A robust multi-purpose hydrological model for Great Britain

PhD ThesisRobust numerical models are an essential tool for informing ood and water management and policy around the world. Physically-based hydrological models have traditionally not been used for such applications due to prohibitively large data, time and computational resource requirements. Given recent advances in computing power and data availability, this study creates, for the rst time, a robust, physically-based hydrological modelling system for Great Britain using the SHETRAN model and national datasets. Such a model has several advantages over less complex systems. Firstly, compared with conceptual models, a national physically-based model is more readily applicable to ungauged catchments, in which hydrological predictions are also required. Secondly, the results of a physically-based system may be more robust under changing conditions such as climate and land cover, as physical processes and relationships are explicitly accounted for. Finally, a fully integrated surface and subsurface model such as SHETRAN o ers a wider range of applications compared with simpler schemes, such as assessments of groundwater resources, sediment transport and ooding from multiple sources. In order to develop a national modelling system based on SHETRAN, a large array of data for the whole of Great Britain and the period 1960-2006 has been integrated into a framework that features a new, user-friendly graphical interface, which extracts and prepares the data required for a SHETRAN simulation of any catchment in Great Britain. This has vastly reduced the time it takes to set up and run a model from months to seconds. Structural changes have also been incorporated into SHETRAN to better represent lakes, handle pits in elevation data and accept gridded meteorological inputs. 306 catchments spanning Great Britain were then modelled using this system. The standard con guration of this system performs satisfactorily (NSE > 0.5) for 72% of catchments and well (NSE > 0.7) for 48%. Many of the remaining 28% of catchments that performed relatively poorly (NSE < 0.5) are located in the chalk in the south east of England. As such, the British Geological Survey 3D geology model for Great Britain (GB3D) has been incorporated for the rst time in any hydrological model to pave the way for improvements to be made to simulations of catchments with important groundwater regimes. This coupling has involved development i of software to allow for easy incorporation of geological information into SHETRAN for any model setup. The addition of more realistic subsurface representation following this approach is shown to greatly improve model performance in areas dominated by groundwater processes. The sensitivity of the modelling system to key inputs and parameters was tested, particularly with respect to the distribution and rates of rainfall and potential evapotranspiration. As part of this, a new national dataset of gridded hourly rainfall was created by disaggregating the 5km UK Climate Projections 2009 (UKCP09) gridded daily rainfall product with partially quality controlled hourly rain gauge data from over 1300 observation stations across the country. Of the sensitivity tests undertaken, the largest improvements in model performance were seen when this hourly gridded rainfall dataset was combined with potential evapotranspiration disaggregated to hourly intervals, with 61% of catchments showing an increase in NSE as a result of more realistic sub-daily meteorological forcing. Additional sensitivity analysis revealed that the slight over-estimation of runo using the initial model con guration which has a median water balance bias of 5% was reduced in 62% of catchments by increasing daily potential evapotranspiration rates by 5%. Similarly, model performance was also found to improve by universally decreasing rainfall rates slightly, which together indicate the possibility of slight under-estimation of potential evapotranspiration derived from available data. In addition to extensive sensitivity testing, the national modelling system for Great Britain has also been coupled with the UKCP09 spatial weather generator to demonstrate the capability of the system to conduct climate change impact assessments. A set of 100 simulations for each of 20 representative catchments across the country were processed for a medium emissions scenario in the 2050s, in order to establish and demonstrate the methodology for conducting such an assessment. The results of these initial simulations suggest that higher potential evapotranspiration rates, combined with modest increases in rainfall under this climate change projection, lead to a general decrease in mean annual river ows. Changes in mean annual ow across the country vary between -26% to +8%, with the biggest reductions in ow found in the south of England and modest increases in runo across Scotland. This work represents a step-change in how the physically-based hydrological model SHETRAN can be used. Not only has this project made SHETRAN much easier to use on its own, but the model can now also be used in conjunction with external applications such as the UKCP09 spatial weather generator and GB3D. This means that the modelling system has great potential to be used as a resource at national, regional and local scales in an array of di erent applications, including climate change impact assessments, land cover change studies and integrated assessments of groundwater and surface water resources

