Moderate Flood Research Articles

Atlantic Coastal Sea Level Variability and Synoptic-Scale Meteorological Forcing

Abstract Anomalous sea levels along the mid-Atlantic and South Atlantic coasts of the United States are often linked to atmosphere–ocean dynamics, remote- and local-scale forcing, and other factors linked to cyclone passage, winds, waves, and storm surge. Herein, we examine sea level variability along the U.S. Atlantic coast through satellite altimeter and coastal tide gauge data within the context of synoptic-scale weather pattern forcing. Altimetry data, derived from sea level anomaly (SLA) data between 1993 and 2019, were compared with self-organizing map (SOM)-based atmospheric circulation and surface wind field categorizations to reveal spatiotemporal patterns and their interrelationships with high-water-level conditions at tide gauges. Regional elevated sea level patterns and variability were strongly associated with synergistic patterns of atmospheric circulation and wind. Recurring atmospheric patterns associated with high-tide flooding events and flood risk were identified, as were specific regional oceanographic variability patterns of SLA response. The incorporation of combined metrics of wind and circulation patterns further isolate atmospheric drivers of high-tide flood events and may have particular significance for predicting future flood events over multiple spatial and temporal scales. Significance Statement Mean sea level and minor to moderate coastal flood events, also called blue-sky or high-tide floods, are increasing along many U.S. coastlines. While the drivers of such events are numerous, here we identified key contributing weather patterns and environmental factors linked to increased risk of regional and local high-water conditions along the Atlantic coast. Our results indicate that the predictability of elevated sea levels and high-tide floods is highly dependent upon atmospheric drivers including wind and circulation patterns and, if applied in a tested modeling framework, may prove useful for predicting future floods at various time scales.

The Oktober Flut: An anomalous extreme high-water event in Annapolis, MD, USA, October 2021

Between 28 and 30 October 2021, Annapolis, Maryland, USA, experienced the third highest flood event on record, referred to as the “Oktober Flut.” Unlike many of the extreme coastal flood events that have impacted Annapolis in the past, the Oktober Flut was not associated with a tropical or post-tropical cyclone. Instead, sustained wind forcing from a series of passing extratropical storms drove anomalously high water levels. The maximum observed hourly water level during the event was 4.88 ft above mean lower low water (MLLW). This exceeded the Moderate Flood Stage, defined by the National Weather Service (NWS) as 3.3 ft (MLLW), and had an annual exceedance probability of 5.2%. In total, flood waters exceeded the NWS Minor Flood Stage (2.6 ft MLLW) for 78 non-consecutive hours over multiple tidal periods. Relative sea level rise and increasing instances of coastal nuisance flooding events, like the Oktober Flut, have the potential to impact the local economy in Annapolis, MD, and operations at the geographically adjacent U.S. Naval Academy. Coastal nuisance flooding events also challenge existing community resilience efforts and initiatives, particularly those related to preparing for natural hazards. This paper provides an overview of the meteorological factors that drove the anomalously high-water levels and coastal flooding at the U.S. Naval Academy. In addition to data analysis from fixed, long-term sensors maintained by federal partners, observations from spotdeployments in advance of the storm are also presented. The results are discussed with respect to the storm impacts on infrastructure and facility preparedness. Lessons learned are documented with the aim of informing other coastal communities on how to better assess local flood-specific action plans, based on the accuracy and timing of forecast data.

Floods on Alluvial Fans: Implications for Reworking Rates, Morphology and Fan Hazards

AbstractFlood events are the agents of change on alluvial fans. However, most alluvial fan experiments have used constant flows to model fans and the channels upon them. Here, we present results from a series of alluvial fan experiments with different patterns of flow variation (i.e., different hydrograph shapes). We conducted experiments with (a) constant flow, (b) alternating high and low flows, (c) a moderate flood peak that decayed slowly, alternating with a constant low flow, and (d) a high flood peak that decayed rapidly, alternating with a constant low flow. We found that different hydrographs generated fans with different slopes, even though all experiments had the same mean flow and sediment supply. In addition, higher peak flows led to increased lateral migration rates and increased erosion and deposition. These results challenge the notion that a single representative flow can be used to approximate the geomorphic effects of a range of flows in a natural stream. Moreover, our findings indicate that hydrograph shape can govern the geomorphic impact of a flood event. This means that altered basin hydrology (for instance, through land cover change) likely exerts an important impact on geomorphic change and natural hazards on alluvial fans.

