Floodplain Research Articles

Sequential Changes in Coastal Plain Rivers Influenced by Rising Sea-Level

Coastal backwater effects on low-gradient coastal plain rivers extend well upstream of the head of the estuary and propagate upstream as sea-level rises. Hydrological, geomorphological, and ecological indicators can serve as sentinels of the upriver encroachment. Analyzing the along-river spatial distribution of these indicators as a space-for-time substitution allows the prediction of sequential changes. Interpretation of results from 20 rivers in Virginia and the Carolinas shows that backwater effects at the leading edge result in higher river stages, increasing floodplain inundation, and raising water tables. Lower slopes and flow velocities reduce sediment transport, reducing river sediment input and floodplain deposition. This inhibits natural levee development, reducing bank heights. These factors combine to increase the frequency and duration of inundation, resulting in semi-permanently flooded wetlands. Anaerobic conditions limit organic decomposition, and ponding allows transported and suspended organic matter to settle, leading to organic muck and peat floodplain soils. This accumulation, coupled with general valley-filling, buries alluvial terrace remnants. Finally, vegetation changes driven by salinity increases occur, resulting in swamp conversions to brackish marsh. Backwater encroachment is strongly controlled by channel bed slope, with relatively steeper channels experiencing slower rates of tidal extension. With accelerating sea-level rise (SLR), the lowest-sloping channels could experience encroachment rates of >1 km yr−1. Hydrological changes associated with SLR are most rapid at the leading, upriver end—averaging 71 km upstream of the head of the estuary in the study rivers at present—and at the lowermost, downstream end of the fluvial-estuarine transition zone.

50-year seasonal variability in East African droughts and floods recorded in central Afar lake sediments (Ethiopia) and their connections with the El Niño–Southern Oscillation

Abstract. Understanding past and present hydrosystem feedbacks to global ocean–atmospheric interactions represents one of the main challenges to preventing droughts, extreme events, and related human catastrophes in the face of global warming, especially in arid and semiarid environments. In eastern Africa, the El Niño–Southern Oscillation (ENSO) was identified as one of the primary drivers of precipitation variability affecting water availability. However, the northern East African Rift System (EARS) still suffers from the underrepresentation of predictive and ENSO teleconnection models because of the scarcity of local to regional historical or palaeo-data. In this paper, we provide a 50-year seasonal flood and drought chronicle of the Awash River catchment from the study of laminated sediment from Gemeri and Afambo lakes (central Afar region, Ethiopia) with the aim of reconstructing the magnitude of regional hydroclimatic events. Pluricentimetric micro-laminated lithogenic facies alternating with plurimillimetric carbonate-enriched facies are investigated in both lakes. We couple dating methods including radiocarbon, short-lived radionuclides, palaeomagnetic field variations, and varve counting on both lake deposits to build a high-resolution age model and to discuss the regional hydrosedimentary dynamics of the Awash River over the last ∼ 700 years with a focus on the last 50 years. Using a multiproxy approach, we observe that following a multicentennial enhanced hydrological period, the two lakes have experienced a gradual decrease in river load inflow since 1979 CE, attaining extreme drought and high evaporative conditions between 1991 and 1997 CE. In 2014, the construction of a dam and increased agricultural water management in the lower Awash River plain impacted the erodibility of local soils and the hydrosedimentary balance of the lake basins, as evidenced by a disproportionate sediment accumulation rate. Comparison of our quantitative reconstruction with (i) lake water surface evolution, (ii) the interannual Awash River flow rates, and (iii) the El Niño 3.4 model highlights the intermittent connections between ENSO sea surface temperature anomalies, regional droughts, and hydrological conditions in the northern EARS.

