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Over the period 1961 – 90 the North East Arid Zone of Nigeria experienced a decline in annual rainfall totals and increased aridity which placed increasing pressure on rain fed, millet-based farming systems. The changes in seasonal rainfall total and distribution have been examined and it has been shown that the rate of decline has been consistent across the region. The decline has been dominated by reduction in the number of rain days during the middle of the rainy season and there is no evidence of a significant change in the length of the growing season. Over the same time period, there has been a small, but significant, increase in mean air temperature which has resulted in a small increase in potential evapotranspiration. Other climatic parameters (vapour pressure, solar radiation and wind speed) appear to have remained stable, although the paucity and dubious quality of much of the historical meteorological data make rigorous statistical analysis difficult. A water balance model (BALANCE) developed by the author, was calibrated for a millet crop grown on a typical sandy loam soil in Maiduguri (Nigeria). The model was necessarily parsimonious, but was shown to perform well when calibrated against observed soil water content. However, the empirical nature and high sensitivity of key parameters relating to bare soil evaporation and drainage mean that it is difficult to parameterise the model by laboratory, or independent field measurements. Applying the calibrated model to daily rainfall and average evapotranspiration data from Nguru (Nigeria) for the period 1961 – 93 showed that, with the exception of extreme drought years, the increased aridity would have had little impact on the viability of traditional millet and millet-cowpea intercropping systems prior to the early 1980s. However, after that date, predicted seasonal millet transpiration, and hence predicted yields, have declined, and long duration cowpea intercrops, which were traditionally matured on residual soil moisture after the millet harvest have had insufficient water. Whilst the BALANCE model has been useful in examining the impact of climatic variability on agro-hydrology, it is not a crop physiological model and the interaction between soil water and crop development is poorly represented. The model cannot, therefore be applied with confidence to investigate the potential yield benefits of physical or agronomic interventions to alleviate the impacts of aridity. Although more complex models exist to do this, they require detailed parameterisation of the crop physiology, which was not possible within the scope of this study.

The impacts of urbanisation on catchment hydrology have been the focus of investigation over the last few decades, but quantifying and predicting the impacts remains an ongoing area of active research. One such area has been improving characterisation of urban land cover to predict urbanisation impacts whereby lumped catchment characterisation of urban land cover limits the ability of attribution and modelling methods to consider the spatial role of land cover in runoff response. This thesis evaluates the potential for spatially explicit characterisations of urban land cover based on landscape metrics, commonly employed in landscape ecology, to explain storm runoff in urban catchments and their application in UK flood estimation methods. Rainfall and channel flow monitoring across two towns containing 18 variably urbanised sub-catchments were used to provide high-resolution time-series of rainfall and runoff and to identify storm events which were quantified using a range of hydrological metrics. Analysing storm runoff along a rural-urban gradient showed a lumped measure of urban extent can generally explain differences in the hydrological response between rural and urban catchments but not between more urbanised catchments in which soil moisture does not play a contributing role. Using high resolution geospatial data can improve the representation of the urban environment and landscape metrics can better represent the form and function of urban land cover, improving estimates of the index flood QMED over lumped catchment descriptors. Regression analysis of hydrological metrics showed the potential of landscape metrics for explaining inter-catchment differences in rainfall-runoff and point to the importance of considering the location and connectivity of urban surfaces. Landscape metrics provide a workable means of overcoming the limitations inherent in using lumped characterisation of complex urban land cover and their ability to express connectivity, size and location of urban land cover promises potential applications in hydrological applications such as UK design flood estimation methods.

