Abstract Accurate measurement of sand and finer suspended sediment concentration profiles in rivers provides essential data for modeling suspended sediment transport. This study advances the application of an in situ laser diffraction instrument to measure the vertical distribution of suspended sediment concentration across multiple size fractions, ranging from clay‐medium silt (<32 μm) to medium sand (250–500 μm), with a level of resolution and accuracy not achievable using traditional sampling techniques. These concentration profiles were used to directly derive Rouse numbers and to compare them with theoretical values calculated from concurrently measured hydraulic parameters. Different hydraulic variables, including mean flow velocity, total and skin‐friction components of shear velocity, flow depth, and energy slope, were used to evaluate theoretical Rouse numbers and determine the scaling factor β. The study used measurements from six gravel‐bed rivers with distinct hydrological and sediment characteristics across New Zealand. Ninety‐nine depth‐integrated and point samples from 13 flood events of varying magnitude were analyzed to calibrate the volumetric concentrations measured by the in situ laser instrument to mass concentrations. New empirical equations for the scaling factor β in the Rouse number formulation were developed using both total and skin‐friction shear velocities, achieving low uncertainty (relative RMSE < 5%). The methodological framework established in this study provides a practical and transferable approach for measuring vertical suspended sediment distributions in rivers with diverse flow and sediment conditions, offering valuable data for improving sediment transport modeling.

The 1987 Edgecumbe earthquake caused vertical displacements of up to 1.3 m along the Rangitaiki River, New Zealand, creating a morphologic disturbance in the form of a knickpoint in the river. Subsequent river surveys identified migration of this knickpoint upstream and general degradation of the river bed. We attempt to simulate this change using a one-dimensional river morphological model. Bed changes in the model show a pattern of progressive profile-smoothing across the earthquake knickpoint, with degradation upstream and aggradation downstream. However, this did not correspond with the observed progressive river degradation both upstream and downstream of the knickpoint. Some of this discrepancy can be attributed to continued settlement post-earthquake, which will be investigated further.

The Holocene evolution of beach, cliff and substrate on an idealized sand/gravel shoreface is investigated using a newly developed numerical model. The model describes a geomorphic system in which a gently sloping alluvial fan composed of sand and gravel is eroded by wave action under stable relative sea level. In this system landward erosion into the sloping surface produces cliffs that increase in height with time. Beneath water level, wave orbital motions impart stress on the seabed, which gradually lowers as a result. Excavation of the alluvial fan, both at the shoreline and in the nearshore, releases sediment that is transported onshore by wave asymmetry, building beaches. With no abrasion of the beach sediment, the beaches build to an elevation and volume that prevents erosion of the backshore, and the system progresses to a steady state where the nearshore has been excavated to closure depth. By contrast, with abrasion of the beach sediment (producing fine material that is assumed to be transported offshore and lost from the system), the beach volume reduces until the beach only provides intermittent protection against backshore erosion, leading to the formation of cliffs which, when they erode during storms, recharge the beach with sediment. In this situation, a translating shoreline develops. Depending on the various rates assumed for abrasion, seafloor lowering and cliff recession, beaches of various sizes and shapes emerge, and these provide a feedback in terms of the frequency of erosion events.

