Traditional irrigation was practiced in Ethiopia since time immemorial. Despite this, water productivity in the sector remained low. A survey on the Godino irrigation scheme revealed that farmers used the same amount of water and intervals, regardless of crop species and growth stage. In an effort to improve the water productivity, two traditional irrigation scheduling methods were compared with two scientific methods, using furrow irrigation. The growth performance and tuber yield of potato (cv. Awash) revealed that irrigation scheduling using a neutron probe significantly outperformed the traditional methods, followed by the SWB model Irrigation Calendar. Since the NP method involves high initial cost and skills, the use of the SWB Calendar is suggested as replacement for the traditional methods. SWB is a generic crop growth model that requires parameters specific to each crop, to be determined experimentally before it could be used for irrigation scheduling. It also accurately describes deficit irrigation strategies where water supply is limited. Field trials to evaluate four potato cultivars for growth performance and assimilate partitioning, and onions' critical growth stages to water stress were conducted. Crop-specific parameters were also generated. Potato and onion crops are widely grown at the Godino scheme where water scarcity is a major constraint. These crop-specific parameters were used to calibrate and evaluate SWB model simulations. Results revealed that SWB model simulations for Top dry matter (TDM), Harvestable dry matter (HDM), Leaf area index (LAI), soil water deficit (SWD) and Fractional interception (FI) fitted well with measured data, with a high degree of statistical accuracy. The response of onions to water stress showed that bulb development (70-110 DATP) and bulb maturity (110-145) stages were most critical to water stress, which resulted in a significant reduction in onion growth and bulb yields. SWB also showed that onion yield was most sensitive to water stress during these two stages. An irrigation calendar, using the SWB model, was developed for five different schemes in Ethiopia, using long-term weather data and crop-specific parameters for potatoes and onions. The calendars revealed that water depth varied, depending on climate, crop type and growth stage. / Thesis (PhD)--University of Pretoria, 2009. / Plant Production and Soil Science / unrestricted

Les retenues collinaires sont des aménagements hydrauliques largement rencontrés en Afrique du Nord, et plus généralement dans les zones arides et semi-arides de la planète. Ils visent à la fois la conservation en eau dans les bassins versants amont et la rétention des matériaux issus de l'érosion afin d'éviter l'envasement des grands barrages en aval. L'implantation et la gestion de l'eau mobilisée par les retenues collinaires doit s'appuyer sur une connaissance de leur fonctionnement hydrologique. Or ce fonctionnement est encore peu connu, en particulier les processus et l'intensité des flux des échanges retenue-souterrain, constituent une question très ouverte. L'objectif de ce travail est de quantifier et d'analyser le fonctionnement des échanges retenue-souterrain sur un bassin versant agricole. L'étude a été menée sur la retenue collinaire du bassin versant expérimental de Kamech, appartenant à l'ORE OMERE. Dans la première partie de ce travail, une approche de bilan hydrologique a été développée et a permis de montrer que les échanges retenue-souterrain sont dominés par l'infiltration, qui représente environ 79 % des pertes à la retenue collinaire et dépasse largement les pertes par évaporation qui ne représente que 21 %.En revanche, l'analyse croisée des dynamiques hydrologiques dans la retenue et dans la nappe au voisinage de la retenue a mis en évidence des échanges qui se produisent dans les deux sens : des échanges dominés par un flux d'infiltration avec la nappe au pied du barrage, par contre, les échanges avec la nappe latérale des versants se produisent dans les deux sens mais restent très fugaces. Les résultats préliminaires de l'approche de modélisation développé dans ce travail a permis de souligner la complexité des échanges retenue-souterrain et montre que la relation entre la hauteur d'eau dans la retenue et le flux d'infiltration n'est pas univoque et présente des comportements différents entre la phase de montée et la phase de descente du niveau d'eau dans la retenue. / Hill reservoirs are hydraulic infrastructures widely used in North Africa, generally in arid and semi arid zones of the planet. These infrastructures are used for