The wastewater industry is facing an increase in regulatory pressure to reduce excessive phosphorus (P) release to rivers. To address this issue there is a need for sustainable treatments, especially in small sewage treatment works (STW) (< 2000 inhabitants) which constitute 75 % of the systems in the UK. Land treatment systems (LTS) have long been used to treat wastewater, principally as a tertiary treatment at small rural sites. LTS are able to remove phosphorus but there are some uncertainties regarding their treatment capability. This research aims to address these uncertainties by developing improved estimations of P removal potential and longevity in LTS in the context of a sustainable water industry. First, the existing knowledge and tools available in long-term P removal behaviour are reviewed. Second, the soil P removal efficiency and accumulation in an LTS case study are estimated. Finally, the case study is used to develop a conceptual and mathematical model of P dynamics in LTS integrating water and solute transport in soils. The model is used to explain system behaviour in order to estimate system longevity under different soil conditions and management scenarios. This research demonstrates that LTS can contribute to P removal for a number of years as a tertiary treatment for small STW and that through a combination of hydrological and solute transport modelling it is possible to get a prediction of P removal and longevity of LTS. Results indicate the need for an alternative methodology to assess P removal capacity that does not only rely on inputs and outputs while able to detect if the system is saturated and the need of improved methodological assessment of sorption processes over time. Further development of the current model to reduce limitations, mainly related to vegetation management and P transformation in the different soil pools, will support LTS contribution to the sustainable management of wastewater treatments and the enhancement of the ecosystem services that they provide.

Human activity has disturbed the natural suspended sediment (SS) balance and the associated geomorphological and ecological functioning of many rivers. Yet, predicting and managing SS is challenging because the processes controlling SS transport over multiple timescales are not well understood. The aim of this research is to improve the prediction and management of SS by investigating the hydro-meteorological and catchment processes driving temporal variation in SS transport. The objectives are (i) to assess SS transport over multiple timescales to uncover the scale-specific processes and process interactions that determine temporal variation in SS transport; (ii) to apply and test a sediment fingerprinting approach based on infrared spectrometry to identify dominant SS sources; and (iii) to evaluate the role of variations in sediment sources in controlling SS concentrations in response to hydro-meteorological variables. The research was carried out in the River Aire, UK. The findings show that SS transport in the River Aire is highly event-driven and supply-limited, while also being influenced by long-term changes in land use. Over the studied period, the dominant SS source was grassland, and its contribution was mainly controlled by antecedent moisture conditions. On the contrary, urban street dust, which was also a dominant sediment source, was less hydrologically driven. The research also demonstrated that while infrared-based fingerprinting can be used to estimate SS source contributions with acceptable model errors, sediment apportionment is strongly influenced by the degree of discrimination between source classes. In order to improve methods to quantify SS transport and sources, and to identify sediment management needs, this research underscores the need to (i) recognise different timescales of SS transport to identify the underlying processes; (ii) develop better approaches for source classification and discrimination to accurately represent the sediment in rivers; and (iii) establish further knowledge on sediment sources variations in different contexts and over multiple spatial and temporal scales.

