scholarly journals Water-level attenuation in broad-scale assessments of exposure to coastal flooding: a sensitivity analysis

2018 ◽  
Author(s):  
Athanasios T. Vafeidis ◽  
Mark Schuerch ◽  
Claudia Wolff ◽  
Tom Spencer ◽  
Jan L. Merkens ◽  
...  
Keyword(s):  
Water Level ◽  
Flood Risk ◽  
Land Surface ◽  
Surface Characteristics ◽  
Water Levels ◽  
Risk Indicators ◽  
Population Exposure ◽  
Modelling Framework ◽  
Complex Interactions ◽  
Flood Exposure

Abstract. This study explores the uncertainty introduced in global assessments of coastal flood exposure and risk when not accounting for water level attenuation due to land-surface characteristics. We implement a range of plausible water-level attenuation values for characteristic land-cover classes in the flood module of the Dynamic and Integrated Vulnerability Assessment (DIVA) modelling framework and assess the sensitivity of flood exposure and flood risk indicators to differences in attenuation rates. Results show a reduction of up to 47 % in area exposure and even larger reductions in population exposure and expected flood damages when considering water level attenuation. The reductions vary by country, reflecting the differences in the physical characteristics of the floodplain as well as in the spatial distribution of people and assets in coastal regions. We find that uncertainties related to not accounting for water attenuation in global assessments of flood risk are of similar magnitude to the uncertainties related to the amount of SLR expected over the 21st century. Despite using simplified assumptions to account for the process of water level attenuation, which depends on numerous factors and their complex interactions, our results strongly suggest that an improved understanding and representation of the temporal and spatial variation of water levels across floodplains is essential for future impact modelling.

scholarly journals Water-level attenuation in broad-scale assessments of exposure to coastal flooding: a sensitivity analysis

2017 ◽  
Author(s):  
Athanasios T. Vafeidis ◽  
Mark Schuerch ◽  
Claudia Wolff ◽  
Tom Spencer ◽  
Jan L. Merkens ◽  
...  
Keyword(s):  
Water Level ◽  
Flood Risk ◽  
Land Surface ◽  
Surface Characteristics ◽  
Water Levels ◽  
Risk Indicators ◽  
Population Exposure ◽  
Modelling Framework ◽  
Complex Interactions ◽  
Flood Exposure

Abstract. This study explores the uncertainty introduced in global assessments of coastal flood exposure and risk by not accounting for water level attenuation due to land–surface characteristics. We implement a range of plausible water level attenuation values in the flood module of the Dynamic Interactive Vulnerability Assessment (DIVA) modelling framework and assess the sensitivity of flood exposure and flood risk indicators to differences in attenuation rates. Results show a reduction of up to 47 % in area exposure and even larger reductions in population exposure and expected flood damages. Despite the use of a spatially constant rate for water attenuation the reductions vary by country, reflecting the differences in the physical characteristics of the floodplain as well as in the spatial distribution of people and assets in coastal regions. We find that uncertainties related to the omission of this factor in global assessments of flood risk are of similar magnitude to the uncertainties related to the amount of SLR expected over the 21st century. Despite using simplified assumptions, as the process of water level attenuation depends on numerous factors and their complex interactions, our results strongly suggest that future impact modelling needs to focus on an improved representation of the temporal and spatial variation of water levels across floodplains by incorporating the effects of relevant processes.

scholarly journals Water-level attenuation in global-scale assessments of exposure to coastal flooding: a sensitivity analysis

2019 ◽  
Vol 19 (5) ◽  
pp. 973-984 ◽  
Author(s):  
Athanasios T. Vafeidis ◽  
Mark Schuerch ◽  
Claudia Wolff ◽  
Tom Spencer ◽  
Jan L. Merkens ◽  
...  
Keyword(s):  
Water Level ◽  
Flood Risk ◽  
Land Surface ◽  
Surface Characteristics ◽  
Global Scale ◽  
Water Levels ◽  
Risk Indicators ◽  
Population Exposure ◽  
Modelling Framework ◽  
Flood Exposure

