Levee Height Research Articles

Extraction of Coastal Levees Using U-Net Model with Visible and Topographic Images Observed by High-Resolution Satellite Sensors.

Coastal levees play a role in protecting coastal areas from storm surges and high waves, and they provide important input information for inundation damage simulations. However, coastal levee data with uniformity and sufficient accuracy for inundation simulations are not always well developed. Against this background, this study proposed a method to extract coastal levees by inputting high spatial resolution optical satellite image products (RGB images, digital surface models (DSMs), and slope images that can be generated from DSM images), which have high data availability at the locations and times required for simulation, into a deep learning model. The model is based on U-Net, and post-processing for noise removal was introduced to further improve its accuracy. We also proposed a method to calculate levee height using a local maximum filter by giving DSM values to the extracted levee pixels. The validation was conducted in the coastal area of Ibaraki Prefecture in Japan as a test area. The levee mask images for training were manually created by combining these data with satellite images and Google Street View, because the levee GIS data created by the Ibaraki Prefectural Government were incomplete in some parts. First, the deep learning models were compared and evaluated, and it was shown that U-Net was more accurate than Pix2Pix and BBS-Net in identifying levees. Next, three cases of input images were evaluated: (Case 1) RGB image only, (Case 2) RGB and DSM images, and (Case 3) RGB, DSM, and slope images. Case 3 was found to be the most accurate, with an average Matthews correlation coefficient of 0.674. The effectiveness of noise removal post-processing was also demonstrated. In addition, an example of the calculation of levee heights was presented and evaluated for validity. In conclusion, this method was shown to be effective in extracting coastal levees. The evaluation of generalizability and use in actual inundation simulations are future tasks.

A global open-source database of flood-protection levees on river deltas (openDELvE)

Abstract. Flood-protection levees have been built along rivers and coastlines globally. Current datasets, however, are generally confined to territorial boundaries (national datasets) and are not always easily accessible, posing limitations for hydrologic models and assessments of flood hazard. Here, we bridge this knowledge gap by collecting and standardizing global flood-protection levee data for river deltas into the open-source global river delta levee data environment, openDELvE. In openDELvE, we aggregate levee data from national databases, reports, maps, and satellite imagery. The database identifies the river delta land areas that the levees have been designed to protect. Where data are available, we record the extent and design specifications of the levees themselves (e.g., levee height, crest width, construction material) in a harmonized format. The 1657 polygons of openDELvE contain 19 248 km of levees and 44 733.505 km2 of leveed area. For the 153 deltas included in openDELvE, 17 % of the land area is confined by flood-protection levees. Around 26 % of delta population lives within the 17 % of delta area that is protected, making leveed areas densely populated. openDELvE data can help improve flood exposure assessments, many of which currently do not account for flood-protection levees. We find that current flood hazard assessments that do not include levees may exaggerate the delta flood exposure by 33 % on average, but up to 100 % for some deltas. The openDELvE is made public on an interactive platform (https://www.opendelve.eu/, 1 October 2022), which includes a community-driven revision tool to encourage inclusion of new levee data and continuous improvement and refinement of open-source levee data.

Late Messinian submarine channel systems in the Levant Basin: Challenging the desiccation scenario

Abstract The question of whether the Mediterranean Sea desiccated during the Messinian salinity crisis (MSC) has been strongly debated for decades. In the Levant Basin, this debate was recently reignited in relation to the latest stage of the crisis after cessation of salt deposition. The desiccation supporters argue that salt truncation—and its subsequent burial by a latest Messinian, clastic-rich evaporitic unit—occurred subaerially on a desiccated seafloor. However, we show that this latest Messinian unit contains a dense net of channels with meanders, levees, and overspill deposits and is very similar to the turbidite channels observed on the modern seafloor. The aggradation characteristics of these buried channels (levee height, channel depth, and channel-floodplain coupling) indicate a marine rather than fluvial origin. Our conclusion adds to the findings of a previous study that salt truncation occurred in deep waters by dissolution. In a wider perspective, we suggest that the flush of clastics into the basin during the last stage of the MSC indicates a combination of wet climate and sea-level rise that started before the Zanclean (earliest Pliocene).

