Levees Research Articles

Analyses of faunal changes of macrobenthos in Ariake Bay after the construction of dike for the Isahaya Reclamation Project ―Research Group for Conservation Ecology on the Ariake Bay―

Analyses of faunal changes of macrobenthos in Ariake Bay after the construction of dike for the Isahaya Reclamation Project ―Research Group for Conservation Ecology on the Ariake Bay―

Evaluation of impact of spur dike designs on enhancement of aquatic habitats in urban streams using 2D habitat numerical simulations

Although channelized urban streams provide aesthetic and economic value, they reduce biodiversity and alter the habitats of aquatic organisms. Spur dikes not only prevent the erosion of riverbanks, but also generally improve aquatic habitats. River 2D is widely used to analyze the aquatic habitats. However, the model often faces a challenge of lacking sediment and riverbed evolution module, which is difficult to predict the change of aquatic habitats. In this study, a depth-averaged habitat model, which couples a two-dimensional water-sediment shallow water model with an Instream Flow Incremental Methodology (IFIM), was provided to evaluate the impact of spur dikes on the improvement of aquatic habitats in the Jinjiang Stream in Chengdu, China.The potential value of aquatic habitats was quantitatively evaluated by a weighted useable area (WUA). Under different spur dike scenarios, the WUA is greater than under natural conditions, that is, the construction of spur dikes is beneficial for improving the habitat of aquatic organisms in urban rivers. In addition, further analysis from the simulation results shows that the three-spur dike scenario with a flow of 40 m³/s represents the best layout of spur dikes. Our study indicates that adjusting the spur dike layout is an effective instrument to enhance aquatic habitats, and can provide a certain reference for water ecological restoration and river management.

Assessing Impacts of Sea Level Rise and Sea Dike Construction on Salinity Regime in Can Gio Bay, South Vietnam

Abstract To protect Ho Chi Minh City (HCMC) from submergence due to the ongoing rapid sea level rise (SLR), the Vietnamese government have proposed the construction of a sea dike in Can Gio Bay. Ca...

From fast-track implementation to livelihood deterioration: The dam-based Ribb Irrigation and Drainage Project in Northwest Ethiopia

The 21st century revival of large-scale water resources development projects makes it important to keep assessing their impacts – preferably from an interdisciplinary perspective – in order to not repeat past mistakes and explore whether they could improve livelihood conditions for rural communities. In this study, costs and benefits of the World Bank-funded Ribb Irrigation and Drainage Project (RIDP) were investigated using a unique systems approach. The impact for farmers with different initial farming systems (rainfed – residual moisture – irrigated) was studied using field observations, document analyses, remote sensing, agronomic data and semi-structured interviews (n = 165). Data on project-induced changes to land and water availability, cropping patterns, farming systems and farm-level economics were collected. The results show that dam and dyke construction has reduced flooding, which has resulted in declining rice productivity (−42%) and concomitant shifts to lower value cropping systems. Results also reveal that the land redistribution has caused widespread livelihood deterioration as households had to give up 25% of their farmland and the communal grazing land was fully converted into farmland. Due to top-down implementation, nontransparent communication, delayed construction and lagging financial compensation, social resistance has appeared in the command area, impeding the construction works. In addition to these problems, if no rapid change to higher value crops can be realized, 20.5% of the farmers (those who already irrigate) will experience a loss of livelihood, 64.1% of the farmers (those with rainfed and residual moisture cultivation) will be on the verge of livelihood deterioration and only 13.5% of the farmers (those with solely rainfed cultivation) will enjoy RIDP-induced improved livelihoods. The fate of this project stresses the importance of investigating initial farming systems, exploring worthy project alternatives, improving participation, communication and benefit-sharing and strengthening the institutional capacity of implementing authorities.