Effects of hydrology and river characteristics on riverine wetland morphology variation in the middle reaches of the Yarlung Zangbo–Brahmaputra river based on remote sensing

River and floodplains are process-response systems that geomorphic states are typically results of hydrologic drivers and geologic setting. Large sand-bed braided rivers geomorphology shows more sensitive dynamic evolution and significant space–time difference. However, few investigations have been focused on it. Here we show that river characteristics including expansion–contraction and elevation heterogeneity of the river cross sections affect erosion and deposition partially and cause spatially differential variation of morphology in the Yanni Wetland, in the middle of Yarlung Zangbo–Brahmaputra River (YBR), and interannual hydrology process is main responsible for temporal river morphology variation as the different impact of each HIs on river morphology. We found the river morphology varied significantly with main channel shifting and branches removing over the past 35 years. Within HIs, bankfull flow (Qbf) is the channel forming discharge equal to 5.6 year flood approximately. The sub-bankfull flow (Qsf), and main channel full flow (Qmf) are channel maintaining discharge. Affected by the broad width, main channel straighten was a result of years of large floods over Qbf. Small and moderate floods within the Qsf and Qbf are also important as the morphology adjustments were mainly observed in sub-channels. And effective discharges with the Nash approach (Q1/2) are more suitable in braided river compared with Wolman-Miller approach (Qef). Our research highlighted complexity response of landform and hydrology to river morphological variations in sand-bed braided riverine wetland. It provides reference basis for studying the ecological importance of flood dispatches and complements the scarcity of research data on morphological evolution in Tibet. And a new method for assessing the HIs with remote sensing was established that is convenient with high accuracy and suitable for wide-valley river with multiple channels. We anticipate our method to be a new view to analyze ecological hydrology, and promote better managing river ecosystems.

GIS-based Flood Risk Assessment in the Urban Catchment of Uyo Metropolis, Nigeria

Flood occurs as a result of rising global temperatures, more precipitation, increased runoff, and an increase in the rate of urban flooding. The goal of this research is to calculate the flood risk assessment of a selected urban catchment in the Nigerian metropolis of Uyo. Secondary data were obtained from Landsat images of the study area using a correlational research design. Using supervised categorization of landuse in the area, the watershed pattern, landuse/landcover, and inundation level were determined using the area's Digital Elevation Model. The study also used a GIS-assisted computer simulation of storm water created by enhanced DEM to assess storm water level and inundation as a function of landuse/landcover change. Storm water generation assessment, inundation modeling, assessment of land cover and level of inundation, and evaluation of flash flood susceptibility using modeled inundation were among the hydrological models and techniques used to analyze the data. The findings revealed that Uyo has a number of streams with varying flow lengths. Uyo has 21 sub-basins, according to the study. In uyo, the total runoff was greater (0.74) inches. In Uyo, the rate of change in catchment behavior, such as catchment precipitation, node flooding, and runoff, increased with the time of day, whereas the rate of change in runoff volume varied somewhat. The hydrograph was not wider because the sections of Uyo metropolitan that were prone to moderate and high floods were higher (78.03 percent ). Based on these findings, the study suggests that better city design is needed to control the impact of flooding in the study area. To prevent the loss of life and property, areas prone to moderate and high flood vulnerability should be closely monitored and secured.

Responses of Phosphate-Solubilizing Microorganisms Mediated Phosphorus Cycling to Drought-Flood Abrupt Alternation in Summer Maize Field Soil.

Soil microbial communities are essential to phosphorus (P) cycling, especially in the process of insoluble phosphorus solubilization for plant P uptake. Phosphate-solubilizing microorganisms (PSM) are the dominant driving forces. The PSM mediated soil P cycling is easily affected by water condition changes due to extreme hydrological events. Previous studies basically focused on the effects of droughts, floods, or drying-rewetting on P cycling, while few focused on drought-flood abrupt alternation (DFAA), especially through microbial activities. This study explored the DFAA effects on P cycling mediated by PSM and P metabolism-related genes in summer maize field soil. Field control experiments were conducted to simulate two levels of DFAA (light drought-moderate flood, moderate drought-moderate flood) during two summer maize growing periods (seeding-jointing stage, tasseling-grain filling stage). Results showed that the relative abundance of phosphate-solubilizing bacteria (PSB) and phosphate-solubilizing fungi (PSF) increased after DFAA compared to the control system (CS), and PSF has lower resistance but higher resilience to DFAA than PSB. Significant differences can be found on the genera Pseudomonas, Arthrobacter, and Penicillium, and the P metabolism-related gene K21195 under DFAA. The DFAA also led to unstable and dispersed structure of the farmland ecosystem network related to P cycling, with persistent influences until the mature stage of summer maize. This study provides references for understanding the micro process on P cycling under DFAA in topsoil, which could further guide the DFAA regulations.