both water conservation in the catchment scale and to reduce siltation of downstream dams. The implementation and the management of water resources mobilized in this infrastructure must be based on knowledge of their hydrological functioning. However, the hydrological functioning of this system is not very known, especially the water flux exchange processes and intensity between the reservoir and the subsurface is still an open question.The main purpose of this study is to quantify and analyse the hydrological functioning of the reservoir-subsurface exchange processes for an agricultural catchment. This study was conducted on the hill reservoir of the experimental observation site of Kamech belonging to the OMERE observatory. In the first part of this study, we develop a water balance approach to estimate reservoir-subsurface exchange flux. The results of this approach shows that reservoir-subsurface exchange flux is dominated by infiltration that represent about 79% of the water outflow, and largely exceeds the water loss by evaporation that represents only 21 % of the total water outflow. However, the cross-analysis of the hydrological dynamics of the hill reservoir and the aquifer in the vicinity of the reservoir revealed that infiltration can occur in both directions: reservoir-subsurface exchange dominated by infiltration with the aquifer located in the foot of the dam, however the water exchange with the lateral aquifer of the hill reservoir can occur in both directions but remain very fleeting. The preliminary results of the modeling approach developed in this work has highlighted the complexity of reservoir-subsurface exchange flux. In fact, the relationship between water level in the hill reservoir and the infiltration flux is not unique and can present different behavior between the rise and decrease phase of the water level in the hill reservoir.

This thesis is a contribution to the work of the Texas Environmental Observatory (TEO), which provides environmental information from the Greenbelt Corridor (GBC) of the Elm Fork of the Trinity River. The motivation of this research is to analyze the short-term water dynamic of soil in response to the substantial rainfall events that occurred in North Texas in 2007. Data collected during that year by a TEO soil and weather station located at the GBC includes precipitation, and soil moisture levels at various depths. In addition to these field measurements there is soil texture data obtained from lab experiments. By comparing existing water dynamic models, water balance equations were selected for the study as they reflect the water movement of the soil without complicated interrelation between parameters. Estimations of water flow between soil layers, infiltration rate, runoff, evapotranspiration, water potential, hydraulic conductivity, and field capacity are all obtained by direct and indirect methods. The response of the soil at field scale to rainfall event is interpreted in form of flow and change of soil moisture at each layer. Additionally, the analysis demonstrates that the accuracy of soil characteristic measurement is the main factor that effect physical description. Suggestions for model improvement are proposed. With the implementation of similar measurements over a watershed area, this study would help the understanding of basin-scale rainfall-runoff modeling.

Modelling of the rainfall-runoff process is one of the basic scientific skills in hydrology. Rainfall-runoff modelling can help to improve water management, handling of the reservoir's storage volume, or also to facilitate adaptation to current climatic conditions. The aim of the diploma thesis is to create a functional rainfall-runoff model on the basis of water balance equations based on the lumped water balance principle of the hydrological model. Several modifications of the general rainfall-runoff model are approached in the diploma thesis. Four types of the daily evapotranspiration determination are used in the calculations. The rainfall-runoff model is compiled from temperature data and precipitation totals in a daily step. The practical application is carried out on a sub-basin of the river Dyje, which is located above Vranov water reservoir. The main output is a series of daily flow rates that were obtained from calibrated rainfall-runoff models. The best rainfall-runoff model takes into account the water from snow cover melting, the value of the Nash Sutcliffe calibration criterion of this model is 0.608. Finally, the hydrological simulation for the period 2021-2060 is performed in the diploma thesis.

