river trainingPresentation (2)

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Slide 1: 

Alok dubey [email protected]

METHODS OF RIVER TRAINING : 

METHODS OF RIVER TRAINING The chief aim of river training method is to achieve ultimate stability i.e. the river attains state of equilibrium and no significant change occurs in its alignment ,slope, regime. Behaviour of flow is affected by available energy of flow which is utilized in transporting the sediment load as well as in overcoming resistance due to viscous action and roughness of bed. Various methods of river training are: Dyke or levee Groyne Spurs Guide bank Bank pitching

Slide 3: 

Dyke or levee A levee or dyke or marginal bund is an embankment running parallel to the river and is constructed to protect one side of it from flooding. The alignment of levees is decided on the basis of location of important cities and fields. Levee should have general curvature of the river so that river does not attach levees.

Slide 5: 

Levees are basically caused by floods. In times of low flow any deposition takes place on the river bed and this raises the height of the river bed.In times of flood the water leaves the channel. As it does so it loses energy and the courser and heavier material is deposited near to the river on the banks. Finer material is carried further onto the flood plain.

Guide banks : 

Guide banks Guide banks are artificial embankments meant for guiding the river flow past a bridge or other hydraulic structures such as weir, barrage without causing damage to the structure. It is earthen embankment with curved heads on both the ends. The intermediate straight portion is shank. It controls velocity of flow near the structure, and the tendency of river to change its course. Components of guide bank are: Upstream curved head Downstream curved head Shank Sloping apron Launching apron Pile protection

Groynes : 

Groynes These are impervious permanent structure constructed on curve of river to protect the river bank from erosion. these are projected from the river banks towards the bed making angle 65 degrees. Types of groyne: Attracting groyne : at 60* Repelling groyne: at 90* Hockey head groyne. T head groyne

Spurs : 

Spurs These are temporary structures permeable in nature provided on curve of a river to protect river bank from erosion. these are projected from the river banks towards the bed making angle 65 degrees. Function of spur: To guide the river flow. To retard velocity of flow and form water pocket on the upstream side where the sediment deposits. Reclamation of land on river banks. Types of spur: Bamboo spur boulder spur timber spur

COMPARISON BETWEEN SPUR AND GROYNESPUR GROYNE : 

1 It is a temporary structure 2 It is permeable structure. 3 It is constructed with bamboo, timber pile. 4 It does not require frequent repair work. 5 Recommended for small rivers. 6 Used for low velocity of flow. 1 It is a permanent structure 2 It is impermeable structure. 3 It is constructed with rubble masonry . 4 It does not require any repair work. 5 Recommended for large rivers. 6 Used for high velocity of flow. COMPARISON BETWEEN SPUR AND GROYNESPUR GROYNE

CANAL HEAD WORKS : 

CANAL HEAD WORKS The water flows through the irrigation canal under the force of gravity. So, the elevation of the head of canal must be higher than the commanded area of irrigation project. The structure constructed to raise the water level is called canal diversion head works. Canal head works may be of two form: Storage head work: when dam is constructed across a river valley to form a storage head work. Diversion head works: when a weir or barrage is constructed across a river to raise the water level and divert water to canal.

OBJECTIVE : 

OBJECTIVE FOLLOWING ARE OBJECTIVES OF DIVERSION HEAD WORKS: To raise water level at the head of canal. To form a storage by constructing dykes on both banks. To control entry of silt in canal To control fluctuation of water level.

SELECTION OF SUITABLE SITE : 

SELECTION OF SUITABLE SITE Site should in hilly area where river valley is available. River should be straight and narrow. River bank should be well defined. Elevation of site should be higher than area to be irrigated. There should be no fissures, cracks or permeable foundation in the storage area. The catchment area should be large. Material of construction should be available in vicinity. Road or railway should be accessible to site.

COMPONENTS OF DIVERSION HEAD WORKS: : 

COMPONENTS OF DIVERSION HEAD WORKS: Weir Barrage Divide wall Under sluices Fish ladder Canal head regulator Silt head excluder. Guide bank

Flow Net Theory : 

Flow Net Theory 1 Streamlines Y and Equip. lines  are . 2 Streamlines Y are parallel to no flow boundaries. 3 Grids are curvilinear squares, where diagonals cross at right angles. 4 Each stream tube carries the same flow.

