Logjams With a Lower Gap: Backwater Rise and Flow Distribution Beneath and Through Logjam Predicted by Two‐Box Momentum Balance
Abstract Logjams with a gap at the bed form naturally in small channels and are used in engineering practice to maintain river connectivity at base flow. Limited understanding of a jam's effect on backwater rise and flow velocity limits assessment of geomorphic and ecological impacts of natural...
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| Format: | Article |
| Language: | English |
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Wiley
2021-08-01
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| Series: | Geophysical Research Letters |
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| Online Access: | https://doi.org/10.1029/2021GL094279 |
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| author | E. Follett I. Schalko H. Nepf |
| author_facet | E. Follett I. Schalko H. Nepf |
| author_sort | E. Follett |
| collection | DOAJ |
| description | Abstract Logjams with a gap at the bed form naturally in small channels and are used in engineering practice to maintain river connectivity at base flow. Limited understanding of a jam's effect on backwater rise and flow velocity limits assessment of geomorphic and ecological impacts of natural logjams, design of river restoration interventions, and representation in flood models. The distribution of flow through and beneath the jam satisfies a two‐box, momentum‐based model constrained by drag generated in the jam, momentum loss in flow through the lower gap, and net pressure force. The model was validated with 68 flume experiments. Backwater rise is predicted from discharge beneath the jam following established models for solid sluice gates. As a result, backwater rise increases with jam resistance, which forces a greater discharge beneath the jam. Below‐jam velocity and Shields parameter increased with ratio of friction coefficient to slope and decreasing gap height. |
| format | Article |
| id | doaj-art-3eabeb660bfe4228b92d1572be3c73b2 |
| institution | OA Journals |
| issn | 0094-8276 1944-8007 |
| language | English |
| publishDate | 2021-08-01 |
| publisher | Wiley |
| record_format | Article |
| series | Geophysical Research Letters |
| spelling | doaj-art-3eabeb660bfe4228b92d1572be3c73b22025-08-20T02:18:54ZengWileyGeophysical Research Letters0094-82761944-80072021-08-014816n/an/a10.1029/2021GL094279Logjams With a Lower Gap: Backwater Rise and Flow Distribution Beneath and Through Logjam Predicted by Two‐Box Momentum BalanceE. Follett0I. Schalko1H. Nepf2Hydro‐environmental Research Centre School of Engineering Cardiff University Cardiff UKLaboratory of Hydraulics, Hydrology and Glaciology (VAW) ETH Zurich Zurich SwitzerlandDepartment of Civil and Environmental Engineering Massachusetts Institute of Technology Cambridge MA USAAbstract Logjams with a gap at the bed form naturally in small channels and are used in engineering practice to maintain river connectivity at base flow. Limited understanding of a jam's effect on backwater rise and flow velocity limits assessment of geomorphic and ecological impacts of natural logjams, design of river restoration interventions, and representation in flood models. The distribution of flow through and beneath the jam satisfies a two‐box, momentum‐based model constrained by drag generated in the jam, momentum loss in flow through the lower gap, and net pressure force. The model was validated with 68 flume experiments. Backwater rise is predicted from discharge beneath the jam following established models for solid sluice gates. As a result, backwater rise increases with jam resistance, which forces a greater discharge beneath the jam. Below‐jam velocity and Shields parameter increased with ratio of friction coefficient to slope and decreasing gap height.https://doi.org/10.1029/2021GL094279logjamlarge woodbackwater risesediment transportnatural flood management |
| spellingShingle | E. Follett I. Schalko H. Nepf Logjams With a Lower Gap: Backwater Rise and Flow Distribution Beneath and Through Logjam Predicted by Two‐Box Momentum Balance Geophysical Research Letters logjam large wood backwater rise sediment transport natural flood management |
| title | Logjams With a Lower Gap: Backwater Rise and Flow Distribution Beneath and Through Logjam Predicted by Two‐Box Momentum Balance |
| title_full | Logjams With a Lower Gap: Backwater Rise and Flow Distribution Beneath and Through Logjam Predicted by Two‐Box Momentum Balance |
| title_fullStr | Logjams With a Lower Gap: Backwater Rise and Flow Distribution Beneath and Through Logjam Predicted by Two‐Box Momentum Balance |
| title_full_unstemmed | Logjams With a Lower Gap: Backwater Rise and Flow Distribution Beneath and Through Logjam Predicted by Two‐Box Momentum Balance |
| title_short | Logjams With a Lower Gap: Backwater Rise and Flow Distribution Beneath and Through Logjam Predicted by Two‐Box Momentum Balance |
| title_sort | logjams with a lower gap backwater rise and flow distribution beneath and through logjam predicted by two box momentum balance |
| topic | logjam large wood backwater rise sediment transport natural flood management |
| url | https://doi.org/10.1029/2021GL094279 |
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