Investigating Climate Change Risk of “ Oil and Gas” City: Case of Dumai City, Indonesia

Based on Climate Resilient Development Policies on 2020-2045, there are four priority sectors threatened by climate change, namely marine and coastal, water, agriculture, and health. Indonesia still depends on oil and gas energy that will threats to infrastructures that support the sustainability of production that can have an impact on people’s lifelines. This study investigates the risk distribution shift of climate change impacts in Dumai, which generally have oil refineries and ports. Risk is calculated by using hazard and vulnerability components. A uniform weighting approach is used to calculate each indicator indices. Using the RCP 8.5 hazard scenario with threats in the form of sea-level rise, moderate flooding, and high-end results in the projection year, this research results in significant differences in affected areas and at risk. The main factors affect the increasing of element at risk are the inundation and the spatial changes. An increase in the risk area means there will be an increase in losses. Moreover, disasters in oil and gas cities have the possibility of collateral hazards and even disruption of the national energy system. The government must take several adaptation steps such as adding eco-buffer zones, walls around refineries, and periodic monitoring of critical infrastructure.

Penerapan Algoritma K-Medoids dalam Menentukan Daerah Rawan Banjir di Kabupaten Karawang


 
 
 Flood disasters often occur during the rainy season. Karawang is one area that is often flooded. Based on the risk index from BNPB, the flood disaster in Karawang affected 84% of the community, so efforts need to be made to reduce and overcome flood disasters. These problems are the beginning of efforts that need to be known which areas are prone to flooding. Therefore, this study aims to determine flood-prone areas in Karawang as an initial effort in tackling flood disasters. The research was conducted by classifying flood-prone areas using the k-medoids algorithm. K-Medoids uses the partition clustering method to group lists and objects into a number of clusters. This algorithm uses objects in a collection of objects that represent a cluster. The attributes used are flood-causing factors such as rainfall, elevation (soil height), population density, and distance to the river. The results of the study found three potential floods, namely low, medium, and high. There are 1 sub-district with low flood potential, 24 sub-districts with moderate flood potential, and 5 sub-districts with high flood potential. The test results using the silhouette coefficient get a value of 0.370.
 
 

Assessment of flood hazard in Owerri West, Imo State, Nigeria using Analytical Hierarchical Process and Index Based Approach

This study aimed at an assessment of flood hazard areas in Owerri Imo State, Nigeria using analytical hierarchical process and index-based approach. The study objectives were to: establish the geophysical factors that contribute to flooding in the study area; classify the established geophysical factors according to the level of flood risk; calculate the reliability index of the classified geophysical factors; determine the flood vulnerable areas using analytical hierarchical process and flood hazard index; and to produce a vulnerability index map defining the extent of flooding vulnerability in the study area. The methodology incorporated in this study involved acquisition of remotely sensed imageries of the study area, pre-processing, Image classification, modelling slope, watershed, Drainage Network, flow accumulation, Soil Classification, classification and standardization, pairwise comparism matrix, normalized weighted Matrix, consistency index check and flood hazard index modelling. The study results revealed that In Owerri West, high flood vulnerability occupied 1.54% with an area coverage of 817.78 hectares, moderate flood vulnerability occupied 28.37% with an area coverage of 15031.98 hectares, low flood vulnerability occupied 24.97% with an area coverage of 13228.25 hectares and no flood vulnerability occupied 1.67% with an area coverage of 882.17 hectares. From the results achieved and the experiences gathered, analytical hierarchy process and flood hazard index-based modelling approach is recommended as it is a robust and efficient tool for mapping flood vulnerability while incorporating robust factors that contribute to flood and having a consistency judgement which judges the reliability of the weights of the factors used during modelling.

