Competition between topography- and compaction-driven flow in a confined aquifer: Some analytical results   总被引：1，自引：0，他引：1  

Henk Kooi 《Hydrogeology Journal》1999,7(3):245-250

 An analysis is presented of the competition between topography- and compaction-driven flow in a confined aquifer. The aquifer crops out and is unconfined in an area with an elevated water table. In the absence of compaction, the elevated water table drives the flow toward areas with a lower water table, and leakage occurs from the aquifer through an overlying aquitard. Under these conditions, recharge occurs in the outcrop area. When sedimentation occurs above the aquifer away from the outcrop area, compaction tends to reverse the flow direction in the aquifer, causing expulsion of groundwater in the outcrop area. The actual flow field arises from the competition between the two driving mechanisms. An analytical expression for the combined flow field is derived in which the contribution from both mechanisms is apparent. The expression is useful as a practical guideline for estimating whether or not compaction can be safely ignored in regional groundwater-flow studies of confined aquifers. Received, July 1998 / Revised, February 1999 / Acccepted, February 1999  相似文献   

Historical and future development of the tidally averaged transport of sandy sediments in the Scheldt estuary: a 2D exploratory model     

Boelens  Thomas  Schuttelaars  Henk  Plancke  Yves  De Mulder  Tom 《Ocean Dynamics》2020,70(4):481-504

Ocean Dynamics - To investigate the historical development of the tidally averaged transport of sandy sediments in the main branch of the Scheldt estuary over the last decades (1950–2013), a...  相似文献   

Bifurcation analysis of 3D ocean flows using a parallel fully-implicit ocean model     

Jonas Thies  Fred Wubs  Henk A. Dijkstra 《Ocean Modelling》2009,30(4):287

To understand the physics and dynamics of the ocean circulation, techniques of numerical bifurcation theory such as continuation methods have proved to be useful. Up to now these techniques have been applied to models with relatively few degrees of freedom such as multi-layer quasi-geostrophic and shallow-water models and relatively low-resolution (e.g., 4° horizontal resolution) primitive equation models. In this paper, we present a new approach in which continuation methods are combined with parallel numerical linear system solvers. With this implementation, we show that it is possible to compute steady states versus parameters (and perform fully implicit time integration) of primitive equation ocean models with up to a few million degrees of freedom.  相似文献   

Bifurcation analysis of wind-driven flows with MOM4     

Erik Bernsen  Henk A. Dijkstra  Fred W. Wubs 《Ocean Modelling》2009,30(2-3):95-105

In this paper, the methodology of bifurcation analysis is applied to the explicit time-stepping ocean model MOM4 using a Jacobian–Free Newton–Krylov (JFNK) approach. We in detail present the implementation of the JFNK method in MOM4 but restrict the preconditioning technique to the case for which the density distribution is prescribed. For a prescribed density field case, we present bifurcation diagrams, for the first time in MOM4, for the wind-driven ocean circulation. In addition, we show that the JFNK method can reduce the spin-up time to a steady equilibrium in MOM4 considerably if an accurate solution is required.  相似文献   

The organic carbon pump in the Atlantic     

Anne Willem Omta  Jorn Bruggeman  Bas Kooijman  Henk Dijkstra 《Journal of Sea Research》2009,62(2-3):179

The growth, sinking and remineralisation of phytoplankton constitute the soft-tissue carbon pump. Here we derive the expression for the strength of this carbon pump in terms of the nutrient utilisation and the carbon:nutrient ratio of plankton. Furthermore, we aim to determine how the physical environment affects this carbon pump. Thereto, we have used a plankton physiological model with a novel representation of the effect of temperature and light on plankton stoichiometry; it predicts that the effect of temperature on the carbon:nutrient ratio depends on the light conditions. Using this model combined with a mechanistic model for the mixed layer, we have studied the biological carbon pump at the BATS site and at various locations along a meridional transect through the Atlantic Ocean. Our results suggest that the soft-tissue carbon pump is stronger at mid-latitudes than in the (sub-)tropics and near the poles as a consequence of latitudinal variations in algal stoichiometry.  相似文献   

Reconstruction of food conditions for Northeast Atlantic bivalve species based on Dynamic Energy Budgets     

Vnia Freitas  Joana F.M.F. Cardoso  Sílvia Santos  Joana Campos  Jan Drent  Sofia Saraiva  Johannes IJ. Witte  Sebastiaan A.L.M. Kooijman  Henk W. Van der Veer 《Journal of Sea Research》2009,62(2-3):75

