References of "Westhoff, Martijn"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailHydrodynamics of shallow reservoirs: recent advances
Dewals, Benjamin ULiege; Erpicum, Sébastien ULiege; Ferrara, Vélia et al

in Armanini, Aronne; Nucci, Elena (Eds.) New challenges in hydraulic research and engineering (2018, June)

The reliable prediction of the flow field in shallow reservoirs is crucial to guide the optimal design and operation of these structures. We highlight here configurations leading to bi-stable flow fields ... [more ▼]

The reliable prediction of the flow field in shallow reservoirs is crucial to guide the optimal design and operation of these structures. We highlight here configurations leading to bi-stable flow fields and we present a radically new, energy-based, approach to predict theoretically the flow fields. [less ▲]

Detailed reference viewed: 40 (5 ULiège)
Full Text
Peer Reviewed
See detailDoes the Budyko curve reflect a maximum power state of hydrological systems? A backward analysis
Westhoff, Martijn ULiege; Zehe, Erwin; Archambeau, Pierre ULiege et al

Conference (2016, April)

Almost all catchments plot within a small envelope around the Budyko curve. This apparent behaviour suggests that organizing principles may play a role in the evolution of catchments. In this paper we ... [more ▼]

Almost all catchments plot within a small envelope around the Budyko curve. This apparent behaviour suggests that organizing principles may play a role in the evolution of catchments. In this paper we applied the thermodynamic principle of maximum power as the organizing principle. In a top-down approach we derived mathematical formulations of the relation between relative wetness and gradients driving runoff and evaporation for a simple one-box model. We did this in an inverse manner such that when the conductances are optimized with the maximum power principle, the steady state behaviour of the model leads exactly to a point on the asymptotes of the Budyko curve. Subsequently, we added dynamics in forcing and actual evaporations, causing the Budyko curve to deviate from the asymptotes. Despite the simplicity of the model, catchment observations compare reasonably well with the Budyko curves subject to observed dynamics in rainfall and actual evaporation. Thus by constraining the – with the maximum power principle optimized – model with the asymptotes of the Budyko curve we were able to derive more realistic values of the aridity and evaporation index without any parameter calibration. [less ▲]

Detailed reference viewed: 22 (3 ULiège)
Full Text
Peer Reviewed
See detailEffective soil hydraulic conductivity predicted with the maximum power principle
Westhoff, Martijn ULiege; Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege et al

Conference (2016, April)

Drainage of water in soils happens for a large extent through preferential flowpaths, but these subsurface flowpaths are extremely difficult to observe or parameterize in hydrological models. To ... [more ▼]

Drainage of water in soils happens for a large extent through preferential flowpaths, but these subsurface flowpaths are extremely difficult to observe or parameterize in hydrological models. To potentially overcome this problem, thermodynamic optimality principles have been suggested to predict effective parametrization of these (sub-grid) structures, such as the maximum entropy production principle or the equivalent maximum power principle. These principles have been successfully applied to predict heat transfer from the Equator to the Poles, or turbulent heat fluxes between the surface and the atmosphere. In these examples, the effective flux adapts itself to its boundary condition by adapting its effective conductance through the creation of e.g. convection cells. However, flow through porous media, such as soils, can only quickly adapt its effective flow conductance by creation of preferential flowpaths, but it is unknown if this is guided by the aim to create maximum power. Here we show experimentally that this is indeed the case: In the lab, we created a hydrological analogue to the atmospheric model dealing with heat transport between Equator and poles. The experimental setup consists of two freely draining reservoirs connected with each other by a confined aquifer. By adding water to only one reservoir, a potential difference will build up until a steady state is reached. From the steady state potential difference and the observed flow through the aquifer, and effective hydraulic conductance can be determined. This observed conductance does correspond to the one maximizing power of the flux through the confined aquifer. Although this experiment is done in an idealized setting, it opens doors for better parameterizing hydrological models. Furthermore, it shows that hydraulic properties of soils are not static, but they change with changing boundary conditions. A potential limitation to the principle is that it only applies to steady state conditions. Therefore the rate of adaptation of hydraulic properties should be faster than the rate of change in boundary conditions. [less ▲]

Detailed reference viewed: 21 (6 ULiège)
Full Text
Peer Reviewed
See detailDoes the Budyko curve reflect a maximum power state of hydrological systems? A backward analysis
Westhoff, Martijn ULiege; Zehe, Erwin; Archambeau, Pierre ULiege et al

in Hydrology and Earth System Sciences (2016), 20

Almost all catchments plot within a small envelope around the Budyko curve. This apparent behaviour suggests that organizing principles may play a role in the evolution of catchments. In this paper we ... [more ▼]