Uncertainties in long-term management of water resources

PhD ThesisA reliable supply of water to communities, industry and agriculture is crucial for a healthy population, and a successful economy. Long-term management of water resources poses significant challenges for decision makers due to uncertainties. Natural variability in hydrological processes, as well as future changes in climate, land use, demography and other socio economic factors are placing increased pressure on water resources and pose a threat to water security. The release of probabilistic climate information, such as the UKCP09 scenarios, provides improved understanding of some uncertainties associated with climate model projections. This has motivated a more rigorous approach to dealing with other uncertainties in order to understand the sensitivity of investment decisions to future uncertainty and identify adaptation options that are as far as possible robust. To understand the implications of this range of uncertainties, a novel integrated systems model has been developed that couples simulations of weather under current and future climates, catchment hydrology, and the water resources system. This systems model was used to assess the likelihood and magnitude of water scarcity. Uncertainty and sensitivity analyses were undertaken to assess the implications of uncertainties on water scarcity, and to subsequently identify water resources management options that are robust to these uncertainties. The integrated systems model has been applied in the Thames catchment which supplies the city of London, UK. This region has some of the lowest rainfalls in the UK, the largest and fastest growing population, and is therefore particularly sensitive to water availability. Results indicate that by the 2080s, when accounting for all uncertainties considered here, there may not be a considerable change in total amount of rainfall relative to the control period (1961-1990). However as a result of an increase in temperature, the annual mean PET is expected to increase by 26.6%. Based on the results, a 24.0% and 1.3% reduction in annual mean daily flow and subsurface storage are projected to occur in the Thames catchment respectively. Moreover, a 1083.0% increase in the total number of drought days relative to the control period (1961-1990) is expected under current population and climate trends by 2080s. Water scarcity in London is most sensitive to climate and population change, and so investment in monitoring to reduce these uncertainties would help improve the robustness of investment decisions. A portfolio of adaptation measures, that includes a combination of desalination plant with capacity of 150 Ml/d, constructing a new i reservoir with 100 Mm3 capacity and 40.0% reduction in leakage, is required to reduce the drought risks. However, sensitivity testing shows that measures taken to reduce per capita water demand are more robust to future uncertainties than major engineering interventions

Resilience of shallow groundwater resources and their potential for use in small-scale irrigation : a study in Ethiopia

PhD ThesisGroundwater use for small-scale irrigation in sub-Saharan Africa is low, though is expected to increase in the near future. There is currently limited understanding of shallow groundwater resources, which are most likely to be exploited by poor rural communities due to their accessibility. This PhD study aimed to determine the potential for use of shallow groundwater for small-scale irrigation and the resilience of the resources to increased abstraction, land-use change and climate variability. Research was conducted principally at a study site in northwest Ethiopia with seasonal rainfall and a predominance of rainfed agriculture. The shallow aquifer comprises a thin weathered regolith above largely impermeable basalt. Hydrochemistry analyses suggested little connection between the shallow aquifer and a deep fractured aquifer. To fill gaps in formal hydrometeorological monitoring, a community-based monitoring programme was initiated. Statistical comparisons confirmed that the datasets were of as high or higher quality as those from formal networks, remote sensing and reanalyses. A recharge assessment estimated annual recharge of 280-430 mm, confirming that a sufficient renewable shallow groundwater resource is available for small-scale irrigation. Four nested catchments were modelled using SHETRAN, a physically-based spatially-distributed modelling program. The modelling identified the foot of hillslopes and narrow valleys as showing the greatest potential for irrigated agriculture as groundwater in those locations remained available and accessible for the longest periods. Potential future scenarios were run in the SHETRAN models considering likely climate variability, land use change and increasing abstraction. Around 35% of arable land in the modelled catchments had shallow groundwater available throughout the dry season. During simulated multi-year droughts, a significant percentage of arable land still had sufficient groundwater available for irrigation of a second growing season. Conversion of pasture and scrubland to cultivated land did not have a significant impact on water resources while degradation of highlands to bareground had a positive impact. The severest impact on water resources resulted from increased coverage of Eucalyptus. Notably, simulation of increased abstraction and irrigation at smallholder levels had little impact on surface and groundwater availability. This study demonstrates the potential for greater exploitation of shallow groundwater for small-scale irrigation by rural communities and the resilience of the resource to climate variability, land use change and increasing abstraction.Newcastle University who funded this PhD through the Faculty of Science, Agriculture and Engineering (SAgE) Doctoral Training Awards (DTA) programme. I am also thankful to NERC/DfID who funded the initial AMGRAF catalyst project (grant no. NE/L002019/1) under the UPGro programme that led to the PhD. I am further grateful to Newcastle University for the award of the Harry Collinson Travel Scholarship, to the Royal Geographical Society with IBG for the Dudley Stamp Memorial Award, and to the International Association of Hydrogeologists for the John Day Bursary

