Flood Layers Research Articles

Rice Planting Increases Biological Nitrogen Fixation in Acidic Soil and the Influence of Light and Flood Layer Thickness

Biological nitrogen fixation (BNF) varies in different soils and is impacted by rice planting. This study was conducted to investigate the extent of BNF in acidic soil planted with rice and to explore if the light and flood layer thickness affected the BNF. Soil and rice together were incubated in a 15N2-labeled closed chamber for whole growth period, and light and water depth effects were measured by labeling aboveground parts of rice plants in a plastic bag and labeling air in bottle without rice plants, respectively. The results showed that the total N fixation of soil and plant was 11.65 kg ha−1; nevertheless, it was only 2.11 kg ha−1 under fallow soil. In planted soil, plants and soil accounted for 25.1% and 74.9% of total 15N fixed, correspondingly. Soil NH4+-N concentration decreased due to uptake by the rice plants. There was higher available iron (Fe2+) in soil with rice plantings than in the fallow soil which was beneficial for BNF. Furthermore, 15N atom% in the roots was found higher than in the aboveground plant parts or leaves whether from experiment with whole rice-soil labeled in 15N2-enriched closed chamber or from that only rice aboveground parts labeled by 15N2, whereas water depth above the soil surface insignificantly influenced BNF without rice planting. Rice planting may significantly increase the amount of N fixation in acidic paddy soils. Further work regarding the role of rice plant and thickness of the water layer in BNF is highly important to gain an improved understanding of the N cycle in the rice ecosystem.

XRF and hyperspectral analyses as an automatic way to detect flood events in sediment cores

Long-term changes in flood activity have often been reconstructed to understand their relationships to climate changes. This requires identification of flood layers according to certain characteristics (e.g., texture, geochemical composition, grain-size) and then to count them using naked-eye observation. This method is, however, time-consuming, and intrinsically characterized by a low resolution that may lead to bias and misidentification. To overcome this limitation, high-resolution analytical approaches can be used, such as X-ray fluorescence spectroscopy (XRF), X-ray computed tomography, or hyperspectral imaging (HSI). When coupled with discriminant algorithms, HSI allows for automatic identification of event layers. Here, we propose a new method of flood layers identification and counting based on the combination of both HSI and XRF core scanner analyses, applied to a Lake Bourget (French Alps) sediment sequence. We use a hyperspectral sensor from the short wave-infrared spectral range to create a discrimination model between event layers and continuous sedimentation. This first step allows the estimation of a classification map, with a prediction accuracy of 0.96, and then the automatic reconstruction of a reliable chronicle of event layers (including their occurrence and deposit thicknesses). XRF signals are then used to discriminate flood layers among all identified event layers based on site-specific geochemical elements (in the case of Lake Bourget: Mn and Ti). This results in an automatically generated flood chronicle. Changes in flood occurrence and event thickness through time reconstructed from the automatically generated floods chronicle are in good agreement with the naked-eye-generated chronicle. In detail, differences rely on a larger number of detected flood events (i.e., increase of 9% of the number of layers detected) and a more precise layer thickness estimation, thanks to a higher resolution. Therefore, the developed methodology opens a promising avenue to increase both the efficiency (timesaving) and robustness (higher accuracy) of paleoflood reconstructions from lake sediments. Also, this methodology can be applied to identify any specific layers (e.g., varve, tephra, mass-movement turbidite, tsunami) and, thereby, it has a direct implication in paleolimnology, paleoflood hydrology and paleoseismology from sediment archives.

Geophysical Prospecting for Groundwater Resources in Phosphate Deposits (Morocco)

The Moroccan phosphate deposits are the largest in the world. Phosphatic layers are extracted in open-pit mines mainly in the sedimentary basins of Gantour and Ouled Abdoun in Central Morocco. The purpose of this study was to prospect and evaluate the water potential of aquifers incorporated in the phosphatic series using the following geophysical methods: Magnetic resonance sounding (MRS), electrical resistivity tomography (ERT), time-domain electromagnetics (TDEM), and frequency-domain electromagnetics (FDEM). The objective was, on the one hand, to contribute to the success of the drinking water supply program in rural areas around mining sites, and on the other hand, to delimit flooded layers in the phosphatic series to predict the necessary mining design for their extraction. The use of geophysical methods made it possible to stratigraphically locate the most important aquifers of the phosphatic series. Their hydraulic parameters can be evaluated using the MRS method while the mapping of their recharge areas is possible through FDEM surveys. The results obtained in two selected experimental zones in the mining sites of Youssoufia and Khouribga are discussed in this paper. The application of the implemented approach to large phosphate mines is in progress in partnership with the mining industry.