Grid edge classification method to enhance levee resolution in dual-grid flood inundation models

Dual-grid models address the computational bottlenecks of large-scale (>103 km2) urban flood modeling with solution updates on a coarse grid that are informed by topographic data on a fine grid. However, dual-grid models may poorly resolve levees, leading to loss of accuracy. Here we present a grid edge classification method whereby specific edges of the coarse grid are flagged to gather nearby topographic data from the fine grid and create a contiguous physical barrier. The method relies on levee location data in a polyline format, and does not require levee height data since that information is stored on the fine grid. Using a 6804 km2 model of the Los Angeles Metropolitan Region with 3 m topographic data and 987 km of levees, the proposed method is implemented and evaluated. Simulations using coarse grids of 15, 30 and 60 m capture flood extent consistent with fine-grid models based on a critical success index (CSI) of 90, 87 and 82%, respectively. Edge classification improves CSI up to 7 percentage points over a model with unclassified coarse grid edges, and reduces the false alarm ratio up to 10 percentage points. Differences in model performance across the study area are noted, including lower accuracy on urbanized alluvial fans. With compute costs that scale with the coarse grid, dual-grid models can efficiently realize more accurate large-scale models of urban flood hazards.

A first assessment of the effect of storm climate trends and uncertainties on Dutch levee design

For the safety assessment and design of levees in the Netherlands probabilistic tools are used, which account for both statistical and model uncertainties in the determination of hydraulic loads. However, climate change induced uncertainties in extreme wind climate or storminess are not yet accounted for. This paper presents a first assessment of the effect of uncertainties in storminess on Dutch levee design. An expert panel was consulted to define a range of plausible trends and uncertainties in extreme wind climate. Three scenarios were defined with variations of the current wind climate, including changes in wind speed high percentiles and in wind direction. For the defined scenarios probabilistic computations were carried out to determine the effect of the wind statistics variations on the water level, wave loads, and required levee height along the Dutch lakes and coast. In the case of an increase in wind percentiles (mean + 5%, standard deviation 12%), the required levee height increases significantly: up to 1.5–4 m along the Dutch coast and up to 1–2 m along the Dutch lakes. Given the large impact of the considered changes, it is first recommended to carry out a more robust assessment of the uncertainties in future storm climate and to measure and monitor evolution of future wind speeds.

On Hypsometric Curve and Morphological Analysis of the Collapsed Irrigation Reservoirs

The impact of irrigation reservoirs requires investigation through hydrological analysis to identify the flood control functions of these reservoirs. However, there is insufficient information concerning important geographical, morphological, and topographic characteristics, such as the reservoir cross-section. Therefore, this study aimed to identify the morphological and topographic characteristics of reservoirs using geographical information instead of measurement data. Ten reservoirs, including the Ga-Gog reservoir located in Miryang City, South Korea, were selected. The topographic information of the reservoirs was obtained using topographic maps and GIS techniques. Based on this information, the volume (V)-area (A)-depth (H) relationship and the hypsometric curve (HC) according to the relative area (a/A) and relative height (h/H) were created. A comparison of the reservoir volume, estimated using topographic information, with the measured volume revealed an error rate between 0.23% and 14.27%. In addition, two collapsed reservoirs located near Miryang City were investigated by creating V-A-H relationships and HCs using topographic information. The morphological characteristics of the reservoirs were identified by analyzing the (1) morphology index, (2) full water storage area-levee height relationship, and (3) full water storage area relationship. The analysis results showed that the collapsed reservoirs had high water depth and a large area relative to other reservoirs. Similar types of reservoirs were grouped by conducting a cluster analysis using basic properties such as the basin area, storage, and levee height. The cluster analysis results, based on HC analysis, grouped the reservoirs into three shapes: convex upward (youthful stage), relatively flat (mature stage), and convex downward (old stage). The HCs of the collapsed reservoirs exhibited a convex downward shape, indicating that they were subjected to considerable erosion due to aging. Moreover, this considerable erosion caused a large quantity of sediment to accumulate in the reservoirs, resulting in an insufficient allowable storage capacity of the reservoir because the flood control capacity was reduced, which may have led to their collapse during heavy rainfalls. Therefore, the identification of potential causes of reservoir collapse through the morphological characteristics and HCs of reservoirs are expected to support the operation and management of reservoirs to reduce flood damage.

