Outline for Diploma Thesis on Hydrogeology in Valle

Date: September 2003 until February 2005 Student: Samira Najih

About the MaVal Project Recently, there is the research project MaVal „Interactions between surface water and groundwater in an Alpine environment: Assessment, Modelling, Ecosystem Response, Impact Analysis“ being carried out. The study area is Canton . The overall aim is to understand, how the hydropower system influences the groundwater table and flooding regime in the bottom valley and therefore affects also the growth and disturbance of vegetation. There are still wetlands of natural importance, which are under natural protection. The project is under the leadership of Prof. Paolo Burlando, ETH Zurich. 3 PhD students are foreseen for the main work: Laura Foglia, working at Istituto di Scienze della Terra (IST), Canobbio (close to Lugano), Wolfgang Ruf (working at ETHZ in Zurich) and a third one starting before end of this year. Université de Lausanne is a partner in this project thorough Prof. Hans-Rudolf Pfeifer, who is also scientific advisor at IST: Three diploma students from Lausanne have already handed in their diploma thesis. The core of the project is to build up a modeling framework in order be able to do long-term simulations. The surface water part is mainly under the main responsibility of Wolfgang Ruf, the groundwater part of Laura Foglia, and the vegetation part by the third PhD student, which name is still unknown. The coupling of the models will be a common work. Further information about the project can be found on the web under: www.maggia.ethz.ch.

Target of the Diploma Studies An important issue in the context of the whole project is the question of the exchange rates of water between the river and the aquifer and vice versa as well as the contribution of hillslope surface and subsurface flow into the boundary of the aquifer. Special features, which are subject to be investigated, since they may play an important role, are the alluvial fans, which enter the bottom of the valley from both sides in a great number. Some of the streamflows of the tributaries are influenced by the management of the hydropower system (water extraction). Under most conditions, the tributaries loose all there water within these aquifers before by infiltration before reaching the main river Maggia. Therefore, an understanding about the flow processes in and around these aquifers is extremely important for modeling the entire system. The question, how the large groundwater flow is influenced by the underground structure of the alluvial fans, still has to be answered.

In this diploma work, a conceptual hydrogeological model for selected areas should be developed. This includes the determination of the origin of the water at different locations, and under different conditions such as low water or floods. Flow paths should be investigated, mixing ratios of water determined, and wherever possible, flux rates estimated independently from the calibration results of the groundwater/surface water models.

The areas to be investigated are: • wetland / floodplain area of • alluvial fan of Moghegno • alluvial fan of Gordevio • optional: alluvial fan of Lodano (interpretation more difficult because of pumping form time to time)

Methodology The use of natural tracers, this means the investigation of the hydrochemistry, will be main target. Chemistry of waters vary in space and time. By comparing the concentration of several compounds such as major anions and cations, silica, oxygen isotope 18O, and 222Radon, and temperature, information about origin, age, and mixing rations can be gathered. The different compounds contain different kind of information, but by combining these, some added information can be obtained. Additionally, some runoff measurements of the tributaries and the determination of the infiltrations points give important information about the water fluxes in the fans. Slug tests may be conducted in the piezometers of Moghegno (but some preliminary studies will be performed before), in order to get information about the horizontal layering of the groundwater body. If there is sufficient time, also pumping tests in some of the piezometers could be performed. For next summer, a larger artificial tracer experiment might be carried out. The results should also be interpreted for this diploma study.

Continuous Data Collection From the surface waters and groundwater piezometers, water samples have been taken during the last year, some are already analyzed for their hydrochemistry (and are available), others still have to be analyzed. This kind of sampling and analysis should be continued for the selected areas, additionally, springs and/or small tributaries at the hillslopes should be included in the sampling program. The time interval foreseen for this is about every two months. For single events like floods, an intense campaign with short interval sampling may be useful. Groundwater sampling require pumping. The runoff measurements of the tributaries can be carried out from time to time. The chemical analysis could be performed partly in Lausanne, partly in Zurich. Radon measurements, which give information about infiltration from the river into the aquifer as well as indication about the residence time, can be undertaken with instruments from Zurich. The analysis has to be done within a few days because radioactivity is measured, the half-time is 3.8 days, however the instrument is mobile and easy to carry.

Supervision The diploma work will be supervised by Prof. Hans-Rudolf Pfeifer, Université Lausanne, in collaboration mainly with Wolfgang Ruf, ETH Zurich, and Laura Foglia, IST, but additionally also with Andrea Salvetti, IST.

Zürich, August 22nd, 2003

Wolfgang Ruf