Physical simulation experiments of remaining oil distribution and production in alluvial fans controlled by dynamic and static factors

In order to study the remaining oil distribution and production in alluvial fans controlled by both static geologic factors and dynamic development factors, 2D and 3D macroscopic physical models have been constructed for the alluvial fan reservoirs in the eastern part of Cangdong sag, Bohai Bay Basin, China. Through considering static reservoir architecture and dynamic displacement rate, perforation position, well type, and well pattern, 7 water flooding physical simulation experiments have been finished, and the remaining oil distribution and production in oilfields with ultra-high water cut controlled by both dynamic and static factors were revealed. The study shows that without considering the economic benefits, drilling horizontal well, drilling infilled vertical well, increasing displacement rate, and plugging off water flooded layers at the initial stage of ultra-high water cut exhibited decreased performance in remaining oil production. After the dynamic factors adjustment, the remaining oil distribution and production is mainly controlled by the interlayer position, reservoir rhythm and the combination relationship between dynamic and static factors. When more injector-producer groups are located in the same single sand body, and the oil wells are uniformly drilled in single sand of different types, the oil recovery efficiency will be higher, and the distribution of the remaining oil will be more uniform. According to the experimental results, the remaining oil controlled by braided sand island and braided river channel could be divided into three types, and the corresponding measures to tap the potential were proposed.

Interannual to millennial‐scale variability of River Ammer floods and its relationship with solar forcing

AbstractThe relationship between River Ammer flood frequency variability, extreme summer climate over Europe, and solar forcing is investigated. First, we used observational data to evaluate extreme weather and climate anomaly patterns associated with flood and solar forcing as well as the possible dynamical mechanisms behind them. Then, the annual resolution flood layer record from the Lake Ammer sediments is analysed to evaluate millennial‐scale variability of floods and possible related extreme climate patterns back to 5,500 years BP. A composite analysis reveals that observed River Ammer flood frequency variability at interannual to multidecadal time scales is connected to large‐scale extreme precipitation and temperature patterns. From a synoptic‐scale perspective, the extreme precipitation pattern associated with floods is related to an increase in the frequency of high upper‐level potential vorticity (PV) events over western Europe and a decrease over eastern Europe and western Russia. Increased (decreased) frequency of upper‐level high PV events is related to more (less) surface extreme precipitation occurrence. Furthermore, we show that increased frequency of upper‐level high PV events over western Europe is associated with enhanced blocking activity over eastern Europe. Therefore, the out of phase interannual to millennial‐scale variations of River Ammer flood frequency and solar irradiance, as presented in previous studies, can be explained by a solar modulation of eastern European‐western Russia summer blocking and associated upstream upper‐level wave breaking activity. In addition, we identify two distinct quasi‐periodic signals in both frequency of Lake Ammer flood layer and solar irradiance records with periods of ~900 years and ~2,300 years. We argue that similar cycles should dominate millennial‐scale variations of blocking activity in eastern Europe‐western Russia as well as extreme precipitation and flood frequency variability over central and western Europe during the last ~5,500 years.