FLOOD INUNDATION MAPPING OF GODAVARI RIVER BY USING 2D HEC-RAS MODEL

Due to increasing urbanization, there are various drastic changes taking place in environment these changes are hazardous for human being as well as animal and environment. Effect of environmental degradation can create environmental issues such as flood, drought etc. Out of this flood is the most common and disastrous hazard in the world. Present study utilizes 2D Unsteady flow modelling for flood inundation mapping in the lower Godavari basin for a reach length of 70 km from Sambaigudem in Telanagana district of Ramanujavaram to Damaracherla in Andhra Pradesh district of Nalgonda. For analysis of this 2D flow modelling and inundation mapping 30m resolution DEM is used. From ancient time majority of cities are developed near or on the banks of the river and these cities were affected due to flood during rainy season or due to the high intensity rainfall. As India is among the most vulnerable to flooding because of its geographical features. Therefore, this study is performed to analyze the flood plain and the extent of the affected areas present on or near the bank of Godavari River and provide mitigation measures for it.

A Study on the Construction and Evaluation of the Water Resource Reutilization System for Farmland Diversion and Drainage

Water is an essential resource for both rural and agricultural areas; it can be wisely distributed and used in the field to protect daily life, production, the natural environment, and the safety and stability of regional drainage and flood control systems. Our research selected a typical plains rural river network area with agriculture as the main industry to investigate the most effective method of farmland diversion and drainage. We comprehensively planned and transformed the water system flow, water conservation engineering, and the ecological environment in the irrigation area through the reutilization system. The reutilization system’s operation and scheduling design is implemented for four specific periods: the water replenishment cycle, agricultural irrigation, agricultural drainage and the rainy period of the flood season. The research period ranges from 2020 to 2023 after the completion of the system. We used monitoring, the recording of hydraulic equipment parameters and data collection to evaluate the balance of water supply and demand in the study area. At the same time, we have tracked and evaluated the four aspects of water quality enhancement, water conservation and flood control, and agricultural irrigation. The results show that the total agricultural water consumption decreased by 2.9%, and the amount of water saved increased by 9.6%. The current segment creates the rivers’ embankment standards. With a 92% irrigation guarantee rate, the current section forms and the embankment standards of the rivers satisfy the design storage volume and the flood level of one in twenty years. The water quality of all the rivers in the area has decreased by 5~10% compared to the average concentration prior to establishment. This study verifies the comprehensive effect and the suitability of the system by comparing the before and after effects, and provides a scientific basis for the method of efficient recycling and utilization of water resources in the rural plains river network area; we also propose the guidance of increasing the digital twin control and long-term operation mechanism to ensure the long-term stable operation of the technology.

Zoning and regulation of compound flooding in coastal cities coupled with tracer method

Urban inland rivers play a significant role in mitigating flooding. However, the influence of their discharge on urban flooding affected by different flood drivers remains to be fully explored. Taking a catchment area in Haikou City, Hainan Province, China as an example, in light of the urban flooding model coupled with the water tracer method, this study investigates the degree of inundation in each flood zone under different inland river flows. The flood zones are determined by the flooding simulation results of three cases, and then are verified by the zonation based on the tide tracer approach. Finally, the tracer method is used to study the impact of urban inland rivers on flooding and the connection of hydraulic and water volume between rivers and pipelines. The results indicate that the inundation area decreased by 3.71 % as the river flow increased from 15 to 25 m3/s. In the process of river flow rising from 5 to 45 m3/s, The average flooding depth in the rainfall-affected area climbs slowly from 0.53 m to 0.62 m; In the tidal-affected area, the average flooding depth drops from 0.52 m to 0.12 m when the inland river flow increases from 5 to 25 m3/s, and rises from 0.12 m to 0.54 m when the inland river flow continues from 25 to 45 m3/s; The percentage of pipelines grows from 18.5 % to 28.0 %. This study provides valuable scientific insights and support for flood prevention planning and flood control strategies in coastal cities.

