Comparison of the ecohydrological models AnnAGNPS and ZIN-AgriTra for a small agricultural catchment 

2021 ◽  
Author(s):  
Johanna Schwenkel ◽  
Stephanie Zeunert ◽  
Huyen Le ◽  
Hannes Müller-Thomy ◽  
Matthias Schöniger ◽  
...  
Keyword(s):  
Mass Balance ◽  
Plant Protection ◽  
Richards Equation ◽  
Computational Time ◽  
Lower Saxony ◽  
Time Step ◽  
Small Stream ◽  
Physically Based ◽  
The Impact ◽  
Precipitation Events

<p>The ecohydrological models AnnAGNPS and ZIN-AgriTra are compared regarding their performance in a small watershed. Both models are presently applied for the transport simulation of plant protection products (PPP) from an agricultural area to a small stream to quantify the impact of reduction measures as part of a comprehensive study.</p><p>The spatial discretization of AnnAGNPS is based on hydrologic response units with homogeneous characteristics (land use, slope and soil type). For the continuous simulations daily time steps are used, only soil moisture is simulated using hourly time steps. The underlying equations are physically based, mostly simple calculation methods are used.<br>ZIN-AgriTra operates on grid cells, which allows a more accurate representation of the flow paths. The model is physically based, e. g. for the unsaturated soil zone the Richards equation is used. This requires detailed soil properties for its parameterization and leads to small computational time steps (minutes to hours) to fulfil the mass balance requirements. The detailed spatial and temporal scales, as well as the complex equations, result in a long computation time in comparison to AnnAGNPS.   <br>AnnAGNPS and ZIN-AgriTra are compared regarding their accuracy in the water balance and the mass balance simulation. For the mass balance different constituents as e. g. sediment, phosphorus and selected pesticides are simulated.</p><p>The study area is located in southern Lower Saxony, Germany. The catchment area has a size of 5 km<sup>2</sup>. The investigated stream (Lahbach) flows along agriculturally cultivated land. The relatively high slopes and the fine soil texture lead to a high fraction of generated discharge (as surface runoff, erosion and rapid interflow) from precipitation events. In the ongoing study the catchment was intensively monitored regarding meteorological and hydrological data. In addition, an event-based monitoring campaign was performed to quantify the reaction of the Lahbach during precipitation events, particularly the change in constituent concentrations. Due to the close cooperation with a local farmer, management measures are known very precisely.</p><p>The different temporal resolution of the input data and the time step of output parameters lead to differences in the agreement between measured and simulated time series among the two models. Overall, ZIN-AgriTra led to a more accurate reproduction of the rainfall-runoff events.</p>

Toward a Robust Canopy Hydrology Scheme with Precipitation Subgrid Variability

2007 ◽  
Vol 8 (3) ◽  
pp. 439-446 ◽  
Author(s):  
Dagang Wang ◽  
Guiling Wang
Keyword(s):  
Land Surface ◽  
Surface Characteristics ◽  
Hydrological Processes ◽  
Canopy Interception ◽  
Time Step ◽  
Covered Area ◽  
Surface Models ◽  
Physically Based ◽  
Interception Loss ◽  
The Impact

Abstract Representation of the canopy hydrological processes has been challenging in land surface modeling due to the subgrid heterogeneity in both precipitation and surface characteristics. The Shuttleworth dynamic–statistical method is widely used to represent the impact of the precipitation subgrid variability on canopy hydrological processes but shows unwanted sensitivity to temporal resolution when implemented into land surface models. This paper presents a canopy hydrology scheme that is robust at different temporal resolutions. This scheme is devised by applying two physically based treatments to the Shuttleworth scheme: 1) the canopy hydrological processes within the rain-covered area are treated separately from those within the nonrain area, and the scheme tracks the relative rain location between adjacent time steps; and 2) within the rain-covered area, the canopy interception is so determined as to sustain the potential evaporation from the wetted canopy or is equal to precipitation, whichever is less, to maintain somewhat wet canopy during any rainy time step. When applied to the Amazon region, the new scheme establishes interception loss ratios of 0.3 at a 10-min time step and 0.23 at a 2-h time step. Compared to interception loss ratios of 0.45 and 0.09 at the corresponding time steps established by the original Shuttleworth scheme, the new scheme is much more stable under different temporal resolutions.