Impacts of forestation on the annual and seasonal water balance of a tropical catchment under climate change

BackgroundThis study aims to assess the effects of a forestation program and climate change on the annual and seasonal water balance of the Bogowonto catchment (597 km2) in Java, Indonesia. The catchment study is rare example in Indonesia where forestation has been applied at the catchment level. However, since the forestation program has been initiated, evaluations of the program only focus on the planting area targets, while the environmental success e.g., impacts on the hydrological processes have never been assessed. This study used a calibrated Soil and Water Assessment Tool (SWAT) model to diagnose the isolated and combined effects of forestation and climate change on five water balance components, namely streamflow (Q), evapotranspiration (ET), surface runoff (Qs), lateral flow (Ql) and base flow (Qb).ResultsThe results show that from 2006 to 2019, forest cover has increased from 2.7% to 12.8% of the total area, while in the same period there was an increase in the mean annual and seasonal temperature, rainfall, and streamflow. Results of SWAT simulations show that changes in the mean annual and seasonal water balance under the forestation only scenario were relatively minor, while changes were more pronounced under the climate change only scenario. Based on the combined impacts scenario, it was observed that the effects of a larger forest area on the water balance were smaller than the effects of climate change.ConclusionsAlthough we found that forestation program has minor impacts compared to that of climate change on the hydrological processes in the Bogowonto catchment, seasonally, forestation activity has decreased the streamflow and surface runoff during the wet season which may reduce the risk of moderate floods. However, much attention should be paid to the way how forestation may result in severe drought events during the dry season. Finally, we urge the importance of accounting for the positive and negative effects in future forestation programs.

Flooding duration and volume more important than peak discharge in explaining 18 years of gravel–cobble river change

AbstractFloods play a critical role in geomorphic change, but whether peak magnitude, duration, volume, or frequency determines the resulting magnitude of erosion and deposition is a question often proposed in geomorphic effectiveness studies. This study investigated that question using digital elevation model differencing to compare and contrast three hydrologically distinct epochs of topographic change spanning 18 years in the 37‐km gravel–cobble lower Yuba River in northern California, USA. Scour and fill were analysed by volume at segment and geomorphic reach scales. Each epoch's hydrology was characterized using 15‐min and daily averaged flow to obtain distinct peak and recurrence, duration, and volume metrics. Epochs 1 (1999–2008) and 3 (2014–2017) were wetter than average with large floods reaching 3206 and 2466 m3/s, respectively, though of different flood durations. Epoch 2 (2008–2014) was a drought period with only four brief moderate floods (peak of 1245 m3/s). Total volumetric changes showed that major geomorphic response occurred primarily during large flood events; however, total scour and net export of sediment varied greatly, with 20 times more export in epoch 3 compared to epoch 1. The key finding was that greater peak discharge was not correlated with greater net and total erosion; differences were better explained by duration and volume above floodway‐filling stage. This finding highlights the importance of considering flood duration and volume, along with peak, to assess flood magnitude in the context of flood management, frequency analysis, and resulting geomorphic changes.

New insights into the spring flood history of the lower Peace and Athabasca Rivers, Northern Canada

Terrace floodbed sediments provide a key to understanding riverine flood history but to date floodbed chronologies have been limited in their temporal resolution. This study reconstructs the spring flood frequency, magnitude, and sediment delivery of the Peace and Athabasca Rivers at the Peace-Athabasca Delta (PAD), northern Canada, for the past four centuries through an algorithm that relates time to total organic matter accumulation in terrace floodbeds. The floodbed chronology is then compared to the historic flood record. Flood frequency, floodbed thickness (flood magnitude), and sediment accumulation histories were site-specific and therefore required integration across sites to produce cogent histories. Floodbeds record a lower flood frequency than the historic record because they tend not to register small or moderate floods that may not overflow the high terraces. Over the past 400 years, the Athabasca River experienced secular trends of increasing flood frequency and sediment delivery and a multicentury fall then rise in flood magnitude. Peace River flood frequency and sediment delivery peaked sometime early in the 20th century while flood magnitude peaked in the late 1800s. The temporal pattern for flood magnitude of the Peace and Athabasca Rivers was negatively correlated. Athabasca River decadal flood frequency and magnitude were positively correlated. Trends of declining Peace River flood frequency, magnitude, and sediment delivery expressed over much of the 20th century may have reversed in the past 20 years. Since year 2000, flood frequencies of the Peace and Athabasca Rivers have exceeded their 20th century averages. Predictions of ecological changes and the fate of the Peace-Athabasca Delta need to be grounded in data. Hopefully these findings will help to dispel misconceptions about the PAD's history and serve to tether predictions about its future to reality.