Almost all catchments plot within a small envelope around the Budyko curve. This apparent behaviour suggests that organizing principles may play a role in the evolution of catchments. In this paper we applied the thermodynamic principle of maximum power as the organizing principle. In a top-down approach we derived mathematical formulations of the relation between relative wetness and gradients driving runoff and evaporation for a simple one-box model. We did this in an inverse manner such that when the conductances are optimized with the maximum power principle, the steady state behaviour of the model leads exactly to a point on the asymptotes of the Budyko curve. Subsequently, we added dynamics in forcing and actual evaporations, causing the Budyko curve to deviate from the asymptotes. Despite the simplicity of the model, catchment observations compare reasonably well with the Budyko curves subject to observed dynamics in rainfall and actual evaporation. Thus by constraining the model with the asymptotes of the Budyko curve we were able to derive more realistic values of the aridity and evaporation index without any calibration parameter. Future work should focus on better representing the boundary conditions of real catchments and eventually adding more complexity to the model. [less ▲]

Detailed reference viewed: 68 (20 ULiège)
See detailCan the maximum power principle predict effective conductivities of a confined aquifer? A lab experiment
Westhoff, Martijn ULiege; Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege et al

Conference (2015, December 14)

Power can be performed by a system driven by a potential difference. From a given potential difference, the power that can be subtracted is constraint by the Carnot limit, which follows from the first and ... [more ▼]

Power can be performed by a system driven by a potential difference. From a given potential difference, the power that can be subtracted is constraint by the Carnot limit, which follows from the first and second laws of thermodynamics. If the system is such that the flux producing power (with power being the flux times its driving potential difference) also influences the potential difference, a maximum in power can be obtained as a result of the trade-off between the flux and the potential difference. This is referred to as the maximum power principle. It has already been shown that the atmosphere operates close to this maximum power limit when it comes to heat transport from the Equator to the poles, or vertically, from the surface to the atmospheric boundary layer. To reach this state of maximum power, the effective thermal conductivity of the atmosphere is adapted by the creation of convection cells. The aim of this study is to test if the soil’s effective hydraulic conductivity also adapts in such a way that it produces maximum power. However, the soil’s hydraulic conductivity adapts differently; for example by the creation of preferential flow paths. Here, this process is simulated in a lab experiment, which focuses on preferential flow paths created by piping. In the lab, we created a hydrological analogue to the atmospheric model dealing with heat transport between Equator and poles, with the aim to test if the effective hydraulic conductivity of the sand bed can be predicted with the maximum power principle. The experimental setup consists of two freely draining reservoir connected with each other by a confined aquifer. By adding water to only one reservoir, a potential difference will build up until a steady state is reached. The results will indicate whether the maximum power principle does apply for groundwater flow and how it should be applied. Because of the different way of adaptation of flow conductivity, the results differ from that of the atmosphere. [less ▲]

Detailed reference viewed: 27 (13 ULiège)
Full Text
See detailDoes the soil’s effective hydraulic conductivity adapt in order to obey the Maximum Entropy Production principle? A lab experiment
Westhoff, Martijn ULiege; Zehe, Erwin; Erpicum, Sébastien ULiege et al

Conference (2015, April)

The Maximum Entropy Production (MEP) principle is a conjecture assuming that a medium is organized in such a way that maximum power is subtracted from a gradient driving a flux (with power being a flux ... [more ▼]

The Maximum Entropy Production (MEP) principle is a conjecture assuming that a medium is organized in such a way that maximum power is subtracted from a gradient driving a flux (with power being a flux times its driving gradient). This maximum power is also known as the Carnot limit. It has already been shown that the atmosphere operates close to this Carnot limit when it comes to heat transport from the Equator to the poles, or vertically, from the surface to the atmospheric boundary layer. To reach this state close to the Carnot limit, the effective thermal conductivity of the atmosphere is adapted by the creation of convection cells (e.g. wind). The aim of this study is to test if the soil’s effective hydraulic conductivity also adapts itself in such a way that it operates close to the Carnot limit. The big difference between atmosphere and soil is the way of adaptation of its resistance. The soil’s hydraulic conductivity is either changed by weathering processes, which is a very slow process, or by creation of preferential flow paths. In this study the latter process is simulated in a lab experiment, where we focus on the preferential flow paths created by piping. Piping is the process of backwards erosion of sand particles subject to a large pressure gradient. Since this is a relatively fast process, it is suitable for being tested in the lab. In the lab setup a horizontal sand bed connects two reservoirs that both drain freely at a level high enough to keep the sand bed always saturated. By adding water to only one reservoir, a horizontal pressure gradient is maintained. If the flow resistance is small, a large gradient develops, leading to the effect of piping. When pipes are being formed, the effective flow resistance decreases; the flow through the sand bed increases and the pressure gradient decreases. At a certain point, the flow velocity is small enough to stop the pipes from growing any further. In this steady state, the effective flow resistance of the sand bed will be compared with the theoretical optimal flow resistance obtained with the MEP principle. For this study, different magnitudes of the forcing will be tested, while also the effect of dry spells will be explored. [less ▲]

