The Influence of Channel Deepening on Tides, River Discharge Effects, and Storm Surge

Abstract

Shipping channels in many estuaries around the world have been deepened by a factor of two or more since the mid-19th century, with deep-draft ships requiring increasingly wide and deep shipping channels (e.g., . At the same time, channelization, reclamation, and diking has often reduced connectivity to wetlands and reduced estuary width. Consequences include increased salinity intrusion (e.g., , altered tidal velocities (e.g., Pareja-Roman et al., 2020) and an upstream movement of the estuary turbidity maximum (see review by Burchard et al., 2018, and references therein). Reduced frictional resistance in a deeper channel leads to reduced damping of long-wave energy.

Compound Flooding in Convergent Estuaries: Insights from an Analytical Model

“…Previous studies (e.g., Ralston et al, 2019;Helaire et al, 2019;Talke et al, 2021) showed that reduced friction due to increased channel depth can alter the tidally averaged water level gradient ( 𝜕𝑍 𝜕𝑥 , Fig. 1b).…”

“…The resulting non-linear interaction and increased friction typically reduces the tidal range, shifts the timing of high and low water (e.g., Godin, 1985;Hoitink and Jay, 2016), and generates tidal distortion (asymmetry) (Parker, 1991). The increased frictional effects also influence subtidal water levels, producing a larger river slope (Kulkulka and Jay, 2003b;Buschman et al, 2009;Talke et al, 2021). However, typical coastal plain systems in the western Atlantic have low river flow relative to tidal discharge amplitudes.…”

“…However, typical coastal plain systems in the western Atlantic have low river flow relative to tidal discharge amplitudes. For example, the ~200 m 3 /s average annual discharge of the Saint Johns River Estuary, Florida, is about 5 % of total discharge (river + tides) (Talke et al, 2021). Similarly, the Delaware River Estuary has mean and median river flows at Trenton, NJ of ~340 m 3 s -1 and 285 m 3 s -1 , respectively, small compared to tidal flow of ~23×10 4 m 3 s -1 at the mouth (USGS, 2018; Munchow et al, 1992).…”

“…Since the cross-sectional area in our model varies smoothly (exponentially) over a large length scale, our approach neglects convective effects. We neglect the riverbed slope, since the bed slope in estuaries is typically small (order 10 -5 ), particularly in modern dredged systems (see e.g., Talke et al, 2021). Within the upstream reaches of tidal rivers, the bed slope often increases and is important dynamically (Kästner et al, 2019); therefore, we restrict our analysis and interpretation to estuarine reaches.…”

“…Other flood events, e.g., Hurricane Sandy, were forced by the combined effects of tide and storm surge (i.e., by storm tides; Orton et al, 2016). Some storm events (such as Hurricanes Irene and Irma) produce both coastal and inland flooding because both storm surge and river flow produce elevated coastal water levels in a spatially varying pattern (e.g., Orton et al, 2012;Ralston et al, 2013;Talke et al, 2021). Collectively, a flooding event that is influenced by both storm tide and precipitation run-off is known as a 'compound flood' (e.g., Zscheischler et al, 2018;Wahl et al, 2015).…”