Hydrological Effects of Agricultural Water Supplies on Paddy Fields using Surface–Groundwater Integrated Model

Agricultural water demands are mainly dependent on the supply from groundwater withdrawals and the supply from agricultural reservoirs. To understand the water cycle of the agricultural catchment, it is necessary to consider the actual situation of the water cycle of paddy fields in catchments through accurate hydrological modeling. In this study, streamflow simulations were implemented in consideration of the levee height of paddy fields and the irrigation period for one sub-catchment of the Boryeong Dam catchment using the integrated surface–groundwater model, CAT (Catchment Hydrologic Cycle Assessment Tool). To consider the agricultural reservoirs in modeling, the catchment was divided into the reservoir sub-catchments, upstream sub-catchments, downstream sub-catchments, and irrigated districts of each sub-catchment. This study aims to analyze the hydrological effects of agricultural reservoirs and groundwater pumping on the hydrological cycle of the catchment and on the soil moisture and groundwater level. As a result of the simulations, we found that the direct flow, baseflow, and groundwater recharge of the catchment increased with the agricultural reservoir supply water. In addition, the effect of drought on soil moisture content and groundwater level in the irrigated paddy fields from agricultural reservoirs was evaluated. The soil moisture increased by about 10% according to the water supply of agricultural reservoirs. The groundwater level rapidly decreased due to the groundwater abstraction during the irrigation period; however, it was analyzed that the water supply from agricultural reservoirs is significantly effective in preventing the decrease in the groundwater level in the irrigation season.

Increased flood height driven by local factors on a regulated river with a confined floodplain, Lower Tisza, Hungary

On artificially confined floodplains, various active processes influence the local peak flow level. However, these active processes are often neglected in flood management because calculations are based on static parameters. The aim of this study is to analyse the processes that contribute to rising local flood levels in a regulated channel and on an artificially confined floodplain of a lowland river. Our goals were to evaluate the role of cross-sectional channel changes, overbank floodplain aggradation, and riparian land-cover changes on local flood level increases since the late nineteenth century and early twentieth century and to assess the height changes of artificial levees. The research was performed in a low-gradient river (Lower Tisza, Hungary), which was regulated in the late nineteenth century; thus, the effects of century-long processes on flood levels could be evaluated. The results suggest that along the 92 km-long reach, the channel was narrowed by 9% and its cross-sectional area decreased by an average of 2%; however, the narrowing was over 30% in some locations. Because of these changes, flood levels increased by an average of 13 cm (maximum = 134 cm) since 1931. Because the artificial levee was constructed in the mid-nineteenth century, the mean overbank floodplain accumulation reached 1.2 m (maximum = 2.6 m), flood levels decreased by an average of 112 cm. During the same period, the land cover of the floodplain changed considerably, increasing the vegetation roughness (i.e., Manning's n) from 0.048 to 0.11. Based on our modelled data, the higher vegetation roughness increased flood levels by 42 cm (Scenario A) or 139 cm (Scenario B), on average, based on the increased vegetation roughness (by 10% or 30%, respectively). By overlapping these data, the results showed that since the river regulation work in the late nineteenth century, the actual flood level increased by an average of 175 cm (maximum = 350 cm) in the case of Scenario A and 272 cm (maximum = 443 cm) in the case of Scenario B. The latter is more consistent with the actual flood stage measurements. As these processes are still active, further increases in the flood level could be expected. In addition, the height of artificial levees decreased by an average of 23 cm (maximum = 75 cm); thus, some levee sections became more susceptible to overtopping during record high floods, especially along the eastern levee. Based on this approach, local hydrological managers can identify the processes that contribute more to peak flow level increases at a given location and determine the correct actions at the correct locations, which could lead to decreases in peak flow levels.

Case study: On hydrological function improvement for an endemic plant habitat in Gangcheon wetland, Korea