Sizable carbon emission from the floodplain of Ob River

The Ob River floodplain is the second largest floodplain in the world. Despite its vast area, estimates of carbon (C) emissions from the Ob River floodplain are largely absent. Here we present seasonal C emission and water area extent from the main channel and the floodplain along a ~4 km reach in the boreal zone of the Ob River. We found strong seasonality in water area extent of the Ob main channel (~1.8 km2) and floodplain (~3 km2) with water covering 34% of land during flood and subsequently declining to ~16% and ~14% during summer and autumn baseflow, respectively. The C emissions also varied seasonally over the open water period, ranging from −0.1 to 0.6 g C m−2 d−1 for the Ob main channel and from 0 to 9 g C m−2 d−1 for the floodplain. The dissolved organic carbon positively affected CO2 concentrations and fluxes in the floodplain during all seasons, whereas pH and oxygen concentration negatively impacted CO2 concentrations and fluxes. Some nutrients (ammonia and phosphate) positively correlated with CO2 and CH4 concentrations in summer. The total C emission from the study reach (1.8 km2 main channel, 3 km2 floodplain) during moderate flooding was 236 ± 51 tons C yr−1 (>99% CO2, <1% CH4) with the floodplain accounting for ~65%. The contribution of the floodplain to the net river C evasion may be even greater during years of high flooding and in northern regions of the Ob River basin, where floodplain soils are more C-rich and are underlain by permafrost, and in years with more extensive flooding.

The Okavango Delta’s waterbirds – Trends and threatening processes

The Okavango Delta is renowned as an extraordinary ecosystem of high biodiversity, listed as both a Ramsar and World Heritage Site, with part protected in the Moremi Game Reserve. This extensive floodplain ecosystem has 444 recorded bird species, with just under a quarter of these waterbirds, including at least 16 breeding and 4 threatened (1 endangered, 3 vulnerable) species. Despite the global importance of this ecosystem, and its transboundary nature, there are surprisingly few long-term assessments of status of the ecosystem or waterbird communities, a key indicator of ecosystem health, with threats such as upstream water extraction, and climate change threatening its outstanding biodiversity. We compiled a comprehensive 53-year dataset comprised of citizen science and other datasets (1970–2019), on 36 waterbird species (Anhingidae, Ardeidae, Ciconiidae, Gruidae, Pelecanidae, Phalacrocoracidae, and Phoenicopteridae), including eight waterbird breeding colonies in the Okavango Delta. We investigated trends in waterbird biodiversity as well as responses to temperature, flow, flooding, and local rainfall. Waterbird breeding colonies were associated with relatively high areas of riparian woodland, and experienced moderate flooding frequencies (> 1 in 5 years). Total abundance of all 36 waterbird species was positively related to river flows. Despite increased citizen science effort over time, total abundance within the Okavango Delta significantly declined with declining average inundation. Four species led these declines (African darter Anhinga rufa, green-backed heron Butorides striata, slaty egret Egretta vinaceigula, squacco heron Ardeola ralloides) and one marabou stork Leptoptilos crumenifer, increasing (only sufficient data to analyse 15 species individually). Decreased inundation within the Delta and other internal factors (urbanisation, tourism, vegetation change) as well as external factors (habitat loss elsewhere) are likely driving these declines. Rigorous monitoring of waterbirds, including the eight breeding colonies across the Delta, is needed to explore these changes closely, providing baselines in the case of water resource developments on the rivers supplying the Okavango Delta. Long-term conservation of the magnificent Okavango Delta and its dependent biodiversity, including its waterbirds, is highly reliant on protection of river flows in three countries to ensure natural flooding regimes, alongside the conservation of neighbouring wetlands.

