Department of Geosciences
and Natural Resource Management

Inspiration catalogue

Title - Keywords - Institutions

Trykafhængig permeabilitet og grundvandsmodellering - Kalk, sprækker, anlægsarbejder, pumpning, grundvandsmodellering - COWI, IGN
Vandplanlægning i en dynamisk forsyningsbranche - Vandplanlægning, beslutningsstøtterværktøjer, grundvandsmodeller - COWI, IGN
Implementation of MODFLOW unstructured grid (MODFLOW-USG) in water resource modeling - Groundwater modelling using new techniques - COWI, IGN
Climate change adaptation at Sunds: Groundwater flooding - Hydrological modelling, can forest help avoid flooding? - GEUS, IGN
Saltwater intrusion solutions - Groundwater protection measures, saltwater, modeling - GEUS, IGN
Use of water stable isotopes to calibrate groundwater-lake models: Case study from Lake Tvorup Hul in National Park Thy - Groundwater-lake interaction, field work, modeling - IGN, GEUS
A groundwater-stream nitrate model for Holtum catchment - Groundwater-stream interaction, field work, flow and nitrate modeling - IGN, GEUS
Use of temperature as a tracer for groundwater upwelling (springs) to stream valleys - Groundwater-stream interaction, field work, flow and heat modeling - IGN
Integrated groundwater-surface water modeling (GSFLOW) of the hydrology in National Park Thy - Integrated hydrological modelling, ¹⁸O, field work. - IGN, GEUS
Forest hydrology: Modeling the water and the Cl cycle in an oak stand - forest, modeling, water balance, Cl- balance - IGN
Forest hydrology and grassland hydrology: Modeling the water in a soil warming experiment in Iceland - forest, modeling, water balance, climate change - IGN
Forest ecology: Are forest reserves sinks for atmospheric nitrogen? old-growth - forest, nitrogen retention, leaching - IGN
Forest hydrology: Afforestation as a measure of climate change adaptation - land use change, forest, tree species, hydrology, modeling - IGN, GEUS
Forest hydrology: Modeling ecosystem hydrology under forest change - role of tree species and climate - tree species, forest management, hydrology, modeling, climate - IGN
Forest ecology: Are forest reserves sinks for atmospheric nitrogen? - old-growth forest, nitrogen retention, leaching - IGN
Rewetting landscape: implications for emission of greenhouse gases - wetland, greenhouse gases, field work, modeling - IGN
Large-scale moisture content estimation using cosmic ray probe - Soil moisture, unsaturated zone - IGN
Spatial variability of soil moisture and soil hydraulic parameters - Soil moisture, unsaturated zone - IGN
Application of remote sensing data in hydrological models - Distributed hydrological modelling, remote sensing, spatial patterns - GEUS, IGN
Applicability of machine learning algorithms in hydrology - Machine learning, hydrological modeling, remote sensing, distributed modelling, spatial patterns - GEUS, IGN
Hydrology and water chemistry of nutrient-poor wetlands: Bøllemosen case study - Nature protection, hydrogeology and geophysics, field work, water balance/model - IGN, GEUS
Lake-aquifer interaction: Hydrogeology of Brahetrolleborg Nørresø, Fyn - Groundwater-lake interaction, water and isotope budgets, field work - IGN, GEUS
Mobilization of phosphorous from aquifer sediments - Mobility of P in groundwater, hydrochemistry, lab work, geochemical modeling - IGN, GEUS, SDU
Tracing intrusion and freshening from groundwater chemistry patterns in coastal aquifers - Saltwater intrusion, hydrochemistry, lab work, geochemical modeling - IGN
Hydrogeological process control on lake phosphorous loading - Lake hydrogeology, field and lab work, iron and phosphorous interactions, reactive transport modelling - IGN, GEUS
Phosphorus transport into a seepage lake – a reactive transport modeling - Groundwater-lake interaction, phosphorus reactive transport, modeling, field work - IGN, GEUS
Estimation of recharge for a South African catchment Field investigations, modeling IGN, IWMI
Tracer experiments in fractured chalk - Tracer experiment, pumping test, modeling - IGN, GEUS
Interception in short vegetation - Field experiments, modeling - IGN, GEUS

1. Trykafhængig permeabilitet og grundvandsmodellering

På mange byggeprojekter i København udføres der anlægsarbejde i kalken. Det gælder f.eks. parkeringskældre, metrostationer, fjernvarmeledninger osv. For at kunne udføre arbejdet, sænkes grundvandet i anlægsperioden. Dette arbejde udføres typisk med pumpeboringer placeret i eller umiddelbart udenfor byggegruben. I København reinfiltreres størstedelen af det oppumpede grundvand typisk i boringer, der er placeret i større afstand fra byggegruberne.

