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Study region: Francolí River (Catalonia, Iberian Peninsula). Study focus: The aim is the reconstruction of the October 2019 flash flood, that was documented through extensive field work: rainfall (300 mm in just a few hours), flood marks, times of flood passage and witnesses' snapshots and reports, channel changes, log drift (20,000 trees) and woody debris at bridges, as well as large damage and six fatalities. The methods are: hydrological model built for the rainfall-runoff in the basin and the flood routing in the river, use of hydraulic principles such as flow at waterfalls, flow against obstacles (trees), etc. and finally 1D/2D free surface numerical models. New hydrological insights: The uppermost 100 km2 produced discharges of 700 m3/s (up to 50 m3/s/km2, locally). Three bridges failed, but their cascading failure (when one failure triggers the next one downstream) was not proved. The main channel widened more than 10 times, dragging away soil and vegetation like a bulldozer. The resulting large wood debris that clogged two bridges worsened the inundation. An anomalous flow downstream, probably a surge of around 1090 m3/s, due to the failure of a woody jam at a narrow bridge, took two lives. Water Authority is now warning flood planners that vegetated, torrential basins may cause catastrophic floods in the valley towns, if their narrow bridges are sensitive to woody debris.

There is described a 1D numerical study of scouring and sedimentation processes on a specific altered river sector. The model developed and analysed by the help of HEC-RAS software package is concerned by the immediate upstream and downstream vicinity of an existing road bridge. The general quasiunsteady (transitory) flowing regime assimilates a given hydrologic development unfolding over a generous time period, from August 1st, 1985 to July 31st, 1988. The present paper considers a casual approach by which the specific crossing structure is replaced by two characteristic cross-sections along the concrete bridge faces. The scourings expansion and depth or the silting spread and height can so be revealed especially along the bothering bridge span but also along the influenced river sector as modelled. [ABSTRACT FROM AUTHOR]

The paper presents a 1D numerical approach aiming to analyse the river-course processes development as emphasised by the river left side upper bed scouring on Timiş River, West of Romania, downstream of a crossing road-bridge. The quasi-unsteady flowing regime is modelled over a hydrologically significant time interval during the spring season of 2005. The analysis looks to reconstruct the side scouring occurrence and progress as a result of river-bed sliding instability under given special conditions produced by accidental high-waters. By employing the HEC-RAS software package, the numerical simulation considers the river sector morphological conditions determined by the crossing structure as transiting the liquid hydrograph and the corresponding sediment transport. [ABSTRACT FROM AUTHOR]

The losses due to the contraction and the expansion of the flow between the upstream and downstream cross sections of a bridge determine the calculation of the water surface profile. Manning's equation is used to calculate friction losses, and all other losses are described in terms of a coefficient times the absolute value of the change in velocity head between adjacent cross sections. HEC-RAS software developed by the US Army Corps of Engineers Hydrologic Engineering Center (HEC) River Analysis System (RAS) is one of the most used free software for calculating surface water profiles in rivers. Calculation of surface water profile in bridge areas involves detailed analysis on the expansion and contraction coefficients impact. The purpose of this study is to analyze and determine the changes in water level, depending on the expansion and contraction coefficients, in the area of the 4 existing bridges, on the measured section of the river course. For the correct hydraulic modeling and difference analysis of water profile, the depths were measured on a 35 km sector of the Siret river and a bathymetric model was created. Results show that an increase of the expansion and compaction coefficient with 0.2 units leads to differences of approximately +/- 20 cm in calculating the surface water level, at a flow rate of 1000 m3/s. [ABSTRACT FROM AUTHOR]

The paper presents a 2D numerical modelling of water flow transition on a sector of Strei River in the range of the DN7 national driveway bridge at km.376+818, outside the built-up area of Deva Town (upstream of Simeria), Romania, in case of a special highwaters phenomenon. The considered synthetical hydrograph follows an exceptional hydrologic event that occurred in the last days of April 2000 on the studied river sector. The numerical simulation looks to estimate (reconstruct) the water levels evolution and velocity distributions under the bridge and on the influenced upstream/downstream river stretches. [ABSTRACT FROM AUTHOR]

