River Tweed Research Articles

Disentangling climate change & land use change effects on river flows: A probabilistic approach

Determining the respective attribution proportions of climate change and land use change to streamflow variations in river systems is of increasing interest to researchers and practitioners tasked with managing river basins. This paper proposes an extension to established techniques of attributing the relative proportions of climate change (CC) and land use change (LUC) drivers to streamflow change by instead considering these proportions as distributed through a probability density function (pdf), rather than as a point value. The novel method is demonstrated for the River Tweed in the UK. Results are determined by the flow, temperature and precipitation data, and upon the algorithms used to identify change points in these vectors. The ratio of the LUC and CC attribution proportions (Land Use and Climate Change Attribution Proportions, LCAP) is more appropriately expressed as a vector of values, each associated with its own probability value within a probability density function. The paper demonstrates that the LCAP ratio pdf can vary considerably over time and that it is possible to track physical changes in the catchment in the evolution of the probability density function. Results show that the land-use change/climate change attribution proportion (LCAP) ratio varies over time and can be expressed as probabilistic estimate. It can be concluded, with a high degree of confidence, that for the Tweed catchment the LUC is a significant driver of streamflow change. Hence this finding may have implications for future catchment flood management utilising nature based solutions (NbS) to reverse landscape degradation and mitigate effects of climate change, provided that the economic and social costs are outweighed by the benefits.

Exploring the potential of deep learning for streamflow forecasting: A comparative study with hydrological models for seasonal and perennial rivers

Improving streamflow prediction plays a significant role in flood warning, mitigation and development purposes. Therefore, this paper aims to compare the prediction capability of a useful conceptual hydrologic model hydrologiska byråns vattenbalansavdelning (HBV) enhanced and equipped with an automatic calibration procedure (Genetic Algorithm) along with two well-known deep learning (DL) algorithms, including Long-Short-Term Memory (LSTM) and Gated Recurrent Unit (GRU). This study was concentrated on the daily streamflow of two river basins with diverse climatic and hydrological conditions, namely the Halilrood River with fragmented and intermittent flows (located in Iran) and the Tweed River with a permanent stream flow (Located across the border of Scotland and northern England). These were particularly selected to address both seasonal and perennial riverine cases. For reproducing the streamflow, 10-year records of the daily discharge, precipitation, and temperature (from satellite and ground resources), and evapotranspiration were used as the main input data. The accuracy of the implemented models was assessed using several indices. The findings show that 1) the LSTM and GRU show better accuracy than the employed hydrologic model for estimating daily discharges (especially in the seasonal river basin); 2) the DL approaches need only meteorological data inputs (precipitation and temperature) and are independent of involved uncertainties in hydrological modeling such as physical characteristics of basins; and 3) best streamflow simulations were achieved by the LSTM (best agreement with the observations). In general, LSTM has the highest priority to be connected with online hydrological rainfall-runoff simulations and dynamical forecast models.

TWEED SAND BYPASSING TRANSITION PROJECT

The Tweed River is located in New South Wales, Australia, just south of the state border with Queensland. The Tweed River Entrance Sand Bypass Project, aka Tweed Sand Bypassing (TSB), was formulated to overcome problems caused by the extension of the Tweed River entrance training walls in the 1960s (Dyson et al., 2001). These issues were primarily: the interception of natural longshore movement of sand, resulting in loss of sand supply to the southern Gold Coast beaches; and sand movement into the river entrance with consequential impacts on vessel navigation. TSB is a joint initiative of the New South Wales and Queensland State Governments. The TSB is similar to the nearby Gold Coast Seaway Sand Bypass (GCSSB) that was commissioned in 1986 to stabiles the Nerang River entrance (Clausner, 1989). Together, these two facilities have come to represent best practice outcomes in sustainable coastal management. A Transition Project was established by TSB to identify the most appropriate operational system / model post-expiry of the CA and to ensure ongoing effective coastal management that meets the legislated objectives. The Transition Project has provided a unique opportunity to improve how TSB functions through the exploration of available options and analysis of historical operational performance.

