Surface Flooding Research Articles

Using CYGNSS Data to Monitor China’s Flood Inundation during Typhoon and Extreme Precipitation Events in 2017

NASA’s Cyclone Global Navigation Satellite System (CYGNSS) mission, launched in 2016, is a small satellite constellation designed to measure the ocean surface wind speed in hurricanes and tropical cyclones. To explore its additional capabilities for applications on the land surface, this study investigated the advantages and limitations of using CYGNSS data to monitor flood inundation during typhoon and extreme precipitation events in southeast China in 2017. The results showed that despite the lack of quantitative evaluation, the CYGNSS-derived surface reflectivity (SR) and flood inundation area was qualitatively consistent with the Global Precipitation Measurement (GPM)-derived precipitation and Soil Moisture Active Passive (SMAP)/Soil Moisture and Ocean Salinity (SMOS)-derived total brightness temperature at circular polarization ( T b C ). The results provide supporting evidence for further designation of Global Navigation Satellite System (GNSS) reflectometry (GNSS-R) constellations to monitor land surface hydrology.

Variations in Surface Albedo Arising from Flooding and Desiccation Cycles on the Bonneville Salt Flats, Utah

AbstractDesert playas, such as those in northern Utah, form a landscape often in stark contrast to surrounding mountain ranges due to their minimal topographic relief, lack of vegetation, and saline soils. Dry highly reflective halite surfaces, which make up many of the desert playas in northern Utah, are generally characterized by a surface albedo over 40%. However, their albedo can be reduced abruptly to less than 20% by flooding due to rainfall, runoff from surrounding higher terrain, or surface winds transporting shallow water across the playas. A weather station installed during September 2016 to study the Bonneville Salt Flats (BSF) in northern Utah provides estimates of surface albedo that can be related to cycles of flooding and desiccation of the halite surface. The normalized difference water index (NDWI) derived from the MODIS MOD09A1 land surface reflectance product estimates the fractional coverage of surface water over the BSF. NDWI values computed over 8-day periods from 2000 to 2018 highlight year-to-year and seasonal variations in playa flooding events over the BSF. Periods of playa flooding were observed with both ground-based observations and NDWI with sharp reductions in albedo when the surface is flooded.

Flooding as a cause of ungulate mortality in floodplain forests in Croatia

Floodplain forests with regular flooding regimes are the largest natural retentions areas in Croatia and are important as natural habitats for ungulates. The aim of this study was to determine the scale of mortality caused by flooding within these forests. Over a 10-year period, data on ungulate mortality (red deer, roe deer and wild boar), flood duration and flooded surface area were recorded. The study was conducted in primary (Posavske Sume—RET I) and secondary (Opeke II—RET II) retention areas within Lonjsko Polje Nature Park (Sava River region, Croatia). The longest flood period and the largest flooded surface area were recorded in RET I. Total ungulate mortality was 749 individuals, with 482 individuals in RET I and 267 individuals in RET II, predominantly wild boar. Flood mortality did not differ by gender. The highest mortality of wild boar was recorded for the juvenile and yearling age classes. Low mortality of red and roe deer can be attributed to their body size and ecological niches. Differences in mortality between the primary and secondary retention areas corresponded to differences in flood regimes, flood column heights and micro relief structures. In both retention areas, wild boar mortality and flood duration, i.e. flooded surface area, were positively correlated. Because the growth rate of the analysed ungulate populations was higher than the recorded mortality, no long-term effect of floods is expected on species abundance in these areas.

Response of growth, yield and water use efficiency of winter wheat to different irrigation methods and scheduling in North China Plain

The knowledge of suitable irrigation methods coupled with effective irrigation scheduling to improve agricultural water use efficiency has become increasingly necessary for farmers in the North China Plain to ameliorate the severe water shortage that has threatened winter wheat (Triticum aestivum L) production. A two-season field experiment was conducted in a winter wheat field amide to compare the efficiency of three irrigation methods sprinkler irrigation (SI), surface drip irrigation (SDI) and flood irrigation (FI) under three irrigation schedules by irrigating while soil moisture decreased to 70%, 60% and 50% of the field capacity respectively. It was found that irrigation methods with suitable irrigation scheduling indeed have the potential to balance the optimal yield and water use efficiency. The results showed that irrigating 180.3 mm and 175.2 mm of water in the two studied seasons respectively was optimal to achieve the highest grain yield. For SDI and SI, this could be achieved by irrigating six times each with 30 mm of water, while for FI irrigating three times each with 60 mm of water gave comparable results. Our studies suggested that irrigating while soil moisture reduced to 60% of the field capacity by SDI was the best in all aspects compared with other irrigation methods and irrigation schedules.

