Water erosion is the detachment and removal of soil material by water. The method could also be natural or accelerated by human action. The rate of erosion could also be very slow to rapidly intensive depending on the soil, the natural landscape, and atmospheric condition. Water erosion is a two-way process involving the detachment and removing and moving of soil particles. Water erosion usually happens when raindrops hit the soil surface and they create displacement in soil particles. Water erosion causes loss of surface soil, reduced crop yields, damaged infrastructure, weed dispersal, and silting of dams and natural waterways. The average annual direct cost of water erosion to dryland farming in Western Australia is estimated to be $10 million, however, the costs are much higher in years of severe summer storms.Scour is engineering form of erosion therefore, scour is the process of removal of material from a stream bed by the erosive action of flowing water. The result in a local lowering of the stream bed below the natural average level and subsequent enlargement of the flow cross-sectional. Scour is distinguished from degradation therein as the latter is not the local phenomenon. once the incoming sediment load to a reach of the sediment river is a smaller amount than the transport capacity of the watercourse, the flow picks up the material from bed and banks thereby lowering the bed level of the river a long stretch. This method is termed degradation. Whereas scour is due to increased turbulence during a small reach, degradation is because of deficient sediment provide in relevance transport capacity over a long reach.
Bridge scouring is the main factors in this era, failure of bridge design and collapse occurs when there is the worst design of piers and foundation has used. Scouring is a slow process and it usually starts near the foundation area of bridge structures and weather condition may cause of this problem. When a sediment stream is partially obstructed by hydraulic structures like bridge piers, abutments, spurs etc., scour happen within the vicinity of the structure. To emphasize the fact that the lowering the bed level happens only within the vicinity of structures. The term used local scour is commonly used in this connection. Local scour around bridge piers happen because of the flow pattern within the area adjacent the pier changes radically causing an area increase within the sediment transport capacity. This cause the development of the scour hole around the pier, that in turn changes the flow pattern. Constriction of the flow at the pier additionally leads to increase the rate within the entire which of the river at the bridge site leading to scour. Especially if the width blockage is large, this form of scour is known as construction scour. The estimation of scour depth around bridge pier is a major concern of a civil or a bridge engineers. The estimation of scour depth leads to the design of too shallow a foundation and consequent exposure of the foundation endangering the safety of the bridge. Therefore, knowledge of the anticipated maximum scours depth for design discharge is important for good and solid design of the foundation of the bridge piers and abutments.
Scour near coastal structures has been the topic of analysis efforts for several years. To adequately study this problem, researchers should address the various effects of waves, wind, tide, currents, and storm surge on both the structure itself and the bed on which the structure resides. Among the foremost common are issues related to toe scour at, the base of piles, toe scour at vertical seawalls and especially scour at horizontal pipelines.
Another Pivotal problem which often confronts the civil engineer is excessive erosion or scouring at the outlet end of culverts. Nature’s methodology of keeping erosion under control on mild slopes is to spread the runoff over a wide area. of the watershed that the flow depths are shallow and resistance to flow rather high. usually, the main road embankment crossing a watershed disrupts the drainage set up of nature therein the runoff from a large space is funneled to culverts where the flow is targeted within a small space. This concentration of flow into a culvert will suddenly increase the scouring ability of the flowing fluid at the culvert outlet since the flow has been accelerated. The accelerated flow must travel a long way before it will distribute again over a wide space when it has passed through the culvert. As time elapses, erosion or scoring will increase, and scour control becomes more difficult and costly. it’s no longer realistic to think about only the initial cost of a culvert and ignore future maintenance.
A hydraulic or infrastructure is mostly studied to produce a practical measure to solve an identified problem when problem identification subsequent stages are determined by a series of choices and actions culminating within the creation of a structure or structures to resolve the problem. Aspects which will influence the ultimate outcome of the design process need to be assessed. Additionally, to hydraulic, geotechnical and engineering characteristics, phenomena such as social conditions, economics, environmental impact, and safety needs also influence the design process. Within the scope of the Dutch Delta works, systematic analysis with respect to the prediction of the formation of scour holes was conducted by the Dutch Ministry of Transport, construction and Water Management and Delft mechanics. When the catastrophic flood disaster in 1953, the Delta plan was formulated to protect the Rhine-Meuse-Scheldt delta against future disasters. Dams with large-scale sluices were planned in some estuaries. The severe scour that was expected necessitated the acquisition of a far better understanding of the scour process.
