The role of small hydropower is becoming increasingly important on a global level. Increasing energy demand and environmental awareness has further triggered research and development into sustainable low-cost technologies. In developing countries, particularly in rural areas, the possibility of local power generation could considerably improve living conditions. With this in mind, the development of a next generation low-head hydropower machines was subject of investigation in the EU-project HYLOW. Being part of the research lines of that project, this thesis presents a numerical modelling approach to improve the design of machines like water wheels for increased hydraulic efficiency. Nowadays, Computational Fluid Dynamics (CFD) enables numerical models to be quite accurate and incorporate physical complexities like free surfaces and rotating machines. The results of the CFD simulations carried out in this research show that a change in blade geometry can result in higher torque levels, thereby increasing performance. Numerical simulations also enabled to determine the optimal wheel-width to channel-width ratio and further improve performance by modifying the channel bed conditions upstream and downstream of the water wheel. With a power rating in the low kilowatt range, low-head hydropower machines like optimised water wheels seem to have a clear potential for small-scale energy generation, thereby contributing to achieving the Sustainable Development Goals by providing local energy solutions.

A considerable amount of scientific evidence has been collected leading to the conclusion that urban wastewater components should be designed as one integrated system, in order to protect the receiving waters cost-effectively. Moreover, there is a need to optimize the design and operation of the sewerage network and wastewater treatment plant (WwTP) considering the dynamic interactions between them and the receiving waters. This book introduces a method called Model Based Design and Control (MoDeCo) for the optimum design and control of urban wastewater components. The book presents a detailed description of the integration of modelling tools for the sewer, the wastewater treatment plants and the rivers. The complex modelling structure used for the integrated model challenge previous applications of integrated modelling approaches presented in scientific literature. The combination of modelling tools and multi-objective evolutionary algorithms demonstrated in this book represent an excellent tool for designers and managers of urban wastewater infrastructure. This book also presents two alternatives to solve the computing demand of the optimization of integrated systems in practical applications: the use of surrogate modelling tools and the use of cloud computer infrastructure for parallel computing.

The enhanced biological removal of phosphorus (EBPR) is a popular process due to high removal efficiency, low operational costs, and the possibility of phosphorus recovery. Nevertheless, the stability of the EBPR depends on different factors such as: temperature, pH, and the presence of toxic compounds. While extensive studies have researched the effects of temperature and pH on EBPR systems, little is known about the effects of different toxic compounds on EBPR. For example, sulphide has shown to inhibit different microbial activities in the WWTP, but the knowledge about its effects on EBPR is limited. Whereas the sulphide generated in the sewage can cause a shock effect on EBPR, the continuously exposure to sulphide potentially generated in WWTP can cause the acclimatization and adaptation of the biomass. This research suggests that sulphate reducing bacteria can proliferate in WWTP, as they are reversibly inhibited by the recirculation of sludge through anaerobic-anoxic-oxic conditions. The research enhances the understanding of the effect of sulphide on the anaerobic-oxic metabolism of PAO. It suggests that the filamentous bacteria Thiothrix caldifontis could play an important role in the biological removal of phosphorus. It questions the ability of PAO to generate energy from nitrate respiration and its use for the anoxic phosphorus uptake. Thus, the results obtained in this research can be used to understand the stability of the EBPR process under anaerobic-anoxic-oxic conditions, especially when exposed to the presence of sulphide.

The unprecedented growth of cities has a significant impact on future flood risk that might exceed the impacts of climate change in many metropolitan areas across the world. Although the effects of urbanisation on flood risk are well understood, assessments that include spatially explicit future growth projections are limited. This comparative study provides insight in the long term development of future riverine and pluvial flood risk for 18 fast growing megacities. The outcomes provide not only a baseline absent in current practise, but also a strategic outlook that might better establish the role of urban planning in limiting future flood risk.

