Riverscapes are the integration of terrestrial and aquatic systems from headwaters to estuaries that provide habitat and ecosystem benefits when in good health. However, current riverscape degradation is pervasive, impairing the function and resulting benefits of these systems. Healthy riverscapes are adaptive and some can 'heal' after disturbance with minimal to no human assistance. As riverscape health is threatened, a need exists to address current degradation and understand the potential for riverscape restoration-concisely communicating what comprises healthy riverscapes is essential to direct limited resources and increase efficacy of restoration and conservation efforts. Healthy riverscapes have (i) space to interact within their valley bottom; (ii) natural flow, sediment, and vegetation regimes appropriate to the biophysical setting and river type; and (iii) structural forcing to support diversity and that creates varied residence times for water, sediment, and vegetation. These three principles are grounded in interdisciplinary science and lessons from riverscape scientists and restoration practitioners across the world. Understanding the context, anthropogenic influences, boundary conditions, and legacy effects influencing riverscapes is essential for the appropriate application of these principles in pursuit of achieving riverscape health. Emphasizing a holistic, biogeomorphic view of riverscapes through these principles can guide policies, restoration actions, and monitoring frameworks that ensure that riverscapes remain capable of accommodating and adjusting to disturbances while continuing to support biodiversity and human benefits.This article is categorized under: Water and Life > Conservation, Management, and Awareness

River restoration is key to realising ambitions to improve the biodiversity of rivers and to contribute to natural flood risk management. However, a dearth of detailed, accurate and consistently acquired, long-term topographic monitoring constrains the available evidence base to evaluate the efficacy of different river restoration approaches. Upland gravel-bed river realignment schemes are emblematic of this challenge. Here, the results from monitoring five contemporary upland river restoration sites in Scotland and the North-West of England are presented. The topography of 9 km of restored reaches at Whit Beck, the River Lyvennet, Swindale Beck, Allt Lorgy and the River Nairn was measured for a period of approximately one decade after each river realignment. The full extent of each scheme was surveyed every 1-3 years, with the frequency dependent on the geomorphic dynamism of the scheme. A variety of geomatics technologies were deployed to survey topography including, robotic total stations, RTK-GNSS, Structure-from-Motion photogrammetry, Terrestrial Laser Scanning and Unmanned Aerial Vehicle LiDAR. This unique dataset has enabled geomorphic change to be mapped and annual sediment fluxes to be quantified. Moreover, the high-resolution topographic datasets enable the geomorphic unit development of each scheme to be mapped using the Geomorphic Unit Toolbox (GUT). Together, this dataset enables three questions to be investigated: (i) what is the geomorphic unit composition of restored rivers?; (ii) how does geomorphic unit diversity develop post-restoration; and (iii) what geomorphic mechanisms are sustaining geomorphic unit diversity? We show that different restoration schemes have contrasting geomorphic unit assemblages, which are influenced by sediment supply, scheme constraints, in-channel and riparian wood and vegetation, and intervention through adaptive management approaches. The sediment budget for Swindale Beck exemplifies the trend in total volumetric topographic change through time; change is greater in the first few years following restoration and then declines once the river has adjusted the imposed boundary conditions. Topographic change initially increases the aerial extent of geomorphic units, the aerial extents of erosion and deposition between surveys then become similar and the extent of the active river channel remains approximately constant. Overall, across all schemes, there is declining geomorphic change with time but geomorphic unit, and thus physical habitat, diversity are maintained. These findings provide strong evidence for how physical habitat diversity and quantity have both increased and been maintained as a consequence of river realignment and should underpin efforts to scale up from demonstration sites to catchment-scale restoration efforts.

Despite growing interest in river and catchment restoration, including a focus on nature-based solutions, assessing effectiveness of restoration programmes continues to prove a challenge. The development of the Eddleston Water project, the Scottish Government’s empirical study of the impact of implementing natural flood management measures on flood risk and habitat restoration, provides the opportunity to review restoration monitoring at a strategic and operational level for this long-running catchment restoration programme. The project has implemented an extensive range of restoration measures along the river and across the 69 km2 catchment. This paper reviews the monitoring strategy and assesses both how the monitoring network developed meets its strategic aims and what subsequent changes were made in monitoring design and implementation. Covering hydrology, hydromorphology and ecology, we explore how all three are integrated to provide a comprehensive assessment of restoration success. Lessons to help inform other river rehabilitation monitoring programmes include the importance of a scoping study and capturing the full range of environmental variables pre-restoration; the limitations of BACI designs; and the need to focus integrated monitoring on a process-based framework and impact cascade, whilst also covering the full trajectory of recovery.