Abstract. This study explores the uncertainty introduced in global assessments of coastal flood exposure and risk when not accounting for water-level attenuation due to land-surface characteristics. We implement a range of plausible water-level attenuation values for characteristic land-cover classes in the flood module of the Dynamic and Integrated Vulnerability Assessment (DIVA) modelling framework and assess the sensitivity of flood exposure and flood risk indicators to differences in attenuation rates. Results show a reduction of up to 44 % in area exposure and even larger reductions in population exposure and expected flood damages when considering water-level attenuation. The reductions vary by country, reflecting the differences in the physical characteristics of the floodplain as well as in the spatial distribution of people and assets in coastal regions. We find that uncertainties related to not accounting for water attenuation in global assessments of flood risk are of similar magnitude to the uncertainties related to the amount of sea-level rise expected over the 21st century. Despite using simplified assumptions to account for the process of water-level attenuation, which depends on numerous factors and their complex interactions, our results strongly suggest that an improved understanding and representation of the temporal and spatial variation of water levels across floodplains is essential for future impact modelling.

scholarly journals Feedback Mechanism in Bifurcating River Systems: the Effect on Water-Level Sensitivity

Water ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1915
Author(s):  
Matthijs R.A. Gensen ◽  
Jord J. Warmink ◽  
Fredrik Huthoff ◽  
Suzanne J.M.H. Hulscher
Keyword(s):  
Water Level ◽  
Flood Risk ◽  
River System ◽  
Feedback Mechanism ◽  
Water Levels ◽  
River Systems ◽  
Water Level Variations ◽  
System Water ◽  
Discharge Distribution ◽  
Single Branch

Accurate and reliable estimates of water levels are essential to assess flood risk in river systems. In current practice, uncertainties involved and the sensitivity of water levels to these uncertainties are studied in single-branch rivers, while many rivers in deltas consist of multiple distributaries. In a bifurcating river, a feedback mechanism exists between the downstream water levels and the discharge distribution at the bifurcation. This paper aims to quantify the sensitivity of water levels to main channel roughness in a bifurcating river system. Water levels are modelled for various roughness scenarios under a wide range of discharge conditions using a one-dimensional hydraulic model. The results show that the feedback mechanism reduces the sensitivity of water levels to local changes of roughness in comparison to the single-branch river. However, in the smaller branches of the system, water-level variations induced by the changes in discharge distribution can exceed the water-level variations of the single-branch river. Therefore, water levels throughout the entire system are dominated by the conditions in the largest branch. As the feedback mechanism is important, the river system should be considered as one interconnected system in river maintenance of rivers, flood-risk analyses, and future planning of river engineering works.

Uncertainty in coastal flooding: modelling and visualisation

2020 ◽  
Author(s):  
John Maskell
Keyword(s):  
Water Level ◽  
Storm Surge ◽  
Return Period ◽  
Flood Risk ◽  
High Water ◽  
Coastal Flooding ◽  
Water Levels ◽  
Tidal Range ◽  
The Uk ◽  
Flood Maps

<p>Two case studies are considered in the UK, where uncertainty and drivers of coastal flood risk are explored through modelling and visualisations. Visualising the impact of uncertainty is a useful way of explaining the potential range of predicted or simulated flood risk to both expert and non-expert stakeholders.</p><p>Significant flooding occurred in December 2013 and January 2017 at Hornsea on the UK East Coast, where storm surge levels and waves overtopped the town’s coastal defences. Uncertainty in the potential coastal flooding is visualised at Hornsea due to the range of uncertainty in the 100-year return period water level and in the calculated overtopping due to 3 m waves at the defences. The range of uncertainty in the simulated flooding is visualised through flood maps, where various combinations of the uncertainties decrease or increase the simulated inundated area by 58% and 82% respectively.</p><p>Located at the mouth of the Mersey Estuary and facing the Irish Sea, New Brighton is affected by a large tidal range with potential storm surge and large waves. Uncertainty in the coastal flooding at the 100-year return period due to the combination of water levels and waves is explored through Monte-Carlo analysis and hydrodynamic modelling. Visualisation through flood maps shows that the inundation extent at New Brighton varies significantly for combined wave and surge events with a joint probability of 100 years, where the total flooded area ranges from 0 m<sup>2</sup> to 10,300 m<sup>2</sup>. Waves are an important flood mechanism at New Brighton but are dependent on high water levels to impact the coastal defences and reduce the effective freeboard. The combination of waves and high-water levels at this return level not only determine the magnitude of the flood extent but also the spatial characteristics of the risk, whereby flooding of residential properties is dominated by overflow from high water levels, and commercial and leisure properties are affected by large waves that occur when the water level is relatively high at the defences.</p>

scholarly journals Flood mapping under an extreme event in a large shallow lake influenced by flood pulse in Southeast Asia

