Land use impacts on floodplain water table response to precipitation events

Abstract

AbstractTwo floodplain sites were instrumented, a bottomland hardwood forest and a historic agricultural field. Continuous, automated, in situ shallow groundwater monitoring was paired with a gridded sampling design to facilitate detailed spatiotemporal analysis of water table response to precipitation events. Data were collected at 30‐min intervals for the duration of the 2011, 2012, 2013, and 2014 water years. Four hundred three precipitation events were observed, with median depth of 3 mm. Results show significantly (p < .001) greater study site median water table response at the agricultural site (0.02 m), relative to the forest (0.01 m). The ratio of water table response magnitude to precipitation depth was 8.3 and 3.3 at the agricultural and forest sites, respectively, a difference of more than 150%. Median shallow groundwater level lag time was shorter with respect to both precipitation and streamflow at the agricultural site (10 and 2 hr for precipitation and flow, respectively), relative to the forest (11.5 and 4.5 hr for precipitation and flow, respectively). Longer lag times indicated slower water table response and potentially increased flood attenuation capacity by the forest site. Results show the agricultural site water table responded to a greater number of precipitation events (including smaller events), reflecting potentially reduced relative flood attenuation capacity. Observed differences highlight the various impacts of forest vegetation on water table dynamics and emphasize the benefits of floodplain forests as a water resource management tool, including for flood mitigation, in mixed‐land‐use watersheds.