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18 pages, 6354 KiB

Open AccessArticle

Generation of Sub-Hourly Rainfall Events through a Point Stochastic Rainfall Model

by Giuseppina Brigandì and Giuseppe T. Aronica

Geosciences 2019, 9(5), 226; https://doi.org/10.3390/geosciences9050226 - 16 May 2019

Cited by 8 | Viewed by 3556

Abstract

The aim of this paper is to present a stochastic model to generate sub-hourly rainfall events at a given point. Historical events used as the input have been extracted by the sub-hourly rainfall series available for a defined rain gauge station based on [...] Read more.

The aim of this paper is to present a stochastic model to generate sub-hourly rainfall events at a given point. Historical events used as the input have been extracted by the sub-hourly rainfall series available for a defined rain gauge station based on a fixed inter-event time and selected if their average intensity was larger than a critical fixed one. The sub-hourly events generated by applying the proposed methodology are completely stochastic and their main characteristics, i.e., shape, duration and average intensity, have been derived as a function of the statistics of the historical events analyzed. In order to characterize the shape, dimensionless hyetographs have been derived. They have been statistically modelled by using the Beta cumulative distribution. Average intensity and duration of the historical events were first modelled separately by fitting several probability distributions and selecting the best one using the more common statistical criteria. Then, their correlation was modelled using the Frank’s copula. In order to test the methodology, two sites in Sicily, Italy, where 10 min’ recorded rainfall data were available, were analyzed. Finally, comparison between the statistics of the simulated events and those of the measured data demonstrates the good performance of the model. Full article

(This article belongs to the Special Issue Hydrology of Urban Catchments)

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18 pages, 6259 KiB

Open AccessArticle

GIS Framework for Spatiotemporal Mapping of Urban Flooding

by Sayed Joinal Hossain Abedin and Haroon Stephen

Geosciences 2019, 9(2), 77; https://doi.org/10.3390/geosciences9020077 - 2 Feb 2019

Cited by 16 | Viewed by 8182

Abstract

This research aims to develop a framework using the Geographic Information System (GIS) to perform modeling and mapping of flood spatiotemporal variation in urban micro-watersheds. The GIS-framework includes a workflow of several methods and processes including delineation of urban watershed, generation of runoff [...] Read more.

This research aims to develop a framework using the Geographic Information System (GIS) to perform modeling and mapping of flood spatiotemporal variation in urban micro-watersheds. The GIS-framework includes a workflow of several methods and processes including delineation of urban watershed, generation of runoff hydrographs, and time series mapping of inundation depths and flood extent. This framework is tested in areas previously known to have experienced flooding at the University of Nevada, Las Vegas main campus, including Black Parking Lot (Blacklot) and East Mall. Calibration is performed by varying Digital Elevation Model (DEM) resolution, rainfall temporal resolution, and clogging factor whereas validation is performed using flood information from news reports and photographs. The testing at the Blacklot site resulted in calibration at 5 m DEM resolution and clogging factor of 0.83. The flood model resulted in an error of 24% between the estimated (26 inches/66 cm) and actual (34 inches/86.36 cm) flood depths. The estimated flood extents are consistent with the reported conditions and observed watermarks in the area. The flood beginning time estimated from the model is also consistent with the news reports. The testing at East Mall site also shows consistent results. The GIS framework provides spatiotemporal maps of flood inundation for visualization of flood dynamics. This research provides insight into flood modeling and mapping for a storm drain inlet-based watershed. Full article

(This article belongs to the Special Issue Hydrology of Urban Catchments)

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19 pages, 9631 KiB

Open AccessArticle

Framework for Offline Flood Inundation Forecasts for Two-Dimensional Hydrodynamic Models

by Punit Kumar Bhola, Jorge Leandro and Markus Disse

Geosciences 2018, 8(9), 346; https://doi.org/10.3390/geosciences8090346 - 13 Sep 2018

Cited by 49 | Viewed by 5056

Abstract

The paper presents a new methodology for hydrodynamic-based flood forecast that focuses on scenario generation and database queries to select appropriate flood inundation maps in real-time. In operational flood forecasting, only discharges are forecasted at specific gauges using hydrological models. Hydrodynamic models, which [...] Read more.

