The height of an overflow dam must be designed low enough to prevent the reservoir water level from exceeding a flood plain during flooding conditions. Because of this constraint, much of the available water storage area is wasted and the available pressure head for power generation will be less than maximum during normal conditions. Crest control gates alleviate this problem by providing a variable spillway height. The Flash Gate Board is a passive automatic crest control gate. Its purpose is to regulate flood water while providing increased water pressure for power generation or for additional water storage for a municipality. The governing equations for the Flash Gate Board system are derived and used to formulate models of the system. Computer simulations are used to examine the system response in a variety of operating conditions. The results of these simulations are presented and discussed. The results include an investigation which developed an optimum gate height to maximize the potential of the Flash Gate Board. An experimental model was developed to verify analytical results and to provide additional insight. Conclusions from the study, recommendations for future work, and modifications for a trouble-free design are discussed. / Master of Science

Accessible flood modeling for low-resource, data-scarce communities currently does not exist. This paper proposes using drone imagery to compensate for the lack of other flood modeling data (i.e. streamflow measurements). Three flood models were run for Dzaleka Refugee Camp, located in Dowa, Malawi. Two of the models (the Soil and Water Assessment Tool (SWAT) and the Hydrologic Engineering Center River Analysis System (HEC-RAS)) are commonly used hydrological-hydraulic based models. The third model, the Water Caused Erosion Patterns (WCEP) model, was proposed by the author to capitalize on the high-resolution drone imagery using geological-geomorphological information. The drone imagery used in this study has a resolution of 3.5cm and shows erosion patterns throughout the refugee camp. By comparing the erosion patterns to flow direction of the surface, the erosion patterns were determined to be water caused or not water caused, the erosion patterns considered water caused were defined as high-risk flood areas, creating the WCEP model. The three models were compared using locations of collapsed houses throughout the camp. It was found that the WCEP model represents the location of collapsed houses significantly better (misclassification rate below 17%) than the SWAT or HEC-RAS models (misclassification rate below 54%, and 67% respectively). The WCEP model was combined with the best hydrological-hydraulic model (SWAT) to create a hydrogeomorphological model which capitalizes on both the drone imagery and the hydrological process. / Master of Science / The negative impact flooding has on communities can be reduced through flood modeling. But commonly used flood models are not accessible to data-scarce communities because of the historical data the models require. This paper explores using aerial imagery taken by a drone to make-up for the lack of historical data at Dzaleka Refugee Camp located in Dowa, Malawi. Drone imagery has a very high spatial resolution (3.5cm), so it is able to provide a lot of details, including marks that show an increase of flooding in certain areas and elevation information. The flood model presented in this paper is created using the found flood marks in drone imagery. The presented model is then compared to two commonly used flood models, and all three flood models are compared to locations of houses that collapsed from flooding throughout the refugee camp. The model created using drone imagery did the best job predicting high-risk locations with misclassification rates below 17%. The drone imagery model was then combined with a commonly used model to create a more comprehensive flood model, capitalizing on all available data.

The Water Resources Development Act of 1986 has increased attention to the ability of flood control benefit assessment methods to serve the joint need of assessing the economic and financial feasibility of a project. The Contingent Value Method is identified as an alternative flood control benefit assessment method. The findings of a case study to test the potential for the Contingent Value Method to be used in future flood control benefit assessment studies is presented. An empirical analysis of willingness to pay offers is conducted to determine the importance of property and nonproperty considerations in willingness to pay is also presented. The study findings suggest that landowners are willing to pay for the property effects and the effects of flood control on the community at large. The study findings do not support a relationship between willingness to pay for flood control and the landowner's level of anxiety over the prospect of future flooding. The findings do suggest that the contingent value method has the potential to be applied to flood control. Prior to any such application, however, several survey design and implementation issues need to be addressed. / Ph. D.

