Measuring water heights in rivers and lakes from lightweight unmanned aerial vehicles (UAVs)

Denmark has since the late 1980ties significantly reduced the N-leaching from agriculture, but must further decrease the N-load to coastal waters from agriculture areas to comply with the Water Framework Directive. Farmers are, however, already fertilizing below economical optimum and new regulatory strategies are required. A new spatially targeted regulation, taking spatial variation in natural N-reduction in groundwater into account, is under development. The objectives of this study were to analyse the potential benefits of a spatially targeted regulation based on detailed N-reduction maps and to analyse how uncertainty in the N-reduction maps affects the efficiency of such a regulation. Two ways of spatially targeting was examined: (i) Identification of target areas with low N-reduction where mitigation measures must be applied to reduce N-leaching to a defined level and (ii) redistribution of N-leaching on non-target areas according to the N-reduction maps, so that high leaching rates are relocated to areas with high N-reduction and vice versa. The study illustrates that there are potential benefits of implementing a spatially targeted regulation based on detailed groundwater N-reduction maps. The potential benefits are larger in Odense study catchment than in Norsminde catchment. The results show, that an increase in N-leaching can be allowed on non-target areas without increasing the N-load to surface water, if farmers at the same time implement a spatially targeted regulation. If spatially targeting is solely done by redistributing the present N-leaching a reduction of 8% in N-load can be obtained in Norsminde and 26% in Odense. Uncertainty on the N-reduction maps due to geological uncertainty is found to lower the efficiency of spatially targeted regulation since wrong target areas can be identified. The study shows that using the mean of an ensemble of N-reduction maps can lower this error. The uncertainty of the N-reduction maps decrease with increasing spatial resolution of the maps, but the study also shows that the spatial resolution greatly influences the efficiency of spatially targeted regulation. Abstract This study investigates the hydrogeology and groundwater chemistry for an agricultural riparian area, EVI2, located at a subglacial stream trench with a sandy aquifer near Holtum stream, Denmark. The groundwater flow, nitrate transport and removal were explored in the riparian area in order to understand small-scale nitrate removal processes and parameters. Different data were collected during field trips. Data investigations consisted of analysis of chemistry measurements, geology data as well as 1D PHREEQC modeling, 2D PHAST modeling and 3D MODFLOW modeling. The results show that a 3D model at catchment scale can be used to examine the groundwater flow and origins of the water in the riparian area EVI2 at local scale. It was observed that nitrate is removed at the agricultural field and that nitrate-polluted water is presence in springs at the wetland area of the study site. Nitrate reduction appeared possible in presence of pyrite and organic material at the agricultural field. The analyses show that the processes controlling the water chemistry at the agricultural field with high probability are denitrification with pyrite and organic material as the electron donors, reductive dissolution of iron oxides and sulfate reduction with organic material. Abstract This work investigates the saltwater-freshwater patterns of a part of the Danish Wadden Sea environment covering Rømø, the Wadden Sea lagoon and the Ballum marsh, located in the south-west part of Denmark. This area is composed of a typical Wadden Sea barrier island, lagoon and reclaimed salt marsh setting. To investigate the system hydrogeological observations, geophysical mapping and chemical analyses have been performed. These results indicate that the Rømø system is in equilibrium and that a developed freshwater lens exists. Further they indicate that on the east coast of Rømø the aquifer is artesian and that freshwater flows from Rømø under the Wadden Sea seabed. In the Ballum marsh the results indicate that the system is in disequilibrium with an ongoing freshening tendency; the thickness of freshwater increases with distance east from the Wadden Sea shoreline. To propose future evolution of the system, a numerical model was set up in FEFLOW 7.0. This model was based on a conceptual geological model of the area. Overall three layers were included in the numerical model. These layers were calibrated and validated with freshwater-head observations. Two layers were calibrated with uniform hydraulic conductivity values and one was calibrated with varying hydraulic-conductivity values using pilot points. The model results indicate that the equilibrium on Rømø occurred within a time interval of 850 - 1125 years after the system was no longer dominated by the sea. Further the results