Radon and water geochemistry at the active Campi Flegrei volcano (Italy): The role of pore-water phenomena

This study provides new 222Rn measurements performed by RAD7 on 31 thermal waters from the Campi Flegrei caldera, the active volcanic-geothermal field close to Naples (Southern Italy). Waters sampled between 2021 and 2023 are characterized for physical parameters, major ions geochemistry and radium content. Rn contents from Somma-Vesuvius, Ischia and Vulcano volcanoes, together with the river plain north to the Campi Flegrei, were obtained for comparison. The Campi Flegrei caldera reaches the highest Rn concentrations respect to the other sites, varying from 0.03 ± 0.02 to ca. 1887 ± 13 Bq/L, although mostly are below 60 Bq/L. We detect a steady-state condition of constant temperature, facies and radon activity that characterizes most sites, with only minor impacts from seasonalilty and Weigel's effects. Just a small fraction of 222Rn derives from its 226Ra parent in solution, while radon activity in local waters is mainly due to emanation from the radium-containing rock reservoir. Our dataset proofs that radon couples with temperature, sulfate and CO2 in relations to rock-leaching and pore-water phenomena that proceed in the reservoir as it warms up and degasses. Rn and CO2 are decoupled in deeply and timely equilibrated geothermal fluids.Two main end-members, i.e., a low radioactive cold diluted and the Rn-richest hypersaline water from the deep geothermal reservoir are recognized; seawater contamination and heating over 70 °C play a major role in radon decrease.Related radium contents, physical parameters and major ions geochemistry are also presented for a comparison with published data.

Latest Pleistocene-Holocene sedimentary evolution from sediment records of the Tam Giang-Cau Hai coastal lagoon system, central Vietnam

The latest Pleistocene-Holocene sedimentary evolution was reconstructed from two boreholes collected in the Tam Giang-Cau Hai coastal lagoon region of central Vietnam. This research was based on analyzing radiocarbon dating, grain size, sedimentary structure, petrological components, and diatom assemblages. Besides, some high-resolution seismic data from the lagoon water body were interpreted to estimate Holocene sediment thickness. Sedimentary records of two boreholes revealed various sedimentary facies under the sea-level change since the Last Glacial Maximum (LGM): Fluvial channel facies, fluvial-lagoonal transition facies, lagoon facies, lagoonal-to-fluvial facies, and flood plain facies. Radiocarbon dating indicated that the coastal lagoon system possibly initiated around 8.8–8.5 cal kyr BP, corresponding to the meltwater pulse 1 C when saltwater intruded into the lagoon system. The borehole-sediment data combined with the high-resolution seismic data shows the thickness of Holocene sediments is approximately 20–35 m in the lagoon region. The study also suggested that the sandy barrier complex along the coast between the lagoon system and the open sea has been likely built during the transgression since 10–8.8 cal kyr BP. Additionally, five ecological zones were identified based on diatom assemblages in borehole HK02 indicating variations in marine and fluvial influence in the coastal lagoon system during the past 8.8 kyr: Dia-HK02–1 indicates a low presence of diatoms, suggesting a weak marine influence in the coastal lagoon system; Dia-HK02–02 shows the strongest marine influence and stable ecological conditions in the coastal lagoon system; Dia-HK02–03 demonstrates a partial decrease in marine influence; Dia-HK02–4 shows an increasing fluvial influence; and Dia-HK02–5 developed under completely dominated fluvial conditions on land.

Dual biomarker traceability and ecological risk assessment of centennial organic contamination in South Dongting Lake

Enhanced anthropogenic activity strength has altered the watershed particulate transport and material cycle resulting in organic pollutant deposition changes in Dongting Lake associated with unclear ecological risk. In the present study, dual biomarkers i.e. n-alkanes and polycyclic aromatic hydrocarbon (PAHs) were applied in the 210Pb-dated sediment cores for traceability of centennial organic pollutants in the lake mouth area. The partial least squares path model and risk quotients method were used to explore the controlling pathways and ecological risk. The results show a range of sedimentary organic carbon (C), nitrogen (N), and phosphorus (P) was at 1.76–185.66, 0.97–89.80, and 0.01–0.97 g m−2 yr−1 with total reserves of 51.68, 18.44, and 0.27 t ha−1, respectively, over the past 179 years. The presence of PAHs rapidly increased by 2.47 fold from 535.60 ng g−1, while PAHs and carcinogenic PAHs (ΣCPAHs) burial fluxes increased by about 6 and 5 folds, respectively. Accompanied by anthropogenic activities and climate change, the exotic sources gradually becoming predominant. The n-alkane diagnostic ratios indicated a shift of organic matter (OM) from autotrophic bacteria, algae, and phytoplankton-derived sources to macrophyte and terrestrial plants. The exotic origins rose to approximately 73.61 %, while endogenous sources decreased to 26.39 %. The direct effects of anthropogenic activities and their indirect negative impacts on climate and sedimentary structure are the key ways for sediment material loading. The nutrient accumulation in sediments coincides with the lake's eutrophication history over the past decades. The ΣCPAHs accounted for about 89.37 ± 17.14 % of the total TEQ, reflecting a strong ecological risk. The contribution of anthropogenic activities such as fuel usage, fertilizer application, hard pavement coverage, and OM loss from the ecosystem to the sources of organic pollutants and their component types may be a focus of attention in the middle reaches of the Yangtze River plain lake.