Required assimilated energy to support observed growth was reconstructed for four common bivalve species (Mya arenaria, Cerastoderma edule, Mytilus edulis and Macoma balthica) from various Northeast Atlantic coastal areas, along the species distributional range. The approach applied was based on the Dynamic Energy Budget (DEB) theory whereby observed growth patterns in the field, in combination with prevailing temperatures, were used to reconstruct the average food intake experienced in the field scaled to the maximum possible. For all species, results suggest food limitation over the range of locations. In general, reconstructed food intake indicated better conditions for C. edule compared to the other species, while M. edulis presented the lowest food conditions in all the areas. Despite the indications for a latitudinal trend in primary production, no clear pattern or relationship between reconstructed food conditions and latitude was observed suggesting that any trend may be overruled by local conditions.  相似文献   

Sensitivity of the Atlantic meridional overturning circulation to South Atlantic freshwater anomalies     

Andrea A. Cimatoribus  Sybren S. Drijfhout  Matthijs den Toom  Henk A. Dijkstra 《Climate Dynamics》2012,39(9-10):2291-2306

The sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to changes in basin integrated net evaporation is highly dependent on the zonal salinity contrast at the southern border of the Atlantic. Biases in the freshwater budget strongly affect the stability of the AMOC in numerical models. The impact of these biases is investigated, by adding local anomaly patterns in the South Atlantic to the freshwater fluxes at the surface. These anomalies impact the freshwater and salt transport by the different components of the ocean circulation, in particular the basin-scale salt-advection feedback, completely changing the response of the AMOC to arbitrary perturbations. It is found that an appropriate dipole anomaly pattern at the southern border of the Atlantic Ocean can collapse the AMOC entirely even without a further hosing. The results suggest a new view on the stability of the AMOC, controlled by processes in the South Atlantic.  相似文献   

The role of hand calculations in ground water flow modeling   总被引：1，自引：0，他引：1  

Haitjema H 《Ground water》2006,44(6):786-791

Most ground water modeling courses focus on the use of computer models and pay little or no attention to traditional analytic solutions to ground water flow problems. This shift in education seems logical. Why waste time to learn about the method of images, or why study analytic solutions to one-dimensional or radial flow problems? Computer models solve much more realistic problems and offer sophisticated graphical output, such as contour plots of potentiometric levels and ground water path lines. However, analytic solutions to elementary ground water flow problems do have something to offer over computer models: insight. For instance, an analytic one-dimensional or radial flow solution, in terms of a mathematical expression, may reveal which parameters affect the success of calibrating a computer model and what to expect when changing parameter values. Similarly, solutions for periodic forcing of one-dimensional or radial flow systems have resulted in a simple decision criterion to assess whether or not transient flow modeling is needed. Basic water balance calculations may offer a useful check on computer-generated capture zones for wellhead protection or aquifer remediation. An easily calculated "characteristic leakage length" provides critical insight into surface water and ground water interactions and flow in multi-aquifer systems. The list goes on. Familiarity with elementary analytic solutions and the capability of performing some simple hand calculations can promote appropriate (computer) modeling techniques, avoids unnecessary complexity, improves reliability, and is likely to save time and money. Training in basic hand calculations should be an important part of the curriculum of ground water modeling courses.  相似文献   

Groundwater Grows     

Henk M. Haitjema 《Ground water》2014,52(3):325-325

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Relative sea-level rise and the conterminous United States: Consequences of potential land inundation in terms of population at risk and GDP loss   总被引：1，自引：0，他引：1  

Toon Haer  Eugenia Kalnay  Michael Kearney  Henk Moll 《Global Environmental Change》2013,23(6):1627-1636

Global sea-level rise poses a significant threat not only for coastal communities as development continues but also for national economies. This paper presents estimates of how future changes in relative sea-level rise puts coastal populations at risk, as well as affect overall GDP in the conterminous United States. We use four different sea-level rise scenarios for 2010–2100: a low-end scenario (Extended Linear Trend) a second low-end scenario based on a strong mitigative global warming pathway (Global Warming Coupling 2.6), a high-end scenario based on rising radiative forcing (Global Warming Coupling 8.5) and a plausible very high-end scenario, including accelerated ice cap melting (Global Warming Coupling 8.5+). Relative sea-level rise trends for each US state are employed to obtain more reasonable rates for these areas, as long-term rates vary considerably between the US Atlantic, Gulf and Pacific coasts because of the Glacial Isostatic Adjustment, local subsidence and sediment compaction, and other vertical land movement. Using these trends for the four scenarios reveals that the relative sea levels predicted by century's end could range – averaged over all states – from 0.2 to 2.0 m above present levels. The estimates for the amount of land inundated vary from 26,000 to 76,000 km². Upwards of 1.8 to 7.4 million people could be at risk, and GDP could potentially decline by USD 70–289 billion. Unfortunately, there are many uncertainties associated with the impact estimates due to the limitations of the input data, especially the input elevation data. Taking this into account, even the most conservative scenario shows a significant impact for the US, emphasizing the importance of adaptation and mitigation.  相似文献