Observations of River Topography and Flow Around Bridges

This investigation was motivated by the amount of river, estuarine, and coastal infrastructure that is susceptible to extreme wave and flooding events. The high velocities and resulting shear stresses associated with high flow velocities are capable of scouring or depositing large quantities of sediment around hydraulic structures. Preventing the failure of these structures and sedimentation in inlets alone costs federal and state agencies billions of dollars annually. In addition to being costly, the manual monitoring of bridge scour - as mandated by the Federal Highway Administration - can be inefficient in states such as Ohio where the flood events that initiate the scour process occur sporadically. According to the National Scour Evaluation Database, there are 23326 bridges over waterways in the state of Ohio, of which 5273 are considered scour susceptible and 191 are considered \u27scour critical\u27. Previous methods for identifying bridge scour have relied on the manual (diver-based) sampling of local water depths that are generally limited to periods of low water flow. As the dynamic scour and deposition of sediments around structures is highest during periods of high flow, traditional sampling methods have limited our ability to predict quantitatively scour or deposition levels and to evaluate sediment transport models. This research is aimed at developing and testing new methods to observe riverbed topographic evolution around piles and under bridges where the structures themselves interfere with GPS based positioning. Simultaneous measurements of the velocity profiles can be used in conjunction with the observed bathymetry to make inferences about bridge scour and the effect of bridge piles on local riverbed topography. Related to problems generated by sediment scour are issues of sediment deposition in navigational channels. On the Maumee River, OH, alone, the Army Corp of Engineers spends millions of dollars annually to dredge an average of 850,000 cubic yards of sediment. With the elimination of open lake disposal of dredged sediments, an inter-agency collaboration of government and private citizens has been formed to identify possible methods for reducing the amount of deposition by reducing the soil erosion along river bank’s. Clearly, development of new observational capabilities and a subsequent increase in observations of riverbed topography and flow around structures will improve our ability to utilize available resources in the most efficient manner

Densely distributed and real-time scour hole monitoring using piezoelectric rod sensors

This study aims to validate a piezoelectric driven-rod scour monitoring system that can sense changes in scour depth along the entire rod at its instrumented location. The proposed sensor is a polymeric slender rod with a thin strip of polyvinylidene fluoride that runs through its midline. Extraction of the fundamental frequency allows the direct calculation of the exposed length (or scour depth) of the slender rod undergoing fluid flow excitation. First, laboratory validation in dry conditions is presented. Second, hydrodynamic testing of the sensor system in a soil-bed flume is discussed. Each rod was installed using a three-dimensional-printed footing designed for ease of installation and stabilization during testing. The sensors were installed in a layout designed to capture symmetric scour conditions around a scaled pier. In order to analyze the system out of steady-state conditions, water velocity was increased in stages during testing to induce different degrees of scour. As ambient water flow excited the portion of the exposed rods, the embedded piezoelectric element outputted a time-varying voltage signal. Different methods were then employed to extract the fundamental frequency of each rod, and the results were compared. Further testing was also performed to characterize the relationship between frequency outputs and flow velocity, which were previously thought to be independent. In general, the proposed driven-rod scour monitoring system successfully captured changing frequencies under varied flow conditions

The effect of dairy, piggery and wool scour effluents on willow growth and the soil characteristics : a thesis presented in partial fulfillment of the requirements for the degree of Master of Applied Science in Soil Science at Massey University

