Multiple states in the flow through a sluice gate

This paper addresses the problem of hydraulic hysteresis for a supercritical open channel flow approaching a sluice gate when subcritical flow can establish downstream, against the gate. The possible flow configurations across the gate are classified on the basis of the Froude number of the incoming and downstream flows, and of the ratio of gate opening to the upstream supercritical flow depth. Within the above parameter space, two regions exist in which the problem admits a dual solution, that is, two different flow configurations can establish for the same gate opening and undisturbed flow conditions. In one of these regions, both smooth flow (i.e. the fluid flows under the gate without interacting with the gate) and free outflow conditions can establish; in the other region, both smooth flow and submerged flow can establish. For flow conditions in the above regions, the configuration that actually establishes depends on the previous history of the flow, thus implying the hysteretic character of the flow

Extended theory of hydraulic hysteresis in open channel flow

The occurrence of hysteresis in a supercritical, open-channel flow approaching an obstacle has been recognized and investigated both experimentally and theoretically over the last few decades. However, the available theory and experimental investigations in the literature do not include the case when subcritical flow, controlled from downstream, can establish across the obstacle. The present work fills this gap by proposing a new theory that includes this occurrence and shows that two different steady flow states can establish for the same obstacle geometry and flow conditions\u2014one with supercritical to subcritical transition far downstream from the obstacle, and the other with supercritical to subcritical transition far upstream from the obstacle. The proposed, more general theory includes the existing theory as a special case. Finally, two specific examples are illustrated and discussed, i.e., the case of flow over a raised bed hump, and the case of flow through a channel contraction

A quantitative criterion to predict the occurrence of tidal bores

-Tidal bores are fascinating phenomena that occurs in the estuary of many tidal rivers worldwide. -Tidal bores have significant repercussions on ecology and morphodynamics of an estuary. -Despite the interest, a predictive criterion for tidal bore occurrence is still missing. -Tidal bore is assessed from a phenomenological standpoint, based on the results of a numerical study. -The predictive criterion for bore occurrence performs well against both numerical and real data

Positive Surge Propagation in Sloping Channels

A simplified model for the upstream propagation of a positive surge in a sloping, rectangular channel is presented. The model is based on the assumptions of a flat water surface and negligible energy dissipation downstream of the surge, which is generated by the instantaneous closure of a downstream gate. Under these hypotheses, a set of equations that depends only on time accurately describes the surge wave propagation. When the Froude number of the incoming flow is relatively small, an approximate analytical solution is also proposed. The predictive ability of the model is validated by comparing the model results with the results of an experimental investigation and with the results of a numerical model that solves the full shallow water equations

A quantitative criterion to predict the occurrence of tidal bores

-Tidal bores are fascinating phenomena that occurs in the estuary of many tidal rivers worldwide. -Tidal bores have significant repercussions on ecology and morphodynamics of an estuary. -Despite the interest, a predictive criterion for tidal bore occurrence is still missing. -Tidal bore is assessed from a phenomenological standpoint, based on the results of a numerical study. -The predictive criterion for bore occurrence performs well against both numerical and real data

Meandering evolution and width variation, a physics-statistical based modeling approach

Many models have been proposed to simulate and understand the long-term evolution of meandering rivers. These models analyze the hydraulics of the in-channel flow and the river bank movement (erosion \u2013 accretion) process in different ways, but some gap still remain, e.g. the stability of long-term simulations when width variations are accounted for. Here we proposed a physics-statistical based approach to simulate the river bank evolution, that erosion and deposition processes act independently, with a specific shear stress threshold for each of them. In addition, we link the width evolution with a parametric probability distribution (PPD) based on a mean characteristic channel width. We are thus able to obtaining stable long-term simulations with realistic and reasonable spatio-temporal distribution of the along channel width

Free surface waves induced by vortex shedding in cylinder arrays

The paper presents and discusses the results of an accurate and extensive experimental investigation on the waves that originate when an array of cylinders is placed in an otherwise uniform open channel flow. The study was originally aimed at providing new and more accurate data to calibrate and validate a theoretical model recently proposed in the literature. However, two interesting characteristics of the phenomenon at hand, never reported in the literature, also emerged from the experimental study, i.e. (i) the wave produced by the cylinders is actually a metachronal wave rather than a pure transverse seiche; (ii) two different resonant conditions exist for each single wave mode, i.e. two typical Strouhal numbers characterize the resonance frequency of vortex shedding from the cylinders in an array. Evidence of the metachronal wave, as well as some preliminary data on the longitudinal component of this wave, are given in the paper. Also, the double resonance condition is experimentally demonstrated and discussed

Multipurpose Use of Artificial Channel Networks for Flood Risk Reduction: The Case of the Waterway Padova\u2013Venice (Italy)

Many rivers are increasingly threatened by extreme floods, and effective strategies for flood risk mitigation are difficult to pursue, especially in highly urbanized areas. A flexible and multipurpose use of the complex networks of artificial channels that typically cross these regions can play a role in flood risk mitigation. A relevant example concerns the possible completion of a waterway from Padova to the Venice Lagoon, in North-Eastern Italy. Once completed, the waterway can boost shipping (which is considerably more climate and environment friendly than road transport), can lead to a urban re-composition of the territory and, serving as a diversion canal for the Brenta River, can reduce hydraulic hazard as well. The goal of the present work was to assess this last point. To this purpose, the 2DEF hydrodynamic model was used to reproduce the complex Brenta\u2013Bacchiglione river network. This network includes river reaches, diversion canals, bed sills, pump stations, and control structures that assures the proper operation of the system in case of flood events. The mixed Eulerian\u2013Lagrangian, semi-implicit formulation of the model provided accurate and computationally efficient results for subcritical regimes. The model results showed that the waterway can divert a significant part of the Brenta floodwaters toward the Venice Lagoon, thus reducing flood hazard in the Brenta River downstream of Padova. The benefits also extend to the Bacchiglione River, whose floodwaters can be diverted into the Brenta River through an existing flood canal; indeed, the waterway withdrawal produces a drawdown profile in the Brenta River that allows diverting larger flow rates from the Bacchiglione River as well. Finally, by conveying the sediment-laden floodwaters of the Brenta River within the Venice Lagoon, the waterway could contribute to counteract the generalized erosion affecting the lagoon