Hydraulic Model Studies Research Articles

ANFIS approach to the scour depth prediction at a bridge abutment

An accurate estimation of the maximum possible scour depth at bridge abutments is of paramount importance in decision-making for the safe abutment foundation depth and also for the degree of scour counter-measure to be implemented against excessive scouring. Despite analysis of innumerable prototype and hydraulic model studies in the past, the scour depth prediction at the bridge abutments has remained inconclusive. This paper presents an alternative to the conventional regression model (RM) in the form of an adaptive network-based fuzzy inference system (ANFIS) modelling. The performance of ANFIS over RM and artificial neural networks (ANNs) is assessed here. It was found that the ANFIS model performed best among of these methods. The causative variables in raw form result in a more accurate prediction of the scour depth than that of their grouped form.

HYDRAULIC MODEL STUDIES FOR SEWA—II DAM SPILLWAY, JAMMU & KASHMIR—A CASE STUDY

ABSTRACT The perennial Himalayan rivers provide potential for large scale hydro power generation. These rivers carry heavy sediments because of steep slopes and young geology consisting of soft, friable rock. This is further aggravated by the seismic character of the Himalayan zone. The rivers during flooding time carry with them lot of sediment which ultimately gets collected in the reservoir. Spillways in Himalayan region are designed for handling both flood releases and flushing of the sediment. Breastwall/sluice spillways have been widely recognized as the most appropriate spillways for dual purpose of flood disposal and flushing of sediment. Present paper describes the hydraulic model studies conducted for Sewa dam spillway, to study the suitability of spillway by assessing the discharging capacity of spillway, performance of stilling basin, flow conditions upstream, downstream of spillway and in front of power intake.

STUDIES FOR A LOW LEVEL AND LOW HEAD ORIFICE SPILLWAY-A CASE STUDY

ABSTRACT Run-of-the-river schemes in cascades with suitable sediment disposal arrangement, instead of large storage dams on the rivers, are in vogue to minimize the deposition of silt in the reservoirs. Teesta low dam spillway stage—III is one such scheme in Teesta valley. It is typically a low level diversion structure with a dam foot power house. This paper describes the hydraulic model studies conducted at C.W&P.R.S for evolving an efficient design of spillway, energy dissipator, power intakes and tailrace channel.

HYDRAULIC MODEL STUDIES FOR TUNNEL SPILLWAY AND ENERGY DISSIPATOR OF PARBATI H.E. PROJECT, STAGE-III, HIMACHAL PRADESH

ABSTRACT Hydraulic design of tunnel spillway is complex and site specific. The diversion structures in the form of upstream and downstream cofferdams and diversion tunnels/channels are needed to divert the river during construction stage. Once the construction is over, these tunnels can be plugged or utilized for various purposes such as power tunnels, silt flushing tunnels, irrigation outlets and spillway tunnel. Various parameters such as approach flow conditions, depth of submergence, inlet and outlet shape, length and slope etc. are considered in design of tunnel spillway. Type of energy dissipator to be provided at the outlet mainly depends on site conditions, orientation of river course with respect to alignment of the tunnels, depth and velocity at the exit portal and tail water level in the river. This paper describes the hydraulic model studies conducted for tunnel spillway of Parbati H.E. Project, stage-Ill, Himachal Pradesh.

HYDRAULIC MODEL STUDIES FOR MYNTDU (LESHKA) DAM SPILLWAY, MEGHALAYA

ABSTRACT Rivers of steep slope with fragile geology have experience problem of heavy sediment load coming from the catchment to the reservoir. Due to continuous deposition of sediment, the live storage capacity of the reservoir reduces, which requires cleaning regularly. To reduce the sediment deposited in the reservoir, spillway is designed in the form of orifice within the dam body or spillway with breastwall. An orifice spillway has advantage of high head for power intake, provides more efficient way for flushing out the sediments and also ease in regulating flood discharge and storage. The present paper describes the hydraulic model studies conducted at CW&PRS for Myntdu (Leshka) Dam Spillway, Meghalaya, to optimize various components of sluice spillway, performance of ski-jump bucket, scour pattern, piezometric pressures on the sluice roof profile and spillway profile.