Evaluation of alternatives to optimize the flood management in the department of Valle del Cauca

In order to optimize the flood management in the department of Valle del Cauca, Colombia, several measures that intend to give back space to the Cauca River were proposed and evaluated. The considered measures were the relocation of dykes, the construction of double dykes, the construction of reservoirs in tributary rivers, the implementation of polders and the construction of parallel channels to the Cauca River. The impact of the proposed measures was determined through mathematical modeling. The selection of the measures that would generate the greatest benefits was done through the evaluation of technical, environmental, economic and social aspects. According to the obtained results, the scenario that simultaneously considers the relocation of dykes to 60 m from the Cauca River, the construction of reservoirs in the rivers Timba, Riofrio and Bugalagrande and the construction of five polders in the floodplain would allow the most proper management of the floods.

Atmospheric Correction Thresholds for Ground-Based Radar Interferometry Deformation Monitoring Estimated Using Time Series Analyses

Ground-based radar interferometry (GBSAR) is a useful method to control the stability of engineering objects and elements of geographical spaces at risk of deformation or displacement. To secure accurate and credible measurement results, it is crucial to consider atmospheric conditions as they influence the corrections to distance measurements. These conditions are especially important considering the radar bandwidth used. Measurements for the stability of engineering objects are not always performed in locations where meteorological monitoring is prevalent; however, information about the range of variability in atmospheric corrections is always welcome. The authors present a hybrid method to estimate the probable need of atmospheric corrections, which allows partly eliminating false positive alarms of deformations as caused by atmospheric fluctuations. Unlike the numerous publications on atmospheric reductions focused on the current state of the atmosphere, the proposed solution is based on applying a classic machine learning algorithm designed for the SARIMAX (Seasonal Autoregressive Integrated Moving Average with covariate at time) time series data model for satellite data shared by NASA (National Aeronautics and Space Administration) during the Landsat MODIS (Moderate Resolution Imaging Spectroradiometer) mission before performing residual estimation during the monitoring phase. Example calculations (proof of concept) were made for ten-year satellite data covering a region for experimental flood bank stability observations as performed using the IBIS-L (Image by Interferometric Survey—Landslide) radar and for target monitoring data (ground measurements).

ASSESSMENT OF FLOOD RISK REDUCTION IN BENGAWAN SOLO RIVER: A CASE STUDY OF SRAGEN REGENCY

Bengawan Solo experiences flooding almost every year and it has been a big problem since it causes damage and losses affecting many people in the area. Sragen is the Regency with the greatest loss due to flooding of the Bengawan Solo River which is the longest river in Java Island with 16,100 km2 basin area. Dykes are the structural intervention usually proposed to deal with flood water. The objective of this study is to conduct an assessment of dyke height requirement in order to reduce flood risk in Sragen Regency along Bengawan Solo River. The assessment is based on risk level according to regulations of the Head of National Disaster Management Agency Number 2 in 2012, regarding the general guidelines for the assessment of disaster risk. Hazard levels are obtained from the relationship between hazard index parameters and exposed population index. Loss levels are obtained from the relationship between the hazard level parameter and the loss index. Flood risk level is determined from the level of losses and capacity. For mitigation purposes, flood risk reduction analysis has been conducted through a structural approach by simulating dyke construction around the Bengawan Solo River. Several scenarios of dyke height (2m, 4m, and 6m) have been simulated to assess flood inundation.

Effects of Large-Scale Coastal Construction on Storm Surge Height in Shallow Coastal Zones of the Yellow Sea, South Korea

Lee, H.-Y.; Jeong, Y.-H.; Kim, D.-H.; Kim, D.-S.; Cho, W.-H., and Hong, S.-J., 2020. Effects of large-scale coastal construction in shallow coastal zones of the Yellow sea on changes in storm surge height. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 252–256. Coconut Creek (Florida), ISSN 0749-0208.Fifty-three percent of the South Korean coastline has been artificially modified due to large-scale land reclamation and dike construction. In particular, 40% of tidal flats have disappeared from the shallow coastal zones on the west coast. The construction of such large-scale coastal developments has caused the typhoon-induced maximum storm surge height to increase by 24% on average. This can primarily be ascribed to the decreased surface area of the tidal flats caused by large-scale coastal construction, given that storm surge energy is significantly dissipated over the extensive tidal flats with high depth-dependent bottom friction coefficients. Additionally, complex interactions between multiple factors, including decreased water volume and simplified coastline, caused, for example, by semi-closed bay reclamation are considered responsible for increased storm surge height.

