Simulated Water Levels Research Articles

Assessment of Cartosat-1 DEM for Modeling Floods in Data Scarce Regions

Digital Elevation Model (DEM) plays an important role in modeling floods. In data scarce developing countries, unavailability of high resolution topography and river cross-sections data are the prime limitations for simulating hydrodynamic models for modeling floods. In the present study, we assess the quality of Cartosat-1 DEMs in providing accurate river cross-sections and floodplain elevations; and hence their suitability in modeling floods. Cartosat-1 DEMs are prepared using Ground Control Points (GCP) of surveyed elevation and bias corrected Shuttle Radar Topography Mission (SRTM) elevation. Surveyed elevation based Cartosat-1 DEM is found to be of best quality while bias corrected SRTM elevation based Cartosat-1 DEM is found to be of reasonable quality on the basis of cross-section representation as well as elevation statistics. Cross-sections derived from the Cartosat-1 DEMs as well as surveyed cross-sections are later used independently in MIKE11 model for 1-dimensional flow modeling. Simulated water levels from models based on Cartosat-1 DEMs are compared graphically with the observed water levels. Modeling performance is also evaluated using different statistical performance criteria. Results show that the models based on Cartosat-1 DEM derived cross-sections perform similar to the model based on surveyed cross-sections. Study concludes that a reasonably accurate DEM, prepared from moderate survey in data scarce region, can be used for deriving requisite river cross-sections for hydrodynamic modeling.

Effects of tide-surge interactions on storm surges along the coast of the Bohai Sea, Yellow Sea, and East China Sea

Abstract A two-dimensional coupled tide-surge model was used to investigate the effects of tide-surge interactions on storm surges along the coast of the Bohai Sea, Yellow Sea, and East China Sea. In order to estimate the impacts of tide-surge interactions on storm surge elevations, Typhoon 7203 was assumed to arrive at 12 different times, with all other conditions remaining constant. This allowed simulation of tide and total water levels for 12 separate cases. Numerical simulation results for Yingkou, Huludao, Shijiusuo, and Lianyungang tidal stations were analyzed. Model results showed wide variations in storm surge elevations across the 12 cases. The largest difference between 12 extreme storm surge elevation values was of up to 58 cm and occurred at Yingkou tidal station. The results indicate that the effects of tide-surge interactions on storm surge elevations are very significant. It is therefore essential that these are taken into account when predicting storm surge elevations.

The Underground Water Level Simulation in Imamzadeh Jafar Plateau by the Use of Mudflow Software

The most secure method in providing water in the dry and semi-dry regions is the use of underground water sources and due to over consumption of water aquifers capacities, most of fields and specially Imamzadeh Jafar are faced with negative performance and balance, which threatens the land subsiding. The plateau with the annual raining of 438 millimeters has 169 deep and semi-deep wells with annual 36.68 million consumption and this issue has increased the research signification, in order to protect and relive the required water aquifers, there is a need to predict the underground water level accurately in different condition. In this research, by the use of balance equation and modflow software in Imamzadeh Jafar, water aquifer was analyzed within seven scenario. The underground water level evaluation for the short run periods for 2 years and middle term of 4 years and 12 years of long term was performed; and the results showed that the performance and balance of the plateau was increased due to increase of water consumption compared to the water aquifer quantity in the region that was negative. To the point that the 1, 3, 4, 5, 7 scenarios (minimum 0.17 and maximum -11.34) and 2, 6 scenarios in different timely periods show that the underground water saving volume is positive (minimum 3.64 and maximum 19.83).

