Water Surface Height Research Articles

Characterizing water surface elevation under different flow conditions for the upcoming SWOT mission

The Surface Water and Ocean Topography satellite mission (SWOT), scheduled for launch in 2021, will deliver two-dimensional observations of water surface heights for lakes, rivers wider than 100 m and oceans. Even though the scientific literature has highlighted several fields of application for the expected products, detailed simulations of the SWOT radar performance for a realistic river scenario have not been presented in the literature. Understanding the error of the most fundamental “raw” SWOT hydrology product is important in order to have a greater awareness about strengths and limits of the forthcoming satellite observations. This study focuses on a reach (∼140 km in length) of the middle-lower portion of the Po River, in Northern Italy, and, to date, represents one of the few real-case analyses of the spatial patterns in water surface elevation accuracy expected from SWOT. The river stretch is characterized by a main channel varying from 100 to 500 m in width and a large floodplain (up to 5 km) delimited by a system of major embankments. The simulation of the water surface along the Po River for different flow conditions (high, low and mean annual flows) is performed with inputs from a quasi-2D model implemented using detailed topographic and bathymetric information (LiDAR, 2 m resolution). By employing a simulator that mimics many SWOT satellite sensor characteristics and generates proxies of the remotely sensed hydrometric data, this study characterizes the spatial observations potentially provided by SWOT. We evaluate SWOT performance under different hydraulic conditions and assess possible effects of river embankments, river width, river topography and distance from the satellite ground track. Despite analyzing errors from the raw radar pixel cloud, which receives minimal processing, the present study highlights the promising potential of this Ka-band interferometer for measuring water surface elevations, with mean elevation errors of 0.1 cm and 21 cm for high and low flows, respectively. Results of the study characterize the expected performance of the upcoming SWOT mission and provide additional insights into potential applications of SWOT observations.

Satellite remote sensing estimation of river discharge: Application to the Yukon River Alaska

A methodology based on general hydraulic relations for rivers has been developed to estimate the discharge (flow rate) of rivers using satellite remote sensing observations. The estimates of discharge, flow depth, and flow velocity are derived from remotely observed water surface area, water surface slope, and water surface height, and demonstrated for two reaches of the Yukon River in Alaska, at Eagle (reach length 34.7 km) and near Stevens Village (reach length 38.3 km). The method is based on fundamental equations of hydraulic flow resistance in rivers, including the Manning equation and the Prandtl-von Karman universal velocity distribution equation. The method employs some new hydraulic relations to help define flow resistance and height of the zero flow boundary in the channel. Estimates are made both with and without calibration. The water surface area of the river reach is measured by using a provisional version of the U.S. Geological Survey (USGS) Landsat based product named Dynamic Surface Water Extent (DSWE). The water surface height and slope measurements require a self-consistent datum, and are derived from observations from the Jason-2 satellite altimeter mission. At both reach locations, the Jason-2 radar altimeter non-winter heights consistently tracked the stage recorded at USGS streamgages with a standard deviation of differences (error) during the non-winter periods of less than 7%. Part of the error may be due to differences in the gage and altimeter crossing locations with respect to the range of stage change and the response to changes in discharge at the upstream and downstream locations. For the non-winter periods, the radar derived slope estimates (mean = 0.0003) were constant over the mission lifetime, and in agreement with previously measured USGS water surface slopes and slopes determined from USGS topographic maps. The accuracy of the mean of the uncalibrated daily estimates of discharge varied between reaches, ranging from 13% near Stevens Village (N = 90) to −21% at Eagle (N = 246) based on the absolute error, and 5% to −6% based on the error of the log of the estimates. Calibrating to the mean of USGS daily discharge estimates from the streamflow rating for the same period of record at each streamgage resulted in mean absolute errors ranging from 1% to 2%, and log errors ranging from 1% or less. The error pattern of the estimates shows that without calibration, even though the mean is well simulated, the high and low end values over the range of estimates may have significant bias.

