Publications from the joint project KliMoBay

Concept of Water Supply for rewetting the fen peatland around research site Karolinenfeld

Timon Lauber 2021, Chair of Hydrology and River Basin Management, Technical University of Munich, Master thesis

In this thesis, the potential surplus of the water balance for an anthropogenically altered peatland around the research site Karolinenfeld has been calculated, to answer the question whether an additional water supply for the considered area is necessary for rewetting the peatland. This study was conducted at the chair of Hydrology and River Basin Management (TUM) and contributes to the KliMoBay (Klimaschutz- und Anpassungspotentiale in Mooren Bayerns) project. In this work, a water balance calculation has been performed using the conceptual modelling software AKWA-M. Since no discharge data of the area outlet are available, the first working step was to calibrate the model against a reference time series for groundwater measurements, which are available for a self-enclosed sheet pile basin within the research area. Therefore, two model approaches namely Dense Soil Base approach and the peatland module “EDOM” provided by AKWA-M, were used. After both approaches were calibrated and validated against the reference time series, the evaluation shows that both model approaches can reproduce the course of the groundwater table adequately. Subsequently, the final model setups were used to transfer the corresponding evaporation rates to the entire area. It has been shown that the model approach EDOM, which originally has been calibrated for peatlands, is not able to simulate land uses as croplands or grasslands. The upscaling of the Dense Soil Base approach provided more plausible results and stated that for the entire area an annual water surplus of 587mm/(a*m²) is available. After including an estimation of the discharge for the research area according to Darcy's Law, the annual rate of surplus water was reduced. In addition, a total of 5 scenarios with different precipitation rates and changed area discharges were set up. Their results form a range in which the total area can theoretically be rewetted by precipitation only. In absolute terms, the estimated drained pore volume of 1.24 million m³ can theoretically be recharged in about 1-4 years by surplus water. But in practice, a climatic water balance has shown that the surplus of precipitation water is not equally distributed over the whole year and therefore, the groundwater table is likely to fall in summer, despite the overall water balance is positive. In conclusion, the simulations can demonstrate that a rewetting of the area is possible by rainwater alone, but a water buffer is recommended for water injection during dry periods.