2020 ◽  
Vol 148 ◽  
pp. 06004
Author(s):  
Sokly Siev ◽  
Vannak Ann ◽  
Takashi Nakamura ◽  
Hideto Fujii ◽  
Chihiro Yoshimura
Keyword(s):  
Southeast Asia ◽  
Water Level ◽  
Shallow Lake ◽  
Flood Risk ◽  
Extreme Event ◽  
Gumbel Distribution ◽  
Flood Pulse ◽  
Water Levels ◽  
Mekong River ◽  
Flood Mapping

Tonle Sap Lake (TSL) in Cambodia is the largest shallow lake in Southeast Asia. Influenced by flood pulse system of the Mekong River, TSL provides diverse benefits including ecosystem services, ecological functioning, and flood water storage in the floodplains. However, extreme events (e.g., flooding) due to rising water level caused by dam break and/or heavy rainfall in the Mekong River Basin could threaten the ecosystems of the lake, community health and economic growth in the region. Flood mapping under such extreme event could be informative in the flood risk and emergency management. In this study, we aim to develop a flood risk boundary map in TSL using an existing 2D hydrodynamic model (Caesar-Lisflood, CL) with rising water levels estimated by Gumbel distribution. As a result, the extreme water level of 1% chance (or 100-year flood return period) exceeding the annual maximum water level at Prek Kdam station was approximately 11.38 m resulting in the largest inundation area of 15193 km2. Overall, the employed method and flood risk mapping are useful for the decision makers to manage flood risks and emergency in the lake. This is to anticipate the consequences of a possible rising water level by an extreme event.

Changes in hydrologic conditions in the Dixie Valley and Fairview Valley areas, Nevada, after the earthquake of December 16, 1954

1957 ◽  
Vol 47 (4) ◽  
pp. 387-396
Author(s):  
C. P. Zones
Keyword(s):  
Ground Water ◽  
Water Level ◽  
Land Surface ◽  
Water Levels ◽  
Temporary Increase ◽  
Valley Fill ◽  
Dixie Valley ◽  
Main Fault ◽  
Hydrologic Conditions ◽  
Total Discharge

abstract The earthquake of December 16, 1954, affected hydrologic conditions in the Dixie Valley and Fairview Valley areas, Nevada. In Dixie Valley the rate of flow of water from wells was temporarily increased and water flowed for more than a month from several wells that had not flowed before. Water levels in wells were higher after the earthquake, but the trend of water levels since the earthquake has varied locally. There is no evidence that ground-water temperatures were affected. The flow of Mud Springs, which is on the main fault on the west side of Dixie Valley, increased substantially immediately after the earthquake, but since has decreased to essentially its pre-earthquake rate. The water level in Fairview Valley was about 4 feet higher after the earthquake. In East Gate Valley and at West Gate, ground-water levels were lower after the earthquake. In June, 1956, the water level in East Gate Valley was 34 feet lower than the pre-earthquake level. At West Gate the water level was about 9 feet lower. In Stingaree Valley the water level began to rise after an initial decline and reached a peak about 11 feet higher than the pre-earthquake level. Possible causes for the rise in ground-water levels in Dixie and Fairview Valleys include tilting of the confined and semiconfined aquifers in the valleys, compaction of the sediments of the valley fill, and increased upward leakage of ground water. It is possible that opening of new fractures and widening of pre-existing fractures in the bedrock between East Gate, Cowkick, and Stingaree valleys has accelerated the rate of movement of ground water between those valleys. The temporary increase in the flow of water from Mud Springs may be due to the opening of fractures in the fault zone along which the water is rising, or to a possible lowering of the land surface at the springs with a resulting increase in artesian head at the spring orifices. It is thought that any increase in the total discharge of ground water in the Dixie Valley and Fairview Valley areas is temporary because the increased discharge is probably from ground-water storage.