There is a regulatory tension within wastewater treatment, between the requirement to meet tightening consents and the need to reduce the carbon footprint of treatment processes. With 75% of wastewater treatment works serving populations of less than 2,000, low-energy tertiary treatment options suitable to small rural works need to be developed. One option that lends itself particularly well to small works is land-based wastewater treatment (LBWWT). The aim of this research was to evaluate the role of LBWWT in the UK water industry and investigate the impact ridge-and-furrow enhanced microtopography (MT) may have upon a particular type of LBWWT - slow-rate (SR) infiltration. This was achieved through meeting three objectives. Firstly, the use of LBWWT was reviewed and assessed. Secondly, the impact of ridge-and-furrow enhanced MT upon the vegetation diversity and nutrient removal of a SR- LBWWT was established by means of a three year field trial. Finally, the cost- effectiveness of SR-LBWWT and the impact of ridging and furrow irrigation upon cost-effectiveness were evaluated using Cost-Effectiveness Analysis (CEA). The first objective comprised of a review of the historical and current use of LBWWT, a review of the relevant changing legislation to identify what may be required of LBWWT and an assessment of LBWWT’s potential to meet these requirements. The result of the evaluation found that, based upon the literature, SR-LBWWT is ‘fit-for-purpose’ as tertiary treatment for small treatment works. To meet the second objective, a SR-LBWWT system trial was established at a small wastewater treatment works in Knowle, Hampshire. The trial consisted of three clay-loam grass plots irrigated with secondary treated effluent. There were two configurations of trial plot - flat and ridge-and-furrowed. Effluent (sub- surface soil water) nutrient concentrations were monitored as was vegetation diversity. In addition a number of physical, hydrological and biogeochemical parameters were monitored and hydrological modelling carried out. Mean nutrient removal performances of 90% for ammonia, 72% for nitrate, and 91% for phosphate were observed with the ridge-and-furrowed plot. Ridging and furrow irrigation was found to not have a significantly detrimental effect upon the trial plots’ removal performance for ammonia, nitrate or phosphate. Extrapolation modelling suggested, however, that this would not be the case for LBWWT systems on predominantly clay or sand soils. Ridging and furrow irrigation was found to have a statistically significant positive effect upon the vegetation diversity of the LBWWT trial plots; with mean final year Shannon-Wiener values of 0.96 and 0.69, for the ridge-and-furrowed and non-ridged plots, respectively. For the final objective, analysis found that SR-LBWWT are cost-effective when compared to horizontal sub-surface flow constructed wetlands (HSSFCW), an established low-energy treatment option. Mean cost-effectiveness ratio values of £208.5 and £262.7 per % effectiveness were observed for LBWWT and HSSFCW, respectively. Following the field trial CEA was extended to include ridge-and-furrowed SR-LBWWT systems. This found that ridging and furrow irrigation improves the cost-effectiveness of SR-LBWWT serving small populations, reducing the mid cost-effectiveness ratio to £193 per % effectiveness. This is a result of the cost-reducing effect of ridge-and-furrowing over laser-level grading; and based upon the findings of the trial that ridging and furrow irrigation can be achieved (in clay-loam soil slow-rate systems) without significant detriment to the water treatment effectiveness of LBWWT. The main conclusions of this thesis are: that SR-LBWWT has a role to play in the UK water industry, as tertiary treatment for small wastewater treatment works. That SR-LBWWT is cost-effective in relation to HSSFCW. That ridging and furrow irrigation increases that cost-effectiveness by reducing the construction and operational costs. That ridging and furrow irrigation can be employed without significant detriment to a SR-LBWWT system’s water treatment performance. And finally, that ridging and furrow irrigation can have a positive impact upon the establishment vegetation diversity of a SR-LBWWT system.

Hydrology is yet to fully understand the role that catchment characteristics have in determining a river’s response to precipitation variability. This thesis assesses the influence that catchment characteristics have on modulating a river’s response to changes in precipitation throughout the UK. Central to this aim is the concept of the precipitation- to-flow relationship (the transformation of precipitation into river flow), which is characterised using the Variogram, a way of indexing temporal dependence (i.e. the average relationship between river flow on a given day and river flow on the previous days). Firstly, 116 catchments were grouped into four clusters, based on the shape of their variogram, which significantly differed in their catchment characteristics demonstrating that catchment characteristics control how, on average, precipitation is transformed into river flow. Furthermore, over 70% of un-gauged catchments could be clustered correctly using information about their soil type, slope and the percentage of arable land. Secondly, a new method which identifies the changes in the variogram parameters over 5-year overlapping moving windows was developed to investigate temporal changes in the variogram parameters. This method was successfully demonstrated to detect changes in multiple aspects of artificially perturbed river flow time series (e.g. seasonality, linear changes and variability). On average >70% of the variability in the catchment variogram parameters was explained by the precipitation characteristics, although there was large variability between catchments. Finally, the influence that the catchment characteristics have on the temporal changes in the variogram parameters was analysed, demonstrating that rivers in relatively impermeable upland catchments have a relationship with precipitation which is closer to linear and less variable than lowland, permeable catchments. This thesis contributes significant new knowledge that can be used for both assessing how individual catchments are likely to respond to projected changes in precipitation and in informing data transfer to un-gauged catchments.

Urban pollutants have been identified as a significant source of environmental pollution, posing a risk to human health, the environment, and are toxic to flora and fauna. Highways are recognised as one of the key sources of pollution, from both vehicles, and surrounding infrastructure. A number of studies have investigated accumulation of sediment and the associated pollutants on highways, and the runoff generated as a result of rainfall. Car parks share many potential contributory sources of pollutants with highways, but there is a lack of studies regarding car parks, despite them being identified as a significant percentage of urban land use. A series of experiments were undertaken in order to develop an understanding of the characteristics of car park sediment. The physical and chemical characteristics of sediment were analysed at different stages throughout the drainage system. Firstly on the sediment accumulated on car park surfaces, followed by that mobilised and transported into a channel drain during simulated rainfall events. Finally, potential treatment of pollutants within sediment in a channel was quantified. The physical and chemical characteristics of car park sediment was shown to be similar during both the accumulation (build-up) and wash-off stages, suggesting that the accumulated sediment is generally mobilised and transported to the channel drain (wash-off). Furthermore, both the physical and chemical characteristics of the sediment were shown to be similar to those found on highways, thorough the build-up and wash-off phases. Finally, potential treatment of organic pollutants (PAH) by biodegradation was demonstrated, but not comprehensively proved.