Measurement of gravitational acceleration with the leak tank method

<p class="Abstract">An experimental device of the mechanics of tank draining under gravity has been constructed. It mainly consists of a cylindrical tank with a circular orifice at the center bottom of the tank. The inner radius of the tank is 134 mm, while there are seven variations of orifice radius, those are 2.25 mm, 2.50 mm, 3.00 mm, 3.50 mm, 4.00 mm, 5.00 mm, and 6.00 mm. The tank is filled by water which is then allowed to flow out throuh the orifice. This experiment can be used to measure the value of gravitational acceleration () on the experiment location. We call this method as the leak tank method. The measurement of g is carried out by measuring the total time to drain the tank from 300 mm initial height of water surface inside the tank for various orifice radius. It is found in this experiment that = (9.89± 0.03) m/s<sup>2</sup>. This result is good enough because it is almost the same as the conventional standar value of 9.80665 m/s<sup>2</sup> with discrepancy of around 0.85%. It indicates that the leak tank method which is described in this paper can be used to estimate the gravitational acceleration value with a good result.</p>

The Effects of Planting Range and Weed Management on Growth and Yield of Rice (Oryza sativa L.) Using Modified SRI (The System of Rice Intensification)

Using modified SRI ( The System Rice of Intensification ) was aimed at determining the optimum planting range and frequency of weeds management that could increase rice productivity. The research was consisted of two factors, planting range and frequency of weeds management. The trials were arranged in factorial using Randomized Block Design (5x4) and three replications. The first factor was five levels of planting range, 20 x 20 cm; 20 x 25 cm; 25 x 25 cm; 25 x 30 cm; and 30 x 30 cm. While the second factor was four levels of weeds management (manually) frequency, once (30 days after planting (DAP); twice (20; 40 DAP); 3 times (20; 30; 40 DAP); and 4 times (10; 20; 30; 40 DAP). Parameters measured were the maximum number of tillers, crops growth rate, net assimilation rate, number of productive tillers, the weight of 1000 seeds, seeds weight per clump, and seeds weight per hectare. The result showed that planting range 20 cm x 25 cm and three times frequency of weeding per planting season was the best interaction with the productivity 9.005 t ha -1 . Rice cultivation technique by giving the height of water surface 10 cm under the soil surface, a distance of furrows 2 m, the dosage of compost 10 ton/ha, planting range 20 x 25 cm , and frequency of weeding three times per planting season could increase rice yield as much as 50.08 %.

Fast global illumination of dynamic water surface based on two stage rendering

Water simulation plays an important role in computer graphics, and its complex optical properties are very computationally intensive due to the variation of phenomena. In this paper, a fast-global illumination method of dynamic water surface with precise reflection and refraction is proposed using a two-stage rendering strategy. At the first stage, we generate an improved Secondary Texture Map (iSDT) based on the distortion of Perlin noise. Our method generates octaves of Perlin noise to construct random height of water surface. For fast rendering the reflection, we utilize 2D mesh modelling water surfaces and optimize the uniform mesh of surface by a layer of detail approach. A 3D geometries’ mirror reflection with respect to 3D perspective view is computed and stored as a texture map. Then the texture map is distorted by octaves of Perlin noise. At the second stage, we combine the iSDT with ray tracing strategy for computing global illumination above the water surface. Experimental results show that our method reduces the rendering time compared with the original ray tracing, and both the opaque and transparent geometries are rendered with plausible high-quality with correct reflection and refraction.

BAM: Bayesian AMHG‐Manning Inference of Discharge Using Remotely Sensed Stream Width, Slope, and Height

AbstractThe forthcoming Surface Water and Ocean Topography (SWOT) NASA satellite mission will measure water surface width, height, and slope of major rivers worldwide. The resulting data could provide an unprecedented account of river discharge at continental scales, but reliable methods need to be identified prior to launch. Here we present a novel algorithm for discharge estimation from only remotely sensed stream width, slope, and height at multiple locations along a mass‐conserved river segment. The algorithm, termed the Bayesian AMHG‐Manning (BAM) algorithm, implements a Bayesian formulation of streamflow uncertainty using a combination of Manning's equation and at‐many‐stations hydraulic geometry (AMHG). Bayesian methods provide a statistically defensible approach to generating discharge estimates in a physically underconstrained system but rely on prior distributions that quantify the a priori uncertainty of unknown quantities including discharge and hydraulic equation parameters. These were obtained from literature‐reported values and from a USGS data set of acoustic Doppler current profiler (ADCP) measurements at USGS stream gauges. A data set of simulated widths, slopes, and heights from 19 rivers was used to evaluate the algorithms using a set of performance metrics. Results across the 19 rivers indicate an improvement in performance of BAM over previously tested methods and highlight a path forward in solving discharge estimation using solely satellite remote sensing.