A methodology for assessing flood risk from multiple sources

Ph. D. Thesis.Antecedent catchment conditions can affect the severity of flooding, and floods are typically worse when multiple flood sources superimpose. Over one million properties in the UK are at risk of flooding from multiple sources, however, groundwater, fluvial and pluvial flood sources are usually considered separately due to their differing characteristics. This PhD study was composed of two parts: (1) developing a methodology for assessing the risk of flooding from multiple sources, including the creation of a groundwater-surface water modelling system and (2) conducting a national assessment identifying catchments with potential for flooding from multiple sources. The modelling system used 1000 years of synthetic weather data to create realistic meteorological inputs for a physically-based, spatially-distributed hydrological catchment model (SHETRAN-GB). The hydrological model then simulated 1/30, 1/100 and 1/1000 year catchment conditions, which were used as inputs for a high resolution hydraulic model (HiPIMS). The hydraulic model then routed rainfall, stream flow and groundwater emergence to generate a detailed and comprehensive assessment of flood risk. Sensitivity tests compared the flood extents and depths from different methods of integrating groundwater and surface water conditions from the hydrological model into the hydraulic model to find the best method for linking the models. The capability of a national automated hydrological model to simulate groundwater levels was tested at five case study catchments using open source hydrogeological datasets. Automated model configurations were unable to reproduce historical groundwater levels, however simple automated improvements did increase performance. Improved parameterisation of a basic subsurface increased model performance more than the introduction of more complex geology, although the latter was found to be erroneous in places. Correlations between observed and simulated groundwater levels ranged significantly but were as high as 0.9 at some locations. At one case study site, the model domain was given subsurface boundary conditions and increased from its topographic watershed to the estimated groundwater catchment. This dramatically increased the model’s performance and its sensitivity to parameters. The automated setups provided a useful modelling base, but local calibration, improved hydrogeological parameters, subsurface boundary conditions and the use of groundwater domains are necessary for producing good simulations in catchments containing groundwater. New indexes were derived for classifying flow regimes to aid the identification of catchments likely to benefit from the developed methodology, and an initial 29 multisource catchments were identified out of a total of 435 analysed. Multisource catchments are distributed around the UK but are typically confined to areas with permeable bedrock, thus are most commonly found in the South of England. This research demonstrated that the inclusion of groundwater in the flood risk assessment increased the flood hazard by prolonging the flood duration from hours to days but did not notably increase flood depths. Furthermore, the patterns of flood extent changed depending on the proportion of the flood waters that were derived from the subsurface. In summary, this study provides a methodology for the better quantification, mapping and understanding of multisource flood risk, and identifies catchments that are likely to benefit from the approach

Simulating and visualising the hydrological and landscape impacts of reservoir engineering at Crummock Water, England

