Trash Screens Research Articles

CCTV image‐based classification of blocked trash screens

AbstractThis study introduces image‐based classification techniques to identify whether trash screens in urban rivers are blocked. The study obtained 755 images from a CCTV camera surveying a trash screen located on an urban river at Tongwynlais in Cardiff. Manual quality control reduced the dataset to 577 images, labelled as either blocked (80%) or unblocked (20%). The performance of a logistic regression for classification of images was investigated using three different subsets of the labelled images: (1) the original dataset, (2) a balanced but under‐sampled dataset with equal number of blocked and unblocked images, and (3) an augmented dataset with an equal number of blocked and unblocked images using Gaussian noise augmentation to increase the number of unblocked images. Results show that our data‐augmentation method enhanced model accuracy by 8%, successfully classifying images as blocked or unblocked with an accuracy of 88%; by overcoming the bias in the dataset these results also highlight potential solutions to overcome the challenges of operating this methodology across a network of cameras. This enables authorities in both data rich and data scarce regions the ability to take advantage of machine learning to open up the next generation of a distributed, data‐driven flood warning systems, protecting people, infrastructure and the environment.

Numerical modeling of interaction of turbulent flow with trash screen in open channels

Trash screens are widely employed at the entrance of hydraulic structures, water intakes, and pumping stations to trap flowing debris that could exasperate downstream troubles. The characteristics of the vertical trash screen flow are measured using a Three-Dimensional Acoustic Doppler Velocimetry instrument for different flow conditions. The governing equations of the flow are numerically solved using k–ω SST, k–ϵ STD, k–ϵ RNG, and Reynolds Stress Model (RSM) and Large Eddy Simulations (LES). ANSYS-Fluent is used for these numerical simulations. The free surface of the vertical trash screen flow is computed by the volume of fluid method. The Grid Convergence Index is used to analyze the impact of the chosen grid structure on the numerical results. Experimental measurements of the velocity field and free surface profiles are compared with the numerical results of 3D simulations for validation. This study aims to identify the behavior of flow through screens in more detail through experimental and numerical simulations. The computed flow profiles considering all five cases agree well with the measured profile, whereas streamwise velocity in most portions of the flow, the k-ω SST outperforms the other models, and the RSM turbulence model is the second most effective.

Dam Safety: Sediments and Debris Problems

Sedimentation of reservoirs has its negative impacts on dams, first by reducing useful storage, altering the benefit/cost ratio originally calculated for the dam, and second by reducing the dams’ capacity for flood routing; increasing flooding hazards on the dam itself and for the downstream. More problems can be created by sediments and floating debris during floods on outlet structures by clogging them and thus creating dangerous situations, or damage trash screens leading to even more problems. If these debris and coarse sediments are allowed in, then they may damage dam structures such as gates, spillways intakes in addition to chutes, stilling basins and power penstocks by the mechanical abrasion impacts of such sediments on them. Frequent inspections, especially after floods must be made to ensure proper functioning of such structure and take actions for reducing the damage. In small reservoirs, dredging; although it adds to maintenance cost, may ease the problem, but in very large reservoirs, this may prove unpractical. Designers, therefore, have a duty to consider sedimentation problem seriously in the initial stages of design by: checking the anticipated accumulation of sediments, allowing enough storage free from siltation, foreseeing their negative impacts on intakes and outlet structures and taking design measures to reduce these impacts. At the same time, dam stability calculations shall have to provision for the anticipated new conditions of silting up at the face of the dam. Operators of dams, on the other hand, shall have to keep open eyes for all the negative issues created by sediments and floating debris, repairing damages caused by them and take measures to reduce their impacts in the future.

Experimental Investigation of Curved Trash Screens

AbstractConventional trash screens are widely used to prevent debris from being transported to downstream reaches of waterways and to allow safe passage along the same waterways. However, debris ac...

An experimental investigation of the impact of aquatic weeds trash racks on water surface profile in open channels

ABSTRACT A considerable quantity of weeds is drafted with flow due to maintenance activities and moving vessels causing serious problem to hydraulic structures and hydropower plants along open channels. Aquatic weed trash screens are normally constructed upstream hydraulic structures to control the drafted weeds and preventing them from passing through the hydraulic structures. The effect of the presence of accumulated aquatic weed upstream trash racks on water surface profile is the main disadvantage of trash racks. In this research, the effect of the presence of trash rack and the accumulated weeds upstream it with different densities on water surface profile is studied experimentally. Ninety runs were applied in the hydraulic lab of Channel Maintenance Research Institute. Equations relating different hydraulic parameters and accumulated weed density to the water surface profile were established. It was concluded that accumulated weed depth is the most effective parameter on heading up, while the blocked area of trash rack screen and extension length of weed upstream the barrier are the most effective parameters on head loss.

