Predictions of coastal wetland loss depend on reliable estimations of sea-level rise (SLR) and biological feedbacks to geomorphology, yet it is difficult to manipulate SLR to generate empirical data of impacts on wetland processes. Typically, data have been generated through small-scale mesocosm experiments, an approach that may not fully capture biological responses to SLR. Using passive and active weirs, we manipulated inundation depths and times in situ and at larger spatial scales than possible in mesocosms. In June 2013, we simulated three flooding scenarios (low, intermediate and high) using passive weirs designed to increase mean low water (MLW) by approximately 8–9, 12–13 and 16–18 cm, respectively, relative to controls. In March 2014, we also conducted a proof-of-concept exercise to demonstrate that active weirs equipped with a pump can increase both MLW and mean high water (MHW), thereby achieving changes in both inundation depth and inundation time. When compared to controls for the three flooding scenarios, passive weirs increased MLW in the low marsh by 9.1 ± 0.8, 11.8 ± 1.1 and 15.65 ± 0.8 cm, respectively, and in the high marsh by 6.3 ± 3.0, 17.0 ± 4.6 and 8.3 ± 2.5 cm, respectively. Passive weirs increased inundation time in low marsh by 0.4 ± 0.0 hd−1 and 2.9 ± 0.0 hd−1 to 24 hd−1 in both weirs for low and intermediate flooding, respectively, but not for high flooding where the control and weirs were both inundated 24 hd−1. At greater elevations, however, passive weirs increased inundation time in high marsh by 0.9 ± 2.2, 5.1 ± 4.1 and 4.0 ± 0 hd−1, respectively. Weirs slowed drainage rates by 5.6 ± 1.4, 3.8 ± 1.4 and 6.1 ± 0.1 cmh−1, respectively. The active weir increased MLW by 25.4 cm, MHW by 10.5 cm and inundation time by 10.7 hd−1 and slowed the drainage rate by 9.6 cmh−1. Weirs can be used to increase inundation depths and times to study SLR impacts on tidal wetlands, and are advantageous because they minimize disturbance; allow for larger-scale studies within tidal wetlands; and can be maintained at little cost and effort, thereby providing more robust estimates of SLR impacts on tidal wetland processes.