Dam breach modelling: influence on downstream water levels and a proposal of a physically based module for flood propagation software

The influence exerted by the method used for computing the dam breach hydrograph on the simulated maximum water levels throughout the downstream valley is essential for selecting a specific computing module to be implemented in the numerical codes used by practitioners. This module should be able to balance the need for a reasonable physical description of the phenomenon and, at the same time, limit as much as possible the maximum number of parameters. In order to feed a debate on this field, in this paper the performances of some parametric models used for the dam breach module implemented in the popular HEC-RAS software, and a simplified but physically based model have been analysed. The performances of the dam breach models have been assessed with reference to the historical event of the Big Bay dam, using both one-dimensional and two-dimensional (1-D and 2-D) flood propagation modelling. The results show that the physically based model considered here, without any operations of ad hoc calibration, has provided the best results in predicting computation of that event. Therefore, it may be proposed as a valid alternative to parametric models, which need the estimation of some parameters that can add further uncertainties in studies like these.

Effect of forecasted typhoon track uncertainties on storm surge predictions for the coast of Shanghai

ABSTRACTA high-resolution typhoon-induced storm surge model based on the unstructured grid finite-volume method was developed for the Shanghai coast. The storm surge generated by Typhoon Prapiroon (2000) was simulated, and the results demonstrated good agreement with observations. The average relative error in the simulated water level was 12.8%. The statistical difference between the predicted and observed typhoon tracks was also analysed using data from 2004 to 2011. After Johnson transformation, the angular deviation follows a normal distribution. Five simulations were conducted for the observed track and four synthetic tracks (deviating 30° and 45° clockwise and counterclockwise from the observed track). The simulations reveal that the surge level is sensitive to the deviation angle. A new predictive scheme with optional angles deviating from the forecasted track was developed and applied to Typhoon Matsa (2005). The results indicate a significant reduction in the error of the peak water level.

Modeling the impacts of urbanization on lake water level using L-THIA

Land use change can have substantial impacts on hydrology and the environment. The long-term hydrologic impact assessment (L-THIA) model was used to quantify the impacts that urbanization has on Lake Maxinkuckee in northern Indiana. Three land use datasets (for the years 1951, 1972, and 1997) were utilized to generate four scenarios, which were used to simulate water level in the lake from 1957-01-01 to 1997-12-31. The model was calibrated to daily lake levels from 1957-01-01 to 1974-12-31 and validated with data from 1975-01-01 to 1997-12-31, with daily R2 and Nash–Sutcliffe (NSE) coefficient values of 0.61 and 0.51, and 0.44 and 0.32, respectively. Simulation results showed the daily lake level gage heights, simulated with the 1951 land use (i.e. the base case), varied between 0.69m and 1.56m with an average of 0.97m with the 1951 land use. Scenario comparison revealed that long-term average and maximum lake level increased slightly with urbanization, due to increase in runoff over the study period. Land use change (defined in this study as urban development) can affect lake level, and should be considered in planning of residential development and recreational areas.

Terrain-driven unstructured mesh development through semi-automatic vertical feature extraction

A semi-automated vertical feature terrain extraction algorithm is described and applied to a two-dimensional, depth-integrated, shallow water equation inundation model. The extracted features describe what are commonly sub-mesh scale elevation details (ridge and valleys), which may be ignored in standard practice because adequate mesh resolution cannot be afforded. The extraction algorithm is semi-automated, requires minimal human intervention, and is reproducible. A lidar-derived digital elevation model (DEM) of coastal Mississippi and Alabama serves as the source data for the vertical feature extraction. Unstructured mesh nodes and element edges are aligned to the vertical features and an interpolation algorithm aimed at minimizing topographic elevation error assigns elevations to mesh nodes via the DEM. The end result is a mesh that accurately represents the bare earth surface as derived from lidar with element resolution in the floodplain ranging from 15 m to 200 m. To examine the influence of the inclusion of vertical features on overland flooding, two additional meshes were developed, one without crest elevations of the features and another with vertical features withheld. All three meshes were incorporated into a SWAN+ADCIRC model simulation of Hurricane Katrina. Each of the three models resulted in similar validation statistics when compared to observed time-series water levels at gages and post-storm collected high water marks. Simulated water level peaks yielded an R2 of 0.97 and upper and lower 95% confidence interval of ∼ ± 0.60 m. From the validation at the gages and HWM locations, it was not clear which of the three model experiments performed best in terms of accuracy. Examination of inundation extent among the three model results were compared to debris lines derived from NOAA post-event aerial imagery, and the mesh including vertical features showed higher accuracy. The comparison of model results to debris lines demonstrates that additional validation techniques are necessary for state-of-the-art flood inundation models. In addition, the semi-automated, unstructured mesh generation process presented herein increases the overall accuracy of simulated storm surge across the floodplain without reliance on hand digitization or sacrificing computational cost.

