Showing papers in "Physics and Chemistry of The Earth in 2008"

Interbasin water transfers and integrated water resources management: Where engineering, science and politics interlock

Abstract: As the pressure on water is increasing, the risk that the required amounts of water will not be available is also increasing in many semi-arid areas. Interbasin water transfers are designed to secure access by artificially conveying water to locations where people need it. These are typical supply oriented engineering measures to large societal challenges. The engineering works are frequently daunting, involving diversion works, tunnels and/or large pumping schemes and reservoirs, and the costs are correspondingly large. The scale of engineering works and funds required are indicative of the magnitude of the needs and interests to be served. Interbasin water transfers trigger pertinent questions from different interests groups and communities involved and affected. This paper assesses the phenomenon of interbasin water transfers from a multi-disciplinary perspective, and attempts to answer the question whether such transfers are compatible with the concept of integrated water resources management. The problems related to interbasin water transfers are first introduced by reviewing four selected interbasin transfers taking place in different parts of the world. Then the criteria for assessing such transfers as proposed by international commissions, policy communities and scientists are reviewed, from which a coherent set of evaluation criteria are distilled for interbasin transfer schemes. This set of criteria is subsequently applied to the River Linking project in India, in order to provide a preliminary assessment. This is followed by a discussion of the temporal, spatial and resource scale effects, and finally conclusions are drawn about the required institutional capacity to control water and to adapt to changing policy environments.

Managing urban water supplies in developing countries Climate change and water scarcity scenarios

Abstract: Urban areas of developing countries are facing increasing water scarcity and it is possible that this problem may be further aggravated due to rapid changes in the hydro-environment at different scales, like those of climate and land-cover. Due to water scarcity and limitations to the development of new water resources, it is prudent to shift from the traditional ‘supply based management’ to a ‘demand management’ paradigm. Demand management focuses on measures that make better and more efficient use of limited supplies, often at a level significantly below standard service levels. This paper particularly focuses on the intermittent water supplies in the cities of developing countries. Intermittent water supplies need to be adopted due to water scarcity and if not planned properly, results in inequities in water deliveries to consumers and poor levels of service. It is therefore important to recognise these realities when designing and operating such networks. The standard tools available for design of water supply systems often assume a continuous, unlimited supply and the supplied water amount is limited only be the demand, making them unsuitable for designing intermittent supplies that are governed by severely limited water availability. This paper presents details of new guidelines developed for the design and control of intermittent water distribution systems in developing countries. These include a modified network analysis simulation coupled with an optimal design tool. The guidelines are driven by a modified set of design objectives to be met at least cost. These objectives are equity in supply and people driven levels of service (PDLS) expressed in terms of four design parameters namely, duration of the supply; timings of the supply; pressure at the outlet (or flow-rate at outlet); and others such as the type of connection required and the locations of connections (in particular for standpipes). All the four parameters are calculated using methods and techniques that recognise the relationship between outflow at a water connection and the pressure experienced at that connection. The paper presents a case study where it is demonstrated that the new guidelines can provide an equitable and acceptable level of service throughout the design horizon of the project.

Integrated water resources management: concepts and issues

Abstract: After the describing the historical developments that led the development of Integrated Water Resources Management (IWRM), the paper defines this important concept. It subsequently deals with the thorny issue of water security as well as water conflict, after which the major issues over which thus far no consensus has been achieved are briefly reviewed. The paper concludes with an analysis of the role of the IAHS International Commission on Water Resources Systems (ICWRS) in promoting IWRM.

Developing suitability maps for rainwater harvesting in South Africa

Abstract: Dry spells are a direct consequence of spatial and temporal variability of rainfall, and these jeopardise the success of rainfed agriculture by causing crop yield reduction and crop failure in rural South Africa. The potential of rainwater harvesting (RWH) to mitigate the spatial and temporal variability of rainfall has brought about its revival during the last two decades. For planning and implementation purposes, it is critical to be able to identify areas suitable for RWH. The paper presents a methodology that enable water managers to assess the suitability of RWH for any given area of South Africa. Previous methodologies developed to assess RWH suitability recognised the importance of the socio-economic factors but did not incorporate them in their assessment. This non-integration of socio-economic factors is pointed as the main cause of failure of rainwater harvesting projects. In this study, in-field RWH and ex-field RWH suitability maps are developed based on a combination of physical, ecological and socio-economic factors. Model Builder, an extension of ArcView 3.3 that enables a weighted overlay of datasets, is used to create the suitability model, comprising the physical, ecological and vulnerability sub-models from which the physical, the ecological and the vulnerability maps are derived respectively. Results indicate that about 30% is highly suitable for in-field RWH and 25% is highly suitable for ex-field RWH. Details of the proposed method as well as the suitability maps produced are presented in this paper. The implementation of this method is envisaged to support any policy shifts towards wide spread adoption of RWH.