Winter cover crops grown in rotation with grain crops can be an efficient integrated pest management tool (IPM). However, cover crop biomass production and thus successful provisioning of ecosystem services depend on a timely planting and cover crop establishment after harvest of a cash crop in the fall. One potential management adaptation is the use of short-season soybeans to advance cover crop planting date in the fall. Cover crops planted earlier in the fall may provide a greater percentage of ground cover early in the season because of higher biomass accumulation that may improve weed suppression. However, adapting to short-season soybeans could have a yield penalty compared to full-season soybeans. In addition, it is unclear if further increasing cover crop growing season and biomass production under environmental conditions in Kentucky could limit nitrogen and water availability for the next cash crop. This thesis combines the use of field trials and a crop simulation model to address the research questions posed. In Chapter 1, field trials evaluating yield and harvest date of soybean maturity group (MG) cultivars from 0 to 4 in 13 site-years across KY, NE, and OH, were used to calibrate and evaluate the DSSAT crop modeling software (v 4.7). The subsequent modeling analysis showed that planting shorter soybean maturity groups (MG) would advance date of harvest maturity (R8) by 6.6 to 11 days per unit decrease in MG for May planting or by 1 to 7.3 days for July planting. The earliest MG cultivar that maximized yield ranged from MG 0 to 3 depending on the location, allowing a winter-killed cover crop to accumulate between 257 to 270 growing degree days (GDD) before the first freeze occurrence when soybean was planted in May, and between 280 to 296 GDD when soybean was planted in July. Winter-hardy cover crops could accumulate 701 to 802 GDD following soybean planted in May and 329 to 416 GDD after soybean planted in July. In Chapter 2, a two-year field trial was conducted at Lexington, KY to evaluate the effect of a soybean – cover crop rotation with soybean cultivars MG 1, 2, 3 or 4 on cover crop biomass and canopy cover, and on weed biomass in the fall and the following spring. Results showed that having cover crops was an efficient management strategy to reduce weed biomass in the fall and spring compared to no cover treatment. Planting cover crops earlier in the fall after a short-season soybean increased cover crop biomass production and percentage of ground cover in the fall, but not the following spring. Planting cover crop earlier after a short-season soybean did not improve weed suppression in the fall or spring compared to a fallow control with full-season soybean. Having a fall herbicide application improved weed control when there was a high pressure of winter annual weeds. By the spring, delaying cover crop termination increased cover crop biomass but also did weed biomass. In Chapter 3, a soybean – cover crop – corn rotation was simulated to evaluate the effect of different soybean MG and cover crop termination, as well as year to year variability on water and nitrogen availability for the next corn crop in Lexington, KY. Simulations showed that when cover crops were terminated early, they did not reduced soil available water at corn planting. However, introducing a non-legume cover crop reduced total inorganic nitrogen content in the soil profile by 21 to 34 kg ha-1 implying 15 to 30 kg ha-1 less in corn nitrogen uptake. Cover crop management that was able to maintain similar available water values than fallow treatment while minimizing nitrogen uptake differences was cover crops planted after soybean MG 4 with an early termination. However, the best management strategies that will maximize ecosystem services from cover crops as well as cash crop productivity may need to be tailored to each environment, soil type, irrigation management, and must consider year-to-year variability.

