Non-inundated Areas Research Articles

Anomalous human activity fluctuations from digital trace data signal flood inundation status

The emergence of mobile platforms equipped with Global Positioning System technology enables real-time data collection affording opportunities for mining data applicable to rapid flood inundation assessment. The collected data can be employed to complement existing methods for rapid flood inundation assessment, such as remote sensing, to enhance situational awareness. In particular, telemetry-based digital trace data related to human activity have intrinsic advantages to be used for inundation assessment. In this study, we investigate the use of Mapbox telemetry data, which provides human activity indices with high spatial and temporal resolutions, for application in rapid flood inundation assessment. Using data from Hurricane Harvey in 2017 in Harris County, Texas, we (1) study anomalous fluctuations in human activities and analyze the differences in activity level between inundated and non-inundated areas and (2) investigate changes in the concentration of human activity, to explore the disruption of human activity as an indicator of flood inundation. Results show that both analyses can provide valuable rapid insights regarding flood inundation status. Anomalous activities can be significantly higher/lower in flooded areas compared with non-flooded areas. Also, the concentration of human activity during the flood propagation period across affected watersheds can be observed. This study contributes to the state of knowledge in smart flood resilience by investigating the application of ubiquitous telemetry-based digital trace data to enhance rapid flood inundation assessment. Accordingly, the use of such digital trace data could provide emergency managers and public officials with valuable insights to inform impact evaluation and response actions.

Classifying Inundation in a Tropical Wetlands Complex with GNSS-R

The use of global navigation satellite system reflectometry (GNSS-R) measurements for classification of inundated wetlands is presented. With the launch of NASA’s Cyclone Global Navigation Satellite System (CYGNSS) mission, space-borne GNSS-R measurements have become available over ocean and land. CYGNSS covers latitudes between ±38°, providing measurements over tropical ecosystems and benefiting new studies of wetland inundation dynamics. The GNSS-R signal over inundated wetlands is driven mainly by coherent scattering associated with the presence of surface water, producing strong forward scattering and a distinctive bistatic scattering signature. This paper presents a methodology used to classify inundation in tropical wetlands using observables derived from GNSS-R measurements and ancillary data. The methodology employs a multiple decision tree randomized (MDTR) algorithm for classification and wetland inundation maps derived from the phased-array L-band synthetic aperture radar (PALSAR-2) as reference for training and validation. The development of an innovative GNSS-R wetland classification methodology is aimed to advance mapping of global wetland distribution and dynamics, which is critical for improved estimates of natural methane production. The results obtained in this manuscript demonstrate the ability of GNSS-R signals to detect inundation under dense vegetation over the Pacaya-Samiria Natural Reserve, a tropical wetland complex located in the Peruvian Amazon. Classification results report an accuracy of 69% for regions of inundated vegetation, 87% for open water regions, and 99% for non-inundated areas. Misclassification of inundated vegetation, primarily as non-inundated area, is likely related to the combination of two factors: partial inundation within the GNSS-R scattering area, and signal attenuation from dense overstory vegetation, resulting in a low signal.

Short Communication: A comparative study of phenotypes and starch production in sago palm (Metroxylon sagu) growing naturally in temporarily inundated and non inundated areas of South Sorong, Indonesia

Abstract. Yater T, Tubur HW, Meliala C, Abbas B. 2019. Short Communication: A comparative study of phenotypes and starch production in sago palm (Metroxylon sagu) growing naturally in temporarily inundated and non-inundated areas of South Sorong, Indonesia. Biodiversitas 20: 1121-1126. Sago palm forests and sago palm semi cultivation are generally spread in swampy areas, seasonally inundated areas and non-inundated areas. The objectives of this study are to determine and compare the phenotypes of and starch production by sago palms growing naturally in the temporarily inundated areas (TIA type) and non-inundated areas (WIA type) in South Sorong District, West Papua Province, Indonesia. Sago palms of both habitats were found to be the same variety based on analysis of vernacular names and general characteristics. Comparison of morphological characters related to starch production of TIA and WIA types showed that there were no significant differences between the two studied types. The distribution of starch along the sago trunk was observed to be uneven, higher starch accumulation was found in the middle part of the trunk which was significantly different from the lower and upper parts of the trunk.