Automated River Reach Definition Strategies: Applications for the Surface Water and Ocean Topography Mission

AbstractThe upcoming Surface Water and Ocean Topography (SWOT) mission will measure water surface heights and widths for rivers wider than 100 m. At its native resolution, SWOT height errors are expected to be on the order of meters, which prevent the calculation of water surface slopes and the use of slope‐dependent discharge equations. To mitigate height and width errors, the high‐resolution measurements will be grouped into reaches (∼5 to 15 km), where slope and discharge are estimated. We describe three automated river segmentation strategies for defining optimum reaches for discharge estimation: (1) arbitrary lengths, (2) identification of hydraulic controls, and (3) sinuosity. We test our methodologies on 9 and 14 simulated SWOT overpasses over the Sacramento and the Po Rivers, respectively, which we compare against hydraulic models of each river. Our results show that generally, height, width, and slope errors decrease with increasing reach length. However, the hydraulic controls and the sinuosity methods led to better slopes and often height errors that were either smaller or comparable to those of arbitrary reaches of compatible sizes. Estimated discharge errors caused by the propagation of height, width, and slope errors through the discharge equation were often smaller for sinuosity (on average 8.5% for the Sacramento and 6.9% for the Po) and hydraulic control (Sacramento: 7.3% and Po: 5.9%) reaches than for arbitrary reaches of comparable lengths (Sacramento: 8.6% and Po: 7.8%). This analysis suggests that reach definition methods that preserve the hydraulic properties of the river network may lead to better discharge estimates.

Airborne Laser Scanning for calibration and validation of inshore satellite altimetry: A proof of concept

Recent developments in satellite altimetry are leading to improved spatial resolution, allowing applications in the coastal zone and over inland waters. Validation of these sensors near the shore remains a challenge, since the process of upscaling from single point measurements (gauges or GPS buoys) to the radar altimetry footprint is a source of uncertainty. Meanwhile, Airborne Laser Scanning (LIDAR) has been proven capable of delivering accurate water surface heights rapidly over large areas. Here, we show a proof of concept by comparing airborne LIDAR heights over Lake Balaton, Hungary with near-concurrent Envisat and Jason-2 altimeter heights and water level gauge data. The accuracy of LIDAR heights was improved by strip adjustment and absolute georeferencing to ground control points; waveform retracking improved the accuracy of altimetry data. LIDAR heights were averaged within the outlines of the altimetry footprints. Bias is measured for LIDAR and altimetry with respect to gauge heights, and standard deviation of heights measures the vertical dispersion of footprints within one track. Results show standard deviation of heights is in the order of millimeters for LIDAR and 40–50cm for altimetry and bias with respect to gauge heights is 5cm for LIDAR compared to 40cm for altimetry. We conclude that LIDAR may be used for calibration and validation of high resolution satellite radar altimetry over inland waters.

Shallow Water Measurements Using a Single Green Laser Corrected by Building a Near Water Surface Penetration Model

To reduce the size and cost of an integrated infrared (IR) and green airborne LiDAR bathymetry (ALB) system, and improve the accuracy of the green ALB system, this study proposes a method to accurately determine water surface and water bottom heights using a single green laser corrected by the near water surface penetration (NWSP) model. The factors that influence the NWSP of green laser are likewise analyzed. In addition, an NWSP modeling method is proposed to determine the relationship between NWSP and the suspended sediment concentration (SSC) of the surface layer, scanning angle of a laser beam and sensor height. The water surface and water bottom height models are deduced by considering NWSP and using only green laser based on the measurement principle of the IR laser and green laser, as well as employing the relationship between NWSP and the time delay of the surface return of the green laser. Lastly, these methods and models are applied to a practical ALB measurement. Standard deviations of 3.0, 5.3, and 1.3 cm are obtained by the NWSP, water-surface height, and water-bottom height models, respectively. Several beneficial conclusions and recommendations are drawn through the experiments and discussions.