Detailed reference viewed: 30 (6 ULiège)
Full Text
Peer Reviewed
See detailHESS Opinions: From response units to functional units: a thermodynamic reinterpretation of the HRU concept to link spatial organization and functioning of intermediate scale catchments
Zehe, Erwin; Ehret, Uwe; Pfister, Laurent et al

in Hydrology and Earth System Sciences (2014), 18(11), 4635--4655

Detailed reference viewed: 17 (4 ULiège)
Full Text
Peer Reviewed
See detailImportance of temporal variability for hydrological predictions based on the maximum entropy production principle
Westhoff, Martijn ULiege; Zehe, Erwin; Schymanski, Stanislaus J.

in Geophysical Research Letters (2014)

This work builds on earlier work by Kleidon and Schymanski (2008) who explored the use of the maximum entropy production (MEP) principle for modeling hydrological systems. They illustrated that MEP can be ... [more ▼]

This work builds on earlier work by Kleidon and Schymanski (2008) who explored the use of the maximum entropy production (MEP) principle for modeling hydrological systems. They illustrated that MEP can be used to determine the partitioning of soil water into runoff and evaporation—which determines hydroclimatic conditions around the Globe—by optimizing effective soil and canopy conductances in a way to maximize entropy production by these fluxes. In the present study, we show analytically that under their assumption of constant rainfall, the proposed principle always yields an optimum where the two conductances are equal, irrespective of rainfall rate, evaporative demand, or gravitational potential. Subsequently, we show that under periodic forcing or periodic variations in one resistance (e.g., vegetation seasonality), the optimal conductance does depend on climatic drivers such as the length of dry spells or the time of closure of stomata. [less ▲]

Detailed reference viewed: 31 (4 ULiège)
Full Text
Peer Reviewed
See detailAdvancing catchment hydrology to deal with predictions under change
Ehret, U.; Gupta, H. V.; Sivapalan, M. et al

in Hydrology and Earth System Sciences (2014), 18(2), 649--671

Detailed reference viewed: 14 (6 ULiège)
Full Text
Peer Reviewed
See detailMaximum entropy production: can it be used to constrain conceptual hydrological models?
Westhoff, Martijn ULiege; Zehe, E.

in Hydrology and Earth System Sciences (2013), 17(8), 3141--3157

This work builds on earlier work by Kleidon and Schymanski (2008) who explored the use of the maximum entropy production (MEP) principle for modeling hydrological systems. They illustrated that MEP can be ... [more ▼]

This work builds on earlier work by Kleidon and Schymanski (2008) who explored the use of the maximum entropy production (MEP) principle for modeling hydrological systems. They illustrated that MEP can be used to determine the partitioning of soil water into runoff and evaporation—which determines hydroclimatic conditions around the Globe—by optimizing effective soil and canopy conductances in a way to maximize entropy production by these fluxes. In the present study, we show analytically that under their assumption of constant rainfall, the proposed principle always yields an optimum where the two conductances are equal, irrespective of rainfall rate, evaporative demand, or gravitational potential. Subsequently, we show that under periodic forcing or periodic variations in one resistance (e.g., vegetation seasonality), the optimal conductance does depend on climatic drivers such as the length of dry spells or the time of closure of stomata. [less ▲]

Detailed reference viewed: 18 (1 ULiège)
Full Text
Peer Reviewed
See detailA thermodynamic approach to link self-organization, preferential flow and rainfall--runoff behaviour
Zehe, E.; Ehret, U.; Blume, T. et al

in Hydrology and Earth System Sciences (2013), 17(11), 4297--4322

Detailed reference viewed: 9 (1 ULiège)
Full Text
Peer Reviewed
See detailQuantifying hyporheic exchange at high spatial resolution using natural temperature variations along a first order stream
Westhoff, Martijn ULiege; Gooseff, M. N.; Bogaard, T. A. et al

in Water Resources Research (2011), 47

Hyporheic exchange is an important process that underpins stream ecosystem function, and there have been numerous ways to characterize and quantify exchange flow rates and hyporheic zone size. The most ... [more ▼]