scholarly journals Improvement of anisotropic porosity models with a merging technique

2018 ◽  
Vol 40 ◽  
pp. 06023
Author(s):  
Martin Bruwier ◽  
Pierre Archambeau ◽  
Sébastien Erpicum ◽  
Michel Pirotton ◽  
Benjamin Dewals
Keyword(s):  
Shallow Water ◽  
Flow Characteristics ◽  
Threshold Value ◽  
Computational Grid ◽  
Computational Time ◽  
Time Step ◽  
Shallow Water Models ◽  
The Cost ◽  
The Impact ◽  
Porosity Model

Anisotropic porosity shallow-water models are used to take into account detailed topographic information through porosity parameters multiplying the various terms of the shallow-water equations. A storage porosity is assigned to each cell to reflect the void fraction in the cell and a conveyance porosity is used at each edge to reproduce the impact of subgrid obstacles on the flux terms. To guaranty the numerical stability, the time step depends on the value of the porosity parameters. This may hamper severely the computational efficiency in the presence of cells with low values of storage porosity. Cartesian grids are particularly sensitive to such a case since the meshing stems directly from the choice of the grid size. In this paper, this problem is addressed by using an original merging technique consisting in merging cells with a storage porosity lower than a threshold value with neighbouring cells. The model was tested for modelling a prismatic channel with different orientations between the Cartesian computational grid and the channel direction. The results show that the standard anisotropic porosity model (without merging) improves the reproduction of the flow characteristics; but at the cost of a significantly higher computational time. In contrast, the computational time is drastically reduced and the accuracy preserved when the merging technique is used with the porosity model.

scholarly journals Analysis of Numerical Methods to Include Dynamic Constraints in an Optimal Power Flow Model

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 885
Author(s):  
Francisco Arredondo ◽  
Edgardo Castronuovo ◽  
Pablo Ledesma ◽  
Zbigniew Leonowicz
Keyword(s):  
Power Flow ◽  
Optimal Power Flow ◽  
Transient Stability ◽  
Computational Time ◽  
Integration Time ◽  
Time Step ◽  
Dynamic Constraints ◽  
Electromechanical Oscillations ◽  
Optimal Power ◽  
The Impact

The optimization of the operation of power systems including steady state and dynamic constraints is efficiently solved by Transient Stability Constrained Optimal Power Flow (TSCOPF) models. TSCOPF studies extend well-known optimal power flow models by introducing the electromechanical oscillations of synchronous machines. One of the main approaches in TSCOPF studies includes the discretized differential equations that represent the dynamics of the system in the optimization model. This paper analyzes the impact of different implicit and explicit numerical integration methods on the solution of a TSCOPF model and the effect of the integration time step. In particular, it studies the effect on the power dispatch, the total cost of generation, the accuracy of the calculation of electromechanical oscillations between machines, the size of the optimization problem and the computational time.

scholarly journals A measure of watershed nonlinearity: interpreting a variable instantaneous unit hydrograph model on two vastly different sized watersheds

2011 ◽  
Vol 15 (1) ◽  
pp. 405-423 ◽  
Author(s):  
J. Y. Ding
Keyword(s):  
Shape Factor ◽  
Overland Flow ◽  
Scale Parameter ◽  
Computational Time ◽  
Convolution Integral ◽  
Unit Hydrograph ◽  
Time Step ◽  
N Value ◽  
Instantaneous Unit Hydrograph ◽  
The Impact

