Scale-dependence of lithological control on topography: Bedrock channel geometry and catchment morphometry in western Scotland

We propose that a scale-dependent topographic signature of erodibility arises due to fluvial and glacial erosion acting on different parts of the landscape at different times. For 14 catchments in western Scotland, we define three levels of substrate erodibility in order of decreasing resistance: quartzite rocks, nonquartzite rocks, and zones of fault-related fracture. Then, using digital topographic and planimetric data coupled with field measurements, we identify regression based scaling relationships between substrate erodibility and morphometric parameters at two spatial scales. Catchment-scale morphometry shows a weak to variable relationship with substrate metrics overall. Erodibility can be inferred from catchment steepness indices (i.e., channel steepness index and relief ratio), but the existence of multiple exceptions could confound a more general application of this approach. Nonetheless, major valley troughs trace fault zones and nonquartzite rocks, leaving much of the higher and steeper ground formed in quartzite. At the reach scale, bedrock channel slope is far more sensitive to substrate erodibility than is channel width. Quartzite outcrops steepen bedrock channels by a factor of 1.5–6.0, and in terms of unit stream power, channels increase their erosional capacity by a factor of 2.7–3.5. Yet only 4%–13% of this increase is due to channel narrowing. Based on a large data set of bedrock channel width (n = 5825) from four rivers, we find that width scales with drainage area (in m<sup>2</sup>) as W = 0.01A<sup>0.28</sup>. Our results are consistent with the view that width-area scaling is similar in all single-thread rivers subject to transport-limited conditions but that for increasingly sediment supply limited settings, erosional thresholds at the channel boundary are the key determinants of bedrock channel width

Prediction of Storm-Wise Soil Erosion in Dryland Farming using a Hillslope Erosion Model

Prediction of storm wise soil erosion and sediment yield is very important, especially in arid and semiarid regions due to small numbers and high intensity of rainfall. Sometimes inappropriate use of the model causes very high or low estimate. However, evaluation of soil erosion by existing models is needed as an important tool for managerial purposes in designation proper water and soil conservation technique. The present study aimed to assess the applicability of Hillslope Erosion Model (HEM) as one of the newest erosion models for prediction of storm-wise sediment yield in Khosbijan Research Center with dryland treatment by using soil erosion standard plots. In order to run the model, runoff depth, vegetation cover density, land surface cover, soil texture, slope steepness and length were determined for 16 storm events. The results showed that the uncalibrated HEM didn’t simulate the observed sediment yields, properly. Calibration of soil erodibility parameter between 0.2 – 1 and developing regression between observed and estimated data indicated that the model could successfully predict the soil erosion rate with determination coefficient of 0.91. These findings indicate that calibration of erodibility factor and regression between observed and estimated could improve storm-wise sediment yield prediction using HEM

KINEROS2-AGWA: Model Use, Calibration, and Validation

KINEROS (KINematic runoff and EROSion) originated in the 1960s as a distributed event-based model that conceptualizes a watershed as a cascade of overland flow model elements that flow into trapezoidal channel model elements. KINEROS was one of the first widely available watershed models that interactively coupled a finite difference approximation of the kinematic overland flow equations to a physically based infiltration model. Development and improvement of KINEROS continued from the 1960s on a variety of projects for a range of purposes, which has resulted in a suite of KINEROS-based modeling tools. This article focuses on KINEROS2 (K2), a spatially distributed, event-based watershed rainfall-runoff and erosion model, and the companion ArcGIS-based Automated Geospatial Watershed Assessment (AGWA) tool. AGWA automates the time-consuming tasks of watershed delineation into distributed model elements and initial parameterization of these elements using commonly available, national GIS data layers. A variety of approaches have been used to calibrate and validate K2 successfully across a relatively broad range of applications (e.g., urbanization, pre- and post-fire, hillslope erosion, erosion from roads, runoff and recharge, and manure transport). The case studies presented in this article (1) compare lumped to stepwise calibration and validation of runoff and sediment at plot, hillslope, and small watershed scales; and (2) demonstrate an uncalibrated application to address relative change in watershed response to wildfire

Gully and Stream Bank Toolbox. A technical guide for gully and stream bank erosion control programs in Great Barrier Reef catchments

