Measuring and Modeling Shallow Groundwater Flow between a Semi-Karst Border Stream and Ozark Forested Riparian Zone in the Central USA

Aims: Quantitative information is limited pertaining to riparian forest and stream shallow groundwater interactions particularly in karst hydro-ecosystems.
Study Design, Place and Duration: Spatiotemporal variability of shallow groundwater flow was monitored along two stream reaches in a riparian Ozark border forest of central Missouri, United States. Each reach was equipped with twelve piezometers and two stream-gauging stations during the 2011 water year (WY).
Methodology: High-resolution (i.e. 15 minute) time-series data were analyzed indicating average groundwater flow per unit stream length was -3 x 10-5 m3 s-1 m-1 (losing stream) for the entire study reach (total reach length = 830m) during the 2011 WY. The HYDRUS – 1D groundwater flow model was forced with observed data and outputs were assessed to improve model end user confidence in karst hydrogeologic systems.
Results and Discussion: Results indicate rapid groundwater response to rainfall events within two to 24 hours nine meters from the stream. Analyses indicated average stream flow loss of 28% and 7% total volume to groundwater during winter and spring seasons, respectively. During the dry season (June-September), the stream was gaining 95% of the time. During the wet season (March-June), the stream was losing 70% of the time. Based on established assessment criteria, shallow groundwater modeling performance with HYDRUS – 1D was deemed very good (NS = 0.95, r2 = 0.99, RMSE = 2.38 cm and MD =1.3 cm).
Conclusion: Results supply greatly needed baseline information necessary for improved understanding of riparian forest management and shallow groundwater transport and storage processes in semi-karst forest ecosystems.