Restrictions on the disposal of agricultural effluents to the waterway means that alternative land based outlets are required in New Zealand. Willow, as a short forest rotation, represents a significant land use that could produce a high dry matter and benefit from the application of effluent irrigation. However, there has been little information on the effect of effluent irrigation on the growth of willow and the removal of nutrients. In order to assess the effects of dairy, piggery and wool scour effluents on willow growth, a greenhouse experiment was established using the Manawatu sandy fine loam soil. A complete nutrient solution and nutrient - free tap water treatments were also included in addition to the effluent treatments. The design of the experiment was a 5 x 2 factorial combination of treatments with four replications in randomized blocks. Two factors (effluents and irrigation rates) each with 5 levels were examined, the levels of irrigation were 12.5 mm, 25 mm, 37.5 mm, 50 mm and 62.5 mm per fortnight. The plant growth, production and macro-nutrients accumulation, and the soil pH, electrical conductivity, and total N, P and cations were monitored Irrigation with effluents affected the growth of willow cutting. The piggery and dairy effluent irrigation increased the willow growth and nutrient accumulation followed the increase in DM yield. The piggery and dairy irrigation accounted for 32% and 18% increase in total DM yield over tap water; while the wool scour effluent resulted in 17% decrease in comparison with tap water. Irrigation with dairy, piggery and wool scour effluents onto the Manawatu fine sandy loam soil, caused a significant increase in pH and EC. The significant change in pH and EC was attributed to the soluble salts in these effluents, especially K in the wool scour effluent. The recovery of N from these effluents was very small and was less than that of P and K in soil. Chemical analysis of willow, treated with dairy, piggery and wool scour effluents up to 8 weeks, showed a relatively high concentration of N, P and K in leaf, and had a very high K and a very low Mg concentration in leaf with wool scour effluent irrigation. However, the efficiency of the N, P and K nutrient accumulated by willow was inversely related to the concentration of these effluents and the DM yield of willow cutting was positively related to the irrigation rates. It was evident that willow cutting was too young to require a large quantity of nutrients at the early growth stage and there was a risk of nutrient loss with increasing irrigation rate. The application of wool scour effluent caused a very high pH and EC, and the willow cutting growth decreased at > 37.5 mm/fortnight irrigation rates. The reasons for the detrimental effects of wool scour effluent on soil properties and willow growth need to be investigated further. The results suggested that it is possible to enhance the willow growth and adjust the soil fertility by application of dairy and piggery effluents irrigation

Evolution of local scour around a collared monopile through tidal cycles

This paper presents the results of an experiment designed to assess the time-development of scour around an offshore wind turbine collared monopile over a number of tidal cycles. One collar shape and location was investigated. The scour developed more slowly and the scour depth was shallower than for the case of a smooth monopile throughout the majority of the first half-cycle. This difference reduced quite rapidly during the second half-cycle and the scour depth at the end of two tidal cycles was essentially the same as for the smooth monopile. The time development of the scour was compared with results from existing empirical models for the time-development of scour under unidirectional flow. As expected, these models give a much smoother evolution of scour and different scour rates than those measured. Time variation in scour depth was better reproduced with a simplified approach for prediction of the time-varying development of scour. This also highlighted a problem with estimation of the time scale for the development of the equilibrium scour depth. Further investigations are needed before this alternative scour protection is completely rejected

Numerical Modeling of Pile Responses under Lateral Loading Considering the Scour Effects

This thesis focuses on the 3D numerical analysis of the laterally loaded pile. For numerical modeling/analysis, ABAQUS, a widely used commercial software, is used. Non-scour and scour conditions are considered for this thesis. Two elastoplastic constitutive models, Mohr-Coulomb model and Cam Clay model, are applied. Unknown material and interface properties are calibrated based on two references which explained the numerical analysis of the laterally loaded pile under the non-scour condition. Different cases of scour depth, Sd, scour width, Sw, and scour slope angle, a, are applied for the laterally loaded pile analysis under the scour condition. From the results of the numerical analysis under the scour condition, scour depth, Sd, can be the main factor for the pile capacity changes. Scour width, Sw, and scour slope angle, a, are also the other factors which have an influence on the reaction force changes of the laterally loaded pile. This thesis also describes the plastic deformation/strain results of the laterally loaded pile analysis. From the plastic strain results depending on the scour width, the plastic strain appears on the scour slope when the scour width is narrow. On the other hand, when scour width is sufficiently wide, the plastic strain distribution would be similar to the one when the scour width is infinite. This strain distribution state can be shown in both Mohr-Coulomb model and Cam Clay model. In the view of the scour slope angle, the plastic strain in Cam Clay model is more smoothly expanded onto the scour slope than Mohr-Coulomb model