Water, environment, and health nexus: understanding the risk factors for waterborne diseases in communities along the Tano River Basin, Ghana.

Freshwater pollution is a major concern in Ghana, directly impacting human health. However, the underlying drivers of exposure and risks are not comprehensively understood, emphasizing the severity and impact of these diseases. This study assessed the interaction between water and human health, specifically focusing on the risk factors for waterborne diseases and the drivers of water pollution among residents near the Tano River Basin, Ghana. A sample size of 400 households was selected from five communities within the basin based on their proximity to the Tano River. In addition, the study combined both spatial and non-spatial data sources to map potential flood zones for the basin. The study found that inadequate sanitation, poor hygiene practices, and contamination from illegal mining were the primary causative factors of waterborne diseases. Additionally, floods and improper waste management significantly contributed to disease outbreaks. The flood susceptibility analysis indicated that areas highly susceptible to flooding cover 21.2% of the basin, predominantly in the southern part. The results highlight the urgent need for comprehensive interventions to address the drivers of waterborne diseases. This study will contribute to the local authorities in developing plans to prevent waterborne diseases and mitigate their economic and public health impacts.

Sustainable urban planning to control flood exposure in the coastal zones of China

ContextSustainable development in coastal zones faces escalating flood risk in the context of climate change and urbanization, and the rapid urban growth in flood zones has been one of the key drivers. Therefore, understanding the Urban Exposure to Flooding (UEF) and its future scenarios is important in coastal zones.ObjectivesThe objectives of this study were: (1) to assess the future dynamics of UEFs in China's coastal zones, and (2) to identify a sustainable way of urban planning in controlling the growth of UEFs.MethodsFuture UEFs in coastal China were assessed during 2020–2050 by combining urban expansion model, scenario analysis, and flood exposure assessment. Alternative scenarios were considered of shared socioeconomic pathways (SSPs), representative concentration pathways (RCPs), strategies of urban planning.ResultsThe results show that the 1000-year flood UEFs along coastal China was expected to grow under SSP2-RCP4.5 from 9,879 km2 in 2020 to 13,424 (12,997–13,981) km2 in 2050, representing an increment of 35.88% (31.56%–41.52%). Alternatively, the strategy of sustainable development planning could reduce the newly added UEF by 16.98% (15.63%–18.67%) in a 1000-year flood scenario.ConclusionsThe findings proved that the ways of urban growth matters in terms of affecting food exposure and risk and flood risk should be incorporated into urban planning for a sustainable landscape. The study could offer methodology and support for sustainable development strategies in reducing future urban flood risk.

Assessing Current Coastal Subsidence at Continental Scale: Insights From Europe Using the European Ground Motion Service