Providing an introduction to the crucially important topic of groundwater, this text covers all major fields of hydrogeology and includes outlines of the occurrence of groundwater in various rock types, the movement and storage of groundwater, the formulation of groundwater balances, the development of groundwater chemistry, as well as the practical application of hydrogeology for groundwater development. Following a unique systems approach to describe and connect its various elements, the text also explores a large selection of examples of groundwater cases from various parts of the world. In addition, theoretical sections and examples are illustrated with a number of drawings, photos and computer printouts. Suitable for education in hydrogeology at postgraduate and graduate level, the text is also a useful reference tool for professionals and decision-makers involved in water or water-related activities. In the revised paperback edition more attention is paid to the processes in the unsaturated zone, especially those relating to groundwater recharge. Also, the investigation methods are highlighted in the sections where the related theory is dealt with, and they are not presented in the last chapter on groundwater management. The References and Bibliography section is also extended, some figures are improved, and the inevitable 'typing errors' are corrected as well. In the third edition, a more formal basis for the hydro-chemical processes described in the chapter on groundwater chemistry has been added. Mass balances and the principles of dispersion and retardation are introduced. Additional illustrations are provided, also explaining the processes occurring along streamlines. Consult: http://introductiontohydrogeology.nl/ for additional information on the book, the author and available software.

Constructed Wetlands (CWs) are among the few natural treatment systems that can guarantee an efficient wastewater treatment and an appealing green space at the same time. However, they require large areas for their construction, which is not available in many cases. In this thesis, two domestic wastewater treatment options were designed and studied with the purpose of having a low space requirement: the Duplex-CW and the Constructed Wetoof (CWR). The Duplex-CW is a hybrid CW composed of a vertical flow CW on top of a horizontal flow filter. The stacked arrangement is the key for reducing the CW footprint. The CWR is a shallow HF CW placed on the roof of a building, thus it does not occupy any land. Several modifications and improvements have been tested, in addition to the study of the treatment performance, in order to select the most appropriate Duplex-CW and CWR design. Overall, this thesis contributes to the development of two efficient domestic wastewater treatment technologies. The Duplex-CW area requirement is still higher than many CWs and therefore further improvements are necessary. The CWR is the foremost option to save land areas since it requires 0 m2 of land per person equivalent.

The Enhanced Biological Phosphorus Removal (EBPR) process is a biological process for efficient phosphate removal from wastewaters through intracellular storage of polyphosphate by Phosphate-Accumulating Organisms (PAO) and subsequent removal through wastage of excess sludge. Although many studies have demonstrated the existence of different PAO clades, the functional differences among these clades and potential implications for the process performance remained unclear. Furthermore, the salinity effects on the EBPR process had not been properly investigated, which is necessary to assess its applicability for the treatment of saline wastewaters. The first part of the thesis focuses on the functional diversity among PAO clades. It demonstrates significant functional differences in the main characteristics of the anaerobic metabolism of two different PAO clades and provides fundamental insight in the metabolic response of PAO to different influent P/C ratios. In addition, it shows how these functional differences provide competitive advantages to specific PAO clades in a selection study and discusses their potential implications on process performance, in particular for combined biological and chemical systems for nutrient removal and recovery. The second part of the thesis describes the salinity effects on the metabolism of PAO and their competitors that do not contribute to phosphorus removal; the so-called Glycogen-Accumulating Organisms (GAO). It shows how salinity affects the different metabolic processes (kinetics and stochiometry) of PAO and GAO and provides a model that describes the salinity effects on their kinetic rates. Finally, it discusses the potential implications of sudden saline shocks in wastewater treatment systems that are not regularly exposed to salinity.

Computers are increasingly used in the simulation of natural phenomena such as floods. However, these simulations are based on numerical approximations of equations formalizing our conceptual understanding of flood flows. Thus, model results are intrinsically subject to uncertainty and the use of probabilistic approaches seems more appropriate. Uncertain, probabilistic floodplain maps are widely used in the scientific domain, but still not sufficiently exploited to support the development of flood mitigation strategies. In this thesis the major sources of uncertainty in flood inundation models are analyzed, resulting in the generation of probabilistic floodplain maps. The utility of probabilistic model output is assessed using value of information and the prospect theory. The use of these maps to support decision making in terms of floodplain development under flood hazard threat is demonstrated.