Som grundlag for design af anlæg til grundvandskontrol udføres geotekniske boringer samt typisk en eller flere prøvepumpninger og flowlogs. Disse oplysninger indarbejdes i en grundvandsmodel, der anvendes til at fastlægge:

Vandmængder der skal oppumpes, renses og reinfiltreres
Antal pumpeboringer
Antal reinfiltrationsboringer

Det er COWIs erfaring, at der i praksis ofte ender med at blive oppumpet mindre vandmængder, end det var forventet ud fra prøvepumpninger og grundvandsmodelberegninger. En mulig forklaring på dette vurderes at være ”trykafhængig permeabilitet”, dvs. en proces hvor sprækkerne i kalken bliver trykket sammen pga. grundvandssænkning.

Det vil være relevant at få afklaret, i hvor høj grad trykafhængig permeabilitet optræder i kalken, da det dermed bliver muligt at estimere vandmængder mere præcist, og dermed optimere antallet af boringer og vandrensningsenheder.

COWI har for nylig gennemført et projekt, hvor der i forbindelse med udgravning af en stor byggegrube ved Fisketorvet blev sænket grundvand i kalken. Her blev der kun oppumpet ca. halvdelen af det forventede. I projektet vil det være relevant at sammenholde forventede hydrauliske parametre ud fra prøvepumpninger og renpumpning med reelle hydrauliske parametre fastlagt ud fra observerede vandmængder. Der findes således at stort datagrundlag, som kan indarbejdes i en detaljeret grundvandsmodel for byggegruben. Her kan der enten tages udgangspunkt i COWIs eksisterende grundvandsmodel, eller de/den studerende kan selv opstille en grundvandsmodel fra bunden. Yderligere findes der data for aktuel og estimeret sænkningsbehov fra adskillelige andre projekter og det kan være relevant at udføre en analyse af disse for at kvantificere problemets omfang.

Projektet forudsætter, at man kan anvende GMS eller lignende grundvandsmodel software.

Kontaktperson: Jesper Damgaard (jdam@cowi.com), Peter Engesgaard (pe@ign.ku.dk) eller Karsten H. Jensen (khj@ign.ku.dk)

2. Vandplanlægning i en dynamisk forsyningsbranche

Vandforsyningen i Danmark er under konsolidering og dette giver nye muligheder (og udfordringer) i forhold til planlægningen af indvindings- og forsyningsstrukturen. I forbindelse med en strukturundersøgelse af indvindings- og forsyningsstrukturen omkring Roskilde Fjord er der dannet et samarbejde mellem 4 vandforsyninger – Frederikssund Forsyning, FORS (Roskilde), Furesø-Egedal Forsyning og HOFOR. Der er gennemført en række undersøgelser, som peger på at der er mulighed for at udbygge udnyttelsen af grundvandsressourcen på Hornsherred og ved Jyllinge til at forsyne området og dets forventede kraftige udbygning samtidig med at HOFOR kan sikres en yderligere leverance af vand fra området til at dække København og omegnskommunernes fremtidige vandbehov. Der er ligeledes identificeret en kapacitet til at behandle mere vand ved Værket ved Slangerup (HOFOR) og udnytte denne ekstra kapacitet til i den fremtidige forsyningsstruktur. Samtidig peges der på, at der skal bygges et nyt vandværk på Hornsherred i stedet for at renovere yderligere på det gamle.

Alt i alt mange brikker i et kompliceret puslespil om den fremtidige forsyningsstruktur. Dette kompliceres yderligere af, at der er dannet et vandsamarbejde på tværs af Nordsjælland (NOVAFOS), hvori indgår Frederikssund og Furesø-Egedal forsyninger.

Hvad er den optimale udnyttelse af grundvandsressourcen i fremtiden? Hvor skal vandet behandles? Hvordan skal ledningsnettet udbygges for at imødekomme fremtidige vandbehov og sikre en stor forsyningssikkerhed? Beslutningsstøtteværktøjer i denne sammenhæng er grundvandsmodeller, ledningsnetsmodeller, økonomiske modeller mv. som indgår i et komplekst samspil med (vand)politiske interesser og en lovgivning, der er gearet til "hver kommune sin vandforsyning".

Kontaktperson: Anders Refsgaard (anre@cowi.com), Peter Engesgaard, IGN (pe@ign.ku.dk)

3. Implementation of MODFLOW unstructured grid (MODFLOW-USG) in water resource modeling

The Danish Nature Agency has for the past 10 years had the task of ensuring groundwater mapping in Denmark. In this context, COWI has carried out several groundwater modeling tasks in order to set up, calibrate, validate, and perform scenario analyzes to assess the impact on, and the distribution of extraction and recharge catchments. Typical modeling codes include GMS- MODFLOW and MIKE SHE. There are well-developed principles and methods to perform the above tasks, but with the latest developments in the model code MODFLOW, COWI sees a potential to test the applicability of the latest development, unstructured grids (USG). For instance, MODFLOW-USG introduces new features of locally refining the grid resolution around specific geological and hydrological features. This could potentially lead to improved groundwater modeling, especially in vicinity of specific relevant areas/features within a regional model. Therefore, COWI wishes to explore opportunities to implement MODFLOW-USG to perform comparative studies of new and existing groundwater modeling approaches.