Flood mapping under uncertainty: a case study in the Canadian prairies

In Canada, approaches for hazard mapping involve using a hydraulic model to generate a flood extent map that distinguishes between inundated and non-inundated areas in a deterministic way. The authors adapt a probabilistic approach to obtain flood hazard maps by accounting for uncertainty in boundary conditions and calibration parameters of a hydrodynamic model, while considering extent, probability, and depth of inundation as important flood indicators. The Qu’Appelle River in the Canadian prairies is considered as a case study to demonstrate the benefits of a probabilistic approach to obtain flooding indicators. The probability and depth of inundation are obtained for all locations in the floodplain, and their uncertainties are evaluated. A sensitivity analysis to determine factors affecting the extent of flooding at multiple locations along the river is also carried out. Further, the criterion to distinguish between flooded and non-flooded areas is modified and its subsequent effect on the flooding indicators is also evaluated. Results show low variability in depth and probability of inundation at most locations along the floodplain. It is also observed that the influence of the roughness parameters on the flooding extents is higher in the steeper stretches of the river, compared to the flatter stretches. Another component of the presented work focusses on evaluating an existing topography-based hazard map for Canada that classifies the country into different levels based on severity of flooding, by comparing it with the probabilistic hazard map obtained in this study. The comparison indicates a good level of agreement between both maps and highlights the reliability of using the topography-based hazard map where hydraulic modeling is infeasible.

Mapping inundation extent, frequency and duration in the Okavango Delta from 2001 to 2012

The frequency and duration of inundation in river systems are important for a variety of applications, such as water resource management, floodplain mapping and habitat restoration. The Okavango Delta, the fifth largest Ramsar site in the world, has experienced a series of large floods since 2007, following the much lower flooding of the 1990s and early 2000s. This study aimed to establish inundation frequency and duration maps of the Okavango Delta for 2001 to 2012 using MOD09Q1 and MOD11A1. An earlier methods paper testing MODIS for flood mapping in the delta showed 99.4% overall accuracy for inundation mapping of the delta, with a kappa coefficient of 80%. A method based on a time-varying threshold derived from bimodal single-band histograms was used to classify the images into inundated and non-inundated areas. The method relies on the difference in reflectance between waterbodies and dry or vegetated soil, with the former having low reflectance and the latter displaying higher reflectance values. The method takes into account seasonal changes in reflectance. Inundation maps showed a gradual decrease in the delta's maximum annual inundation extent from 2001 to 2003, followed by a gradual increase from 2004 to 2012, with maximum inundation extent during 2010–2012.

A Review of Flood-Related Storage and Remobilization of Heavy Metal Pollutants in River Systems.

Recently observed rapid climate changes have focused the attention of researchers and river managers on the possible effects of increased flooding frequency on the mobilization and redistribution of historical pollutants within some river systems. This text summarizes regularities in the flood-related transport, channel-to-floodplain transfer, and storage and remobilization of heavy metals, which are the most persistent environmental pollutants in river systems. Metal-dispersal processes are essentially much more variable in alluvia than in soils of non-inundated areas due to the effects of flood-sediment sorting and the mixing of pollutants with grains of different origins in a catchment, resulting in changes of one to two orders of magnitude in metal content over distances of centimetres. Furthermore, metal remobilization can be more intensive in alluvia than in soils as a result of bank erosion, prolonged floodplain inundation associated with reducing conditions alternating with oxygen-driven processes of dry periods and frequent water-table fluctuations, which affect the distribution of metals at low-lying strata. Moreover, metal storage and remobilization are controlled by river channelization, but their influence depends on the period and extent of the engineering works. Generally, artificial structures such as groynes, dams or cut-off channels performed before pollution periods favour the entrapment of polluted sediments, whereas the floodplains of lined river channels that adjust to new, post-channelization hydraulic conditions become a permanent sink for fine polluted sediments, which accumulate solely during overbank flows. Metal mobilization in such floodplains takes place only by slow leaching, and their sediments, which accrete at a moderate rate, are the best archives of the catchment pollution with heavy metals.

Evaluating flood inundation impact on wetland vegetation FPAR of the Macquarie Marshes, Australia