The Impacts of Flood, Drought, and Turbidites on Organic Carbon Burial Over the Past 2,000 years in the Santa Barbara Basin, California

AbstractClimate conditions and instantaneous depositional events can influence the relative contribution of sediments from terrestrial and marine environments and ultimately the quantity and composition of carbon buried in the sediment record. Here, we analyze the elemental, isotopic, and organic geochemical composition of marine sediments to identify terrestrial and marine sources in sediment horizons associated with droughts, turbidites, and floods in the Santa Barbara Basin (SBB), California, during the last 2,000 years. Stable isotopes (δ13C and δ15N) indicate that more terrestrial organic carbon (OC) was deposited during floods relative to background sediment, while bulk C to nitrogen (C/N) ratios remained relatively constant (~10). Long‐chain n‐alkanes (C27, C29, C31, and C33), characteristic of terrestrial OC, dominated all types of sediment deposition but were 4 times more abundant in flood layers. Marine algae (C15, C17, and C19) and macrophytes (C21 and C23) were also 2 times higher in flood versus background sediments. Turbidites contained twice the terrestrial n‐alkanes relative to background sediment. Conversely, drought intervals were only distinguishable from background sediment by their higher proportion of marine algal n‐alkanes. Combined, our data indicate that 15% of the total OC buried in SBB over the past 2,000 years was deposited during 11 flood events where the sediment was mostly terrestrially derived, and another 12% of deep sediment OC burial was derived from shelf remobilization during six turbidite events. Relative to twentieth century river runoff, our data suggest that floods result in considerable terrestrial OC burial on the continental margins of California.

Surface flooding of Antarctic summer sea ice

AbstractThe surface flooding of Antarctic sea ice in summer covers 50% or more of the sea-ice area in the major summer ice packs, the western Weddell and the Bellingshausen-Amundsen Seas. Two CRREL ice mass-balance buoys were deployed on the Amundsen Sea pack in late December 2010 from the icebreaker Oden, bridging the summer period (January–February 2011). Temperature records from thermistors embedded vertically in the snow and ice showed progressive increases in the depth of the flooded layer (up to 0.3–0.35 m) on the ice cover during January and February. While the snow depth was relatively unchanged from accumulation (<10 cm), ice thickness decreased by up to a meter from bottom melting during this period. Contemporaneous with the high bottom melting, under-ice water temperatures up to 1°C above the freezing point were found. The high temperature arises from solar heating of the upper mixed layer which can occur when ice concentration in the local area falls and lower albedo ocean water is exposed to radiative heating. The higher proportion of snow ice found in the Amundsen Sea pack ice therefore results from both winter snowfall and summer ice bottom melt found here that can lead to extensive surface flooding.

Development of an Automated Tool for Delineation of Flood Footprints from SAR Imagery for Rapid Disaster Response: A Case Study

Floods are one of the most common natural disasters. In recent times, microwave synthetic aperture radar (SAR) satellite images have been used widely for mapping flood affected areas due to its all-weather capability and acquisition during day and night. Here, in this paper, an automated algorithm is proposed to delineate flood extent from SAR images without any human intervention. The algorithm consists of pre-processing steps like applying orbit file, calibrate to sigma naught, speckle filtering, terrain correction and linear to decibel conversion. The water layer is delineated using multi-segmentation and Otsu’s thresholding technique. Further, flood layer is extracted by postprocessing steps using majority filter, applying permanent water body mask and eliminating hill shadows. The algorithm is tested on a significant number of satellite images covering floods in India, which are having diverse terrain and flooding patterns. In this paper, the steps involved in delineating flood from SAR image of VH polarization from SENTINEL-1 satellite covering chronic flood-prone stretch of part of Ganga River in Bihar state is presented. Accuracy assessment is carried out with the flood layer derived from RADARSAT SAR HV polarized data acquired on the same day and an accuracy of about 96% is obtained. The total processing time taken for the extraction of the flood layer is 9 min. This automation process is beneficial for the generation of rapid flood inundation maps, with high accuracy, which is helpful for flood monitoring and relief management during a disaster.

Identification method of water-flooded layer based on analytic hierarchy process——Taking the Keshang Formation reservoir in the J188 well area as an example

Most oil fields in China have entered the high water cut stage, the identification of water flooded layers is a very important task. At present, the identification of water-flooded layers usually adopts the combination of qualitative method and quantitative method to carry out the work. However, the qualitative method is difficult to be characterized by quantitative numerical values, so the work efficiency is very low; the quantitative method needs to be taken in the actual operation. The oil-water relative permeability of the reservoir, the viscosity of the oil and water, and the original oil saturation, the calculation accuracy of these parameters are inevitably large errors. This paper explores a semi-quantitative method to overcome the insufficiency of qualitative methods, the simplification of quantitative parameters, and the error of water-flooded layer identification. The analytic hierarchy process was used to identify the water-flooded layer in the Keshang Formation reservoir in the 188 well area. The water production rate, oil saturation, production index and relative permeability index were integrated into a comprehensive water-flooded layer identification index. The results show that the total water-flooded layer identification coincidence rate reaches 70%. The method of water flooded layer identification based on analytic hierarchy process is feasible.