Also, the MODFLOW-USG implementation is of great interest in other COWI related groundwater modeling works and therefore the objectives below can be modified to simulation of dewatering related to construction work (such as Metro stations and buildings in the Copenhagen area).

Objectives:

Implement exiting geological layers and hydrological features into the MODFLOW-USG framework
Develop calibration/validation schemes for MODFLOW-USG modeling
Simulate abstraction catchment using MOD-PATH3DU
Analyze differences in calibration/validation using common MODFLOW vs. MODFLOW-USG.
Analyze the simulated catchments with common MODPATH vs. MOD-PATH3DU

Contact person: Sachin Karan (snkn@cowi.com), Peter Engesgaard (pe@ign.ku.dk)

4. Climate change adaptation at Sunds: Groundwater flooding

The town of Sunds located in central Jutland is facing problems with increasing groundwater level resulting in complains from house owners in the area. Groundwater floods the cellars of many houses and creates problems for infrastructure. The high groundwater level is caused by a steadily increasing precipitation during the last century in combination with renovation of sewer pipes that previously drained the groundwater from the town.

Solutions are needed to avoid the problems with groundwater flooding. One option is to reduce groundwater discharge. This can be done by e.g. increasing the fraction of paved area resulting in more overland flow to the sewer system. Alternatively, forest can be established upstream to the town. Evapotranspiration from forests has been shown to be higher than for farm land and afforestation therefore has the potential to decrease groundwater recharge. This is especially the case for conifer forest where the evaporation during winter is relatively high. Another type of solution is the increase drainage within the city. This could be done in different ways, e.g., locally at the individual house or collectively in long drainage pipes installed next to the sewer system or in the most critical places.

Objectives:

Based on the DK-model (MIKE SHE) to set up a local hydrological model for the town of Sunds
To use the hydrological model to describe evaporation and transpiration from land surface using an energy based description.
To test alternative solutions to the groundwater problem at Sunds including:
Quantify the effect of forest on the water resources and groundwater level
Predict the impact of afforestation in a future (wetter) climate
Quantify the effect of increasing the fraction of paved area
Quantify the impact of installing

The project will be part of EU Interreg project TopSoil (www.topsoil.eu). The project will be carried out in collaboration with the Department of Geosciences and Natural Resource Management.

Contact persons: Torben Sonnenborg (tso@geus.dk), Karsten Høgh Jensen (khj@ign.ku.dk)

5. Saltwater intrusion solutions

Coastal areas are the most productive and economically dominant regions of the world. The high water demand in these regions, however, puts tremendous pressure on their freshwater resources and ecosystems. This leads to problems like saltwater intrusion. A set of innovative, practical concepts have been developed for protection, enlargement and utilization of freshwater resources in coastal areas. These subsurface water solutions (SWS) combine innovations in water well design and configuration, allowing for advanced groundwater management, and maximum control over freshwater resources.

Objectives

The objective of the project is to test alternative subsurface water solutions as answers to the freshwater challenges in coastal areas. Typical applications of SWS are (Figure 1):

Freshmaker, enlarging, protecting and utilizing freshwater lenses with horizontal wells.
ASR-coastal, temporal storage of freshwater in brackish groundwater. Standard aquifer storage and recovery (ASR) approaches are unsuitable in brackish groundwater environments.
Freshkeeper, dual zone abstraction against water well salinization. Fresh and brackish groundwater are pumped simultaneously from different depths, providing control over the position of the fresh-brackish interface.

Methods
The Marielyst area on the southern part of Falster Island is facing saltwater intrusion problems both from the sea and fossil marine waters in the deeper part of the exploited fractured chalk aquifer. Saltwater intrusion is increasing due to drainage pumping and abstractions for water supply and irrigation especially during the summer period and may increase in the future due to climate change and sea level rise.

The current project will include the following tasks:

Construction of a saltwater intrusion model (based on FEFLOW or SEAWAT) for the Falster area, including dual-porosity descriptions of the chalk aquifers
Analysis of the feasibility of alternative SWS solutions for controlling saltwater intrusion based on model analysis
Analysis of the robustness of alternative SWS solutions when confronted with climate change and sea level rise

The project will be part of the EU project SUBSOL (www.subsol.org).

Contact persons: Torben Sonnenborg (tso@geus.dk), Klaus Hinsby (khi@geus.dk), Peter Engesgaard (pe@ign.ku.dk)

6. Use of water stable isotopes to calibrate groundwater-lake models: Case study from Lake Tvorup Hul in National Park Thy

Water stable isotopes can be used to map and quantify groundwater-lake exchanges of water and solutes because of a contrast in concentration between groundwater and lake water. A newly developed USGS model can no handle coupled flow and solute transport in groundwater-stream-lake systems.