Flow Net Theory : 

Flow Net Theory

Slide 25: 

Flow Net Portion of a flow net is shown below F Y Stream tube

THEORY OF SEEPAGE FLOW : 

THEORY OF SEEPAGE FLOW The steady seepage flow through an isotropic and homogeneous soil mass can be represented by the lapalacian equation, Here, Æ = flow potential = Kh, where, K- coefficient of permeability, h = seepage head at any point in the soil. The above equation represents two sets of curve which intersect each other orthogonally. One set of curves is known as equipotential lines and the other set of curves is known as stream lines. Streamlines: The path along which the sub-surface water flows through the soil indicates the streamline. Equipotential Lines Every streamline possesses a certain head H (i.e. the depth of water on upstream side), when it just enters the soil. On different streamlines there may be a point of equal residual head ‘h’. If these points are joined, then a curve is obtained which is known as equipotential line.

Hydraulic gradient : 

Hydraulic gradient Flow of pore water in soils is driven from positions of higher total head towards positions of lower total head. The level of the datum is differences in total head . The hydraulic gradient is the rate of change of total head along the direction of flow. i = Dh / Ds In diagram there are two points, a small distance Ds apart, hz1 and hz2 above datum. The difference in pore pressure is entirely due to the difference in altitude of the two points . The hydraulic gradient isi = (h2 - h1) / Ds

CAUSES OF FAILURE OF WEIR OR BARRAGE ON PERMEABLE FOUNDATION : 

CAUSES OF FAILURE OF WEIR OR BARRAGE ON PERMEABLE FOUNDATION 1 FAILURE DUE TO SUBSURFACE FLOW: By piping or undermining: removal of soil particles due to scouring. By uplift pressure: due to upward force of uplifting water. 2 FAILURE DUE TO SURFACE FLOW: Hydraulic jump: when water flows with very high velocity over crest of weir. By scouring.

PRECAUTIONS AGAINST FAILURE : 

PRECAUTIONS AGAINST FAILURE The length of the impervious layer should be designed so that the path of the percolating water is increased reducing the exit gradient. Sheet piles should be provided on the upstream and downstream side of the impervious floor to increase to length of percolating water so that the uplift pressure is considerable reduced. The thickness of the impervious floor should be such that the weight of floor is a sufficient to counterbalance the uplift pressure. Inverted filter should be provided with concrete blocks on the top so that the percolating water does not wash out the soil particles. Loose talus should be provided for a sufficient length with heavy boulders (40 to 50 kg). Deep foundation like well foundation should be provided for the barrage piers.

WEIR : 

Weir is constructed across to raise the water level from lower level to higher level. There are three types of weir: Masonry weir Concrete weir Rock fill weir Components of weir are: Weir breast Crest shutters Apron Cut-off Launching apron Sheet piles WEIR

BARRAGE : 

BARRAGE When water level on the up stream side of weir is required to be raised to different levels at different time, then barrage is constructed. Components of barrage include: Barrage piers Adjustable gates Cut off Sheet piles Apron Upstream glacis

Slide 35: 

Divide wall: wall constructed perpendicular to weir or barrage, it may be constructed of stone masonry,cemenrt concrete. Function of divide wall: To form still water pocket in front of canal head. To settle down suspended silt. To control eddy current To provide a straight approach. To resist overturning effect of weir or barrage Under sluices: openings provided at the base of weir or barrage. These openings are provided with adjustable gates. when suspended silt deposited in front of canal head regulator becomes appreciable then gates are opened and deposited slit loosens.

Slide 37: 

Fish ladder: provided parallel to divide wall for the free movement of fishes. Due to construction of weir and barrage the natural flow of fishes is obstructed. so for free movement of fishes along river fish ladder is essential. Canal head regulator: a structure constructed at the head of canal to regulate flow of water. it consists of a no. of piers which divide total width of canal into a no. of span. Silt excluder: when a water pocket is formed in front of canal head regulator due to divide wall it is found that lower layer contains heavy silt, upper layer contains fine silt.

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