The relationship between environmental agencies and polluters is especially challenging in the context of micro and small sized enterprises (McSEs) in developing countries. The focus is mainly at end-of-pipe solutions that are usually unaffordable for McSEs. In order to engage them in achieving national environmental policy goals, this thesis reflexively combines the theoretical fields of Action Research and Negotiation/Conflict Resolution to fill the gaps in knowledge. A methodology was developed that is problem-driven and iterative by using longitudinal data collection rather than snap-shots. Along with a comparative study of two regional tannery cases, a new approach based on Action Research named SASI (Systematic Approach for Social Inclusion) was designed and tested for six years on cleaner production (CP) implementation with a third tannery case. The results highlight how institutional barriers in Colombia negatively affect the McSEs. The research shows that CP implementation needs comprehensive, systemic mechanisms based on participatory approaches that take into account the concerns and contexts of McSEs. Doing Action Research through SASI generated both theoretical insight and positively changed the lives of the tanners engaged in the research. It contributed to breaking the cycles of their exclusion and simultaneously facilitated innovation and use of local knowledge.

In The Netherlands, Belgium and other European countries, manganese is removed by conventional groundwater treatment with aeration and rapid (sand) filtration. Such a treatment process is easy to operate, cost effective and sustainable, because it does not make use of strong oxidants such as O3, Cl2, ClO2 and KMnO4 with the associated risk of by-product formation and over or under dosing. However, application of aeration-filtration is also facing drawbacks, especially the long ripening time of filter media. Due to the long ripening time, water companies have to waste large volumes of treated water, making this process less sustainable. Also, costs associated with filter media ripening (man power, electricity, operational and analysis costs) are high. Therefore decreasing the filter ripening time, regarding manganese removal is a big issue. Although already extended research has been carried out into manganese removal, the controlling mechanisms, especially of the start up face of filter media ripening, are not fully understood yet. The emphasis of this thesis is to provide a better understanding of the mechanisms involved in the ripening of virgin filter media, regarding manganese removal and how to shorten or completely eliminate the long ripening period of filters with virgin material. This thesis therefore highlights the role of the formation of a manganese oxide coating on virgin filter media. Characterization and identification revealed that the responsible manganese oxide for an effective manganese removal was Birnessite. It was found that Birnessite, formed at the beginning of the ripening process was of a biological origin. Based on the knowledge that manganese removal in conventional groundwater treatment is initiated biologically, long ripening times may be reduced by creating conditions favouring the growth of manganese oxidizing bacteria, e.g., by limiting the back wash frequency and / or intensity. Additionally, this thesis also shows that the use of freshly prepared manganese oxide, containing Birnessite, can completely eliminate filter media ripening time.

Quantitative research with respect to the combination of engineering and socialcultural- religious aspects based on the Tri Hita Karana philosophy in Subak irrigation schemes is original in the field of land and water development. A scenario analysis needs a good and careful system approach. Based on a Generic Algorithm the RIBASIM model was applied using the dependable 80% of discharge and shifting the start of land preparation. The results provide evidence that the cropping pattern of the fifth scenario results in an overall optimal agriculture production of the Subak schemes. The recoverable flow considered in the river basin scheme model plays an important role in the optimisation. Nevertheless, if a normal hydro-climate occurs, the other scenarios, especially the first scenario, can be applied as well. When the indigenous knowledge of farmers is compromised with present day knowledge of agricultural and technological developments, capability of these farmers increases, thus reflects the applicability of the Tri Hita Karana philosophy on harmony among people and harmony among people and nature.