Die Modellierung von komplexen Systemen, wie dem Untergrund, ist ein Hilfsmittel zur Beschreibung der in der Realität ablaufenden Prozesse. Die Durchführung von Experimenten an einem Modell, um qualitative Aussagen über ein reales System zu erhalten, wird als Simulation bezeichnet. Dabei können vielfältige Modelle, wie z.B. physikalische und mathematische, zum Einsatz kommen. Die ungesättigte Bodenzone (vadose Zone) bezeichnet den Bereich zwischen der Landoberfläche und dem Grundwasserspiegel, innerhalb dessen der Wassergehalt geringer als bei Vollsättigung, und der Druck geringer als der Atmosphärendruck ist. Dieser Bodenbereich hat für die Landwirtschaft, Geobiologie, aerobe Abbauprozesse und Grundwasserneubildung eine große Bedeutung. Für die Nachbildung von Strömungs- und Stofftransportprozessen der ungesättigten Bodenzone existieren numerische Simulationsprogramme. Ziel der vorliegenden Arbeit ist eine umfangreiche Validierung des Programms PCSiWaPro® (entwickelt an der TU-Dresden, Institut für Abfallwirtschaft und Altlasten) für unterschiedliche Anwendungsfälle. Ein weiteres Ziel der Arbeit besteht in der Untersuchung der Anwendbarkeit des aktuellen Stands des Simulationsprogramms PCSiWaPro® auf unterschiedliche Praxisfälle bei Kombination der ungesättigten Bodenzone mit technischen Anlagen. Vier Anwendungsfälle mit unterschiedlichen Zielen wurden dafür im Rahmen dieser Arbeit untersucht: die Simulation von dezentraler Abwasserversickerung (Kleinkläranlage - KKA) anhand entsprechender Säulen- und Feldversuche, die Berechnung der Grundwasserneubildung am Beispiel von Lysimetern, der Wasserhaushalt von Erddämmen und die Modellierung von Deponieabdeckungssystemen. Die Anwendungsfälle unterscheiden sich durch den Zweck der Simulation, die Geometrie, die Größe, die festgelegten Anfangs- und Randbedingungen, die Simulationszeit, die Materialien, das Koordinatensystem sowie die Ein- und Ausgabewerte. Die Simulationsergebnisse konnten eindeutig zeigen, dass das Programm PCSiWaPro® für alle im Rahmen der vorliegenden Arbeit untersuchten Fälle, mit unterschiedlichen Strömungsregimen, Stofftransport-Parametern, Randbedingungen, Koordinatensystemen sowie Raum- und Zeitdiskretisierungen anwendbar ist. Die Simulationsergebnisse der Säulenversuche am Beispiel dezentraler Abwasserversickerung zeigten eine sehr gute Übereinstimmung zwischen gemessenen und mittels PCSiWa-Pro® berechneten Werten des Wasser- und Stoffhaushaltes (Druckhöhe, Abfluss und Stoff-konzentration) der untersuchten Bodentypen B3 (schwachschluffiger Sand), B4 (Grobsand) und B5 (mittelschluffiger Sand). Die Wurzel des mittleren quadratischen Fehlers (RMSE) betrug für die Berechnung der Druckhöhe 1,84 cm bei B5, 3,61 cm bei B3 und 1,27 cm bei B4. Die relative Abweichung betrug für die Berechnung der Druckhöhe 2,19 % bei B5, 1,3 % bei B3 und ca. 5,3 % bei B4. Die Durchführung der Sensitivitätsanalyse der für die Modellierung relevanten Parameter zeigte eine sehr hohe Sensitivität der VAN GENUCHTEN-Parameter und der gesättigten hydraulischen Leitfähigkeit des Bodens. Darüber hinaus führten die Parameter nach DIN 4220 und die mithilfe von Pedotransferfunktionen aus Siebanalysen genommenen Parameter zu unterschiedlichen Ergebnissen. Im Rahmen des am Institut für Abfallwirtschaft und Altlasten durchgeführten Projektes EGSIM wurden die Programme SENSIT und ISSOP (in Zusammenarbeit mit DUALIS GmbH IT Solution) entwickelt und zur Parameteridentifikation/-kalibrierung benutzt. Die im Rahmen dieser Arbeit erzielten Ergebnisse konnten nachweisen, unter welchen Bedingungen eine Nachklärung des vollbiologisch gereinigten Abwassers innerhalb der Bodenzone möglich ist, so dass am Ort der Beurteilung (Grundwasseroberfläche) kein unzulässiger Schadstoffeintrag erfolgt. In Bezug auf die KKA-Feldmodelle ist die Anwendung des rotationssymmetrischen Koordinatensystems als Voraussetzung der Realität besser zu entsprechen und nicht als Option zu betrachten. Darüber hinaus wurden anhand der Feldmodelle verschiedene Szenarien mit kontinuierlicher und diskontinuierlicher Versickerung sowie zwei unterschiedlich großen Einleitflächen durchgeführt. Das Programm PCSiWaPro® ist sowohl für ungesättigte als auch für variabel-gesättigte porösen Medien anwendbar. Dies wurde im Rahmen der Simulation des Wasserhaushaltes eines Erddamms nachgewiesen. Die durchschnittliche relative