Prospects and challenges of simulating river channel response to future climate change

Abstract

Due to the predicted impacts of future climate on hydrology, morphological changes to river channels are expected. Quantifying the magnitudes and rates of future channel change is important for sustainable river channel management. To date, reviews of simulation approaches for investigating river channels and the modelling of environmental change impacts on channel form and process have focused on contemporary process or palaeo perspectives. Hence, herein we review numerical modelling approaches available for reach-scale simulation of future river channels and the predicted in-channel hydro-and morphodynamic changes modelled. We found that despite their widespread availability, hydrodynamic, morphodynamic and cellular models have yet to be used routinely in future in-channel simulations, with cellular models in particular under-represented. Our review shows that predictions of within-channel changes vary greatly between hydro-climatic regions and under contrasting climate change scenarios, mainly due to varying input discharge scenarios; however, increased sediment transport and flood risk are usually predicted. Key challenges in simulating future channel change include representations of external forcing conditions, adequate temporal and spatial scales, transport equations, changing channel materials and lateral erosion; calibration and validation; simulation chains with multiple models; and identification of feedback systems and nonlinearity. Nevertheless, despite these challenges, models with increasing complexity have recently been developed and so there is increasing potential in their application. One-dimensional hydro-and morphodynamic simulations, and cellular models, can be modified to reflect the requirements of future representations, such as grain size properties, whilst there is also now an increasing capability to include a greater quantity of external forcing conditions. Some studies, however, have demonstrated the need to develop twodimensional models for application in centennial-scale studies. We recommend that a wider range of Downloaded from scenarios and the combined effects of multiple external forcing factors should be included, whilst studies are also needed from more hydrologically diverse reaches.

Changes in floodplain inundation under nonstationary hydrology for an adjustable, alluvial river channel

“…Deterministic prediction of channel adjustment is beyond the current reach of our knowledge due to the complex dynamics that characterize alluvial channel change at timescales ranging from a single flood to several years of floods with differing magnitudes and durations. Even the most advanced high-resolution morphodynamic models are currently limited by computational power and theoretical shortcomings extending from our incomplete knowledge of system thresholds, feedback mechanisms, and the spatial and temporal scales over which they are relevant [Asahi et al, 2013;Kasprak, 2015;Lane, 2013;Lotsari et al, 2015;Williams et al, 2016]. As we aim to examine broad relationships between nonstationary flood regimes, channel adjustment, and flood inundation, we take a simpler, stochastic approach.…”

Topographical change caused by moderate and small floods in a gravel bed ephemeral river – a depth-averaged morphodynamic simulation approach

“…For example, at Rambla de la Viuda, large floods have not yet occurred since the beginning of the MLS measurement approaches. As has also been stated earlier (Verhaar et al, 2008;Lotsari et al, 2015), the roughness conditions defined for small discharge events might not be suitable for simulating extreme events. Therefore, the work and refinement of the model will continue, and the applicability of the model for larger floods will be tested, when validation data are available.…”

Continuous prediction of clay‐bed stream erosion in response to climate model output for a small urban watershed

“…There are visual indicators of channel widening evident in reach M3, mainly bank undercutting with signs of mass wasting, pock marks with exposed smooth unweathered clay material. In a review on the prospects and challenges of predicting river change in response to a changing climate, Lotsari, Thorndycraft, and Alho () pose an open question on whether the research community should focus on enhancing multidimensional modelling (example 2D and 3D) or instead work on improving 1D models to include morphodynamic routines. They conclude by proposing an idealized model for future analyses would be 2D, morphodynamic, unsteady, and capable of simulating the century scale.…”