Hyporheic exchange is an important process that underpins stream ecosystem function, and there have been numerous ways to characterize and quantify exchange flow rates and hyporheic zone size. The most common approach, using conservative stream tracer experiments and 1-D solute transport modeling, results in oversimplified representations of the system. Here we present a new approach to quantify hyporheic exchange and the size of the hyporheic zone (HZ) using high-resolution temperature measurements and a coupled 1-D transient storage and energy balance model to simulate in-stream water temperatures. Distributed temperature sensing was used to observe in-stream water temperatures with a spatial and temporal resolution of 2 and 3 min, respectively. The hyporheic exchange coefficient (which describes the rate of exchange) and the volume of the HZ were determined to range between 0 and 2.7 × 10−3 s−1 and 0 and 0.032 m3 m−1, respectively, at a spatial resolution of 1–10 m, by simulating a time series of in-stream water temperatures along a 565 m long stretch of a small first-order stream in central Luxembourg. As opposed to conventional stream tracer tests, two advantages of this approach are that exchange parameters can be determined for any stream segment over which data have been collected and that the depth of the HZ can be estimated as well. Although the presented method was tested on a small stream, it has potential for any stream where rapid (in regard to time) temperature change of a few degrees can be obtained. [less ▲]

Detailed reference viewed: 17 (2 ULiège)
Full Text
Peer Reviewed
See detailQuantifying spatial and temporal discharge dynamics of an event in a first order stream, using distributed temperature sensing
Westhoff, Martijn ULiege; Bogaard, T. A.; Savenije, H. H. G.

in Hydrology and Earth System Sciences (2011), 15(6), 1945--1957

Detailed reference viewed: 13 (1 ULiège)
Full Text
See detailHigh resolution temperature observations to identify different runoff processes
Westhoff, Martijn ULiege

Doctoral thesis (2011)

Detailed reference viewed: 19 (1 ULiège)
Full Text
Peer Reviewed
See detailDirect observations of surface water-groundwater interaction using electrical resistivity tomography
Noell, U.; Wießner, C.; Ganz, C. et al

in IAHS-AISH Publication (2011)

Detailed reference viewed: 15 (1 ULiège)
Full Text
Peer Reviewed
See detailQuantifying the effect of in-stream rock clasts on the retardation of heat along a stream
Westhoff, Martijn ULiege; Bogaard, T. A.; Savenije, H. H. G.

in Advances in Water Resources (2010), 33(11), 1417-1425

With the introduction of Distributed Temperature Sensing (DTS) into the field of hydrology, temperature has become a powerful tracer in both space and time. However, the interpretation of the observed ... [more ▼]

With the introduction of Distributed Temperature Sensing (DTS) into the field of hydrology, temperature has become a powerful tracer in both space and time. However, the interpretation of the observed temperature signal is often not straightforward due to its non-conservative behavior. The objective of this research is to explore and quantify the retardation of heat along a small first order stream, with the long-term objective of identifying different runoff mechanisms by using heat as a tracer. We carried out two tracer experiments. A small water storage basin was emptied into the stream over time periods of 50 and 18 min increasing stream discharge roughly by a factor of two. Salt was added as a tracer in both experiments. In the second experiment the temperature of the added water was additionally cooled to about 0 °C by adding snow into the storage basin. The electrical conductivity was measured at three points along the 565 m long stream while the temperature was measured with a resolution of 2 m and 3 min using the DTS system. During the second experiment, we observed a significant time lag between the salt breakthrough curves (BTC) and the heat BTCs. We routed the water with a hydraulic model, which we coupled with a 1-D advection-dispersion model, and in case of heat we also coupled it with an energy balance. We used the salt BTCs to calibrate the transient storage zones, after which we applied the energy balance to simulate the heat BTCs. Although heat exchange with the streambed delays the advection of heat, it could not fully explain the retarded BTC we observed. We hypothesize that the retardation of heat is caused by its storage in the many rock clasts present in the stream and positioned on top of the streambed. To allow for water-rock clast interaction, we included the fraction of rock clasts in the storage term of the advection-dispersion equation. In this approach we only have to add one additional parameter to account for the fraction of rock clasts in the cross-sectional area of the stream. By applying a fraction of 35% we were able to simulate the retarded heat BTC correctly. Although the fraction of rock clasts in the stream will change with different water levels, it is a straightforward approach, which enables us to couple the hydraulic model directly with the advection-dispersion model, while ensuring that the retardation of heat is simulated correctly. [less ▲]