Bridge scour has been a topic of interest and importance to people from the time of the earliest civilization. Most likely the initially recorded references to the topic appear in the Leonardian manuscripts. In modern time, the first systematic studies of bridge pier scour were undertaken in Germany at the Zeuner laboratory by Engles in the early 20th century (Rose and Ince,1957). Later, a significant study of scour at piers and scour countermeasures was undertaken at the Chatou laboratory by Chabert and Engeldinger (1956). Their wonderful information was the first to Illustrate the vital distinction between clear water and live bed scour. At about a similar time, Laursen and others published results from the comprehensive investigation of bridge scour at The Lowa Institute of Hydraulic analysis, (Laursen and Toch, 1956; and Laursen, (1962,1963). Perhaps the most important contribution of the Lowa studies was the conception of adapting Straub’s (1934) solution to scour in the long rectangular contraction to the case of local scour at piers and abutments. Another earlier U.S.A scour studies of note were conducted at Colorado State University by Shen et al. (1966,1969) on the pier scour and Liu et al. (1961) on scour at abutments. Garde et al. (1961) and Gill (1972,1981) additionally created a necessary contribution to data of scour at abutments. Meanwhile, Lacey (1930,1934), blench (1969) and others were incorporating methodology of estimation of local scour in the development of the regime theory of flow in alluvial channels. In Canada, the Canadian Goods Road Association published practical guidelines on bridge hydraulics, (Neill 1964,1973, and 1987). Here are some examples of bridge failure mechanisms.
Figure 1 Bridge Failure Mechanisms
Figure 2 Bridge Failure Mechanisms
Factors Influence Scouring:
The geomorphic, flood flow transport, bed sediments and bridge geometric factors that may affect the depth of scour at any structure foundations like bridge piers, Culverts, pipelines. According to Grahams in 1983 these are the main reason for scouring at any infrastructures.
• Geomorphic Factors:
Geomorphic Factors influencing bridge to scour are often divided into catchment characteristic and river characteristics. Generally, these influences are more important and useful for general scour instead of for localized scour. The catchment characteristic includes climate factors and the geography, vegetation and soil characteristics of the catchments. These factors are of primary importance because they determine the water and sediment transport rates at the bridge site. Also, the potential for debris accumulating at bridge foundations and exacerbating any scour depends on the type and quantity of vegetation within the catchment. The scour of floating woody debris that accumulates on a bridge in bank erosion. each flow and solid in mountainous regions have also been cited as significant sources of woody debris to waterways. Similarly, aggradation problems were experienced following a serve storm in 1994 at several bridges on the highway which follows the shore of Lake Wanaka in New Zealand (Case Studies D.3a to D.3d). Rivers in flat regions are typically alluvial, with wide channels incorporating flood channels and having fine bed materials. Similarly, aggradation problems were faced in 1994 storm in different bridges on the highway towards Lake Wanaka in New Zealand.
Figure 3 Debris Flow Effect at Bridge
Figure 4 Bank Erosion New Zealand
• Flood Flow Transport Factors:
Transport factors relate to water transport, sediment transport, and debris transport. they’re significant roles for determinant general scour and localized scour. The water flow is characterized for scour functions, using a flood flow hydrograph, the spatial and temporal distributions of fluid velocity and flow depth. Consideration of sediment transport determines whether conditions are the live bed or clear water scour. below live-bed conditions, the sediment transport rate and bed from characteristics are important factors. Bridge scour will be much increased by the accumulation of floating debris at bridge foundations.
Not all bridge scour issues are rainfall influence. Volcanic activity may result in large floods which might transport large quantities of debris and sediment. On Christmas Eve,1953, the railway bridge over the Whangaehu Rivers near Tnagiwai (North Island, New Zealand) failing once a lahar caused by the unexpected release of a large volume of water from the crater lake on Mount Ruapehu. the amount of water discharged from the lake has approximately estimated at 2 million cubic meters, the resulting flood hydrograph having a very steep rising and producing a flood.
