Page - 259 - in Book of Full Papers - Symposium Hydro Engineering

recommended to always include RoS in raw water delivery contracts, thus making sure that the residual risk of water deficit periods is well understood and agreed upon in advance. As these trends and shifts will continue to impact flow volumes and variability in the future, societal demands towards infrastructure, i.e. dams, fulfilling an increased buffering function in the hydrological cycle are also likely to increase. Since some of these dam functions and requirements are contrarian to each other, e.g. flood protection and drinking water supply, it can be expected that dam and reservoir management will become more challenging in the coming decades. Water industry experts are therefore required to plan and prepare possible remedies and solutions well in advance. At Neustadt dam, one remedial measure includes the calibration and operation of a mid-term reservoir management model (MBM), which helps the operator in determining beginning and duration of hydrological surplus periods, based on current and modelled inflow and actual storage content, during which raw water withdrawals can safely be increased beyond RWW365 without compromising RoS [7]. In the future, this model could also be expanded by a module accounting for the water volume occasionally stored in the water catchments snowpack during the winter. Alternatively, one could consider increasing storage capacity from currently 0.48 of mean annual flow to a higher level. Compared to new dam construction, the incremental costs of dam heightening are usually considered smaller. Nevertheless this approach requires careful economic and hydrologic analysis. It must also be pointed out that it does not solve the problem of decreasing inflows per se but merely increases the useable percentage of that flow. An alternative solution includes increasing mean annual reservoir inflow by means of a 5.6 km long gravity transfer tunnel tapping into neighbouring streams at higher altitude than the reservoirs full supply level. An initial survey has revealed that the catchment area could thus be tripled. A geological, hydrological and economic scoping study for this investment is scheduled for 2018. 4. CONCLUSIONS This investigation revealed clear signs of a changing meteorology, hydrology and phenology in the Southern region of one of Germany’s most important water towers. The breakpoint identified in 1987/88 and the sudden shifts associated with it are particularly noteworthy. It contradicts the notion that these changes do manifest themselves in a gradual and linear fashion. The evidence suggests an increased duration and intensity of the vegetation season. In the absence of significant aquifers in the catchment area, the considerable decreases in reservoir inflow observed in the last three decades have most likely been caused by increased actual evapotranspiration. Which portion of the increased evapotranspiration has been caused by modified forest management and decreased forest damage due to improved air quality has not been a subject of this 259