We use two-dimensional physics-based numerical modeling to study multi-decadal evolution of vegetation and morphology under different flow regimes in real-world gravel-bed braided rivers. To assess model realism, we focus on two rivers in Canterbury (New Zealand) that, despite having been subjected to the introduction of similar invasive vegetation species in the last similar to 100 years, show very different trajectories of vegetation presence due to their different flow regimes: the Lower Waitaki River and the Waimakariri River. The former, featuring a naturally damped flow regime-and having experienced further artificial flow damping due to hydropower generation from the 1930s, experienced vegetation encroachment; while the latter, featuring a flashy flow regime, retains an unvegetated braided planform. We propose an innovative calibration and validation procedure to determine an optimal setup of vegetation parameters that allows the model to robustly reproduce the trajectories of both rivers, thereby proving that the model responds sensibly to different hydrological conditions. Then, we isolate the impact of hydropower-related flow regime modifications on vegetation encroachment in the Lower Waitaki by running the calibrated model with a natural flow regime that does not feature the effect of hydropower generation, and find that vegetation encroachment would have happened even without flow alteration, albeit to a milder degree. Finally, we apply to simulation results a conceptual framework based on a synthetic parameter that compares the relative strength of hydrological and vegetation controls, and discuss the use of this parameter as a predictor of vegetation presence across flow regimes. We study how numerical models can predict the amount of vegetation that establishes on the gravelly bed of wide rivers. We focus on two rivers in New Zealand: the Waimakariri River, having frequent and intense floods, and the Lower Waitaki River, with less frequent and intense floods. This milder character of the Waitaki relates to the presence in the river catchment of three natural lakes that store flood flows and release them slowly, and to the additional storage of artificial hydropower reservoirs. Both rivers have been exposed to invasive vegetation that tends to spread on their beds; however, vegetation spread was significantly more pronounced in the Waitaki than in the Waimakariri. First, we find the parameter values that allow the model to reproduce the vegetation changes seen in both rivers. Then, we simulate the vegetation changes that would have happened in the Waitaki had the hydropower reservoirs not been built, finding there would still have been significant vegetation spread. Finally, we interpret the intensity of vegetation spread as depending on the frequency of floods and on the speed of vegetation growth: a higher vegetation presence is found if vegetation grows faster and if the floods are more spaced in time. Calibration and validation on two rivers with same vegetation species but different hydrology ensures model's sensible response and realismNumerical modeling allows quantification of the impact of a hydropower scheme on vegetation encroachment in a braided riverThe ratio between inter-flood period duration and vegetation growth timescale is a key control and predictor of vegetation presence

River planform results from the complex interaction between flow, sediment transport and vegetation, and can evolve following a change in these controls. Disentangling this complex causation path as a preliminary measure to devising restoration measures is not straightforward. We propose a modelling approach that can be used as tool for analysis of observed trajectories and to forecast future behaviours in dam- and vegetation- impacted braided rivers.We focus two iconic braided river cases in New Zealand’s South Island: the Lower Waitaki River and the Waimakariri River. The Waitaki is impacted by the combined effects of exotic vegetation and a hydropower scheme that has altered the flow regime. As the Waitaki River is unable to clear vegetation efficiently, vegetation encroachment has promoted a shift towards a single-thread morphology. In contrast, the more active Waimakariri River, despite having been subjected to similar vegetation, retains a largely unvegetated channel due to its ability to naturally clear vegetation.A two-dimensional physics-based numerical model capable of accounting for the evolution of morphology and vegetation in braided reaches is constructed and applied to the two rivers.Calibration and validation of the vegetation parameter settings, which is critical to obtaining realistic planform styles, is carried out in applications to the two test cases by selecting the parameter values that allow the model to predict vegetation encroachment in the Waitaki and efficient vegetation clearing in the Waimakariri. The model responds sensibly to changes in parameters, showing that more aggressive vegetation types cause a sharper reduction of braiding.The calibrated model is applied to reconstruct planform changes in the Lower Waitaki under a reconstructed natural flow regime, showing that, even in the absence of the hydropower scheme, the river would have suffered from vegetation encroachment due to its naturally steady hydrology.Finally, summary metrics that represent vegetation presence in each model are computed and their dependence on the flood frequency is analysed. We find that vegetation presence across rivers and flow regimes can be explained as a function of the duration of periods of vegetation growth, intervening between floods that cause vegetation removal.

Understanding the physical processes as well as the hydrological and morphological factors that influence channel bank erosion is important for river restoration and the management of the floodplain and associated ecosystems. In this study, we introduced an innovative approach to quantify river bank erosion and its contribution to a reach fine sediment budget by combining repeat bank erosion surveys using a jetboat-mounted LiDAR scanner with concurrent high-frequency suspended sediment load measurements into and out of the surveyed reach. Using this information, we established a sediment budget for a 5.5-km-long study reach of the lower Oreti River, Southland, New Zealand. A total of three surveys were conducted along the study reach to understand changes in the bank erosion contribution to suspended sediment load at different time scales. The first two surveys were separated by a short period of 8 weeks, and the third survey followed 2.5 years later. The measured volumes of fine sediment rendered from bank erosion equated to 25% and 29% of the measured outflowing suspended load over these two inter-survey epochs, respectively. By comparison, the net contribution of measured bank erosion and derived fine sediment deposition on the riverbed to the outflowing suspended load was 12% over the first, shorter epoch and 25% for the second, 2.5-year epoch. These results highlight the important role of in-channel sediment deposition in the variability of net suspended sediment exports from channel reaches experiencing bank erosion. The approach used in this study has a unique capability to accurately monitor bank erosion and obtain high-resolution topography data capturing changes in river banks over different time periods.