Lake Tvorup Hul in National Park Thy is affected by what is called brownification from high humus concentrations (unclear water, which affects light penetration to underwater vegetation). Currently we are investigating the potential for restoring the lake by either changing the land use (forest) or drainage patterns around the lake.

The project will involve some field work (water leveling, stream discharge. isotope sampling), but primarily be based on existing data. A 3D Modflow/Mt3D model will be developed and calibrated using groundwater heads, stream discharge, lake levels and water stable isotope concentrations.

The model can be used to e.g. investigate if changes in drainage can improve lake water quality.

Contact person: Peter Engesgaard (pe@ign.ku.dk)

7. A groundwater-stream nitrate model for Holtum catchment

Currently, we are investigating the potential for a differential regulation of application of N fertilizers based on what is called robust and vulnerable areas. The goal is to reduce nitrate concentrations in groundwater, lakes and streams.

Typically there are longer time series of nitrate concentrations in streams than in groundwater, which is also the case for the Holtum catchment.

Traditionally, models have not been able to simulate nitrate transport in streams so a direct comparison with stream concentrations has been difficult. However, a new USGS model can now account for coupled 3D groundwater flow and nitrate transport(Modflow), 1D flow and nitrate transport in streams (STR package), and flow and nitrate mass balance for lakes (LAK package).

The project will involve field work (mainly stream discharge and nitrate sampling) and the conversion of existing flow models to a new USGS model. The model will then be calibrated in terms of flow (heads, discharge) and times series of nitrate in the Holtum stream.

The project will be carried out in collaboration with GEUS (Anker Højberg).

Contact person: Peter Engesgaard (pe@ign.ku.dk)

8. Use of temperature as a tracer for groundwater upwelling (springs) to stream valleys

A newly started project will investigate the potential for multi-scale thermal imaging of stream valleys to identify areas with groundwater upwelling (springs) including satellite data, drones equipped with thermal-infrared camera, and on- and below ground temperature measurements.

The project will include a lot of field work instrumenting a field site with temperature probes and hopefully surveys with drones. The data will used to develop a flow and heat transport model accounting for subsurface (groundwater) and surface (overland) flows in order to quantify the importance of upwelling and subsequent overland flow to stream discharge.

Contact person: Peter Engesgaard (pe@ign.ku.dk), Majken Zibar

9. Integrated groundwater-surface water modeling (GSFLOW) of the hydrology in National Park Thy

National Park Thy consists of many 10s of small to large dune lakes. Some are permanent year-around, some only appear during winter time with significant recharge (high water table) and disappears in summer during periods with low recharge and high evapotranspiration. The water table is therefore dynamic and likely much more dependent on climatic forcing than in other locations. Currently we are using water stable isotopes sampled in 13 lakes and 60 wells to understand the hydrologic connection between rainfall, groundwater and lakes. We have developed a 3D groundwater model using Modflow and LAK3 (Lake water budget package).

The aim is to integrate the groundwater model into GSFLOW, which combines Modflow and a surface water/root zone model in order to have an integrated hydrologic tool that can handle most of the hydrologic cycle.

Objectives:

Sampling of lakes and wells for stable isotopes (field work)
Develop a GSFLOW model
Calibration of GSFLOW model using parameter optimization
Analysis of lake water budgets in relation to time series of water stable isotopes

Contact person: Peter Engesgaard (pe@ign.ku.dk)

10. Forest hydrology: Modeling the water and the Cl cycle in an oak stand

The water use of forests is often higher than from low vegetation. However, the estimates of evapotranspiration in forests are uncertain; they are usually based on modeling of short time series 3-5 years and with limited possibilities for validation. We have soil moisture data from 3 plots in an oak forest close to Copenhagen from more than 10 yrs (in later years with continuous measurements) which are suitable for calibration of soil-water-atmosphere (SWAT) models. At the same time we measure input and soil water concentrations of different elements including Cl. Cl is an inert element that can be used to validate the water balance calculated by the model.

Objectives:

To calibrate a SWAT-model to three plots in Vestskoven.
To establish a Cl balance for the plots for independent validation of the percolation estimates.

Contact person: Per Gundersen (pgu@ign.ku.dk), Jesper Riis Christiansen (jrc@ign.ku.dk), Per Bjergager

11. Forest hydrology and grassland hydrology: Modeling the water in a soil warming experiment in Iceland

Following an earthquake in southern Iceland geothermal patterns changed and lead to ‘soil warming’ below a small spruce forest and a grassland. This has been used to set up experimental gradients of soil warming where biologist are looking at the major questions in climate change (http://landbunadur.rala.is/landbunadur/wgrala.nsf/key2/hhjn8s6gwu.html). However, no one is concerned about the hydrology because the precipitation is relative high.

There are local climate data, some soil physics and time series of surface soil moisture which are suitable for calibration of soil-water-atmosphere (SWAT) models. We have obtained soil water chemistry data which after setting up the model can be used to calculate leaching fluxes.