INVESTIGATING DREDGE PLACEMENT OPTIMISATION TO BENEFIT SURF AMENITY

Dredge material removed from the Tweed River Entrance is deposited offshore from Gold Coast beaches to assist in mitigating erosion. Research was undertaken by the Queensland Government Hydraulics Laboratory (QGHL), in collaboration with Tweed Sand Bypassing (TSB), to investigate the potential of targeting dredge depositions to also improve surf amenity. A time-domain numerical wave model (SWASH) was developed as a design tool and calibrated using physical model data. Overall, SWASH reproduced wave heights over and in the lee of the mound with reasonable accuracy. However, tuning of the breaking parameters (α and β) is necessary to accurately simulate the onset and persistence of the breaking process. The results of both physical and numerical modelling highlight the importance of sand mound shape in disrupting the wave field, resulting in breakpoint variability in the mound's lee, which could potentially create more favorable surfing conditions.

Marine Vegetation Management Strategies: a framework for estuary wide prioritization of protection and rehabilitation

Intertidal systems are constrained by landscape morphology. Where these systems do occur, they often experience a wide range of anthropogenic impacts, further exacerbated by sea‐level rise (SLR). By mapping natural morphological constraints, anthropogenic impacts and modeled SLR, at an estuary‐wide scale the Marine Vegetation Management Strategies (MVMS) identify and prioritize sites and interventions that could address key threats and risks to the system enabling rehabilitation. Development of MVMS is part of an initiative within the broader New South Wales (NSW) state government's Marine Estate Management Strategy to deliver healthy coastal habitats. The MVMS are being developed to take a policy of “no net loss of key fish habitats” toward more active management of intertidal systems that maximize and sustain the ecosystem values and services. Spatial indicators were developed for a pilot estuary (Tweed River) to map and quantify “macrophyte potential” which is defined as the capacity for macrophytes (mangrove and saltmarsh) to deliver ecosystem services now and into the future (under scenarios of SLR). The approach incorporates datasets which indicate the geophysical nature of the landscape, anthropogenic exposure, and vulnerability to SLR. This strategic science‐based approach is being rolled out across coastal NSW, with the mapping products and associated resources identified as key tools to assist in the adopting of a more integrated approach to managing coastal wetlands.

Water quality and the health of remnant leaf oyster (Isognomon ephippium) populations in four Australian estuaries

Leaf oysters (Isognomon ephippium) are large intertidal bivalves that form shellfish reefs. They have a patchy and restricted distribution in estuaries in northern New South Wales, Australia, where the water quality is impacted by a range of anthropogenic stressors from coastal agriculture, urbanisation, industry and recreational activities, along with natural stochastic events such as flooding. Little, however, is currently known about the tolerance of leaf oysters to poor water quality. This study investigated the condition of leaf oyster populations in four estuaries, by assessing the density, size-frequency and condition index. These biological parameters were modelled against habitat water quality parameters including nutrient loads, organic and inorganic carbon, algal biomass, sedimentation and total alkalinity. The water quality assessments were replicated during dry conditions and after rain in two estuaries. Leaf oyster density, size, and body condition significantly differed among the four estuaries. Density ranged from as few as 0.04 oysters per m2 in the heavily impacted Richmond River, up to 267 oysters per m2 in the Tweed River. Overall water quality was also significantly different among the four estuaries, and significant declines in water quality were observed after rain. Distance based linear models revealed significant correlations between biological indicators of leaf oyster reef health and a range of water quality parameters. Leaf oysters with higher condition occur in locations with high dissolved oxygen and salinity levels, whereas low pH and high nutrient run-off were associated with low density and poorer oyster condition. Nevertheless, dense populations were found to persist in areas with pH below 7.9, in high turbidity (over 27 NTU) and areas dominated by fine silt. Their ability to form dense reefs on estuarine soft muddy bottom habitats with low water flow, suggests that leaf oysters could be used to complement rock oysters in future intertidal shellfish reef restoration programs.

Updrift morphological impacts of a coastal protection strategy. How far and for how long?