AbstractBeside climate‐change‐induced sea‐level rise (SLR), land subsidence can strongly amplify coastal risk in flood‐prone areas. Mapping and quantifying contemporary vertical land motion (VLM) at continental scales has long been a challenge due to the absence of gridded observational products covering these large domains. Here, we fill this gap by using the new European Ground Motion Service (EGMS) to assess the current state of coastal VLM in Europe. First, we compare the InSAR‐based EGMS Ortho (Level 3) with nearby global navigation satellite systems (GNSS) vertical velocity estimates and show that the geodetic reference frame used to calibrate EGMS strongly influences coastal vertical land velocity estimates at the millimeter per year level and this needs to be considered with caution. After adjusting the EGMS vertical velocity estimates to a more updated and accurate International Terrestrial Reference Frame (ITRF2014), we performed an assessment of VLM in European low elevation coastal flood plains (CFPs). We find that nearly half of the European CFP area is, on average, subsiding at a rate faster than 1 mm/yr. More importantly, we find that urban areas and populations located in the CFP experience a near −1 mm/yr VLM on average (excluding the uplifting Fennoscandia region). For harbors, the average VLM is even larger and increases to −1.5 mm/yr on average. This demonstrates the widespread importance of continental‐scale assessments based on InSAR and GNSS to better identify areas at higher risk from relative SLR due to coastal subsidence.

County-level carbon compensation zoning based on China's major function-oriented zones

Large but overlooked carbon inequalities among counties in China matter for the design of mitigation strategies. Here, we investigated the spatial heterogeneity of carbon inequality across 2236 county-level units nationwide from 2000 to 2020, refining carbon compensation zone types based on land functional zoning and estimating their carbon compensation values using a modified compensation model. Our results showed that China's carbon inequality consistently exceeded the cautionary threshold of 0.4 on the Gini coefficient. Significant spatial variations in carbon intensity were observed, notably concentrated in the North China Plain and Yangtze River Delta, indicating a pronounced core-periphery structure. The nonlinear relationships among carbon emission pressure (CEP), land use intensity (LUI), economy contributive coefficient (ECC), and ecological support coefficient (ESC) were identified. CEP and ECC posed initial increases followed by decreases with LUI, while ESC decreased with increasing LUI. The inverted U-curve between ECC and CEP suggested that most county-level cities have yet to reach the decoupling tipping point. Based on spatial comparative advantage, we identified 625 payment zones, 666 equilibrium zones, and 945 recipient zones, culminating in nine types of carbon compensation zones aligned with land functional objectives. Our study provides a new county-level carbon compensation zoning approach that can achieve carbon equity.

Quantitative impacts of dominant large-scale circulation systems on surface ozone pollution in China

Tropospheric ozone pollution has been worsened over most regions of China, adversely affecting human health and ecosystems. The long-term ozone concentration depends largely upon atmospheric circulations. Here, we conducted meteorological adjustment to quantitatively assess the influences of meteorological factors on the ozone evolution in China's seven city clusters during the warm season (April to October) from 2013 to 2020. Our analysis indicated that northern and eastern regions experienced ozone increases driven by emission changes. Southern regions, particularly the Pearl River Delta (PRD), exhibited ozone rise primarily due to meteorological conditions despite emission changes. In the Sichuan Basin (SCB) and Central Yangtze River Plain (CYP), where ozone levels decreased, meteorological conditions played a significant role in suppressing the ascent of ozone. Empirical orthogonal functions (EOF) analyses suggested that the spatiotemporal trend of meteorology-associated ozone was strongly correlated with the variation of East Asian Trough (EAT), South Asian High (SAH) and the western Pacific subtropical high (WPSH). The top three EOF patterns explained 33.4 %, 21.8 %, and 16.0 % of the total variance in meteorology-associated ozone. Absolute principal component scores-multiple linear regression (APCS-MLR) analyse quantitatively identified that enhanced EAT and SAH with a northward location of WPSH were favourable to surface ozone formation in central and eastern regions, but unfavourable to ozone formation in edge regions such as SCB.

Study of flood protection water levels for railway projects in the plains river network area

The Taihu Lake basin is characterised by a developed water system and a longitudinal river network, which is prone to flooding during the flood season. This poses a threat to the construction and operation of river-related railways, bridges, and other infrastructures, and therefore the design value of the water level of the river channel must be provided prior to the construction of roads and bridges in the basin. The Yanyi Railway traverses numerous river systems without the benefit of measured hydrological data. In order to address this deficiency, two methods were constructed using the Taihu Lake basin model: the historical water level frequency analysis method and the typical design storm method of the basin. These methods were employed to calculate the flood protection water level of each river under different design schemes and to analyze the reasons for the differences in the results. The results indicate that the water level results of the historical water level frequency analysis method are also applicable to the construction of the Yanyi Railway, provided that an economic perspective is taken.