Chemical impact on the hydro-mechanical behaviour of high-density FEBEX bentonite

Abstract: The effect of the salinity of the saturating fluid on the hydro-mechanical properties of the FEBEX compacted bentonite was investigated by means of swelling, compressibility and permeability tests in which deionised water and solutions of different concentrations and compositions were used as saturating fluids The solutions were chosen to simulate natural and extreme conditions in a high-level radioactive waste repository excavated in crystalline or clay host rocks The swelling capacity of the bentonite decreases with the increase in salinity of the pore water, although this difference becomes less patent for high vertical loads and high densities and when the salinity of the solution is very low The samples saturated with solutions containing high concentration of ions are also less deformable and consolidate more rapidly than the samples saturated with low-salinity solutions The hydraulic conductivity of the highly compacted saturated FEBEX bentonite increases when high-salinity permeants are used, especially for low densities and when the stress level is low The influence of the composition of the solution on the hydro-mechanical properties of the bentonite was also checked

Determining the unsaturated hydraulic conductivity of a compacted sand-bentonite mixture under constant-volume and free-swell conditions

Abstract: Highly compacted sand–bentonite mixtures are often considered as possible engineered barriers in deep high-level radioactive waste disposals. In situ, the saturation of these barriers from their initially unsaturated state is a complex hydro-mechanical coupled process in which temperature effects also play a role. The key parameter of this process is the unsaturated hydraulic conductivity of the barrier. In this paper, isothermal infiltration experiments were conducted to determine the unsaturated hydraulic conductivity according to the instantaneous profile method. To do so, total suction changes were monitored at different locations along the soil specimen by using resistive relative humidity probes. Three constant-volume infiltration tests were conducted showing, unexpectedly, a decrease of the hydraulic conductivity during infiltration. One test performed under free-swell conditions showed the opposite and standard trend. These observations were interpreted in terms of microstructure changes during wetting, both under constant-volume and free-swell conditions.

Trend analysis of rainfall in the headstreams of the Zambezi River Basin in Zambia

Abstract: Changes in catchment response as a result of climate change and/or variability continue to be of concern to hydrologists and water managers and thus identification and study of changes in rainfall as a major input into the hydrologic system remains pivotal in water resources management and planning for reliable input into modelling catchment response systems. An attempt has been made in this study to analyse long-term rainfall data obtained from five rain gauges (Kabompo, Kasempa, Mwinilunga, Mongu and Kaoma) located in the headstream regions of the Zambezi river basin in Zambia and to determine if these time series belonged to similar regime, have had any significant trends and if there was any homogeneity in trends among stations. To detect change in regime, the data were separately subjected to intervention analysis (using Cumulative Summation or CUSUM technique) and step change analysis (using rank-sum test) and subsequently the trend in each of the time series were determined using Mann–Kendall-statistic. The analyses undertaken to identify possibility of any intervention due to either natural and/or manmade causes, through the CUSUM technique, did not show signs of any major interventions except for Mongu station, where a change in regime was observed around 1980. This was even confirmed through step change analysis using the rank-sum test. Though the five stations showed marginal downward trends, these were not significant. Even, the test of homogeneity in trends observed at different stations showed homogeneity between them. Based on these findings, it was concluded that the rainfall data in the entire sub-basin belonged to a similar climate regime and the rainfall data for the entire period could be used for developing rainfall-response relationship except for Mongu, where the time series from 1981 onwards appear to have been subjected human/instrumental errors and needs to be investigated and updated.

Surface and groundwater water quality assessment using multivariate analytical methods: a case study of the Western Niger Delta, Nigeria

Abstract: This study investigates the natural and anthropogenic processes that influence the chemistry of surface and groundwater within the western Niger Delta region using multivariate statistical techniques. A total of 137 surface and groundwater samples were collected between 2003 and 2007 during the rainy and dry seasons, from 15 sites and analysed for their physico-chemical constituents. The chemical data set generated were subjected to Principal Component Analysis (PCA)/Factor Analysis (FA) and Hierarchic Cluster Analysis (HCA). PCA is a procedure for reducing data redundancy, while FA establishes the general relationship among variables. CA is used to detect spatial similarity among sampling sites. The results indicate five dominant processes or factors for surface water that explained 77.11% of the variance in the data set. In groundwater, the factors account for 80.55% of the total variance. Cluster analysis revealed a random spatial distribution of the chemical components investigated. This is consistent with the multipurpose nature of land use in the study area. The multiple natural and anthropogenic sources indicated by this study, and their unsystematic distribution show that proper land use planning and firm implementation of existing environmental laws is imperative in this oil producing region, in order to have effective surface water and groundwater resource management.