Abstract. The linear unit hydrograph used in hydrologic design analysis and flood forecasting is known as the transfer function and the kernel function in time series analysis and systems theory, respectively. This paper reviews the use of an input-dependent or variable kernel in a linear convolution integral as a quasi-nonlinear approach to unify nonlinear overland flow, channel routing and catchment runoff processes. The conceptual model of a variable instantaneous unit hydrograph (IUH) is characterized by a nonlinear storage-discharge relation, q = cNsN, where the storage exponent N is an index or degree of watershed nonlinearity, and the scale parameter c is a discharge coefficient. When the causative rainfall excess intensity of a unit hydrograph is known, parameters N and c can be determined directly from its shape factor, which is the product of the unit peak ordinate and the time to peak, an application of the statistical method of moments in its simplest form. The 2-parameter variable IUH model is calibrated by the shape factor method and verified by convolution integral using both the direct and inverse Bakhmeteff varied-flow functions on two watersheds of vastly different sizes, each having a family of four or five unit hydrographs as reported by the well-known Minshall (1960) paper and the seldom-quoted Childs (1958) one, both located in the US. For an 11-hectare catchment near Edwardsville in southern Illinois, calibration for four moderate storms shows an average N value of 1.79, which is 7% higher than the theoretical value of 1.67 by Manning friction law, while the heaviest storm, which is three to six times larger than the next two events in terms of the peak discharge and runoff volume, follows the Chezy law of 1.5. At the other end of scale, for the Naugatuck River at Thomaston in Connecticut having a drainage area of 186.2 km2, the average calibrated N value of 2.28 varies from 1.92 for a minor flood to 2.68 for a hurricane-induced flood, all of which lie between the theoretical value of 1.67 for turbulent overland flow and that of 3.0 for laminar overland flow. Based on analytical results from the small Edwardsville catchment, the 2-parameter variable IUH model is found to be defined by a quadruplet of parameters N, c, the storm duration or computational time step Δt, and the rainfall excess intensity i(0), and that it may be reduced to an 1-parameter one by defaulting the degree of nonlinearity N to 1.67 by Manning friction. For short, intense storms, the essence of the Childs – Minshall nonlinear unit hydrograph phenomenon is encapsulated in a peak flow equation having a single (scale) parameter c, and in which the impact of the rainfall excess intensity increases from the linear assumption by a power of 0.4. To illustrate key steps in generating the direct runoff hydrograph by convolution integral, short examples are given.

scholarly journals Effect of horizontal divergence on estimates of firn-air content

2020 ◽  
pp. 1-10
Author(s):  
Annika N. Horlings ◽  
Knut Christianson ◽  
Nicholas Holschuh ◽  
C. Max Stevens ◽  
Edwin D. Waddington
Keyword(s):  
Mass Balance ◽  
Temporal Variability ◽  
Satellite Altimetry ◽  
Spatiotemporal Variability ◽  
Accurate Calculation ◽  
Time Step ◽  
Ice Flow ◽  
Air Content ◽  
Ice Sheet Mass Balance ◽  
The Impact

Abstract Ice-sheet mass-balance estimates derived from repeat satellite-altimetry observations require accurate calculation of spatiotemporal variability in firn-air content (FAC). However, firn-compaction models remain a large source of uncertainty within mass-balance estimates. In this study, we investigate one process that is neglected in FAC estimates derived from firn-compaction models: enhanced layer thinning due to horizontal divergence. We incorporate a layer-thinning scheme into the Community Firn Model. At every time step, firn layers first densify according to a firn-compaction model and then thin further due to an imposed horizontal divergence rate without additional density changes. We find that horizontal divergence on Thwaites (THW) and Pine Island Glaciers can reduce local FAC by up to 41% and 18%, respectively. We also assess the impact of temporal variability of horizontal divergence on FAC. We find a 15% decrease in FAC between 2007 and 2016 due to horizontal divergence at a location that is characteristic of lower THW. This decrease accounts for 16% of the observed surface lowering, whereas climate variability alone causes negligible changes in FAC at this location. Omitting transient horizontal divergence in estimates of FAC leads to an overestimation of ice loss via satellite-altimetry methods in regions of dynamic ice flow.

scholarly journals Snow Processes and Climate Sensitivity in an Arid Mountain Region, Northern Chile

Atmosphere ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 520
Author(s):  
Francisco Jara ◽  
Miguel Lagos-Zúñiga ◽  
Rodrigo Fuster ◽  
Cristian Mattar ◽  
James McPhee
Keyword(s):  
Mass Balance ◽  
Air Temperature ◽  
Reanalysis Data ◽  
Human Populations ◽  
Arid Environments ◽  
Northern Chile ◽  
Blowing Snow ◽  
Physically Based ◽  
Snow Model ◽  
The Impact

