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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #368257

Research Project: Managing Water and Sediment Movement in Agricultural Watersheds

Location: Watershed Physical Processes Research

Title: A dynamic water-balance/nonlinear-reservoir model of a perched phreatic aquifer-river system with hydrogeologic threshold effects

item O'REILLY, ANDREW - University Of Mississippi
item HOLT, ROBERT - University Of Mississippi
item DAVIDSON, GREGG - University Of Mississippi
item PATTON, AUSTIN - University Of Mississippi
item Rigby Jr, James

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2020
Publication Date: 4/4/2020
Citation: O'Reilly, A.M., Holt, R.M., Davidson, G.R., Patton, A., Rigby Jr, J.R. 2020. A dynamic water-balance/nonlinear-reservoir model of a perched phreatic aquifer-river system with hydrogeologic threshold effects. Water Resources Research. 56. Article e2019WR025382.

Interpretive Summary: Rivers provide one of the major sources of recharge for aquifers but the hydraulic connection can be complex and intermittent. This study found that the hydraulic connection of the Sunflower River to the underlying aquifer is stage-dependent as the infiltration from the main channel is limited by fine sediment. When water levels rise the river flows over sandbars and forest edges which provide preferential pathways to the aquifer. This work helps quantify the timing and degree of connection of the region's rivers with the aquifer which will allow better estimates of recharge from rivers and thus better groundwater management.

Technical Abstract: Heterogeneity in the hyporheic zone or near-field geology can impart a threshold effect on groundwater-surface water (GW-SW) exchange. Variations in the texture of streambed sediments and lithologic variations in adjacent and underlying geology are examples of common heterogeneities. Hydrologic interaction with these heterogeneities leads to distinct types of “behavior” that “switch” when surface-water or groundwater levels rise above or fall below the interface of the layers of differing lithology. A simple dynamic water-balance/linear-reservoir model was developed to investigate threshold effects at a location on the Big Sunflower River in the Lower Mississippi River Valley, USA. Four conceptual models, each of which simulates a perched aquifer as a dynamical system that receives recharge from the riverbank and loses water to an underlying regional aquifer, were tested using combinations of zero, one, or two thresholds representing layered heterogeneity in riverbank and/or aquifer lithology. Models were run using hourly stream-gage measurements and calibrated to a 382-day period of corresponding measurements in a nearby well. Final model performance was assessed for a 3.5-year period representing varied hydrologic conditions. The best performance was demonstrated by the model incorporating threshold effects (root-mean-square error of 0.268 m), which elucidated four modes of GW-SW system behavior controlled by both riverbank (riverbed hydraulic conductivity) and aquifer (transmissivity and storage coefficient) properties. The dynamical system modeling approach incorporates the salient hydrologic processes of a GW-SW system with layered heterogeneity. Based upon fundamental mass-conservation concepts, the simple dynamic water-balance/linear-reservoir model has broad applicability to a wide range of hydrogeologic settings.