Long-term Temporal and Spatial Morphological Variability of a Nourished Beach Using the EOF Analysis

Choi, T.J.; Choi, J.Y.; Park, J.Y., and Yang, Y.J., 2020. Long-term temporal and spatial morphological variability of a nourished beach using the EOF analysis. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 428–432. Coconut Creek (Florida), ISSN 0749-0208.Byeonsan Beach located at the west coast of Korea has been eroded seriously since 2006 after the construction of the Saemangeum dike. For this reason beach nourishment has been conducted from 2011 until 2017, and the result was successful by turning the beach in erosional phase of -4.1 cm/yr (2006 to 2010) into depositional condition of +2.0 cm/yr (2011 to 2017). Based on the EOF analysis of sixty-nine beach surveys during 13-year period from 2006 to 2019, the first four modes accounted for nearly 83% of total variability, leading to the interpretations of beach-nourishment effect, artificial construction, the influence of beach ridges migration, and irrigation-channel effect, respectively.

The alteration of lateral circulation under the influence of human activities in a multiple channel system, Changjiang Estuary

Extensive coastal engineering activities including channel dredging and constructions of large infrastructure have greatly altered hydrodynamics in the Changjiang Estuary. While the changes in longitudinal circulation have been well-documented, limited studies have focused on the alteration in lateral circulation and its impact on estuarine circulation in the Changjiang Estuary. Lateral circulation in an estuary plays an important role in modulating estuarine circulation, sediment transport, and morphological change. Different from many of previous numerical studies, we utilize an unstructured-grid numerical model configured in a way to allow inundation over dikes and tidal flats. Numerical model experiments show significant changes in lateral circulation and stratification along the North Passage in response to the altered geometry and bathymetry due to the channel deepening and the dike construction. Both the channel deepening and the dike construction led to an enhanced stratification. Further analysis suggests that the along-channel, the lateral, and the vertical (including up- and downwelling and vertical mixing) effects are all important in modulating the intra-tidal stratification-destratification process. The channel deepening enhances both the lateral and the vertical effects around the high-water slack. The construction of dikes that completely blocks the lateral water exchange between the North Passage and surrounding tidal flats, changes the system from a multiple-channel system into a single-channel system. With dike construction, the estuarine circulation tends to have a horizontally sheared pattern with weaker friction and a stronger stratification.

Basic Tyre Appreciation: An Overview

The usefulness of tyre in a vehicle cannot be over emphasized, yet it is one of the most over looked aspect of a vehicle. Due to the high rate of non-compliance with tyre regulations, a review on the basic tyre information required for its optimum utilization and safety purposes was carried out. This paper, therefore, explores the standard manufacturers’ guide and specifications, rules and regulations including other relevant information to increase user’s awareness. Also, tyre sidewall markings, (identification/classification), alignment, inflation and major reasons why tyres are black were discussed so as to avail users with one stop bank of basic tyre information.

Floodplain losses and increasing flood risk in the context of recent historic land use changes and settlement developments: Austrian case studies

AbstractFloodplains play a central role in flood risk management since they function as retention areas which attenuate and decelerate flood waves. However, during the last decades land use has changed distinctly on floodplains which has led to a change in topography due to the construction of levees and dykes. Using geographic information system analysis we assessed floodplain developments over 60 years for five Austrian rivers. We used these findings as input for hydrodynamic‐numerical modelling. A comparison of computations of current and historic floodplain topographies demonstrated the complex impacts that changes on floodplains have on catchment level flood risk. Results showed that the losses of floodplains were in general linked to a deterioration in hydrological (flood peaks and travel times) and hydraulic (water level) parameters. In rare cases the unintentional overtopping of dykes resulted in an improved reduction of the peak of the flood wave, but included a worsening of local hydraulic conditions. Hence, this study demonstrates that general conclusions about an alteration of flood risk cannot be easily reached, with a demand for further site‐specific assessment. This novel way of investigating the trends of flooding characteristics by including the historic development within a catchment offers valuable information to planners for a future flood risk management.