Hydrological research in humid tropics is particularly challenging because of highly variable hydrological conditions and high socio-economic stresses caused by rapid population increase, as is the case of Nicaragua. The objective of this research is to understand the surface and subsurface runoff generation processes in a poorly gauged coastal catchment in Nicaragua under variable humid tropical conditions. Specifically, it focuses on identifying geomorphological and hydro-climatic controls on catchment response at different spatio-temporal scales and studies the link between hydrological processes and ecosystem conditions (i.e. mangrove forest). Catchment topography, geology and land use control surface and subsurface runoff generation. Spatio-temporal variability of precipitation affects availability of water resources, determines sources of surface runoff generation and induces changes in groundwater-surface interactions. Sustainable water resources management must prevent drastic alterations in catchment structural characteristics defined by forested areas and tidal sand ridges. Catchment response to hydro-climatic and geomorphologic controls supports the mangrove ecosystem freshwater needs. The outcome of this work is a contribution to the hydrological knowledge of poorly gauged catchment in humid tropics. It also provides scientific hydrological insights to support water resources management on the South Pacific coast of Nicaragua.

After World War II, international development became the world leading development model, but its effectiveness is much debated. Nowadays, it is acknowledged that international development can effectively support development through knowledge and capacity development (KCD). Nonetheless, understanding what capacity really consists of in operational terms and what its development entails remains a challenge. This book investigates KCD processes in water utilities in Sub-Saharan Africa. The three cases analysed reveal that the learning impact of KCD on utilities depends on whether they are able to close their learning cycle, i.e., to ensure that improved capacity is also translated into mainstream behaviour. This finding challenges conventional wisdom for which KCD translates "automatically" into improved performance. Hence the need to focus KCD evaluation on both capacity improvement and capacity application. The proposed learning-based framework for KCD identifies two distinct but interrelated stages in KCD, namely knowledge transfer and knowledge absorption. Knowledge absorption usually takes time due to slow organisational processes that govern it. However, in practice it is often taken for granted. The framework also identifies the key factors that shape learning processes in water utilities. The book argues that water utilities in Sub-Saharan Africa can reinvent themselves by embracing change management approaches and striving to become learning organisations.

Urban flood risks and their impacts are expected to increase as urban development in flood prone areas continues and rain intensity increases as a result of climate change while aging drainage infrastructures limit the drainage capacity in existing urban areas. Flood mitigation strategies are required as part of sound urban flood management plans to assess flood risk and identify technically feasible and cost-effective options to reduce the risk. Central to the development of flood mitigation strategies is the efficient prediction of flood propagation characteristics in urban areas. Detailed predictions of flood flows in urban areas require the use of high resolution topographic data. However, due to computational demand topographic data is often generalised to a more manageable resolution and floodplain models are built at much coarser resolutions. The research presented in this thesis addresses the problem of capturing small-scale features in coarse resolution urban flood models with the aim of improving flood forecasts in geometrically complex urban environments. The approach adopted in the research used a two-dimensional surface flow modelling system that can extract and incorporate useful information available in high resolution topographic data into coarse grid models. The thesis also presents modelling of the complex interaction between surcharged sewer and flows associated with urban flooding and incorporation of infiltration process in surface flow modelling tools. Case study results showed that the incorporating volume-depth and flow-area-depth relationships extracted from high resolution topographic data significantly improved the results of coarse grid urban flood models while taking the advantage of reduced computational time to ensure efficient prediction of urban flood characteristics.

Climate change, rapid population growth and urbanization are causing water shortage and pollution, especially in arid and semi-arid regions of the world due to the growing demand in different sectors and disposal of inadequately treated wastewater to water bodies. To tackle these challenges, further treatment and reuse of wastewater effluent using soil aquifer treatment (SAT) is an attractive cost-effective and environmentally friendly option that is employed with no intensive use of electricity and chemicals. This study highlights the prospects of using SAT for treatment and reuse of primary effluent (PE), especially in developing countries where wastewater is not treated to secondary and tertiary effluent levels due to lack of investment and operation costs to run sizable wastewater treatment plants (WWTPs). Coupled with experimental studies that show SAT efficiency to remove suspended solids, bulk organic matter, nutrients and pathogens indicators from PE, the thesis provides step-by-step tools that could be used for development of new SAT scheme. Furthermore, the study provides a water quality prediction model that estimates the potential contaminants removal which could be used to assess the need for reclaimed water post-treatment. This thesis is envisaged to contribute to the current knowledge on the necessity of water reuse.