By examining a coastal zone with a long-term history of management strategies, the focus of this paper is on the evolution of a beach system on the updrift of a sequence of coastal interventions. Here, we review previous assessments of the natural morphodynamic adjustments of the Letitia Spit (New South Wales, Australia) in response to the construction of the Tweed River training walls (c. 1964) and a subsequent permanent artificial sand bypassing system (c. 2001) downdrift of our study site. In addition, the temporal and spatial scale of the changes on the sediment deposits is investigated for a period of 53 years (1967 to 2020). The results showed that while the immediate updrift sector (~1 km long) responds rapidly (from the first few months to two-three years) to the introduction of the coastal management structures, the extension of those impacts further updrift along the beach (~3 km) is gradual and takes decades. About two to three decades were necessary to reach a new equilibrium state after the accretionary period caused by the training wall obstruction of the littoral drift, whereas the erosional state derived from the commencement of the artificial bypassing continued for about one decade before the new equilibrium was reached. Overall, this paper contributes to the understanding of the evolution of an updrift beach in response to coastal protection works and highlights the importance of long-term morphological monitoring of the beach – from the dune to the depth of closure – for informing the planning of future coastal interventions and improving morphodynamic conceptual models focused on coastal structures and adjacent coastlines.

Assessment of microplastics in discharged treated wastewater and the utility of Chrysaora pentastoma medusae as bioindicators of microplastics

Microplastics are ubiquitous pollutants in aquatic environments globally. Wastewater treatment plants are considered to be a major source of microplastics and jellyfish have been proposed as potential bioindicators of microplastic pollution. We tested whether treated wastewater influenced the concentration and/or composition of microplastics in the receiving water by comparing the concentration and composition of microplastics in seawater collected in the wastewater plume and at sites distant from treated wastewater releases in the Gold Coast Broadwater, Australia, and at sites within the nearby Tweed River estuaries, which receives >10 times less wastewater discharge. In addition, tiger sea nettle Chrysaora cf. pentostoma medusae were collected to determine whether more microplastics occurred in the guts of the medusae nearby diffusers and whether the microplastics ingested by medusae were representative of those present in the water column. The concentration and composition of microplastics at the wastewater release sites did not significantly differ from sites that were distant from them. Eighty three percent of medusae contained microplastics in their guts and the composition of the ingested microplastics differed significantly from that in the surrounding water. We concluded that discharged treated wastewater had no detectable effect on levels or composition of microplastics in the receiving water and that C. pentostoma are unsuitable bioindicators because the microplastics they ingested did not represent those available in their environment.

Refurbishing the historic Old Tweed Bridge, Scotland – the challenges and innovations

The historic Old Tweed Bridge is a three-span listed masonry arch crossing the River Tweed. Structural integrity concerns resulted in the bridge being temporarily closed to the public and propped. This paper discusses the challenges associated with the construction works necessary to refurbish the bridge permanently. The works involved installing a temporary propping and encapsulation structure, excavating the bridge infill, taking down and rebuilding the walls, casting a concrete saddle above the arches, waterproofing and resurfacing. Other innovative works involved closing the gap between the voussoirs and arch barrel using a bespoke arch pulling system and repairing voussoir stones in situ with a lime-based material. There were significant environmental challenges on the project as the bridge is located in an ecologically sensitive area. The River Tweed is one of the UK's great salmon rivers, which restricted working in the river and required strict pollution controls. Alternative roosts for bats were provided and netting was required around the bridge as part of an advanced works contract to mitigate the risk of birds nesting in the bridge.

Cuthbert’s relics and the origins of the diocese of Durham

AbstractThe established view of the Viking-Age Northumbrian Church has never been substantiated with verifiably contemporary evidence but is an inheritance from one strand of ‘historical research’ produced in post-Conquest England. Originating c. 1100, the strand we have come to associate with Symeon of Durham places the relics and see of Cuthbert at Chester-le-Street from the 880s until a move to Durham in the 990s. By contrast, other guidance, including Viking-Age material, can be read to suggest that Cuthbert was at Norham on the river Tweed and did not come to Durham or even Wearside until after 1013. Further, our earliest guidance indicates that the four-see Northumbrian episcopate still lay intact until at least the time of Æthelstan (r. 924–39). The article ends by seeking to understand the origins of the diocese of Durham and its historical relationship with both Chester-le-Street and Norham in a later context than hitherto sought.