SWAT model application in a data scarce tropical complex catchment in Tanzania

Abstract: This study intended to validate the Soil and Water Assessment Tool (SWAT) model in data scarce environment in a complex tropical catchment in the Pangani River Basin located in northeast Tanzania. The validation process involved the model initialization, calibration, verification and sensitivity analysis. Both manual and auto-calibration procedures were used to facilitate the comparison of the results with past studies in the same catchment. For this study, some model parameters including Soil depth (SOL_Z) and Saturated hydraulic conductivity (SOL_K) were assumed uniform within the study catchment and were therefore lumped comprising the huge computation resource requirement of the SWAT model. Results indicated that the same set of important parameters was identified with or without the use of observed flows data. Some of the parameters had physical interpretation and could therefore relate directly to hydrological controlling factors within the catchment. Despite swapping ranking importance of parameters, these results suggest the suitability of the SWAT model for identifying hydrological controlling factors/parameters in ungauged catchments. Results of calibration and validation at the daily timescale gave moderately satisfactory Nash–Sutcliffe Coefficient of Efficiency (CE) of 54.6% for calibration and 68% for validation while simulated and observed mean annual flow discharges gave an Index of Volumetric Fit (IVF) of 100%. The study further indicated the improvement of model estimation when more reliable spatial representation of rainfall was used. Although in this study SWAT model has performed satisfactorily in data poor and complex catchment, the authors recommend a wider validation effort of the model before it is adopted for operational purpose.

Building adaptive capacity to cope with increasing vulnerability due to climatic change in Africa – A new approach

Abstract: The world community faces many risks from climate change, with most scenarios indicating higher temperatures and more erratic rainfall in Africa Predictions for southern Africa suggest a general decrease in total seasonal rainfall, accompanied by more frequent in-season dry spells that will significantly impact crop and livestock production, and hence economic growth in the region The hardest hit will be the rural poor in the drier areas, where crop failure due to drought is already common and chronic food emergencies afflict the region in most years Lessons can be learnt on how the rural poor currently cope with the vagaries of climate and these can be used to help them adapt their current production systems to the future threats of further climate change But this assumes the institutions that work towards the economic empowerment of the rural poor have the requisite skills to understand their current coping strategies and how adaptation can be facilitated A new initiative led by Midlands State University and the Zambian Meteorological Office proposes that improving the ability of institutions that train the ‘Future Change Agents’, who will subsequently support smallholder communities in adapting their agricultural practices to current climate variability, is the first step in building adaptive capacity to cope with future climate change The capacity of African scientists, regional organizations and decision-makers in dealing with the issues of climate change and adaptation will be enhanced on a continuing basis, and the impacts of their agricultural development programs improved

In situ characterization of the Callovo-Oxfordian pore water composition

Abstract: Up to 2005, knowledge on the Callovo-Oxfordian pore water composition was mainly built on geochemical modeling. A predictive geochemical model had been defined from physico-chemical and mineralogical properties obtained on rock samples. Since then, pore water characteristics have been obtained in situ at five depths between −430 and −505 m with three experimental set-ups. The first one based on water equilibration, the second one combining gas circulation and water sampling, and the third one originally devoted to hydrogeological measurements. These results show an overall convergence of the measured water compositions independently of the experimental concepts and of the sampling depths. Observed and calculated ionic concentrations differ by less than a factor of three for the major species, except for potassium and strontium. The experimental data yielded by this study will help to improve the geochemical modeling.

Assessment of groundwater quality in shallow wells within the southern districts of Malawi

Abstract: Lack of safe drinking water is a major problem in developing countries. Within Africa most people rely mainly on local groundwater sources for their water needs. These can be deep boreholes or shallow wells, the latter are normally found in poorer communities as they are the least expensive to construct. Over time water from these sources can be contaminated leading to fatal consequences. Previous monitoring of the quality of water from boreholes and shallow wells have been irregular, with the focus being mainly on boreholes. Information on seasonal water quality changes in shallow wells used by rural communities in Malawi has generally been lacking. A study was conducted from 2006 to 2007 to determine the quality of water from shallow wells in three districts in southern Malawi namely, Balaka, Chikwawa and Zomba districts. Water samples from 21 covered and five open shallow wells were analysed for chemical, microbiological and physical parameters using a portable water testing kit. Sampling was carried out at four different times of the year i.e. in August and October 2006 (dry season) and February and April 2007 (wet season). Microbiological data indicated that around 80% of the samples, obtained from the covered wells, failed to meet safe drinking water limits, set by World Health Organisation guidelines and Malawi Bureau of Standards, of zero total and faecal colony forming units (cfu)/100 ml. Values in excess of 1000 cfu/100 ml were noted in 10% of the samples, indicating gross contamination and the probability of pathogens being present. Contamination levels were higher during the wet season than the dry season in all three districts. Arsenic, ammonia, nitrate, nitrite and sulphate were all within the acceptable limits. Elevated levels of hardness, turbidity were noted in certain wells.