Here you will learn about the difference in water use of forests vs low vegetation. You will be able connect your work to major questions related to climate change.

Cl is an element that can be used to validate the water balance calculated by the model.

Objectives:

To calibrate a SWAT-model to forest and grassland on the same site.
To use the calibrated model to look at the effect of warming and to provide percolation estimates.
To calculate element fluxes including using Cl as inert tracer to roughly validate the percolation results.

Contact persons: Per Gundersen (pgu@ign.ku.dk), Jesper Riis Christiansen (jrc@ign.ku.dk).

12. Forest ecology: Are forest reserves sinks for atmospheric nitrogen?

Two old growth forests in Denmark are leaching nitrate from the root zone, i.e. nitrogen from deposition is not retained. Thus we ask if forest reserves under elevated nitrogen deposition generally have high nitrate leaching because there is no removal of N with biomass harvest?

Objectives:

Literature search for data on soil solution nitrate concentration and N-leaching fluxes from old growth forests.
Visit forest reserves in DK, S-SE, N-DE to sample soil for N-extration

Contact person: Per Gundersen (pgu@ign.ku.dk)

13. Forest hydrology: Afforestation as a measure of climate change adaptation

Evapotranspiration from forests has been shown to be higher than for farm land and afforestation therefore has the potential to decrease extreme runoff events. In addition, the drainage efficiency of the soils below forest is expected to be lower than for agricultural land where artificial drainage systems are often installed. Thus, forests may acts as buffers to reduce extreme runoff events and slowly release water during drier periods. However, long term impacts on water balance and groundwater formation and hence climate adaptation potential are not clear as it is expected that soil drainage capacity will change over time as a consequence of forest stand development.

Objectives:

Analyze 4 decades of groundwater level data and runoff from a unique experiment where forest has been planted on two areas, one drained and one un-drained
Investigate the link between precipitation events (short and long term) and runoff from the forest area
Develop a conceptual model for the effect of forest development on runoff partitioning in to groundwater and surface runoff by combining changes in evapotranspiration and drainage efficiency over time
Predict the impact of afforestation in a future (wetter) climate

The project will be carried out in collaboration with the Department of Geosciences and Natural Resource Management and GEUS.

Contact persons: Jesper Riis Christiansen, jrc@ign.ku.dk, Torben Sonnenborg, tso@geus.dk

14. Forest hydrology: Modeling ecosystem hydrology under forest change - role of tree species and climate

Forests are instrumental to maintain our drinking water reserves. However, it is less well known how forest development and management regime impacts the amounts of the groundwater formation in the long term and how this is influenced by climatic variability. The project will use a unique experimental study site in Denmark where the groundwater level has been followed for almost 6 decades. We seek a student to combine groundwater level observations with hydrological modeling to estimate the development of the forest water balance over time. It may be possible to do field work to support modeling: soil sampling for soil physical properties and measurement of groundwater level loggers. This project is relevant for both shorter (30 ECTS) and longer (45-60 ECTS) projects as the amount of field work is flexible.

Objectives:

To understand how afforestation will impact percolation and groundwater formation under temperate forests
To model the water balance over the forest rotation under different management regimes and include historic data on stand development and climate variability
To measure soil physical characteristics and seasonal variation in groundwater levels

Contact person: Jesper Riis Christiansen, jrc@ign.ku.dk

15. Forest ecology: Are forest reserves sinks for atmospheric nitrogen?

Objectives:

Literature search for data on soil solution nitrate concentration and N-leaching fluxes from old growth forests.
Visit forest reserves in DK, S-SE, N-DE to sample soil for N-extration

Contact person: Per Gundersen (pgu@ign.ku.dk)

16. Rewetting landscape: implications for emission of greenhouse gases

Large-scale land use changes are happening in Denmark as previously drained wetlands are being restored by reintroducing wet conditions in the soil. Apart from changing the hydrological functioning of the restored wetlands the altered soil hydrology will impact the dynamics of greenhouse gases, in particular the strong greenhouse gas, methane. Rewetting has been proposed as a mitigation strategy to reduce carbon dioxide emissions from wetlands as rewetting effectively stops oxidation of organic carbon. However, it can be hypothesized that rewetting boosts methane production. However, very little is known of the short- and long-term consequences for the balance between carbon dioxide and methane emissions from soils following rewetting of previously drained wetlands.

Objectives:

Literature study on the current knowledge for Danish wetlands
Characterising hydrology in drained and restored wetlands
Measuring the exchange of methane and carbon dioxide with a new system, SkyLine 2D
Modeling and scaling fluxes in space and time

Contact persons:Jesper Riis Christiansen, jrc@ign.ku.dk, Klaus Steenberg Larsen (ksl@ign.ku.dk)

17. Large-scale moisture content estimation using cosmic ray probe

Soil moisture exerts a critical control on the processes of evapotranspiration and recharge and is thus essential for the water balance. We are still confronted with a mismatch between the measurement scale and the scale of numerical models. Stationary cosmic ray probes provide measurements at a scale of diameter 600 m, which is a much more appropriate scale in relation to hydrological models. Multiple sites are installed with stationary probes, both within the HOBE catchment (Voulund, Harrild Hede and Gludsted), and in Vestskoven close to Ballerup. The stationary probes give a refined temporal variation of soil moisture at given locations, while a mobile detector mounted on a vehicle provides a spatial coverage.