This Toolbox is a guide to targeting, designing and implementing gully and stream bank erosion control activities in Great Barrier Reef (GBR) catchments. This third edition builds on 7 years of implementing these activities in multiple programs and it aims to inform the ongoing efforts to reduce the amount of fine sediment and associated nutrients delivered to the GBR lagoon. Sub‑soil erosion, predominantly from gullies and stream banks, contributes the vast bulk of the fine sediment load delivered to the GBR. The large area and extensive erosion in GBR catchments, and the limited resources available, make it important for erosion control to be targeted to cost‑effective sites and implemented using best practice based on best available information. Landholder support and site maintenance increase the likelihood that sediment reductions will persist over the long term

Cost-effectiveness of changing land management practices in sugarcane and grazing to obtain water quality improvements in the Great Barrier Reef: Evaluation and synthesises of existing knowledge

This report aims to shape future assessments of cost-effectiveness and profitability of practice change within the Paddock to Reef Program for improved Great Barrier Reef (GBR) outcomes. A framework is provided to ensure that costs are more reconcilable and comparative. This will assist with ensuring the best return on investment is received for future government funding programs designed to address GBR water quality. The report evaluates and synthesises peer reviewed and published research on cost-effectiveness and profitability of changing land management practices in sugarcane and grazing land production systems for water quality improvements in catchments adjacent to the Great Barrier Reef. Methodological approaches to cost-effectiveness, key determinants of cost, assumptions and limitations in bio-physical modelling, and profitability in the literature have all been examined. The scope of the literature search included all grey and published literature on international, national, and Great Barrier Reef studies on paddock/property, region/catchment, and country levels

Using high-resolution topography for spatial prioritisation of gully erosion management across catchments of the Great Barrier Reef, Australia

The Great Barrier Reef (GBR) running along ~2 000km of the north-eastern coast of Australia is a UNESCO World Heritage site and is the largest living structure on Earth. The GBR is at the forefront of environmental issues currently faced by Australia, with significant economic, environmental, social, and cultural value. Terrigenous fine sediment affects water quality in the GBR and contributes to the degradation of significant marine environments. Gully erosion is believed to be an important contributor of this fine sediment, and this has garnered recent attention from the Australian Government. A key challenge to managing gully erosion across catchments of the GBR is the large scale of the combined area (>400 000 km2). Recent advances in Light Detection and Ranging (LiDAR) have enabled generation of high-resolution (~1 m) digital elevation models (DEMs) over large areas. Over recent years airborne LiDAR data captures have covered many areas of the GBR catchments, with ~50 000 km2 of topography data with a spatial resolution of 1 m or finer. This newly available source of high-resolution data presents an opportunity to map and predict locations of gully erosion across large areas, reducing the need for time-consuming fieldwork. However, there is a need for further development of suitable methods to exploit this data. The core aim of this PhD has been to develop a set of tools and algorithms for using high-resolution topography data to map gullies and areas susceptible to future gully erosion. Novel analysis methods were developed into open-source computer programs with a general focus on creating resources to assist researchers and practitioners managing and assessing gully erosion over large areas. The overall approach is split into to two broad categories of analysis. The first focuses on gully management at small scales (tens of square kilometres), and the second focuses on large scales (hundreds to thousands of square kilometres). The algorithms developed from each of the two halves are designed to work in unison to prioritise gully erosion management first at large scales and subsequently at small scales. This PhD has developed and assessed novel methods for using high-resolution topography data to map and predict gully erosion across catchments of the GBR. A core focus has been on proposing 'standard' methods for computing the required inputs for topographic models of gully occurrence in the landscape. The broader goal of this was to help move the field closer to a set of tools that allow researchers to readily compare model results between landscapes and regions free of bias introduced by variations in sampling procedures. This work has highlighted the potential benefit of using high-resolution topography, particularly airborne LiDAR, but that consistency with methodologies is key to enabling comparisons across landscapes. The methods developed also have applications to other environments, particularly semi-arid regions, and have all been developed in open-source programming languages to help facilitate adoption. Results from applying two different topographic models of gullies showed that land clearing and a transition from natural forests to agricultural landscapes has likely led to increased gullying across catchments of the GBR. This finding is consistent with other studies globally and provides important context for gully management priorities in this region