STUDY ON THE PERFORMANCE OF WONOGIRI RESERVOIR AS FLOOD CONTROL STRUCTURE

The Wonogiri reservoir was built with a primary function as flood control, especially in areas prone to flooding along the Bengawan Solo River. To find out the performance of the Wonogiri reservoir in flood control of Bengawan Solo, a study was conducted on flood hydrograph characteristics of the reservoir inflow by considering the contribution inflow from all sub-watersheds in the reservoir catchment area, at the end of December 2007. Calculation analysis flood hydrograph of Wonogiri Reservoir inflow is done with the calibration of Wuryantoro and Keduang sub-watersheds. Results of the calibration were then used reference to simulate flood hydrograph inflow in each sub-watershed catchment areas. Flood routing in the reservoir was done with the assumption that the inflow of the reservoir was left to face up a height of water in the reservoir 135.3 m (the lower flood control limit) and 138.3 m (the upper flood control limit) and then the spillway gates full-opening. Results of this research indicated that the maximum discharge inflow into the reservoir on the event of Wonogiri flood at the end of December 2007 was ranged from 3,331 to 4,993 m3/s; and it was occurred on December 26, 2007 at between 04:00 - 06:00 am. The most dominant flood hydrograph contribution into the reservoir was derived from Keduang sub-watershed. The flood in the reservoir was simulated as that the spillway gates were closed until water level of reservoir reached the minimum height of 135.3 m and 138.3 m and only until then the spillway gates full-opening. The reservoir water level reached 135.47 m on December 26, 2007 at 6:00 am and outflow was generated when the gates opened to reach 550 m3/s and then increased up to 642 m3/s at 14:00 after then it gradually decreases. The water level simulation was unable to reach 138.3 m because up to December 27, 2007 at 23:00 the water level reservoir reaches only 136.44 m. The Wonogiri reservoir flood control function still can run well and able to reduce the peak flood of 85%.

Optimal Spatial Design of Capacity and Quantity of Rainwater Harvesting Systems for Urban Flood Mitigation

This study adopts rainwater harvesting systems (RWHS) into a stormwater runoff management model (SWMM) for the spatial design of capacities and quantities of rain barrel for urban flood mitigation. A simulation-optimization model is proposed for effectively identifying the optimal design. First of all, we particularly classified the characteristic zonal subregions for spatial design by using fuzzy C-means clustering with the investigated data of urban roof, land use and drainage system. In the simulation method, a series of regular spatial arrangements specification are designed by using statistical quartiles analysis for rooftop area and rainfall frequency analysis; accordingly, the corresponding reduced flooding circumstances can be simulated by SWMM. Moreover, the most effective solution for the simulation method is identified from the calculated net benefit, which is equivalent to the subtraction of the facility cost from the decreased inundation loss. It serves as the initially identified solution for the optimization model. In the optimization method, backpropagation neural network (BPNN) are first applied for developing a water level simulation model of urban drainage systems to substitute for SWMM to conform to newly considered interdisciplinary multi-objective optimization model, and a tabu search-based algorithm is used with the embedded BPNN-based SWMM to optimize the planning solution. The developed method is applied to the Zhong-He District, Taiwan. Results demonstrate that the application of tabu search and the BPNN-based simulation model into the optimization model can effectively, accurately and fast search optimal design considering economic net benefit. Furthermore, the optimized spatial rain barrel design could reduce 72% of inundation losses according to the simulated flood events.