The three-dimensional behavior of geotextile tubes is studied using finite element modeling. Two initial shapes are investigated, one with a flat length-to-width ratio of 2:1 and the other with a flat length-to-width ratio of 5:1. The tubes are modeled resting on elastic foundations. For each initial shape, the elastic foundation is modeled using two different stiffnesses; one allows a minimum amount of "sinking" into the foundation and the other allows a considerable amount. The weight of the geotextile is included. Hydrostatic pressure is applied internally to each initially flat tube to model the pumped slurry. The shape of the tube is studied along with the contact region between the tube and its foundation, the stresses which develop in the geotextile along the planes of symmetry, and the relationship between the height of the tube and the amount of applied hydrostatic pressure. / Master of Science

Seasonally fluctuating water levels, known as flood pulses, influence the population dynamics and catches of fishes from river-floodplains. Although different measures of flood pulses, here called flood pulse variables, have been correlated to changes in catches of river-floodplain fishes, the flood pulse variables that have the strongest relationships to catches have not been identified. Furthermore, it is unclear if flood pulses influence catches of river-floodplain fishes with different life history strategies in different ways. Catches of 21 taxa from approximately 18,000 fishing trips were modeled as a function of fishing effort, gear type, seasonal flood pulse variables, and interannual flood pulse variables. These models were analyzed to understand which flood pulse variables had the strongest relationships to catches, and evaluate different flood pulse influences among taxa with different life history strategies. High water flood pulse variables generally had positive influences on catches in future years, while low water flood pulse variables generally had negative influences on catches in future years. Flood pulses generally had stronger influences on the catches of fishes with high fecundities and smaller eggs than on catches of fishes with low fecundities and larger eggs. Variation was observed in strengths and directions of flood pulse influences on catches of fishes with similar and different life history strategies. While my results were generally consistent with prevailing knowledge of how flood pulses influence catches of fishes, other biological factors of specific fish populations may further explain population responses to flood pulses. / Master of Science / Seasonally fluctuating water levels, known as flood pulses, influence the population dynamics and catches of fishes from river-floodplains. Although different measures of flood pulses, here called flood pulse variables, have been related to changes in catches of riverfloodplain fishes, the flood pulse variables that have the strongest relationships to catches have not been identified. Furthermore, it is unclear if flood pulses influence catches of riverfloodplain fishes with different life history strategies in different ways. Catches of 21 taxa from approximately 18,000 fishing trips were modeled as a function of fishing effort, gear type, seasonal flood pulse variables, and interannual flood pulse variables. These models were analyzed to understand which flood pulse variables had the strongest relationships to catches, and evaluate different flood pulse influences among taxa with different life history strategies. High water flood pulse variables generally had positive influences on catches in future years, while low water flood pulse variables generally had negative influences on catches in future years. Flood pulses generally had stronger influences on the catches of fishes that produce many smaller eggs than on catches of fishes that produce fewer and larger eggs. Variation was observed in strengths and types of flood pulse influences on catches of fishes with similar and different life history strategies. While my results were generally consistent with prevailing knowledge of how flood pulses influence catches of fishes, other biological factors of specific fish populations may further explain population responses to flood pulses.

Doctor of Philosophy / Department of Biology / Craig Paukert / River discharge influences fish and invertebrate communities and understanding how hydrologic variables contribute to fish and invertebrate composition can provide information for restoration and management. This study examines the relationship between several flow regime metrics that may influence fish and invertebrate community structure in large river systems such as the Kansas River. First, I examined how hydrology influences macroinvertebrate (drifting and benthic) density and fish communities before, during, and after flooding in both main and secondary channels. I found that drifting invertebrate density increased during flooding potentially providing increased prey opportunities for fishes. I also found that fluvial dependent and generalist fish species use inundated habitats more than fluvial specialists. My results suggest that the flux of water into inundated habitats supports a unique subset of invertebrate and fish communities of the main channel. Next, I examined the importance of lateral connectivity on fish and invertebrate composition by examining differences in seasonally and permanently inundated secondary channels in relation to main channel reaches. I found that drifting and benthic invertebrate assemblages and fish assemblages differed between seasonally inundated and permanently connected secondary channels. These results suggest that maintenance of diverse secondary channel connections is useful in preserving native biota in the Kansas River. Finally, I tested if hydrologic variables influenced recruitment of four native Kansas River fishes. I found that recruitment for two of the four fish species (flathead catfish, Pylodictis olivaris, and shovelnose sturgeon, Scaphirhynchus platorynchus) increased in high flow years. These results indicate that a natural and variable flow regime may be important for maintaining fish community structure in the Kansas River. The results of this study have implications for management strategies that include the use of high flows to provide a pulse of insect prey to the main channel for fishes, restoration of natural high and low flow variability as important to fish recruitment, and diversity in secondary channel connectivity (seasonal and permanently connected) that promotes unique fish and invertebrate communities.