Wetlands are one of the most important ecosystems for the biodiversity of plants and animals. Especially, Gangcheon wetland in NamHan river, Korea is a very valuable one because Aster altaicus var. uchiyamae, which is one of endemic plants is inhabited. However, Gangcheon wetland was impaired by a river improvement project called ‘Four Major Rivers Project’. After the project, Gangcheon wetland restoration work was performed, for the rehabilitation of wetland functions but the habitat of Aster altaicus var. uchiyamae could not be restored. Actually, Aster altaicus var. uchiyamae can grow in a habitat made by mixing of gravel and sand from flood inundation of the river but there was no inundation after the project because of the rise of levee height. Therefore, this study evaluated wetland functions using Hydrogeomorphic(HGM) approach and analyzed flood inundation using HEC-GeoRAS model after the project for diagnosis of the functions and the habitat. Then we proposed a plan to improve the functions of Gangcheon wetland as a habitat for Aster altaicus var. uchiyamae. The reference wetland is Gangcheon wetland before the project and the wetland functions after the project were compared with the reference one. As a result of the function assessment, hydrological, biogeochemical, and plant habitat functions were deteriorated. The study wetland has three zones of A, B, and C for Aster altaicus var. uchiyamae habitats and particularly, hydrologic functions for zone C which is poor as the habitat should be improved. In particular, the habitat of Aster altaicus var. uchiyamae was adversely affected by the decrease in inundation depth and water level of the river. These hydrologic functions should be improved and the levee height be lowered for obtaining more proper habitat of Aster altaicus var. uchiyamae. This suggestion might be helpful for establishment of the habitat of Aster altaicus var. uchiyamae. Also, it could be expected that the overall function of Gangcheon wetland will be improved because biogeochemical and plant habitat functions are rehabilitated by the improved hydrological function.

Storm Surge Hazard Assessment of the Levee of a Rapidly Developing City-Based on LiDAR and Numerical Models

Rapidly developing cities could require an urgent hazard assessment to ensure the protection of their economy and population against natural disasters. However, these cities that have rapidly developed should have historical records of observations that are too short to provide sufficient data information for such an assessment. This study used ocean numerical models (i.e., Finite-Volume Community Ocean Model (FVCOM) and Parabolic Mild-Slope Wave Module (MIKE 21 PMS) to reconstruct data for a storm surge hazard assessment of the levee at Weifang (China). LiDAR (Light Detection and Ranging) data were also used to obtain 3D point cloud data and the structure of the levee. The designed levee height was calculated based on the simulations and 3D point cloud data, and the results were compared with measured heights to evaluate whether the levee is sufficiently high to satisfy the safety requirement. The findings of this work will enhance the marine disaster prevention capacity of the region and could help reduce economic losses associated with marine-related disasters. The results could also provide support for future work on disaster prevention in the field of coastal marine engineering.

Analysis of Morphological Characteristics of Collapsed Reservoirs in Korea

The purpose of this study is to analyze the basic specifications or items of 17,313 reservoirs distributed throughout Korea and in particular, to establish the relationships among the morphological characteristics of the reservoirs. In addition, the morphology index, the storage (S)–area of full water (A)–levee height (H) (S–A–H) relationship, and the storage(S)–area of full water (A) (S–A) relationship were determined for collapsed reservoirs. In this study, histograms for 11 parameters, such as storage capacity, area of full water, levee height, and basin area, were plotted, and the distributions of the reservoir parameters were examined. The morphology index was used to classify the reservoirs based on the depth, and the coefficient values of the relationships of S–A–H and S–A were used to compare S with both A and H or only A. The coefficient value of S–A–H was inversely proportional to S, and when the coefficient value was high, the storage was small. The coefficient value of S–A was proportional to S, and when the coefficient value was small, the storage wassmall. Cluster analysis was performed based on the given items to determine the characteristics of all the reservoirs and only the collapsed reservoirs. From the cluster analysis results, the reservoirs were divided into five groups: A, B, C, D, and E. There were 7,714 (14) in Group A, 6,053 (4) in B, 2,633 (2) in C, 745 (1) in D, and 168 (0) in E for all the reservoirs and collapsed reservoirs (with the values of the collapsed reservoirs in parenthesis). The morphological indexes werelow in the order of A > B > C > D > E, and the coefficient values of S–A–H were high in the order of A > B > C > E > D. The coefficient values of S–A were low in the order of A > B > D > C > E. Based on the clustered analysis results for 21 collapsed reservoirs, the reservoirs were clustered in the order of A (14) > B (4) > C (2) > D (1) > E (0). A reservoir with shallow water depth and small storage capacity has an inherent probability of collapsing. Therefore, the results of this study are useful for reservoir management and operation, as well as for the prevention of reservoir collapse.

Natural levee evolution in vegetated fluvial-tidal environments.

