published_or_final_version / Real Estate and Construction / Master / Master of Science in Construction Project Management

A linear reservoir cell model is presented which is proposed as a good candidate for real time flood forecasting applications. The model is designed to be computationally efficient since it should be able to run on a P.C and must operate online in real time. The model parameters and forecasts can be easily updated in order to allow for a more accurate forecast based on real time observations of streamflow and rainfall. The final model, once calibrated, should be able to operate effectively without requiring highly skilled and knowledgeable operators. Thus it is hoped to provide a tool which can be incorporated into an early warning system for mitigation of flood damage, giving water resources managers the extra lead-time to implement any contingency plans which may be neccssary to ensure the safety of people and prevent damage to property. The use of linear models for describing hydrological systems is not new, however the model presented in this thesis departs from previous implementations. A particular departure is the novel method used in the conversion of observed to effective rainlfall. The physical processes that result in the rainfall to runoff conversion are non-linear in nature. Most of the significant non-linearity results from rainfall losses, which occur largely due to evaporation and human extraction. The remaining rainfall is converted to runoff. These losses are particularly significant in the South African climate and in some regions may be as much as 70-90 % of the total observed rainfall. Loss parameters are an integral part of the model formulation and allow for losses to be dealt with directly. Thus, input to the model is observed rainfall and not the "effective" rainfall normally associated with conceptual catchment models. The model is formulated in Finite Difference form similar to an Auto Regressive Moving Average (ARMA) model; it is this formulation which provides the required computational efficiency. The ARMA equation is a discretely coincident form of the State-Space equations that govern the response of an arrangement of linear reservoirs. This results in a functional relationship between the reservoir response constants and the ARMA coefficients, which guarantees stationarity of the ARMA model. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2001.

The objective of this study was to determine if numerical models commonly used for large scale applications could also be used to model flow through flood control structures in the Rigolets Pass between Lake Borgne and Lake Pontchartrain. For this purpose a small scale physical model was built. It showed that bi-stable flow can develop downstream of a constriction. Small changes in the distribution of the approaching flow significantly impacted flows downstream of the constriction. This behavior could not be properly reproduced by a small scale 2-dimensional RMA2 model of identical dimensions. A large scale RMA2 model of the Rigolets testing possible locations and geometries of flood control structures showed that this pass is very sensitive to variations in the cross sectional flow area. Even minor reductions can significantly increase headlosses and velocities. To reduce negative impacts a flood control structure should be built in a wide and shallow area of the pass.

Pluvial flooding is caused by rainfall events that overwhelm drainage systems and do not allow excess water to be absorbed by soils or water infrastructure. This type of flooding occurs frequently in urban systems and leads to public inconveniences and infrastructure deterioration, which could cost more than fluvial flooding over time. Increased rainfall intensity, which is projected to increase with climate change, could result in increased pluvial flooding. This study aims to examine the vulnerability of pluvial flooding in Portland, OR (2010-2017) by incorporating an interdisciplinary framework that examines the physical and socioeconomic vulnerability of flooding through citizen-reported flooding data. We use a spatially dense network of 5-minute interval rainfall measurement to examine 3-day storm events associated with flooding reports to correlate storm size with the frequency of reports. Additionally, we use a Topographic Wetness Index (TWI) to identify the hotspots of pluvial flooding over space and characterize the sociodemographic and building characteristics of hotspots by performing a spatial analysis using census tract and tax lot level data. We investigate how individual neighborhood characteristics (i.e. ethnicity, education, gender, age, income) and building characteristics (i.e. building type, building age) contribute to reported flooding. This research seeks to identify where pluvial flooding occurs across the city, and how flood management planning can better address flood vulnerability through the biophysical and socioeconomic characteristics that exists amongst communities in Portland.

Design flood estimation is often required in hydrologic practice. For catchments with sufficient streamflow data, design floods can be obtained using flood frequency analysis. For catchments with no or little streamflow data (ungauged catchments), design flood estimation is a difficult task. The currently recommended method in Australia for design flood estimation in ungauged catchments is known as the Probabilistic Rational Method. There are alternatives to this method such as Quantile Regression Technique or Index Flood Method. All these methods give the flood peak estimate but the full streamflow hydrograph is required for many applications. The currently recommended rainfall based flood estimation method in Australia that can estimate full streamflow hydrograph is known as the Design Event Approach. This considers the probabilistic nature of rainfall depth but ignores the probabilistic behavior of other flood producing variables such as rainfall temporal pattern and initial loss, and thus this is likely to produce probability bias in final flood estimates. Joint Probability Approach is a superior method of design flood estimation which considers the probabilistic nature of the input variables (such as rainfall temporal pattern and initial loss) in the rainfall-runoff modelling. Rahman et al. (2002) developed a simple Monte Carlo Simulation technique based on the principles of joint probability, which is applicable to gauged catchments. This thesis extends the Monte Carlo Simulation technique to ungauged catchments. The Joint Probability Approach/ Monte Carlo Simulation Technique requires identification of the distributions of the input variables to the rainfall-runoff model e.g. rainfall duration, rainfall intensity, rainfall temporal pattern, and initial loss. For gauged catchments, these probability distributions are identified from observed rainfall and/or streamflow data. For application of the Joint Probability Approach to ungauged catchments, the distributions of the input variables need to be regionalised. This thesis, in particular, investigates the regionalisation of the distribution of rainfall duration and intensity. In this thesis, it is hypothesised that the distribution of storm duration can be described by Exponential distribution. The developed new technique of design flood estimation can provide the full hydrograph rather than only peak value as with the Probabilistic Rational Method and Quantile Regression Technique. The developed new technique can further be improved by addition of new and improved regional estimation equations for the initial loss, continuing loss and storage delay parameter (k) as and when these are available. / (M. Eng.) (Hons)