The paper presents a new methodology for hydrodynamic-based flood forecast that focuses on scenario generation and database queries to select appropriate flood inundation maps in real-time. In operational flood forecasting, only discharges are forecasted at specific gauges using hydrological models. Hydrodynamic models, which are required to produce inundation maps, are computationally expensive, hence not feasible for real-time inundation forecasting. In this study, we have used a substantial number of pre-calculated inundation maps that are stored in a database and a methodology to extract the most likely maps in real-time. The method uses real-time discharge forecast at upstream gauge as an input and compares it with the pre-recorded scenarios. The results show satisfactory agreements between offline inundation maps that are retrieved from a pre-recorded database and online maps, which are hindcasted using historical events. Furthermore, this allows an efficient early warning system, thanks to the fast run-time of the proposed offline selection of inundation maps. The framework is validated in the city of Kulmbach in Germany. Full article

(This article belongs to the Special Issue Hydrology of Urban Catchments)

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18 pages, 6914 KiB

Open AccessArticle

Ensemble Radar-Based Rainfall Forecasts for Urban Hydrological Applications

by Mayra Codo and Miguel A. Rico-Ramirez

Geosciences 2018, 8(8), 297; https://doi.org/10.3390/geosciences8080297 - 7 Aug 2018

Cited by 10 | Viewed by 4998

Abstract

Radar rainfall forecasting is of major importance to predict flows in the sewer system to enhance early flood warning systems in urban areas. In this context, reducing radar rainfall estimation uncertainties can improve rainfall forecasts. This study utilises an ensemble generator that assesses [...] Read more.

Radar rainfall forecasting is of major importance to predict flows in the sewer system to enhance early flood warning systems in urban areas. In this context, reducing radar rainfall estimation uncertainties can improve rainfall forecasts. This study utilises an ensemble generator that assesses radar rainfall uncertainties based on historical rain gauge data as ground truth. The ensemble generator is used to produce probabilistic radar rainfall forecasts (radar ensembles). The radar rainfall forecast ensembles are compared against a stochastic ensemble generator. The rainfall forecasts are used to predict sewer flows in a small urban area in the north of England using an Infoworks CS model. Uncertainties in radar rainfall forecasts are assessed using relative operating characteristic (ROC) curves, and the results showed that the radar ensembles overperform the stochastic ensemble generator in the first hour of the forecasts. The forecast predictability is however rapidly lost after 30 min lead-time. This implies that knowledge of the statistical properties of the radar rainfall errors can help to produce more meaningful radar rainfall forecast ensembles. Full article

(This article belongs to the Special Issue Hydrology of Urban Catchments)

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19 pages, 12522 KiB

Open AccessArticle

Development of a New Simulation Tool Coupling a 2D Finite Volume Overland Flow Model and a Drainage Network Model

by Javier Fernández-Pato and Pilar García-Navarro

Geosciences 2018, 8(8), 288; https://doi.org/10.3390/geosciences8080288 - 3 Aug 2018

Cited by 14 | Viewed by 4784

Abstract

Numerical simulation of mixed flows combining free surface and pressurized flows is a practical tool to prevent possible flood situations in urban environments. When dealing with intense storm events, the limited capacity of the drainage network conduits can cause undesirable flooding situations. Computational [...] Read more.

Numerical simulation of mixed flows combining free surface and pressurized flows is a practical tool to prevent possible flood situations in urban environments. When dealing with intense storm events, the limited capacity of the drainage network conduits can cause undesirable flooding situations. Computational simulation of the involved processes can lead to better management of the drainage network of urban areas. In particular, it is interesting to simultaneuously calculate the possible pressurization of the pipe network and the surface water dynamics in case of overflow. In this work, the coupling of two models is presented. The surface flow model is based on two-dimensional shallow water equations with which it is possible to solve the overland water dynamics as well as the transformation of rainfall into runoff through different submodels of infiltration. The underground drainage system assumes mostly free surface flow that can be pressurized in specific situations. The pipe network is modeled by means of one-dimensional sections coupled with the surface model in specific regions of the domain, such as drains or sewers. The numerical techniques considered for the resolution of both mathematical models are based on finite volume schemes with a first-order upwind discretization. The coupling of the models is verified using laboratory experimental data. Furthermore, the potential usefulness of the approach is demonstrated using real flooding data in a urban environment. Full article

(This article belongs to the Special Issue Hydrology of Urban Catchments)

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27 pages, 4783 KiB

Open AccessArticle

Flood Risk Mapping Using GIS and Multi-Criteria Analysis: A Greater Toronto Area Case Study

by Daniela Rincón, Usman T. Khan and Costas Armenakis

Geosciences 2018, 8(8), 275; https://doi.org/10.3390/geosciences8080275 - 27 Jul 2018

Cited by 138 | Viewed by 30137

Abstract

Given the increase in flood events in recent years, accurate flood risk assessment is an important component of flood mitigation in urban areas. This research aims to develop updated and accurate flood risk maps in the Don River Watershed within the Great Toronto [...] Read more.