Abweichung zwischen gemessenen und mittels PCSiWaPro® berechneten Wasserständen des entsprechenden Beobachtungspunkts im untersuchten Dammkörper lag bei 0,08 % (entspricht 5,8 cm bei einer Müchtigkeit von ca. 70 m) und das Bestimmtheitsmaß (R2) betrug 0,987. Die Simulation des Wasserhaushaltes unterschiedlicher Deponieabdichtungssystemen mittels PCSiWaPro® zeigte im Allgemeinen ein funktionierendes Ableiten des auf Deponien anfallenden Regenwassers (auch bei Starkregenereignissen). Darüber hinaus haben die durchgeführten Bewuchs-Modelle nachweisen können, dass die Vegetation der Deponieoberflächen den Wassergehalt, durch Pflanzenwurzelentzug bzw. Evapotranspiration, reduzieren können. Die Simulationsergebnisse der durchgeführten Szenarien des Wasserhaushaltes von Lysimetern zur prognostischen Berechnung der Grundwasserneubildung mittels PCSiWaPro® konnten nachweisen, dass das Programm für die Berechnung der Grundwasserneubildungsrate für diesen Zweck anwendbar ist. Die relativen Abweichungen der be-rechneten von den gemessenen Grundwasserneubildungsraten sind auf die verwendeten Materialparameter sowie auf Vernachlässigung der möglicherweise in Lysimetern sich befin-denden Makroporen (duale Porosität) zurückzuführen. / The modelling of complex systems such as the underground is a means to describe the processes occurring in the reality. The conducting of experiments on a model to obtain qualitative evidence about a real system is referred to as a simulation. Thereby, various models (e.g. physical and mathematical models) can be used. The unsaturated zone (vadose zone) is the region between the land surface and the water table, in which the water content is less than full saturation, and the pressure is lower than the atmospheric pressure. The unsaturated zone is very significant for agriculture, geobiology, aerobic degradation processes and groundwater recharge. The processes of water flow and solute transport in the unsaturated zone can be described by means of numerical simulation programs. The aim of the present work is a comprehensive validation of the simulation program PCSiWaPro® (developed at the TU-Dresden, Institute of Waste Management and Contaminated Site Treatment) for different applications. Another aim of this work is to investigate the applicability of the current version of PCSiWaPro® for different cases of a combination between the unsaturated zone and technical facilities. Four application cases with different objectives were investigated within the present work, which are: the simulation of decentralized wastewater infiltration with corresponding column and field experiments, the computation of groundwater recharge by means of lysimeters, the water balance of earth dams and the modelling of landfill covering systems. The application cases differ from each other by the objective of the simulation, the geometry, the size, the specified initial and boundary conditions, the simulation time, the applied materials, the coordinate system, the input and output data. The simulation results clearly showed that PCSiWaPro® is applicable for all investigated cases under consideration of different flow and solute transport regimes, parameters, boundary conditions, spatial and temporal discretization, and coordinate systems. The simulation results of the experimental soil columns for the decentralized treated wastewater infiltration case showed a very good agreement between measured and computed values of water and solute balance (pressure head, flow and solute concentration) of the investigated soil types B3 (slightly silty sand), B4 (coarse sand / gravel) and B5 (medium silty sand). The root of the mean squared error (RMSE) for the computation of the pressure head was 1,84 cm at B5, 3,61 cm at B3 and 1,27 cm at B4. The relative deviation in case of pressure head computation was 2,19 % at B5, 1,3 % at B3 and 5,3 % at B4. The implementation of the sensitivity analysis of the relevant parameters for the modelling showed a very high sensitivity of the VAN GENUCHTEN parameters and the saturated hydraulic conductivity of the soil. Moreover, the parameters according to DIN 4220 led to different results than the estimated ones according to pedotransfer methods based on sieve analysis. Within the project EGSIM, which was carried out at the Institute for waste management and contaminated sites treatment