Controlling Arsenic Cross-contamination in Multi-aquifer System of Gangetic Flood Plain Through Optimal Well Spacing Based on Aquifer Response Modelling—A Case Study from Buxar District and Neighbouring Areas, Bihar, India

Controlling Arsenic Cross-contamination in Multi-aquifer System of Gangetic Flood Plain Through Optimal Well Spacing Based on Aquifer Response Modelling—A Case Study from Buxar District and Neighbouring Areas, Bihar, India

Identifying Temporal Change in Urban Water Bodies Using OpenStreetMap and Landsat Imagery: A Study of Hangzhou City

As one of the most important ecosystems, the water body is losing water during the rapid development of the city. To understand the impacts on water body change during the rapid urbanization period, this study combines data from the OpenStreetMap platform with Landsat 5/Thematic Mapper images to effectively and accurately identify small urban water bodies. The findings indicate that the trained U-net convolutional neural network (U-Net) water body extraction model and loss function combining Focal Loss and Dice Loss adopted in this study demonstrate high precision in identifying water bodies within the main urban area of Hangzhou, with an accuracy rate of 94.3%. Trends of decrease in water areas with a continuous increase in landscape fragmentation, particularly for the plain river network, were observed from 1985 to 2010, indicating a weaker connection between water bodies resulting from rapid urbanization. Large patches of water bodies, such as natural lakes and big rivers, located at divisions at the edge of the city are susceptible to disappearing during the rapid outward expansion. However, due to the limitations and strict control of development, water bodies, referring to as wetland, slender canals, and plain river networks, in the traditional center division of the city, are preserved well. Combined with the random forest classification method and the U-Net water body extraction model, land use changes from 1985 to 2010 are calculated. Reclamation along the Qiantang River accounts for the largest conversion area between water bodies and cultivated land, constituting more than 90% of the total land use change area, followed by the conversion of water bodies into construction land, particularly in the northeast of Xixi Wetland. Notably, the conversion of various land use types within Xixi Wetland into construction land plays a significant role in the rise of the carbon footprint.

Predicting the geospatial distribution of Chinese rice nutrient element in regional scale for the geographical origin—A case study on the traceability of Japonica rice

AbstractEffective geographical origin discrimination of Chinese rice requires a large database of samples to ensure sufficient data for origin verification at a regional scale. In this study, environmental similarity was used to establish a spatial database of rice nutrient element, and then the validity of the database was verified using the back propagation artificial neural networks modeling (BPNN). The spatial distribution model of 14 rice nutrient element (Al, Ba, Ca, Cu, Cr, Fe, K, Mg, Mn, Mo, Na, Ni, Rb, and Zn) on regional scale was built using an environmental similarity method for the first time. Elemental concentrations of 692 samples were used to build a simulated geographical origin prediction model for northeastern (N‐E), middle to lower Yangtze River plain (Y‐R), southwestern (S‐W), and southeastern (S‐E) in China. The results indicated that the performance of the environmental similarity model for these four growing regions was S‐W > N‐E > S‐E > Y‐R based on the lowest ranking root mean square error (RMSE) for each region. For example, the RMSEs of Zn in S‐W, N‐E, S‐E, and Y‐R regions were 2.0, 2.4, 2.7, and 3.7 mg/kg, respectively. A case study on the traceability of Japonica rice was shown that Japonica rice could be discriminated with higher origin accuracy using a simulated database (91.8%) than by the actual database (87.0%) using the BPNN model. This indicates that a simulated rice element database could improve the accuracy of geographical origin discrimination for Chinese rice and potentially be applied to other large national‐scale crop datasets.