Seasonal snow and glaciers in arid mountain regions are essential in sustaining human populations, economic activity, and ecosystems, especially in their role as reservoirs. However, they are threatened by global atmospheric changes, in particular by variations in air temperature and their effects on precipitation phase, snow dynamics and mass balance. In arid environments, small variations in snow mass and energy balance can produce large changes in the amount of available water. This paper provides insights into the impact of global warming on the mass balance of the seasonal snowpack in the mountainous Copiapó river basin in northern Chile. A dataset from an experimental station was combined with reanalysis data to run a physically based snow model at site and catchment scales. The basin received an average annual precipitation of approximately 130 mm from 2001 to 2016, with sublimation losses higher than 70% of the snowpack. Blowing snow sublimation presented an orographic gradient resultant from the decreasing air temperature and windy environment in higher elevations. Under warmer climates, the snowpack will remain insensitive in high elevations (>4000 m a.s.l.), but liquid precipitation will increase at lower heights.

Assessment of Unsteadiness Modeling for Transient Natural Convection

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
M. Fadl ◽  
L. He ◽  
P. Stein ◽  
G. Marinescu
Keyword(s):  
Natural Convection ◽  
Numerical Stability ◽  
Thermal Design ◽  
Computational Time ◽  
Time Step ◽  
Loosely Coupled ◽  
Accuracy Requirement ◽  
Transient Natural Convection ◽  
Renewable Power ◽  
The Impact

Turbine flexible operations with faster startups/shutdowns are required to accommodate emerging renewable power generations. A major challenge in transient thermal design and analysis is the time scale disparity. For natural cooling, the physical process is typically in hours, but on the other hand, the time-step sizes typically usable tend to be very small (subseconds) due to the numerical stability requirement for natural convection as often observed. An issue of interest is: What time-step sizes can and should be used in terms of stability as well as accuracy? In this work, the impact of flow temporal gradient and its modeling is examined in relation to numerical stability and modeling accuracy for transient natural convection. A source term-based dual-timing formulation is adopted, which is shown to be numerically stable for very large time-steps. Furthermore, a loosely coupled procedure is developed to combine this enhanced flow solver with a solid conduction solver for solving unsteady conjugate heat transfer (CHT) problems for transient natural convection. This allows very large computational time-steps to be used without any stability issues, and thus enables to assess the impact of using different time-step sizes entirely in terms of a temporal accuracy requirement. Computational case studies demonstrate that the present method can be run stably with a markedly shortened computational time compared to the baseline solver. The method is also shown to be more accurate than the commonly adopted quasi-steady flow model when unsteady effects are non-negligible.

scholarly journals State updating of a distributed hydrological model with Ensemble Kalman Filtering: effects of updating frequency and observation network density on forecast accuracy

2012 ◽  
Vol 16 (9) ◽  
pp. 3435-3449 ◽  
Author(s):  
O. Rakovec ◽  
A. H. Weerts ◽  
P. Hazenberg ◽  
P. J. J. F. Torfs ◽  
R. Uijlenhoet
Keyword(s):  
Hydrological Model ◽  
Forecast Accuracy ◽  
Markov Property ◽  
Distributed Hydrological Model ◽  
Time Step ◽  
Observation Network ◽  
Physically Based ◽  
Spatially Distributed ◽  
Observation Uncertainty ◽  
The Impact

Abstract. This paper presents a study on the optimal setup for discharge assimilation within a spatially distributed hydrological model. The Ensemble Kalman filter (EnKF) is employed to update the grid-based distributed states of such an hourly spatially distributed version of the HBV-96 model. By using a physically based model for the routing, the time delay and attenuation are modelled more realistically. The discharge and states at a given time step are assumed to be dependent on the previous time step only (Markov property). Synthetic and real world experiments are carried out for the Upper Ourthe (1600 km2), a relatively quickly responding catchment in the Belgian Ardennes. We assess the impact on the forecasted discharge of (1) various sets of the spatially distributed discharge gauges and (2) the filtering frequency. The results show that the hydrological forecast at the catchment outlet is improved by assimilating interior gauges. This augmentation of the observation vector improves the forecast more than increasing the updating frequency. In terms of the model states, the EnKF procedure is found to mainly change the pdfs of the two routing model storages, even when the uncertainty in the discharge simulations is smaller than the defined observation uncertainty.