Objectives:

Analyze cosmic-ray neutron intensities using different probes placed at different locations
Compare results with measurements by small-scale soil moisture sensors
Compare with theoretical modeling results
Estimation of large-scale hydraulic parameters

Contact persons: Mie Andreasen (mie.andreasen@geo.ku.dk), Majken C.L. Zibar (mcl@ign.ku.dk), Karsten Høgh Jensen (khj@ign.ku.dk)

18. Spatial variability of soil moisture and soil hydraulic properties

Soil moisture data have been collected using a wide range of sensors and detectors representing different spatial scales. We wish to identify whether there exist soil moisture spatial patterns that are stable in time, and which environmental conditions control the observed pattern. The study could include the measurement of soil hydraulic properties on soil cores in th lab and measurements of water pressure (both time series and spatial distribution).

Objectives:

Analysis of soil moisture data
Collection of soil cores for additional measurement of hydraulic properties
Geostatistical analysis of spatial structures
Analysis of spatial patterns and correlation to landscape characteristics
Analysis and test of up-scaling methods

Contact persons: Mie Andreasen (mie.andreasen@geo.ku.dk), Karsten H. Jensen (khj@ign.ku.dk), Majken C.L. Zibar (mcl@ign.ku.dk)

19. Application of satellite remote sensing data in hydrological models

Satellite remote sensing data offer temporal and spatially distributed data of land surface characteristics which can be used for driving, validating or calibrating distributed hydrological models. This study will explore the use of data from different satellite types in hydrological modeling on variable spatial scales either in Denmark or internationally. Satellite data can be utilized for deriving spatially consistent time series of relevant model input such as rainfall, potential evapotranspiration, vegetation and albedo. In addition valuable spatial pattern information can be derived from input such as land surface temperature and estimates evapotranspiration for hydrological model evaluation.

Objectives:

Deriving hydrological relevant variables from remote sensing data
Testing different types of data for different problems and for different geographical locations
Application of remote sensing data in distributed hydrological models
Spatial pattern evaluation and calibration of hydrological models
Continue the research within the HOBE and SPACE projects

Contact persons: Karsten H. Jensen (khj@ign.ku.dk), Simon Stisen (sst@geus.dk)

20. Applicability of machine learning algorithms in hydrology

Machine learning algorithms offer fast and simple techniques for modeling of complex relationships. Among the range of such algorithms, Random Forests (RF) stands out for its ability to deal with complex nonlinear relationships between variables and its opportunities to address uncertainty. RF is a versatile ensemble learning technique based on a combination of a large set of decision trees. Each tree is trained by selecting a random set of variables and a random sample from the training dataset. Within Hydrology related fields, RF is gaining attention and has successfully been applied to downscale satellite precipitation, to map high-resolution soil properties/vegetation or to conduct seasonal streamflow forecasting. The aim of the proposed Master thesis project is to further expand the applicability of RF in Hydrology and to test how it can best possibly complement traditional hydrological modeling. The project will be carried out in collaboration with GEUS.

Objectives:
Get familiarized with the concepts behind RF and how they are implemented in scripting languages; e.g. Python
Possible applications of RF are:
1. Spatial downscaling of coarse scale soil moisture estimates retrieved by satellite remote sensing (SMOS) with the support of finer scale remote sensing data (MODIS) and in-situ data collected during the HOBE project (www.hobe.dk). Finally, the downscaled soil moisture can be utilized to evaluate simulated spatial patterns of soil moisture by a hydrological model which has previously been setup for the HOBE catchment.
2. Mapping of the redox interface depth at national scale using multiple explaining variables in connection with an Innovation Fond Denmark project.

Contact persons:Simon Stisen (sst@geus.dk), Julian Koch (juko@geus.dk) and Majken C.L. Zibar (mcl@ign.ku.dk)

21. Hydrology and water chemistry of nutrient-poor wetlands: Bøllemosen case study

The Bøllemosen case bog is encircled by forest and therefore generally nutrient poor. However, there are recent indications of deterioration of its ecological state which call for restorative actions. The bog has been previously biologically characterized, and, regarding nutrient loading, it is clear that the bog receives nutrients by atmospheric deposition. However, little remains known about the hydrology and hydrogeochemistry of the bog, which may largely control the ecological state of the habitat. Therefore, in the proposed project the influence of nutrient input from hydrological pathways will be addressed, in a first assessment of the hydrogeology of Bøllemosen.

