Decadal‐scale impacts of changing mangrove extent on hydrodynamics and sediment transport in a quiescent, mesotidal estuary

Abstract. In addition to ice and water, glaciers expel sediment. As a result, changing glacier dynamics and melt will result in changes to glacier erosion and sediment discharge, which can impact the landscape surrounding retreating glaciers, as well as communities and ecosystems downstream. To date, the available models of subglacial sediment transport on the sub-hourly to decadal-scale exist in one dimension, usually along a glacier's flow line. Such models have proven useful in describing the formation of landforms, the impact of sediment transport on glacier dynamics, the interactions between climate, glacier dynamics, and erosion. However, because of the large role of sediment connectivity in determining sediment discharge, the geoscience community needs modeling frameworks that describe subglacial sediment discharge in two spatial dimensions over time. Here, we present SUGSET_2D, a numerical model that evolves a two-dimensional subglacial till layer in response to the erosion of bedrock and changing sediment transport conditions below the glacier. Experiments employed on test cases of synthetic ice sheets and alpine glaciers demonstrate the heterogeneity in sediment transport across a glacier's bed. Furthermore, the experiments show the non-linear increase in sediment discharge following increased glacier melt. Lastly, we apply the model to Griesgletscher in the Swiss Alps where we use a parameter search to test model outputs against annual observations of sediment discharge measured from the glacier. The model captures the glacier's inter-annual variability and quantities of sediment discharge. Furthermore, the model's capacity to represent the data depends greatly on the grain size of sediment. Smaller sediment sizes allow sediment transport to occur in regions of the bed with reduced water flow and channel size, effectively increasing sediment connectivity into the main channels. Model outputs from the three test-cases together show the importance of considering heterogeneities in water discharge and sediment availability in two dimensions.

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SPATIAL EXTENT AND VOLUME OF SAND ON THE UPPER SHOREFACE OF THE GLACIATED RHODE ISLAND SOUTH SHORE; RELATIONSHIP TO DECADAL SCALE SHORELINE CHANGE AND LONGSHORE SEDIMENT TRANSPORT

10.1130/abs/2017am-299022 ◽

2017 ◽

Author(s):

Bryan A. Oakley ◽

◽

Cody J. Murphy ◽

Robert J. Hollis

Keyword(s):

Sediment Transport ◽

Rhode Island ◽

Shoreline Change ◽

Spatial Extent ◽

Longshore Sediment Transport ◽

Decadal Scale ◽

South Shore

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Modelling braided river morphodynamics using a particle travel length framework

Earth Surface Dynamics ◽

10.5194/esurf-7-247-2019 ◽

2019 ◽

Vol 7 (1) ◽

pp. 247-274 ◽

Cited By ~ 2

Author(s):

Alan Kasprak ◽

James Brasington ◽

Konrad Hafen ◽

Richard D. Williams ◽

Joseph M. Wheaton

Keyword(s):

Sediment Transport ◽

Path Length ◽

Numerical Models ◽

Hybrid Approach ◽

Length Distribution ◽

Transport Processes ◽

Model Verification ◽

Event Scale ◽

Volumetric Assessment ◽

Decadal Scale

Abstract. Numerical models that predict channel evolution are an essential tool for investigating processes that occur over timescales which render field observation intractable. The current generation of morphodynamic models, however, either oversimplify the relevant physical processes or, in the case of more physically complete codes based on computational fluid dynamics (CFD), have computational overheads that severely restrict the space–time scope of their application. Here we present a new, open-source, hybrid approach that seeks to reconcile these modelling philosophies. This framework combines steady-state, two-dimensional CFD hydraulics with a rule-based sediment transport algorithm to predict particle mobility and transport paths which are used to route sediment and evolve the bed topography. Data from two contrasting natural braided rivers (Rees, New Zealand, and Feshie, United Kingdom) were used for model verification, incorporating reach-scale quantitative morphological change budgets and volumetric assessment of different braiding mechanisms. The model was able to simulate 8 of the 10 empirically observed braiding mechanisms from the parameterized bed erosion, sediment transport, and deposition. Representation of bank erosion and bar edge trimming necessitated the inclusion of a lateral channel migration algorithm. Comparisons between simulations based on steady effective discharge versus event hydrographs discretized into a series of model runs were found to only marginally increase the predicted volumetric change, with greater deposition offsetting erosion. A decadal-scale simulation indicates that accurate prediction of event-scale scour depth and subsequent deposition present a methodological challenge because the predicted pattern of deposition may never “catch up” to erosion if a simple path-length distribution is employed, thus resulting in channel over-scouring. It may thus be necessary to augment path-length distributions to preferentially deposit material in certain geomorphic units. We anticipate that the model presented here will be used as a modular framework to explore the effect of different process representations, and as a learning tool designed to reveal the relative importance of geomorphic transport processes in rivers at multiple timescales.

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