River relocation is the diversion of a river into an entirely new channel for part of their length (often called river diversions). Relocations have been common through history and have been carried out for a wide range of purposes, but most commonly to construct infrastructure and for mining. However, they have not been considered as a specific category of anthropogenic channel change. Relocated channels present a consistent set of physical and ecological challenges, often related to accelerated erosion and deposition. We present a new classification of river relocation, and present a series of case studies that highlight some of the key issues with river relocation construction and performance. Primary changes to the channel dimensions and materials, alongside changes to flow velocity or channel capacity, can lead to a consistent set of problems, and lead to further secondary and tertiary issues, such as heightened erosion or deposition, hanging tributaries, vegetation loss, water quality issues, and associated ecological impacts. Occasionally, relocated channels can suffer engineering failure, such as overtopping or complete channel collapse during floods. Older river relocation channels were constructed to minimise cost and carry large floods, and were straight and trapezoidal. In some countries, modern relocated channels represent an exciting new challenge in that they are now designed to replicate natural rivers, the success of which depends on understanding the characteristics, heterogeneity, and mechanisms at work within the natural channel. We discuss shortcomings in current practice for river relocation and highlight areas for future research for successful rehabilitation of relocated rivers.

Arid and semi-arid regions typically lack high-resolution river gauging data causing difficulties in understanding rainfall-runoff patterns. A common predictive method for discharge estimation within ungauged catchments is regional flood frequency estimation (RFFE), deriving peak discharge estimates from similar, gauged catchments and applying them to the catchment of interest. The majority of RFFE equations are developed for larger catchments where flow events may be larger and of greater interest. We test a series of RFFE methods derived for the Pilbara region, applying them to new ungauged small catchments under 10 km². Rainfall values are derived from a guideline Australian design rainfall database, Australian Rainfall and Runoff 2019 (ARR2019) which was recently updated with an additional 30 years of rainfall data. RFFE equations are compared to a direct rainfall model to evaluate their performance within small catchments, identifying key limitations and considerations when modelling small headwater catchments.

There are numerous situations where engineers and managers need to estimate flow resistance (roughness) in natural channels. Most estimates of roughness in small streams come from humid areas. Ephemeral streams in arid and semi-arid areas have different morphology and vegetation that leads to different roughness characteristics, but roughness in this class of stream has seldom been studied. A lack of high-resolution spatial data hinders our understanding of channel form and vegetation composition. High resolution structure-from-motion (SfM)-derived point clouds allow us to estimate channel boundary roughness and quantify the influence of vegetation during bankfull flows. These point clouds show individual plants at centimetre accuracy. Firstly, a semi-supervised machine learning procedure called CANUPO was used to identify and map key geomorphic features within a series of natural channels in the Pilbara region of Western Australia. Secondly, we described the variation within these reaches and the contribution of geomorphic forms and vegetation to the overall in-channel roughness. Channel types are divided into five reach types based on presence and absence of geomorphic forms: bedrock; alluvial single channel (≥cobble or sand dominated); alluvial multithread; composed of either nascent barforms or more established; stable alluvial islands. Using this reach classification as a guide, we present estimates of Manning’s roughness within these channels drawing on an examination of 650 cross sections. The contribution of in-channel vegetation toward increasing channel roughness was investigated at bankfull flow conditions for a subset of reaches. Roughness within these channels is highly variable and established in-channel vegetation can provide between a 35–55% increase in total channel roughness across all channel types. This contribution is likely higher in shallow flows and identifies the importance of integrating vegetation and geomorphic features into restorative practices for these headwater channels. These results also guide Manning’s selection for these semi-arid river systems and contribute to the vegetation-roughness literature within a relatively understudied region.

Sediment dynamics and rates of landscape denudation in dryland regions are difficult to quantify due to long residence times of sediment on hillslopes and floodplains, often exceeding millions of years. Such extended durations complicate the interpretation of single cosmogenic nuclide analyses. This study applies paired ¹⁰Be and ²⁶Al measurements in detrital samples to constrain basin‐wide denudation rates and sediment fluxes within the semi‐arid Upper Fortescue catchment, located in the Pilbara, northwestern Australia. Morphometric data, lithology and dual cosmogenic nuclide concentrations are integrated to quantify long‐term basin‐wide denudation rates and evaluate first‐order controls on sediment production, transport and catchment evolution. A stepwise series of corrections were conducted for topographic shielding, lithology and apparent sediment burial.Corrected nuclide concentrations yield basin denudation rates in the Upper Fortescue catchment that range from 0.83 to 3.02 m/Ma. These values are comparable to channel bedrock rates (2.5 ± 0.8 m/Ma; n = 4) and moderately higher than estimates from mesa summits and alluvial fan surfaces (0.8 ± 0.6 m/Ma; n = 13) previously derived from ⁵³Mn measurements. Nine of eleven detrital samples exhibit ²⁶Al/¹⁰Be ratios between 4.7 and 5.8, lower than the nominal production ratio of 6.75, indicating that sediments must have experienced a complex exposure history. Two conceptual scenarios are proposed to explain these ratios: (a) extended burial in colluvium or channel sediments lasting several hundred thousand years, and/or (b) complex exposure as a result of production rate attenuation at depth in slowly eroding (<5 m/Ma) bedrock, when sub‐surface rock become exposed, probably through spalling of large meter‐sized blocks from vertical cliff surfaces along escarpments and gorges, ubiquitous in the region. In scenario (b), most of our data are explained by materials being sourced from the average depth of 0.5 to 1 m. However, progressive downstream transport of channel sediments increases the likelihood of storage at shallow depth for a prolonged period in riverbanks, colluvium and floodplains. Field evidence combined with cosmogenic nuclide data supports a hybrid model involving both scenarios. These findings demonstrate the effectiveness of dual‐nuclide analysis in quantifying long‐term catchment‐scale denudation and provide new insights into sediment source‐to‐sink processes in arid landscapes.