Simulation of Sediment Transport due to Dam Removal and Control of Morphological Changes. Yan Ding* and Eddy Langendoen** * National Center for Computational Hydroscience and Engineering, The University of Mississippi, University, MS 38677, U.S.A.
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Simulation of Sediment Transport due to Dam Removal and Control of Morphological Changes
Yan Ding* and Eddy Langendoen**
* National Center for Computational Hydroscience and Engineering,
The University of Mississippi, University, MS 38677, U.S.A.
**Channel and Watershed Processes Research Unit
USDA Agricultural Research Service
National Sedimentation Laboratory, Oxford, MS 38655, U.S.A.
Numerical Simulation of Post Dam Removal Sediment Dynamics Along the Kalamazoo River Between Otsego and Plainwell, Michigan
Numerical Simulation of Morphological Changes due to Marmot Dam Removal in Sandy River, Oregon
Preliminary Study on Optimal Control of Sediment Release in the Dam Removal Process
Financial issue : Operating and maintenance costs outweigh the benefits - including hydropower, flood control, irrigation, or recreation,
Functional issue: where the dam no longer serves any useful purpose,
Ecological issues: restoring flows for fish and wildlife, reinstating the natural sediment and nutrient flow,
Safety issues: eliminating safety risks,
Recreational issues: restoring opportunities for recreation.
The impacts of removal have been addressed by different studies. Generally they can be divided into main categories.
(1) Short-Term Ecological Impacts of Dam Removal Sediment Release, Increased Sediment Concentration and Contaminated Sediment, and
(2) Long-Term Impacts of Dam Removal (Flow change regimes, temperature, sediment transport and water quality)
DA: 2,020 sq mi
Relief: 686 ft
Impoundment Area: 3,290,000 sq ft
Volume of deposit: 457,000 cu yd (56% main-stem channel)
Impoundment Area: 701,000 sq ft
Volume of deposit: 77,600 cu yd
Changes in channel geometry
Time series of hydraulic variables and sediment yield
Composition of bed and bank materials
Erosion resistance and shear strength of bed and bank materials
Rates of flow and sediments entering the channel
Bed evolution and sediment transport
CONCEPTS simulates long-term response of channels to loadings of water and sediments, and to instream structures
BST – shear strength
Jet test – erodibility
Dams In Scenario
POC4 – Dams In Scenario
G8 – Dams In Scenario
Otsego City Dam
Objective of control in this case:
Validation of sediment transport model
Minimize the morphological changes (erosion and deposition) at downstream by diverting extra sediments from the reservoir (dredging?)
Upland Soil Erosion
(AGNPS or SWAT)
Channel Network and
Channel Network Flow and Sediment Routing
Dynamic Wave Model for Flood Wave Prediction
where Q = discharge; Z=water stage;
A=Cross-sectional Area; q=Lateral outflow;
=correction factor; R=hydraulic radius
n = Manning’s roughness
Non-equilibrium transport of non-uniform sediments
A=cross-section area; Ctk=section-averaged sediment concentration of size class k; Qtk=actual sediment transport rate; Qt*k=sediment transport capacity; Ls=adaptation length andQlk= lateral inflow or outflow sediment discharge per unit channel length; Ut=section averaged velocity of sediment
Major J. J. et al (2012), USGS Technical Report, http://pubs.usgs.gov/pp/1792/
Reservoir deposition profile
(Source: PGE photogrametry, 1999)
Reservoir sediment size composition (Stillwater Science, 1999)
Simulation Period 10/19/2007 – 09/30/2008
Downstream Water Depth Hydrograph
Upstream Discharge Hydrograph
Simulation Results: 1-Year Bed Evolution
Water year series selected for simulation
Sediment Control Model
Sediment Transport Simulation Model
According to the extremum condition, all terms multiplied by A and Q can be set to zero, respectively, so as to obtain the equations of the two Lagrangian multipliers, i.e, adjoint equations (Ding & Wang 2003)
Lateral Outflow ql
where T=control duration; L = channel length; t=time; x=distance along channel; Z=predicted water stage; Zobj(x) =maximum allowable water stage in river bank (levee) (or objective water stage); x0= target location where the water stage is protective; = Dirac delta function
To evaluate the discrepancy between predicted and maximum allowable stages, a weighted form is defined as
Xiao Land Di Reservoir, Yellow River, China
Consider the equation of morphological change:
The objective function for control of morphological changes can be written as
and measuring function as,
can be taken equal to
i.e. the sediment transport capacity.
It means that for minimizing morphological change in a cross section, it is needed to make sediment transport rate in the section close to the sediment transport capacity.
Hypothetical Case (2): Reservoir Sediment Release
Excess Erosion Problem Downstream
Given Q = Q(t)
Control Objective: To minimize morphological change downstream
Simulation time = 1 year
Sediment Properties: Uniform sediment of d = 20 mm
Bed load adaptation length = 125 m,
suspended load adaptation coefficient = 0.1, and
mixing-layer thickness = 0.05 m.
Hypothetical Case (2) – Scenario (3): Model Results
Morphological changes after storm
Upstream flood flow (given)
Engineering difficulty: how to divert the sediments based on the optimal schedule?
1-D channel evolution models are capable of simulating sedimentation in reservoir sediment release process due to dam removals in rivers.
Coupling with simulation model of flow and sediment transport (CCHE1D), adjoint optimization model can achieve the best control of sedimentation due to the sediment releases.
Streambank erosion may be significant if dams are removed.
Fine-grained deposits (cohesive?), Parent (pre-dam) bed material
Rejuvenation of side channels, Vegetation, Uncertainty analysis, and application of sediment conotrl
The research of CCHE1D was partly supported by the USDA Agriculture Research Service under Specific Research Agreement No. 58-6408-1-609 (monitored by the USDA-ARS National Sedimentation Laboratory) and The University of Mississippi.