Given the increase in flood events in recent years, accurate flood risk assessment is an important component of flood mitigation in urban areas. This research aims to develop updated and accurate flood risk maps in the Don River Watershed within the Great Toronto Area (GTA). The risk maps use geographical information systems (GIS) and multi-criteria analysis along with the application of Analytical Hierarchy Process methods to define and quantify the optimal selection of weights for the criteria that contribute to flood risk. The flood hazard maps were generated for four scenarios, each with different criteria (S1, S2, S3, and S4). The base case scenario (S1) is the most accurate, since it takes into account the floodplain map developed by the Toronto and Region Conservation Authority. It also considers distance to streams (DS), height above nearest drainage (HAND), slope (S), and the Curve Number (CN). S2 only considers DS, HAND, and CN, whereas S3 considers effective precipitation (EP), DS, HAND, and S. Lastly, S4 considers total precipitation (TP), DS, HAND, S, and CN. In addition to the flood hazard, the social and economic vulnerability was included to determine the total flood vulnerability in the watershed under three scenarios; the first one giving a higher importance to the social vulnerability, the second one giving equal importance to both social and economic vulnerability, and the third one giving more importance to the economic vulnerability. The results for each of the four flood scenarios show that the flood risk generated for S2 is the most similar to the base case (S1), followed by S3 and S4. The inclusion of social and economic vulnerability highlights the impacts of floods that are typically ignored in practice. It will allow watershed managers to make more informed decisions for flood mitigation and protection. The most important outcome of this research is that by only using the digital elevation model, the census data, the streams, land use, and soil type layers, it is possible to obtain a reliable flood risk map (S2) using a simplified method as compared to more complex flood risk methods that use hydraulic and hydrological models to generate flood hazard maps (as was the case for S1). Full article

(This article belongs to the Special Issue Hydrology of Urban Catchments)

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22 pages, 8536 KiB

Open AccessArticle

Development of a General Protocol to Enhance the Hydrological Analysis Techniques for Urban Catchments in Ireland

by Elisa Longo and John Paul Rooney

Geosciences 2018, 8(7), 252; https://doi.org/10.3390/geosciences8070252 - 9 Jul 2018

Cited by 2 | Viewed by 3796

Abstract

The hydrological analysis of urban catchments is a critical consideration for all major civil engineering projects. The purpose of this article is to develop a general protocol to enhance the established techniques for estimating runoff from Irish urban catchments. The chosen case study [...] Read more.

The hydrological analysis of urban catchments is a critical consideration for all major civil engineering projects. The purpose of this article is to develop a general protocol to enhance the established techniques for estimating runoff from Irish urban catchments. The chosen case study is the Rye Water catchment, which is covering two significant urban centres, Maynooth and Leixlip. The findings were compared with the flow data available on the Office of Public Works (OPW) website, to verify the reliability of the proposed approach. The study showed that the methodology described in this paper is applicable to Irish catchments and the protocol, with minor improvements can be adopted in Ireland to support designers in their approach to extreme rainfall events. Full article

(This article belongs to the Special Issue Hydrology of Urban Catchments)

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8 pages, 1737 KiB

Open AccessTechnical Note

Technical Note on the Dynamic Changes in Kalman Gain when Updating Hydrodynamic Urban Drainage Models

by Morten Borup, Henrik Madsen, Morten Grum and Peter Steen Mikkelsen

Geosciences 2018, 8(11), 416; https://doi.org/10.3390/geosciences8110416 - 13 Nov 2018

Cited by 4 | Viewed by 3035

Abstract

To prevent online models diverging from reality they need to be updated to current conditions using observations and data assimilation techniques. A way of doing this for distributed hydrodynamic urban drainage models is to use the Ensemble Kalman Filter (EnKF), but this requires [...] Read more.

To prevent online models diverging from reality they need to be updated to current conditions using observations and data assimilation techniques. A way of doing this for distributed hydrodynamic urban drainage models is to use the Ensemble Kalman Filter (EnKF), but this requires running an ensemble of models online, which is computationally demanding. This can be circumvented by calculating the Kalman gain, which is the governing matrix of the updating, offline if the gain is approximately constant in time. Here, we show in a synthetic experiment that the Kalman gain can vary by several orders of magnitude in a non-uniform and time-dynamic manner during surcharge conditions caused by backwater when updating a hydrodynamic model of a simple sewer system with the EnKF. This implies that constant gain updating is not suitable for distributed hydrodynamic urban drainage models and that the full EnKF is in fact required. Full article

(This article belongs to the Special Issue Hydrology of Urban Catchments)

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