Stratification variability in a lagoon system in response to a passing storm

Abstract

AbstractShallow lagoon systems with limited river flow and precipitation are often regarded as being well‐mixed; however, stratification can occasionally occur in shallow lagoons in response to intense river runoffs and precipitation. Understanding the stratification behaviors of a shallow lagoon system is critical for future environmental assessment and management strategies. Thus, in this study, stratification and mixing mechanisms in a shallow lagoon system (the Maryland Coastal Bays) were investigated on an episodic scale during Hurricane Sandy (2012) by using a numerical model. The strength of stratification (Brunt‐Väisälä frequency, N in s−1) in the lagoon system varied spatially; and was determined by river flow, precipitation, winds, and remote forcing. During the pre‐Sandy period (October 25–28, 2012), the bays were relatively mixed without sufficient river flow and precipitation. Driven by intense river flow from the northern creeks (peak: 82.47 m3 s−1), high precipitation (peak: 3.29 × 10−6 m s−1), and strong storm winds (mean: 12.15 m s−1) during the Sandy period (October 28–31, 2012), the water column in the northern creeks of the bays became stratified (mean N2: ~ 0.01 s−2). During the post‐Sandy period (October 31–November 3, 2012), the St. Martin River among the northern creeks showed strong stratification (mean N2: ~ 0.03 s−2) due to weaker winds (mean: 5.70 m s−1) and residual high river flow and precipitation from the Sandy period. The wind was found to be the most dominant source of mixing in the bays, while remote forcing and wind regulated the stratification near the Ocean City Inlet.