A Preliminary Study of Past Geological Disasters in the Trowulan Majapahit Cultural Heritage Area, Mojokerto Regency, East Java

Abstract Numerous sites found buried in the Trowulan Cultural Heritage Area makes the area suspected of being the capital of the Majapahit Kingdom (13-15th century). The condition of the buried site raises an assumption of a past catastrophic event that hit and buried part of Trowulan area, causing the downfall of the Majapahit Kingdom. This assumption is supported by the existence of several books and inscriptions from the Majapahit Kingdom period that record events interpreted as geological disasters. Although there is a lot of evidence, however, what kind of geological disaster that hit the Trowulan area is not known for certain. This study aims to identify what kind geological disasters that buried the Trowulan Capital area based on previous studies and GIS analysis. The results inferred that flash floods and volcanic eruptions contributed to the burial of Trowulan Capital Region, which is supported by the geographical conditions of the capital city of Trowulan where the northern part is a flood plain and the southern part is part of the Jatirejo alluvial fan. Stratigraphic data collection needs to be carried out in the future as supporting evidence to know the detailed sequence of disaster events and the direction of the disaster flow.

Urban flash flood prediction modelling using probabilistic and statistical approaches

The development of a detailed strategy to mitigate the negative consequences of any natural calamities depends on accurately identifying sensitive zones where natural hazards frequently happen. In the present investigations, three widely utilized probabilistic approaches viz., frequency ratio (FR), statistical index (SI), and weighting factor (WF) have been utilized for prediction of flsh flood susceptibility zones in the Coochbehar urban and peri-urban area (CUPUA) (area = 26.22 km2). Ten flash flood conditioning factors have been used in this assessment based on previous literatures and experts' opinions. In the FR model, 29.40 % area is observed in the high and very high flood zones, whereas 36.27 % and 31.16 % area is identified in SI and WF model, respectively. The FR model demonstrates that five conditioning factors, viz., topographic position index (TPI), land use and land cover (LULC), normalized difference vegetation index (NDVI), distance to drainage (DtD) and rainfall were highly impacted in flash flood prediction (FFP) analysis; in SI model, LULC is the major influencing parameter, and in WF model LULC, rainfall, NDVI, and distance to road (DtR) are the effective parameters. The success rate curve of the FR, SI and WF models manifest SI model has highest training (AUC=0.903) and prediction (AUC=0.925) accuracy, and FR and WF also have very good accuracy as their AUC values are 0.899 and 0.877 (in success rate curve) and 0.900 and 0.881 (in prediction rate curve). Therefore, the application of probabilistic approaches in this active flash flood-prone region is excellently performed, and the results of this study will help hydrologists, engineers, and water management administrators to control the areas that are extremely susceptible to flash floods and reduce possible damages.

Geophysical Investigation of Bulding Distress in Gashua, Nigeria

Gashua is the Headquarter of Bade local government in Yobe State, it has a population of about 125, 000 according to the 2006 population census. It is a densely populated town located in a flood plain within the Chad Basin. In an attempt to proffer solutions to the prevailing building distress in Gashua and its environs, this study was carried out to accurately characterize the subsurface geology of the area, thereby reducing the incidence of building failure in the area to minimum. In this study, electrical resistivity method was used to determine the causes of building distress and failure in Gashua and its environs. Vertical Electrical Sounding (VES) using Schlumberger array and Electrical Resistivity Tomography (ERT) were adopted for the study. The results of the VES survey showed that the area is composed of five geologic layers which are; the topsoil, clay, sand, sandy-clay, and sand. The ERT results showed that most of the building foundations in the study area were laid within the second layer which is a clay formation. The findings of this study showed that the building distress and failure which are common in the study area were caused by the volumetric changes of the clay formation due to hydrological dynamics. The clay formation absorbs water during the raining season and swells up, and during the dry season it shrinks, this changes in the volume of the clay formation underlying the building foundation in the study area induces a significant mechanical stress on the buildings leading to the formation of cracks, voids, fissures and fracturing of the buildings, which eventually culminate into collapse. In this study, electrical resistivity method of geophysical investigation has demonstrated to be a veritable tool for geotechnical soil evaluation. Based on the findings of this study, geophysical investigation of a proposed site...