ĐÁNH GIÁ KHẢ NĂNG LỰA CHỌN VỊ TRÍ ĐỔ VẬT LIỆU NẠO VÉT LUỒNG HÀNG HẢI TRÊN VÙNG BIỂN CẢNG HẢI PHÒNG

In order to keep essential depths in shipping channels to and from Hai Phong ports, regular dredging activities are maintained with about 3.6 million tons of sediments per year. Due to almost all the sediments of dredged material in the channels are composed of mud and silt, they are not easy to be used for land filling or other purposes. Moreover, disposing these materials on land is facing difficulties because of requiring the design and construction of dikes, requiring compaction and drainage of dumped materials. Therefore, disposal of dredged material from shipping channels in Hai Phong sea has become urgent. Based on integrated approach, the combination of numerical modeling and multicriteria decision analysis-GIS (natural condition, socio-economic and environment-ecosystem conditions) was made and the most suitable dumping sites were proposed in the regions with water depth ranging between 18–27 m. Their total receiving capacity was estimated about 206 million tons for 40–50 years.

Application of Analytical Hierarchy Process (AHP) Method in Determining Dike Construction for Handling Tidal Flood

Tambak Lorok in Semarang is one of the areas that often undergoes tidal floods. The construction of dam and dike infrastructure is an effort to overcome tidal floods. As one part of the flood control system, the dike has an important role. The construction projects requires an alternative selection method of dike construction in order to function optimally. This research aims to determine the order of priority criteria and alternative construction of dikes. The data were obtained through questionnaires to experts in the field of dike construction. The aspects of criteria used to analyze alternative dike construction are : functions and benefits, site conditions, costs and construction implementation. The dike construction alternatives include a Concrete Sheet Pile (CSP), Parapet Wall with reinforced Corrugated Concrete Sheet Pile/CCSP and landfill with Geotube Components. The questionnaire were processed using the Analytical Hierarchy Process (AHP) method with the Expert Choice v.11 application. The results showed consistency ratio (CR) of 5%, which means that research data were consistent and could be accounted for. Based on weighting in pairwise comparisons, the priority criteria in selecting type of dike construction are : functions and benefits (33%), site conditions (32%), cost (18%) and construction implementation (17%) The priority alternative dike construction is reinforced Corrugated Concrete Sheet Pile/CCSP (39.7%), landfill with geotube components (3.28%) and Cylindrical Concrete Piles (CSP) (27.5%). Dike construction with reinforced CCSP is a top priority in the handling of tidal floods in the Tambak Lorok.

Dramatic decrease of flood frequency in the Mekong Delta due to river-bed mining and dyke construction

Here we present a proof of concept evaluation of the impacts of riverbed-mining on river-wetland connectivity by analyzing the temporal trends of the flood frequencies in the Vietnamese Mekong Delta (VMD), while accounting for the effect of dyke constructions. We focus on the Long Xuyen Quadrangle (LXQ), which is significant in terms of biodiversity and economic contribution to the VMD as it is one of the most important food baskets of Southeast Asia that depends on seasonal flooding. Our results indicate that the flood frequency in LXQ has decreased significantly over the past 20 years (1995–2015). Time-series analyses of water level data at Chau Doc, Tan Chau, and Can Tho stations confirmed that the overall descending trend is statistically significant (p-value < 0.001 and tau ~ 0.1). However, the river discharge at Kratie showed no significant trend (p-value = 0.98) over the same period. This indicates that the flood frequency is associated with the lowering of the riverbed (incision) other than climatic factors. The connectivity analysis also revealed a remarkable drop in the inundation duration after early 2000, which corresponds to the previous observations of the shifting shoreline of the VMD from construction to shrinking. Finally, regression and principal component analyses underpinned the strong causality between the riverbed-mining and the decreased seasonal flooding patterns in LXQ, while accounting for the effect of the dyke system over the last decades (R2 = 0.75). This study offers compelling evidences on the relationship between sand-mining in the river and the disrupted flood regimes in VMD. The reduction in water and sediments that is necessary for sustaining current rates of agricultural production in the long term would endanger the livelihoods of millions of VMD inhabitants.