Vegetation is a key measure of changes in wetland hydrology and ecology induced by flood inundation. The fraction of photosynthetically active radiation absorbed by the canopy (FPAR) is an indicator of presence and state of vegetation, which can be estimated from remote sensing data. This study investigates the spatio-temporal variations of FPAR under inundation by integrating remotely sensed images and hydrological data in a GIS environment. Taking the Macquarie Marshes as a study area, it aims to model the behavior of vegetation after an ecologically significant flood using Moderate Resolution Imaging Spectroradiometer (MODIS) FPAR products, so as to reveal the impacts of flood on wetland vegetation. Flow data from four gauging stations at upstream, mid-stream and downstream were analysed. The modified Normalized Difference Water Index (mNDWI) was used to extract inundation extent from MODIS images. Image ratio and lagged cross-correlation methods were employed to disclose the vegetation response to flooding. Vegetation in the Marshes went through considerable structural changes during the identified flood event. FPAR was relatively more stable in the inundated areas than the non-inundated areas. FPAR values in both inundated and non-inundated areas exhibited a similar trend in the “non-flood period”, but a different trend in the “flood period”. Lagged cross-correlation analysis shows diverse vegetation responses to flood inundation between the inundated and non-inundated areas. It proves the water retention of wetland inundation and confirms vegetation in the non-inundated areas more sensitive to soil moisture conditions. This study proposes a feasible method for efficiently studying vegetation dynamics of flood inundation at both spatial and temporal scales. These methodology and results can provide baseline information for eco-hydrological studies of floodplain-wetland ecosystems.

Flood Mapping and Flood Dynamics of the Mekong Delta: ENVISAT-ASAR-WSM Based Time Series Analyses

Satellite remote sensing is a valuable tool for monitoring flooding. Microwave sensors are especially appropriate instruments, as they allow the differentiation of inundated from non-inundated areas, regardless of levels of solar illumination or frequency of cloud cover in regions experiencing substantial rainy seasons. In the current study we present the longest synthetic aperture radar-based time series of flood and inundation information derived for the Mekong Delta that has been analyzed for this region so far. We employed overall 60 Envisat ASAR Wide Swath Mode data sets at a spatial resolution of 150 meters acquired during the years 2007–2011 to facilitate a thorough understanding of the flood regime in the Mekong Delta. The Mekong Delta in southern Vietnam comprises 13 provinces and is home to 18 million inhabitants. Extreme dry seasons from late December to May and wet seasons from June to December characterize people’s rural life. In this study, we show which areas of the delta are frequently affected by floods and which regions remain dry all year round. Furthermore, we present which areas are flooded at which frequency and elucidate the patterns of flood progression over the course of the rainy season. In this context, we also examine the impact of dykes on floodwater emergence and assess the relationship between retrieved flood occurrence patterns and land use. In addition, the advantages and shortcomings of ENVISAT ASAR-WSM based flood mapping are discussed. The results contribute to a comprehensive understanding of Mekong Delta flood dynamics in an environment where the flow regime is influenced by the Mekong River, overland water-flow, anthropogenic floodwater control, as well as the tides.

Ecosystem specific yield for estimating evapotranspiration and groundwater exchange from diel surface water variation

The White method, routinely used to estimate phreatophyte transpiration from diel groundwater variation, also provides measures of total evapotranspiration (ET) and groundwater fluxes in surface waters. Such applications remain rare, however, and critically require accurate representation of stage-dependent variation in specific yield (Sy). High-resolution stage data from three Florida swamps were used to evaluate different relationships between Sy and stage (ecosystem specific yield, ESY). A discretized form, ESYD, assumes constant Sy near unity for inundated conditions, applying soil Sy for belowground stage and open water Sy (Sy,OW ≈ 1.0) for aboveground stage. A mixture approach, ESYM, applies a stage-dependent interpolation between Sy,Soil and Sy,OW using stage-area relationships and assumes rapid lateral equilibration between inundated and non-inundated wetland areas. Finally, an empirical formulation, ESYRR, uses measured ratios of rain to rise to estimate stage-specific Sy. All formulations yielded reasonable ET rates (ET ≈ PET) at high stage; ESYD markedly overestimated ET (ET/PET > 3) at intermediate stage, whereas ESYM and ESYRR maintained ET/PET near 1.0. Estimated groundwater fluxes using ESYM and ESYRR correlated well with Darcy-estimated flows, but were larger, likely due to uncertainties in Darcy parameters. Well transects across wetlands documented equal water elevation and diel variation across inundated and non-inundated areas, verifying rapid equilibration that reduces Sy and explaining overestimation by ESYD. However, equilibration area varied within and among wetlands, explaining observed differences between ESYM and ESYRR, and suggesting ESYRR may be preferred. Stage histograms followed the shape of ESYRR, highlighting reciprocal influences of ESY on stage stability. Copyright © 2012 John Wiley & Sons, Ltd.

