Effects of hydropeaking on groundwater mixing: from laboratory experiments to field scale observations

2021 ◽  
Author(s):  
Mónica Basilio Hazas ◽  
Francesca Ziliotto ◽  
Giorgia Marcolini ◽  
Massimo Rolle ◽  
Gabriele Chiogna
Keyword(s):  
Groundwater Flow ◽  
Transport Processes ◽  
Mixing Enhancement ◽  
Two Dimensional ◽  
Field Scale ◽  
Flow Topology ◽  
Temporal Scales ◽  
Spatial And Temporal Scales ◽  
Flow And Transport ◽  
River Stage

<p>Hydropeaking, an artificial flow regime consisting on strong and frequent river stage fluctuations, is known to have important effects on groundwater-surface water interaction. It influences the transient dynamics of water flow and also of solute and energy fluxes between aquifers and rivers. In this work, we focus on the effects of hydropeaking at multiple spatial and temporal scales. We start the investigation at the laboratory scale using quasi-two-dimensional flow-through experiments in which we can characterize  flow and transport mechanisms, as well as the topology of the flow field, at high spatial and temporal resolution. We measure and model the spatial moments, the dilution index and the Okubo-Weiss parameter of a transient plume, and find a correlation between changes in flow topology and mixing enhancement. We then investigate a two-dimensional field scale cross section representative of the Adige aquifer in North-East Italy, where two rivers differently affected by hydropeaking influence groundwater flow, and we investigate the system considering hourly and mean daily fluctuations in the river stage. We characterize the transient groundwater dynamics for this and for other aquifers affected by hydropeaking using the Townley number, analyzing the potentiality of such systems for chaotic advection. Finally, at regional scale we use a three-dimensional transient model to show how the Adige aquifer is differently affected by hydropeaking depending on dry and wet years. Moreover, we apply the continuous wavelet transform to identify the main temporal scales of variability detected in the groundwater fluctuations and how they change with time. Our work therefore highlights the relevance of the effect of hydropeaking on groundwater flow and transport processes, and its impact on flow topology and mixing enhancement at multiple spatial and temporal scales.</p>

scholarly journals Field experimental design for pesticide leaching – a modified large-scale lysimeter

2005 ◽  
Vol 7 ◽  
pp. 41-44
Author(s):  
Bertel Nilsson ◽  
Jens Aamand ◽  
Ole Stig Jacobsen ◽  
René K. Juhler
Keyword(s):  
Large Scale ◽  
Preferential Flow ◽  
Fracture Network ◽  
Transport Processes ◽  
Natural Fracture ◽  
Field Scale ◽  
Flow Paths ◽  
Undisturbed Soil ◽  
Flow And Transport ◽  
Preferential Flow Paths

Recent research on Danish groundwater has focused on clarifying the fate and transport of pesticides that leach through clayey till aquitards with low matrix permeability. Previously, these aquitards were considered as protective layers against contamination of underlying groundwater aquifers due to their low permeability characteristics. However, geological heterogeneities such as fractures and macropores have been recognised as preferential flow paths within low permeable clayey till (e.g. Beven & Germann 1982). The flow velocities within these preferential flow paths can be orders of magnitude higher than in the surrounding clay matrix and pose a major risk of transport of contaminants to the underlying aquifers (e.g. Nilsson et al. 2001). Previous studies of transport in fractured clayey till have focused on fully saturated conditions (e.g. Sidle et al. 1998; McKay et al. 1999). However, seasonal fluctuations of the groundwater table typically result in unsaturated conditions in the upper few metres of the clay deposits, resulting in different flow and transport conditions. Only a few experiments have examined the influence of unsaturated conditions on flow and solute (the dissolved inorganic and organic constituents) transport in fractured clayey till. These include smallscale laboratory column experiments on undisturbed soil monoliths (e.g. Jacobsen et al. 1997; Jørgensen et al. 1998), intermediate scale lysimeters (e.g. Fomsgaard et al. 2003) and field-scale tile drain experiments (e.g. Kjær et al. 2005). The different approaches each have limitations in terms of characterising flow and transport in fractured media. Laboratory studies of solute transport in soils (intact soil columns) are not exactly representative of field conditions due to variations in spatial variability and soil structure. In contrast, field studies hardly allow quantification of fluxes and mechanisms of transport. Column and lysimeter experiments are often limited in size, and tile-drain experiments on field scale do not provide spatial resolution and often have large uncertainties in mass balance calculations. Thus, in order to represent the overall natural fracture network systems on a field scale with respect to acquiring insights into flow and transport processes, the lysimeter needs to be larger than normal lysimeter size (< 1 m3). A modified large-scale lysimeter was therefore constructed by the Geological Survey of Denmark and Greenland (GEUS) at the Avedøre experimental field site 15 km south of Copenhagen (Fig. 1). This lysimeter consisted of an isolated block (3.5 ×3.5 ×3.3 m) of unsaturated fractured clayey till with a volume sufficient to represent the overall preferential flow paths (natural fracture network) within lowpermeable clayey till at a field scale.

scholarly journals Concentration Data and Dimensionality in Groundwater Models: Evaluation Using Inverse Modelling

1998 ◽  
Vol 29 (3) ◽  
pp. 149-178 ◽  
Author(s):  
Heidi Christiansen Barlebo ◽  
Mary C. Hill ◽  
Dan Rosbjerg ◽  
Karsten Høgh Jensen
Keyword(s):  
Groundwater Flow ◽  
Cross Section ◽  
Nonlinear Regression ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Concentration Data ◽  
Flow And Transport ◽  
Two Dimensional Model

A three-dimensional inverse groundwater flow and transport model that fits hydraulic-head and concentration data simultaneously using nonlinear regression is presented and applied to a layered sand and silt groundwater system beneath the Grindsted Landfill in Denmark. The aquifer is composed of rather homogeneous hydrogeologic layers. Two issues common to groundwater flow and transport modelling are investigated: 1) The accuracy of simulated concentrations in the case of calibration with head data alone; and 2) The advantages and disadvantages of using a two-dimensional cross-sectional model instead of a three-dimensional model to simulate contaminant transport when the source is at the land surface Results show that using only hydraulic heads in the nonlinear regression produces a simulated plume that is profoundly different from what is obtained in a calibration using both hydraulic-head and concentration data. The present study provides a well-documented example of the differences that can occur. Representing the system as a two-dimensional cross-section obviously omits some of the system dynamics. It was, however, possible to obtain a simulated plume cross-section that matched the actual plume cross-section well. The two-dimensional model execution times were about a seventh of those for the three-dimensional model, but some difficulties were encountered in representing the spatially variable source concentrations and less precise simulated concentrations were calculated by the two-dimensional model compared to the three-dimensional model. Summed up, the present study indicates that three-dimensional modelling using both hydraulic heads and concentrations in the calibration should be preferred in the considered type of transport studies.

Sign in / Sign up

Export Citation Format

Share Document