As groundwater flow is generally slow, most groundwater models use time steps larger than one day. These models are used to quantify the influence of groundwater recharge, pumping or changes to the surface water system. Groundwater models are also used to calculate the influence of sea level rise. In alluvial coastal areas, the sea is an important boundary condition. In tidal areas with a shallow slope of the beach, part of the beach only inundates during high tides. The flow resistance of the phreatic aquifer retains the infiltrated seawater. This results in a groundwater level that is higher than mean sea level. Therefore, it can be challenging to incorporate the influence of tides in a groundwater model with time steps larger than the tidal period (just over 12 hours). Several methods to schematize the sea boundary condition have been developed by others in the past. In our research, we explore some of the most practical methods in a MODFLOW 6 groundwater model, from simple (just using mean sea level and a constant resistance) to complex (spatial and temporal variation of the boundary properties). Models with larger time steps and different schematizations are compared to models with smaller time steps and a varying location of the sea, focusing mainly on water quantity. We will use synthetic cross-sectional models in which we can vary the slope of the beach, the aquifer transmissivity and the amplitude of the tides. We will also test the methods on a simplified model of one of the Dutch Wadden Islands, with large natural areas that only flood at high tides. Modelled heads are compared to available head measurements close to the sea. Practical guidelines to schematize the sea boundary condition and possible pitfalls when modeling sea level rise are presented.