Earth-tide-induced fluctuations in the salinity of an inland river, New South Wales, Australia: a short-term study.

Wybong Creek discharges salts into the agriculturally and industrially important Hunter River in New South Wales, Australia. Abrupt increases in salinity occur periodically in the mid-Wybong Creek catchment. In order to understand the processes which cause these abrupt increases, changes in surface and groundwater were investigated. It is shown that salinity increases can be attributed to highly discrete groundwater discharge directly into the river from below. Hourly electrical conductivity data measured in the river showed regular, diurnal electrical conductivity fluctuations of up to 350μScm-1. These fluctuations could not be attributed to barometric pressure, temperature, or evapotranspiration. Instead, a similar periodicity in surface water electrical conductivity and groundwater height in nearby groundwater wells was found. Fluctuations were of similar periodicity to the orthotides which cause fluctuations in surface water height and are induced by Earth tides. The geology in the mid-catchment area indicates conditions are optimal for Earth tides to impact groundwater. The reporting of orthotidal changes in water chemistry in this article is believed to be the first of its kind in the scientific literature, with the large fluctuations noted having important implications for water monitoring and management in the catchment. Further research investigating Earth-tide-induced phases of groundwater heights will better constrain the relationships between surface water chemistry and groundwater height.

Optimal conditions for chlorothalonil and dissolved organic carbon in horizontal subsurface flow constructed wetlands

ABSTRACTThe most efficient system of horizontal subsurface flow constructed wetlands (HSSFCW) for removing dissolved organic carbon (DOC) in the presence of chlorothalonil pesticide (CLT) present in synthetic domestic wastewater was determined using the macrophyte Phragmites australis. Two concentrations of CLT (85 and 385 μg L−1) and one concentration of glucose (20 mg L−1) were evaluated in four pilot scale horizontal surface flow constructed wetlands coupled with two sizes of silica gravel, igneous gravel, fine chalky gravel (3.18–6.35 mm), coarse gravel (12.70–25.40 mm) and two water surface heights (20 and 40 cm). For a month, wetlands were acclimated with domestic wastewater. Some groups of bacteria were also identified in the biofilm attached to the gravel. In each treatment periodic samplings were conducted in the influent and effluent. Chlorothalonil was quantified by gas chromatography (GC-ECD m), DOC by an organic carbon analyzer and bacterial groups using conventional microbiology in accordance with Standard Methods. The largest removals of DOC (85.82%–85.31%) were found when using fine gravel (3.18–6.35 mm) and the lower layer of water (20 cm). The bacterial groups quantified in the biofilm were total heterotrophic, revivable heterotrophic, Pseudomonas and total coliforms. The results of this study indicate that fine grain gravel (3.18–6.35 mm) and both water levels (20 to 40 cm) can be used in the removal of organic matter and for the treatment of agricultural effluents contaminated with organo-chloride pesticides like CLT in HSSFCW.

Inland and Near Shore Water Profiles Derived from the High Altitude Multiple Altimeter Beam Experimental Lidar (MABEL).

The Advanced Topographic Laser Altimeter System (ATLAS) on the Ice, Cloud, and Land Elevation Satellite (ICESat-2) mission is a six beam, low energy, high repetition rate, 532 nm laser transmitter with photon counting detectors. Although designed primarily for detecting height changes in icecaps, sea ice and vegetation, the polar-orbital satellite will observe global surface water during its designed three year life span, including inland water bodies, coasts, and open oceans. In preparation for the mission, an ICESat-2 prototype or the Multiple Altimeter Beam Experimental Lidar (MABEL), was built and flown on high altitude aircraft experiments over a range of inland and near-shore targets. The purpose was to test the ATLAS concept and to provide a database for developing an algorithm that detects along track surface water height and light penetration under a range of atmospheric and water conditions. The current analysis examines the datasets of three MABEL transects observed from 20 km above ground of coastal and inland waters conducted in 2012 and 2013. Transects ranged from about 2 to 12 km in length and included the middle Chesapeake Bay, the near shore Atlantic coast at Virginia Beach, and Lake Mead. Results indicate MABEL's high capability for retrieving surface water height statistics with a mean height precision of approximately 5-7 cm per 100m segment length. Profiles of attenuated subsurface backscatter, characterized using a Signal to Background Ratio written in Log10 base, or LSBR 0 , were observed over a range of 1.3 to 9.3 meters depending on water clarity and atmospheric background. Results indicate that observable penetration depth, although primarily dependent on water properties, was greatest when solar background rate was low. Near shore bottom reflectance was detected only at the Lake Mead site down to maximum of 10 m under a clear night sky and low turbidity of approximately 1.6 Nephelometric Turbidity Units (NTU). The overall results suggest that the feasibility of retrieving operational surface water height statistics from space-based photon counting systems such as ATLAS is very high for resolutions down to about 100m, even in partly cloudy conditions. The capability to observe subsurface backscatter profiles is achievable but requires much longer transects of several hundreds of meters.