in collaboration with DUALIS GmbH IT Solution, the programs SENSIT and ISSOP were developed and used for parameter identification/ calibration. The results obtained in this Work showed under which conditions is a secondary treatment of full biologically treated wastewater in the soil possible, so that no unallowable pollutants entry in the groundwater occurs. With regard to the field models of this application the implementation of the rotationally symmetric coordinate system should be considered as a condition and not as an option for a better corresponding to the reality. Furthermore, different scenarios of the field models were carried out with continuous and discontinuous infiltration, as well as under different initiation areas. PCSiWaPro® could be applied for both unsaturated and variably-saturated porous media. This could be proven by the simulation of the water balance in an earth dam. The average relative deviation between measured and simulated water levels of the corresponding observation point in the investigated dam embankment was 0,08 % (corresponding to 5,8 cm at 70 m thickness) and the coefficient of determination (R2) was 0,987. In general, the simulation of the water balance using PCSiWaPro® of different landfill covering systems showed a successful draining of the falling rainwater (even under heavy rainfall). In addition, the implemented vegetation models have proven that the vegetation of the landfill surface can reduce the water content in the landfill by evapotranspiration and water uptake by roots. The water balance simulation results of the scenarios for the computation of groundwater recharge by means of lysimeters showed that the program is applicable for this case. The relative deviation of the simulated from the measured groundwater recharge rates occur due to the implemented material parameters as well as to the neglect of macro pores effects (dual porosity).

A series of field, rainshelter, growth cabinet and modelling studies were conducted to investigate hot pepper response to different irrigation regimes and row spacings; to generate crop-specific model parameters; and to calibrate and validate the Soil Water Balance (SWB) model. Soil, climate and management data of five hot pepper growing regions of Ethiopia were identified to develop irrigation calendars and estimate water requirements of hot pepper under different growing conditions. High irrigation regimes increased fresh and dry fruit yield, fruit number, harvest index and top dry matter production. Yield loss could be prevented by irrigating at 20-25% depletion of plant available water, confirming the sensitivity of the crop to mild soil water stress. High plant density markedly increased fresh and dry fruit yield, water-use efficiency and dry matter production. Average fruit mass, succulence and specific leaf area were neither affected by row spacing nor by irrigation regimes. There were marked differences among the cultivars in fruit yields despite comparable top dry mass production. Average dry fruit mass, fruit number per plant and succulence were significantly affected by cultivar differences. The absence of interaction effects among cultivar and irrigation regimes, cultivars and row spacing, and irrigation regimes and row spacing for most parameters suggest that appropriate irrigation regimes and row spacing that maximize productivity of hot pepper can be devised across cultivars. To facilitate irrigation scheduling, a simple canopy cover based procedure was used to determine FAO-type crop factors and growth periods for different growth stages of five hot pepper cultivars. Growth analysis was done to calculate crop-specific model parameters for the SWB model and the model was successfully calibrated and validated for five hot pepper cultivars under different irrigation regimes or row spacings. FAO basal crop coefficients (Kcb) and crop-specific model parameters for new hot pepper cultivars can now be estimated from the database, using canopy characteristics, day degrees to maturity and dry matter production. Growth cabinet studies were used to determine cardinal temperatures, namely the base, optimum and cut-off temperatures for various developmental stages. Hot pepper cultivars were observed to require different cardinal temperatures for various developmental stages. Data on thermal time requirement for flowering and maturity between plants in growth cabinet and open field experiments matched closely. Simulated water requirements for hot pepper cultivar Mareko Fana production ranged between 517 mm at Melkassa and 775 mm at Alemaya. The simulated irrigation interval ranged between 9 days at Alemaya and 6 days at Bako, and the average irrigation amount per irrigation ranged between 27.9 mm at Bako and 35.0 mm at Zeway. / Thesis (PhD)--University of Pretoria, 2010. / Plant Production and Soil Science / unrestricted