An experimental study on angled trash screen in open channels

Trash screens are widely employed at entrance of hydraulic structures (culverts, barrages…, etc.), water intakes, and pumping stations to trap flowing debris that could instigate downstream troubles. Traditional trash screen (perpendicular-vertical screen to the flow direction) can cause problems of increasing head loss through it, especially with the blockage ratio. This experimental study presents a concept of an adjusted screen with circular bars to find a solution for such problem. In this regard, angled screen models with different angles, blockage ratios, and flow discharges were investigated. The results indicated that the head loss coefficients reduced by reducing the screen angle, so angled screen (α < 90°) reduced the loss in comparison with the traditional trash screen (α = 90°). The values of head loss coefficient increased with increasing blockage ratio, and flow discharge. The screen losses increase strongly when the screen becomes blocked by 40% or more. Screen angle, blockage ratio, and discharge influence effectively the head loss of a screen. Furthermore, a new equation for the head loss, the key element in designing screens, is proposed based on the different tested parameters, and should be useful in designing trash screens.

Optimal Power Distribution among Hydropower Units Taking into Account Head Loss in Units’ Trash Screens

As is known, the importance of renewable energy sources is rapidly growing. The paper addresses one of the important issues paying attention to the optimization of hydropower plant units’ regimens. Considering the unit operating characteristics as unequal at different head levels, the authors propose to take into account the real head of water column for each unit to define the actual performance specifications. Further, this information can be utilized in the optimization process to minimize water expenditure at hydropower plant. The authors have derived the objective function and the restrictions related to the process of real power production. Then, they have proposed a new optimization algorithm instead of traditional ones, assuming that it has advantages in speed and simplicity. The block diagrams of the proposed algorithm as well as the necessary and sufficient explanations have been presented. As a final point, the results of conducted tests and conclusion indicate that the algorithm solves the problem satisfactorily. It could be integrated into the group power control system to perform operations at a hydropower plant in an effective way.

A new method for estimating trash screen blockage extent

This paper presents findings from research that examined the potential for developing equations that predict the extent to which trash screens at culverts are likely to become blocked. This was assessed using multiple regression analysis in which the average area of debris blockage at screen faces calculated from field inspection records obtained from 140 screen sites in Belfast, Northern Ireland, was correlated with pertinent driving variables including channel properties, flow characteristics, landuse types, the degree of social deprivation and the properties of the screens themselves. This analysis enabled the development of simple empirical equations requiring input data that can be extracted from readily available sources. The key variables identified and the properties of the equation coefficients are discussed within the context of their statistical significance.

Modeling Probability of Blockage at Culvert Trash Screens Using Bayesian Approach

Trash screens are commonly installed at culvert entrances to prevent the ingress of debris that might otherwise become lodged within the structure. However, these can be a hazard in themselves if not cleared at an appropriate interval. There are currently no tools available to support making decisions regarding screen inspection requirements based upon potential site-by-site blockage risks. The analysis reported here was performed to address this issue. The parameter considered as key in the decision-making process was the probability of screen blockage. To determine this for any screen under consideration, a stochastic predictive model was developed using inspection records, obtained from 140 screens in Belfast, Northern Ireland, to relate blockage probabilities to seven potential drivers extracted from channel, land-use, meteorological, temporal, and social deprivation factors, employing a logistic regression approach. To allow for randomness in the data set, a Bayesian framework was adopted through which the uncertainty associated with any prediction could be reported using appropriate credible intervals. The predictive accuracy of the model was also assessed using appropriate measures and, despite documented uncertainties, was shown to be well within acceptable limits.

Is proximity to the North Atlantic Drift and the Continental Shelf Current sustaining freshwater European eel populations in western Scotland?

Summary1. We report on freshwater resident eel numbers in western Scotland based on two time series of data, independent of each other, spanning 28 years and that do not rely upon fisheries information.2. Data from eel captures on trash screens of a pumping station (1982–2003) on Loch Lomond and electrofishing data from a stream in Lochaber, the Allt Coire nan Con (1989–2010), are compared with similar time series eel population data from elsewhere in the British Isles and more widely in Europe.3. Over the period of the study, indices of eel numbers from across Europe declined by between 72 and 95%; in stark contrast, neither time series from western Scotland showed evidence for decline between 1982 and 2010.4. We provisionally conclude that freshwater populations in western Scotland are being maintained by regional processes directly related to the proximity of the leading edge of the North Atlantic Drift and the Continental Shelf Current and the direction of prevailing winds.

Improved methods for predicting trash delivery to culverts protected by trash screens

AbstractThe risk of flooding associated with blockage of culverts by natural and anthropogenic debris is often reduced by fitting a trash screen at the structure's inlet. However, screens can actually exacerbate flood risk if not properly designed and maintained. In this paper, findings from a project that has been tasked with developing decision support tools to help the asset manager prioritise screen clearance strategies are explored. The scientific knowledge base surrounding this complex issue has been extended using an empirical approach by correlating the probability of delivery of significant debris loads to trash screens, as determined using data from 140 screen sites in Belfast, Northern Ireland, with pertinent driving variables including channel properties, flows, land use types and the degree of social deprivation. This analysis has enabled fundamental relationships to be developed that, once validated, will help planners to establish the potential loads of debris that may be delivered to screens and will therefore offer a robust means to rank culverts in terms of blockage potential and therefore flood risk.

