BRIDGE - Eawag

80% of Switzerland's drinking water is groundwater. Climate change-induced droughts and increasing demand for irrigation systems put groundwater under considerable pressure. Groundwater models play an important role in managing this valuable resource. However, there is great potential to improve current modelling practices, in particular, by improving the characterisation of the subsurface and by providing a more realistic representation of the interactions between surface water and groundwater. This project is based on the following joint developments of Eawag, Université de Neuchâtel (UNINE) and Universiät Basel (UNIBAS): (1) By using state-of-the-art mass spectrometry, we complement the existing tracers for hydrologic systems with non-toxic gases that can be injected into the subsurface. In this way, we extend the spatial and temporal scale of the available tracer methods and enable new ways of characterising the subsurface. (2) By building integrated models, we enable the coupled simulation of hydrological processes on the surface, in the subsurface and of operational infrastructure such as pumps, drainage and irrigation systems. The explicit simulation of tracer transport moreover makes model calibration much more robust. (3) By developing new technical and computational methods for the real-time assimilation of data, we ensure that hydrological models are always close to the real system state and can thus be used continuously to support operational decision-making.

Our BRIDGE Discovery Project will make it possible to combine these three new developments and bring them to an operational level. In close cooperation with stakeholders, we are developing and evaluating the efficiency of our hydrological service based on two pilot studies: one to increase the efficiency of irrigation in vegetable cultivation and one to produce drinking water in a complex urban environment.

BRIDGE will allow us to move this fundamental research to an operational level through 12 work packages. In close collaboration with the relevant stakeholders, we develop and assess the efficiency of our hydrogeological service for two pilot studies: one to increase the efficiency of irrigation for agriculture, and the second one to predict the influence of a renaturation on well capture zones. Project vision, economic, societal, environmental impacts: Develop a cutting-edge water resources science and technology service based on the integration of the three aforementioned developments. There is no comparable, commercial service available in Switzerland. Envisioned clients include drinking water producers, the agricultural sector and governmental institutions. A constant revenue stream is generated through the sale of our expertise for hydrologic systems characterization (Service 1) and real-time hydrological forecasting for optimized daily operation (Service 2) based on a subscription service. Both services will increase water use efficiency and will provide an important contribution to resolving the numerous conflicts of aims between stakeholders which currently slow down water resources projects, most notably the renaturation of rivers. Our project is thus an important step forward to making more rational and efficient decisions, and to tackle several UN Sustainable Development Goals, most importantly #6 (clean water), #2 (no hunger) and #15 (life on land).Project team: The project will be managed by Profs. Brunner (UNINE), Schilling (UNIBAS) and Kipfer (EAWAG). We have a long track record of jointly developing these technologies and have highly complementary competencies. Our consortium includes the ETH domain and Universities, and is rooted in the French and German parts of Switzerland.

Hugo Delottier, Hydrogeological Processes, Centre for Hydrogeology and Geothermics (CHYN), University of Neuchâtel, Switzerland
Qi Tang, Hydrogeology Research Group, Department of Environmental Sciences, University of Basel, Switzerland
Morgan Peel, Environmental Isotopes Group, W+T, Swiss Federal Institute of Aquatic Science and Technology (EAWAG), Switzerland
Annette Affolter Kast, Hydrogeology Research Group, Applied and Environmental Geology Working Group, Department of Environmental Sciences, University of Basel, Switzerland