One‐dimensional expression to calculate specific yield for shallow groundwater systems with microrelief

Although the importance to account for microrelief in the calculation of specific yields for shallow groundwater systems is well recognized, the microrelief influence is often treated very simplified, which can cause considerable errors. We provide a general one-dimensional expression that correctly represents the effect of a microrelief on the total specific yield that is composed of the soil and surface specific yield. The one-dimensional expression can be applied for different soil hydraulic parameterizations and soil surface elevation frequency distributions. Applying different van Genuchten parameters and a simple linear microrelief model, we demonstrate that the specific yield is influenced by the microrelief not only when surface storage directly contributes to specific yield by (partial) inundation but also when water levels are lower than the minimum surface elevation. Compared with a simplified representation of the soil specific yield, in which a mean soil surface is assumed for the calculation of soil specific yield, the correct representation can lead to lower as well as higher soil specific yields depending on the specific interaction of the soil water retention characteristics and the microrelief. The new equation can be used to obtain more accurate evapotranspiration estimates from water level fluctuations and to account for the effect of microtopographic subgrid variability on simulated water levels of spatially distributed hydrological models. Copyright © 2015 The Authors Hydrological Processes Published by John Wiley & Sons Ltd

Photosynthesis and growth adaptation of Pterocarya stenoptera and Pinus elliottii seedlings to submergence and drought

To uncover adaptation capacities of two flooding-tolerant plant species, Pterocarya stenoptera (a native species) and Pinus elliottii (an exotic species from southeastern USA), to alternating submergence and drought, we investigated their physiological and growth responses to water stress. Water treatments, including control, continuous flooding (CF), and periodic flooding and drought (PF), were applied to seedlings in order to simulate water level fluctuation in the hydrofluctuation zone of the Three Gorges Reservoir Region. Results showed that net photosynthetic rate (P N), stomatal conductance, and intrinsic water-use efficiency of both plant species were negatively affected under CF and PF compared with the corresponding controls. The P N of both species under PF was comparable to that under CF. At the end of the experiment, the ratio of intercellular to ambient CO2 concentration was not statistically different between water treatments, while that of P. elliottii was significantly higher than that of P. stenoptera. Although P. stenoptera formed lenticels under flooding conditions, P. elliottii seedlings allocated more mass to leaves and increased the relative growth rate of height to enhance the photosynthetic efficiency. Our results illustrated that P. stenoptera and P. elliottii seedlings developed different adaptive strategies in response to flooding, both CF and PF. Therefore, both P. stenoptera and P. elliottii are promising candidates for the vegetation reconstruction of the riparian zones in the Three Gorges Reservoir Region.

Improved simulation of river water and groundwater exchange in an alluvial plain using the SWAT model

Hydrological interaction between surface and subsurface water systems has a significant impact on water quality, ecosystems and biogeochemistry cycling of both systems. Distributed models have been developed to simulate this function, but they require detailed spatial inputs and extensive computation time. The soil and water assessment tool (SWAT) model is a semi-distributed model that has been successfully applied around the world. However, it has not been able to simulate the two-way exchanges between surface water and groundwater. In this study, the SWAT-landscape unit (LU) model – based on a catena method that routes flow across three LUs (the divide, the hillslope and the valley) – was modified and applied in the floodplain of the Garonne River. The modified model was called SWAT-LUD. Darcy's equation was applied to simulate groundwater flow. The algorithm for surface water-level simulation during flooding periods was modified, and the influence of flooding on groundwater levels was added to the model. Chloride was chosen as a conservative tracer to test simulated water exchanges. The simulated water exchange quantity from SWAT-LUD was compared with the output of a two-dimensional distributed model, surface–subsurface water exchange model. The results showed that simulated groundwater levels in the LU adjoining the river matched the observed data very well. Additionally, SWAT-LUD model was able to reflect the actual water exchange between the river and the aquifer. It showed that river water discharge has a significant influence on the surface–groundwater exchanges. The main water flow direction in the river/groundwater interface was from groundwater to river; water that flowed in this direction accounted for 65% of the total exchanged water volume. The water mixing occurs mainly during high hydraulic periods. Flooded water was important for the surface–subsurface water exchange process; it accounted for 69% of total water that flowed from the river to the aquifer. The new module also provides the option of simulating pollution transfer occurring at the river/groundwater interface at the catchment scale.