Eng. D. ThesisThe Earth’s 57,000 large water reservoirs have significant impacts on hydrology and landscapes. Meanwhile, environmental degradation is destabilising the climate, ecosystems, and hydrological functionality. In Europe and North America, landscape-scale environmental management schemes are being proposed, including reservoir decommissioning to rehabilitate river catchments. Yet, some proposed schemes have failed due to poor stakeholder engagement and shifting environmental baselines. This research has developed novel approachesto address these issues. It has applied these to Crummock Water raised lake in England, where United Utilities and the Environment Agency are investigating the feasibility of removing infrastructure to renaturalise the lake and the River Cocker. The hydrological impacts of anthropogenic modifications in Crummock Water’s catchment were assessed using existing data, expanded hydrometric monitoring, hydrological modelling, and archival research. Circa 1880, Crummock Water’s outlet was excavated and two timber weirs installed to control outflows. In 1903, the extant masonry weir was built, raising the lake level ~0.6 m. Abstraction reduces lake levels, which necessitates sluice operations to maintain outflows during dry periods, causing further drawdown. Hydrological models of reservoircontaining catchments should include reservoir processes. SHETRAN 4.5 (‘Reservoir’)software was developed to integrate reservoir structures and operations into a physically-based, spatially-distributed hydrology model. A SHETRAN-Reservoir model of the Crummock Water catchment substantially outperformed a SHETRAN-Standard model, particularly during and after dry periods. Several reservoir decommissioning scenarios were constructed. Simulations indicate that decommissioning would ameliorate drawdown of Crummock Water and make the River Cocker’s flow regime more dynamic. The simulated landscape impacts of reservoir engineering at Crummock Water were shown in the context of long-term catchment evolution using 4D landscape visualisation. The catchment’s evolution was conceptualised, before being digitally reconstructed and rendered using GeoVisionary software. The resulting 4D landscape model spanned 14,000 years, from the last Ice Age to (simulated) renaturalisation scenarios in 2030. The effects of 4D landscape visualisation on stakeholder attitudes were investigated, using surveys and workshops with 45 participants in two treatments (‘long’ and ‘short’ visualisation). It was hypothesised that ii presenting extended landscape evolution information would change (H1) stakeholder beliefs around catchment naturalness, and (H2) attitudes towards reservoir renaturalisation. Results showed that the workshops changed both beliefs and attitudes towards renaturalisation. Furthermore, the extended evolution information had a statistically significant effect on attitudes (H2), but not on beliefs (H1). This EngD has developed tools to support decision-making in reservoir engineering and landscape-scale environmental projects: firstly, hydrological and landscape models to show the impacts of reservoir decommissioning at Crummock Water; secondly, a generic freelyavailable physically-based, spatially-distributed modelling package for simulating the hydrological impacts of reservoir operations; thirdly, a new approach to visualising simulated hydrological changes, such as lake levels, and landscape evolution in 4D, and; fourthly, an approach to visualising proposed environmental management schemes in the context of longterm landscape evolution, to reset shifting environmental baselines. Finally, the research findings have been synthesised into a landscape visualisation development framework to support enhanced stakeholder engagement in future landscape-scale projects.Engineering and Physical Science Research Council (EPSRC) and United Utilities pl

Modeling climate and land use change impacts on water resources and soil erosion in the Dano catchment (Burkina Faso, West Africa)