scholarly journals Assessment of Unsteadiness Modelling for Transient Natural Convection

2017 ◽  
Author(s):  
M. Fadl ◽  
L. He ◽  
P. Stein ◽  
G. Marinescu
Keyword(s):  
Natural Convection ◽  
Numerical Stability ◽  
Thermal Design ◽  
Computational Time ◽  
Steam Turbines ◽  
Time Step ◽  
Loosely Coupled ◽  
Accuracy Requirement ◽  
Renewable Power ◽  
The Impact

Flexible operations of steam turbines with faster startups and shutdowns are required to accommodate emerging renewable power generations, needing more advanced prediction tools for transient thermal design and analysis. A major challenge is the time scale disparity. For a natural cooling, the physical process is typically in hours or tens of hours, but on the other hand, the time step sizes typically usable tend to be very small (in seconds or sub-seconds) due to the numerical stability requirement for natural convection as often observed. A general issue to be addressed is what time step sizes can be and should be used in terms of stability as well as accuracy. In the present work, the impact of the temporal gradient in unsteady flow and its modelling is examined in relation to numerical stability and modelling accuracy for natural convectio n. A source term based dual timing for mulation is adopted and implemented in a commercial code, which is shown to be numerically stable for very large time steps for natural convection analysis. Furthermore, a loosely coupled partitioned procedure is developed to combine this enhanced flow solver together with a solid conduction solver for solving transient conjugate heat transfer problems for natural convection. This allows very large computational time steps to be used without any stability issues, and thus enables to assess the impact of using different time step sizes entirely in terms of the temporal accuracy requirement. Computational case studies demonstrate that the present method is more stable at a markedly shortened computational time than the baseline solver. The method is also shown to be more accurate than the commonly adopted quasi-steady methods when unsteady effects are non-negligible.

Development of a Simulation System for Estimating the Impact Force of Tsunami Drift Using the Explicit MPS Method

2021 ◽  
Author(s):  
Yasuhiro Aida ◽  
Tomoki Ikoma ◽  
Koichi Masuda
Keyword(s):  
Large Scale ◽  
Impact Force ◽  
Particle Method ◽  
Simulation System ◽  
Computational Time ◽  
Water Tank ◽  
Time Step ◽  
Mps Method ◽  
Fluid Particles ◽  
The Impact

Abstract When a large-scale tsunami occurs, structures in the coastal area will be destroyed by the impact of tsunami drifts. In the design of tsunami evacuation facilities and petroleum complexes, it is necessary to estimate the impact force of tsunami drift, which varies in size, shape and mass. Although some design equations have been proposed to estimate the impact force of tsunami drift, the impact force varies depending on various conditions such as the draft of the tsunami drifts, the attitude of the collision, the condition of the surrounding flow field, and the rigidity of the structure, etc. No reasonable design equation has been developed yet to meet all these conditions. Therefore, it is necessary to estimate the impact force of tsunami drift by water tank experiments and numerical simulations. In order to simulate the impact of a tsunami drift on a structure by numerical simulation, it is necessary to solve the coupling of fluid, floating object and structure. In this study, we have developed a simulation system that can simulate the impact force of a tsunami drift with the MPS method, which is a kind of particle method. This simulation system introduces an explicit method for pressure calculation, which allows for relatively large scale numerical calculations. In addition, the system is able to reproduce the deformation of structures as an elastic body due to the impact of tsunami drift. In particular, we have introduced an analytical method that allows us to set the computational time step that satisfy the CFL conditions for elastic and fluid particles, respectively, for stable simulation even when there is a large difference between the velocity of fluid particles and the velocity of structural particles caused by elastic waves. As a result of the comparison of the impact force on the cantilevered beam of the tsunami drift with the simulation and the water tank test, the deformation of the structure at the time of impact was reproduced with more than 90% accuracy.

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