Using hydraulic modeling to address social impacts of small dam removals in southern New Jersey

Small relic mill dams are common in the watersheds of southern New Jersey, dotting the landscape with many small neighborhood lakes. Originally built in the late 1800s, most of these dams have become increasingly unable to handle current design storms due to increased urbanization of the watersheds. Several of these dams have also been classified as “high hazard” by the New Jersey Department of Environmental Protection Dam Safety Division because their failure has the potential for loss of life or extensive property damage. The current private owners are generally unable to afford the high repair costs needed to rehabilitate the dams to current safety standards, and are therefore more inclined to remove them. This research analyses both the physical and social impacts of the removal of two small dams in southern New Jersey, and integrates the two seemingly disparate concepts. Using hydraulic modeling and previous case studies, it is predicted that there will be limited effects to the hydrological and biological characteristics of the stream corridor. A survey distributed to the affected homeowners that live on these lakes shows that the community, however, expects significant impacts to the bio-physical characteristics of the stream corridor, as well financial impacts to their property value and social impacts to their recreational activities. The current study exposes the widening gap between policy makers and landowners, and highlights where complete stakeholder interaction could and should occur.

Stormwater overflow in stepped channel

Sharp bends in drainage channels are sometimes engineered to suit local topography, especially in densely populated cities where land is limited. A hydraulic model study of a steep urban drainage channel is carried out to investigate the causes of an overflow incident in Hong Kong urban area, and to develop the drainage improvement measures to prevent flooding. The stepped drainage channel has a sharp bend in the middle and several trash racks are located along the channel. Experiments are performed on a 1:16 Froude scale model. In the first phase, experiments on a purposely built straight channel model are performed to study the bottom roughness of the stepped channel flow isolating the effect of the bend. After the straight channel experiments, four trash rack scenarios are tested in the exact model with detailed channel features. The flow in the drainage channel is supercritical and highly aerated. Based on the theory of skimming flow in stepped channels, a hydraulic assessment suggests that the bend and trash racks may be dominant causes of the overflow. The experiments show that sharp bend causes a spiral flow leading to significant lateral overflow. The trash racks are observed to generate a serious ski-jump type overshooting flow. It is found that the stormwater overshoot and flooding can be prevented by the repositioning of appropriately sized trash racks and the containment of the spiral flow. The proposed channel improvement design has been implemented on site and found to work successfully in heavy rainstorms after installation. The present study offers novel insights into the design of urban drainage works.

Hydraulic model study of the Tai Hang Tung Storage Scheme

The Tai Hang Tung Storage Scheme (THTSS) is an essential component of theWest Kowloon Drainage Improvement (Stage 2) Project that aims to solve the flooding problem in Mongkok—a congested and densely populated district of the Hong Kong Special Administration Region. Over the years rapid development and changes in land use have resulted in significant increases in surface stormwater runoff, and the existing drainage system failed to cope with severe rainstorms. Rather than digging up roads and widening/adding existing drains, an economic drainage improvement plan calls for the construction of a 100, 000m3 underground storage tank upstream of the flooding black spots, below an existing football field in the vicinity of the Tai Hang Tung–Tat Chee Road junction. The upstream storage can serve to attenuate peak floods and protect downstream areas from flooding. Due to the complicated flows in the stormwater drainage system (including subcritical and supercritical open channel flows, pressurized flow in closed conduit, side weir overflows, and transitional flows at junctions), a 1:22 undistorted Froude scale physical model was designed and constructed to study the feasibility and performance of the THTSS scheme. As a complement, a 1D numerical model of the unsteady flow was developed to study water stages and flow characteristics for different side-weir arrangements. The key findings of the physical and numerical model studies are reported herein. The studies have resulted in an optimal design of the flood storage scheme; the physical model tests and numerical model results indicate that THTSS can enhance the flood control capacity to cope with a one in 50-year rainstorm.