Detailed reference viewed: 20 (2 ULiège)
Full Text
Peer Reviewed
See detailStream Temperature Response to Three Riparian Vegetation Scenarios by Use of a Distributed Temperature Validated Model
Roth, T. R.; Westhoff, Martijn ULiege; Huwald, H. et al

in Environ. Sci. Technol. (2010), 44(6), 2072-2078

Elevated in-stream temperature has led to a surge in the occurrence of parasitic intrusion proliferative kidney disease and has resulted in fish kills throughout Switzerland’s waterways. Data from ... [more ▼]

Elevated in-stream temperature has led to a surge in the occurrence of parasitic intrusion proliferative kidney disease and has resulted in fish kills throughout Switzerland’s waterways. Data from distributed temperature sensing (DTS) in-stream measurements for three cloud-free days in August 2007 over a 1260 m stretch of the Boiron de Morges River in southwest Switzerland were used to calibrate and validate a physically based one-dimensional stream temperature model. Stream temperature response to three distinct riparian conditions were then modeled: open, in-stream reeds, and forest cover. Simulation predicted a mean peak stream temperature increase of 0.7 °C if current vegetation was removed, an increase of 0.1 °C if dense reeds covered the entire stream reach, and a decrease of 1.2 °C if a mature riparian forest covered the entire reach. Understanding that full vegetation canopy cover is the optimal riparian management option for limiting stream temperature, in-stream reeds, which require no riparian set-aside and grow very quickly, appear to provide substantial thermal control, potentially useful for land-use management. [less ▲]

Detailed reference viewed: 19 (0 ULiège)
Full Text
Peer Reviewed
See detailIdentifying seepage in ditches and canals in ploders in \textscThe \textscNetherlands by distributed temperature sensing
Hoes, O. A. C.; Luxemburg, W. M. J.; Westhoff, Martijn ULiege et al

in Lowland Technology International (2009), 11(2), 21-26

Seepage in ditches and canals, a common feature in polders in The Netherlands, is investigated making use of temperature sensing by fiber optic cable. By its high spatial and temporal resolution ... [more ▼]

Seepage in ditches and canals, a common feature in polders in The Netherlands, is investigated making use of temperature sensing by fiber optic cable. By its high spatial and temporal resolution capabilities the technique reveals the complex ensemble of all effects that define the water temperature on the bottom of the watercourses in three polders where a 1300 meter long cable was located. From the temperature signature the location of suspected seepage zones in the water courses can be determined more precisely. The study shows that the sensing of seepage through temperature is time dependent as the signature can temporarily fade and can be extremely localized. This shows the potential for the applied technique. [less ▲]

Detailed reference viewed: 9 (1 ULiège)
Full Text
Peer Reviewed
See detailA distributed stream temperature model using high resolution temperature observations
Westhoff, Martijn ULiege; Savenije, H. H. G.; Luxemburg, W. M. J. et al

in Hydrology and Earth System Sciences (2007), 11(4), 1469-1480

Detailed reference viewed: 13 (1 ULiège)
Full Text
Peer Reviewed
See detailDistributed fiber-optic temperature sensing for hydrologic systems
Selker, John S.; Thévenaz, Luc; Huwald, Hendrik et al

in Water Resources Research (2006), 42(12), 12202

Instruments for distributed fiber-optic measurement of temperature are now available with temperature resolution of 0.01°C and spatial resolution of 1 m with temporal resolution of fractions of a minute ... [more ▼]

Instruments for distributed fiber-optic measurement of temperature are now available with temperature resolution of 0.01°C and spatial resolution of 1 m with temporal resolution of fractions of a minute along standard fiber-optic cables used for communication with lengths of up to 30,000 m. We discuss the spectrum of fiber-optic tools that may be employed to make these measurements, illuminating the potential and limitations of these methods in hydrologic science. There are trade-offs between precision in temperature, temporal resolution and spatial resolution, following the square root of the number of measurements made; thus brief, short measurements are less precise than measurements taken over longer spans in time and space. Five illustrative applications demonstrate configurations where the distributed temperature sensing (DTS) approach could be used: (1) lake bottom temperatures using existing communication cables, (2) temperature profile with depth in a 1400 m deep decommissioned mine shaft, (3) air-snow interface temperature profile above a snow-covered glacier (4) air-water interfacial temperature in a lake, and (5) temperature distribution along a first-order stream. In examples 3 and 4 it is shown that by winding the fiber around a cylinder, vertical spatial resolution of millimeters can be achieved. These tools may be of exceptional utility in observing a broad range of hydrologic processes including evaporation, infiltration, limnology, and the local and overall energy budget spanning scales from 0.003 to 30,000 m. This range of scales corresponds well with many of the areas of greatest opportunity for discovery in hydrologic science. [less ▲]

Detailed reference viewed: 20 (5 ULiège)