Figure 5 Floating Debris Effects at Bridge Piers
• Bed Foundation Sediment:
Bed-sediment factors at waterways in which infrastructure sites like bridges, culverts, pipelines, Creeks including particle size distribution and for noncohesive sediments, the partial distribution of sediment sizes, each areally and vertically. Scour at structure especially at bridges supported on cohesive soils is extremely complicated phenomena. The scour condition of fine-grained soils can’t be evaluated based on grain size characteristic due to the complicated physiochemical interaction between colloidal particles, the effect of pore water pressure, and the result of preloading. Not only do most of these factors vary significantly with time at a specific site, but they vary from part of a site to a different part, and from one site to a different site, even within the same deposit of fine-grained soil. Bedrock level determines the probably limit for bridge foundation depth. Bridge foundation on the rock is often subject to scour if the rock is erodible. According to figure given below limit of scouring exceeding 2meter in siltstone and shale layers under the spillway at Saylorville Dam on the Des Moines Rivers, near Johnston Lowe USA.
Figure 6 Flooding USA 1993
The siltstone cap-rock was thought to protect the underlying sedimentary rock. The cut across the rock layers occurred because of the results of the first-time flow through the spillway during flooding in 1993. The process of scour in soft rock is caused also by weathering and abrasion. According to Figure and analysis, 1.7(b) shows scour of weathered ignimbrite within the river channel downstream of a spillway on the Aniwhenua Barrage. The jointed, weakly-commented ignimbrite blocks fail by plucking under pressure gradients established by the flow. Scour depth of two to three meters have been recorded.
Figure 7 Weathered Effects New Zealand
Figure 8 Failure of Railway Bridge New Zealand
The main objective of this project is to promote studies and analysis leading to practices and system of soil conservation and environmental protection. one in all the main step towards researching this objective is the identification, selection, and use of the appropriate methodologies is a prerequisite for the development of soil conservation practices that are adapted to specific agroecological and socioeconomic conditions, for sustainable agriculture in countries around the world.
Most of the world’s soil formed in sediments deposited over geological time by water erosion or through the action of glaciers and volcanic eruptions. the issues with soil erosion are found in its consequences. soil erosion, accelerated relative to natural rates by human activities, reduces crop productivity and cause damage resulting from sediment transport and deposition. Sediment damage to water resources is of increasing importance, significantly in developed countries like united states. The aim of this project primarily with erosion processes, significantly in the terms of definition and measurements, with a goal of predicting and controlling erosion. The quantification of the forms, rate, and extent of erosion has been the primary goal of soil erosion-related research worldwide. As a result, more is known is concerning the erosion process than the results of water erosion.
This research is determining to scour or erosion in different waterways structures like Bridges, Culverts, Creeks, and Pipelines. In this general and very significant issues usually happened after a natural disaster including Flooding, Weather effects, Cyclones etc. My research is based on different factors of scour and their methods that how we can protect any waterways structures from erosion also known as scouring. There are pivotal methods that’s lead to protect waterways structure in any kind of heavy rainfalls and other natural way impact sources. The aim of this research being an Engineer is very important and useful. Strong infrastructure with the reliable design is the main key is a success for any Engineer, especially Civil Engineer which mostly deals with infrastructures like Railway, highway, bridges, Dams, Sewerage lines, and Culverts etc. There is the number of different structures that deal with natural waterways, but my research is based upon following waterways structures which usually damaged the cause of scouring. There is three main natural waterways structure that includes.
• Scour at Bridge Piers
• Scour at Culverts
• Scour at Pipelines
According to details given above these are the key focal point in my research work. Successful Design structure in natural waterways is the main and very important initial step for Engineers. Scour usually starts when you have not enough strong foundation of structures and it can be caused by your design failure as well. Weather condition is also very important in waterways structure especially in a hill station, as most of the time rain falling land sliding, flooding usually happened. Designing engineers need to consider these natural disasters while preparing a structure design. Civil engineers also need to consider cost and their liability factors to success the structures life. Scouring is a slow but continuous process when the water starts removing sand and backfilling material from the vicinity of foundation then structures start getting weak and damage. Secondly, reinforcement of material their strength and bonding are a very important factor to control erosion in natural waterways structures. We can use different types of material to control erosion according to site condition and requirement. In this research, I will discuss different approaches and method to control water erosion for waterways structures like bridges, culverts, and pipelines.
Scour at waterways structure is very common now a day, especially when you have not enough rigid material near the foundation of structures. In Rural area of some countries including India, Nepal etc. As they have faced a high rate of floods due to rainfalls and weather condition factors. In the rural area, they used gravel material around culverts to resist erosion, but during the flood and intensive acceleration of flow this ductile material not able to resist.
The significance of Study:
This study will contribute