Floodplains in the United Kingdom have evolved from natural landscapes to artificially modified ecosystems through managing lateral and vertical floodplain connectivity leading to synergy or trade-offs in ecosystem service delivery. Research methods have been limited in understanding the processes by which ecosystem service values are formed and the data required to support ecosystem service assessment. Developing a methodology while complex and challenging is necessary in order to take the ecosystem approach forward to support decision making for policy makers, planners and stakeholders. The aim of this research was to develop a method to assess the delivery of ecosystem services in response to changes in floodplain connectivity and evaluate the performance. A case study floodplain was selected at Tempsford, downstream of the River Ivel in Bedfordshire, United Kingdom as an example for opportunities to deliver multiple ecosystem services. A sequential integrated modelling system was applied utilising a linked ISIS 1D-2D hydrodynamic model and WaSim, a 1D soil water balance model to simulate changes in floodplain connectivity and generate model data to improve estimates of ecosystem services indicators. A non- monetary multi-criteria analysis methodology was applied to further develop indicators for ecosystem services assessment and to assess the impacts of the model scenarios on ecosystem services delivery. The integration of the WaSim model was unsuccessful as the model performed poorly in the calibration and validation process and was not fit for its intended purpose. It was deduced that potential groundwater seepage in the regional aquifer occurs outside of the field study site, which cannot be modelled in WaSim. To demonstrate the impact of lateral connectivity controls on the water table position, an empirical method was developed using the mean observed water table position to represent a ‘no drainage system’ vertical connectivity scenario. The results showed that in low frequency/high magnitude flood events, increasing the lateral connectivity by lowering embankments provides synergy and benefits to flood alleviation, water supply and freshwater fish habitat and trade-offs and disbenefits to flood damage, agricultural productivity, terrestrial habitat and recreation. In high frequency/low magnitude flood events, decreasing the lateral connectivity by raising embankments still provides the same synergy and trade-offs yet lower benefits and disbenefits. Marginally decreasing the lateral connectivity creates a higher level of benefits and a lower level of disbenefits to promote multi-functional land use in the floodplain. Managing the control of floodplain connectivity needs to be carefully planned to enable multifunctional land use in a floodplain.

Globally agricultural production is facing serious challenges to provide adequate food supply to meet a growing population. However, the reduced capacity of soil to support and sustain agricultural production as a result of soil fertility decline is impacting negatively on agricultural growth. Increase in the price of inorganic fertilisers and limited availability of nutrients from organic amendments has reduced progress in improving soil fertility. This research therefore aims at contributing knowledge towards evaluating the maximisation/optimisation of nutrients in compost and secondary treated sewage effluent (STSE) amended soils to meet the nutritional requirements of crops for sustainable crop production and environmental protection. STSE was irrigated on soils (sandy loam and clay loam) amended with greenwaste compost in soil incubation, glasshouse/pot and lysimeter studies. Perennial ryegrass (Lolium perenne) was grown in the pots and lysimeter studies. The incubation experiment showed that for a clay loam, N mineralisation in treatments with STSE alone and combinations of compost and STSE was higher than the applied N. Increasing compost quantity in compost and STSE nutrient integration resulted in reduced net N mineralisation in the clay loam soil. In the sandy loam, increasing compost contribution in compost and STSE nutrient integration resulted in an increase in net N mineralisation. Cation exchange capacity, microbial diversity, quality of available carbon and drying and rewetting cycles influenced the net nitrogen mineralisation dynamics in both soil types. Increasing the contribution of STSE while reducing compost quantity resulted in increased nitrogen use efficiency and ryegrass dry matter yield. The environmental threat to ground and surface water pollution through NO3 --N leaching may be enhanced by the inclusion of STSE in integrated compost and STSE nutrient supply to plants. Similarly, the threat to eutrophication due to phosphorous leaching is likely to be higher with integration of compost and STSE. Ryegrass dry matter yield reduced with increasing compost contribution while the concentration of N in ryegrass herbage for the combinations of compost and STSE was above the minimum requirement for N in herbage for productive grazing and dairy cattle in the pot experiment. Using compost and STSE of similar characteristics, the ideal approach to maximise nutrient potential from compost through irrigation with STSE is when 25% compost is integrated with 75% STSE with respect to nitrogen supply.