Efficient incorporation of channel cross-section geometry uncertainty into regional and global scale flood inundation models

This paper investigates the challenge of representing structural differences in river channel cross-section geometry for regional to global scale river hydraulic models and the effect this can have on simulations of wave dynamics. Classically, channel geometry is defined using data, yet at larger scales the necessary information and model structures do not exist to take this approach. We therefore propose a fundamentally different approach where the structural uncertainty in channel geometry is represented using a simple parameterisation, which could then be estimated through calibration or data assimilation. This paper first outlines the development of a computationally efficient numerical scheme to represent generalised channel shapes using a single parameter, which is then validated using a simple straight channel test case and shown to predict wetted perimeter to within 2% for the channels tested. An application to the River Severn, UK is also presented, along with an analysis of model sensitivity to channel shape, depth and friction. The channel shape parameter was shown to improve model simulations of river level, particularly for more physically plausible channel roughness and depth parameter ranges. Calibrating channel Manning’s coefficient in a rectangular channel provided similar water level simulation accuracy in terms of Nash–Sutcliffe efficiency to a model where friction and shape or depth were calibrated. However, the calibrated Manning coefficient in the rectangular channel model was ∼2/3 greater than the likely physically realistic value for this reach and this erroneously slowed wave propagation times through the reach by several hours. Therefore, for large scale models applied in data sparse areas, calibrating channel depth and/or shape may be preferable to assuming a rectangular geometry and calibrating friction alone.

Impact of Simulated Water Level Regulation on Sediment Nutrient Release

Representative sediment samples rich in nitrogen and phosphorus (both continuous and intermittently submerged) were used to conduct dynamic water level (WL) regulation experiments with various WL velocity modes (0, 3, and 6 cm/day). The experiments lasted three WL regulating cycles (6 months), and each single cycle included four WL dynamic phases: decline, stable, ascend, and re-stable. During the experiment, a greater nutrient stock caused higher nutrient release fluxes for continuously submerged sediments when compared to corresponding intermittently submerged sediments regardless of WL regulation. Moreover, continuous submerged sediment nutrient release showed a similar “U” pattern to the intermittently submerged sediment, and nutrient concentrations within the water phase generally increased with rising WL and decreased with dropping WL. Rapid WL regulation such as 6 cm/day promoted nitrogen release, and slow WL regulation at 3 cm/day favored phosphorus leaching. When three WL regulation cycles were finished, WL regulation of 6 cm/day resulted in 18 and 25 % decline of sediment mean organic matter (OM) content for continuous and intermittently submerged sediment, respectively. However, increased WL regulation cycles impacted on sediment nitrogen and phosphorus stock in different manners. For example, a WL regulation of 6 cm/day led to a 582 mg/kg decline and 322 mg/kg increase for intermittently submerged sediment in terms of total nitrogen (TN) and total phosphorus (TP) content, respectively. Results indicated that direct WL regulation insignificantly affected sediment nutrient release, but changed the overlying water conditions such as pH and redox potential (redox), and then indirectly changed the nutrient release dynamics.

Prediction–Correction Method for Parallelizing Implicit 2D Hydrodynamic Models. II: Application

AbstractA two-dimensional (2D) hydrodynamic model is developed for the Jing-Dongting river–lake system, with the computation domain (3,900 km2) covered by a channel-refined grid of 300,000 cells. The model provides good descriptions of the river–lake characteristics (strongly coupled, annular branches, varying flow regimes). In a simulation of a 1-year unsteady flow process, the mean absolute error in simulated water levels is 0.11–0.15 m, and the mean absolute relative error in simulated cross-section discharges is 4.3–8.5%, compared with field data. The accuracy of the 2D model is obviously better than those of existing one-dimensional (1D) and 1D–2D nested models. The prediction–correction parallelization (PCP) method is then tested by simulating the river–lake system using 64 subdomains. The complexities of real rivers are revealed to have almost no negative effects on the quasi-coupled solutions and accuracy of the PCP method. In tests, the mean absolute error in water level is found to be approxima...

