2019 CSDMS meeting-088: Difference between revisions

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{{CSDMS meeting abstract template 2019
{{CSDMS meeting abstract template 2019
|CSDMS meeting abstract=Numerical simulation of fluvial morphodynamic processes can identify important dynamics at time and space scales difficult to observe in the field. However, simulations involving large spatial scales and/or the long timescales characteristic of morphodynamic processes are often untenable due to long simulation times. The morphological acceleration factor (morfac) applies a scalar multiplier to the sediment continuity equation, and is often applied in morphodynamic simulations to reduce computational time. While the use of morfac in coastal simulations is relatively common, its applicability in field-scale fluvial models is generally confined to steady-flow simulations over reach-scale spatial domains. Here we explore the viability of using morfac to simulate large-scale, long-term morphodynamics in a gravel-bed river. Using Delft3D to simulate a 60-day period with a significant discharge event in the Nooksack River, Washington, we systematically adjust morfac values (ranging from 5 to 20) to compare with a baseline condition of no acceleration. Model results suggest that morfac based modification of the  inflow hydrograph time-series significantly alters downstream flood wave propagation. Higher morfac values result in greater flood-wave attenuation and lower celerity, reducing the morphological impact at locations further downstream. In general, relative error compared to the baseline increases farther downstream, due to this altered flood-wave propagation. Furthermore, even for the lowest morfac values absolute cumulative volume change errors are on the order of 10%, indicating that the use of morfac in fluvial simulations is best restricted to short-term and/or smaller-scale modeling efforts. Funded by the National Science Foundation.
|CSDMS meeting abstract=Numerical simulation of fluvial morphodynamic processes can identify important dynamics at time and space scales difficult to observe in the field. However, simulations involving large spatial scales and/or the long timescales characteristic of morphodynamic processes are often untenable due to long simulation times. The morphological acceleration factor (morfac) applies a scalar multiplier to the sediment continuity equation, and is often applied in morphodynamic simulations to reduce computational time. While the use of morfac in coastal simulations is relatively common, its applicability in field-scale fluvial models is generally confined to steady-flow simulations over reach-scale spatial domains. Here we explore the viability of using morfac to simulate large-scale, long-term morphodynamics in a gravel-bed river. Using Delft3D to simulate a 60-day period with a significant discharge event in the Nooksack River, Washington, we systematically adjust morfac values (ranging from 5 to 20) to compare with a baseline condition of no acceleration. Model results suggest that morfac based modification of the  inflow hydrograph time-series significantly alters downstream flood wave propagation. Higher morfac values result in greater flood-wave attenuation and lower celerity, reducing the morphological impact at locations further downstream. In general, relative error compared to the baseline increases farther downstream, due to this altered flood-wave propagation. Furthermore, even for the lowest morfac values absolute cumulative volume change errors are on the order of 10%, indicating that the use of morfac in fluvial simulations is best restricted to short-term and/or smaller-scale modeling efforts. Funded by the National Science Foundation.
|CSDMS meeting posterPDF=Jacob_Morgan_CSDMS_Conference_Poster_final.pdf
|CSDMS meeting posterPNG=Jacob_Morgan_CSDMS_Conference_Poster_final.png
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Latest revision as of 17:58, 29 May 2019





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The efficacy of using a morphological acceleration factor to simulate large-scale and long-term fluvial morphodynamics

Jacob Morgan, University of Washington Seattle Washington, United States. jamor@uw.edu
Nirnimesh Kumar, University of Washington Seattle Washington, United States. nirni@uw.edu
Alexander Horner-Devine, University of Washington Seattle Washington, United States. ahr@uw.edu
Shelby Ahrendt, University of Washington Seattle Washington, United States. sahrendt@uw.edu
Erkan Istanbulluoglu, University of Washington Seattle Washington, United States. erkani@uw.edu
Christina Bandaragoda, University of Washington Seattle Washington, United States. cband@uw.edu


Jacob Morgan CSDMS Conference Poster final.png

Numerical simulation of fluvial morphodynamic processes can identify important dynamics at time and space scales difficult to observe in the field. However, simulations involving large spatial scales and/or the long timescales characteristic of morphodynamic processes are often untenable due to long simulation times. The morphological acceleration factor (morfac) applies a scalar multiplier to the sediment continuity equation, and is often applied in morphodynamic simulations to reduce computational time. While the use of morfac in coastal simulations is relatively common, its applicability in field-scale fluvial models is generally confined to steady-flow simulations over reach-scale spatial domains. Here we explore the viability of using morfac to simulate large-scale, long-term morphodynamics in a gravel-bed river. Using Delft3D to simulate a 60-day period with a significant discharge event in the Nooksack River, Washington, we systematically adjust morfac values (ranging from 5 to 20) to compare with a baseline condition of no acceleration. Model results suggest that morfac based modification of the inflow hydrograph time-series significantly alters downstream flood wave propagation. Higher morfac values result in greater flood-wave attenuation and lower celerity, reducing the morphological impact at locations further downstream. In general, relative error compared to the baseline increases farther downstream, due to this altered flood-wave propagation. Furthermore, even for the lowest morfac values absolute cumulative volume change errors are on the order of 10%, indicating that the use of morfac in fluvial simulations is best restricted to short-term and/or smaller-scale modeling efforts. Funded by the National Science Foundation.