Natural levees are common features in river, delta and tidal landscapes. They are elevated near‐channel morphological features that determine the connection between channel and floodbasin, and consequently affect long‐term evolution up to delta‐scales. Despite their relevance in shaping fluvial‐tidal systems, research on levees is sparse and often limited to fluvial or non‐tidal case studies. There is also a general lack of understanding of the role of vegetation in shaping these geomorphic units, and how levee morphology and dimensions vary in the transition from fluvial to coastal environments, where tides are increasingly important. Our goal is to unravel the effects of fluvial‐tidal boundary conditions, sediment supply and vegetation on levee characteristics and floodbasin evolution. These conditions were systematically explored by 60 large‐scale idealized morphodynamic simulations in Delft3D which self‐developed levees over the course of one century. We compared our results to a global levee dataset compilation of natural levee dimensions. We found that levee height is determined by the maximum water level, provided sufficient levee building sediments are available. Discharge fluctuations increased levee width and triggered more levee breaches, i.e. crevasses, that effectively filled the fluvio‐tidal floodbasin. The presence of wood‐type (sparse) vegetation further increased the number of crevasses in comparison with the non‐vegetated scenarios. Conversely, reed‐type (dense) vegetation strongly dampened tidal amplitude and reduced the accommodation space and sedimentation further into the floodbasin, resulting in narrower levees, no crevasses and limited floodbasin accretion. However, dense vegetation reduced tidal forces which allowed levee growth further downstream. Ultimately, the levees merged with the coastal barrier, eliminating the floodbasin tides entirely. Our results elucidate the mechanisms by which levee and crevasse formation, and vegetation may fill fluvio‐tidal wetlands and affect estuary evolution. This brings new insights for geological reconstructions as well as for the future management of deltas and estuaries under sea‐level rise. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

Levees Formed by Turbidity Currents: A Depth‐Averaged Modeling Treatment

AbstractThe formation of levees with accompanying channels is a ubiquitous feature of turbidity flows both in submarine canyons and on submarine fans. We examine the latter situation using numerical and theoretical calculations based on a depth‐averaged model for subaqueous turbidity currents, introduced by Parker et al. (1986, https://doi.org/S0022112086001404) and reinterpreted by Halsey et al. (2017, https://doi.org/10.1002/2016JC012635). Using a novel similarity solution to these equations, applied to a two‐component sand/mud flow, we show that in a well‐defined limit levees form along rays emanating from the source of the flows, which in our case is the outlet of a submarine canyon. The width of the channel between the levees decreases as particle size increases and increases with increasing slope of the surface. The levees form with a characteristic right‐triangle shape, with the steep slope facing inward toward the channel. The levee height is comparable to the height of the turbidity flow. Levees form even in the absence of preexisting scour. We confirm these analytical results with numerical simulations of the depth‐averaged equations. Further downslope, the formation of levees seems to be inconsistent with an erosion law introduced by Garcia and Parker (1991, 10.1061/(ASCE)0733-9429(1991)117:4(414)), calling the applicability of this law to natural systems into question.

Interdependent Infrastructure as Linked Social, Ecological, and Technological Systems (SETSs) to Address Lock‐in and Enhance Resilience

AbstractTraditional infrastructure adaptation to extreme weather events (and now climate change) has typically been techno‐centric and heavily grounded in robustness—the capacity to prevent or minimize disruptions via a risk‐based approach that emphasizes control, armoring, and strengthening (e.g., raising the height of levees). However, climate and nonclimate challenges facing infrastructure are not purely technological. Ecological and social systems also warrant consideration to manage issues of overconfidence, inflexibility, interdependence, and resource utilization—among others. As a result, techno‐centric adaptation strategies can result in unwanted tradeoffs, unintended consequences, and underaddressed vulnerabilities. Techno‐centric strategies that lock‐in today's infrastructure systems to vulnerable future design, management, and regulatory practices may be particularly problematic by exacerbating these ecological and social issues rather than ameliorating them. Given these challenges, we develop a conceptual model and infrastructure adaptation case studies to argue the following: (1) infrastructure systems are not simply technological and should be understood as complex and interconnected social, ecological, and technological systems (SETSs); (2) infrastructure challenges, like lock‐in, stem from SETS interactions that are often overlooked and underappreciated; (3) framing infrastructure with a SETS lens can help identify and prevent maladaptive issues like lock‐in; and (4) a SETS lens can also highlight effective infrastructure adaptation strategies that may not traditionally be considered. Ultimately, we find that treating infrastructure as SETS shows promise for increasing the adaptive capacity of infrastructure systems by highlighting how lock‐in and vulnerabilities evolve and how multidisciplinary strategies can be deployed to address these challenges by broadening the options for adaptation.