Simulation of environmental change in response to operation of dams in Huaihe Basin

This paper describes the model simulation of a portion of the Huaihe Basin upstream of the river mouth at Hongze Lake, with an area of 130 520 km2. The MIKE 11 modeling system was used to assess the flows and water quality in the Huaihe, Shayinghe, Honghe, Guohe, and Pihe rivers. The hydraulic part of the model was used to study the propagation of flows in the Huaihe River, which was calibrated with data from 2002–2003 and verified with data from 2004–2005. In general, there was agreement between measured and simulated discharges at all the hydrological stations. Except for some places close to large gates, there was reasonable agreement between measured and simulated water levels in the simulated rivers. The MIKE 11 WQ (water quality) model was used to study general sanitary parameters describing the river water quality in areas influenced by human activities. The water quality model simulated dissolved oxygen (DO), chemical oxygen demand (COD) and ammonia nitrogen (NH3-N). The difference between the simulated and observed concentrations was within the range that could be expected from water quality modeling, taking into account uncertainties such as pollution loads, and monitoring and sampling frequency. This model setup was also suitable for the subsequent scenario modeling of periods of water project operation. In the simulation of the Pihe River, increasing the discharge at Hengpaitou Dam was shown to cause a significant improvement in water quality downstream of Lu'an City. In the Shayinghe and Huaihe rivers, the effect was less visible. This suggests that the poor water quality in the Huaihe Basin is mainly caused by extensive discharge of domestic and industrial wastewater.

Analyzing the physics of non-tidal barotropic sea level anomaly events using multi-scale numerical modelling in Singapore regional waters

The hydrodynamic flows in the Singapore regional waters (SRW) are the result of a complex mix of tide, seasonal and meteorological effects. The study of non-tidal effects or sea level anomalies (SLA) in this region has shown that it is possible to model some of these anomalies. The present study addresses the non-tidal barotropic water levels and currents in the Singapore region in detail. This analysis includes a multi-scale approach, and addresses amongst others hydrodynamic model grid resolution and the importance of resolving non-linear tide–surge interaction. The results show that the water level and current anomalies phenomena in a complex region like SRW can be effectively modelled using an approach combining non-tidal barotropic and multi-scale numerical modelling. A detailed investigation of the levels of non-linear tide–surge interaction is carried out by simulating SLA events in the Singapore regional waters during North-East (positive SLA) and South-West (negative SLA) monsoons based on ECMWF numerical weather forcing conditions. The results of combining both approaches suggest that the finer grid resolution improves the accuracy of water level and current anomalies simulations. Furthermore, the results also indicate that for the simulations of non-tidal barotropic flows in this area, non-linear tide–surge interaction is important and should be taken into account. Finally, the behaviour of the non-tidal barotropic flow in the region and its changes with tidal variation in the shallow region of the Singapore Strait is now much better understood. Therefore, for reliable operational forecast of sea level, the inclusion of non-linear tide–surge interaction should be required in numerical models to reproduce both tides and surges with improved accuracy in this region.

Determining return water levels at ungauged coastal sites: a case study for northern Germany