The process of interpretation, and the ways in which knowledge builds upon interpretations, has profound implications in scientific and managerial terms. Despite the significance of these issues, geomorphologists typically give scant regard to such deliberations. Geomorphology is not a linear, cause-and-effect science. Inherent complexities and uncertainties prompt perceptions of the process of interpretation in geomorphology as a frustrating form of witchcraft or wizardry — a dark art. Alternatively, acknowledging such challenges recognises the fun to be had in puzzle-solving encounters that apply abductive reasoning to make sense of physical landscapes, seeking to generate knowledge with a reliable evidence base. Carefully crafted approaches to interpretation relate generalised understandings derived from analysis of remotely sensed data with field observations/measurements and local knowledge to support appropriately contextualised place-based applications. In this paper we develop a cognitive approach (Describe-Explain-Predict) to interpret landscapes. Explanation builds upon meaningful description, thereby supporting reliable predictions, in a multiple lines of evidence approach. Interpretation transforms data into knowledge to provide evidence that supports a particular argument. Examples from fluvial geomorphology demonstrate the data-interpretation-knowledge sequence used to analyse river character, behaviour and evolution. Although Big Data and machine learning applications present enormous potential to transform geomorphology into a data-rich, increasingly predictive science, we outline inherent dangers in allowing prescriptive and synthetic tools to do the thinking, as interpreting local differences is an important element of geomorphic enquiry.

Larger‐than‐average grain deposits in gravel bed rivers potentially exert a distinctive influence upon fluvial morphodynamics and flow resistance. They are products of historical contingency, sourced from rare events that supply atypically coarse material. Larger‐than‐average grain lag deposits are emblematic attributes of the Tongariro River, New Zealand. They are deposited on bar edges and heads. Derived from lahar valley floor deposits that subsequently became terraces, these materials are less likely to be reworked across a range of flows compared to other bar material. Conceptual models that consider channel configuration and incorporate distributions of particle mobility and flood flows are necessary to assess the role of larger‐than‐average grain deposits on river morphodynamics.

Bars are key morphological units in river systems, fashioning the sediment regime and bedload transport processes within a reach. Reworking of these features underpins channel adjustment at larger scales, thereby acting as a key determinant of channel stability. Despite their importance to channel evolution, few investigations have acquired spatially continuous data on bar morphology and sediment‐size to investigate bar reworking. To this end, four bars along a 10 km reach of a wandering gravel‐bed river were surveyed with terrestrial laser scanning (TLS), comparing downstream changes in slope, bed material size and channel planform. Detrended standard deviations (σz) were extracted from TLS point clouds and correlated to underlying physically measured median grain‐size (D50), across a greater range of σz values than have hitherto been reported. The resulting linear regression model was used to create a 1 m resolution median grain‐size map. A fusion of airborne LiDAR and optical‐empirical bathymetric mapping was used to develop reach‐scale digital elevation models (DEMs) for rapid two‐dimensional hydraulic modelling using JFlow® software. The ratio of dimensionless shear stress over critical shear stress was calculated for each raster cell to calculate the effectiveness of a range of flood events (2.33–100 year recurrence intervals) to entrain sediment and rework bar units. Results show that multiple bar forming discharges exist, whereby frequent flood flows rework tail and back channel areas, while much larger, less frequent floods are required to mobilise the coarser sediment fraction on bar heads. Valley confinement is shown to exert a primary influence on patterns of bar reworking. Historical aerial photography, hyperscale DEMs and hydraulic modelling are used to explain channel adjustment at the reach scale. The proportion of the bar comprised of more frequently entrained units (tail, back channel, supra‐platform) relative to more static units (bar head) exerts a direct influence upon geomorphic sensitivity. © 2018 John Wiley & Sons, Ltd.

River sensitivity describes the nature and rate of channel adjustments. An approach to analysis of geomorphic river sensitivity outlined in this paper relates potential sensitivity based on the expected capacity of adjustment for a river type to the recent history of channel adjustment. This approach was trialled to assess low, moderate and high geomorphic sensitivity for four different types of river (10 reaches in total) along the Lower Tongariro River, North Island, New Zealand. Building upon the River Styles framework, river types were differentiated based upon valley setting (width and confinement), channel planform, geomorphic unit assemblages and bed material size. From this, the behavioural regime and potential for adjustment (type and extent) were determined. Historical maps and aerial photographs were geo-rectified and the channel planform digitised to assess channel adjustments for each reach from 1928 to 2007. Floodplain width controlled by terraces, exerted a strong influence upon reach scale sensitivity for the partly-confined, wandering, cobble-bed river. Although forced boundaries occur infrequently, the width of the active channel zone is constrained. An unconfined braided river reach directly downstream of the terrace-confined section was the most geomorphically sensitive reach. The channel in this reach adjusted recurrently to sediment inputs that were flushed through more confined, better connected upstream reaches. A meandering, sand-bed river in downstream reaches has exhibited negligible rates of channel migration. However, channel narrowing in this reach and the associated delta indicate that the system is approaching a threshold condition, beyond which channel avulsion is likely to occur. As this would trigger more rapid migration, this reach is considered to be more geomorphically sensitive than analysis of its low migration rate alone would indicate. This demonstrates how sensitivity is fashioned both by the behavioural regime of a reach and flow/sediment input from upstream. The approach to assess geomorphic river sensitivity outlined here could support ‘room to move’ or ‘freedom space’ approaches to river management by relating likely channel adjustments for the type of river under consideration to the area of land that is required to contain ‘natural’ patterns and rates of geomorphic functionality.