Sorption of strontium onto illite/smectite mixed clays

Abstract: Radioactive strontium is a by-product of the fission of uranium and plutonium and its mobility in the environment is largely dominated by sorption onto soil minerals, especially clays. In this study, the sorption behaviour of Sr in illite/smectite mixtures was analyzed from a mechanistic point of view. Sorption of Sr onto smectite and illite, previously homoionised in Na, was studied under different pHs, ionic strengths and radionuclide concentrations. Sorption experiments were also carried out with smectite and illite, mixed in two different proportions: 50–50% and 75–25%. Sr sorption data that were obtained from the single mineral systems were modelled considering both ionic exchange and surface complexation and using a non-electrostatic model. The selectivity coefficients and complexation constants obtained for the individual minerals were incorporated into a model to predict the adsorption of Sr in binary adsorbent systems and the model predictions were consistent with Sr experimental adsorption data.

Swelling pressures of MX-80 bentonite in solutions of different ionic strength

Abstract: Bentonites are part of the engineered barrier system (EBS) of repositories for radioactive wastes. High salinity and high pH of the pore space solutions may cause changes in the mineralogical composition and of the swelling capacity of the bentonites, possibly affecting the long term performance of the EBS. Results of a 3 years study on the changes of MX-80 bentonite properties after reaction with solutions of different ionic strength and pH are presented. The effects of seven characteristic saline solutions potentially occurring in repositories in granite, clay and salt formations were investigated, with comparison with one “pure water” experiment. Each solution reacted differently with the bentonite, resulting in different mineralogy and swelling pressure (SWP). SWP were highest in contact with water (>4 MPa), significantly lower in contact with low ionic strength solutions (∼2 MPa) and lowest in contact with high saline brines (mostly under 1 MPa). An alteration and partial dissolution of montmorillonite was observed. Mg, Al and Si contents in the solutions increased with reaction time. Concomitantly in the octahedral layers of montmorillonite, Mg was substituted by Al and the interlayer charge decreased. Later, a loss of some octahedral layers led to an excess of Si in the montmorillonite particles. The correlation between the alteration process, the charge reduction and SWP is presented. Tentative explanations are given for the activation of bentonites with acids. Key factor for the observed mineralogical alteration may be the acidity of water in the interlayer space. This also may explain that the alteration in compacted experiments with a high solid–liquid ratio (less water, higher acidity) is faster than in batch experiments with a lower solid–liquid ratio. All results can be explained by processes which lead to a pyrophyllitization/kaolinitization and Si-excess of the montmorillonite particles. An illitization seems less likely. The expected kaolinitization/pyrophyllitization and Si-excess may lead in the long run to a significant or even total loss of swelling capacity of compacted bentonites, if high saline solutions and cement are involved. Therefore, the question to be answered is not, whether or not bentonites are stable under the conditions of a repository in salt, but rather, what degree of swelling capacity is needed for what length of time.

Rainwater and reclaimed wastewater for sustainable urban water use

Abstract: Concern about the sustainability of urban water use is the strong motivation to understand the potential of rainwater use and water recycling in urbanized cities The history of water supply in Tokyo and its experience may provide useful information to develop sustainable urban water use and find future possible tasks in rapidly growing cities Besides, various innovative strategies to meet the current and future water demand in Tokyo may help us to consider new approaches adjusting to the developing mega cities in Asia In this paper, the past and current practices on utilization of latent water resources such as rainwater and reclaimed wastewater in Tokyo are summarized from the viewpoint of sustainable water use The storage of rainwater is a useful measure for water demand in emergency cases In addition, the rainwater use can work as a kind of environmental education to make citizens aware of sustainable urban water use There are 850 facilities for rainwater use in Tokyo Since reclaimed wastewater use has several benefits, a huge water volume has been utilized for various purposes such as washing, water-cooling, toilet flushing, waterway restoration and creation of recreational waterfront From the viewpoint of human health risk, new micropollutants such as estrogens, endocrine disrupters and surfactants should be considered as quality guideline parameter besides the conventional ones Importance of infiltration facilities should be also highlighted to secure the sound water cycle Groundwater recharge through the infiltration facilities provide a potential storage of water resource which can be withdrawn in the future if necessary

Potential for community based adaptation to droughts: Sand dams in Kitui, Kenya

Abstract: This paper presents the results of an evaluation of the effects of a local water harvesting project in Kenya concerning the construction of small scale sand dams by communities. Sand dams are small structures built in ephemeral rivers to store excess water to overcome periods of drought. For this evaluation we developed a method using socio-economic vulnerability indicators, which are linked to the state water resources system, enabling the assessment of the impacts of changes in water management. Data for this evaluation was gathered by hydrological research and by interviewing local inhabitants during field research. It appeared that the sand dams have a large impact on the local community. In 10 years time, more than 100,000 people have better access to water through a relative low cost measure. The increased water availability, especially during dry periods, results in higher farm yields. The average income of farmers living near dams rose with 60%. The local water balance is almost not influenced as the sand dams store less than 3% of total yearly runoff.