Wicken Fen represents a remnant of the once extensive peat fenlands of East Anglia, which survived large-scale drainage efforts intended to bring land into agricultural production due to its importance within the local economy and subsequently as a site of interest to scientists. Wicken Fen is managed so as to conserve a variety of habitats lost as a result of drainage and therefore does not represent a truly natural environment. Traditional management practices on Sedge Fen, the largest part of Wicken Fen, involve maintaining a 3 – 4 year harvesting cycle and controlling soil water levels. Previous hydrological studies of Wicken Fen have determined that soil water levels are strongly influenced by precipitation and evapotranspiration. The evaporative flux at Sedge Fen is commonly estimated by using meteorological data within empirical formulae such as the Penman Monteith equation owing to measurement difficulties. Furthermore, there has been little investigation of the evaporative loss from fens within the UK. This study aims to investigate the evaporative loss from Sedge Fen so as to better inform hydrological management and to describe evapotranspiration estimation techniques which may be employed at other fen sites. Eddy covariance measurements demonstrated that evapotranspiration from Sedge Fen was typically less than reference evapotranspiration estimates. Evapotranspiration estimates may be improved by consideration of surface parameters which can be described using meteorological data. Meteorological differences existed between Sedge Fen and the surrounding area, resulting in differing evapotranspiration estimates depending on where data was collected. Evapotranspiration measurements were used within a simple water budget model of Sedge Fen and demonstrated the lateral movement of soil water, a hydrological flux previously assumed to be of little consequence within the hydrological balance of Sedge Fen.

Stodmarsh National Nature Reserve includes the largest reedbed in Southern England and is an important habitat for breeding waders and several rare bird species, including Bitterns. A succession of drought years in the 1990s brought the issue of the hydrology and water requirements of the wetland to the attention of managers and there is concern about future water supplies to the reserve. This study aims to calculate the amount of water required by the site in order to maintain optimum habitat conditions. The greatest area of uncertainty in the water balance is the evapotranspiration rate of the reedbeds and therefore a secondary aim is to increase understanding of this flux. Detailed hydrological measurements were carried out over two years to establish the water balance of the site. Evapotranspiration was measured using the Bowen ratio technique, accompanied by additional physiological and meteorological measurements. Results showed that evapotranspiration from reeds was generally less than reference evapotranspiration and that stornatal resistance was the most important factor controlling evapotranspiration rates. The hydrology of the site was modelled using a thirty year historical data series to quantify the return periods of flood and drought conditions of different severity. These were used to predict water resource requirements and availability and confidence limits were attached to the results. In 70% of years, summer deficits in the rainfall-evapotranspiration balance require the addition of water from the Lampen Stream. In 10% of these years, the entire surmner discharge of the Lampen Stream would be insufficient to meet site water requirements and an additional source of water is required. Competition with other water users and limits on abstraction will increase the number of years an additional water source is required. In addition future climate change is likely to increase summer water requirements whilst decreasing resource availability.

