On the Tidal Prism: The Roles of Basin Extension, Bottom Friction and Inlet Cross-Section

Abstract

The prism of the Lignano tidal inlet was approximately constant over the last forty years, although the section width has halved. This has led to questions concerning the factors that most influence the tidal prism, and on the applicability of the well-known A–P relationship. A conceptual scheme of the sea–channel–lagoon system has been used to perform a sensitivity analysis of different parameters that characterize both the basin and the inlet cross-section. A 2D hydrodynamic model has been applied to evaluate the prism and compare it to the one derived by a static method, which is the basis of the analytical derivation of the A–P linkage. Three regimes have been found in the prism variability as a function of the basin extension: a linear static regime between prism and basin area; an asymptotic regime in which the prism depends only on the basin bottom friction; and an intermediate one. In addition, the roles of the inlet and channel sizes on the prism value have been investigated. The results, compared to the empirical relationships between the prism and the inlet cross-section, show that a variation in the cross-sectional area does not always corresponds to a change in tidal prism.

The tidal prism as a dynamic response of a nonlinear harmonic system

“…In fact, recently, Reef et al (2020), using a numerical approach, have shown that when the characteristic size of the lagoon basin increases, the tidal prism tends to an asymptotic value. Petti et al (2021), again using a numerical approach, found the same behavior, highlighting how the prism tends to an asymptotic value both when the surface of the basin grows and when the cross-sectional area of the inlet increases, in both cases with the same tidal amplitude.…”

“…9). The main features of the computational domain derive from the numerical simulations performed by Petti et al (2021), with the aim of understanding the effects on the tidal prism of some geometric and hydrodynamic characteristics of the tidal inlet, channel, and the lagoon basin.…”

“…For each test, the X section, length L c , and hydraulic radius R of the channel as well as tidal amplitude and period offshore a m and T were kept constant (Table II). The length L j of the jetties, in the tests in which their presence was planned, was assumed to be equal to 1000 m. Regarding the Gauckler-Strickler roughness coefficient k s , a constant value equal to 40 m 1=3 s À1 was assumed at sea, in the channel and in the lagoon, which corresponds to the uniform value adopted by Petti et al (2021), following Marchi's approach (1990). Furthermore, this value was successfully used to carry out several simulations of the main hydrodynamic processes in the northern Adriatic nearshore, in Italy (Petti et al, 2018;.…”

A review of tidal embayment shoaling mechanisms in the context of future wetland placement

“…In addition to implying that inlets with high Qℓ will have smaller values of Across, Equation 22 also implies that inlets with higher frictional dissipation (parameterized by a larger Manning's n) must have a larger cross-sectional area in which to convey the same tidal prism as a lower-friction inlet (cf. Petti et al 2021).…”

“…Given an inlet with fixed Across, increasing the tidal prism Ω (e.g., by increasing the volume of the inland tidal basin) necessitates an increase in current speeds through the inlet to conserve mass. The relationship between Ω and velocity is asymptotic, with its upper limit constrained by friction (currents cannot become indefinitely fast) and basin length (the tide can only propagate inland by some finite length during a 6 hr rising limb; see Petti et al [2021]), but for reasonably small basins, it is expected that increasing the basin volume with Across constant will generate an increase in velocity.…”