Spatiotemporal Flood Risk Determination and Management for a Large River Basin

The Chao Phraya River Basin (CPRB) of Thailand faces flooding almost every year. The severest flood occurred in the CPRB in 2011 with the highest property damage costs (46.5 billion USD) and the highest casualty (813 deaths). The objectives of this study were thus to (1) determine flood risk indices and categorize them into four risk zones (low, moderate, high, and very high) across 994 sub-districts in the CPRB during the six rainy months (May–October); and (2) propose specific measures for flood risk management for each of the categorized risk zones. The flood risk indices were assessed as the product of two hazard variables (flood levels and monthly cumulative precipitation) and the vulnerability variable (land uses). The findings revealed spatiotemporal variations in flood risk. Spatially, the sub-districts deemed to be in the high or very high flood risk zone were mainly located close to the Chao Phraya River (CPR), where the flood levels reached 1.1 – 4 m in depth; whereas the sub-districts detected in the low or moderate flood risk zone were located further away from the CPR. Temporally, more sub-districts were detected in the high or very high risk zone in September when heavy rainfalls were observed. Specific measures are proposed herein to manage flood risk regarding the categorized zones during three periods. The preventive and mitigation measures should be prepared before flooding; emergency responses should be practically implemented during flooding; and the recovery after flooding should cover both infrastructural and environmental damage and mental/physical illnesses amongst the affected people. Intensive measures are recommended for the sub-districts located in both the high and very high risk zones. These measures may be properly loosened for the sub-districts located in the low and moderate risk zones.

Spatial Multi-Criteria Evaluation of Proportional Accountability of Flood Causal Factors and Vulnerable Areas in Makurdi, Benue State, Nigeria

There have been considerable reports on flood frequency, vulnerability and risk especially on Makurdi. However, not much has been known about the proportional contribution of the causal factors and distribution among vulnerable areas. This aspect remains fundamental in flood disaster and risk management decisions and actions. It is on this premise that this study applied the spatial multi-criteria evaluation technique (SMCE). The four (4) broad categories of flood causative factors: Climatic (rainfall) , soil (textural distribution of clay and sand content), morphometric (slope, linear and areal) and Land Use / Land Cover (built-up land, bare land, farm land, vegetated land, wetland and water bodies/broad river) were used for the analytic hierarchy process and weighted sum overlay technique. The analysis revealed percentage contributions of the most effective flood causing factors as follows: Rainfall (44.89%), morphometry (34.02%), Landuse / Landcover (12.8%) and soil (6.28%). The weighted sum overlay result shows that low flood vulnerability areas occupy 43.11% (460.782 km 2 ), moderate flood vulnerability areas 31.13% (332.717 km 2 ) and high flood vulnerability 25.75% (275.238 km 2 ). Since this study identified rainfall as the major determinant of flooding it recommends that annual and seasonal rainfall predictions should be enhanced in Makurdi. Also, the area with high flood vulnerability which coincides with built-up area should drive the promotion of flood resilience city structures and enforced by relevant public institutions such as Federal Ministry of Environment, Urban Planning Departments, Works and Housing. Therefore, remediation actions can be applied for the high vulnerability areas while mitigation actions can be focused more on the moderate flood vulnerability areas. Keywords: Spatial, Multi-criteria, Vulnerability, Flood, Mitigation DOI: 10.7176/JRDM/77-03 Publication date: July 31 st 2021

An early warning system for wave-driven coastal flooding at Imperial Beach, CA

Waves overtop berms and seawalls along the shoreline of Imperial Beach (IB), CA when energetic winter swell and high tide coincide. These intermittent, few-hour long events flood low-lying areas and pose a growing inundation risk as sea levels rise. To support city flood response and management, an IB flood warning system was developed. Total water level (TWL) forecasts combine predictions of tides and sea-level anomalies with wave runup estimates based on incident wave forecasts and the nonlinear wave model SWASH. In contrast to widely used empirical runup formulas that rely on significant wave height and peak period, and use only a foreshore slope for bathymetry, the SWASH model incorporates spectral incident wave forcing and uses the cross-shore depth profile. TWL forecasts using a SWASH emulator demonstrate skill several days in advance. Observations set TWL thresholds for minor and moderate flooding. The specific wave and water level conditions that lead to flooding, and key contributors to TWL uncertainty, are identified. TWL forecast skill is reduced by errors in the incident wave forecast and the one-dimensional runup model, and lack of information of variable beach morphology (e.g., protective sand berms can erode during storms). Model errors are largest for the most extreme events. Without mitigation, projected sea-level rise will substantially increase the duration and severity of street flooding. Application of the warning system approach to other locations requires incident wave hindcasts and forecasts, numerical simulation of the runup associated with local storms and beach morphology, and model calibration with flood observations.