Temporal Pier Scour Evolution under Stepped Hydrographs

The present study was aimed at measuring the scour hole profile at bridge piers under clear water scour. Scour tests were performed under both steady state flow and under stepped hydrographs. Multiple smaller flood events were run to determine how flood history affects scour hole development. Various equilibrium scour depth equations and proposed temporal scour models were compared. The similarity of the scour hole profiles with time and flow history were evaluated. Experiments were conducted in a 14.8 m long, 1.19 m wide, 1.22 m deep rectangular flume with a model bridge pier. A uniform sediment bed (d50= 1.5 mm) was used throughout the study. Scour hole profiles were measured using a light sensor. Three steady state flow experiments with a constant flow depth and different bed shear stresses and velocities were run. These three flow conditions were later used to model eight unique stepped hydrographs. The order of flood events was found not to effect the scour depth or scour hole shape. The scour hole maintained the same non-dimensional, longitudinal similarity regardless of flow history or time for both steady and unsteady flows. This finding indicated steady state scour evolution models can be used to model scour under stepped hydrographs. Several equilibrium scour depth equations were evaluated and it was found the CSU equation (FHWA, 2001) was just as accurate as several proposed temporal scour models. Best-fit power and logarithmic temporal scour depth equations were obtained from each steady state test. These equations along with models proposed by Melville and Chiew (1999) and Chang et al. (2004) were found to predict steady state temporal scour evolution with reasonable accuracy. Using the method of superposition, these methods were used to predict scour depths under stepped hydrographs. For stepped hydrographs, the scour development for each event (or each step) followed the temporal scour evolution under steady flow conditions. It was found that the order and frequency of events did not change the scour development pattern. It was determined that the power and logarithmic function accurately predicted final scour depths (± 10% and ± 12%, respectively) and temporal scour evolution. The models proposed by Melville and Chiew (1999) and Chang et al. (2004) were found to provide no greater accuracy in predicting final scour depths than the CSU equation (FHWA, 2001). More research is needed on temporal scour evolution under steady flow conditions in order to predict scour during floods

DEVELOPMENT OF SCOUR IN COHESIVE SOILS BY NORMAL IMPINGEMENT OF A SUBMERGED CIRCULAR TURBULENT JET

Scour is an important issue due to the potential great extent of loss and risks associated with scouring. The work described herein constitutes laboratory testing of the time development of scour holes in clayey soils produced by a submerged vertical circular impinging jet. Long term laboratory tests were performed on three types of manufactured pottery clays, Buffstone clay (50.3-51.7% clay), P300 clay (48.7-50.7% clay), and M370 clay (51.1-51.3% clay). Detailed measurements of the entire scour hole were performed on a 2 mm grid using a computer controlled laser optical profiler after scouring times of 5 min, 10 min, 15 min, 20 min, 30 min, 40 min, 50 min, 1 h, 1.5 h, 2 h, 4 h, 8 h, 16 h, 24 and then at every 24 h interval until the scour hole was considered to have reached equilibrium based on the criterion used by Mazurek et al. (2001). This resulted in long test durations ranging from 120 h to 384 h. For the time development of the scour hole, a three-dimensional scour hole surface was produced using the data taken by an optical profiler. Thereafter, four cross sections of the scour hole were extracted from the three-dimensional scour hole surface. Dimensions considered for analysis were taken from both the three-dimensional scour hole surface and the cross sections of the scour hole. The volume of the scour hole, and the centreline and maximum scour hole depths were extracted from the scour hole surface. The section-wise maximum scour depth, radius of the scour hole, half-width about the jet centreline, and half-width about the section-wise maximum scour depth were extracted for each cross-sections. The growth of these dimensions were observed with time. For a significant portion of scouring, the centreline and maximum scour hole depths increased linearly with the logarithm of time. For the majority of the tests, the half-widths decreased with time. Temporary ceasing of the increment of the centreline and maximum scour hole depths was observed, called “plateaus”, in the time development plot. Scour hole dimensions for the cross-sections showed variability from the average scour hole dimensions. However, for most of the tests this variability decreased with time as the scour test proceeded. To decide on whether the equilibrium state of the scour hole was achieved, all of the aforementioned scour hole dimensions were evaluated. The characteristic scour hole dimension to decide on the equilibrium condition was termed as the “critical equilibrium dimension”. Four of the scour tests reached an overall equilibrium state, the section wise maximum scour hole depth was the critical equilibrium dimension for three of those. The half-widths were the critical equilibrium dimension for one of the tests. However, previous studies did not consider the “side slope erosion” of the scour hole, hence neglected the section-wise maximum scour depth and half widths for identifying equilibrium condition. Dimensionless scour hole profiles were developed using the centreline scour depth as the scale for scour hole depth and the half-width about the centreline depth as the scale for radial distance from the jet centreline. A general equation of the dimensionless equilibrium scour hole profile was developed by fitting a sine function to the equilibrium scour test profiles using linear regression analysis. Dimensionless scour hole profiles with time during the scour test were compared to the dimensionless profile at equilibrium. It was observed that while for some scour tests the equilibrium scour hole shape formed quickly compared to the time to equilibrium, for some scour tests the equilibrium shapes did not form until the scour hole stopped growing