The Application of the Fisher Discriminant Method in Water Flooded Layer Discriminant

The Application of the Fisher Discriminant Method in Water Flooded Layer Discriminant

Reclaiming Tropical Saline-Sodic Soils with Gypsum and Cow Manure

Saline-sodic soils are a major impediment for agricultural production in semi-arid regions. Salinity and sodicity drastically reduce agricultural crop yields, damage farm equipment, jeopardize food security, and render soils unusable for agriculture. However, many farmers in developing semi-arid regions cannot afford expensive amendments to reclaim saline-sodic soils. Furthermore, existing research does not cover soil types (e.g., Luvisols and Lixisols) that are found in many semi-arid regions of South America. Therefore, we used percolation columns to evaluate the effect of inexpensive chemical and organic amendments (gypsum and cow manure) on the reclamation of saline-sodic soils in the northeast of Brazil. Soil samples from two layers (0–20 cm and 20–40 cm in depth) were collected and placed in percolation columns. Then, we applied gypsum into the columns, with and without cow manure. The experiment followed a complete randomized design with three replications. The chemical amendment treatments included a control and four combinations of gypsum and cow manure. Percolation columns were subjected to a constant flood layer of 55 mm. We evaluated the effectiveness of sodic soil reclamation treatments via changes in soil hydraulic conductivity, chemical composition (cations and anions), electrical conductivity of the saturated soil-paste extract, pH, and the exchangeable sodium percentage. These results suggest that the combined use of gypsum and cow manure is better to reduce soil sodicity, improve soil chemical properties, and increase water infiltration than gypsum alone. Cow manure at 40 ton ha−1 was better than at 80 ton ha−1 to reduce the sodium adsorption ratio.

Magnetic detection of paleoflood layers in stalagmites and implications for historical land use changes

Flooding events are major natural hazards that present significant risk to communities worldwide. Calculations of flood recurrence rate through time are important tools for regulating land use, determining insurance rates, and for the design and construction of levees and dams. Typically, flood recurrence rates are based on limited historical data or on evidence preserved in the geologic record as overbank deposits, tree ring scars, or high water scour marks. However, these approaches are either limited in their ability to produce continuous time series of flooding events or do not consider the effects of regional land use change. Here we use scanning superconducting quantum interference device (SQUID) microscopy to rapidly image the magnetization associated with flood layers in a polished surface of an annually laminated stalagmite from Spring Valley Caverns (SVC) in southeastern Minnesota. A time series of magnetization peaks, each of which corresponds to a flooding event, yields an average flood recurrence rate of ≤5 events per century for the last 500 years. This rate increases to ∼7 events per century since 1900, coincident with historical timber and agricultural land-use changes in Minnesota. This approach produces a continuous record of well-dated, extreme-precipitation events that can be examined within the context of land use change.

Convergent human and climate forcing of late-Holocene flooding in Northwest England