A methodology for the pre-selection of suitable sites for surface and underground small dams in arid areas: A case study in the region of Kidal, Mali

Abstract: A cost-effective project design in developing countries requires that a detailed preliminary territorial analysis is conducted in order to select the optimal sites for intervention and adequately plan the fieldwork. In most cases only large-scale cartography is available, which does not provide adequate information on environmental and morphological parameters. For this purpose, remote sensing techniques can supply large amount of data with high spatial and temporal resolution, and are therefore a very useful mapping tool especially in areas where very little information is available such as most developing countries. In this work, we present a methodology for the assessment of the suitability of sites for the installation of small dams (barrages), a technology widely used for water harvesting in arid climates. The selection criteria are defined both in a qualitative and quantitative way, and are based on a territorial analysis using satellite data (images, digital elevation models) and hydrological and climatological information that are easily and freely available. Qualitative criteria imply the identification of suitable valleys, wadi beds and rock formations, based on visual interpretation of satellite images and large-scale available cartography; other qualitative selection criteria concern the distance from settlements and infrastructures, faults localisation. Quantitative criteria are expressed in terms of indexes that synthesise the effectiveness and feasibility of the possible interventions: the alluvial plan index ( α ), calculated as a benefit/cost ratio in terms of volume of water that can be stored versus volume of the dam; the hydrologic index ( P ), based on the analysis of the contributing watersheds to each site and the pluviometric patterns in the area; the combined coefficient ( β ), concern both morphologic and hydrologic aspects; the soil water holding capacity, estimated from the analysis of vegetation patterns using satellite indices. The methodology, applied to the region of Kidal in Mali, allowed the individuation of 66 sites, whose only 17 sites passed the proposed selection criteria. The 17 sites are classified in ground of values of β coefficient. The results served to organize the subsequent field surveys, which was conducted on the three sites that had obtained the highest scores of β , thus considerably reducing the time and cost of the survey. In one of this three sites, most effective considered, a project design of small dam is elaborated.

Sealing ability of Wyoming bentonite pellets foreseen as buffer material – Laboratory results

Abstract: The NAGRA concept for a high level waste repository includes bentonite pellets for backfilling around the spent nuclear fuel canisters. Pellets have therefore been produced from granulated Wyoming bentonite (Am. Colloid., brand name MX-80), which have been tested as part of NAGRA’s research program with respect to its sealing properties. Two types of pellet material were used, one containing only bentonite and the other containing a mixture of 70% bentonite and 30% sand. As reference, standard granulated MX-80 bentonite material was also used. The pellets were industrially crushed in order to give better grain size distribution with respect to field compaction. In all tests a 0.2 M NaCl test solution was used, simulating the groundwater composition of Opalinus Clay host rock. Swelling pressure and hydraulic conductivity were measured for all three materials at five different samples densities, ranging from 1500 kg/m 3 to 2050 kg/m 3 after full water saturation. The results unambiguously show that there is no significant difference at any density between the MX-80 pellet material and the original granulated MX-80 material with respect to swelling pressure or hydraulic conductivity. Thus, the basic sealing properties in the pellet materials are not affected by the drying or compaction treatment.

Is normative integrated water resources management implementable? Charting a practical course with lessons from Southern Africa

Abstract: At the seventh Waternet/WARFSA/GWP-SA Symposium, Lewis Jonker described the “perceived failure of implementing IWRM in South Africa.” This paper starts from Jonker’s observation – which can certainly be defended – and argues that attempts to implement full Integrated Water Resources Management (IWRM) are doomed to failure and disappointment. The paper therefore offers a more practical ‘expedient’ solution. The paper is based on research done in Tanzania (Ruaha Basin) and South Africa (Olifants Basin) that is further informed by a growing literature critical of the IWRM paradigm as currently understood and practiced. As a guide to actual policies and their implementation in developing countries, IWRM has led to mis-guided priorities and paralysis of development programmes. An alternative approach is one in which basin managers identify priority problem areas, and focus specifically on finding solutions to these problems within an integrated framework, rather than starting with a broad set of principles and trying to implement these. The paper proposes that a shift away from IWRM as a normative concept is now overdue, and argues for realism and action by focusing attention on and prioritizing the critical needs of poor people in Africa. People cannot wait forever .