하천제방의 월류 붕괴 메커니즘 규명을 위한 모형실험

본 연구에서는 월류에 의한 붕괴 메커니즘의 규명을 위해 모형제방(제방고 0.4~0.8m)과 실물제방(제방고 1.0m)을 대상으로 월류 붕괴실험을 수행하였다. 월류에 의한 제방붕괴는 1단계에서는 월류에 의해 비탈표면에서 세굴이 발생되었으며, 월류의 유속은 완만히 증가되었다. 2단계에서는 붕괴단면이 커지고 유속도 급격히 증가되었다. 3단계에서는 월류에 의해 제방 단면이 완전히 붕괴되고 붕괴면적이 넓어져 유속이 상대적으로 감소되었다. 월류에 의한 제방의 붕괴각(<TEX>${\theta}$</TEX>)은 큰 자중, 감소된 전단저항력 및 월류의 흐름에 의한 추가 소류력으로 인해 랭킨토압의 사면붕괴각보다 크게 나타났다. 제방고(H)가 증가될수록 월류에 의한 제방의 월류 유속(<TEX>${\upsilon}$</TEX>)이 증가되었으며, 이로 인해 소류력이 추가로 작용되어 제방의 붕괴각(<TEX>${\theta}$</TEX>)과 붕괴면적(A)이 함께 증가되었다. 모형실험과 실물실험에 사용된 모래 시료가 동일한 입경크기로 한계세굴유속이 같아 월류 유속변화에 의해 세굴 특성이 지배되는 것으로 나타났다. This research conducted the two types of model tests to examine the failure parameters by levee overflow, those were the pilot-scale levee (model height 0.4~0.8 m) and real scale levee (model height 1.0 m). The procedure of levee failure by overflow was succeeded to the following three steps: At first step, the local scouring on levee slope was happened and the overflow velocity was increased slowly. At second step, the enlarged scouring surface and the rapid overflow velocity were succeeded. At last, the levee section was broken totally and the overflow velocity was decreased because of the wide failure surface of levee. The levee failure angle (<TEX>${\theta}$</TEX>) was appeared bigger than slope failure angle of Rankine earth pressure. The enlarged levee height (H) made the faster overflow velocity (<TEX>${\upsilon}$</TEX>) of the levees, therefore additional tractive force was applied to it, futhermore the failure angle (<TEX>${\theta}$</TEX>) and failure surface (A) were enlarged. Because the sand sample for pilot-scale and real scale tests had the same diameter, the critical scouring velocity of each type was also the same, and the scouring properties were governed by variation of overflow velocity.

Lidar-based mapping of flood control levees in South Louisiana

ABSTRACTFlood protection in south Louisiana is largely dependent on earthen levees, and in the aftermath of Hurricane Katrina the state’s levee system has received intense scrutiny. Accurate elevation data along the levees are critical to local levee district managers responsible for monitoring and maintaining the extensive system of non-federal levees in coastal Louisiana. In 2012, high resolution airborne lidar data were acquired over levees in Lafourche Parish, Louisiana, and a mobile terrestrial lidar survey was conducted for selected levee segments using a terrestrial lidar scanner mounted on a truck. The mobile terrestrial lidar data were collected to test the feasibility of using this relatively new technology to map flood control levees and to compare the accuracy of the terrestrial and airborne lidar. Metrics assessing levee geometry derived from the two lidar surveys are also presented as an efficient, comprehensive method to quantify levee height and stability. The vertical root mean square error values of the terrestrial lidar and airborne lidar digital-derived digital terrain models were 0.038 m and 0.055 m, respectively. The comparison of levee metrics derived from the airborne and terrestrial lidar-based digital terrain models showed that both types of lidar yielded similar results, indicating that either or both surveying techniques could be used to monitor geomorphic change over time. Because airborne lidar is costly, many parts of the USA and other countries have never been mapped with airborne lidar, and repeat surveys are often not available for change detection studies. Terrestrial lidar provides a practical option for conducting repeat surveys of levees and other terrain features that cover a relatively small area, such as eroding cliffs or stream banks, and dunes.