Hydraulic Design and Maintainance of Trash Screens in Open Canal Systems

Hydraulic Design and Maintainance of Trash Screens in Open Canal Systems

Design of turbulent fountain irrigation trash screens

Floating trash in surface irrigation waters can block or reduce the flow of irrigation water and significantly increase irrigation costs. Dimensional analysis was applied to experimental data to develop equations for designing irrigation trash screens and for modifying a trash screen to compensate for variations in water flow. The equations were based on providing adequate horizontal flow across the screen to float aquatic algae off the screen and thereby prevent blockage.

Trash Screens on Culverts in Urban Areas

ABSTRACTThis PAPER DEALS with the performance of trash screens on culverts on urban watercourses. An assessment of the scope of problems associated with screens has been obtained from a survey of land drainage authorities in urban areas in England and Wales. The findings have been analysed and this has resulted in the development of four basic design criteria for screens. A detailed survey of the performance of some 17 sites in the river Ravensbourne catchment of the Thames Water Authority was undertaken over a number of years allowing relationships to be identified between debris amounts and types of upstream catchment area, screen/culvert area ratios, and priority of location.The paper describes considerations to be taken when providing a screen and advocates an individual design for each location rather than installing a standard arrangement. The lack of practical information in the UK, and the high level of problems experienced overall underlines the need for proper consideration to be given to this subject. Current research work is being undertaken to obtain preferred efficient screen configurations, but it is concluded that this should complement rather than replace the need for good trash screen design.

Self-Cleaning, Non-Powered Trash Screens for Small Irrigation Flows

ELIMINATION of trash in irrigation water supplies is becoming a more important consideration in surface irrigation systems. When irrigators used earth distribution ditches and sod cutouts they seldom had a problem with trash. With increased use of siphon tubes and gated pipe and their smaller outlets, trash has become a real problem to the irrigator. Resetting siphon tubes or cleaning gate openings can be a major task. Uneven, inefficient irrigation resulting when furrow streams are not kept at the desired flow rate hurts yields. With the development of cablegation system automated gated pipe (Kemper et al., 1981) irrigation, trash removal became a priority need.

Mechanized Wheel and Belt Screens for Farm Irrigation Turnouts

ABSTRACT ROTATING wheel and traveling belt trash screens were developed for farm canal turnouts to prevent trash and debris from entering farm irrigation systems. They are driven by electric motors or water-powered paddle wheels. The screens are particularly useful for automated irrigation systems. The head loss is small, and they are not adversely affected when the farm delivery is terminated by automated downstream valve closures while canal turnouts remain open. Different screens, bearings, and bushings were tested for this application. Hydraulic tests were conducted to determine head losses with different wheel screens..

Aspects of the biology of estuarine fish populations sampled from power station trash screens

In the absence of previous investigations the present study considers fish populations in the Medway (England) Estuary; their type, composition and migration patterns. Seasonal growth of first‐year plaice and flounder is also investigated. Fish were sampled monthly between 1973 and 1975 using power station trash screens as the quantitative sampling method. A total of 46,228 fish, 49 species and weighing 325.0 kg were taken. Monthly samples were dominated by sprats which, with 13 other species, formed more than 90 percent of the catch in most months. Based on seasonal distributions and length‐frequency changes in consecutive months a model of fish migration patterns was constructed. In most cases emigration and immigration were separated by one or more months between spring and autumn, while in clupeoids they appeared to occur coincidentally during spring and summer.

Hydraulic Design for Combined Sewer Diversion

The City of Richmond is building two diversion structures that will join two existing sewers to a retention basin where combined sewage and storm runoff will be stored for later treatment. This scheme will minimize the discharge of combined sewage to the James River. Levels in the sewers and diversion structures vary with flow, river level, and interaction between the connected diversion structures. In order to accurately predict and minimize levels in the sewers upstream of the diversion structures, a 1:18 hydraulic model was tested. The model showed that levels could be reduced in both the flow to the river mode and diversion mode by streamlining various elements of the diversion structures. A flow distribution device reduced unacceptably high velocities at the trash screens.

Passage of floods at the Novosibirsk hydroelectric power station

1. The arrangements for passing spring floods through the Novosibirsk hydroelectric power station very significantly influence the effective utilization of the water resources of the river and the reservoir. 2. The effectiveness of the utilization of the Ob' River during the spring flood period at the Novosibirsk power station was raised by the reconstruction of the turbogenerators (the station's installed capacity was increased by 55 MW), an increase in storage in the reservoir by a greater preflood drawdown, and raising the NPL by 20cm; by effecting a power-type program for filling the reservoir with the surplus flows of the spring flood season (the program requires a corresponding preliminary regulation of the upstream and downstream levels); and by the application of several operating measures, including an effective campaign against blockages of the trash screens. 3. The passage of spring floods through the Novosibirsk power station could be even more efficient if the accuracy of flow forecasting could be improved. 4. The measures described in this article for raising the efficiency of river-flow and reservoir-storage utilization during the passage of floods, taking local conditions into account, can be utilized at other hydraulic schemes and power stations.