scholarly journals Calibrating 1D hydrodynamic river models in the absence of cross-sectional geometry: A new parameterization scheme

2021 ◽  
Author(s):  
Liguang Jiang ◽  
Silja Westphal Christensen ◽  
Peter Bauer-Gottwein
Keyword(s):  
Cross Section ◽  
Power Law ◽  
Water Surface ◽  
Surface Elevation ◽  
Flow Depth ◽  
Flow Area ◽  
Water Surface Elevation ◽  
Hydraulic Roughness ◽  
Wide Range ◽  
Cross Section Geometry

Abstract. Hydrodynamic modeling has been increasingly used to simulate water surface elevation which is important for flood prediction and risk assessment. Scarcity/inaccessibility of in-situ bathymetric information has hindered hydrodynamic model development at continental-global scales. Therefore, river cross-section geometry has commonly been approximated using highly simplified generic shapes. However, strong correlations appear between cross-section shape parameters and hydraulic roughness in a hydraulic inversion approach. This study introduces a novel parameterization of 1D hydrodynamic models that reduces ambiguity by combining cross-section geometry and roughness into a conveyance parameter. Flow area and conveyance are expressed as power-law functions of flow depth, and thus are assumed to be linearly related in log-log space at reach scale. Data from a wide range of river systems show that the linearity approximation is globally applicable. Because the two are expressed as power-law functions of flow depth, no further assumptions about channel geometry are needed. Therefore, the hydraulic inversion approach allows for calibrating flow area and conveyance curves in the absence of bathymetry and hydraulic roughness. Its feasibility and performance are illustrated using satellite observations of river width and water surface elevation.

scholarly journals Calibrating 1D hydrodynamic river models in the absence of cross-section geometry using satellite observations of water surface elevation and river width

2021 ◽  
Vol 25 (12) ◽  
pp. 6359-6379
Author(s):  
Liguang Jiang ◽  
Silja Westphal Christensen ◽  
Peter Bauer-Gottwein
Keyword(s):  
Cross Section ◽  
Water Surface ◽  
Power Laws ◽  
Satellite Observations ◽  
Surface Elevation ◽  
Flow Area ◽  
Water Surface Elevation ◽  
Hydraulic Roughness ◽  
River Models ◽  
Cross Section Geometry

Abstract. Hydrodynamic modeling has been increasingly used to simulate water surface elevation which is important for flood prediction and risk assessment. Scarcity and inaccessibility of in situ bathymetric information have hindered hydrodynamic model development at continental-to-global scales. Therefore, river cross-section geometry is commonly approximated by highly simplified generic shapes. Hydrodynamic river models require both bed geometry and roughness as input parameters. Simultaneous calibration of shape parameters and roughness is difficult, because often there are trade-offs between them. Instead of parameterizing cross-section geometry and hydraulic roughness separately, this study introduces a parameterization of 1D hydrodynamic models by combining cross-section geometry and roughness into one conveyance parameter. Flow area and conveyance are expressed as power laws of flow depth, and they are found to be linearly related in log–log space at reach scale. Data from a wide range of river systems show that the linearity approximation is globally applicable. Because the two are expressed as power laws of flow depth, no further assumptions about channel geometry are needed. Therefore, the hydraulic inversion approach allows for calibrating flow area and conveyance curves in the absence of direct observations of bathymetry and hydraulic roughness. The feasibility and performance of the hydraulic inversion workflow are illustrated using satellite observations of river width and water surface elevation in the Songhua river, China. Results show that this approach is able to reproduce water level dynamics with root-mean-square error values of 0.44 and 0.50 m at two gauging stations, which is comparable to that achieved using a standard calibration approach. In summary, this study puts forward an alternative method to parameterize and calibrate river models using satellite observations of river width and water surface elevation.

scholarly journals Quantification of the Effect of Bridge Pier Encasement on Headwater Elevation Using HEC-RAS

Hydrology ◽  
2019 ◽  
Vol 6 (1) ◽  
pp. 25
Author(s):  
Abhijit Subedi ◽  
Suresh Sharma ◽  
Anwarul Islam ◽  
Niraj Lamichhane
Keyword(s):  
Water Surface ◽  
The United States ◽  
Concrete Cover ◽  
Surface Elevation ◽  
Water Surface Elevation ◽  
Percentage Decrease ◽  
Wide Range ◽  
Bridge Superstructure ◽  
Analysis System ◽  
Water Elevation