Concern is growing that climate change may amplify global flood risk but short hydrological data series hamper hazard assessment. Lake sediment reconstructions are capturing a fuller picture of rare, high-magnitude events but the UK has produced few lake palaeoflood records. We report the longest lake-derived flood reconstruction for the UK to date, a 1500-year record from Brotherswater, northwest England. Its catchment is well-suited physiographically to palaeoflood research, but its homogeneous, dark brown sediment matrix precludes visual identification of flood layers. Instead, an outlier detection routine applied to high-resolution particle size measurements showed a >90% match, in stratigraphic sequence, to measured high river flows. Our late-Holocene palaeoflood reconstruction reveals nine multi-decadal periods of more frequent flooding (510–630 CE, 890–960, 990–1080, 1470–1560, 1590–1620, 1650–1710, 1740–1770, 1830–1890 and 1920–2012), and these show a significant association with negative winter North Atlantic Oscillation (wNAO) phasing and some synchrony with solar minima. These flood-rich episodes also overlap with local and regional land-use intensification, which we propose has amplified the flood signal by creating a more efficient catchment sediment conveyor and more rapid hillslope-channel hydrological connectivity. Disentangling anthropogenic and climatic drivers is a challenge but anthropogenic landscape transformation should evidently not be underestimated in palaeoflood reconstructions. Our paper also demonstrates that flood histories can be extracted from the numerous lakes worldwide containing organic-rich, visually homogeneous sediments. This transformative evidence base should lead to more reliable assessments of flood frequency and risks to ecosystems and infrastructure.

EFFICIENCY OF OIL RESERVOIR CYCLIC IMPACT IN C-VI FORMATION AT ASHITSKY AREA, ARLAN OIL FIELD

Background The work is devoted to the study of the effectiveness of cyclic impact on the reservoir deposits of the C-VI Ashit experimental site of the Arlansky oil field. Changes in hydrodynamic pressure during cyclic exposure are taken into account. At the present stage of the development of oil fields it’s necessary to use all promising methods for oil recovery increasing. One of the known methods is still a hydrodynamic method of influence on the reservoir. In this regard, the calculations of the cyclic impact on the reservoir require additional calculation refinements, resulting in reservoir replacement by a two-layer model. Aims and Objectives To calculate the effects of this impact on the studied reservoir using a two-layer model. Results The elastic-capillary cyclic method of waterflooding is based on a periodic change in the conditions of exposure to heterogeneous reservoirs, in which an unsteady distribution of reservoir pressure is created and an unsteady movement of liquids and gas occurs. To study the effectiveness of the cyclic impact on the oil reservoir on the example of the Ashit area of the Arlansky oil field, a two-layer model consisting of a water-cut and oil-saturated layer is considered. The model considers the behavior of the deposit when exposed to a pressure pulse. The total interlayer fluid flow from the non-watered and flooded layers is calculated. Calculates the parameters of the equipment required for cyclic exposure. The paper concludes that it is possible to apply a cyclic impact on the C-VI stratum of the Ashtitsky experimental section of the Arlansky field in order to increase oil recovery.

Retention of alluvial sediment in the tidal delta of a river draining a small, mountainous coastal watershed

Small mountainous coastal watersheds are thought to be responsible for transporting disproportionately large volumes of sediment to the global ocean. In comparison with low-relief passive margin rivers, their geologic setting is associated with high rates of sediment production, high peak flows due to uniformity in runoff lag-times, and limited floodplain development. However, mountainous watersheds are often associated with estuarine deltas, and because the stream gauges used to calculate water and sediment fluxes tend to be located above the head of tides, the relative magnitude of sediment discharged to the ocean vs. retained in deltas is uncertain. The aim of this study was to determine the estuarine trap efficiency for the Salinas River in central California (USA), a watershed known both for its extremely high rate of sediment production and its extensive lowland delta, thereby helping to resolve the role of estuarine deltas in ocean sediment discharge. Sediment retention rates were calculated for the Late Holocene, using soil maps to estimate the areal extent of the delta prior to land reclamation, and radionuclide, pollen, pollution, and flood chronologies in concert with sediment bulk density measurements to constrain deposition rates. Results suggest that less than 1% of the sediment delivered to the coastal zone by the river was retained in the estuarine delta. Deposition rates distant from distributary channels matched long-term rates of sea level rise, suggesting that the formation of accommodation space acted as a primary control on sediment accretion. However, along tidal-fluvial distributary channels, accretion rates were much greater, and discrete flood layers were present, suggesting that accretion along distributaries was driven by flood events. In addition, long-term variability in sediment accretion rates broadly matched other records of alluvial flooding in central and southern California, suggesting that high precipitation intervals leave an imprint – although subtle – in the sedimentary record of estuaries. By documenting high sediment discharge to the ocean (99% of fluvial load), this study highlights the importance of small mountainous watersheds in global oceanic sediment transport, and further emphasizes the joint roles of accommodation space formation and sediment supply in controlling rates of estuarine sediment accretion.