<p>Drainage water recycling (DWR) is the practice of capturing, storing, and reusing subsurface drained agricultural water to support supplemental irrigation and has recently been proposed as a practice for improving the crop production and water quality performance in the tile-drained landscape of the U.S. Midwest. This study describes the development of a modeling framework to quantify the potential irrigation and water quality benefits of DWR systems in tile-drained landscapes and the application of the model using ten years of measured weather, tile drain flow and nutrient concentrations, water table, and soil data from two sites in the U.S. Midwest. From this modeling framework, the development and testing of an open-source online tool is also presented.</p><p></p><p>A spreadsheet model was developed to track water flows between a reservoir and drained and irrigated field area at each site. The amount of tile drain flow and associated nutrient loads that could be captured from the field and stored in the reservoir was estimated to calculate the potential water quality benefits of the system. Irrigation benefits were quantified based on the amount of applied irrigation annually. A reservoir size representing 6% to 8% of the field area with an average depth of 3.05 m was sufficient in meeting the annual irrigation requirements during the 10-year period at each site. At this reservoir size, average annual nitrate-N loads were reduced by 20% to 40% and soluble reactive phosphorus loads by 17% to 41%. Variability in precipitation within and across years, and differences in soil water characteristics, resulted in a wide range of potential benefits at the two sites.</p><p>An online tool was developed from the model, and a variance-based global sensitivity analysis was conducted to determine influential and low-sensitivity input parameters. The input parameter, depth of root zone, was the most influential input parameter suggesting that the estimation of total available water for the field water balance is a critical component of the model. Input settings describing the irrigation management and crop coefficients for the initial establishment and mid-season crop growth periods were also influential in impacting the field water balance. Reservoir seepage rate was influential in regard to the reservoir water balance, particularly at larger reservoir sizes. Sensitivity analysis results were used to develop a user-interface for the tool, Evaluating Drainage Water Recycling Decisions (EDWRD).</p><p>This study shows that DWR is capable of providing both irrigation and water quality benefits in the tile-drained landscape of the U.S. Midwest. The developed modeling framework supports future research on the development of strategies to implement and manage DWR systems, and the online tool serves as a resource for users to increase their awareness and understanding of the potential benefits of this novel practice.</p><p></p>

Ethiopia has long since been an area strongly affected by drought. Although there is a relativelylarge amount of fresh water present in the country, variability in rainfall and lack ofinfrastructure lead to the result that most of the population is undersupplied with water. In thisregion where water is such a valuable commodity, the Abay River is a large, mainly untappedresource. Agriculture is the largest economic activity in Ethiopia but the productivity ofagriculture here is one of the lowest in the world, making food security a serious problem for acountry with a fast growing population. The development of irrigation projects is hoped toensure food security at the household level. The Koga Dam is a key project for the Ethiopiangovernment, as a step towards achieving food self-sufficiency at both national and regionallevels for a country that has a history of draughts and