The deterioration of bridge substructure is a serious concern across the United States. The pier encasement is one of the most common practices for repairing and strengthening the bridge substructure. It is a rehabilitation process of existing pile piers during the repair or replacement of the bridge superstructure, which involves enclosing part of an existing pile pier with a polyethylene or PVC pipe large enough to provide at least three inches of concrete cover over the existing pier when filled. However, this process of enclosing pile piers might elevate water level due to increase in pier width, which could be hazardous in high-risk flood zones. Furthermore, it may create an adverse impact on the stability of the bridge due to scouring around the pier foundation. In order to gain knowledge on the backwater effect due to pile encasement, Hydraulic Engineering Center-River Analysis System (HEC-RAS) was used in this research to perform hydraulic simulations near the bridge sites. These simulations were carried out for various channel configurations and pier sizes with a wide range of flows, which resulted into 224 HEC-RAS models in order to investigate the effects of pile pier encasement on the headwater elevation. This study demonstrated that the water elevation measured in the upstream of the bridge showed no-rise condition, especially for wider channel sections with flatter slopes. However, the water elevation at the immediate upstream of the bridge was slightly higher, and the increasing pattern was only noticeable for a smaller channel width (20 ft), and specifically, for increased flow rate. As the area of flow was decreased resulting in increased water surface elevation due to encasement, a generic power equation in the form of Y = aXb was suggested for various channel slopes for the increased water surface elevation (Y) for each percentage decrease in channel area (X).

scholarly journals Sentinel-3 radar altimetry for river monitoring – a catchment-scale evaluation of satellite water surface elevation from Sentinel-3A and Sentinel-3B

2021 ◽  
Vol 25 (1) ◽  
pp. 333-357
Author(s):  
Cecile M. M. Kittel ◽  
Liguang Jiang ◽  
Christian Tøttrup ◽  
Peter Bauer-Gottwein
Keyword(s):  
Water Surface ◽  
Open Loop ◽  
Surface Elevation ◽  
Catchment Scale ◽  
Spatiotemporal Resolution ◽  
Radar Altimetry ◽  
Water Surface Elevation ◽  
Satellite Constellation ◽  
In Situ Data ◽  
Wide Range

Abstract. Sentinel-3 is the first satellite altimetry mission to operate both in synthetic aperture radar (SAR) mode and in open-loop tracking mode nearly globally. Both features are expected to improve the ability of the altimeters to observe inland water bodies. Additionally, the two-satellite constellation offers a unique compromise between spatial and temporal resolution with over 65 000 potential water targets sensed globally. In this study, we evaluate the possibility of extracting river water surface elevation (WSE) at catchment level from Sentinel-3A and Sentinel-3B radar altimetry using Level-1b and Level-2 data from two public platforms: the Copernicus Open Access Hub (SciHub) and Grid Processing on Demand (GPOD). The objectives of the study are to demonstrate that by using publicly available processing platforms, such databases can be created to suit specific study areas for any catchment and with a wide range of applications in hydrology. We select the Zambezi River as a study area. In the Zambezi basin, 156 virtual stations (VSs) contain useful WSE information in both datasets. The root-mean-square deviation (RMSD) is between 2.9 and 31.3 cm at six VSs, where in situ data are available, and all VSs reflect the observed WSE climatology throughout the basin. Some VSs are exclusive to either the SciHub or GPOD datasets, highlighting the value of considering multiple processing options beyond global altimetry-based WSE databases. In particular, we show that the processing options available on GPOD affect the number of useful VSs; specifically, extending the size of the receiving window considerably improved data at 13 Sentinel-3 VSs. This was largely related to the implementation of GPOD parameters. While correct on-board elevation information is crucial, the postprocessing options must be adapted to handle the steep changes in the receiving window position. Finally, we extract Sentinel-3 observations over key wetlands in the Zambezi basin. We show that clear seasonal patterns are captured in the Sentinel-3 WSE, reflecting flooding events in the floodplains. These results highlight the benefit of the high spatiotemporal resolution of the dual-satellite constellation.

scholarly journals The FLOod Probability Interpolation Tool (FLOPIT): A Simple Tool to Improve Spatial Flood Probability Quantification and Communication

Water ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 666
Author(s):  
Mahkameh Zarekarizi ◽  
K. Joel Roop-Eckart ◽  
Sanjib Sharma ◽  
Klaus Keller
Keyword(s):  
Flood Risk ◽  
Water Surface ◽  
The United States ◽  
Surface Elevation ◽  
Exceedance Probability ◽  
Water Surface Elevation ◽  
Inundation Maps ◽  
Probability Maps ◽  
Flood Probability ◽  
Floodplain Development

Understanding flood probabilities is essential to making sound decisions about flood-risk management. Many people rely on flood probability maps to inform decisions about purchasing flood insurance, buying or selling real-estate, flood-proofing a house, or managing floodplain development. Current flood probability maps typically use flood zones (for example the 1 in 100 or 1 in 500-year flood zones) to communicate flooding probabilities. However, this choice of communication format can miss important details and lead to biased risk assessments. Here we develop, test, and demonstrate the FLOod Probability Interpolation Tool (FLOPIT). FLOPIT interpolates flood probabilities between water surface elevation to produce continuous flood-probability maps. FLOPIT uses water surface elevation inundation maps for at least two return periods and creates Annual Exceedance Probability (AEP) as well as inundation maps for new return levels. Potential advantages of FLOPIT include being open-source, relatively easy to implement, capable of creating inundation maps from agencies other than FEMA, and applicable to locations where FEMA published flood inundation maps but not flood probability. Using publicly available data from the Federal Emergency Management Agency (FEMA) flood risk databases as well as state and national datasets, we produce continuous flood-probability maps at three example locations in the United States: Houston (TX), Muncy (PA), and Selinsgrove (PA). We find that the discrete flood zones generally communicate substantially lower flood probabilities than the continuous estimates.