On Watery Borders, Borderlands, and Tania Kovats’ Head to Mouth

With a relational view of landscapes and natural environments as continuously “in process” and formed from the over-layered and interdependent connections between nature and culture, the human and the non-human, this paper considers some recent practices by artists who have worked in the largely rural border region of Northern England and Southern Scotland. Expanding from a focus on the artist Tania Kovats’ 2019 Berwick Visual Arts exhibition, Head to Mouth, and a wider frame of non-anthropocentric ecological thought in relation to the visual arts, it explores the significance of diverse creative engagements with water, here with the River Tweed, and their potential value in a current cross-border context of social and environmental challenges and concern.

Motivations and experiences of sheltering in place during floods: Implications for policy and practice

Whilst much research considers evacuation behaviours during floods and other natural hazard events, and how to motivate greater compliance to evacuation orders, there is little research documenting peoples’ reasons for, and experiences of, sheltering at their home or business during floods. Focusing on the experiences of residents and business owners who sheltered during a major flood event, this study explores the motivations for staying during floods, residents’ practices while sheltering, and the attendant challenges and impacts. Semi-structured interviews and a questionnaire were conducted with residents and business owners in the Richmond, Brunswick and Tweed river catchments in New South Wales in the months following an extensive flood event in 2017. The research identified a culture of sheltering during floods in these communities that is passed down through families and communities. Nuanced personal and locally specific factors influenced decisions to shelter, and official warnings and evacuation orders were often considered inaccurate or too late, or disregarded due to ‘warning fatigue’. Findings also reveal that sheltering can be physically and psychologically challenging, and often involves actively defending people, property, and possessions from floodwaters. This study highlights the critical importance of context to understanding sheltering decisions, and consequently, the need for nuance in emergency management responses and risk communication. It also shows the importance of understanding what sheltering involves and its impacts, particularly given increasing pressure to urbanise and develop flood plains.

Working across scales in integrated catchment management: lessons learned for adaptive water governance from regional experiences

Integrated Catchment Management (ICM) has in recent years been promoted by a wealth of “top-down” government policies, while a number of “bottom-up” community-based initiatives have also been set up. At the same time, adaptive water governance, built around multi-level, integrative and participatory institutional arrangements, is called for in order to enhance adaptive capacity of social–ecological systems to global changes. Working across scales, aligning planning processes, and multi-actor collaboration are key issues in the linking of top-down and bottom-up ICM, hence providing insights into how adaptive water governance can work in practice. The paper presents a study of how ICM actors work across scales and reconcile national and local priorities in 15 regional experiences chosen to reflect a diversity of scales, histories and governance arrangements. It is complemented with an in-depth, illustrative example, taken from the Tweed River Basin in Scotland, where a local charity has gradually developed and helped bridge gaps between local communities and government. Research results present the ways in which “trusted intermediaries” can successfully close the gap across levels of governance, i.e. between communities, business, and governmental interests at multiple scales. Local “trusted intermediaries” perform well, with their local knowledge, at building rapport with key actors and effectuate change on the ground. The research also indicates the need for a legal framework, or at least an established policy structure, that acts to harness the good will and interests of local actors while improving implementation of broader, national objectives. There appears to be no specific mechanism for multi-level collaboration, although results indicate that more formal and coercive forms of partnership are necessary at later stages to ensure implementation, for example, via the establishment of formal duties on public bodies or legally binding agreements between ICM stakeholders.