TRANSITION FOR DESILTING BASIN WITH OPEN CHANNEL FLOW

ABSTRACT Desilting basin forms an integral part of the water conductor system of run-of-the- river schemes for hydro power generation while suspended sediment concentration is very high during monsoon. Transitions are provided to gradually reduce the velocity of flow entering into the basin. If transition is too long there is deposition of medium and coarse sediment on the bed of the transition itself. If transition is too short, there is uneven distribution of flow and higher turbulence. As such optimization of transition length, shape and bed slope is necessary to avoid deposition on the transition bed and more or less uniform distribution of flow entering into the desilting basin. As far open channel desilting basin is concerned inlet transition is very difficult to design due to substantial difference in depths on upstream and downstream of transition and also due to sub critical expansion. This objective could be achieved by providing a simple hump. The results of the hydraulic model studies conducted at CWPRS, Pune are discussed.

Neural Networks for Estimation of Scour Downstream of a Ski-Jump Bucket

The estimation of scour downstream of a ski-jump bucket has remained inconclusive, despite analysis of numerous prototypes as well as hydraulic model studies in the past. It is partly due to the complexity of the phenomenon involved and partly because of limitations of the traditional analytical tool of statistical regression. This paper addresses the latter part and presents an alternative to the regression in the form of neural networks. The depth of the scour hole developed along with its width and length is predicted using neural network models. A network architecture complete with trained values of connection weight and bias and requiring input of grouped parameters pertaining to discharge head, tail water channel depth, bucket radius, lip angle, and median sediment size is recommended in order to predict the depth, the location of maximum scour, as well as the width of scour hole. The neural network predictions have been compared with traditional statistical schemes. Although the common and simple feed forward back propagation network took a very long time to train as compared to some advanced schemes, it was found to impart equally reliable training as the latter. Use of causative variables in grouped forms was found to be more rewarding than that of their raw forms probably due to lesser scaling effect.

HYDRAULIC MODEL STUDIES FOR A DUAL PURPOSE SPILLWAY WITH 21 M DEPTH OF OVERFLOW—A CASE STUDY

ABSTRACT The perennial Himalayan rivers provide potential for large scale power generation. Excessive sediment load especially during monsoon is a typical characteristic of such rivers. Flushing of sediment through spillway is an effective technique to control sedimentation. In order to achieve this, spillways with very low crest and very high depth of overflow of the order of 21 m and associated energy dissipation arrangement are envisaged. The present paper describes the hydraulic model studies conducted for Chamera H.E. Project, Stage—II, Himachal Pradesh, to evolve a spillway crest profile free of sub-atmospheric pressure, a stilling basin at the toe of the spillway and power intake alignment to ensure smooth entry of water to the head race system.

A hydraulic box model study of the Mediterranean response to postglacial sea‐level rise

This paper quantifies the role of changing sea level in affecting Mediterranean stratification using a new model of the strait‐basin system, which allows for explicit time dependence. During the last deglaciation, Fairbank's Meltwater Peak 1B leads to rapidly rising global sea levels and a freshening of the oceans and hence increasing influx of ever freshening Atlantic water into the Mediterranean basin. Owing to long residence times, the salinity of the deep and intermediate water reservoirs would have decreased more slowly, so that the basin was more stably stratified for a period, with possible implications for sapropel formation. Our model is used to estimate the size of this reservoir effect in comparison to the freshwater influx from the opening of the Black Sea at the Bosphorus. It is found that this mechanism affects the stratification to a similar degree as the Black Sea opening. Other climatic mechanisms have also affected the freshwater budget of the Mediterranean at this time, but their sizes are more difficult to quantify.

MODEL STUDY FOR VORTEX OBVIATION IN A CHANNEL CONFLUENCE

ABSTRACT Hydraulic model studies can be employed to study the functioning of a hydraulic structure or a machine. In this work, a physical model study was conducted for an existing Lower Mettur Barrage Power House in Tamil Nadu State to simulate the intake canals where there was a vortex problem, reducing the net available head and consequently the power generation. Various trials of the possible alterations to intake canals were attempted and the final feasible one was evolved and validated.