Design of a water quality monitoring network for the Limpopo River Basin in Mozambique

Abstract: The measurement of chemical, physical and biological parameters is important for the characterization of streams health. Thus, cost-effective and targeted water quality (WQ) monitoring programmes are required for proper assessment, restoration and protection of such systems. This research proposes a WQ monitoring network for the Limpopo River Basin (LRB) in Mozambique located in Southern Africa, a region prone to severe droughts. In this Basin both anthropogenic and natural driven processes, exacerbated by the increased water demand by the four riparian countries (Botswana, South Africa, Zimbabwe and Mozambique) are responsible for the degradation of surface waters, impairing their downstream use, either for aquatic ecosystem, drinking, industrial or irrigation. Hence, physico-chemical, biological and microbiological characteristics at 23 sites within the basin were studied in November 2006 and January 2007. The physico-chemical and microbiological samples were analyzed according to American Public Health Association (APHA) standard methods, while the biological monitoring working party method (BMWP) was used for biological assessment. The assessment of the final WQ condition at sampled points was done taking into account appropriate indexes, the Mozambican standards for receiving waters and the WHO guidelines for drinking WQ. The assessed data indicated that sites located at proximities to the border with upstream countries were contaminated with heavy metals. The Elephants subcatchment was found with a relatively better WQ, whereas the Changane subcatchment together with the effluent point discharges in the basin were found polluted as indicated by the low dissolved oxygen and high total dissolved solids, electric conductivity, total hardness, sodium adsorption ratio and low benthic macroinvertebrates taxa. Significant differences (p < 0.05) were found for some parameters when the concentrations recorded in November and January were tested, therefore, indicating possible need for monthly monitoring of WQ. From this study it was concluded that a systematic WQ monitoring network composed of 16 stations would fit the conditions of the LRB. Ambient, earl warning, operational and effluents are the main monitoring types recommended. Additional research at a Basin scale was also recommended to identify the major sources of pollution, their transport and impacts to the downstream ecosystem.

Determinants of tillage frequency among smallholder farmers in two semi-arid areas in Ethiopia

Abstract: Traditional tillage systems practiced by farmers in semi-arid regions of Ethiopia are characterized by repeated and cross plowing with an indigenous plow called Maresha . Repeated and cross plowing have led to land degradation. Conservation tillage systems that advocate minimum soil disturbance can alleviate land degradation problems. However, before introducing reduced tillage systems, it was found necessary to study why farmers undertake repeated plowing. The study was undertaken in two semi-arid areas called Melkawoba and Wulinchity located in the central rift valley of Ethiopia and on two major crops; Tef ( Eragrostis Tef (Zucc.)) and maize ( Zea mays XX ). Fifty farmers from each area were randomly selected and interviewed using a structured questionnaire. The results showed that farmers in the study area plow repeatedly in order to completely disturb unplowed strips of land left between adjacent furrows. Unplowed strips are the results of the V-shaped furrows created by the Maresha plow. Farmers generally do not plow before the soil is wetted by rainfall. Wetting and drying cycles due to dry spells occurring between rainfall events force farmers to plow frequently to avoid moisture losses through surface runoff, evaporation and weed transpiration. Tef fields are plowed 4–5 times while maize fields are plowed 3–4 times. Tillage frequency increased with the education level and experience of farmers; with their perception about the purpose of tillage such as moisture conservation, weed control and soil warming; and with resource availability such as area of land and family labor. Tillage frequency was higher for Tef than for maize and in heavy soils than in light soils.

Behaviour of a bentonite barrier in the laboratory: Experimental results up to 8 years and numerical simulation

Abstract: The conditions of the bentonite in an engineered barrier for high-level radioactive waste disposal were simulated in a series of tests performed in cylindrical cells (length 60 cm, diameter 7 cm). Inside the cells, six blocks of FEBEX bentonite compacted to dry density 1.65 g/cm3 were piled up, giving rise to a total length similar to the thickness of the clay barrier in a repository according to the Spanish concept. The bottom surface of the material was heated at 100 °C and the top surface was injected with granitic water. The duration of the tests was 6, 12, 24 and 92 months. The temperatures inside the clay and the water intake were measured during the tests and, at the end, the cells were dismounted and the dry density, water content and hydro-mechanical properties were measured at different positions. The injection of water provokes, near the hydration surface, a decrease of the dry density due to the increase of the water content and the clay swelling, while heating gives rise to an increase of the dry density and a reduction of the water content in the hottest areas. A fully coupled thermo-hydro-mechanical (THM) formulation has been adopted as a general framework to analyse these experiments. This work presents the comparisons between the variables recorded online during the tests (water intake and temperature) and the model results. The main results of the postmortem analysis (water content and dry density) are also modelled.