Salinity in Soils and Tsunami Deposits in Areas Affected by the 2010 Chile and 2011 Japan Tsunamis

The accumulation of data sets of past tsunamis is the most basic but reliable way to prepare for future tsunamis because the frequency of tsunami occurrence and their magnitude can be estimated by historical records of tsunamis. Investigation of tsunami deposits preserved in geological layers is an effective measure to understand ancient tsunamis that occurred before historical records began. However, the areas containing tsunami deposits can be narrower than the area of tsunami inundation, thus resulting in underestimation of the magnitude of past tsunamis. A field survey was conducted after the 2010 Chile tsunami and 2011 Japan tsunami to investigate the chemical properties of the tsunami-inundated soil to examine the applicability of tsunami inundation surveys considering water-soluble salts in soil. The soil and tsunami deposits collected in the tsunami-inundated areas are rich in water-soluble ions (Na+, Mg2+, Cl−, Br− and SO42−) compared with the samples collected in the non-inundated areas. The analytical result that the ratios of Na+, Mg2+, Br− and SO42− to Cl− are nearly the same in the tsunami deposits and in the tsunami-inundated soil suggests that the deposition of these ions resulting from the tsunami inundation does not depend on whether or not tsunami deposits exist. Discriminant analysis of the tsunami-inundated areas using the ion contents shows the high applicability of these ions to the detection of tsunami inundation during periods when the amount of rainfall is limited. To examine the applicability of this method to palaeotsunamis, the continuous monitoring of water-soluble ions in tsunami-inundated soil is needed as a future study.

Surface energy balance using satellite data for the water balance of a traditional irrigation—wetland system in SW Iran

A water balance of a large traditional irrigation area and a downstream adjoining wetland was determined using the surface energy balance approach (SEB), based on satellite data, to calculate the actual evaporation of both the irrigated area and the wetland at four different dates in a dry year and information of two additional images. The contribution of capillary flow by the shallow groundwater table was estimated by evaluating the actual evapotranspiration values of adjoining rangelands and non-inundated wetland areas. Those values were used to separate the total evapotranspiration into a soil moisture change component due to capillary rise, and into a component attributable to supply of river water. The only field data used for the estimated monthly water balance were air temperature, wind speed, and water inflow, since rainfall and outflow could be ignored in the year 2000. The results provided an insight for conditions of a drought year within the irrigated area, the distribution of water to irrigation and the wetland and showed the linkage between inundated wetland area and discharge.

A simple raster-based model for flood inundation simulation

In this paper the development of a new model for simulating flood inundation is outlined. The model is designed to operate with high-resolution raster Digital Elevation Models, which are becoming increasingly available for many lowland floodplain rivers and is based on what we hypothesise to be the simplest possible process representation capable of simulating dynamic flood inundation. This consists of a one-dimensional kinematic wave approximation for channel flow solved using an explicit finite difference scheme and a two-dimensional diffusion wave representation of floodplain flow. The model is applied to a 35 km reach of the River Meuse in The Netherlands using only published data sources and used to simulate a large flood event that occurred in January 1995. This event was chosen as air photo and Synthetic Aperture Radar (SAR) data for flood inundation extent are available to enable rigorous validation of the developed model. 100, 50 and 25 m resolution models were constructed and compared to two other inundation prediction techniques: a planar approximation to the free surface and a relatively coarse resolution two-dimensional finite element scheme. The model developed in this paper outperforms both the simpler and more complex process representations, with the best fit simulation correctly predicting 81.9% of inundated and non-inundated areas. This compares with 69.5% for the best fit planar surface and 63.8% for the best fit finite element code. However, when applied solely to the 7 km of river below the upstream gauging station at Borgharen the planar model performs almost as well (83.7% correct) as the raster model (85.5% correct). This is due to the proximity of the gauge, which acts as a control point for construction of the planar surface and the fact that here low-lying areas of the floodplain are hydraulically connected to the channel. Importantly though it is impossible to generalise such application rules and thus we cannot specify a priori where the planar approximation will work. Simulations also indicate that, for this event at least, dynamic effects are relatively unimportant for prediction of peak inundation. Lastly, consideration of errors in typically available gauging station and inundation extent data shows the raster-based model to be close to the current prediction limit for this class of problem.

A simple procedure to model water level fluctuations in partially inundated wetlands

When modelling groundwater behaviour in wetlands, there are specific problems related to the presence of open water in small-sized mosaic patterns. A simple quasi two-dimensional model to predict water level fluctuations in partially inundated wetlands is presented. In this model, the ratio between inundated and non-inundated areas provides an adequate description of water storage properties. This concept can be implemented in any hydrological model. Two examples of such an implementation in the soil water flow model SWATRE are presented in this paper.