Bøllemosen is a bog located near Skodsborg 16 km north of Copenhagen. The bog is one of 261 protected EU habitats in Denmark. Danish authorities therefore are responsible for securing or improving its ecological state.

Objectives:

Conduct a literature search to find existing (historical) hydrogeological data regarding Bøllemosen.
Establish a network of piezometers (existing + new) for sampling and necessary to evaluate the catchment boundary.
Conduct geoelectrical investigations in conjuncture with hand drillings and borehole information from existing borehole and create a conceptual hydrogeological model.
Observe the hydrological behavior of surface hydrological features such as ditches, ponds, etc.
Conduct water sampling and analyze for chemistry and stable isotopes of water.
Integrate the information to create a conceptual hydrogeological model and a water balance for Bøllemosen.
Setup a numerical distributed hydrogeological model for Bøllemosen.

Contact persons: Majken Zibar, Søren Jessen (sj@ign.ku.dk), Bertel Nielsson (GEUS)

22. Lake-aquifer interaction: Hydrogeology of Brahetrolleborg Nørresø, Fyn

Brahetrolleborg Nørresø on Fyn appears to exchange water with the surrounding groundwater aquifer, but a more thorough description of the exchange is needed. In previous work, a monitoring network (including water table, flux, water chemistry and δ18O measurements) has been established to carry out a preliminary assessment of the hydrology and hydrogeology of the lake. The aim of the proposed Master thesis project is to extend the existing knowledge, by collecting and analyzing observation time series to understand better the role of the lake in the catchment and setup a hydrological model to describe this. The study will include field work, make use of water chemistry and isotopes as tracers, and include hydrological groundwater modelling.

Objectives:

Gather time series of surface water inflow/outflow to/from the lake, groundwater potentials and lake water levels, water chemistry samples, and stable isotopes of surface- and groundwater, etc.
Develop and refine a thorough conceptual understanding of the interaction between groundwater and surface water at the lake.
Establish a water balance and setup an advanced hydrological model for the lake and its catchment.

Contact persons: Søren Jessen (sj@ign.ku.dk), Jacob Kidmose (GEUS), and Catharina S. N. Madsen

23. Mobilization of phosphorous from aquifer sediments

Phosphorous entering lakes and streams may cause eutrophication and hence degrade the biodiversity and recreational value of these recipients. The overall anthropogenic phosphorous loading, e.g. via waste water, to the environment has been reduced in the past decades. However, only very limited knowledge exist on the natural phosphorous cycling along the subsurface flow paths through aquifers. The proposed master thesis project will investigate the release of phosphorous from Danish aquifer sediments. The sediments are currently collected when new boreholes are drilled are as part of the Danish groundwater monitoring network (GRUMO). Once released from aquifer sediment to the groundwater, phosphorous may be transported with the groundwater flow. The study will address the mobilization and transport of phosphorous through Danish aquifers by measuring he released from and adsorption to the aquifer sediments, and by conducting modelling for typical conceptual model situations.

Objectives:

Make laboratory experiments to determination ‘release’ and ‘transport’ of phosphorous in collected Danish aquifer sandy sediments.
Conduct a geochemical characterization of sediments, e.g., using XRD and wet chemical extraction techniques.
Evaluate the forms of phosphorous released/transported (co-operation with University of Southern Denmark).
Use the results to setup a model describing the mobilization of phosphorous from and retardation within aquifers.

Contact persons: Søren Jessen (sj@ign.ku.dk), Jacob Kidmose (GEUS), Kasper Reitzel (University of Southern Denmark, SDU) and Catharina S. N. Madsen

24. Tracing intrusion and freshening from groundwater chemistry patterns in coastal aquifers

The process of cation exchange in coastal aquifers gives rise to characteristic hydrochemical ‘signatures’ of the groundwater that reveal the direction of groundwater movement. For example, intrusion of Na-Cl seawater in to a fresh aquifer with a Ca-HCO3 type groundwater results in a Ca-Cl2 water type. And during freshening, the flushing of a saline aquifer by fresh Ca-HCO3 water forms a Na-HCO3 water type. These effects are typically visible when data are plotted in Piper diagrams and Stiff diagrams, which are commonly used by the industry in hydrological investigations. However, the cation exchange processes are non-linear and the salt-freshwater interface may move forth and back. The net result is, that the hydrochemical ‘signatures’ may become blurred or masked. The aim of the proposed project is to unmask these patterns, via reactive transport modeling of cation exchange during repeated (modelled) intrusion and freshening. The results of conceptual model cases will be compared to hydrochemical data from the SaltCoast projects activities at Rømø and Brede Stream estuary/delta in south-western Denmark.

Objectives:
Collect estuary/delta sediment and depth-matched water samples.
Measure in the laboratory the amounts of exchangeable cations, and the cation exchange coefficients to be used in the modelling.
Setup a 1D model to derive the hydrochemical ‘signatures’ arising from single and repeated events of intrusion and freshening.
Develop an automated plotting scheme of the 1D-model result into e.g. Piper diagrams.
Conceptualize the findings in order to broaden the applicability thereof by industry users.