Measuring, modelling and managing gully erosion at large scales: A state of the art

Soil erosion is generally recognized as the dominant process of land degradation. The formation and expansion of gullies is often a highly significant process of soil erosion. However, our ability to assess and simulate gully erosion and its impacts remains very limited. This is especially so at regional to continental scales. As a result, gullying is often overlooked in policies and land and catchment management strategies. Nevertheless, significant progress has been made over the past decades. Based on a review of >590 scientific articles and policy documents, we provide a state-of-the-art on our ability to monitor, model and manage gully erosion at regional to continental scales. In this review we discuss the relevance and need of assessing gully erosion at regional to continental scales (Section 1); current methods to monitor gully erosion as well as pitfalls and opportunities to apply them at larger scales (section 2); field-based gully erosion research conducted in Europe and European Russia (section 3); model approaches to simulate gully erosion and its contribution to catchment sediment yields at large scales (section 4); data products that can be used for such simulations (section 5); and currently existing policy tools and needs to address the problem of gully erosion (section 6). Section 7 formulates a series of recommendations for further research and policy development, based on this review. While several of these sections have a strong focus on Europe, most of our findings and recommendations are of global significance.info:eu-repo/semantics/publishedVersio

‘Breaking New Ground’; An investigation into coseismic ground cracking following the 2016 Mw 7.8 earthquake near Kaikoura, New Zealand

Seismic shaking can cause landsliding throughout mountainous topography. Posing a direct hazard to the people and infrastructure that occupy these environments, landsliding receives considerable attention from the scientific community. However, few studies have detailed and analysed another form of earthquake-induced damage – ground cracks. Cracks could be a potential indicator of incipient landsliding and/or a surface expression of the retention of damage by hillslopes. Existing damage makes hillslopes more vulnerable to future failure. As such, ground cracking poses a lingering hazard presenting a need to better understand it – in particular its geomorphological characteristics and most influential controlling factors, and therefore how it can be detected/modelled. In 2016 the Mw 7.8 Kaikoura earthquake in New Zealand resulted in extensive ground cracking, providing an ideal case study. A ground crack inventory was digitally compiled using visual interpretation of post-event aerial photography. A detection attempt using a post-event digital terrain model (DTM) to semi-automatically extract cracks was unsuccessful. However, comparing this with an attempt using higher-resolution sample data emphasizes the necessity to consider the interdependence between feature scale and data resolution when attempting to detect/analyse. Feature analysis found that cracks are preferentially 7 m (~3-8 m) in length. Lack of small features may be due to minimum strain thresholds and strain accumulation. Larger cracks have likely developed into landsliding. Both offer new insight into internal hillslope forcing. Cracks preferentially form in a slope perpendicular direction, indicating a topographic control on propagation. Further potential controls were statistically analysed using Fuzzy Logic, which then informed a spatial prediction. The most influential control is proximity to landsliding, suggesting that in most cases cracking is an expression of incipient landsliding. Cracking preferentially occurs at ridgetop locations and on hillslopes facing the source of shaking. The latter is the inverse of behaviour exhibited by landsliding, highlighting the interdependence between directional shaking, local slope aspect and normal/shear stress. This conforms to and provides a new novel insight into the topographic site effects theory. Whilst quantitatively unsuccessful, the best performing spatial prediction model showed great promise in locating ground cracks in areas of high hazard, providing a solid foundation for improvement through further research so that eventually models like this can better inform ongoing hazard monitoring

Geomorphological connectivity and sensitivity examined in a recently degraded gravel-bed stream: implications for river-floodplain rehabilitation