Urban informal settlements or slums are growing rapidly in cities in sub-Saharan Africa. Most often, a sewer system is not present and the commonly-used low-cost onsite wastewater handling practices, typically pit latrines, are frequently unplanned, uncontrolled and inefficient. Consequently, most households dispose of their untreated or partially treated wastewater on-site, generating high loads of nutrients to groundwater and streams draining these areas. However, the fate of nutrients in urban slums is generally unknown. In excess, these nutrients can cause eutrophication in downstream water bodies. This book provides an understanding of the hydro-geochemical processes affecting the generation, fate and transport of nutrients (nitrogen and phosphorus) in a typical urban slum area in Kampala, Uganda. The approach used combined experimental and modeling techniques, using a large set of hydrochemical and geochemical data collected from shallow groundwater, drainage channels and precipitation. The results show that both nitrogen-containing acid precipitation and domestic wastewater from slum areas are important sources of nutrients in urban slum catchments. For nutrients leaching to groundwater, pit latrines retained over 80% of the nutrient mass input while the underlying alluvial sandy aquifer was also an effective sink of nutrients where nitrogen was removed by denitrification and anaerobic oxidation and phosphorus by adsorption to calcite. In surface water, nutrient attenuation processes are limited. This study argues that groundwater may not be important as regards to eutrophication implying that management interventions in slum areas should primarily focus on nutrients released into drainage channels. This research is of broad interest as urbanization is an ongoing trend and many developing countries lack proper sanitation systems.

Population growth in the Blue Nile Basin has led to fast land-use changes from forest to agricultural land, which resulted in speeding up the soil erosion processes producing highly negative impacts on the local soil fertility and agricultural productivity. The eroded sediment is transported downstream by water and sinks in the lower basin where it significantly reduces reservoir storage and irrigation canals capacity. The only effective solution to mitigate the sedimentation problem is to limit the sediment inputs from upstream by locally implementing erosion control practices. However, given the vastness and remoteness of the involved areas, this first requires the knowledge of the most critical zones. The book identifies the sources of the sediment depositing in the Lower Blue Nile Basin and quantifies the amounts involved providing essential information for the planning and implementation of any interventions aiming at reducing soil erosion. The methods used consist of extensive field work covering most of the basin, watershed, hydrodynamic and morphodynamic modelling and, for the first time, the mineralogical analysis of the sediment at the sources and sinks. The method is successful in indentifying the areas providing most of the transported sediment, where it is recommended to start with erosion control practices.

The rate of global increase in water abstraction for irrigation has been declining since the 1970's due to declining potentials for large and medium-scale irrigation developments, and is expected to further decline in the next decades. As such the significant proportion of the expected increase in production would have to be supplied from existing irrigated and /or cultivated lands. This in turn could be achieved by enhancing land and water productivity through improved performance and optimal operation and maintenance. With less than 15% of over 5 million ha irrigation potential harnessed, irrigation devolvement in Ethiopia remained low. Over 70% of the developed irrigation in the country belongs to small-scale irrigation serving smallholder farmers. While accelerated development of new irrigation, particularly of large and medium-scale schemes is relevant in Ethiopia, ensuring the performance and sustainability of existing schemes is also equally important. The existing irrigation schemes in Ethiopia are generally characterized by an overall performance and technical sustainability levels of below expectation. This thesis evaluates the performance of two large-scale (Wonji-Shoa and Metahara) and two community-managed (Golgota and Wedecha) irrigation schemes located in the Awash River Basin of Ethiopia. The study focussed on hydraulic/water delivery performance in the large-scale schemes, and on comparative and internal irrigation service (utility) evaluation in the community-managed schemes. Water delivery performance was evaluated using routine data and hydrodynamic modelling. Farmers' utility was evaluated using qualitative responses of water users. Major performance challenges in each category of schemes were addressed and operational/water management options for improvement were identified.

