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When wastewater infiltrates into the soil, groundwater may be contaminated. If the distance from source of pollution to point of groundwater abstraction is small, there is a real chance of abstracting pathogenic microorganisms. In this book, the transport of Escherichia coli in aquifers under saturated conditions is studied. Starting point is the well known colloid filtration theory. Straining or physical sieving, geochemical heterogeneity, variable deposition rate coefficients, and preferential flow mechanisms are then included in the theory. The case of Sanaa, the capital of Yemen, served to evaluate the importance of bacteria transport processes in a field situation. This book is useful for hydrogeologists concerned with microbiological contamination of aquifers.

The doctoral research study conducted in Kenya gives the first insight into the performance of a constructed treatment wetland receiving pulp and paper mill wastewater in the tropics. The wetland effectively removed organic matter, suspended solids, phenols and nutrients. BOD and phenols reduction rates are reported for the first time. Design parameters and guidelines for the set-up and maintenance of a full-scale wetland are recommended. The study concludes that integrating a full-scale wetland, as a tertiary stage with the existing treatment ponds would significantly improve the quality of water in River Nzoia downstream of the effluent discharge.

Multi-channel estuaries, such as the Mekong Delta in Vietnam and the Scheldt in the Netherlands, have characteristics of both the river and the sea, forming a unique environment influenced by tidal movements of the sea and freshwater flow of the river. This study addresses a number of knowledge gaps in multi-channel estuaries by developing a predictive analytical approach for salinity intrusion and discharge estimate in multi-channel estuaries. The new approach agrees well with 1-D hydrodynamic models and observations, indicating its applicability in practice. Most importantly, the study has successfully developed a new theory and a new equation to quantify tidal pumping due to ebb-flood channel residual circulation and the related salt dispersion.

In this thesis a range of modelling techniques is explored to deal effectively with flood risk management. In particular, attention is paid to floods caused by failure of hydraulic structures such as dams and dikes. The methods considered here are applied for simulating dam and dike failure events, flood water routing in downstream areas, and flood risk reduction, providing a unified framework for addressing a variety of flood related events. Numerical, statistical and constraint based methods are applied to the problem of breach modelling and flood water mitigation.

Lake Victoria(East Africa) has in recent years undergone dramatic ecosystem changes that are not well understood. This research carried out between 2000 and 2004 found evidence of strong influence of wind-induced waves and currents on transport of surficial sediments. Paleolimnological reconstructions from bottom sediments concurred with earlier studies showing the occurrence of eutrophication, and suggested climate change to be a co-driver of lake ecosystem change. It is argued that eutrophication could have led to destruction of some littoral plants and induced changes in fish populations. The study recommends the introduction of measures to reduce nutrient exports to the lake.

Use and Fate of Pesticides in Vegetable-based Agroecosystems in Ghana presents the results of a doctoral study conducted on pesticide use in vegetable production in Ghana, West Africa. It covers the various aspects of pesticide use, behavior, and impacts in vegetable-based agroecosystems and presents the results of surveys conducted in Ghana. The doctoral study carried out between 2003 and 2007 aimed to provide a better understanding of the potential impact of pesticide usage on the ecosystem, which will contribute to better pesticide management. The results of the study establish essential, but yet missing, information on the levels and fate of pesticide residues in the environment of Ghana as well as the public health implications of the use of pesticides in agriculture. Students, scientists, farmers, agricultural extension officers and regulatory agencies will find this book very useful.

This book, based on a research conducted in the Wadi Laba, Eritrea, gives a comprehensive insight of the oldest, but the least understood indigenous water management systems for spate irrigation that relied on earthen/brushwood structures and customary water rights. The research further analyses the technical, institutional and environmental factors that led to the below expectation performance of the concrete headwork and contemporary water laws centred water management reforms as far as increasing the annually irrigated area, doubling the production and improving the standard of living are concerned. This research presents a Soil Water Accounting Model (SWAM), which is also supplied on a CD. This new model can be easily used by (spate)irrigation and water management experts to maximize the yield per unit quantity of water and irrigated land. A new sodicity analyses approach is also proposed.

Mangroves inhabit tropical coastlines and are particularly abundant along deltas and bays where rivers bring freshwater and sediment to the sea. This habitat witnesses great variability in sedimentation and erosion rates, partly governed by variation in hydrodynamics of rivers as well as the sea. Sedimentation and hydrodynamics have a great impact on coastal and mangroves dynamics. Sediment accretion creates new mud flats for colonization whilst exposure to waves and currents may strongly hinder colonization and promote coastal erosion. This study has experimentally quantified responses of mangroves to sedimentation and hydrodynamics. It integrated these findings with demographic and phenological data to develop a simple models and predict mangrove colonization success. Three common Southern Thailand mangrove genera were investigated: Avicennia, Rhizophora and Sonneratia. Responses of the three species were quite different. In sheltered coastal bays, mangroves were able to colonize newly-formed mudflats. Abrupt high sedimentation, however, led to vast mortality in Avicennia but it had less impact on survival and growth of Rhizophora and Sonneratia. Water turbulence had great impact on Rhizophora seedling growth and survival. In contrast, Avicennia and Sonneratia were able to survive and grow well in exposure condition. The integrating models showed that water turbulence and seedling herbivory had the most important impacts on mangrove colonization success. In 30-year simulations, Avicennia was the most successfully colonizing species followed by Sonneratia. Probable sea level rise scenarios seriously reduced colonization success of all species.

Population pressure and depletion of natural resources are forcing land use changes that are intended to improve agricultural productivity. Farmers from high potential highlands are migrating into semi-arid lowlands in search of land and livelihoods. The semi-arid areas were primarily used for ranching and wildlife. Settlement of smallholder farmers has led to land sub-division and intensification of agriculture. Uncontrolled abstraction of irrigation water from rivers that serve downstream users has also aggravated the situation. Therefore, the recent land use changes have led to conflict over water and land resources. The book presents the hydrological impacts of rainwater harvesting and management systems, which can upgrade rainfed agriculture and increase land productivity, on water resources management and socio-economic development in water scarce upper Ewaso Ngiro river basin in Kenya.

Potential impacts of climate change/variability on regional or local precipitation patterns and, subsequently, the hydrology of individual river basins have received a growing attention. This research aims to improve our understanding of the hydrological response of a large river basin (the Meuse in northwestern Europe) to climate variability and land use change. Based on the statistical trend results in combination with the hydrological modelling results, the historical rainfall-runoff relations in the Meuse basin and the hydrological effects of human activities (particularly land use changes) during the 20th century have been assessed

Groundwater recharge estimation in crystalline basement aquifers in semi-arid tropical areas is best estimated at monthly time scales as this best captures the dynamics of recharge processes in these areas. Whilst it is standard practice to use at least two methods to estimate the recharge it may be cheaper and equally accurate to obtain a first order monthly recharge estimate as a function of number of rain days in the month, average monthly rainfall, daily interception threshold, average root depth, effective porosity and average depth to water table. This is so because evaporative fluxes, mostly interception, are largely responsible for determining the potential for recharge in such areas.