The study assesses the effect of climate and land use change on water resources and soil ero-sion in the Dano catchment, Burkina Faso. Field measurements and derived process under-standing are complemented by a physically based modeling approach that is also used to simu-late the impact of land use and climate change. Extensive hydro-meteorological (e. g. precipitation, discharge), pedological (e. g. texture, bulk density) and soil erosion measurements (e. g. suspended sediment load) are investigated to gain knowledge on governing hydrological and soil erosion processes. Data from erosion plot measurements suggest statistically significant differences of runoff and soil erosion between differently used plots. The data and the retrieved understanding are used to setup and drive the physically based spa-tially distributed hydrological and soil erosion model SHETRAN. Statistical performance measures (R², NSE, KGE) range between 0.66 and 0.8 for the calibration and validation of dis-charge. Achieved quality measures of suspended sediment load are lower than for hydrology but comparable to other SHETRAN studies. The impact of land use and land cover (LULC) change on water resources and soil erosion is studied by applying observed and modeled land use maps to the period 1990 – 2030. The past LULC change is studied using land use maps of the years 1990, 2000, 2007 and 2013. Based on these maps future LULC scenarios were developed for the years 2019, 2025 and 2030. Ob-served and modeled climate data cover the period 1990 – 2030. The observed past and modeled future LULC maps are used to feed SHETRAN. The isolated and combined influence of LULC and climate change is investigated. The land use investigation from 1990 to 2013 suggests a decrease of savanna at annual rates of 1.15% while cropland and settlement areas have increased. The simulations that assumed a constant climate and a changing LULC show in-creasing water yield (3.9% – 77.5%) and mainly increasing specific sediment yield (-1.4% – 115.78%). The simulations that assume constant LULC and climate as changing factor indicate increases in water yield of 24.5% to 46.7% and in sediment yield of 31.1% to 54.7%. The com-bined application of LULC and climate change signals a clear increase in water yield (20.3% – 73.4%) and specific sediment yield (24.7% to 90.1%). Actual evapotranspiration is estimated to change across all simulations by -6.8% to 3.35%. The predicted climate change signal is investigated in detail by comparing the future period 2021 – 2050 with the historical period 1971 – 2000. Representative concentration pathways (RCP) 4.5 and 8.5 of six datasets of the CORDEX framework were used to study the future change in tem-perature and precipitation. Most of the used climate models predict an increase of temperature between 0.9°C and 2.0°C. Large uncertainties among the climate models exist regarding the climate change signal of future precipitation. Some climate models predict an increase (5.9% – 36.5%) others a decreased (6.4% – 10.9%) or a mixed signal. The application of the historical and future climate data to SHETRAN shows that future changes in discharge and specific sedi-ment yield follow the predicted precipitation signal. Simulated future discharge change ranges from -43% to +207%. The future change in sediment yield is in the same order

A three-dimensional variably-saturated subsurface modelling system for river basins

PhD ThesisThere are many circumstances where lateral flows in the upper soil layers above the regional groundwater table are important for hillslope and catchment hydrology, and in particular for the transport of contaminants. Perched water tables frequently occur in Quaternary drift sequences, reducing rates of recharge to the underlying aquifers and altering contaminant migration pathways; recent experimental and modelling studies have demonstrated the potential importance of lateral flows in the unsaturated zone, even in homogeneous soils; and lateral interflow at the hillslope scale, and its role in generating storm runoff, is the subject of intense current debate amongst hydrologists. A numerical model for simulating transient three-dimensional variably-saturated flow in complex aquifer systems (the Variably-Saturated Subsurface flow, or VSS, model), capable of representing these conditions, is presented in this thesis. The VSS model is based on the extended Richards equation for saturated as well as unsaturated conditions, and also includes capabilities for modelling surface-subsurface interactions, stream-aquifer interactions, prescribed head and flow boundary conditions, plant and well abstractions, and spring discharges. A simple but novel approach is taken to solving the three-dimensional non-linear Richards equation on a flexible-geometry finite-difference mesh, using Newton-Raphson iteration and an adaptive convergence algorithm. The VSS model is implemented as a module of the catchment flow and transport modelling system, SHETRAN. The reliability of the full SHETRAN modelling system is demonstrated using verification and validation tests, including comparisons against analytical solutions for simple cases, and simulations of storm runoff in a small Mediterranean catchment. Simulations of flow and contaminant transport in complex sequences of Quaternary drift deposits demonstrate the full capabilities of the modelling system under real-world conditions

Community-based ('citizen science') monitoring for catchment characterisation, modelling and management