Contact persons: Søren Jessen (sj@ign.ku.dk), Peter Engesgaard and Rena Meyer

25. Hydrogeological process control on lake phosphorous loading

Phosphorous is easily adsorbed to iron oxides. Therefore, when groundwater rich in iron and phosphorous discharges to a lake, the phosphorous may become immobilized via oxidation of the iron in the oxic lake bottom, before the water enters the lake. This may prevent a lake fed by groundwater from becoming eutrophic. However, if the groundwater discharge to the lake is very high, and occurs only in a small part of the lake bottom area, then the flow velocity may exceed a threshold above which the time require for oxidation of the iron and removal of phosphorous is not long enough. In such a case, phosphorous will be added to the lake water column and the lake may become eutrophic.

Objectives:

Conduct field and laboratory experiments to investigate the kinetics of phosphorous and iron removal in the presence and absence of the surface lake sediments which transmits groundwater to the lake.
Model the kinetics of iron and phosphorous removal in relation to flow velocities of groundwater discharge.
Assess the hydrogeological threshold condition required for iron-and-phosphorous-rich groundwater discharge to directly load lake water with bioavailable phosphorous.

Contact persons: Søren Jessen (sj@ign.ku.dk), Catharina S. N. Madsen, Jolanta Kazmierczak og Jacob Kidmose

26. Phosphorus transport into a seepage lake – a reactive transport modeling

It has been found that Lake Væng located in central Jutland is eutrophic due to groundwater-driven phosphorus transport into the lake. The objective of this study is to understand processes responsible for phosphorus mobilization and transport in the aquifer.

Feflow flow model, groundwater chemistry database and conceptual hydrogeochemical model were set up for the lake for the period 2011-2014. Development of a new Feflow plug-in (piChem) allowed for coupling Feflow flow models with 1D PhreeqC reactive transport models in order to simulate hydrogeochemical processes and contaminant transport in aquifers and at the groundwater-lake interface.

The project will involve field work (mainly hydraulic head and seepage measurements) and the development of the existing flow model into a reactive transport model. The model will be calibrated in terms of flow (heads, groundwater discharge to the lake) and groundwater chemistry in the aquifer interacting with Lake Væng.

The project will be carried out in collaboration with GEUS (Jolanta Kazmierczak) with an office space at the Hydrogeochemistry Department.

Contact person: Peter Engesgaard (pe@ign.ku.dk), Jolanta Kazmierczak (jka@geus.dk)

27. Estimation of recharge for a South African catchment

Managing groundwater resources requires knowledge of the aquifer systems and their interactions with terrestrial, rivers and wetland systems, and importantly the replenishment of groundwater. Replenishment of groundwater can occur as diffuse or focused recharge. Diffuse recharge is recharge that is distributed over the catchment in response to precipitation. Focused recharge occurs from rivers and varies more in space and time than diffuse recharge. Though both components are difficult to estimate particularly under arid and semi-arid conditions, most uncertainties are related to the focused recharge and particularly for ephemeral rivers. Previous studies have shown that focused recharge is the most uncertain component of the water balance, due to lack of field evidence.

Objectives:
Hydrogeological field work including measurements of hydraulic heads, slugtests, pumping tests, infiltration test, and core sampling.
Geophysical field investigations.
Field investigations of focused recharge using various field techniques including differential river gauging and heat tracing.

Contact person: Karsten H. Jensen (khj@ign.ku.dk), Karen Villholth (K.Villholth@cgiar.org)

28. Tracer test in fractured chalk

A significant part of the water abstracted for water supply in Denmark comes from chalk aquifers. Due to the geography of Denmark the abstraction takes place near the coast and it as such vulnerable to salt water intrusion. It is important to get an improved understanding of the hydraulic behaviour as well as migration of salt in chalk systems which often are subject to significant fracturing. GEUS is currently undertaking a project near Marielyst at the island of Falster where field investigations are carried out. This offers a unique opportunity to be part of this project.

Objectives:

To obtain a better understanding of flow and transport in fractured chalk
To carry out hydraulic tests for estimating hydraulic properties
To estimate transport parameters by tracer tests
To apply a numerical flow and transport model for data interpretation

Contact persons: Karsten H. Jensen (khj@geo.ku.dk), Torben Sonnenborg (tso@geus.dk)

29. Interception in short vegetation

The significance of interception in short vegetation such as agricultural crops is unknown as measurements are scarce if existing at all. In this study experimental field techniques will be developed and implemented at the agricultural site Voulund. The data will serve the purpose of quantifying interception losses in short crops and for developing and testing an interception model.

Objectives:
Development of experimental techniques for measuring interception/throughfall in short crops (Voulund site)
Quantification of the water balance components
Development and testing of interception and throughfall models for short crops

Contact persons: Karsten H. Jensen (khj@ign.ku.dk), Torben Sonnenborg (tso@geus.dk)