scholarly journals Flood risk assessment of river “Kelani Ganga” exceeding its threshold water level

2020 ◽  
Vol 157 ◽  
pp. 02006
Author(s):  
Charith Dushyantha ◽  
Irina Ptuhina
Keyword(s):  
Risk Assessment ◽  
Water Level ◽  
Extreme Value Theory ◽  
Flood Risk ◽  
Value Theory ◽  
Extreme Value ◽  
Water Levels ◽  
Suitable Model ◽  
Flood Risk Assessment ◽  
Maximum Water

Flood risk assessment curves were developed for a flood risk assessment carried out in Colombo, Sri Lanka. Annual maximum water levels at three gauging stations in Kelani Ganga were used as data to prepare the flood risk assessment. Information sources include the Ministry of Disaster Management, Irrigation department and Department of Metrology. Current approaches to risk assessment function development were improved by using the extreme value theory. The most suitable model from the extreme value theory was defined by the behaviour of the probabilistic density function. The probability of a threshold water level exceeding in a given year can be predicted by using the developed model. According to the results of the flood risk assessment at the three gauging stations along river Kelani Ganga, the Hanwella station is at an 89.3% high risk of inundating the area with the water level reaching up to 9.6m in 10 years of time. These results can be used to develop hazard maps for these areas as one of the criteria that must be taken into consideration when choosing the optimal site for construction.

Lake Mead and Hoover Dam monitoring in Nevada and Arizona states, USA using InSAR

2020 ◽  
Author(s):  
Mehdi Darvishi ◽  
Georgia Destouni ◽  
Fernando Jaramillo
Keyword(s):  
Los Angeles ◽  
Water Level ◽  
Land Surface ◽  
Ground Deformation ◽  
The United States ◽  
Water Levels ◽  
Lake Mead ◽  
Water Level Changes ◽  
Hoover Dam ◽  
The Impact

<p>Man-made reservoirs and lakes are key elements in the terrestrial water system. The increased concern about the impact of anthropogenic interventions on and the dynamics of these water resources has given rise to various approaches for representing human-water interactions in land surface models. Synthetic aperture radar interferometry (InSAR) has become a powerful geodetic tool for this purpose, by evidencing changes of ground and water surfaces across time and space. In this research, the Lake Mead and associated Hoover Dam are studied using Small Baseline Subset (SBAS) technique. Lake Mead is the largest reservoir in the United States, in terms of water capacity, supplies water and hydropower for millions of people in Las Vegas, Los Angeles and southwestern part of the USA. In recent years, rising temperature, increasing evaporation and decreasing precipitation have decreased water levels substantially, and probably modified its surrounding groundwater and surface as well.</p><p>This study aims to identify a hydrology-induced ground deformation around the lake Mead and a probable Hoover dam movement displacement. For the reservoir, we used the SBAS technique using 138 SAR data, including ERS1/2, Envisat, ALOS PALSAR and Sentinel-1, covering a time-spam between 1995 and 2019. For the analysis on the dam, we used the SBAS technique from 2014 to 2019 with descending and ascending modes of Sentinel-1A/B imageries. We found two main deformation patterns around the lake associated with the water level changes. Firstly, ERS and Sentinel-1 data evidenced a ground deformation that manifested itself as as a subsidence pattern in 1995 that has gradually changed into an uplift up to 2019. Secondly, the correlation trend between the deformation and water level changes has changed from negative to positive, with a transition point around March 2008. A possible interpretation for this is that the ground has initially reacted to the water fluctuations in the reservoir before March 2008 but after no longer plays a dominant role in the deformation occurring around the lake. The findings will help us to have a better understanding over the changes happened around the lake due to the water level changes and provide the valuable information for more effective management and maintenance of hydraulic structures and facilities near by the lake and water control in the future.</p>

Groundwater modelling for time periods of up to hundreds of thousands of years.