Water security in north China and countermeasure to climate change and human activity

Abstract: This paper addresses the emergent issues by the case study of Haihe River Basin in North China. The advantage of the water international study and the background for the cause of these problems from natural change and in particular human activity are analyzed. The key points are addressed as four aspects: (a) the study of the water cycle process impacted by climate change and high intensity human activity; (b) water utilization related to new economic partner change, such as saving water model; (c) study on eco-hydrology, and the interaction of water and ecology impacted by climate change and human activity; and (d) reasonable water allocation that includs water diversion from south to north and saving water issue in the local areas. Several suggestions are proposed both on the study on the water cycle, which is a very important base of water security in north China, and on the application study of water resources and eco-environmental rehabilitation. These key issues will benefit both the advantage of water science and the sustainable development in China.

Reactive transport modeling of geochemical interactions at a concrete/argillite interface, Tournemire site (France)

Abstract: Mineralogical and petrographical investigations of a borehole sealed by concrete (“engineered analogue” of concrete/clay interactions) overcored at the Tournemire site offer the possibility to perform reactive transport modeling over a timescale of 15 years, which is significantly longer than standard durations of laboratory experiments. The HYTEC code was used to simulate mineralogical evolutions in the Tournemire argillite matrix and along small fractures, as well as in concrete, assuming either thermodynamic equilibrium approach or kinetic control coupled to diffusive transfer. The mineralogical profiles calculated in thermodynamic equilibrium and with kinetics are very similar in the concrete. In contrast, kinetics of dissolution and precipitation reactions is found to be necessary for a better reproduction of the experimental observations in the argillite samples compared to thermodynamic equilibrium calculations, in particular with respect to the extent of the alkaline perturbation. The major effects observed when considering kinetics in the calculations are to smooth the sharpness and intensity of the mineralogical transformation fronts, these fronts being predicted to occur deeper inside the argillite matrix (

Challenges for integrated water resources management

Abstract: During the past century, while world population tripled, the use of water increased sixfold. Irrigation accounts for 70% of global water withdrawals, industry for 20%, and municipal use for 10%. To meet the water resources challenges, a series of transitions is under way, with major implications for water management. The present paper underlines the major issues and the new role of engineers in charge of development and project management.

The influence of conservation tillage methods on soil water regimes in semi-arid southern Zimbabwe

Abstract: Planting basins and ripper tillage practices are major components of the recently introduced conservation agriculture package that is being extensively promoted for smallholder farming in Zimbabwe. Besides preparing land for crop planting, these two technologies also help in collecting and using rainwater more efficiently in semi-arid areas. The basin tillage is being targeted for households with limited or no access to draught animals while ripping is meant for smallholder farmers with some draught animal power. Trials were established at four farms in Gwanda and Insiza in southern Zimbabwe to determine soil water contributions and runoff water losses from plots under four different tillage treatments. The tillage treatments were hand-dug planting basins, ripping, conventional spring and double ploughing using animal-drawn implements. The initial intention was to measure soil water changes and runoff losses from cropped plots under the four tillage practices. However, due to total crop failure, only soil water and runoff were measured from bare plots between December 2006 and April 2007. Runoff losses were highest under conventional ploughing. Planting basins retained most of the rainwater that fell during each rainfall event. The amount of rainfall received at each farm significantly influenced the volume of runoff water measured. Runoff water volume increased with increase in the amount of rainfall received at each farm. Soil water content was consistently higher under basin tillage than the other three tillage treatments. Significant differences in soil water content were observed across the farms according to soil types from sand to loamy sand. The basin tillage method gives a better control of water losses from the farmers’ fields. The planting basin tillage method has a greater potential for providing soil water to crops than ripper, double and single conventional ploughing practices.

Quality of groundwater from shallow wells of selected villages in Blantyre District, Malawi

Abstract: Access to adequate and safe drinking water still remains a challenge in developing countries. Some people especially in the rural areas use untreated surface and groundwater. An assessment of groundwater quality from shallow wells was carried out in nine villages in Blantyre district of Malawi. Water samples from nine randomly selected shallow wells (7 covered or protected and 2 open) were analysed for biological (total and faecal coliforms), chemical (hardness, nitrate, nitrite, sulphate, ammonia, pH, electrical conductivity and arsenic) and physical (total dissolved solids and turbidity) parameters of water using a portable water testing kit (Paqualab 50). Sampling was carried out four times during the year, i.e. twice in the dry season (August and October) and twice in the wet season (February and April) to find out if the quality of water changes with season. Results indicate that drinking water from shallow wells is heavily polluted by both total and faecal coliforms. The pollution level was higher in the wet season compared to the dry season. All the samples tested in the wet season did not meet the guideline value of 50 total coliforms (colony forming units) per 100 ml of the sample water (50 cfu/100 ml) set by the Malawi Ministry of Water Development (MoWD) for untreated water for drinking purposes (e.g. groundwater), while 22% of the samples met the guideline during the dry season. The difference in the contamination level between the dry and wet season was not significant for total coliforms ( p = 0.13 > 0.05 ). All chemical (hardness, nitrate, nitrite, sulphate, ammonia, pH, electrical conductivity and arsenic) and physical (total dissolved solids and turbidity) parameters tested except for turbidity were within the guideline values set by MoWD for untreated water. About 11% of the wells tested failed to meet the turbidity guideline value for the Ministry of Water Development of 25 NTU while about 22% failed to meet the World Health Organisation (WHO) and Malawi Bureau of Standards (MBS) for treated water of 5 NTU in both the dry and wet season. There is need to carry out a further analysis of quality of water from shallow wells in Blantyre and other districts.