HAVUZLU BALIK GEÇİDİ HİDROLİĞİNİN DENEYSEL İNCELENMESİ

In this study, the pool and weir fishway which is the most commonly used fishway in the world and in our country, was investigated experimentally. The experiments were conducted in an open channel system. The velocity area of the flow in five pools created by using weirs was measured by using aquistic doppler velocimeter. The orifices on the weirs were reduced in the ratio of ½ that of given in the literature for the grayling ( Thymallus thymallus ) or the brown trout ( Salmo trutta ) to pass. In the experiments for a discharge value of Q=6.2 L/s, the difference between the height of the water surface of downward and upward side of the first weir was found to be 2 cm and 1 cm for the others. For Q=12.2 L/s, these differences between the water surface heights were 5.5 cm for all weirs. The maximum velocities were obtained next to downward of the orifices. Moreover, far from the high velocity areas near the orifices, lower velocity areas in the pools that fishes could rest during the passes were determined. Keywords: Pool and weir fishway, aquistic doppler velocimeter, open channel, orifice

EVALUATION OF A NOVEL UAV-BORNE TOPO-BATHYMETRIC LASER PROFILER

We present a novel topo-bathymetric laser profiler. The sensor system (RIEGL BathyCopter) comprises a laser range finder, an Inertial Measurement Unit (IMU), a Global Navigation Satellite System (GNSS) receiver, a control unit, and digital cameras mounted on an octocopter UAV (RiCOPTER). The range finder operates on the time-of-flight measurement principle and utilizes very short laser pulses (<1 ns) in the green domain of the spectrum (λ=532 nm) for measuring distances to both the water surface and the river bottom. For assessing the precision and accuracy of the system an experiment was carried out in October 2015 at a pre-alpine river (Pielach in Lower Austria). A 200 m longitudinal section and 12 river cross sections were measured with the BathyCopter sensor system at a flight altitude of 15-20 m above ground level and a measurement rate of 4 kHz. The 3D laser profiler points were compared with independent, quasi-simultaneous data acquisitions using (i) the RIEGL VUX1-UAV lightweight topographic laser scanning system (bare earth, water surface) and (ii) terrestrial survey (river bed). Over bare earth the laser profiler heights have a std. dev. of 3 cm, the water surface height appears to be underestimated by 5 cm, and river bottom heights differ from the reference measurements by 10 cm with a std. dev. of 13 cm. When restricting the comparison to laser profiler bottom points and reference measurements with a lateral offset below 1 m, the values improve to 4 cm bias with a std. dev. of 6 cm. We report additionally on challenges in comparing UAV-borne to terrestrial profiles. Based on the accuracy and the small footprint (3.5 cm at the water surface) we concluded that the acquired 3D points can potentially serve as input data (river bed geometry, grain roughness) and validation data (water surface, water depth) for hydrodynamic-numerical models.