Morphodynamic stability and characteristic length scales of bifurcations and confluences loops

2021 ◽  
Author(s):  
Niccolò Ragno ◽  
Marco Redolfi ◽  
Marco Tubino
Keyword(s):  
Froude Number ◽  
Water Surface ◽  
Characteristic Length ◽  
Coupled Model ◽  
Surface Elevation ◽  
Momentum Balance ◽  
Water Surface Elevation ◽  
Control Volumes ◽  
Almost All ◽  
Fluvial Environments

<p>The morphodynamics of multi-thread fluvial environments like braided and anastomosing rivers is fundamentally driven by the continuous concatenation of channel bifurcations and confluences, which govern the distribution of flow and sediment among the different branches that are reconnecting further downstream. Almost all studies performed to date consider the two processes separately, although they frequently appear as closely interconnected. In this work, we tackle the problem of analyzing the coupled morphodynamics of such bifurcation-confluence systems by studying the equilibrium and stability conditions of a channel loop, where flow splits into two secondary anabranches that rejoin after a prescribed distance. Through the formulation of a novel theoretical model for erodible bed confluences based on the momentum balance on two distinct control volumes, we show that the dominating anabranch (i.e. that carrying more water and sediment) is subject to an increase of the water surface elevation that is proportional to the square of the Froude number. This increase in water surface elevation tends to reduce the slope of the dominating branch, which produces a negative feedback that tends to stabilize the bifurcation-confluence system. A linear analysis of the coupled model reveals that the stabilizing effect of the confluence depends on the ratio between the length of the connecting channels and the average water depth, independently of the channel slope and Froude number. Furthermore, the effect of the confluence is potentially able to stabilize the channel loop in conditions where the classic stabilizing mechanism at the bifurcation (i.e. the topographical effect related to the gravitational pull on the sediment transport) is very weak, as expected when most of the sediment is transported in suspension. The identification of a characteristic length scale that produces a coupling between the confluences and bifurcations opens intriguing possibilities for interpreting the self-adjustment of the planform scale of natural multi-thread rivers.</p>

scholarly journals Study on Backwater Effect Due to Polavaram Dam Project under Different Return Periods

Water ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 576 ◽  
Author(s):  
Amarnath C R ◽  
Shashidhar Thatikonda
Keyword(s):  
Unsteady Flow ◽  
Water Surface ◽  
Water Levels ◽  
Surface Elevation ◽  
Flood Frequency Analysis ◽  
Discharge Data ◽  
Gate Operation ◽  
Water Surface Elevation ◽  
Flow Simulations ◽  
Flood Discharge

In this study, we present a scenario to evaluate the backwater impacts on upstream of the Polavaram dam during floods. For this purpose, annual peak discharges across the different gauge stations in river stretch considered for flood frequency analysis. Statistical analysis is carried out for discharge data to estimate probable flood discharge values for 1000 and 10,000 years return period along with 0.1 and 0.14 million m3/s discharge. Furthermore, the resulting flood discharge values are converted to water level forecasts using a steady and unsteady flow hydraulic model, such as HEC-RAS. The water surface elevation at Bhadrachalam river stations with and without dam was estimated for 1000 and 10,000 years discharge. Unsteady 2D flow simulations with and without the dam with full closure and partial closure modes of gate operation were analysed. The results showed that with half of the gates as open and all gates closed, water surface elevation of 62.34 m and 72.34 m was obtained at Bhadrachalam for 1000 and 10,000 years. The 2D unsteady flow simulations revealed that at improper gate operations, even with a flow of 0.1 million m3/s, water levels at Bhadrachalam town will be high enough to submerge built-up areas and nearby villages.

scholarly journals Case Study of Transient Dynamics in a Bypass Reach

Water ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1585
Author(s):  
Anton J. Burman ◽  
Anders G. Andersson ◽  
J. Gunnar I. Hellström ◽  
Kristian Angele
Keyword(s):  
Water Surface ◽  
Operating Conditions ◽  
Surface Elevation ◽  
Water Surface Elevation ◽  
Positive Effects ◽  
Downstream Distance ◽  
Hydropower Plants ◽  
Wetted Area ◽  
Bed Stability

The operating conditions of Nordic hydropower plants are expected to change in the coming years to work more in conjunction with intermittent power production, causing more frequent hydropeaking events. Hydropeaking has been shown to be detrimental to wildlife in the river reaches downstream of hydropower plants. In this work, we investigate how different possible future hydropeaking scenarios affect the water surface elevation dynamics in a bypass reach in the Ume River in northern Sweden. The river dynamics has been modeled using the open-source solver Delft3D. The numerical model was validated and calibrated with water-surface-elevation measurements. A hysteresis effect on the water surface elevation, varying with the downstream distance from the spillways, was seen in both the simulated and the measured data. Increasing the hydropeaking rate is shown to dampen the variation in water surface elevation and wetted area in the most downstream parts of the reach, which could have positive effects on habitat and bed stability compared to slower rates in that region.

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