Impacts of land-use and land-cover changes on flow regimes of the Usangu wetland and the Great Ruaha River, Tanzania

Abstract: A study was conducted to investigate the hydrological impacts of land-use and land-cover changes on flow regimes of the Great Ruaha River. Remote sensing and GIS techniques were used to inventory temporal changes of land-use and land-cover changes in the watershed. Hydrological data were analyzed to reveal the alterations and trends for three time periods; pre-1974, 1974–1975, and post-1985. It was revealed that there was a steady increase in cultivated area, from 121.2 km 2 to 874.3 km 2 between 1973 and 2000 while the woodland area decreased significantly over years. The minimum dry season area of the wetland declined significantly, with major changes occurring between 1984 and 2000. River flows were found to be highly variable within and between the years, and sensitive to land-use and land-cover changes. There was a slight shift of the time peak flows, from April to early February during the post-1985 period. The Q 50 flow progressively declined from 19.23 m 3 s −1 in the pre-1974 to 16.51 m 3 s −1 and 9.04 m 3 s −1 for 1974–1975 and post-1985 period. The Q 95 (low flow) declined from 2.84 m 3 s −1 to 0.11 m 3 s −1 and 0.0 m 3 s −1 for pre-1974, 1974–1975 and post-1985 period. The study concludes that the modification of the land use and cover has resulted in changes in temporal distribution of runoff. The study highlights the importance of considering effects of land-use and land-cover changes on ecosystems and water resources for an informed decision on proper catchment planning and management.

New archaeointensity results from archaeological sites and variation of the geomagnetic field intensity for the last 7 millennia in Greece

Abstract: In this study six new intensity determinations are presented, obtained from five well dated archaeological sites, located in northern Greece and in Paros, Cyclades Islands. The fired structures consisted of ceramic and pottery kilns belonging to the Hellenistic, Roman and Byzantine periods. Between 8 and 21 samples of highly fired baked clays, tiles and bricks were taken, homogeneously distributed over the structures. The samples were analysed using the classical Thellier method, providing the past intensities and directions of the geomagnetic field recorded at each site. The intensity values have been corrected for anisotropy of thermal remanent magnetisation and cooling rate effects. Differences in the mean archaeointensities per site ranging from 1% to 11%, before and after TRM anisotropy and cooling rate corrections, were obtained. The new results indicate a decrease of 20% of the geomagnetic field strength in Greece, during the last four centuries BC. In order to compare our results with previously published data, a catalogue of archaeo- and palaeointensity results for the Aegean area has been established, covering the last 7 millennia. It consists of 336 data from Greece, western Turkey and Former Yugoslavia, collected from various authors. Weighting factors have been applied to these data, that then have been treated with a hierarchical Bayesian modelling, and a geomagnetic field intensity variation curve for Greece was constructed. A good agreement is observed when comparing the curve for Greece with the Bulgarian secular variation curve (SVC) for intensity. Satisfactory coincidence is also found with the archaeointensity data from Mesopotamia. Despite the presence of some time gaps, a more precise secular variation intensity curve has been constructed for Greece which, combined with a forthcoming directional SVC, will help for dating purposes.

Damage and sealing of clay rocks detected by measurements of gas permeability

Abstract: Various damage and sealing experiments have been performed on samples of the Callovo-Oxfordian argillite and the Opalinus clay in order to enhance the knowledge about the development of the excavation damaged zone around nuclear waste repositories in clay formations. Stress-induced damage and permeability changes were examined in triaxial compression tests. Preliminary criteria were derived for the detection of dilatancy, percolation, and failure boundaries. By measuring the gas permeability changes due to re-compaction and re-saturation, the self-sealing behaviour of strongly damaged clay samples was investigated. Short-term re-compaction by increasing the confining stress up to 15 MPa reduced the permeability by several orders of magnitude to 10−19–10−20 m2. After water re-saturation, the permeability of the damaged samples decreased significantly to 10−21 m2. All laboratory observations suggest a high self-sealing capacity of the studied clay rocks.