitat.
Lead Companies
Colorado State University
Lead Researcher (s)
- Robert Queen
Low-head or Run-of-River (RoR) dams exist on all types of rivers throughout the United States, yet the exact mechanisms of how sediment moves around the structures have not been well researched. Due to the increasing use of RoR dams in small hydroelectric projects, there is a need to better understand the controlling factors of how sediment passes over these dams. A one-dimensional morphodynamic model was developed to investigate the effects of RoR dams on channel morphology over long time scales. The model solves the gradually varied flow equations to compute the flow field in the vicinity of the dam, computes grain-size-specific sediment transport rates, and uses sediment mass conservation and vertical storage bookkeeping to calculate the evolution of bed elevation, the bed surface grain-size distribution, and the vertical pattern of stratigraphy. The model’s hydraulic calculations were calibrated using data collected from a series of flume experiments performed with a model RoR dam to better capture the non-hydrostatic flow over a dam. Numerical experiments designed to investigate how the grain-size distribution of the sediment supply rate, flow rate (steady and unsteady), and dam height act as controls on sediment passage over RoR dams were conducted using parameters reported in the literature for a RoR dam in northern Delaware. These one-dimensional simulations were complemented with a few simulations using, a two-dimensional morphodynamic model, Nays2DH. The 1D simulation results show that the stored sediment upstream of RoR dams does depend on the sediment supply, dam height, grain-size and flow discharge. Once sedimentation in the reservoir has reached equilibrium, high flow events will reduce or scour the sediment while lower flows will typically increase the amount of sediment behind the dam. Finally, a dam that stores more sediment will have greater downstream effects in terms of changes to grain-sizes and bed elevation due to the increased time it takes to pass sediment over the dam and reach an equilibrium condition on the upstream side of the dam.
Technology Application
Conventional Hydro
Research Category
Environmental and Sustainability
Research Sub-Category
Sediment Transport
Status
complete
Completion Date
2018
- Conventional Hydro
Marmot Dam Removal
Lead Companies
U.S. Geological Survey
Lead Researcher (s)
- Jon Major, Cascades Volcano Observatory
Immediate sediment response to removal of Condit Dam on the White Salmon River.
Technology Application
Conventional Hydro
Research Category
Environmental and Sustainability
Research Sub-Category
Sediment Transport
Status
complete
Completion Date
2012
- Conventional Hydro
Maximizing the habitat restoration potential of controlled releases at hydropower dams; Understanding impacts of hydrograph form on sediment transport
Lead Companies
University of Idaho
Lead Researcher (s)
- Megan Kenworthy
Technology Application
Conventional Hydro
Research Category
Environmental and Sustainability
Research Sub-Category
Sediment Transport
Status
complete
Completion Date
2018
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Contact Marla Barnes at: marla@hydro.org