Impacts of hydrological restoration on lowland river floodplain plant communities

Many lowland floodplain habitats have been disconnected from their rivers by flood defence banks. Removing or lowering these banks can reinstate regular flooding and thus restore these important wetland plant communities. In this study we analyse changes in wetland hydrology and plant community composition following the lowering of flood defence banks at a floodplain of the River Don in the United Kingdom (UK). The aim of the restoration project was to improve the quality of “floodplain grazing marsh” habitat, which is a group of wetland communities that are of conservation interest in the UK. We analyse changes in species richness and community composition over a period of 6 years, and compare the presence of indicator species from the target floodplain grazing marsh plant communities. The lowering of the flood banks increased the frequency of flood events, from an estimated average of 1.7 floods per year to 571 floods per year. The increased flooding significantly increased the proportion of time that the wetland was submerged, and the heterogeneity in hydrological conditions within the floodplain. There were significant differences in composition between the pre-restoration and restored plant communities. Plants with traits for moisture tolerance became more abundant, although the communities did not contain significantly more ‘target’ floodplain grazing marsh species at the end of the study period than prior to restoration. Colonisation by floodplain grazing marsh species may have been limited because environmental conditions were not yet suitable, or because of a shortage of colonising propagules. While the desired target plant community has not been achieved after 5 years, it is encouraging that the community has changed dynamically as a result of hydrological changes, and that moisture-tolerant species have increased in occurrence. Over the next few decades, the restored flood regime may cause further environmental change or colonisation events, thus helping increase the occurrence of desired floodplain grazing marsh indicator species.

Changes in Fish Assemblages after Dike Construction in the Saemangeum Area

In the Saemangeum area, construction of a dike began in 1991 and was completed in 2006; desalination is currently being conducted. In order to investigate the influence of dike construction on fish assemblages, we analyzed the changes in fish assemblages using fish monitoring data accumulated before, during, and after construction of the Saemangeum Dike. Analysis of changes in the salinity of the Saemangeum Reservoir between 1997 and 2014 revealed that the overall salinity decreased, and this pattern became evident after completion of the dike. Long-term changes in fish assemblages were also confirmed in freshwater areas (Mankyeong and Dongjin Rivers) and the Saemangeum Reservoir. In freshwater areas, different fish assemblages were collected before and after dike construction according to NMDS analysis, and the proportion of freshwater fish continuously increased during analysis of ecological types. In the Saemangeum Reservoir, differences in fish assemblages were observed before, during, and after dike construction (PERMANOVA, F = 2.5325, P = 0.017). Moreover, the numbers of families and species decreased during dike construction; in terms of species composition, the proportion of brackish water fish increased, while that of marine fish decreased. Currently, a salinity gradient exists in the Saemangeum area between the rivers and the dike, and the M1-3 and D1-3 sites were classified as freshwater sites. Desalination is expected to increase freshwater areas in the future; as the change will happen over a very long period of time, differentiated management plans for each site of the Saemangeum area should be implemented through continuous monitoring.