Risk‐based planning analysis for a single levee

AbstractTraditional risk‐based analysis for levee planning focuses primarily on overtopping failure. Although many levees fail before overtopping, few planning studies explicitly include intermediate geotechnical failures in flood risk analysis. This study develops a risk‐based model for two simplified levee failure modes: overtopping failure and overall intermediate geotechnical failure from through‐seepage, determined by the levee cross section represented by levee height and crown width. Overtopping failure is based only on water level and levee height, while through‐seepage failure depends on many geotechnical factors as well, mathematically represented here as a function of levee crown width using levee fragility curves developed from professional judgment or analysis. These levee planning decisions are optimized to minimize the annual expected total cost, which sums expected (residual) annual flood damage and annualized construction costs. Applicability of this optimization approach to planning new levees or upgrading existing levees is demonstrated preliminarily for a levee on a small river protecting agricultural land, and a major levee on a large river protecting a more valuable urban area. Optimized results show higher likelihood of intermediate geotechnical failure than overtopping failure. The effects of uncertainty in levee fragility curves, economic damage potential, construction costs, and hydrology (changing climate) are explored. Optimal levee crown width is more sensitive to these uncertainties than height, while the derived general principles and guidelines for risk‐based optimal levee planning remain the same.

Optimal Design and Benefit/Cost Analysis of Reservoir Dams by Genetic Algorithms Case Study: Sonateh Dam, Kordistan Province, Iran

This paper presents a method concerning the integration of the benefit/cost analysis and the real genetic algorithm with various elements of reservoir dam design. The version 4.0 of HEC-RAS software and Hydro-Rout models have been used to simulate the region and flood routing in the reservoir of the dam, respectively. A mathematical programming has been prepared in MATLAB software and linked with the optimal programming then employed to maximize the benefit/cost ratio of the reservoir dam construction. After a sensitivity analysis, mutation and crossover probability are assumed to be 0.05 and 0.7, respectively. The objective function of the study is benefit/cost ratio. The combined methodology has been provided to help to compute the optimal normal water level, length of spillway and downstream levee height of a reservoir dam considering flood control and cost of construction. This is the first attempt to optimize these important parameters, in the construction of a reservoir dam, together considering flood control and economical aspects. It has been displayed that the proposed method provides strong and suitable solutions to determine these parameters. The results showed that there is potential for application of genetic algorithms to such optimization problems, where the objective function is nonlinear and other optimization techniques may be troublesome to apply and find the global optimum.

Evaluating the role of coastal habitats and sea-level rise in hurricane risk mitigation: An ecological economic assessment method and application to a business decision.

Businesses may be missing opportunities to account for ecosystem services in their decisions, because they do not have methods to quantify and value ecosystem services. We developed a method to quantify and value coastal protection and other ecosystem services in the context of a cost-benefit analysis of hurricane risk mitigation options for a business. We first analyze linked biophysical and economic models to examine the potential protection provided by marshes. We then applied this method to The Dow Chemical Company's Freeport, Texas facility to evaluate natural (marshes), built (levee), and hybrid (marshes and a levee designed for marshes) defenses against a 100-y hurricane. Model analysis shows that future sea-level rise decreases marsh area, increases flood heights, and increases the required levee height (12%) and cost (8%). In this context, marshes do not provide sufficient protection to the facility, located 12 km inland, to warrant a change in levee design for a 100-y hurricane. Marshes do provide some protection near shore and under smaller storm conditions, which may help maintain the coastline and levee performance in the face of sea-level rise. In sum, the net present value to the business of built defenses ($217 million [2010 US$]) is greater than natural defenses ($15 million [2010 US$]) and similar to the hybrid defense scenario ($229 million [2010 US$]). Examination of a sample of public benefits from the marshes shows they provide at least $117 million (2010 US$) in coastal protection, recreational value, and C sequestration to the public, while supporting 12 fisheries and more than 300 wildlife species. This study provides information on where natural defenses may be effective and a replicable approach that businesses can use to incorporate private, as well as public, ecosystem service values into hurricane risk management at other sites.

제방 월류시 붕괴매개변수 도출을 위한 모형실험

According to the damage investigation in 2002, the failures of river levee were caused by overflow, erosion, and unstable body conditions due to piping, inappropriate embanking materials, and poor compaction. Especially, overflow was identified as a main reason that induces levee failure by 39.5% from the distribution of failure types. The major parameters, such as levee collapsing angle (), levee collapsing rate (k) affect inundation velocity and area size during the analysis of inundation modeling, however, domestic research effort on this area is still insufficient. In this paper authors conducted levee failure experiments of 4 levee height types, 0.20 m, 0.25 m, 0.30 m, and 0.40 m based on theassumption of Froude Similarity (${\lambda}_{Fr}