The Tongariro Power Development Scheme ( TPDS) is used to regulate flow in the headwaters of the largest catchment on the North Island of New Zealand ( the Waikato). Two small dams, the Rangipo Dam and the Poutu Intake Dam, were constructed in 1973 and 1983. The flow regime of the river is managed to divert freshes into the power scheme, but allows flows larger than 100 m(3) s(-1) to be released, to rework and transport sediment through the catchment. Analysis of aerial photos and maps spanning 1928 to 2007, alongside field measurements, show that there have been few hydrogeomorphic adjustments since dam construction. This includes limited changes to channel geometry, channel planform and bed material organization immediately downstream of the dams. In addition, offsite effects are minimal, both 500 m downstream of each dam, and in the more sensitive, less confined reaches in the lower catchment (11 km downstream of the Poutu Intake dam). The limited changes can be attributed to the locations of the dams within reaches characterised by bedrock gorges and confined within terraces. These locations act to flush sediments and impose margins that allow minimal adjustment of the channel. Bed material within this reach is characterised by the presence of a boulder lag. This is sourced from long-term incision into lahar deposits, and acts to limit the rate of incision, creating a steep and stable base upon which active fractions are transported. Just as importantly, significant storage in the low-relief volcanic plateau located in the upper catchment acts to disconnect and store the high sediment yields generated by active volcanic cones in the western sub-catchment upstream of the dams. This limits the rate of sediment supply to regulated reaches. Findings from this study show that analysis of reach-scale controls is essential in framing dam site locations in relation to the distribution of reaches and landscape units across the catchment. In this instance, tributary inputs downstream of the dams do not replenish the sediment and flow removed at the dam locations, as has been observed in other regulated systems. Rather, the river itself is resilient to change and flow variability is well managed allowing geomorphically effective floods to occur. Landscape setting is a key consideration in determining the hydrogeomorphic impact of flow regulation.

No single approach effectively synthesizes analysis of river channel form. The diversity of river channels renders research aims and site specificity critical to any investigation, framed within an open-ended approach to enquiry. This inevitably entails a trade-off between resolution, scale, and time: information collected must reflect the specific needs of the task at hand at a given site. In this chapter, investigative techniques used to assess river channel form are appraised in relation to channel planform, cross section, long profile, and three-dimensional morphology. Analysis of three-dimensional forms provides the most rigorous approach to link form adjustment to channel processes, enabling predictive modeling of river behavior.

To quantify sediment flux in river systems requires not only measurements (or estimates) of how much sediment moves through channel cross-sections or reaches over a given time period, but also consideration of how representative those measurements are and how long those rates of sediment movement will be sustained. Geomorphic analysis must accompany application of engineering principles to develop this understanding, explaining controls on sediment availability for a particular system. Geomorphic controls on sediment flux are discussed here in terms of four principles: landscape setting, landscape connectivity, reach sensitivity and sediment organization. These principles are applied in the Tongariro catchment. The landscape setting of this catchment is fashioned primarily by the volcanic history of the area, with abundant sediment supply. Landscape connectivity is limited, with many sediment stores in upland areas disconnected from the lower course of the river. Reach sensitivity downstream of the gorge is limited by the area of active channel inset within terraces. Significant channel adjustments have occurred in the braided reach beyond the terrace-confined reaches. This reach has acted as an efficient trap for gravel-sized materials, such that further downstream, the meandering and multi-channeled delta reaches comprise sand-sized materials. These latter reaches have shown negligible channel adjustments over the last 80 years. Collectively, these inter-related controls determine variability in sediment availability in the Tongariro catchment over time, thereby exerting a dominant influence upon sediment flux. Human disturbance is concluded to have had a negligible impact on sediment flux in this resilient system.

