Development of ST:REAM: a reach‐based stream power balance approach for predicting alluvial river channel adjustment

Abstract

River channel sediment dynamics are important in integrated catchment management because changes in channel morphology resulting from sediment transfer have important implications for many river functions. However, application of existing approaches that account for catchment‐scale sediment dynamics has been limited, largely due to the difficulty in obtaining data necessary to support them. It is within this context that this study develops a new, reach‐based, stream power balance approach for predicting river channel adjustment. The new approach, named ST:REAM (sediment transport: reach equilibrium assessment method), is based upon calculations of unit bed area stream power (ω) derived from remotely sensed slope, width and discharge datasets. ST:REAM applies a zonation algorithm to values of ω that are spaced every 50 m along the catchment network in order to divide the branches of the network up into relatively homogenous reaches. ST:REAM then compares each reach's ω value with the ω of its upstream neighbour in order to predict whether or not the reach is likely to be either erosion dominated or deposition dominated. The paper describes the application of ST:REAM to the River Taff in South Wales, UK. This test study demonstrated that ST:REAM can be rapidly applied using remotely sensed data that are available across many river catchments and that ST:REAM correctly predicted the status of 87.5% of sites within the Taff catchment that field observations had defined as being either erosion or deposition dominated. However, there are currently a number of factors that limit the usefulness of ST:REAM, including inconsistent performance and the need for additional, resource intensive, data to be collected to both calibrate the model and aid interpretation of its results. Copyright © 2014 John Wiley & Sons, Ltd.

Quantifying River Channel Stability at the Basin Scale

“…One such approach to emerge is the Stream Reach Equilibrium Assessment Method (ST:REAM) of Parker et al [118], where specific stream power is applied as an index of sediment discharge and balances between adjacent reaches indicate predominant sediment transporting behaviour. In ST:REAM, a single reference flow is used in the stream power calculation, corresponding to the Flood Estimation Handbook (FEH) index flood (with return period of two years) based on the network of flow gauging stations in England and Wales [119].…”

“…While Parker et al [118] reported strong correspondence between ratios of specific stream power and the sequence of erosion-or deposition-dominated reaches in the River Taff, South Wales, UK, four significant issues remain as potential limitations:…”

“…The global zonation scheme of Gill [137], for example, is an aggregation routine based on analysis of variance which iteratively breaks a sequence of values into zones that are as internally homogeneous and as distinct as possible from adjacent zones (for a summary, see [138]). The latter method has been used to characterise reach scale behaviour in planform dynamics in the lower Mississippi River [139], as criteria to identify functional reach boundaries in the ST:REAM approach of Parker et al [118,140] and is employed here in the case study. These algorithms thus hold considerable potential for demarcating reaches of similar energy status based on notable breaks in the downstream sequence of AGE.…”

“…The employment of flow duration curves in the energy auditing methodology intrinsic to Equation (7) represents a marked difference with other approaches that use single, representative discharges derived from either regional expressions (e.g., [2,116,120,184]) or broad hydrological models (e.g., [118,123,125]). Indeed, Biron et al [126] considered the weakest area in most stream power mapping approaches to be the single, regional-based estimation of bankfull discharge.…”

“…Despite the coarse resolution of the datasets, though, reasonable correlations were made with observed reaches in two UK gravel bed rivers classified as predominantly erosional, transporting and depositional. Thresholds of specific stream power differential were adopted, differing from the stream power ratio method of Parker et al [118]. However, total stream power (per unit length) was also considered and acknowledged as representing the total energy available to perform geomorphological work, shape the channel and control reach-scale sediment budgets, whereas specific stream power was considered to relate more to localised unit load sediment flux.…”