Environmental Assessment of Xinhe Beach Development

The proliferation of beach renovation is affecting the change of the landform of the coast and threatening the ecological environment. Therefore, it is necessary to assess the impact on the environment after the beach is transformed. The survey area is located near the Shipu fishing port in the south of Ningbo City, Zhejiang Province. Based on the Delft-3D grid nesting model and wave-fluid coupling model, the astronomical tide and hydrodynamic environment of the 30 days before the construction were simulated. After the beach was rebuilt and sand was added and the spur dike was added, the astronomical tide and hydrodynamic environment were again simulated. Finally, based on the simulated data, the water level, velocity field, effective wave height distribution, and siltation and siltation of Xinhe Beach were obtained. Xinhe Beach's environmental damage risk indicators can be evaluated based on water level, velocity field, effective wave height direction and sediment erosion and deposition. Artificial sanding and construction of spur dikes will change the hydrodynamics and scouring and siltation of Xinhe Beach, but have little effect on the coastal terrain and ecological environment.

Flow Characteristics Of Tigris River Within Baghdad City During Drought

The main source of water supply in Iraq is the surface water, especially Tigris and Euphrates Rivers and their tributaries. In the recent years there was a great drop in the water levels of Tigris River within Baghdad City which had affected the operation of twelve water supply projects located on the banks of Tigris River in Baghdad City, due to significant climate changes, and the expansion of hydraulic construction (dams) and implementation of new irrigation projects in Turkey, these factors have greatly reduced the water flowrates of river by about 46%. In the present study the flow characteristics of Tigris River within Baghdad City was studied, the reach involved was about 49km in which it represents the urban zone beginning from the north of the Baghdad City at Al-Muthana Bridge to the confluence of Tigris River with the Diyala River south of Baghdad, using steady flow one-dimensional hydraulic model to achieve raising of water levels within this reach during drought periods. This model was implemented using HEC-RAS software.Three sets of observation data were used to calibrate the model to estimate suitable Manning roughness coefficient (n) considering the root mean square error (RSME) as an accurate indicator. The results showed that n of value 0.032 for the main river bed and 0.040 for flood banks of the river gave the best results with minimum RMSE of 0.076. Several treatments were suggested such as construction of barrage, inflatable weir, and the use of obstruction for the purpose of raising water levels. Moreover, selection of the suitable site of these treatments or hydraulic structures was studied, as well as their cost was analyzed. The results show that the proper solution for maintain the required water levels that ensure continuous operation of water supply project was the construction of an inflatable weirs, due to low initial cost, simplicity of operation, their ability to inflate and deflate quickly and easily to prevent upstream flooding, and offering a high level of control and easy method for recapturing water.

Flooding in the Mekong Delta: the impact of dyke systems on downstream hydrodynamics

Abstract. Building high dykes is a common measure of coping with floods and plays an important role in agricultural management in the Vietnamese Mekong Delta. However, the construction of high dykes causes considerable changes in hydrodynamics of the Mekong River. This paper aims to assess the impact of the high-dyke system on water level fluctuations and tidal propagation in the Mekong River branches. We developed a coupled 1-D to 2-D unstructured grid using Delft3D Flexible Mesh software. The model domain covered the Mekong Delta extending to the East (South China Sea) and West (Gulf of Thailand) seas, while the scenarios included the presence of high dykes in the Long Xuyen Quadrangle (LXQ), the Plain of Reeds (PoR) and the Trans-Bassac regions. The model was calibrated for the year 2000 high-flow season. Results show that the inclusion of high dykes changes the percentages of seaward outflow through the different Mekong branches and slightly redistributes flow over the low-flow and high-flow seasons. The LXQ and PoR high dykes result in an increase in the daily mean water levels and a decrease in the tidal amplitudes in their adjacent river branches. Moreover, the different high-dyke systems not only have an influence on the hydrodynamics in their own branch, but also influence other branches due to the Vam Nao connecting channel. These conclusions also hold for the extreme flood scenarios of 1981 and 1991 that had larger peak flows but smaller flood volumes. Peak flood water levels in the Mekong Delta in 1981 and 1991 are comparable to the 2000 flood as peak floods decrease and elongate due to upstream flooding in Cambodia. Future studies will focus on sediment pathways and distribution as well as climate change impact assessment.