Stage-discharge equations for lakes without disharge measurements Simon Andersson In 2015 all lakes, rivers, coastal water and groundwater should be of good ecological statusaccording to the water framework directive from the European Union. In the process ofimproving the quality of Swedish water bodies, knowledge of where problems occur isneeded in order to utilize the resources optimally. The ability of lakes to store water is animportant factor since it controls the flow of water through the country. A stage-dischargeequation is a mathematical relation between discharge from a lake and its water level. Bybetter understanding of stage-discharge equations for lakes, their storage capacity can bedescribed better in hydrological models. This master thesis aims to evaluate methods for determining stage-discharge equations forlakes where a variable amount of field measurements is available. The methods developed inthe project were evaluated by comparison with measured stage-discharge equations made bySMHI (Swedish Meteorological and Hydrological Institute). First, relations between lakeproperties and stage-discharge equations were evaluated. In the second part of the project,tests were made to observe if a stage-discharge equation could be developed from data ofwater levels in a lake and modeled inflow to the lake. Finally, possibilities of estimatingstage-discharge equation through Sjölyftet were evaluated. Sjölyftet is a project financed bythe Swedish Public Employment Service in which unemployed people in Sweden makesimple hydrological measurements for SMHI. The results showed that the use of the same constant standard parameters for all lakes in thestage-discharge equation gives large errors. The use of catchment areas, lake areas and outletwidths gave better results than applying constant standard parameters in stage-dischargeequations. The best method for estimating stage-discharge equations was obtained whenmeasurements of water level for lakes where used. The measurements from Sjölyftet couldnot be evaluated properly because validation data were missing. Although, the data collectedfrom Sjölyftet might be useful in the future.