famine. If this project succeeds, it will be amodel for projects to come and proof that dams and water management can bring change to theregion, particularly concerning food security. Sedimentation is a problem for many dams aroundthe world, and especially in this region. It is likely that the volume of the Koga reservoir willdecrease over time due to reservoir siltation. Variability in climate is also predicted for the regionwhich could mean years with below average rain. These two factors combined could mean adecrease in water supply for the irrigation project in the future. This study applies existingknowledge of sedimentation and annual climate variability relative to the Koga reservoir to asimple reservoir model in order to investigate current and future annual changes in thereservoir’s volume. Climate and volume change were incorporated into the water balance model.Results showed that the dam should be capable of providing enough irrigation water to farm yearround assuming average climate and climate variability and no sedimentation. However, as lowas an 11% decrease in storage could result in the reservoir drying out for at least one month ayear. / Etiopien har sedan länge varit utsatt för vattenbrist. Trots att det finns ganska mycket sötvatten ilandet leder variation i nederbörd och brist på infrastruktur till att en stor del av befolkningensaknar vatten i tillräcklig utsträckning. När vatten är en sådan värdefull råvara är Blå Nilen(Abay floden är den inhemska beteckningen) en stor och outnyttjad resurs för regionen.Jordbruk är den största näringen i Etiopien men jordbrukets produktivitet är en av de lägsta ivärlden. Med tanke på landets snabbt växande befolkning är livsmedelsförsörjningen därför enallvarligutmaning. Utvecklingen av bevattningsprojekt förväntas trygga livsmedelsförsörjningenpå familjenivå. Kogadammen är ett centralt projekt både på nationell och på regional nivå. Denetiopiska regeringen som ser den som ett steg mot livsmedelssäkerhet mot bakgrund av landetshistoria av regnbrist och svält. Om projektet lyckas, kommer det att bli en modell för framtidaprojekt och ett bevis på att dammar och vattenförvaltning kan ge förändra situationen, särskiltmed avseende på livsmedelssäkerhet. Sedimentering är ett problem för många dammar runt om ivärlden, särskilt i denna region. Risken är stor att Kogadammens vattenvolym kommer attminska på grund av igenslamning. Klimatets variabilitet förutspås dessutom öka i regionen ochkan innebära år med såväl mindre som mer regn än idag. Sedimenteringen och den ökadenederbördsvariabiliteten kan möjligtvis innebära en minskad tillgång på bevattningsvatten iframtiden. Denna studie använde sig av befintlig kunskap om sedimentering och årligaklimatvariationer för att studera tänkbara förändringar i Kogadammens vattenvolym.Existerande data användes i en enkel reservoarmodell för att undersöka årliga volymförändringari reservoaren idag och i framtiden. Dammens månatliga vattenbalans beräknades årsvis underolika antaganden om klimat och volymförändringar. Beräkningarna visar att dammen bör kunnaleverera tillräckligt med vatten för att bevattna hela projektområdet om ingen klimatförändringeller volymminskning sker. Men om en volymminskning skulle inträffa, skulle dammensannolikt inte kunna leverera tillräckligt med vatten för bevattning under torrsäsongenmednuvarande odlingsmönster.

Das Wechselspiel Boden-Pflanze und die damit verbundenen Wassergehaltsänderungen im Boden bestimmen die Funktionalität einer Wasserhaushaltsschicht. Untersuchungen an der Lysimeterstation Bautzen/Nadelwitz machen deutlich, dass vielfältige Faktoren (z. B. nFK, Durchwurzelungstiefe) die Mächtigkeit einer Wasserhaushaltsschicht bestimmen. Der Bodeneinbau mit einem Verdichtungsgrad von 90% - 92% Proctordichte gewährleistet ein setzungsstabiles Korngerüst unter Gewährleistung der geforderten nFK und LK. Durch die Erweiterung des Feinbodenartendreiecks mit den Ebenen „Durchwurzelung“, „nutzbare Feldkapazität“ und „Standsicherheit“ wird eine fachübergreifende Eignungsbeurteilung von Böden ermöglicht. Die wasserhaushaltspezifische Anwendung des Dreiecks der Phasenzusammensetzung nach RUDERT erlaubt die Ausweisung von Schwankungsbreiten bzgl. der Einbaukenngrößen, ohne Abweichungen von den geforderten bodenphysikalischen Anforderungen an eine Wasserhaushaltsschicht hinnehmen zu müssen.