DEVELOPMENT OF SCOUR IN COHESIVE SOILS BY NORMAL IMPINGEMENT OF A SUBMERGED CIRCULAR TURBULENT JET

Scour is an important issue due to the potential great extent of loss and risks associated with scouring. The work described herein constitutes laboratory testing of the time development of scour holes in clayey soils produced by a submerged vertical circular impinging jet. Long term laboratory tests were performed on three types of manufactured pottery clays, Buffstone clay (50.3-51.7% clay), P300 clay (48.7-50.7% clay), and M370 clay (51.1-51.3% clay). Detailed measurements of the entire scour hole were performed on a 2 mm grid using a computer controlled laser optical profiler after scouring times of 5 min, 10 min, 15 min, 20 min, 30 min, 40 min, 50 min, 1 h, 1.5 h, 2 h, 4 h, 8 h, 16 h, 24 and then at every 24 h interval until the scour hole was considered to have reached equilibrium based on the criterion used by Mazurek et al. (2001). This resulted in long test durations ranging from 120 h to 384 h. For the time development of the scour hole, a three-dimensional scour hole surface was produced using the data taken by an optical profiler. Thereafter, four cross sections of the scour hole were extracted from the three-dimensional scour hole surface. Dimensions considered for analysis were taken from both the three-dimensional scour hole surface and the cross sections of the scour hole. The volume of the scour hole, and the centreline and maximum scour hole depths were extracted from the scour hole surface. The section-wise maximum scour depth, radius of the scour hole, half-width about the jet centreline, and half-width about the section-wise maximum scour depth were extracted for each cross-sections. The growth of these dimensions were observed with time. For a significant portion of scouring, the centreline and maximum scour hole depths increased linearly with the logarithm of time. For the majority of the tests, the half-widths decreased with time. Temporary ceasing of the increment of the centreline and maximum scour hole depths was observed, called “plateaus”, in the time development plot. Scour hole dimensions for the cross-sections showed variability from the average scour hole dimensions. However, for most of the tests this variability decreased with time as the scour test proceeded. To decide on whether the equilibrium state of the scour hole was achieved, all of the aforementioned scour hole dimensions were evaluated. The characteristic scour hole dimension to decide on the equilibrium condition was termed as the “critical equilibrium dimension”. Four of the scour tests reached an overall equilibrium state, the section wise maximum scour hole depth was the critical equilibrium dimension for three of those. The half-widths were the critical equilibrium dimension for one of the tests. However, previous studies did not consider the “side slope erosion” of the scour hole, hence neglected the section-wise maximum scour depth and half widths for identifying equilibrium condition. Dimensionless scour hole profiles were developed using the centreline scour depth as the scale for scour hole depth and the half-width about the centreline depth as the scale for radial distance from the jet centreline. A general equation of the dimensionless equilibrium scour hole profile was developed by fitting a sine function to the equilibrium scour test profiles using linear regression analysis. Dimensionless scour hole profiles with time during the scour test were compared to the dimensionless profile at equilibrium. It was observed that while for some scour tests the equilibrium scour hole shape formed quickly compared to the time to equilibrium, for some scour tests the equilibrium shapes did not form until the scour hole stopped growing