Left ventricular flow propagation velocity: insights from a combined hydraulic and numerical model study

Left ventricular flow propagation velocity: insights from a combined hydraulic and numerical model study

Case Study on Hydraulic Performance of Brent Reservoir Siphon Spillway

The Brent Reservoir was constructed in the mid-1830s and its siphon spillways were completed in 1936 to protect the dam from overtopping in the event of an extreme flood. Since completion, there have been problems with the hydraulic performance of the siphons, some of which primed simultaneously, causing flooding downstream. A physical hydraulic model study has been conducted to investigate the hydraulic performance of the siphons in order to establish reliable stage discharge relationships. The existing bellmouth siphon system was found to be unsuitable, causing the siphons to prime suddenly at discharges of around 3 m³/s. This was due to the sudden removal of an air pocket from the siphon’s crown. The model tests were carried out in two stages. In the first stage, the existing geometry was examined. Based on the results from stage 1 of the experiments, it was concluded that the air inlet requires redesign and various options to improve the air regulation should be considered. In the second stage, various options to regulate the inlet of air and establish stable siphon performance over the entire range of discharges were considered. It was found that the most stable conditions are provided by an air slot being cut into the spillway hood at an appropriate level. This geometry provides excellent air-regulated stability, unimpaired spillway capacity, and is insensitive to tail water level and wave conditions in the reservoir.

ASSESSING CHANGES IN WATERSHED FLOW REGIMES WITH SPATIALLY EXPLICIT HYDRAULIC MODELS1

ABSTRACT: Urbanization, farming, and other watershed activities can significantly alter storm hydrographs and sediment erosion rates within a watershed. These changes routinely cause severe economic and ecological problems manifested in the form of increased flooding and significant changes in channel morphology. As the activities within a watershed influence the hydrologic, hydraulic, and ecological conditions within a river, interdisciplinary approaches to predict and assess the impacts that different land uses have on streams need to be developed. An important component of this process is ascertaining how hydrologic changes induced by specific watershed activities will affect hydraulic conditions and the accompanying flood levels, sediment transport rates, and habitat conditions within a stream. A conceptual model for using spatially explicit (two‐dimensional) hydraulic models to help evaluate the impacts that changes in flow regime might have on a river is presented. This framework proposes that reproducing and quantifying flow complexity allows one to compare the hydraulic conditions within urban, urbanizing, and non‐urban streams in a more biologically and economically meaningful way. The justification, advantage, and need for such a method is argued through the results of one‐ and two‐dimensional hydraulic model studies. The implementation of this methodology in watershed urbanization studies is described.

Implications of large-scale heterogeneities for hydraulic model studies at the potential site of a radioactive waste repository at Gorleben, Germany

The Gorleben salt dome, a potential repository site for all types of radioactive waste, is located near the community of Gorleben in the north-eastern part of Lower Saxony. The investigation of the suitability of the site has been suspended due to a moratorium by the Federal Government and the electricity utilities. Before this moratorium, hydrogeological investigations were conducted in an area of more than 380km2 around the salt dome to study the aquifer system in the sediments above it. During the extensive field investigations and data evaluation, the existence of heterogeneities on various scales has been verified. These heterogeneities mainly reflect differences in lithology. On scales of decameters to kilometers, the site is characterized by a predominance of aquifers with intercalated aquitards. The salt dome is crossed by a subglacial erosion channel in which the lowermost aquifer is partly in contact with the cap rock or the salt itself. The density of the groundwater, which is a function of salt concentration, varies spatially. It generally increases with depth, often up to that of saturated brine at considerable depth. The change in groundwater density has to be considered together with spatially variable hydrogeological parameters because it has a pronounced influence on groundwater movement and contaminant transport.The groundwater modelling was carried out stepwise. Three-dimensional, porous media, freshwater models represent the overall hydrogeological structure and neglect the small-scale heterogeneities. These models are used to evaluate regional groundwater movement. They provide the characteristic features of the main flow paths under freshwater conditions. Preliminary uncertainty and sensitivity analyses have been performed using such freshwater models. Two-dimensional, porous media, variable salinity models are used to calculate changes in the flow field, density distribution, flow paths and travel times compared to freshwater simulations. They have demonstrated the sensitivity of the salt/fresh water system to major changes in the hydrogeological structure, as well as other important factors like initial density distribution and the period of time being modelled. Comparison of measured and calculated hydrochemical data shows the importance and validity of incorporating hydrogeological structures in these flow and transport models. Simple three-dimensional, variable salinity models representing only the main hydrogeological structures on a large scale confirm the importance of the third dimension for the flow field. They show that the flow of the salt water corresponds to that derived from density data analyses. Recent model development will soon enable more sophisticated three-dimensional sensitivity studies that take into account the spatial variability of the hydrogeological parameters and the variability in groundwater density.