The Abay / Upper Blue Nile basin contributes the largest share of discharge to the river Nile. However, the basin exhibits large spatio-temporal variability in rainfall and runoff. Moreover, human activities also impact hydrological processes through intensive agriculture, overgrazing and deforestation, which substantially affect the basin hydrology. Thus, understanding hydrological processes and hydro-climatic variables at various spatio-temporal scales is essential for sustainable management of water resources in the region. This research investigates the hydrology of the basin in depth using a range of methods at various spatio-temporal scales. The methods include long-term trend analysis of hydroclimatic variables, hydrologic responses analysis of land cover change, stable isotope techniques and process based rainfallrunoff modelling. A combination of field investigations with new measurements of precipitation, water levels and stable isotopes as well as existing hydro-climatic data offered gaining new insights about runoff generation processes in headwater catchments. The use of rainfall-runoff modelling in two meso-scale catchments of the Abay basin depict that a single model structure in a lumped way for the entire Abay basin cannot represent all the dominant hydrological processes. The results of the different approaches demonstrated the potential of the methods to better understand the basin hydrology in a data scarce region.

This thesis aims to explore the potential and limitations of low-cost, space-borne data in flood inundation modelling under unavoidable, intrinsic uncertainty. In particular, the potential in supporting hydraulic modelling of floods of: NASA's SRTM (Shuttle Radar Topographic Mission) topographic data, SAR (Synthetic Aperture Radar) satellite imagery of flood extents and radar altimetry of water levels are analyzed in view of inflow and parametric uncertainty. To this end, research work has been carried out by either following a model calibration-evaluation approach or by explicitly considering major sources of uncertainty within a Monte Carlo framework. To generalize our findings, three river reaches with various scales (from medium to large) and topographic characteristics (e.g. valley-filling, two-level embankments, large and flat floodplain) are used as test sites. Lastly, an application of SRTM-based flood modelling of a large river is conducted to highlight the challenges of predictions in ungauged basins. This research indicates the potential and limitations of low-cost, space-borne data in supporting flood inundation modelling under uncertainty, including findings related to the usefulness of these data according to modelling purpose (e.g. re-insurance, planning, design), characteristics of the river and considerations of uncertainty. The upcoming satellite missions, which could potentially impact the way we model flood inundation patters, are also discussed.

The Gezira Scheme is Sudan's oldest and largest gravity irrigation system. The scheme has played an important role in the economic development of the country, and is a major source of foreign exchange. The farming system of the Gezira Scheme is dominated by crop production. The main crops grown are sorghum, wheat, groundnut and the oilseed crop sesame. Sunflower (Helianthus annuus L.) is an important oil crop in the world and a new edible oil crop in Sudan. Knowledge of the effects of irrigation scheduling on sunflower production and water productivity under water stress conditions is becoming increasingly important. Irrigation scheduling is particularly important since many field crops are more sensitive to water deficit at specific phonological stages. Sunflower has several growth stages: emergence, vegetative, reproductive, flowering, seed formation and maturity. Water stress in each stage results in reduction in seed yield and oil content. The treatments in the test plots, which were conducted to study the effect of water stress at different growth stages, showed that sunflower was significantly affected by water stress that occurred in the sensitive flowering and seed formation stages. Highest seed yield was obtained when water stress was avoided during these stages. The AquaCrop model was used to simulate the seed yield and water productivity. The model was able to precisely simulate seed yield, but overestimated water productivity under different irrigation treatments.