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The primary aim of this study was to evaluate, calibrate and verify the SDF run-off coefficients at a quaternary catchment level in the C5 secondary drainage region (SDF basin 9) and other selected SDF basins in South Africa by establishing the catchment parameters and SDF/probability distribution-ratios. The probability distribution-ratios were based on the comparison between the flood peaks estimated by the SDF method and statistical analyses of observed flow data. These quaternary run-off coefficients were then compared with the existing regional SDF run-off coefficients, whilst the run-off coefficient adjustment factors as proposed by Van Bladeren (2005) were also evaluated. It was evident from this study that the calibrated run-off coefficients obtained are spread around those of Alexander (2003), but were generally lower in magnitude. The adjusted run-off coefficients (Van Bladeren, 2005) had a tendency to decrease in magnitude with increasing recurrence interval, whilst some of the adjusted run-off coefficients exceeded unity. The extent to which the original SDF method overestimated the magnitude and frequency of flood peaks varied form basin to basin, with the SDF/probability distribution-ratios the highest in the Highveld and southern coastal regions with summer convective precipitation. In these regions the flood peak-ratios were occasionally different by up to a factor of 3 or even more. The southern coastal regions with winter orographic/frontal precipitation demonstrated the best flood peak-ratios, varying from 0.78 to 1.63. The adjusted SDF method results (Van Bladeren, 2005) were only better in 26% of all the basins under consideration when compared to those estimated by the original SDF method. On average, the adjusted SDF/probability distribution-ratios varied between 0.30 and 6.58, which is unacceptable. The calibrated version of the SDF method proved to be the most accurate in all the basins under consideration. On average, the calibrated SDF/probability distribution-ratios varied between 0.85 and 1.15, whilst at some basins and individual return periods, less accurate results were evident. Verification tests were conducted in catchments not considered during the calibration process with a view to establish whether the calibrated run-off coefficients are predictable and to confirm that the method is reliable. The verification results showed that the calibrated/verified SDF method is the most accurate and similar trends were evident in all the basins under consideration. On average, the verified SDF/probability distribution-ratios varied between 0.82 and 1.19, except in SDF basins 6 and 21 where the 5 to 20-year return period flood peaks were overestimated by 41% and 56% respectively, which is still conservative. The secondary aim of this study was to develop a customised, user-friendly Design Flood Estimation Tool (DFET) in a Microsoft Office Excel/Visual Basic for Applications environment in order to assess the use and applicability of the various design flood estimation methods. The developed DFET will provide designers with a software tool for the rapid investigation and evaluation of alternative design flood estimation methods either at a regional or site specific scale. The focus user group of the application will comprises of engineering technicians, engineering technologist and engineers employed at civil engineering consultants, not necessarily specialists in the field of flood hydrology. The DFET processed all the catchment, meteorological (precipitation) and hydrological (observed flows) data used as input for the various design flood estimation methods. / AFRIKAANSE OPSOMMING: Die primêre doelwit van die studie was om die SDF-afloopkoëffisiënte