Urban flood estimation and evaluation of the performance of an Urban Drainage system in a Semi-Arid Urban Area Using SWMM.

Estimation of urban runoff peak and volume is a fundamental step in determining the transferring capacity of urban drainage systems. The main aim of this study was to present an application of the Storm Water Management Model (SWMM) in order to estimate urban flooding of a semi-arid area (Zanjan city in the northwest of Iran). The performance of an urban drainage system in the study area was also investigated. According to the results, SWMM is an effective tool for urban flood estimation in a semi-arid area. In this study, urban peak flow was simulated via a calibrated model with acceptable accuracy. Based on the results of the model simulation, the capacity of the main canals in the study area is sufficient for peak runoff transferring for a design storm with 50-year return periods, without retrofitting. Whereas, based on local observation and model results, localized and surface flooding can be observed in some urban areas. PRACTITIONER POINTS: In this study, urban flooding of a semi-arid area located in the northwest of Iran was estimated via a water Management Model (SWMM). According to the results, the SWMM model has considerable predictive capability for runoff evaluation in semi-arid regions when it is correctly calibrated via measured data. Also Modeling results showed that the main urban drainage network of the study watershed has an acceptable capacity for transmitting the runoff and flood waters, however the large amount of building materials and garbage that have been dumped in the canals could cause inundation problems.

Performance assessment of two-dimensional hydraulic models for generation of flood inundation maps in mountain river basins

Hydraulic models for the generation of flood inundation maps are not commonly applied in mountain river basins because of the difficulty in modeling the hydraulic behavior and the complex topography. This paper presents a comparative analysis of the performance of four two-dimensional hydraulic models (HEC-RAS 2D, Iber 2D, Flood Modeller 2D, and PCSWMM 2D) with respect to the generation of flood inundation maps. The study area covers a 5-km reach of the Santa Bárbara River located in the Ecuadorian Andes, at 2330 masl, in Gualaceo. The model's performance was evaluated based on the water surface elevation and flood extent, in terms of the mean absolute difference and measure of fit. The analysis revealed that, for a given case, Iber 2D has the best performance in simulating the water level and inundation for flood events with 20- and 50-year return periods, respectively, followed by Flood Modeller 2D, HEC-RAS 2D, and PCSWMM 2D in terms of their performance. Grid resolution, the way in which hydraulic structures are mimicked, the model code, and the default value of the parameters are considered the main sources of prediction uncertainty.

Experimental investigation to estimate the discharge coefficient of a grate inlet under surcharge conditions

ABSTRACTPressure pipe flow conditions appear in sewer systems when flow exceeds the hydraulic capacity of the conduit, causing some outflow to be produced. In these cases, water exits through manholes and inlets causing surface flooding. According to some recent studies, the flow leaving the pressured sewer can be estimated assuming orifice flow conditions although it requires the use of proper values of the discharge coefficient in order to obtain realistic results. In this paper, an experimental approach to calculate discharge coefficients through an inlet for surcharged pipe conditions is presented. Tests were carried out using a real laboratory platform simulating a road lane. Different surcharged flows through the inlet from 10 to 50 l/s were considered. The range of the obtained discharge coefficient has been between 0.13 and 0.41 for surcharged flow from 10 l/s to 50 l/s. Sensitivity analysis demonstrated that discharge coefficients can be considered constant for any street longitudinal slope.

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.

Characterizations and accumulation of lacustrine source rocks in the Zhu I Depression, Pearl River Mouth Basin, China

The study of source rocks is a key component in the exploration and discovery of hydrocarbon plays in the offshore petroliferous basins of China. Geochemical analyses, drilling, seismic, and microfossil data were integrated to document the formation mechanism of lacustrine source rocks contained in the Wenchang Formation in the Zhu I Depression of the Pearl River Mouth Basin, China. Several factors that control the development of lacustrine source rocks were evaluated in this study, including tectonics, sedimentary conditions, palaeoclimate, the supply of organic matter, and redox conditions. The deposition and occurrence of source rocks is a combined function of these factors. Lacustrine source rocks are characterized by high organic matter contents (average TOC value = 1.33 wt.%) and are dominated by type I and type II1–2 kerogen, which primarily originate from planktonic algae. The rifting of basement rocks, syn‐sedimentary faults, and palaeoclimate played significant roles in controlling the geochemical properties of the source rocks (e.g., controlling the abundance and types of organic matter). The Eocene lacustrine source rocks were deposited when the palaeoclimate was characterized by humid to semi‐humid, subtropical to tropical weather that did not have a stable temperature or humidity. Controlled by large‐scale faults, “Half‐graben patterns” and “Graben patterns” are the two main palaeotopographic patterns where the thermal stratification of deep lake water resulted in flourishing planktonic algae in its surface zones. Dysoxic to anoxic conditions prevailed during the deposition of the lacustrine source rocks. An underfilled basin situation caused the occurrence of abundant organic matter during the period of maximum surface flooding.