Bridge Scour : Basic Mechanisms and Predictive Formulas

This report aims at presenting basic knowledge on bridge scour and the processes governing its evolution as well as summarizing the most common formulas used to calculate scour depth at bridges. Design procedures concerning bridge scour in several different countries are also discussed, including United States, Australia, and the United Kingdom. The situation in Sweden with regard to bridge scour is briefly reviewed and several case studies are presented where marked scour holes have been detected at bridges. Two cases of bridge failures in Sweden are included where local scour was the main reason for the collapse.Bridge scour is typically separated into pier, abutment, and contraction scour, where each mechanism is controlled by different physics and governing parameters. Each type of bridge scour is discussed separately in the report with sections on basic mechanisms, governing parameters, common predictive formulas, and concluding remarks.The report also includes a brief summary on the expected influence of climate change on bridge scour. Larger and more intense rainfalls in the future imply larger flows in the rivers with increased bridge scour as a result.The report deals only with scour induced by bridges; other types of scour, such as general scour due to longitudinal transport gradients in the river, scour related to secondary flows in river bends, or scour downstream hard bottom, are not discussed. Most of the formulas included to estimate bridge scour are valid for friction material and only a few examples are given that are applicable to cohesive sediment, mainly related to recommended design procedures from different countries. Also, the objective of bridge scour analysis is often to estimate the maximum scour depth, occurring at equilibrium conditions under a certain flow, implying that most of the formulas are valid for such conditions

Scour and fill in ephemeral streams

The classical concept that mean bed elevation over an entire stream reach is lowered by scour during flood-wave passage and is restored by deposition in the waning flood phase (mean-bed scour and fill) can be challenged. The alternative that both scour and fill occur concurrently at different migrating loci within a reach (local scour and fill) is more consistent with published field data. The field and laboratory investigations reported herein suggest that mean-bed scour and fill in a uniform channel is minor compared to local scour and fill caused by bedform migration, and that maximum local scour and fill may occur on the waning flood in some instances. The field experiment, utilizing a rectilinear array of buried maximum-scour indicators (scour-cords), produced data for contouring of maximum scour and fill in an ephemeral streambed during two floods. In the first flood, 24 em of scour and fill was measured for a bankfull flow depth of 23 cm. In the second, maximum scour and fill was at least 66 cm for a bankfull flow depth of 34 cm. Estimates of antidune amplitudes for the two floods, based on theoretical models and laboratory and field observations, are 28 to 64 cm and 48 to 97 cm, respectively. This indicates that all scour and fill measured by the scour-cord array could have been caused by antidune migration. Laboratory experiments were conducted in an 18 m-long open-circuit flume with automated sediment and water input-rate controls. A series of experiments in a 26.7 cm-wide sand-bed channel with rigid walls, at grade for a simulated flood patterned after those typical of ephemeral streams, showed that mean-bed scour and fill was less than 3 percent of local scour and fill. For these experiments, mean sand size was 0.3 mm, channel slope was .009, maximum water depth was 40 mm, maximum local scour and fill was 22 mm, and maximum mean-bed scour and fill was 0.6 mm. Maximum mean bed elevation variation was thus only two sand-grain diameters. Fill occurred at peak flow followed by scour to the pre-flood mean bed elevation on the waning flood. Maximum local scour and fill took place near the end of the simulated floods, when bedform amplitudes were the greatest. A series of simulated-flood experiments in a sand-bed channel with erodible sand banks showed scour and fill behavior qualitatively similar to that of the rigid-wall channel. Bank erosion, channel meandering, and braiding prevented quantitative scour and fill measurements in these alluvial-bank experiments. Measured flow and bedform parameters and scour and fill data derived from small laboratory scour-chains were compatible with those estimated from the theoretical model used in the field experiment