A Hydraulic Model Study of Intake Structure

In the intake structure of a nuclear power plant, undesirable pump operating characteristics such as vortices and nonuniform pump-approach flow around the pump bells take place frequently due to poorly arranged intake geometry. Therefore, prior to the construction or renovation of intake structure or internal auxiliary facilities, a hydraulic modeling test should be performed to predict the undesirable hydraulic phenomena. In this study, a three-dimensional turbulence model was applied for a numerical modeling test, and a 1:10 scale, geometrically undistorted physical model was employed to investigate the hydraulic behavior and simulate pump operating conditions in the intake structure of Kori Nuclear Units 3 and 4 in Korea. The results from these numerical and physical model tests were compared, and an antivortex device was also proposed to ensure a stable suction condition of the pumps.

Flip Bucket without and with Deflectors

Flip buckets are commonly used to discharge flow away from a hydraulic structure into a plunge pool to dissipate energy. In the past, flip buckets have often been designed in accordance with site-related hydraulic model studies. Consequently, limited generalized design guidelines are available. The present study considers flip buckets either in a prismatic rectangular channel or extended by a lateral deflector resulting in a curved jet trajectory. The main features of flip buckets are investigated, including scale effects in hydraulic models, bucket pressure distribution, and nappe trajectories with and without the presence of deflectors. An analysis is presented mainly involving the approach Froude number, the so-called bend number, and the bucket takeoff angle. It is demonstrated that the near field of a bucket-deflected jet follows the conventional parabola of a mass point, provided that the takeoff angle is correctly accounted for and that the flow is scaled using the Froude similarity law. Furthermor...

A Sensitivity Study for the Second Order Reliability-Based Design Model of Rubble Mound Breakwaters

The reliability-based risk assessment and structural design model (REBAD) (Balas, 1998) introduced in this paper, is a worthwhile tool in the preliminary design of maritime structures which are portrayed by vast failure consequences and significant resource expenditures. REBAD model in which the Second-Order Reliability Method (SORM) is utilized together with a cost-optimization algorithm, is implemented to Mersin yacht harbor which is constructed near the city of Mersin located on the Turkish coast of Mediterranean Sea. SORM is established on a more correct approximation of the failure surface than the first-order method. The failure mode probability is predicted by approximating the failure surface by a quadratic surface with the identical curvature at the design point. First, REBAD is implemented to the main breakwater by utilizing the Hudson failure function to determine the size of armor units, then failure mode response functions were obtained for the fixed exceedance probability of several damage levels. Combining with the hydraulic model study carried out by Ergin and Özhan (1994) and REBAD outcome, the trunk section of main breakwater and design functions were determined. The second order reliability-based sensitivity study was also carried out to systematically compare limit state equations of Hudson and Van der Meer.Authors concluded that, Van der Meer failure function is a more reliable design function for this case study which illustrated the affect of uncertainties encountered in Turkey on the design practice of rubble mound breakwaters. Since REBAD enabled the first application of reliability-based design practice for coastal structures in Turkey, it is the commencement for the development of a national reliability-based design standard of maritime structures.