The study of river complexity and sensitivity to future human land-use activities and climate change is a fast growing field within the discipline of fluvial geomorphology. Associated with this is a need to improve river rehabilitation and catchment management approach, design and effectiveness. This study aimed to investigate drivers of the recent geomorphological sensitivity of the Baviaanskloof River-floodplain, an upland system in South Africa, by integrating the concepts of geomorphological connectivity and Panarchy. The understanding generated was used to evaluate the approach of the State agency, Working for Wetlands (WfWet), to river-floodplain rehabilitation in the catchment.The concepts of geomorphological connectivity and Panarchy provide useful frameworks for understanding interactions between geomorphological processes and structure across scales of space and time. Geomorphological connectivity explains the degree to which water and sediment is linked in a river landscape, determined by the distribution of erosional and depositional landforms (Brierley et al. 2006; Fryirs et al. 2007a; Fryirs et al. 2007b). Panarchy attempts to explain lagged response to disturbances, non-linear interactions, and sudden shifts in system state, and has been applied largely to ecological systems. Panarchy theory, when combined with the concept of geomorphological connectivity, provides a guiding framework for understanding river complexity in greater depth. The first results chapter of this study investigated river long-term and recent geomorphological history, towards understanding the nature and timing of river geomorphological cycling between erosion and deposition. Optically Stimulated Luminescence dating of alluvial fan and floodplain sedimentary units was conducted, for analysis of river-floodplain long-term history (100s to 1 000s of years). Interviews with 11 local landowners, combined with analysis of historic aerial imagery and river-floodplain topographic surveys, provided a means of describing recent (last few decades) geomorphological dynamics. The results indicated that the Baviaanskloof is naturally a cut- and-fill landscape over scales of several hundred to thousands of years, characterized by the alternation between phases of high fluvial energy and alluvial fan expansion, and low energy conditions associated with floodplain accretion. Recent and widespread river-floodplain degradation was compressed into a short period of approximately 30 years, suggesting that one or more drivers have pushed the system beyond a threshold, resulting in increased water and sediment connectivity. The second results chapter investigated the role of human land-use activities and flooding frequency and magnitude, as drivers of recent river-floodplain degradation. Human impacts were investigated by describing land-use activities for the preceding 80 years, and relating these activities to changes in river-floodplain form and behavior. Temporal trends in flood events of different frequency and magnitude were investigated by analyzing rainfall data, integrated with landowner reports of flood-inducing rainfall magnitudes. The findings indicated that human land-use activities have been an important driver of recent river- floodplain degradation, through the enhancement of water and sediment connectivity across spatial scales of the catchment. Episodic and high magnitude floods synergized with human driven increased connectivity, precipitating stream power and geomorphological threshold breaches, resulting in a shift in river behaviour. The third results chapter investigated the influence of tributary-junction streams and fans on the geomorphological form, behavior and sensitivity of the Baviaanskloof River. Local- scale topographic impacts of tributary fans and streams were described using topographic surveys and geomorphological mapping techniques. Tributary streams form a major control on the behaviour of the river, by influencing the degree of coarse sediment connectivity with the main channel. Although tributary fans buffer the river from disturbances occurring in the wider catchment, they initiate topographic variations along the floodplain, influencing local-scale patterns of deposition and erosion along the river. The main river responds to water and sediment inputs from tributary junction streams by locally adjusting longitudinal slope, maintaining an overall constant slope of 0.0066 m/m. The response of the Baviaanskloof River to tributary junction fans and streams is however variable, and is fashioned by complex interactions between geomorphological and anthropogenic factors. The final two chapters of the thesis evaluate the findings of the study within the context of river-floodplain rehabilitation approaches in South Africa, and within the theoretical, philosophical and methodological context of the research. The first of these two chapters evaluates the approach of the WfWet programme to river-floodplain rehabilitation in the Baviaanskloof. The chapter indicates that the present practice of WfWet is to reinstate a pre-degradation state, which is not suited to the Baviaanskloof River-floodplain, since the river-floodplain has passed a geomorphological threshold, resulting in a new set of interacting processes and landforms. The author presents a conceptual model illustrating the existence of geomorphological adaptive cycles interacting across spatial and temporal scales, thereby attempting to explain a river Panarchy specific to the Baviaanskloof. From this conceptual model, a hierarchical rehabilitation framework, targeting geomorphological processes and structure situated at different spatial and temporal scales of the landscape is suggested. The final chapter discusses the implications of integrating the concepts of geomorphological connectivity and river Panarchy theory in studies of river complexity and sensitivity to geomorphological change. The author suggests that there is scope for further investigation of the application of the two concepts within the discipline of fluvial geomorphology, particularly with regard to developing quantitative approaches to measuring and describing connectivity and Panarchy