Quantifying the level of erosion-induced hazards on tidal riverbanks

Abstract

One of the most damaging and costly geoengineering hazards is riverbank erosion. This study aims to comprehensively determining and mapping hazard Levels of the riverbank subjected to erosion, along the tidal Shatt al Arab River, as a case study, southern Iraq. This research employs hydrological, sedimentological and geotechnical measurements to analysis the susceptibility level of the riverbank's stability. The ratio between the ebb and flood shear stress and the soil bank materials' critical shear stress was suggested as a practical way to comprehensively determine instability levels against erosion. Accordingly, the results showed that the southern and central stretches of the river have hazardous (<1.0) or critical (between 1.0 and 2.0) states of the shear stress ratio, while the northern stretch is in a stable state, typically ranging between 2.0 and 3.0 but may exceed 4.0.

The northern river stretch, where soil layers have less susceptibility to erosion, corresponded to no change in the meanders (no-lateral migration indicated from the satellite imagery data) over the 48-year interval 1972–2020. The northern part of the river has stable conditions on the riverbanks and are gaining soil at a slight deposition rate of about 0.5 ​m/yr. In comparison, the southern river part showed that the meanders most likely agreed with the satellite imagery data which were prone to erosional processes and loss of bank materials.

It suggests that the shear stress ratio is a key to practically identify erosion-induced bank levels of tidal rivers and it could be used to develop strategies for mitigating the problem. The assessment of riverbank instability levels using the ratio of critical soil shear stress to fluid shear stress is a comprehensive, plausible way to better understand the susceptibility of tidal rivers.