op ‘n kwartinêre opvangsgebiedvlak in die C5-sekondêre dreineringsgebied (SDFopvangsgebied 9) en ander gekose SDF-opvangsgebiede in Suid-Afrika te evalueer, te kalibreer en te verifieer deur die opvangsgebiedparameters en SDF/waarskynlikheidsverspreiding-verhoudings vas te stel. Dié waarskynlikheidsverspreiding-verhoudings was gebaseer op die vergelyking tussen die vloedpieke soos beraam deur die SDF-metode en statistiese analises van waargenome vloeidata. Dié kwartinêre afloopkoëffisiënte is met die bestaande streeksgebonde SDF-afloopkoëffisiënte vergelyk, terwyl die afloopkoëffisiënt-aanpassingsfaktore soos voorgestel deur Van Bladeren (2005) ook geëvalueer is. Dit het duidelik uit die studie geblyk dat die gekalibreerde afloopkoëffisiënte verspreid rondom die van Alexander (2003) is, maar in die algemeen laer in omvang. Die aangepaste afloopkoëffisiënte (Van Bladeren, 2005) was geneig om af te neem in grootte met ‘n toename in die herhalingsperiode, terwyl sommige afloopkoëffisiënte ‘n waarde van 1 oorskry het. Die omvang waartoe die oorspronklike SDF metode die grootte en herhaalperiode van vloedpieke oorskat het, wissel van opvangsgebied tot opvangsgebied, met die SDF/waarskynlikheidsverspreiding-verhoudings die hoogste in die Hoëveld en suidelike kusstreke gekenmerk deur konveksie-somerreënval. In hierdie streke het die vloedpiekverhoudings gereeld verskil tot en met ‘n faktor van 3 of selfs meer. Die suidelike kusstreke met kenmerkende ortografiese/frontale winterreënval het oor die beste vloedpiekverhoudings beskik wat gewissel het tussen 0.78 en 1.63. Die resultate van die aangepaste SDF-metode (Van Bladeren, 2005) was slegs in 26% van al die opvangsgebiede beter as die beramings van die oorspronklike SDF-metode. Die aangepaste SDF/waarskynlikheidsverspreiding-verhoudings het, met verwysing na gemiddeldes, tussen 0.30 en 6.58 gewissel, wat onaanvaarbaar is. Die gekalibreerde weergawe van die SDF-metode was die mees akkurate metode in al die opvangsgebiede van belang. Die gekalibreerde SDF/waarskynlikheidsverspreiding-verhoudings het, met verwysing na gemiddeldes, tussen 0.85 en 1.15 gewissel, terwyl die resultate van sommige opvangsgebiede en individuele herhalingsperiodes minder akkuraat was. Verifikasietoetse is uitgevoer in die opvangsgebiede wat nie tydens die kalibrasieproses gebruik was nie om vas te stel of die gekalibreerde afloopkoëffisiënte voorspelbaar is en om te bevestig dat die metode betroubaar is. Die verifikasieresultate het getoon dat die gekalibreerde/geverifieerde SDFmetode die mees akkurate metode is en dat soortgelyke tendense duidelik was in al die relevante opvangsgebiede. Die geverifieerde SDF/waarskynlikheidsverspreiding-verhoudings het, met verwysing na gemiddeldes, tussen 0.82 en 1.19 gewissel, behalwe in SDF-opvangsgebiede 6 en 21 waar die 5- en 20-jaar herhalingsperiode-vloedpieke onderskeidelik met 41% en 56% oorskat is, wat steeds konserwatief is. Die sekondêre doelwit van die studie was om ‘n gebruikersvriendelike “Design Flood Estimation Tool” (DFET) in ‘n Microsoft Office Excel/Visual Basic for Applications omgewing te ontwikkel om die gebruik en toepaslikheid van die verskeie ontwerpvloedberamingsmetodes te bepaal. Die DFET sal ontwerpers voorsien van ‘n sagtewareprogram om alternatiewe ontwerpvloedberamingsmetodes op streek- of plaaslike skaal te ondersoek en te evalueer. Die fokus-gebruikersgroep vir die toepassing van die program sal bestaan uit ingenieurstegnici, ingenieurstegnoloë en ingenieurs werksaam by raadgewende siviele ingenieurs, nie noodwendig vakkundiges in die veld van hidrologie nie. Die DFET was gebruik om al die opvangsgebied-, meteorologiese (reënval) en hidrologiese (waargenome vloeie) data vir die verskeie ontwerpvloedberamingsmetodes te verwerk.