This work explores coastal zones in the vicinity of tidal inlets, which are commonly utilized for navigation, sand mining, waterfront developments and fishing and recreation, are under particularly high population pressure and will only be exacerbated by foreshadowed climate change (CC). Although few recent studies have investigated CC impacts on very large tidal inlet systems, the nature and magnitude of CC impacts on the more commonly found small tidal inlets (STIs) remains practically un-investigated to date. The combination of pre-dominant occurrence in developing countries, socio-economic relevance and low community resilience, general lack of data, and high sensitivity to seasonal forcing makes STIs potentially very vulnerable to CC impacts. This study was undertaken to develop methods and tools that can provide insights on potential CC impacts on STIs, and to demonstrate their application to assess these CC impacts. Two process based snap-shot modeling approaches for data poor and data rich environments are used to assess CC impacts and an innovative reduced complexity model is developed to obtain rapid predictions of CC impacts on the STI's stability. Results show that STIs are unlikely to change their types, but that their stability level is likely to change under CC impacts. The main driver for the change is the future variations in wave directions, not SLR as is commonly thought.

Mountains are water towers of our world, but their role in global water resources may be altered due to changing climate. This book provides an integrated assessment of the spatial and temporal variability of both recent and future climate change impacts in the Yellow River source region (YRSR) with specific focus on extremes. The book is structured across four different topics from detecting contemporary hydro-climatic changes, comparing three different statistical downscaling methods, assessing elevation dependency of expected changes in temperature, and projecting future climate-induced hydrologic changes in the YRSR. The detection of historical hydro-climatic changes in recent decades indicates that climate change may already be happening and may pose a serious threat to water availability in this region. However, an ensemble of climate change projections for the periods 2046-2065 and 2081-2100 based on two GCMs and three emission scenarios demonstrates that the future water availability of this region would increase due to climate change. This discrepancy suggests that contemporary hydro-climatic experience based on past records alone may not always provide a reliable guide to the future. This study makes an important contribution toward an improved understanding of climate change impacts in the YRSR. The knowledge generated has major implications for water resources management in the Yellow River and will be instructive for climate change impacts studies in other mountain areas.

The field of ecohydraulics integrates hydrodynamic and eco-dynamic processes. While hydrodynamic processes are usually well described by partial differential equations (PDE's) based on physical conservation principles, ecosystem dynamics often involve specific interactions at the local scale. Because of this, Cellular Automata (CA) are a viable paradigm in ecosystem modelling. All cells in a CA system update their states synchronously at discrete steps according to simple local rules. The classical CA configuration consists of uniformly distributed cells on a structured grid. But in the field of hydrodynamics, the use of unstructured grids has become more and more popular due to its flexibility to handle arbitrary geometries. The main objective of this research is to identify whether the CA paradigm can be extended to unstructured grids. To that end the concept of Unstructured Cellular Automata (UCA) is developed and various UCA configurations are explored and their performance investigated. The influence of cell size was analyzed in analogy with the Finite Volume Method. A characteristic parameter -min distance of UCA- was put forward and tested by numerical experiments. Special attention was paid to exploring the analogies and differences between the discrete CA paradigm and discrete numerical approximations for solving PDE's. The practical applicability of UCA in ecohydraulics modelling is explored through a number of case studies and compared with field measurements.

This study was built to investigate the impact of subsurface drainage on iron toxicity in Tropical Savannah irrigated rice valley bottoms. The research leaned upon two complementary approaches: field investigations and designed experiments. Important results, covering several fields, where achieved. For example, It appeared that single-season irrigation schemes present higher iron toxicity and acidity risks than double-season ones - 750 up to 1800 mg/l of Fe2+ higher in the single-season scheme of Moussodougou than in the double-season scheme of Tiefora. Furthermore, a statistical analysis of flow time series (ARIMA model) data was performed. It showed that with a simple water level measurement probe installed at the main gate of the scheme, it becomes possible not only to quantify irrigation water consumption, but also to diagnose farmers' irrigation schedule, providing them a means to defuse potential conflicts due to inequity in water distribution. Finally, it was shown that subsurface drainage increases ferrous iron concentration in hematite dominant soils soil - from 935 mg/l to more than 1106 mg/l in the case of the soil of Moussodougou - but also fortunately alleviate soil acidity - from pH 5.6 to 7.3 in Moussodougou. This effect will eventually reduce ferrous iron intake by rice roots, alleviating toxicity.