We estimate return periods and levels of extreme still water levels for the highly vulnerable and historically and culturally important small marsh islands known as the Halligen, located in the Wadden Sea offshore of the coast of northern Germany. This is a challenging task as only few water level records are available for this region, and they are currently too short to apply traditional extreme value analysis methods. Therefore, we use the Regional Frequency Analysis (RFA) approach. This originates from hydrology but has been used before in several coastal studies and is also currently applied by the local federal administration responsible for coastal protection in the study area. The RFA enables us to indirectly estimate return levels by transferring hydrological information from gauged to related ungauged sites. Our analyses highlight that this methodology has some drawbacks and may over- or underestimate return levels compared to direct analyses using station data. To overcome these issues, we present an alternative approach, combining numerical and statistical models. First, we produced a numerical multidecadal model hindcast of water levels for the entire North Sea. Predicted water levels from the hindcast are bias corrected using the information from the available tide gauge records. Hence, the simulated water levels agree well with the measured water levels at gauged sites. The bias correction is then interpolated spatially to obtain correction functions for the simulated water levels at each coastal and island model grid point in the study area. Using a recommended procedure to conduct extreme value analyses from a companion study, return water levels suitable for coastal infrastructure design are estimated continuously along the entire coastline of the study area, including the offshore islands. A similar methodology can be applied in other regions of the world where tide gauge observations are sparse.

Modelling the time variance of the river bed roughness coefficient for improved simulation of water levels

ABSTRACTAquatic macrophytes create seasonally variable changes in river bed roughness. These changes in roughness influence the hydrodynamic behaviour of the river, for example, elevated water levels for the same discharge. In most hydrodynamic river models, the roughness is assumed constant in time, which may lead to high errors in the river water level results. When the river water level results are applied to water quality studies, biased estimates may be obtained of river flow velocities, dilution and other water quality processes. This article investigates how models implemented in two common hydrodynamic modelling software packages (MIKE11 and InfoWorks RS) can be adopted to take into account the time-varying river bed roughness due to plant growth. Albeit the use of a different approach by the two models, it is shown that both can account for that influence. After application to the Grote Nete river catchment in Belgium, far more accurate river water level results are obtained. Overall, the increase in accuracy of the water level simulations outweighs the increase in model complexity required to enable simulation of the vegetation changes. The model results can also be used to correct discharge estimates based on the measured water levels as shown for this case study.

Understanding the Geophysical Sources of Uncertainty for Satellite Interferometric (SRTM)-Based Discharge Estimation in River Deltas: The Case for Bangladesh

Like most river deltas, Bangladesh represents a geographically small region with numerous crisscrossing rivers. The total number of rivers in Bangladesh exceeds 300, of which 57 rivers are transboundary. Given the widespread unavailability of flow data across the entire river basins of Ganges, Brahmaputra, and Meghna, combined with a declining measurement network and political challenges of sharing the data, satellite remote sensing of discharge has recently become a viable alternative. This study was motivated by the need to understand the geophysical sources of uncertainty of satellite interferometric-based discharge estimation in Bangladesh. A consequential goal of this study was to contextualize the understanding as a function of river’s geophysical characteristics (river width, reach averaging length, and bed/water slope) and also to explore a pragmatic approach to uncertainty reduction using water level climatology. Discharge was estimated according to the slope-area (Manning’s) method using elevation data from Shuttle Radar Topography Mission (SRTM). A high-resolution hydrodynamic (HD) model was accurately calibrated to simulate water level and flow dynamics along the river reaches of the river network and serve as reference for comparison with satellite-based estimates. It was found that satellite interferometric (SRTM)-based discharge estimates yielded estimation error variance an order smaller than the natural flow variability only if the river width was at least three times larger the width of the native resolution of satellite elevation data. Rivers narrower than this width (for SRTM, this cutoff is 270 m) yielded a coefficient of variation larger than 1 due to contamination of land elevation data in hydraulic parameter calculations. It was also found that water level climatology can be useful in significantly reducing the estimation uncertainty for these narrow rivers. While reach averaging length appeared insensitive to accuracy for wide rivers (width ${\bf \gt\! 1\nbsp\hbox{km}}$ ), a few rivers seemed to have an optimal reach averaging length at which the highest accuracy is obtained. Finally, it was found that if reach-averaged hydraulic parameters (area, slope, and radius) are used for the calculation of reach-averaged discharge, the needed linear (bias) correction factors, although unique and arbitrary for each river reach, can improve accuracy of flow simulations.