indicate that the Wadden Sea lagoon is in equilibrium as model simulations indicate 4550 years of freshening to dilute the saltwater from the North Sea to salinity concentrations corresponding to the Wadden Sea. Finally the results indicate a freshening-time interval of the Ballum marsh area of 850 - 1575 years from present day conditions. Abstract Saltwater intrusions are threatening fresh water resources especially in low-lying coastal areas worldwide. In this study we present a regional scale 3-dimensional density driven groundwater flow and transport model of seawater intruding the coastal aquifers in the transboundary region of Southern Jutland and Northern Germany. Here geophysical and geological mapping show saltwater intrusions up to 20 km inland from the present coast. The 1700km 2 large investigation area adjacent to the Wadden Sea was partly flooded before a dike was build approx. 200 years ago. Based on a detailed heterogeneous geological voxel model spanning from Miocene through Quaternary deposits a large scale groundwater flow model was developed with MODFLOW. Hydraulic parameters were estimated during calibration against head, stream discharge and C-14 age observations using automated regularized inversion. Subsequently a density driven flow and transport model using SEAWAT was set up to simulate the development of the saltwater intrusion during the last ten thousand years. The SEAWAT model was compared to the saltwater extent delineated based on geophysical and geological data. Two features were found that impact the progression of seawater. The complex heterogeneous geology with features such as buried valleys forms preferential flow paths for the seawater in the deeper aquifers. The dike construction changed the conditions in the shallower aquifers from being seawater saturated during flooding (before the dike construction) to being dominated by refreshing (after the dike construction). In this study hydrogeological, geophysical and geochemical data was complimentarily used together with groundwater flow and transport simulations to understand the development of the coastal groundwater system from the past to the future on a regional scale. Abstract The uncertainty of the input structure in groundwater models has long been recognized as a key contributor to the uncertainty of certain types of hydrological forecasts. However, this contribution to uncertainty is most often neglected by using a single model realization. Traditionally, defining the input structures to groundwater models is a manual task, where geological, geophysical and sometimes hydrological data is interpreted in a manual workflow. Most often the geologist setting up the models are well aware of the uncertainties related to the structure, but its contribution is not transferred through the groundwater model. A possible solution to this problematic aspect has been the emergence of effective algorithms for multi-point statistic [1]. An example of such an algorithm is SNESIM. Here, the manual interpretation of the structure can be used as a Training Image. However, for effective use of the algorithm, the probabilities must also be assessed for each lithological unit simulated in each cell of the model, which can be cumbersome. However, once these tasks have been completed, multiple structural realizations can be generated, and these can be assessed in a hydrological model [2]. We present an alternative and highly effective method for generating TI for structural realizations directly from geophysical and lithological data. We applied the concept for a survey area located around the Kasted well field north-west of Aarhus, Denmark. The training image was generated using the clay-fraction resistivity clustering method [3, 4]. An example of a data driven TI can be seen from the figure below The TI was generated as the mode model of a sequential indicator simulation using 200 model realizations. This type of modelling also allows for easy estimation of the probabilities of cluster distributions, which is important for stochastic structure generation using SNESIM. The main benefits of the proposed methodology is the transparent and objective workflow, and the time it takes for model development. The latter is Abstract Quantifying and understanding stream-aquifer interaction is essential for the assessment of water, nutrient and contaminant exchange between land surface, soil, aquifers, and surface waters. In agricultural catchments it is of particular importance because of the risk of leaching of excess nutrients to streams and aquifers. In Denmark, 60 % of the land is agricultural and half of the agricultural land is tile drained. In this study, we investigate a small heavily tile drained agricultural catchment (Knivsbæk Catchment, 12 km 2 ) on Skovbjerg hill island in western Denmark. Our objective is to quantify and understand the runoff to the stream using geophysical, hydraulic and numerical methods. We present the results of a geophysical mapping campaign. Here we mapped the