The role of geomorphic structure, referred to as physical heterogeneity, and its influence upon the colonization of habitat by macroinvertebrates was analysed in the peri-urban, Twin Streams Catchment, in West Auckland, New Zealand. Using a cross-scalar approach, 4 riffle-run assemblages were analysed in each of 2 River Styles (a confined, low sinuosity, gravel bed river and a partly confined, low sinuosity, bedrock, cobble, and gravel bed river). Each of these 8 locations comprised 2 distinct sampling areas; the upstream zone had a more heterogeneous river bed with a high diversity of physical features and flow, whilst the downstream area had a more homogeneous structure. Microhabitat features sampled at each site included streambed material, bank margins, fine grained organic debris, wood, and boulders. Habitat mosaics and their associated macroinvertebrate relationships followed a semi-predictable but interrupted pattern, supporting the view that river systems are a patchy discontinuum. Homogeneous zones were more frequently characterised by higher proportions of Trichoptera than heterogeneous zones, whilst heterogeneous zones were frequently characterised by Plecoptera and Ephemeroptera. Diversity was maximised when the species pools from heterogeneous and homogeneous sites were combined for any given site. Functional habitats influenced macroinvertebrate assemblages in non-linear and complex ways. Wood and organic debris habitats were associated with high diversity, abundance, and sensitive species whereas streambed habitat was usually associated with low diversity. A diverse range of physical zones that approximates the ‘natural range of behaviour’ for the given type of stream was considered to provide a more effective platform for rehabilitation planning than emphasising heterogeneity of physical structure in its own right.

Monitoring and assessment are integral components in adaptive management programmes that strive to improve the condition of river systems. Unfortunately, these procedures are generally applied with an emphasis upon biotic attributes and water quality, with limited regard for the geomorphic structure, function and evolutionary trajectory of a river system. Geomorphic principles convey an understanding of the landscape context within which ecohydrologic processes interact. Collectively, geo-eco-hydrologic understanding presents a coherent biophysical template that can be used to frame spatially and temporally rigorous approaches to monitoring that respect the inherent diversity, variability and complexity of any given river system. This understanding aids the development of management programmes that 'work with nature.' Unless an integrative perspective is used to monitor river condition, conservation and rehabilitation plans are unlikely to reach their true potential.

This investigation created and tested a template to rapidly assess geomorphic river condition in urban settings. This extension to the River Styles Framework (R) (Brierley and Fryirs, 2005) entailed mapping the heterogeneity in bed material, habitat, and flow characteristics for different types of rivers, integrating parameters from geomorphology, ecology, and hydrology. Analysis was carried out at 27 sites in the Twin Streams catchment in West Auckland, New Zealand. The method successfully recorded the extent of degradation of physical structure following European settlement of the catchment. With the exception of one subcatchment, streams were found to be largely intact in the headwaters. Many of these headwater streams were found to be of exceptional quality, with high physical heterogeneity. Geomorphic condition is more degraded in downstream areas. Fine-grained sediment has smothered stream courses in the lower half of the catchment, covering bed material and creating homogenous structure and flow, decreasing quality of habitat for biota. In this more urbanized area, with more stormwater drains, riparian vegetation is limited and of poor to moderate quality. Understanding of geomorphic responses to human disturbance is critical in the design and implementation of effective management strategies that seek to improve the ecological condition of urban streams.

This study examines the evolution of a small urbanizing catchment in Waitakere City, New Zealand over the period since European settlement. Geomorphic changes are interpreted from the use of historical documents complemented by sediment analysis at eight sites throughout the catchment. Differing forms and rates of geomorphic adjustment are characterized for five different types of stream. Reach sensitivity to change and trajectory of change are related to the capacity for adjustment of differing stream types and their position within the catchment. These relationships are analyzed using the recovery diagram developed by Fryirs and Brierley (2000). Profound disturbance has been experienced, and streams have responded to a series of land use changes over a relatively short time frame (around 160 years). The system responded quickly to forest clearance and subsequent phases of pasture, horticulture, viticulture, and urbanization. Significant geomorphic recovery is under way along most stream courses. While Substantial increases in sediment yield are inferred, the fine-grained nature of these deposits has not significantly altered geomorphic features of headwater streams. In mid-catchment, benches have developed along overwidened channels. Prospects for geomorphic recovery are much more limited along lowland reaches, where Cumulative impacts have brought about Significant changes to river morphology, Such that recovery to predisturbance conditions is no longer a realistic prospect over management time frames (50-100 years). The relative geomorphic resilience Of this urbanizing catchment is considered to reflect the geologic imprint upon this landscape (a dissected volcano), the reforestation of headwater reaches within a short interval of initial clearance, and the location of urban impacts that are concentrated in the lower part of the river system.