The measurement of the morphologic characteristics of evolving sediment beds around hydraulic structures is crucial for the understanding of the physical processes that drive scour. Although there has been significant progress towards the experimental characterization of the flow field in setups with complex geometries, little has been done with respect to the quantitative investigation of dynamic sediment bed geometry, mainly due to the limited capabilities of conventional instrumentation. Here, a recently developed computer vision technique is applied to obtain high-resolution topographic measurements of the evolving bed at the base of a cylinder during clear water scour, without interrupting the experiment. The topographic data is processed to derive the morphologic characteristics of the bed such as the excavated volume and the slopes of the bed. Subsequently, the rates of scour and the bathymetry at multiple locations are statistically investigated. The results of this investigation are compared with existing flow measurements from previous studies to describe the physical processes that take place inside a developing scour hole. Two distinct temporal phases (initial and development) as well as three spatial regions (front, side and wake) are defined and expressions for the statistical modelling of the bed features are derived. [ABSTRACT FROM AUTHOR]

The performance of a stream restoration project that incorporates a bridge crossing is evaluated within a 3-year monitoring period. A goal of the project was to alleviate and prevent future sediment aggradation within the waterway of a low-clearance bridge crossing. The stream restoration project included two rock cross vanes and stepped riprap and vegetation bank stabilization. Monitoring of the project involved the collection of channel survey data, pebble counts, and general observations of instream structure condition and sediment movement. The evaluated performance of the restoration structures is related to the general hydrologic conditions, the historical changes in the watershed and channel, and the hydraulic conditions created by the low-clearance bridge crossing. Backwater effects created by the bridge crossing are found to be a substantial cause of the failure of the stream restoration project to meet its goals. The low-clearance bridge hydraulics are preventing a rock cross vane located upstream of the bridge from creating a scour hole in the centre of the channel; instead, aggradation is occurring in this portion of the channel. However, degradation is occurring downstream of the bridge causing the failure of the second rock cross vane and of the riprap and vegetation bank. Although the hydraulic conditions may stem from the initial design of the bridge crossing, any restoration structure should be designed according to the current site hydraulics. In addition to providing insight into the design and construction of stream restoration structures, the results have implications for the design and management of bridge crossings. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Bahlui River cross Iasi basically dividing the city in two. The length of water in the city is about 11 km. Following the complex work upstream, Iasi is protected from floods with probability of 1%. A sustainable development of the river for recreational and tourism is further needed. This article presents a consistent and spectacular solution for leisure and tourism development for the central area of Iasi, crossed by the Bahlui River. To achieve constructive solution works crossing, bridge hydraulic calculation method of the normative PD 95-2002 must be improved. The article proposes a method for calculating this correction. [ABSTRACT FROM AUTHOR]

The two-dimensional (2D) depth-averaged river model Finite-Element Surface-Water Modeling System (FESWMS) was used to simulate the hydraulic conditions at a contracted bridge site. The site studied was the James River bridges near Mitchell, South Dakota. The parallel bridges are located in a crossing between the two bends of a meander. The floodplain alignment relative to the channel and skewed bridges produces complex 2D flow patterns that cannot be predicted accurately by using a one-dimensional (1D) river model. The 2D model was validated by using flow measurements collected by the USGS during three high-flow events with return periods ranging from 25 to 100 years. The validated model was used to examine the site characteristics that influence the concentrated flow on the right side of the main channel and the exchange of flow between the main channel and floodplains. The rating curves derived from the 2D model and the results of soil erosion tests were used to evaluate live-bed and clear-water contraction scour at the bridge site. The scour analysis was conducted by using the equations in Hydraulic Engineering Circular No. 18 (HEC-18) and a method that accounts for the soil erodibility by using a curve of measured erosion rate versus shear stress. The study found that channel meandering, the no-flow boundary condition imposed by the walls of the river valley and skewed roadway embankment, and the dense trees along the left bank are the three main factors that create the unique hydraulic conditions at the bridge site. It is shown that using a 2D flow model could improve the estimation of contraction scour by providing more accurate information on the hydraulic parameters. The predicted scour depth was very sensitive to the critical shear stress and slope of the curve of erosion rate versus shear stress. Therefore, design should incorporate uncertainty in soil properties. It is also shown that an unsteady-flow approach to scour would produce a more realistic curve of predicted scour depth versus time. However, the cumulative effects of multiple flood events must be evaluated if time-dependent scour is used in design. [ABSTRACT FROM AUTHOR]