In this paper we develop a two-dimensional modelling framework suitable to study the morphological evolution of vegetated braided rivers. The mathematical model features a unisize-sediment morphological model, which includes accounting for bank erosion, and a vegetation model. While these model components had already appeared separately in different contexts, here we improve and tailor them for modelling vegetated braided river dynamics. We implement a numerical solution to this problem in the framework of the pre-existing morphological model GIAMT2D. We devise a hydrograph-splitting technique to avoid excessive run times in the multi-decadal applications needed to appreciate vegetation-driven morphological change. This hydrograph-splitting technique uses the full model to solve for flood periods, while applying a fixed-bed approximation and only updating vegetation density during low-flow periods. Finally, we apply the developed formulation, tools and techniques to simulate an idealised reach of the Lower Waitaki River (Aotearoa – New Zealand), where we reproduce vegetation encroachment and morphological change observed between 1936 and 1964.

Discrete particle dynamics is one of the least understood aspects of river bedload transport, but in situ measurement of stone movement during floods poses a significant technical challenge. A promising approach to address this knowledge gap is to use sensors embedded within stones. Sensors must be waterproof and recoverable after being transported downstream and potentially buried by other sediment. To address this challenge rugged sensors (Kinematic Loggers) were developed for deployment inside stones (ranging in size from cobbles to boulders) during floods. The sensors feature a 9-axis inertial measurement unit, 3-axis high-g accelerometer, 128 MB flash memory, and a 433 MHz LoRa radio transmission module for sensor recovery. The sensors are enclosed in rugged waterproof housings for deployment in extreme conditions (i.e., bedload transport during floods). Novel relay units and drone-based recovery systems were also developed for finding the sensors after field deployments. Firmware to control the sensors and relay units was developed, as well as software for configuring the sensors and an android application for communicating with the sensors via the LoRa radio transmission module. This paper covers the technical development of the sensors, mounting them inside stones, and field recovery tests. Although designed for measurement of coarse bedload transport and particle dynamics during floods, the sensors are equally applicable for deployment in other harsh environments, such as to study landslide and rockfall dynamics.

In this paper, we utilize a numerical morphological simulation approach to study braiding channel dynamics under steady flow. We conduct 11 different runs in a laboratory configuration, with each initial condition featuring a unique small‐amplitude perturbation pattern of the bed topography. From these infinitesimal initial differences, braided channels evolve into patterns that are macroscopically different and unique to each run, thus showing sensitive dependence on the initial condition and hence a chaotic behavior. Leveraging the analogy of braiding and fluid turbulence put forward by Paola (1996), by introducing a Reynolds‐type decomposition of bed elevations into a reference and a fluctuating component we characterize braided channel dynamics through statistics of bed fluctuations. We observe that, over the simulation time frame, braiding is not statistically homogeneous, but is stationary in a spatially averaged sense. We prove that braiding is anisotropic and extract two distinct length scales associated with the correlations of bed fluctuations in the streamwise and cross‐channel direction. We observe that, under the time averaging window that yields stationary braiding, braiding shows hints of ergodic behavior, as the time statistics of one run converge to the ensemble statistics computed across all the other runs.

This paper contributes a field study of suspended sediment transport through aquatic vegetation. The study was run over a 3 month period which was selected to coincide with scheduled weed cutting activities. This provided the opportunity to obtain data points with no vegetation cover, as well as to investigate the effects of weed cutting on Suspended Sediment Concentrations (SSC), particle size distributions and river hydraulics. Aquatic vegetation cover was quantified through remote sensing with Unmanned Aerial Vehicles and biomass estimated from ground truth sampling. SSC was highly dependent on aquatic vegetation abundance, and the distance upstream that had been cleared of aquatic vegetation. The data indicates that fine sediment was being trapped and stored by aquatic vegetation, then likely remobilised after vegetation removal. Investigation of suspended sediment spatial dynamics illustrated changes in particle size distribution due to preferential settling of coarse particles within aquatic vegetation, for example D50 decreased from 36.08 mu m to 15.64 mu m after suspended sediment travelled 304.2 m downstream and passed similar to 3700 kg of aquatic vegetation biomass. Hydraulic resistance in the study reach (parameterized by Manning's n) dropped by over 70% following vegetation cutting. Prior to cutting hydraulic resistance was discharge dependent (likely due to vegetation pronating at higher flows), while post cutting hydraulic resistance was approximately invariant of discharge. Aerial surveying captured interesting changes in aquatic vegetation cover prior to vegetation cutting, where some very dense regions of aquatic vegetation were naturally removed (without any high flow events) leaving behind unvegetated riverbed and fine sediment. The weed cutting boat had a lower impact on SSC than was originally expected, which indicates that it may offer a less damaging solution to aquatic vegetation removal in rivers than some other approaches such as mechanical excavation. This paper contributes valuable field data (which are generally scarce) on the research topic of flow-vegetation-sediment interactions, to supplement laboratory and numerical studies.