Укрепление и защита берегов в Калачевском районе Волгоградской области с помощью кустарниковой растительности

The critical abrasion situation manifests itself on the coastal part of the Kalachevsky district due to the increasing anthropogenic load. The most important element of the complex of measures to combat silting of reservoirs and coastal abrasion, as well as an effective measure to strengthen the banks is forest vegetation. The objectives of the research were to study the soil, forest and climatic conditions of the object under study, to develop an assortment of shrubs and features of the formation of protective forest stands, as well as criteria for selecting an adapted assortment of tree and shrub vegetation and methods of caring for the soil and plantings. During the research, the most promising types of shrubs for creating upper protective forest stands were identified: Ligustrum vilgare L., Berberis vulgaris L., Cotoneaster lucidus Schltdl., Amelanchier Medik., Ribes aureum Pursh., Rosa canina L. It was found that the useful role of forest stands is manifested in their ability to convert surface runoff into subsurface runoff, to clean surface stock water from fine-grained soil, to weaken the speed of movement and to extinguish the energy of waves, binding the soil with roots. Recommendations are given for the creation and placement of anti-abrasion plantings, depending on the steepness and height of the slope. It is stated that one of the main measures for the care of the aboveground part of the plantings is the pruning of the crown, carried out taking into account the biological characteristics of their growth and development, including the removal of dry and damaged branches, thinning of the crown, preservation of the previously given crown size, rejuvenation of the crown. It is recommended to place shrubs depending on the landscape, soil and climatic conditions and features of abrasive processes in areas of constant, periodic, episodic flooding and strong moderate and weak flooding of the coastline.

Land Use and Land Cover Change Assessment in the Context of Flood Hazard in Lagos State, Nigeria

Incessant flooding is a major hazard in Lagos State, Nigeria, occurring concurrently with increased urbanization and urban expansion rate. Consequently, there is a need for an assessment of Land Use and Land Cover (LULC) changes over time in the context of flood hazard mapping to evaluate the possible causes of flood increment in the State. Four major land cover types (water, wetland, vegetation, and developed) were mapped and analyzed over 35 years in the study area. We introduced a map-matrix-based, post-classification LULC change detection method to estimate multi-year land cover changes between 1986 and 2000, 2000 and 2016, 2016 and 2020, and 1986 and 2020. Seven criteria were identified as potential causative factors responsible for the increasing flood hazards in the study area. Their weights were estimated using a combined (hybrid) Analytical Hierarchy Process (AHP) and Shannon Entropy weighting method. The resulting flood hazard categories were very high, high, moderate, low, and very low hazard levels. Analysis of the LULC change in the context of flood hazard suggests that most changes in LULC result in the conversion of wetland areas into developed areas and unplanned development in very high to moderate flood hazard zones. There was a 69% decrease in wetland and 94% increase in the developed area during the 35 years. While wetland was a primary land cover type in 1986, it became the least land cover type in 2020. These LULC changes could be responsible for the rise in flooding in the State.

Role of effective discharge on morphological changes for a regulated macrochannel river system

Effective discharge plays a major part in sediment and nutrient transport, landscape modification, and river restoration. However, a complete understanding of effective discharge is still missing because of heterogeneity in various fluvial processes. The present study investigates the role of effective discharge for suspended sediment transport in a regulated macrochannel river system, the Brahmani River, India. The natural flow-sediment regime and channel pattern of the Brahmani River have been altered by the Rengali dam. The effective discharge is estimated with both analytical and deterministic methods using long-term hydrological data. The results show the control of regulated flow and sediment regime in the post-dam period contributes to the reduction in effective discharge (1849 m3/s to 820 m3/s), where frequent moderate floods are able to transport a maximum portion of sediment load. An effective discharge integrated stream power curve is formulated, which accurately predicts the channel transition (from sinuous to weakly braided) in the post-dam period. Finally, the proposed probability of braiding captures the chute formation correctly, which further highlights the hierarchy of energy dissipation and morphological continuum in the Brahmani River.