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      authors => protected'Delottier,&nbsp;H.; Peel,&nbsp;M.; Doherty,&nbsp;J.; Schilling,&nbsp;O.&nbsp
         ;S.; Brunner,&nbsp;P.' (97 chars)
      title => protected'Assessing the worth of noble gas tracer concentrations in alluvial river-aqu
         ifer systems using data space inversion' (115 chars)
      journal => protected'Water Resources Research' (24 chars)
      year => protected2026 (integer)
      volume => protected62 (integer)
      issue => protected'7' (1 chars)
      startpage => protected'e2025WR041730 (37 pp.)' (22 chars)
      otherpage => protected'' (0 chars)
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      description => protected'Alluvial systems are dynamic, structurally complex environments. Groundwater
          that is extracted from these systems is widely used for domestic consumptio
         n. Numerical models play an important role in the management of this extract
         ion. To provide support for decision-making, models must assimilate data tha
         t inform the spatial and temporal dynamics of the interactions between alluv
         ial surface water (SW) and groundwater (GW). In theory, assimilation of nobl
         e gas tracer data into numerical models that solve the advection-dispersion 
         equation as it pertains to gas tracer concentrations can reduce the uncertai
         nties of management-salient predictions made by these models. To date, howev
         er, this has not been undertaken; nor has its decision-support efficacy been
          tested. A modeling framework is introduced whereby data space inversion, a 
         highly efficient method for evaluation of post-data-assimilation uncertainti
         es of complex simulators, is used to evaluate benefits accrued through assim
         ilation of noble gas tracer concentrations (i.e., <sup>222</sup>Rn; <sup>37<
         /sup>Ar; <sup>4</sup>He) along with more classical observations. The ability
          of noble gas concentrations to reduce the uncertainties of predictions made
          using an integrated surface-subsurface hydrological model is rigorously eva
         luated in simulation experiments that span a range of plausible hydraulic an
         d hydrological conditions. Outcomes of these experiments demonstrate that me
         asurements of <sup>222</sup>Rn and <sup>4</sup>He concentrations are able to
          constrain temporally-variable predictions, such as the magnitudes of SW-GW 
         exchange fluxes, as well as solute breakthrough curves that reflect the resi
         dence times of potential pollutants following an aquifer contamination event
         . <sup>37</sup>Ar concentrations can also provide important information on S
         W-GW interactions, especially the residence times of bank filtrate.' (1891 chars)
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      authors => protected'Fischer,&nbsp;M.; Delottier,&nbsp;H.; Tang,&nbsp;Q.; Schilling,&nbsp;O.&nbsp
         ;S.; Schiavoni,&nbsp;V.; Brunner,&nbsp;P.' (117 chars)
      title => protected'An automated IoT-Based infrastructure for real-time soil water deficit predi
         ction' (81 chars)
      journal => protected'In: Nunes Alonso,&nbsp;A.; Palmieri,&nbsp;R. (Eds.), Distributed application
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          2026, held as part of the 21st international federated conference on distri
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      categories => protected'IoT-based infrastructure; environmental and meteorological time-series; phys
         ics-based mo dels; agricultural water management' (124 chars)
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      doi => protected'10.1007/978-3-032-27358-1_7' (27 chars)
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      authors => protected'Peel,&nbsp;M.; Solanki,&nbsp;K.; Brunner,&nbsp;P.; Hunkeler,&nbsp;D.; Schill
         ing,&nbsp;O.&nbsp;S.; Kipfer,&nbsp;R.' (113 chars)
      title => protected'A controlled and scalable noble gas injection method for quantitative tracer
          tests in hydrogeological studies' (109 chars)
      journal => protected'Water Research' (14 chars)
      year => protected2026 (integer)
      volume => protected294 (integer)
      issue => protected'' (0 chars)
      startpage => protected'125505 (10 pp.)' (15 chars)
      otherpage => protected'' (0 chars)
      categories => protected'noble gases; artificial tracers; drinking water; quantitative tracer tests' (74 chars)
      description => protected'Dissolved noble gases have been recognized for decades as ideal artificial h
         ydro(geo)logical tracers, as they are chemically inert, invisible, and non-t
         oxic. However, their widespread adoption has historically been limited by th
         e difficulty of tracer injection, sampling, and analysis procedures. Develop
         ments in portable, high-resolution dissolved gas measurement technology over
          the last two decades have rekindled interest in the use of gas tracer metho
         ds for routine hydrogeological investigations, such as well-to-well tracer t
         ests, intra-well tests, or studies of river infiltration towards alluvial aq
         uifers. The application of gases in aqueous environments still poses unique 
         challenges compared to other tracer methods, as potential exsolution and deg
         assing need to be accounted for, and, if possible, avoided during tracer inj
         ection. Here, we present a simple and efficient methodology that addresses t
         hese challenges and allows the efficient, on-site preparation and injection 
         of highly concentrated tracer solutions with controlled dissolved gas concen
         trations. We applied the method in a large drinking water wellfield and perf
         ormed well-to-well tracer tests in an unconfined aquifer using helium-4 (<su
         p>4</sup>He), neon-20 (<sup>20</sup>Ne) and krypton-84 (<sup>84</sup>Kr). Kn
         own tracer quantities were injected together with fluorescent dyes into an o
         bservation well upgradient of a pumping well. Gas tracer breakthrough was mo
         nitored in the pumping well with a portable mass spectrometer. Breakthrough 
         curves of <sup>4</sup>He and <sup>84</sup>Kr compared favorably with fluores
         cent dye tracers, and enabled reliable estimates of groundwater flow velocit
         ies, travel times, and tracer recovery. These findings illustrate how noble 
         gases can substitute or complement other artificial tracer methods, even in 
         large-scale settings. The methodology can be extended to other gases (e.g., 
         neon-22, xenon isotopes, light hydrocarbons), significantly expanding the ra
         nge of artificial tracer...' (2055 chars)
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Delottier, H.; Peel, M.; Doherty, J.; Schilling, O. S.; Brunner, P. (2026) Assessing the worth of noble gas tracer concentrations in alluvial river-aquifer systems using data space inversion, Water Resources Research, 62(7), e2025WR041730 (37 pp.), doi:10.1029/2025WR041730, Institutional Repository