Evaluation of evolutionary algorithms for the optimization of storm water drainage network for an urbanized area

The studies pertaining to urban storm water drainage system have picked up importance lately in light of pluvial flooding. The flooding is mostly due to urban expansion, reduction in infiltration rate and environmental change. In order to minimize flooding, hydrologists are using conceptual rainfall–runoff models as a tool for predicting surface runoff and flood forecasting. Manual calibration is often a tedious process because of the involved subjectivity, which makes the automatic approach more preferable. In this study, three evolutionary algorithms (EAs), namely SFLA, GA and PSO, were used to calibrate SWMM parameters for the two study areas of the highly urbanized catchments of Delhi, India. The work incorporates auto-tuning of a widely used SWMM, via internal coupling of SWMM with all three EAs in MATLAB environment separately. Results were tested using statistical parameters, i.e., Nash–Sutcliffe efficiency (NSE), Percent Bias (PBIAS) and root-mean-square error–observations standard deviation ratio (RSR). GA results were in good agreement with the observed data in both the study area with NSE and PBIAS values lying between 0.60 and 0.91, and 1.29 and 7.41%, respectively. Also, RSR value was near zero, indicating reasonably good model performance. Subsequently, the model reasonably predicted the flooding hotspots that should be controlled to prevent any possible inundation of the surrounding areas. SFLA results were also promising, but better than PSO. Thus, the approach has demonstrated the potential use and combination of single-objective optimization algorithms and hydrodynamic models for assessing the risk in urban storm water drainage systems, providing valuable information for decision-makers.

Flooding regimes increase avian predation on wildlife prey in tidal marsh ecosystems.

Within isolated and fragmented populations, species interactions such as predation can cause shifts in community structure and demographics in tidal marsh ecosystems. It is critical to incorporate species interactions into our understanding when evaluating the effects of sea‐level rise and storm surges on tidal marshes. In this study, we hypothesize that avian predators will increase their presence and hunting activities during high tides when increased inundation makes their prey more vulnerable. We present evidence that there is a relationship between tidal inundation depth and time of day on the presence, abundance, and behavior of avian predators. We introduce predation pressure as a combined probability of predator presence related to water level. Focal surveys were conducted at four tidal marshes in the San Francisco Bay, California where tidal inundation patterns were monitored across 6 months of the winter. Sixteen avian predator species were observed. During high tide at Tolay Slough marsh, ardeids had a 29‐fold increase in capture attempts and 4 times greater apparent success rate compared with low tide. Significantly fewer raptors and ardeids were found on low tides than on high tides across all sites. There were more raptors in December and January and more ardeids in January than in other months. Ardeids were more prevalent in the morning, while raptors did not exhibit a significant response to time of day. Modeling results showed that raptors had a unimodal response to water level with a peak at 0.5 m over the marsh platform, while ardeids had an increasing response with water level. We found that predation pressure is related to flooding of the marsh surface, and short‐term increases in sea levels from high astronomical tides, sea‐level rise, and storm surges increase vulnerability of tidal marsh wildlife.

Climate Change and Eutrophication: A Short Review

Water resources are vital not only for human beings but essentially all ecosystems. Human health is at risk if clean drinking water becomes contaminated. Water is also essential for agriculture, manufacturing, energy production and other diverse uses. Therefore, a changing climate and its potential effects put more pressure on water resources. Climate change may cause increased water demand as a result of rising temperatures and evaporation while decreasing water availability. On the other hand, extreme events as a result of climate change can increase surface runoff and flooding, deteriorating water quality as well. One effect is water eutrophication, which occurs when high concentrations of nutrients, such as nitrogen and phosphorus, are present in the water. Nutrients come from different sources including agriculture, wastewater, stormwater, and fossil fuel combustion. Algal blooms can cause many problems, such as deoxygenation and water toxicity, ultimately disrupting normal ecosystem functioning. In this paper, we investigate the potential impacts of climatic factors affecting water eutrophication, how these factors are projected to change in the future, and what their projected potential impacts will be.