The two-dimensional (2D) depth-averaged river model Finite-Element Surface-Water Modeling System (FESWMS) was used to predict flow distribution at the bend of a compound channel. The site studied was the Highway 13 bridge over the Big Sioux River in Flandreau, South Dakota. The Flandreau site has complex channel and floodplain geometry that produces unique flow conditions at the bridge crossing. The 2D model was calibrated using flow measurements obtained during two floods in 1993. The calibrated model was used to examine the hydraulic and geomorphic factors that affect the main channel and floodplain flows and the flow interactions between the two portions. A one-dimensional (1D) flow model of the bridge site was also created in Hydrologic Engineering Centers River Analysis System (HEC-RAS) for comparison. Soil samples were collected from the bridge site and tested in an erosion function apparatus (EFA) to determine the critical shear stress and erosion rate constant. The results of EFA testing and 2D flow modeling were used as inputs to the Scour Rate in Cohesive Soils (SRICOS) method to predict local scour at the northern and southernmost piers. The sensitivity of predicted scour depth to the hydraulic and soil parameters was examined. The predicted scour depth was very sensitive to the approach-flow velocity and critical shear stress. Overall, this study has provided a better understanding of 2D flow effects in compound channels and an overall assessment of the SRICOS method for prediction of bridge pier scour. [ABSTRACT FROM AUTHOR]

The effect of a single-peaked flood wave on pier scour is investigated both theoretically and experimentally. The conditions considered involve clear-water scour of a cohesionless material of given median sediment size and sediment nonuniformity, an approach flow characterized by a flow depth and velocity, a circular-shaped cylindrical bridge pier, and a flood hydrograph defined by its time to peak and peak discharge. A previously proposed formula for scour advance under a constant discharge was applied to the unsteady approach flow. The generalized temporal scour development along with the end scour depth are presented in terms of mainly the densimetric particle Froude number based on the maximum approach flow velocity and the median sediment size. The effect of the remaining parameters on the end scour depth is discussed and predictions are demonstrated to be essentially in agreement with model observations. [ABSTRACT FROM AUTHOR]

Bridge pressure flow scour at clear water threshold condition is studied theoretically and experimentally. The flume experiments reveal that the measured scour profiles under a bridge are more or less 2-dimensional; all the measured scour profiles can be described by two similarity equations, where the horizontal distance is scaled by the deck width while the local scour by the maximum scour depth; the maximum scour position is located just under the bridge about 15% deck width from the downstream deck edge; the scour begins at about one deck width upstream the bridge while the deposition occurs at about 2.5 deck widths downstream the bridge; and the maximum scour depth decreases with increasing sediment size, but increases with deck inundation. The theoretical analysis shows that: bridge scour can be divided into three cases, i.e. downstream unsubmerged, partially submerged, and totally submerged. For downstream unsubmerged flows, the maximum bridge scour depth is an open-channel problem where the conventional methods in terms of critical velocity or bed shear stress can be applied; for partially and totally submerged flows, the equilibrium maximum scour depth can be described by a scour and an inundation similarity number, which has been confirmed by experiments with two decks and two sediment sizes. For application, a design and field evaluation procedure with examples is presented, including the maximum scour depth and scour profile. [ABSTRACT FROM AUTHOR]