Impact of Historical Channel Deepening on Tidal Hydraulics in the Delaware Estuary

Abstract

In estuaries and tidal rivers, the landward amplification or attenuation of tidal range depends on the competing effects of friction and convergence. In funnel-shaped estuaries, the tendency for amplification is a consequence of mass conservation: the landward decrease in cross-sectional area requires an increment in water elevation or velocity for volume to be conserved. This response to funneling can be attenuated by friction as the tide propagates over the relatively shallow topography. The observable responses of tidal range (amplification, damping, or no change) can be used to classify an estuary as "hypersynchronous," "hyposynchronous," or "synchronous," respectively (de Miranda et al., 2017). One of the main factors that determine the extent of synchronicity is then local topography, which largely modulates frictional effects. Changes in bed morphology can occur naturally over relatively long geological time scales (Hall et al., 2013), but humans have deepened estuarine channels over the last century, in some cases doubling the natural thalweg depth (Ralston et al., 2019). In the late 1800s, river engineers sought to ensure navigability through dredging, so technical guidelines focused on sediment management rather than the impact of dredging on tides (Brooks, 1841). The role of channel deepening in sea level became a topic of interest when historical records revealed that tidal amplitudes worldwide have changed at rates not explained by astronomical forcing (see Haigh et al., 2020; Talke & Jay 2020, for a detailed review). Assessing the effect of channel deepening on tides is key to evaluate shifts in sediment concentration and turbidity (Dijkstra et al., 2019; Winterwerp & Wang, 2013), which play a role in estuarine ecology and water quality (McSweeney et al., 2017).

Evolving tides aggravate nuisance flooding along the U.S. coastline

“…Similarly, large-scale dredging in the Delaware River leads to doubling of the depth (from 6.1 to 12.2 m) since the 1910s and a considerable increase in tidal range in Philadelphia ( 46 ). Tidal range (and NF) at the mouth of the Delaware (Lewes) decreased over time, which shows that tidal effects on NF are spatially variable within individual estuaries.…”

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

“…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., Ralston & Geyer, 2019), 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.…”

Effect of Estuary Urbanization on Tidal Dynamics and High Tide Flooding in a Coastal Lagoon

“…Adequately simulating historical wetland effects on tides poses a challenge, since most historical charts include little quantitative detail on bathymetry above the MLW datum. Previous efforts on modeling historical tidal change in river estuaries have therefore neglected wetland regions (e.g., Pareja‐Roman et al., 2020; Ralston et al., 2019), or used modern Lidar data as a proxy for the historical marsh extent (e.g., Helaire et al., 2019; Talke et al., 2021). An assumption made in those studies is that most of the momentum from tides is conveyed in deeper channels.…”

“…Tidal properties in estuaries (e.g., tidal range, current speed) are changing worldwide, largely due to anthropogenic alterations to geomorphology and surface area (see reviews by Talke and Jay (2020) and Haigh et al (2020)). Dynamical reasons for these changes include altered frictional effects, land reclamation, resonance, and alterations in tidal exchange at inlets (De Leo et al, 2022;Orton et al, 2020;Pareja-Roman et al, 2020;. Tidal ranges and HTF frequency may be particularly sensitive to SLR and bathymetric changes in shallow estuaries where even modest interventions may significantly amplify the tidal response .…”