Simulation study on effect of permeable pavement on reducing flood risk of urban runoff

Permeable pavement is part of the low impact development (LID) measurement, which can decrease urban surface runoff coefficient and flood peak flow. In this paper, a two-way, six-lane road in Nanjing was selected as the study area. Storm water management model (SWMM) was used to simulate the effect of different pavement structures (drainage surface, permeable pavement and permeable road) under different rainfall conditions on reducing surface runoff and controlling urban stormwater. The simulation results show that the drainage surface can reduce part of surface runoff, but it has no influence on the reduction and hysteresis of flood peak. The permeable pavement can reduce part of surface runoff and flood peak and can delay peak time. The permeable road has better effect on reducing runoff coefficient and flood peak, which can effectively reduce the pressure of urban drainage and reduce the risk of stormwater flood.

Impacts of Fire and Flood on Land-Surface–Atmosphere Energetics in a Sub-tropical Barrier Island Freshwater Swamp

Climate change is predicted to lead to a drier and warmer climate in sub-tropical eastern Australia. Drier landscapes are more susceptible to fire, however, increases in daily precipitation extremes, and possible expansion of tropical weather systems into higher latitudes, implies that flooding may also become more common. We use the eddy-covariance technique to evaluate turbulent heat fluxes, and a net radiometer to measure surface albedo, over a groundwater dependent barrier island swamp. Measurements are made for dry and vegetated surface conditions, and following the natural occurrences of a wildfire and flooding. Results show that the wetland Bowen ratio has a value near 1 for typical dry and vegetated conditions, and is dominated by the latent heat flux when inundated by water. The largest changes in the partitioning of available energy into turbulent heat fluxes occur in the days immediately after the wildfire when the surface is dry, with the midday sensible heat flux nearly eight times greater than the latent heat flux. The key influences on energy partitioning are the atmospheric conditions for a dry and vegetated surface, and the surface conditions for either a burnt or a flooded surface.

Urban Flood Estimation and Evaluation of the Performance of an Urban Drainage System in a Semi-Arid Urban Area Using SWMM.

Estimation of urban runoff peak and volume is a fundamental step in determining the transferring capacity of urban drainage systems. The main aim of this study was to present an application of the Storm Water Management Model (SWMM) in order to estimate urban flooding of a semi-arid area (Zanjan city in the northwest of Iran). The performance of an urban drainage system in the study area was also investigated. According to the results, SWMM is an effective tool for urban flood estimation in a semi-arid area. In this study, urban peak flow was simulated via a calibrated model with acceptable accuracy. Based on the results of the model simulation, the capacity of the main canals in the study area is sufficient for peak runoff transferring for a design storm with 50 year return periods, without retrofitting. Whereas, based on local observation and model results, localized and surface flooding can be observed in some urban areas.

Computerized Seed and Range Selection Method for Flood Extent Extraction in SAR Image Using Iterative Region Growing

This study presents a novel method to capture the flood-affected area in SAR image. It initially locates a pixel in HH-polarized SAR image whose intensity value is equal or close to minimum intensity value in that image. This is adapted since SAR reflectance values of flooded area are less than the other regions due to the water surface smoothness that makes the flood surface a specular reflector with nearly no return to the sensor. Thereafter, the identified seed point is confirmed locally based on two parameters corresponding to intensities and percentage of occurrence of intensities around the seed. Densely populated range around the seed point is computed in the second step. Subsequently in the third step, from the seed point, regions are grown till the intensity value of that point is within the range. These three steps are continued till all flooded regions are captured in SAR image. The algorithm works with minimum human interaction. This method is validated by applying on RADARSAT-2 data and is found that the classification accuracy is 95%, in comparison with “mean shift” and “LPQ”.

Infiltration capacity of cracked pavements

Understanding the hydrological behaviour of urban surfaces is imperative in the design of surface water drainage systems and flood mitigation strategies, as well as for the modelling of groundwater recharge and pollution. This study has examined the hydrological behaviour of cracked impervious surfaces through field infiltration testing and image analysis of the cracks themselves. Infiltration tests were undertaken on a section of concrete slab pavers paving. The results showed that cracks in impervious surfaces allow significant volumes of water to infiltrate through them, with infiltration rates comparable to those found in sands and gravels. Using a regression model, infiltration rates were related directly to crack characteristics obtained from image processing software, thereby enabling the first published quantitative link between percentage cracked area and infiltration capacity. The implications of accounting for this infiltration for surface water management systems are estimated to be in the order of £20 million annually for the construction industry in England.