PhD ThesisDespite there being well-established meteorological and hydrometric monitoring methods, many smaller UK catchments remain ungauged. This leaves characterisation, modelling, forecasting and management activities a challenge when working on a local level. Many ‘citizen science’ projects are encouraging the public to participate in data collection activities and generate new knowledge across a range of environmental disciplines, but they have not been fully investigated within catchment science. This project has designed and implemented an innovative community-based monitoring scheme within the 42km2 Haltwhistle Burn catchment (Northumberland, UK) to explore the feasibility, reliability, value and sustainability of citizen science within the catchment management process. Like many rural UK catchments, the Haltwhistle Burn responds rapidly, experiences flash flooding, and does not benefit from any traditional monitoring networks. Various simple, lowcost and internet-based methods have enabled the public to collect and share rainfall, river level, water quality and flood-related observations successfully over a 29-month period. This generated a patchwork of heterogeneous catchment information. Although a wide range of people actively participated, 73% of the total number of observations were generated by just four dedicated individuals or households. Despite monitoring efforts being sporadic and unpredictable, rainfall and river level observations were favoured. Participation levels also intensified during high flows or flood events; web-based tools, particularly Twitter, then played an important role in sharing these real-time observations. However, spatial and temporal monitoring efforts are biased towards individual capabilities and interests, and should therefore fill data gaps rather than replace traditional monitoring schemes. Training, ongoing facilitation and feedback help to generate meaningful and good quality data. A traditional hydrometric monitoring network was installed to aid in assessing the quality and value of community-based observations. Examples presented here verify that citizen science can generate high quality data, provided that robust validation and verification measures are in place. Evidence suggests that participants were conscious of collecting consistent datasets, but this does not guarantee reliable data from every citizen scientist. The value of community-based observations have been demonstrated by using them to build and run a physically-based, spatially-distributed hydrological model. Results reveal how the local network of community-based observations, when used alongside traditional sources of hydro- Abstract iv information, supports the characterisation of catchment response more accurately than when using traditional observations alone. Community-derived datasets appeared to be most valuable during local flash flood events, particularly towards peak discharge. Such information is often missed or poorly represented by ground-based gauges, or significantly underestimated by rainfall radar, as this study clearly demonstrates. Community-based observations were also used to tailor the design of a natural flood management (NFM) scheme above the town of Haltwhistle. Post-installation monitoring has revealed that image-based observations collected using simple monitoring methods can provide concerned locals with meaningful and relatable (therefore valuable) information. Such outcomes are important when relieving common barriers affecting the widespread uptake of NFM. It is acknowledged that the long-term retention of volunteers and the sustainability of citizen science is a challenge. The full monitoring period exposed that participation levels escalated, peaked and then tailed off within Haltwhistle. However, the winter 2015/16 widespread floods reactivated mass data collection. Driven by an existing community-led group, an additional case study site in Northumberland (Acomb) also demonstrates how the public want to monitor, acknowledge the benefits of local datasets, and are capable of initiating and funding their own monitoring scheme. Sustainable (long-term) citizen science therefore requires strong leadership and pertinent (flood risk) motivations. Raising volunteers’ awareness on how to maximise the value of their own monitoring efforts will also reduce monitoring fatigue. Furthermore, options have been explored to demonstrate how citizen science can be scaled up to a regional and national level, and be integrated into the existing flood risk and catchment management process. Although the co-production of environmental knowledge is not a new phenomenon, evolving technology and communications provides a timely and cost-effective solution to mass data collection. Without this data, very little information would be available to characterise catchments and implement localised management measures with confidence. This participatory approach also offers the public an exciting opportunity to share valuable local knowledge, gain ownership, and be actively part of the catchment management process. Overall, it is concluded that citizen science and the wider community-based monitoring toolkit should now be seen as a fundamental component of any catchment study. The findings and impact generated as a result of this Ph.D. have therefore made a significant contribution to research in this area, and lay the foundations for future community-based projects.part-funded by Tyne Rivers Trust’s Catchment Restoration Fund projec