EVALUATION OF A NOVEL UAV-BORNE TOPO-BATHYMETRIC LASER PROFILER

Abstract. We present a novel topo-bathymetric laser profiler. The sensor system (RIEGL BathyCopter) comprises a laser range finder, an Inertial Measurement Unit (IMU), a Global Navigation Satellite System (GNSS) receiver, a control unit, and digital cameras mounted on an octocopter UAV (RiCOPTER). The range finder operates on the time-of-flight measurement principle and utilizes very short laser pulses (<1 ns) in the green domain of the spectrum (λ=532 nm) for measuring distances to both the water surface and the river bottom. For assessing the precision and accuracy of the system an experiment was carried out in October 2015 at a pre-alpine river (Pielach in Lower Austria). A 200 m longitudinal section and 12 river cross sections were measured with the BathyCopter sensor system at a flight altitude of 15-20 m above ground level and a measurement rate of 4 kHz. The 3D laser profiler points were compared with independent, quasi-simultaneous data acquisitions using (i) the RIEGL VUX1-UAV lightweight topographic laser scanning system (bare earth, water surface) and (ii) terrestrial survey (river bed). Over bare earth the laser profiler heights have a std. dev. of 3 cm, the water surface height appears to be underestimated by 5 cm, and river bottom heights differ from the reference measurements by 10 cm with a std. dev. of 13 cm. When restricting the comparison to laser profiler bottom points and reference measurements with a lateral offset below 1 m, the values improve to 4 cm bias with a std. dev. of 6 cm. We report additionally on challenges in comparing UAV-borne to terrestrial profiles. Based on the accuracy and the small footprint (3.5 cm at the water surface) we concluded that the acquired 3D points can potentially serve as input data (river bed geometry, grain roughness) and validation data (water surface, water depth) for hydrodynamic-numerical models.

Water Surface Height Determination with a GPS Wave Glider: A Demonstration in Loch Ness, Scotland

AbstractA geodetic GPS receiver has been installed on a Wave Glider, an unmanned water surface vehicle. Using kinematic precise point positioning (PPP) GPS, which operates globally without directly requiring reference stations, surface heights are measured with ~0.05-m precision. The GPS Wave Glider was tested in Loch Ness, Scotland, by measuring the gradient of the loch’s surface height. The experiment took place under mild weather, with virtually no wind setup along the loch and a wave field made mostly of ripples and wavelets. Under these conditions, the loch’s surface height gradient should be approximately equal to the geoid slope. The PPP surface height gradient and that of the Earth Gravitational Model 2008 geoid heights do indeed agree on average along the loch (0.03 m km−1). Also detected are 1) ~0.05-m-sized height changes due to daily water pumping for hydroelectricity generation and 2) high-frequency (0.25–0.5 Hz) oscillations caused by surface waves. The PPP heights compare favorably (~0.02-m standard deviation) with relative carrier phase–based GPS processing. This suggests that GPS Wave Gliders have the potential to autonomously determine centimeter-precise water surface heights globally for lake modeling, and also for applications such as ocean modeling and geoid/mean dynamic topography determination, at least for benign surface states such as those encountered during the reported experiment.

ICESat‐derived inland water surface spot heights

AbstractAccurate measurement of water surface height is key to many fields in hydrology and limnology. Satellite radar and laser altimetry have been shown to be useful means of obtaining such data where no ground gauging stations exist, and the accuracy of different satellite instruments is now reasonably well understood. Past validation studies have shown water surface height data from the ICESat instrument to have the highest vertical accuracy (mean absolute errors of ∼10 cm for ICESat, compared, for example, with ∼28 cm from Envisat), yet no freely available source of processed ICESat data currently exists for inland water bodies. Here we present a database of processed and quality checked ICESat‐derived inland water surface heights (IWSH) for water bodies greater than 3 arc sec (∼92 m at the equator) in width. Four automated methods for removing spurious observations or outliers were investigated, along with the impact of using different water masks. We find that the best performing method ensures that observations used are completely surrounded by water in the SRTM Water Body data. Using this method for removing spurious observations, we estimate transect‐averaged water surface heights at 587,292 unique locations from 2003 to 2009, with the number of locations proportional to the size of the river.