published_or_final_version / abstract / Earth Sciences / Doctoral / Doctor of Philosophy

Gävle kommun har planer på att exploatera Gävle stad söderut. Planerna finns enligt översiktsplanen Gävle Stad 2025 för bland annat områdena Järvsta och Ersbo. Dessa områden avvattnas mot Järvstabäcken. Detta examensarbete är en utredning av Järvstabäckens avrinningsområde med hänsyn till avrinningsområdets beskaffenhet, klimatförändringar och planerad exploatering. Utifrån dessa faktorer analyseras riskpunkter för översvämning inom avrinningsområdet. Utredningen av avrinningsområdet har genomförts via fältbesök, litteraturstudier och modellering i MIKE FLOOD.   Problematiken kring avrinningsområdet ligger i att Järvstabäcken redan är högt belastad. Med utökade exploateringsområden för bostäder och handelsområden i Hemlingby och Järvsta förväntas Järvstabäcken belastas ytterligare. Ersbo industriområde förväntas även påverka dagvattenflödena då mer andel hårdgjorda ytor tas i anspråk vid utökat handelsområde i kombination med planerad snötipp på industriområdet. Snötippen förväntas påverka flödet under smältperioden.   Riskpunkter för översvämningar återfinns i lågpunkter och passager under E4, Södra Kungsvägen, Upplandsleden och Bomhusvägen. I dessa punkter bör fördröjning av dagvattnet anläggas för att öka kontrollen över flödena och minska risken och kostnaderna för återställande av byggnader och infrastruktur vid översvämning. Riskpunkter i anslutning till befintlig bebyggelse och planerade bostadsområden bör prioriteras för utredning. / Gävle municipality's plans to exploit the city to the south are under the general plan for the areas Järvsta and Ersbo, these areas are dewatered to Järvsta stream. This thesis is an investigation of the Järvsta stream regarding flood risk areas within the basin with consideration to the planned development areas. Investigation of the catchment area has been carried out through field visits, literature studies and modeling with MIKE FLOOD. The problem with Järvsta stream is that it is already heavily loaded. With increased development areas for housing and commercial areas in Hemlingby and Järvsta expected Järvsta stream to be even more loaded in case of extreme rainfall. Ersbo industrial area is also expected to affect surface water flows, hence higher proportion paved surface in combination with the planned landfill for snow in the industrial area expect to impact the flow frequencies. The landfill for snow in Ersbo affects the flow frequencies during the melt period. Risk Points of flooding is found in low points and passages under E4, Södra Kungsvägen, Upplandsleden and Bomhusvägen. These points should delay stormwater to increase control over flows and reduce the risk of flooding and cost of restoration of the buildings and infrastructure. Risk points adjacent to the existing residential areas and planned residential areas should be prioritized for investigation.

The object of this dissertation is to describe the influence of water works on the outflow from a watershed through the Hydrologic Modelling System Hec HMS. It is a direct application to the particular watershed of the Bílský Stream. In the theoretical part about relevant literature, solutions to the topics related to this issue are found. It focuses especially on the water balance in the watershed; the outflow from the watershed and other factors by which the watershed is influenced; extreme flows and flood activity with appropriate security steps such as water basins. At the end of the part on the literature, there are five different systems for creating hydrologic models with the specialisation on the Hec HMS model. The practical part is about preparing input data for the hydrologic model and its subsequent creation. Particular runoff from different N-year precipitation (N = 2, 10, 50 and 100) are compared. Two hydrologic models have been created for comparison, one with the watershed without a reservoir and the second one with a reservoir included. The resultant part is about watching flows, volumes of runoffs and the tranformation of the flood wave in a reservoir between N-year precipitation and two different models of watershed.