Fischer, M.; Delottier, H.; Tang, Q.; Schilling, O. S.; Schiavoni, V.; Brunner, P. (2026) An automated IoT-Based infrastructure for real-time soil water deficit prediction, In: Nunes Alonso, A.; Palmieri, R. (Eds.), Distributed applications and interoperable systems. 26th IFIP WG 6.1 international conference, DAIS 2026, held as part of the 21st international federated conference on distributed computing techniques,, 105-120, doi:10.1007/978-3-032-27358-1_7, Institutional Repository

Dissolved noble gases have been recognized for decades as ideal artificial hydro(geo)logical tracers, as they are chemically inert, invisible, and non-toxic. However, their widespread adoption has historically been limited by the difficulty of tracer injection, sampling, and analysis procedures. Developments in portable, high-resolution dissolved gas measurement technology over the last two decades have rekindled interest in the use of gas tracer methods for routine hydrogeological investigations, such as well-to-well tracer tests, intra-well tests, or studies of river infiltration towards alluvial aquifers. The application of gases in aqueous environments still poses unique challenges compared to other tracer methods, as potential exsolution and degassing need to be accounted for, and, if possible, avoided during tracer injection. Here, we present a simple and efficient methodology that addresses these challenges and allows the efficient, on-site preparation and injection of highly concentrated tracer solutions with controlled dissolved gas concentrations. We applied the method in a large drinking water wellfield and performed well-to-well tracer tests in an unconfined aquifer using helium-4 (⁴He), neon-20 (²⁰Ne) and krypton-84 (⁸⁴Kr). Known tracer quantities were injected together with fluorescent dyes into an observation well upgradient of a pumping well. Gas tracer breakthrough was monitored in the pumping well with a portable mass spectrometer. Breakthrough curves of ⁴He and ⁸⁴Kr compared favorably with fluorescent dye tracers, and enabled reliable estimates of groundwater flow velocities, travel times, and tracer recovery. These findings illustrate how noble gases can substitute or complement other artificial tracer methods, even in large-scale settings. The methodology can be extended to other gases (e.g., neon-22, xenon isotopes, light hydrocarbons), significantly expanding the range of artificial tracers available for routine hydrogeological investigations.

Peel, M.; Solanki, K.; Brunner, P.; Hunkeler, D.; Schilling, O. S.; Kipfer, R. (2026) A controlled and scalable noble gas injection method for quantitative tracer tests in hydrogeological studies, Water Research, 294, 125505 (10 pp.), doi:10.1016/j.watres.2026.125505, Institutional Repository

Department Water Resources and Drinking Water

BRIDGE - Integrated Hydrological Modelling for Operational Forecasting and Decision-making

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