Diagenesis and iron paleo-redox proxies: New perspectives from magnetic and iron speciation analyses in the Santa Barbara Basin

Sedimentary redox proxies are usually employed to reconstruct the paleo-redox conditions of bottom water environments, assuming that porewater and bottom water dissolved oxygen concentrations are similar. Using a combination of geochemical and magnetic techniques, we investigate the relationship between iron speciation and mineralogy in recent (~1760–2009 CE) sediments retrieved from the Santa Barbara Basin (SBB) – a modern silled basin with low-oxygen (dissolved O2 < 10 μmol/kg) and sporadically anoxic (no O2 detected) bottom waters. Magnetic analyses reveal that biogenic magnetite is preserved in SBB sulfidic porewaters on at least decadal to centennial time scales. Highly-reactive Fe (oxyhydr)oxides remain preserved despite observed sulfidic porewaters, indicating incomplete pyrite conversion, and producing low Fepy [pyrite Fe]/FeHR ratios. We attribute this observation to restricted porewater reaction kinetics under high sedimentation rates. Our results also reveal non-steady state diagenesis caused by instantaneous depositional events (e.g., turbidites and flood layers). The most reducing water column suggested by Fe speciation coincided with the Macoma layer, where in situ colonization of hypoxia-intolerant bivalve shells argues for the most oxygenated bottom water in the 250 year record. A turbidite potentially introduced fresh unsulfidized FeHR that buffered upward-diffusing sulfide from underlying sediments. Subsequent pyrite precipitation following re-establishment of sulfidic porewaters could have facilitated a “false positive” interpretation. In comparison, redox-sensitive metal enrichments (MoEF, UEF, and ReEF) were not obscured by post-depositional diagenesis and appear to accurately record redox geochemistry at the sediment-water interface.

Fingerprint of tropical climate variability and sea level in sediments of the Cariaco Basin during the last glacial period

AbstractHigh‐resolution palaeorecords of climate are critical to improving current understanding of climate variability, its sensitivity and impact on the environment in the past and in the future. Sediments from the Cariaco Basin off the coast of Venezuela have proven to be sensitive recorders of tropical palaeoclimate variability down to an annual scale. However, the fingerprint of climate and sea level in the sediments of the last glacial period is still not completely understood. In this study, lamination analysis of sediments from the Cariaco Basin is extended to the last glacial period. Detailed sedimentological and geochemical analysis (laser ablation–inductively coupled plasma–mass spectrometry) reveals couplets of light‐coloured, terrigenous‐rich and dark‐coloured, biogenic opal‐rich laminae, which are interpreted to reflect the seasonal migration of the Intertropical Convergence Zone. In addition, a previously undescribed, nearly pure terrigenous lamina type is observed, which is referred to hereafter as a ‘C‐layer’. The C‐layers in the sedimentary sequence are interpreted as flood layers that originate from local rivers. The occurrence of these C‐layers is investigated for two core locations in the Cariaco Basin over the last 110 kyr by continuous X‐ray fluorescence scanning. Dansgaard–Oeschger oscillations are most clearly traced by proxies reflecting productivity and marine organic matter content of the sediment. In contrast, the abundance of terrigenous material differs at times between the two sites. On an interglacial to glacial timescale, the ability to record events causing C‐layers is likely to be influenced by changes in sea level and source proximity. On a millennial scale, both sediment cores contain more C‐layers during warmer interstadials compared with colder stadials during Marine Isotope Stage 3. This finding implies that interstadials were not only wetter than stadials, but probably also characterized by increased rainfall variability, leading to an enhanced frequency of flooding events in the hinterland of the Cariaco Basin.