Salmon and sea trout spawning migration in the River Tweed: telemetry-derived insights for management

Management of multiple exploited stocks of anadromous salmonids in large catchments requires understanding of movement and catchment use by the migrating fish and of their harvesting. The spawning migration of sea trout (Salmo trutta) and Atlantic salmon (Salmo salar) was studied in the River Tweed, UK, using acoustic telemetry to complement exploitation rate data and to quantify catchment penetration. Salmon (n = 79) and sea trout (n = 65) were tagged in the tidal-influenced Tweed in summer–autumn. No tagged salmon left the river before spawning, but 3% (2010) and 8% (2011) of pre-spawning sea trout dropped out. Combined tag regurgitation/fish mortality in salmon was 12.5%, while trout mortality was 6% (2010) and 0% (2011). The estimated spawning positions of salmon and sea trout differed; tagged salmon were mostly in the main channel while trout occurred mostly in the upper Tweed and tributaries. Early fish migrated upstream slower than later fish, but sea trout moved through the lower-middle river more quickly than salmon, partly supporting the hypothesis that the lower exploitation rate in autumn of trout (1 vs 3.3% for salmon) there is generated by differences in migration behaviour.

Policy implementation of catchment-scale flood risk management: Learning from Scotland and England

Abstract Recent years have seen a gradual adoption of a “catchment-scale” approach to flood risk management into European policy-making which, amongst other objectives, promotes rural land use change to reduce flood risk. While some exploratory studies of land managers’ attitudes exist, research is lacking on how public policies can be mobilised locally to implement these ideas. Two local initiatives were analysed in the transboundary River Tweed basin in Scotland and England during which public authorities negotiated with land managers. A combination of documents (N = 21) and interviews (N = 63) forms the basis of the data analysed. The results showed that implementation is highly dependent on the local policy framework, the activities of implementers, and land managers’ responses to (combination of) policy instruments. Several factors were identified influencing implementation such as devolution arrangements (i.e. from national to regional/local), the level of local interest on flood risk, local attitudes to compromise and collaboration, available policy instruments, and the existence of participatory catchment organisations. With limited scope for stand-alone regulatory action or funding in the short term, synergies and measures promoting co-benefits in flood risk management should be further sought in the Water Framework Directive River Basin Management Plans, as well as in cross-compliance and the new agri-environment-climate strategies of the common agricultural policy.

MODELLING BEACH MORPHODYNAMICS FOR SOUTHERN GOLD COAST BEACH NOURISHMENT PROJECT AT BILINGA BEACH

A new cross shore process model NSBEACH (New SBEACH) has been applied to the Southern Gold Coast Nourishment Project at Bilinga beach (Australia) where nearshore nourishment and bar movement with beach berm and dune building have been simulated. Following the extension of the Tweed River training walls in the late 1960s, the downdrift Southern Gold Coast beaches to the north suffered extensive and prolonged erosion. Between 1988 and 1996, 6.6 million m3 of sand was deposited in both onshore and nearshore locations along the beaches of the Southern Gold Coast. Extensive post-nourishment beach monitoring data shows the recovery of Bilinga beach with the nearshore nourished material transported onshore. There have been many unsuccessful attempts to numerically model the beach recovery processes following the nearshore nourishment on the Southern Gold Coast. Most coastal models have been developed for prediction of storm erosion and as such have limited abilities in simulating bar movement and onshore accretion with beach recovery over extended periods of time. NSBEACH (New SBEACH) has been developed with the ability to simulate short term storm erosion and the longer duration recovery processes under natural or nourished conditions. NSBEACH has been successfully applied at Bilinga beach over an extended simulation period of 8 months with both erosion and accretion responses of the beach successfully simulated.

Spatially weighted functional clustering of river network data.

Incorporating spatial covariance into clustering has previously been considered for functional data to identify groups of functions which are similar across space. However, in the majority of situations that have been considered until now the most appropriate metric has been Euclidean distance. Directed networks present additional challenges in terms of estimating spatial covariance due to their complex structure. Although suitable river network covariance models have been proposed for use with stream distance, where distance is computed along the stream network, these models have not been extended for contexts where the data are functional, as is often the case with environmental data. The paper develops a method of calculating spatial covariance between functions from sites along a river network and applies the measure as a weight within functional hierarchical clustering. Levels of nitrate pollution on the River Tweed in Scotland are considered with the aim of identifying groups of monitoring stations which display similar spatiotemporal characteristics.