Benchmarking wide swath altimetry‐based river discharge estimation algorithms for the Ganges river system

AbstractThe objective of this study is to compare the effectiveness of three algorithms that estimate discharge from remotely sensed observables (river width, water surface height, and water surface slope) in anticipation of the forthcoming NASA/CNES Surface Water and Ocean Topography (SWOT) mission. SWOT promises to provide these measurements simultaneously, and the river discharge algorithms included here are designed to work with these data. Two algorithms were built around Manning's equation, the Metropolis Manning (MetroMan) method, and the Mean Flow and Geomorphology (MFG) method, and one approach uses hydraulic geometry to estimate discharge, the at‐many‐stations hydraulic geometry (AMHG) method. A well‐calibrated and ground‐truthed hydrodynamic model of the Ganges river system (HEC‐RAS) was used as reference for three rivers from the Ganges River Delta: the main stem of Ganges, the Arial‐Khan, and the Mohananda Rivers. The high seasonal variability of these rivers due to the Monsoon presented a unique opportunity to thoroughly assess the discharge algorithms in light of typical monsoon regime rivers. It was found that the MFG method provides the most accurate discharge estimations in most cases, with an average relative root‐mean‐squared error (RRMSE) across all three reaches of 35.5%. It is followed closely by the Metropolis Manning algorithm, with an average RRMSE of 51.5%. However, the MFG method's reliance on knowledge of prior river discharge limits its application on ungauged rivers. In terms of input data requirement at ungauged regions with no prior records, the Metropolis Manning algorithm provides a more practical alternative over a region that is lacking in historical observations as the algorithm requires less ancillary data. The AMHG algorithm, while requiring the least prior river data, provided the least accurate discharge measurements with an average wet and dry season RRMSE of 79.8% and 119.1%, respectively, across all rivers studied. This poor performance is directly traced to poor estimation of AMHG via a remotely sensed proxy, and results improve commensurate with MFG and MetroMan when prior AMHG information is given to the method. Therefore, we cannot recommend use of AMHG without inclusion of this prior information, at least for the studied rivers. The dry season discharge (within‐bank flow) was captured well by all methods, while the wet season (floodplain flow) appeared more challenging. The picture that emerges from this study is that a multialgorithm approach may be appropriate during flood inundation periods in Ganges Delta.

Steady nonuniform shallow flow within emergent vegetation

AbstractSurface flow redistribution on flat ground from crusted bare soil to vegetated patches following intense rainfall events elevates plant available water above that provided by rainfall. The significance of this surface water redistribution to sustaining vegetation in arid and semiarid regions is undisputed. What is disputed is the quantity and spatial distribution of the redistributed water. In ecohydrological models, such nonuniform flows are described using the Saint‐Venant equation (SVE) subject to a Manning roughness coefficient closure. To explore these assumptions in the most idealized setting, flume experiments were conducted using rigid cylinders representing rigid vegetation with varying density. Flow was induced along the streamwise x direction by adjusting the free water surface height H(x) between the upstream and downstream boundaries mimicking the nonuniformity encountered in nature. In natural settings, such H(x) variations arise due to contrasts in infiltration capacity and ponded depths during storms. The measured H(x) values in the flume were interpreted using the SVE augmented with progressively elaborate approximations to the roughness representation. The simplest approximation employs a friction factor derived from a drag coefficient (Cd) for isolated cylinders in a locally (but not globally) uniform flow and upscaled using the rod density that was varied across experiments. Comparison between measured and modeled H(x) suggested that such a “naive” approach overpredicts H(x). Blockage was then incorporated into the SVE model calculations but resulted in underestimation of H(x). Biases in modeled H(x) suggest that Cd must be varying in x beyond what a local or bulk Reynolds number predicts. Inferred Cd(x) from the flume experiments exhibited a near‐parabolic shape most peaked in the densest canopy cases. The outcome of such Cd(x) variations is then summarized in a bulk resistance formulation that may be beneficial to modeling runon‐runoff processes on shallow slopes using SVE.

Advances in Remote Sensing of Flooding

With the publication of eight original research articles, four types of advances in the remote sensing of floods are achieved. The uncertainty of modeled outputs using precipitation datasets derived from in situ observations and remote sensors is further understood. With the terrestrial laser scanner and airborne light detection and ranging (LiDAR) coupled with high resolution optical and radar imagery, researchers improve accuracy levels in estimating the surface water height, extent, and flow of floods. The unmanned aircraft system (UAS) can be the game changer in the acquisition and application of remote sensing data. The UAS may fly everywhere and every time when a flood event occurs. With the development of urban structure maps, the flood risk and possible damage is well assessed. The flood mitigation plans and response activities become effective and efficient using geographic information system (GIS)-based urban flood vulnerability and risk maps.