The impact of large to extreme flood events on floodplain evolution of the middle and lower reaches of the Yangtze River, China

Fluvial floodplain evolution is poorly understood despite its importance in sediment deposition, the carbon cycle, and the unique ecosystems it represents. Here we present how different magnitude and frequency of river floods contribute to floodplain evolution by analyzing three profiles of the middle and lower reaches of the Yangtze River. To investigate the formation of the Yangtze flood deposits we determine the percentage of flood events with different magnitude that can be identified from sediment cores and analyze their contribution to floodplain deposition. Our study demonstrates that magnitude of flood events strongly controls the identifiability of flood event deposition, and therefore the evolution of floodplains. Analyses show that detectability of flood layers resulted from large floods is remarkably influenced by sedimentation rates within the floodplain. High occurrence frequency of large to extreme flood events tend to correspond to high sedimentation rates, regardless of decreasing suspended sediment loads over the wet season. This implies that frequent large to extreme floods can counterbalance the decrease in suspended sediment load to maintain a high sedimentation rate in the floodplain. High flood stage is a principal factor that accounts for acceleration of floodplain sedimentation induced by large to extreme floods in the middle and lower Yangtze River. However, acceleration of sedimentation is limited by the quantity of sediment supply.

Factors influencing flashflood deposit preservation in shallow marine sediments of a hyperarid environment

Flashfloods entering marine basins can introduce large quantities of terrigenous sediment that deposit on the shallow seafloor. Over time, biological and physical disturbances can induce post-depositional sediment transport to deeper depths. In the hyperarid desert region surrounding Eilat, Israel, flashfloods discharge into the northern Gulf of Eilat-Aqaba, Red Sea episodically. Their deposits may leave useful records of flood events in the marine sediment record. What is poorly understood, however, are the processes of post-depositional alteration of flashflood sediments and the resulting effects on the preservation of the deposits. To address this knowledge gap, short sediment cores (~15–30 cm length, 13 m water depth) were collected at bi/tri-monthly intervals following two different flashflood events in the Gulf of Eilat-Aqaba. Concurrently, mechanisms for resuspension, transport, and vertical mixing of flashflood sediments were investigated by measuring near-bottom water currents and suspended sediment concentrations, photographing demersal fish activities, and measuring the depths and magnitudes of bioturbation using fluorescent sediment tracers. The aim was to record the changing grain size of surface flashflood sediments over time, and identify correlative physical and biological factors. The results show that the original fine-grained flashflood deposits coarsened rapidly following each event. Of the mechanisms recorded, currents generally were too weak to entrain sediment, but did influence the transport of sediment in suspension to deeper depths. Demersal fish resuspended sediment when present, and bioturbation was strongest in the upper 2 cm of the seabed. Despite the rapid reworking of surficial sediments and dissipation of surface flood layers, irregular lenses of fine sediment persisted within the shallow seafloor (down core). Deposition within seafloor holes and depressions, and rapid burial by biologically constructed sediment mounds and ensuing flashflood deposits are proposed as mechanisms for this patchy, localized preservation of flood layers. These findings are useful for identification and interpretation of isolated fine-grained layers in older sedimentary deposits, and for understanding the dynamics influencing the marine sediment stratigraphy in arid, coastal environments.

Improvement and Validation of NASA/MODIS NRT Global Flood Mapping

The remote-sensing based Flood Crop Loss Assessment Service System (RF-CLASS) is a web service based system developed and managed by the Center for Spatial Information Science and Systems (CSISS). The system uses Moderate Resolution Imaging Spectroradiometer (MODIS)-based flood data, which was implemented by the Dartmouth Flood Observatory (DFO), to provide an estimation of crop loss from floods. However, due to the spectral similarity between water and shadow, a noticeable amount of false classification of shadow can be found in the DFO flood products. Traditional methods can be utilized to remove cloud shadow and part of mountain shadow. This paper aims to develop an algorithm to filter out noise from permanent mountain shadow in the flood layer. The result indicates that mountain shadow was significantly removed by using the proposed approach. In addition, the gold standard test indicated a small number of actual water surfaces were misidentified by the proposed algorithm. Furthermore, experiments also suggest that increasing the spatial resolution of the slope helped reduce more noise in mountains. The proposed algorithm achieved acceptable overall accuracy (&gt;80%) in all different filters and higher overall accuracies were observed when using lower slope filters. This research is one of the very first discussions on identifying false flood classification from terrain shadow by using the highly efficient method.