Surface elevation change and vegetation distribution dynamics in a subtropical coastal wetland: Implications for coastal wetland response to climate change

The response of coastal wetlands to sea-level rise is receiving global attention and observed changes in the distribution of mangrove and salt marsh are increasingly associated with global climate change, particularly sea-level and temperature rise, and potentially elevated carbon dioxide. Processes operating over smaller-spatial scales, such as rainfall variability and nutrient enrichment are also proposed as possible short-term drivers of changes in the distribution of mangrove and salt marsh. We consider the response of mangrove and salt marsh in a subtropical estuary to changes in environmental variables over a 12 year period by comparing rates of surface elevation change and vegetation distribution dynamics to hydrological and climatic variables, specifically water level and rainfall. This period of analysis captured inter-annual variability in sea level and rainfall associated with different phases of the El Niño Southern Oscillation (ENSO). We found that the mangrove and salt marsh trend of increasing elevation was primarily controlled by position within the tidal prism, in this case defined by inundation depth and distance to the tidal channel. Rainfall was not a primary driver of elevation trends in mangrove and salt marsh, but rainfall and water level variability did influence variability in elevation over the study period, though cross-correlation of these factors confounds identification of a single process driving this variability. These results highlight the scale-dependence of coastal wetland vegetation distribution dynamics; the longer-term trend of surface elevation increase and mangrove encroachment of salt marsh correlated with global sea-level trends, while short-term variability in surface elevation was related to local variability in water level and rainfall. Rates of surface elevation increase were found to lag behind rates of water level change within the Tweed River, which may facilitate further expansion of mangrove into salt marsh. This study advocates integration of ecological and geomorphic techniques to understand the response of coastal wetlands to sea-level rise and climatic perturbations.

Biology of the Mountain Crayfish Euastacus sulcatus Riek, 1951 (Crustacea: Parastacidae), in New South Wales, Australia

The biology and distribution of the threatened Mountain Crayfish Euastacus sulcatus, was examined through widespread sampling and a long-term mark and recapture program in New South Wales. Crayfish surveys were undertaken at 245 regional sites between 2001 and 2005, and the species was recorded at 27 sites in the Clarence, Richmond and Tweed River drainages of New South Wales, including the only three historic sites of record in the state, Brindle Creek, Mount Warning and Richmond Range. The species was restricted to highland, forested sites (220-890 m above sea level), primarily in national park and state forest reserves. Adult crayfish disappear from the observable population during the cooler months, re-emerging in October when the reproductive season commences. Females mature at approximately 50mm OCL, and all mature females engage in breeding during a mass spawning season in spring, carrying 45-600 eggs. Eggs take six to seven weeks to develop, and the hatched juveniles remain within the clutch for a further 2.5 weeks. This reproductive cycle is relatively short, and represents a more protracted and later breeding season than has been inferred for the species in Queensland. A combination of infrequent moulting and small moult increments indicated an exceptionally slow growth rate; large animals could feasibly be 40-50 years old. Implications for the conservation and management of E. sulcatus are discussed.

Flexible regression models over river networks.

Many statistical models are available for spatial data but the vast majority of these assume that spatial separation can be measured by Euclidean distance. Data which are collected over river networks constitute a notable and commonly occurring exception, where distance must be measured along complex paths and, in addition, account must be taken of the relative flows of water into and out of confluences. Suitable models for this type of data have been constructed based on covariance functions. The aim of the paper is to place the focus on underlying spatial trends by adopting a regression formulation and using methods which allow smooth but flexible patterns. Specifically, kernel methods and penalized splines are investigated, with the latter proving more suitable from both computational and modelling perspectives. In addition to their use in a purely spatial setting, penalized splines also offer a convenient route to the construction of spatiotemporal models, where data are available over time as well as over space. Models which include main effects and spatiotemporal interactions, as well as seasonal terms and interactions, are constructed for data on nitrate pollution in the River Tweed. The results give valuable insight into the changes in water quality in both space and time.