Evaluation of the Structure of Urban Stormwater Pipe Network Using Drainage Density

In mega cities such as Seoul in South Korea, it is very important to protect the cities from surface flooding even for a short time period due to the enormous economic damage. That is why stormwater pipe networks are commonly applied to mega cities with large impervious areas to drain runoff from the city. Therefore, the stormwater pipe networks in urban catchments should be carefully designed for quick and efficient runoff removal. In this study, the structures of different stormwater pipe networks were evaluated based on the relationship between peak rainfall and runoff in the urban catchments in South Korea. More than 400 historical rainfall events from five urban catchments were used to develop respective linear regression models for estimating peak runoff for different pipe network structures. The developed regression models exhibited greater than 0.9 in determination coefficients and demonstrated overall the broader ranges in peak runoff with the greater rainfall amount, especially when the pipe networks were branched. This implies that the effect of pipe network structures on runoff is more profound in the branched networks whose runoff water flow is one-directional and thus tends to concentrate to the catchment outlet. In the case of the looped networks in which runoff paths are multiple, rainfall runoff can be routed to several alternative water paths depending on rainfall events resulting in the reduced peak runoff. The structures of pipe networks can be measured in drainage density which is defined as the ratio of total pipe length to catchment area. As a result, the range of the estimated runoff at the 95% confidence level increased as the drainage density increased, which implies increased uncertainty with the looped networks which commonly involve more pipe installation for unit area as compared to the branched. However, the looped networks with multiple water paths can reduce the time to drain rainfall from the catchments and thus the 95% confidence interval becomes narrow, which means greater reliability in peak runoff estimation. It would therefore be favorable to adopt looped stormwater pipe networks within an affordable budget and the complexity of pipe networks needs to be counted to reduce urban flood risk.

Understanding the Implementation Challenges of Urban Resilience Policies: Investigating the Influence of Urban Geological Risk in Thessaloniki, Greece

Urban Resilience has recently emerged as a systematic approach to urban sustainability. The malleable definition of resilience has rendered its operationalisation an intriguing task for contemporary cities trying to address their organisational problems and confront uncertainty in a holistic manner. In this article we investigate the implementation challenges emerging for Resilient Strategies by the inattention paid to urban geological risk. We conceptualise urban geological risk as the combination of urban geohazards, geological vulnerability and exposure of the built environment and focus on the case study of Thessaloniki, Greece, a city that joined the 100 Resilient Cities initiative in 2014 and published its “Resilience Strategy 2030” (RS) in 2017. After a review of the RS, historical records of natural hazard events and with evidence gathered through interviews with city officials, we emphasize on earthquakes and surface flooding as the most relevant geohazards for Thessaloniki to tackle in its journey towards urban resilience. First, we examine geological vulnerability to earthquakes in conjunction with exposure of the built environment, as an outcome of ageing building stock, high building densities and the urban configuration, in Acheiropoietos neighbourhood, within the historic centre of the city. Then, we explore geological risk to surface flooding in Perea, in Thermaikos Municipality, with a particular focus on flash floods, by demonstrating how limited consideration of local geomorphology as well as semi-regulated urban expansion and its limited connection with emergency planning increase exposure of the built environment to surface flooding. Finally, we come up with the major implementation challenges Thessaloniki’s RS faces with regard to urban geohazards.

Depositional history of the western Nile Delta, Egypt: Late Rupelian to Pleistocene

The availability of onshore and offshore three-dimensional seismic surveys facilitated detailed seismic sequence-stratigraphic interpretation of a large swath of the western Nile Delta evolution since the late Oligocene. The resulting sequence-stratigraphic framework is calibrated against more than 60 wells. The interpretation of repetitive sequence boundaries, that is, unconformities, on seismic sections was constrained by high-resolution abundance and diversity within biostratigraphic data sets and lithofacies-stacking patterns interpreted from well logs. Our series of depositional facies maps reflect environments of undifferentiated lowstand and transgressive systems tracts, that is, depositional elements interpreted between the lower bounding unconformity surface (sequence boundary) and maximum flooding surface above. These typically constitute terrestrial distributary channels and floodplains landward of strike-aligned lowstand deltas and marine shoreline deposits at and over the relict shelf break area of the underlying sequence boundary. Basinward deep-marine shales, slope channels, splays, fans, and terminal channel lobes define the remainder of the deposition over the rather extensive deep-marine slope apron region of the western Nile Delta. Incised valleys, canyons, and broad slope channels often confine any of the above-mentioned depositional facies at the lower bounding unconformity of each sequence.