<p><!--[if !mso]> <object classid="clsid:38481807-CA0E-42D2-BF39-B33AF135CC4D" id=ieooui></object><mce:style><! st1\:*{behavior:url(#ieooui) } --></p><p>Hydrological investigations were performed in the Lubigi papyrus wetland in suburban Kampala, Uganda, impacted by human encroachment for settlement and agriculture. The first aim was to investigate the water flow variations and the dampening effect of the wetland. A second aim was to estimate the effective wetland volume and area, and relate this to the wetland function for treatment of the suburban runoff. A study site with well defined inflows and outflows was chosen, and three transects were cut through the papyrus to be able to study the water movement beneath the floating papyrus mat. Water flow measurements showed a flow dampening effect of the wetland on peak flows after rains, and the water balance revealed that the precipitation on the wetland was only 4 % of the inflow during the study. The tracer added at the inlet was rapidly detected downstream in the canal in the middle of the wetland, indicating a strong short-circuiting effect of the human made canal. At the outlet the tracer concentration was lower than the detection limit, suggesting a good mixing in the downstream part of the wetland, which was also supported by other water quality measurements in the transects. Ammonium-N concentrations at the inflow and outflow indicated a net export of ammonium-N, but the observed flow variations suggest that intensive water sampling campaigns are necessary for a proper evaluation of the water treatment function. The calculated effective volume and area amounted to 74 and 46 %, respectively, of the theoretically estimated, with a corresponding loss in the flow dampening and water treatment function of the wetland.</p><p> </p> / Rapporten är ett resultat av ett Minor Field Study stipendium finansierad av Sida.

<!--[if !mso]> <object classid="clsid:38481807-CA0E-42D2-BF39-B33AF135CC4D" id=ieooui></object><mce:style><! st1\:*{behavior:url(#ieooui) } --> Hydrological investigations were performed in the Lubigi papyrus wetland in suburban Kampala, Uganda, impacted by human encroachment for settlement and agriculture. The first aim was to investigate the water flow variations and the dampening effect of the wetland. A second aim was to estimate the effective wetland volume and area, and relate this to the wetland function for treatment of the suburban runoff. A study site with well defined inflows and outflows was chosen, and three transects were cut through the papyrus to be able to study the water movement beneath the floating papyrus mat. Water flow measurements showed a flow dampening effect of the wetland on peak flows after rains, and the water balance revealed that the precipitation on the wetland was only 4 % of the inflow during the study. The tracer added at the inlet was rapidly detected downstream in the canal in the middle of the wetland, indicating a strong short-circuiting effect of the human made canal. At the outlet the tracer concentration was lower than the detection limit, suggesting a good mixing in the downstream part of the wetland, which was also supported by other water quality measurements in the transects. Ammonium-N concentrations at the inflow and outflow indicated a net export of ammonium-N, but the observed flow variations suggest that intensive water sampling campaigns are necessary for a proper evaluation of the water treatment function. The calculated effective volume and area amounted to 74 and 46 %, respectively, of the theoretically estimated, with a corresponding loss in the flow dampening and water treatment function of the wetland. / Rapporten är ett resultat av ett Minor Field Study stipendium finansierad av Sida.

The main objective of this research is to devise a risk-based methodology for developing emergency operation schedules (EOS). EOS are decision tools that provide guidance to reservoir operators in charge of making real-time release decisions during major flood events. A computer program named REOS was created to perform the computations to develop risk-based EOS. The computational algorithm in REOS is divided in three major components: (1) synthetic streamflow generation, (2) mass balance computations, and (3) frequency analysis. The methodology computes the required releases to limit storage to the capacity available based on the probabilistic properties of future flows, conditional to current streamflow conditions. The final product is a series of alternative risk-based EOS in which releases, specified as a function of reservoir storage level, current and past inflows, and time of year, are associated with a certain risk of failing to attain the emergency operations objectives. The assumption is that once emergency operations are triggered by a flood event, the risk associated with a particular EOS reflects the probability of exceeding a pre-established critical storage level given that the same EOS is followed throughout the event. This provides reservoir operators with a mechanism for evaluating the tradeoffs and potential consequences of release decisions. The methodology was applied and tested using the Addicks and Barker Reservoir system in Houston, TX as a case study. Upstream flooding is also a major concern for these reservoirs. Modifications to the current emergency policies that would allow emergency releases based on the probability of upstream flooding are evaluated. Riskbased EOS were tested through a series of flood control simulations. The simulations were performed using the HEC-ResSim reservoir simulation model. Rainfall data recorded from Tropical Storm Allison was transposed over the Addicks and Barker watersheds to compute hypothetical hydrographs using HEC-HMS. Repeated runs of the HEC-ResSim model were made using different flooding and residual storage scenarios to compare regulation of the floods under alternative operating policies. An alternative application of the risk-based EOS in which their associated risk was used to help quantify the actual probability of upstream flooding in Addicks and Barker was also presented.

Includes bibliographical references. / Cover title. "February 2003." 4/8/03: Also available via Internet.

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