Rainfall in the northeast arid zone of Nigeria is limited and has been found to be declining over the last three decades (Hess et al., 1995). This problem of inadequate rainfall is further exacerbated by runoff especially on the degraded lands (fako). Such runoff-prone lands are potential areas for water harvesting. In dry years, harvested runoff water can considerably improve the environmental conditions for plant growth and can make the difference between death and survival. However, water conservation techniques will only show a benefit if the soil is able to hold the extra water within the root zone of the crops. A clear understanding of soil properties and moisture variations on these lands should provide the baseline information needed for applied soil and water management research. Aerial photographs and photo mosaics were used to identify several fako lands out of which three sites were selected for detailed study. The three sites were located at Jawa (12° 48.71’ N, 11° 02.21* E), Zurkaya (12° 49.15’ N, 11° 05.52’ E) and along Dumburi road (12° 54.31!N, 11° 07.49!E). The fako lands have compacted loamy and clay loamy soils with low infiltration rate and hydraulic conductivity. Dry bulk density values range between 1.34 gem ̄3 to 1.61 gem ̄3 and saturated hydraulic conductivity obtained were between 1 mm/h and 6 mm/h. Water retention characteristic curves revealed that the fako soils have good water holding capacity. Slopes are generally gentle and range from 0.1% to about 1%. Volume of water harvested depends on the runoff yield of an area. Models can be used to estimate runoff on the fako lands. The model to be used will depend upon the available information, the required accuracy and the resolution of the output and the time resources that can be directed at the modelling exercise. As the rainfall data available for the area is in daily time step, a model that can use daily rainfall as input to estimate runoff is required. In order to develop such a model, accurate rainfall-runoff records for several years should be obtained. High-resolution rainfall data for 13 site-years were collected between 1992 and 1994. The EUROSEM model (Morgan et al., 1992) was applied to simulate the rainfall events and partition them into overland flow and infiltrated water. The model was however calibrated and validated before being used for the simulations. For the calibration and validation, a rainfall simulator (USDA, 1972) was constructed and 32 rainfall-runoff events at intensities of between 25 mmh ̄1 and 169 mmh ̄1 were artificially generated on the three sites. A graph of measured versus simulated runoff events showed good agreements in both calibration and validation. Coefficients of determination and efficiency were 0.82 each in calibration and 0.83 and 0.74 in validation. Predicted runoff by the EUROSEM model was regressed against daily rainfall to obtain a linear regression model for predicting runoff from daily rainfall for the fako lands of north-east Nigeria. The model can be regarded as an integral expression of the physiographic and climatic characteristics that govern the relations between rainfall and runoff on the fako areas. Runoff coefficient and threshold value obtained for the area were 0.44 and 16 mm respectively. The linear model was compared to the curve number model and the runoff estimates by both models were similar. The developed linear model was combined with a water balance model, BALANCE (Hess, 1994) and applied to microcatchment water harvesting investigations. The BALANCE model was used to estimate the water balance components for the area. The Ritchie equation in the BALANCE model was calibrated and validated with field data. Measured versus predicted soil moisture plot gave R2 values of 0.90 and 0.89 in calibration and validation respectively. Growth of neem tree (Azadirachta indica) on a typical fako land was simulated with different microcatchment sizes in three categories of years (dry, average and wet). Simulation results indicated that augmenting rainfall through runoff water harvesting technique could provide enough water to sustain growth and ensure rapid establishment of the neem tree seedlings. However, due to reduced dry spell some deep percolation may result during the peak of the rainy season (August - mid September) especially in wet years. A microcatchment size of 12m2 (basin-runoff area ratio of 1: 2) was found to sustain year round survival of the tree and minimum drainage for all categories of years. Complementary to water harvesting in the conservation measure, effect of three soil cover treatments (bare, perforated polyethylene cover and solid polyethylene cover) on soil evaporation was investigated. As expected, the solid cover was found to have the most effect in reducing soil evaporation but this is not suitable in the current situation because it limits infiltration of rain and free air circulation. The perforated cover treatment is preferred as it can also significantly reduce soil evaporation and at the same time allow unrestricted infiltration of rain and free exchange of gases between the soil and atmosphere.

Fogwater Harvesting has been demonstrated to be able to provide water for small rural communities in arid and semi-arid regions. Fog droplets coalesce on mesh screens and flow by gravity into a supply network. The technology is simple and can be maintained and managed by the users. The challenge is identifying suitable communities, environmental conditions and ensuring the system meets user demand sustainably. Following the First International Conference on Fog and Fog Collection (19-24 July 1998), a general project cycle for fogwater harvesting for domestic water supply is proposed and discussed. Methodologies and examples are reviewed and placed in an interdisciplinary project framework.