Pressures on braided river systems in New Zealand are increasing due to anthropogenic stresses such as demand for irrigation water, braidplain conversion to farmland and invasive vegetation, as well as extreme natural events associated with earthquakes and climate change. These pressures create issues around preserving braided river physical environments and associated ecosystems, and managing hazards such as floods, aggradation and erosion. A need for more robust understanding and quantification of braided river morphodynamic processes underpins many of these issues. Here, we present eight morphodynamic research challenges to service this need. The first four research challenges relate to managing aggradation‐related flooding hazards; the last four address issues stem largely from recent dairy expansion, which has created huge pressure to take land and irrigation water from the alp‐fed braided rivers and to alter flow regimes at their mouths. Hāpua, the freshwater lagoons found where most braided rivers meet the coast, show complex morphodynamic behaviour in response to the interplay of river and coastal processes, and their special ecosystems are sensitive to river flow and sediment load changes. We discuss how physical laboratory experiments and novel numerical modelling can help to understand the morphological processes braided rivers undergo, and we show how those research advances could inform planning and legal decisions to regulate land rights and irrigation water allocation on New Zealand's braidplains. We illustrate these environmental and engineering issues and research challenges with examples from the Kowhai, Waiho, Waiau, Rangitata and Hurunui Rivers. © 2020 John Wiley & Sons, Ltd.

Periphyton (benthic algae) forms the base of the lotic food web but, under particular conditions, can grow to nuisance levels. River managers need to understand under what conditions the rivers might develop nuisance periphyton biomass in order to set water quality and quantity limits and support healthy ecosystems. Factors that promote periphyton growth (e.g., light, temperature, nutrients) and the frequency of flows that remove periphyton (the periphyton removal flow) have long been recognized as primary controls on periphyton abundance. Predicting differences in periphyton removal flows (PRFs) between rivers has remained a challenge. The main objective of this study is to investigate how bed sediment mobility affects periphyton removal and whether it can be used to better predict PRFs at unmonitored sites with acceptable levels of certainty. We calculated the sediment based PRFs at 113 periphyton monitoring sites in rivers of different sizes and different environmental conditions by finding, for a range of particle sizes, the entrainment flow that produced the strongest correlation between periphyton biomass (measured by Chlorophyll a, chl a) and days since the last exceedance of that flow. We then grouped the monitoring sites based on the size of sediment mobile at the PRF and identified a suite of environmental variables that best distinguished these groups using a discriminatory function analysis. We then predicted PRFs at unvisited sites using the same river groupings and associated sediment-based flow metrics. Sediment-based PRFs were able to be identified at 93 of the 113 monitoring sites. Across these sites, the variance in chl a explained by the sediment-based PRF (R-2) ranged from 0.37 to 0.88 and averaged 0.58. 94% of these rivers with periphyton data were successfully discriminated into three periphyton removal flow groups, together with a non-identified group, by including 33 out of 44 tested environmental variables (e.g., temperature, nutrient concentrations, rainfall, width). The groups were then used to predict sediment-based periphyton removal flows for unvisited sites across a broad range of conditions. The value of our analysis lies in the ability to predict a range of sediment-based periphyton removal flows using only channel slope, substrate composition and wetted width. While acknowledging that sediment mobility is only one of several mechanistic controls on periphyton, this finding nonetheless offers a simple means to identify the range of sediment-based periphyton removal flows in a river reach, which can help inform river managers about the potential effects of changes in river flows on periphyton chl a.