2020 ◽  
Author(s):  
Gerrit H. de Rooij ◽  
Thomas Mueller
Keyword(s):  
Surface Water ◽  
Water Level ◽  
Coastal Plain ◽  
Land Surface ◽  
Hydraulic Head ◽  
Water Levels ◽  
Analytical Models ◽  
Time Interval ◽  
Mountain Range ◽  
Time Step

<p>Occasionally, there is an interest in groundwater flows over many millennia. The input parameter requirement of numerical groundwater flow models and their calculation times limit their usefulness for such studies.</p><p>Analytical models require considerable simplifications of the properties and geometry of aquifers and of the forcings. On the other hand, they do not appear to have an inherent limitation on the duration of the simulated period. The simplest models have explicit solutions, meaning that the hydraulic head at a given time and location can be calculated directly, without the need to incrementally iterate through the entire preceding time period like their numerical counterparts.</p><p>We developed an analytical solution for a simple aquifer geometry: a strip aquifer between a no flow boundary and a body of surface water with a prescribed water level. This simplicity permitted flexible forcings: The non-uniform initial hydraulic head in the aquifer is arbitrary and the surface water level can vary arbitrarily with time. Aquifer recharge must be uniform in space but can also vary arbitrarily with time.</p><p>We also developed a modification that verifies after prescribed and constant time intervals if the hydraulic head is such that the land surface is covered with water. This excess water then infiltrates in areas where the groundwater level is below the surface and the remainder is discharged into the surface water. The hydraulic head across the aquifer is modified accordingly and used as the initial condition for the next time interval. This modification models the development of a river network during dry periods. The increased flexibility of the model comes at the price of the need to go through the entire simulation period one time step at a time. For very long time records, these intervals will typically be one year.</p><p>Given the uncertainty of the aquifer parameters and the forcings, the models are expected to be used in a stochastic framework. We are therefore working on a shell that accepts multiple values for each parameter as well as multiple scenarios of surface water levels and groundwater recharge rates, along with an estimate of their probabilities. The shell will generate all possible resulting combinations, the number of which can easily exceed 10000, then runs the model for each combination, and computes statistics of the average hydraulic head and the aquifer discharge into the surface water at user-specified times.</p><p>A case study will tell if this endeavor is viable. We will model the aquifer below the mountain range north of Salalah in Oman, which separates the desert of the Arabian Peninsula from the coastal plain at its southern shore. Rainfall estimates from the isotopic composition of stalactites in the area indicate distinct dry and wet periods in the past 300 000 years. In combination with estimated sea level fluctuations over that period, this provides an interesting combination of forcings. We examine the dynamics of the total amount of water stored in the aquifer, and of the outflow of water from the aquifer into the coastal plain.</p>

scholarly journals Estimating the long-term historic evolution of exposure to flooding of coastal populations

2015 ◽  
Vol 15 (6) ◽  
pp. 1215-1229 ◽  
Author(s):  
A. J. Stevens ◽  
D. Clarke ◽  
R. J. Nicholls ◽  
M. P. Wadey
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Flood Risk ◽  
Population Change ◽  
Opportunity To Learn ◽  
Population Data ◽  
Population Exposure ◽  
Coastal Flood ◽  
Flood Exposure ◽  
And Sea Level

Abstract. Coastal managers face the task of assessing and managing flood risk. This requires knowledge of the area of land, the number of people, properties and other infrastructure potentially affected by floods. Such analyses are usually static; i.e. they only consider a snapshot of the current situation. This misses the opportunity to learn about the role of key drivers of historical changes in flood risk, such as development and population rise in the coastal flood plain, as well as sea-level rise. In this paper, we develop and apply a method to analyse the temporal evolution of residential population exposure to coastal flooding. It uses readily available data in a GIS environment. We examine how population and sea-level change have modified exposure over two centuries in two neighbouring coastal sites: Portsea and Hayling Islands on the UK south coast. The analysis shows that flood exposure changes as a result of increases in population, changes in coastal population density and sea level rise. The results indicate that to date, population change is the dominant driver of the increase in exposure to flooding in the study sites, but climate change may outweigh this in the future. A full analysis of changing flood risk is not possible as data on historic defences and wider vulnerability are not available. Hence, the historic evolution of flood exposure is as close as we can get to a historic evolution of flood risk. The method is applicable anywhere that suitable floodplain geometry, sea level and population data sets are available and could be widely applied, and will help inform coastal managers of the time evolution in coastal flood drivers.

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