Aquatic vegetation, hydraulics and sediment transport have complex interactions that are not yet well understood. These interactions are important for sediment conveyance, sediment sequestration, phasing of sediment delivery from runoff events, and management of ecosystem health in lowland streams. To address this knowledge gap detailed field measurements of sediment transport through natural flexible aquatic vegetation are required to supplement and validate laboratory results. This paper contributes a field study of suspended sediment transport through aquatic vegetation and includes mechanical removal of aquatic vegetation with a weed cutting boat. It also provides methods to quantify vegetation cover through remote sensing with Unmanned Aerial Vehicles (UAVs) and estimate biomass from ground truth sampling. Suspended sediment concentrations were highly dependent on aquatic vegetation abundance, and the distance upstream that had been cleared of aquatic vegetation. When the study reach was fully vegetated (i.e. cover >80%), the maximum recorded SSC was 14.6 g/m (during a fresh with discharge of 2.47 m/s), during weed cutting operations SSC was 76.8 g/m at 0.84 m/s (weedcutting boat 0.5-1 km upstream from study reach), however following weed cutting operations (4.6 km cleared upstream), SSC was 139.0 g/m at a discharge of 1.52 m/s. The data indicates that fine sediment was being sequestered by aquatic vegetation and likely remobilised after vegetation removal. Investigation of suspended sediment spatial dynamics illustrated changes in particle size distribution due to preferential settling of coarse particles within aquatic vegetation. Hydraulic resistance in the study reach (parameterized by Manning’s n) dropped by over 70% following vegetation cutting. Prior to cutting hydraulic resistance was discharge dependent, while post cutting hydraulic resistance was approximately invariant of discharge. Aerial surveying captured interesting changes in aquatic vegetation cover, where some very dense regions of aquatic vegetation were naturally removed leaving behind unvegetated riverbed and fine sediment.

Purpose This study analyses the hysteresis relationship between suspended sediment concentration (SSC) and flow (Q) during runoff events to investigate the effect of hydrological factors and catchment characteristics on suspended sediment dynamics. Methods Continuous records of flow and suspended sediment concentration, proxied by turbidity, collected from 17 catchments across New Zealand with different size, land cover and erosion terrain characteristics were analysed for this purpose. We first classified the hysteresis patterns in terms of their shape and direction during events, then analysed hysteresis indices and related them to event hydrology and catchment characteristics. In total, 1553 events were analysed. Results The results indicate some clear differences between pasture- and forest-dominated catchments, with pasture-dominated catchments having event flow peaks generally lagging the peak of sediment concentration whereas in forest-dominated catchments the opposite occurred. Moreover, pasture catchments typically showed higher ratios of flow-weighted concentration on rising to falling stages of hydrographs compared with largely forested catchments. This shows that the sources of sediment respond faster during flood events in pasture-dominated catchments. A principal component and classification analysis of hydrological and sediment-related variables showed that the main variables controlling the hysteresis patterns within each catchment were flood total runoff and flood duration. Conclusions These results are of immediate value to river management programmes and policies concerned with mitigating suspended sediment delivery to impacted waterways and to developing and testing event-scale catchment-based suspended sediment routing models. Future research could aim to reduce ambiguity in interpreting Q-SSC hysteresis driving factors by statistical analysis of larger datasets spanning more catchments and by using other information streams such as high spatio-temporal resolution sediment tracing.

The river mouth lagoons of New Zealand's gravel-bed braided rivers are highly dynamic, responding to changes in waves and river flows at timescales of hours and days to years. Unlike other freshwater-dominated coastal wetlands and lagoons, they exist along open coasts that are typically retreating with cliffed hinterlands. These lagoons are common on New Zealand's high energy, coarse sediment coastlines and are known locally as ‘hāpua’. This paper employs field observations from the Hurunui hāpua, to investigate the main processes controlling the dynamics of hāpua lagoons. Based on two years of time-lapse imagery, plus concurrent wave, river flow and sea level data an improved conceptual model of lagoon dynamics was developed. The model describes how onshore bar migration of river sourced gravel and sand drives initial constriction/offsetting of the river mouth following floods. It also explains how gravel deposition in the lagoon reduces the threshold flow required to cause primary breach of the barrier opposite the point the river enters the lagoon. Three processes are identified which affect lagoon width: wave overwashing of the gravel barrier narrows the lagoon; migration of the highly dynamic lagoon outlet channel ‘resets’ the barrier position to seaward; and river floods occurring while the outlet channel is offset from the river flush sediment from the lagoon system, eroding its bed and banks. Both processes affecting lagoon widening rely on lagoon outlet channel migration, indicating that outlet channel dynamics are an important control on lagoon size.

This paper reports the morphology of a natural patch of Ranunculus penicillatus and presents high-resolution measurements of flow velocities in its wake using a stereoscopic PIV field measurement system. The patch was 3.80 m long, 1.24 m wide and caused substantial changes to downstream mean velocities and turbulence. Vertical profiles of streamwise mean velocity were not logarithmic and flow was redirected under the positively buoyant canopy, enhancing vertical turbulent mixing in the wake and generating a large region where the velocity covariance u′w′¯ was positive. Turbulent kinetic energy was enhanced downstream from the patch lateral shear layer, but not at the centre of the wake. Spectra downstream from the patch showed that turbulence was neither dominated by fine-scale nor large-scale structures, likely due to the low energy of the flow conditions and lack of a developed vortex street within the measurement domain. Sedimentation was observed at the upstream end of the patch, but not underneath the floating canopy. The methods and results of this work will be useful for planning other in situ studies. Also, the reported data on macrophyte geometry and biometrics will assist with the design of more realistic replicas for use in laboratory studies.

This study advances understanding of the flow dependency of invertebrate drift in rivers and its relevance to drift-feeding fish. Background drift concentration varied spatially and with flow over natural flow recession (lower mid-range to low flow) in a reach of a New Zealand river, largely consistent with passive entrainment. Seven taxonomic groups (dominated by Leptophlebiidae and Chironomidae) exhibited positive drift concentration–flow relationships, and one (sandy/stony-cased caddisflies (Conoesucidae)) exhibited negative relationships. A mechanistic drift transport model accurately predicted the slope, but not y intercept, of the drift concentration–flow relationship for the total drift community that positively responded to flow but performed more poorly at the taxon or size-class level. Partitioning the relative influence of drift entry and dilution revealed that positive drift concentration–flow relationships arose from entry overwhelming dilution with increasing flow. Drift transport models have potential for predicting relative (%) effects of flow change on concentration and rate of drift-prone invertebrates. This paves the way for drift transport models to inform inputs to net rate of energy intake models for drift-feeding fish.

Hysteresis in the relationship between suspended sediment concentration and flow during run-off events is commonly used to inform on sediment sources and hydrological pathways. Less attention, however, has been paid to comparing the water and sediment hydrographs, which provide a more direct appreciation of in-event sediment dynamics and their relationship with the upstream catchment characteristics. The aim of this study is to better understand the catchment and hydrological controls on the phasing of water and sediment discharges during events and, in particular, to explore what controls sediment concentrations late on event recessions. Continuous records of flow and turbidity data (calibrated to suspended sediment concentration) were collected from 17 catchments across New Zealand for this purpose. Relationships between event sediment yield and peak flow showed, as anticipated, higher event sediment loads were generated in pasture compared with forested catchments and were also higher from catchments in more erodible terrain. One novel result was that these differences were greater during smaller, more frequent events, whereas the loads from larger flood events tended to converge between pasture and forest catchments. Another novel result was that event sediment load tends to be evenly split between rising and falling stages of the hydrograph in pasture catchments, but forested catchments yield more of their event loads on flood recessions, probably because of delayed erosion or more sediment sources remote from the channel network. Land cover, distance of the sediment sources from the monitoring site, and size of the catchments control sediment concentrations late on event recession. Pasture-dominated and more erodible catchments show longer sediment recessions and therefore stay dirtier for longer time periods. In addition, the size of previous flood events appeared to control the extent of sediment exhaustion after the flood peaks in some catchments.

The diffusive and nonspecific nature of nonpoint source contaminants such as sediment makes their management and mitigation challenging. Conventional source‐based tracing techniques for sediment simply apportion downstream sediment load to diffuse upstream sources classified by a limited number of source types including underlying rock type, land cover, and/or erosion process. Here, we develop a grid‐based sediment tracing technique that improves the precision of source contribution estimates and enhances the granularity of sediment source maps. We test the proposed technique using source and suspended sediment samples collected from the Emu Creek Catchment (911 km2), south‐east Queensland, Australia. Geochemical tracers were employed to distinguish sediments derived from the heterogenous and complex underlying rock types. Importantly, the proposed technique provided a greater spatial resolution of the sediment sources by assigning sediment contributions into grid sources rather than the area‐specific source types.