Effect of Diversion headwork

EFFECTS OF CONSTRUCTION OF DIVERSION HEADWORKS ON THE BEHAVIOUR OF RIVERS Following are the changes that take place in the behavior of the river after the construction of a diversion headworks. The silt carrying capacity of river is decreased because heading up of water causes flattening of the surface slope on the U/S side of the weir. Because of reduction in silt carrying capacity, the pond formed on U/S side starts silting. Because of silting on U/S side, the water passing D/S of the weir contains less amount of silt. To make up for the deficiency of the silt, the D/S flowing water starts scouring the bed and banks. The scouring may lead to undermining the stability of the weir. Because of silting of the pond, the afflux goes on increasing and thus more and more areas on U/S are submerged. At last, a stage is reached when no more…

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Silt control at head regulator

SILT CONTROL AT HEAD REGULATOR Excess silt entering into the main canal has to be prevented by all the possible means. If excess silt gets to enter the main canal, it will cause silting of the whole canal system and ultimately. The capacity of the canal will be reduce. The silt entry into the main canal from a river can be controlled by the following measures. Divide wall in the river creates a quiet pocket behind the head regulator. The quiet pocket renders top layers of water silt free and only top layers of water are admitt into the canal. Provid raised crest for the head regulator. This measure automatically eliminates lower silt-laden layers of water. Providing a wide head regulator also causes less entry of silt into the canal. The entry of water into the canal should be smooth. Smooth entry does not cause any disturbance and as such…

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Regulation of head regulator
REGULATION OF HEAD REGULATOR

Regulation of head regulator

REGULATION OF HEAD REGULATOR In order to control silt entry into the canal, following two methods of regulation of a head regular may be adopted. Open flow regulation. Still pond regulation. Open flow regulation. In this method undersluices are kept open to pass the surplus river water D/S. Bottom layers of silt laden water are lead to under sluices and passed to the D/S. The top layers of water having comparatively less silt, are diverted to the canal. In this operation the pocket behind the undersluices remains clear of silt. Stilling pond Regulation. In this case a separate pocket is formed in the river and head regulator is fixed in this pocket. Only that much water is admitted in to the pocket as is required by the canal. The excess water remains passing D/S over the weir proper. In this case water, in the pocket is almost still. This pocket…

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Fish ladder
FISH LADDER

Fish ladder

FISH LADDER A fish ladder is a fish pass provide along the divider wall to enable migrating fishes to move from U/S to D/S and D/S to U/S direction, in different seasons. Fish ladders are provide on all such works which hinder their movements. The fish ladder is always locat along the divider wall as some water always remains here. The fish ladder consists of a rectangular trough having a sloping floor joining water levels on D/S and U/S of the weir. The difference in water level on the U/S and D/S sides of the weir is divide into several water steps with the help of a baffle   walls, constructed across the inclined floor. The slope of the fish ladder should not be steeper than 1: 10 so that velocity of flow in it does not exceed 2 m/sec. To exercise effective control on the flow through the fish…

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Main canal head regulator
MAIN CANAL HEAD REGULATOR

Main canal head regulator

MAIN CANAL HEAD REGULATOR It is a masonry or concrete structure, constructe at the head of the canal taking off from the river. It is constructe U/S of the under sluices and located in one bank. Its alignment is kept at an angle varying from 90° to 120° with the axis of the weir. The head regulator consists of a number of spans separat by piers and each span is fitted with a steel gate which can be move up or down. In the grooves made in the piers, with the help of either manual labour or winches. In old regulators, the spans use to be quite small, but the modern trend is to use larger spans of 8 to 18 m. Following are the functions of a main canal head regulator. (i) To open or close the discharge in the canal and when require. (ii) To check the silt…

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Divide wall

DIVIDE WALL It is also called groyne, or groyne wall. It is an embankment constructed in the river, U/S of the weir. Its axis is kept at right angles to the axis of the weir. The embankment is protected from all the sides with the help of stone or concrete blocks. The divide wall separates weir from undersluices. It extends a little U/ S of canal regulator and on D/S end upto loose protection of the under sluices. It may be made of concrete or masonry, with top width of 1.5 m to 3 m. This wall should be designed for following conditions. (i) Silt pressure upto full tank level on the face opposite to the face lying towards the head regulator and minimum possible or no water on the face lying towards the head regulator. (ii) During high floods the water level behind the weir should be assumed about…

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Scouring or under sluices
Scouring or under sluices

Scouring or under sluices

SCOURING OR UNDER SLUICES These are the openings in the weir. They are forme by depressing the weir. They have gates fitt in them. The scouring sluices are locat on the side of the weir on which head regulation of the canal, taking off from here, is locat. If two canals are taking off on either side of the river two sets of under sluices should be locat on either side of the weir. Undersluices perform the following functions. A clear well-defined approach channel is preserve in the river just U/S of the canal head regulator. Silt entry into the off taking canals is controlled. When sluices remain close for a few days, silt gets accumulat in the get just U/S of the sluices. This can be easily scour to the D/S side by opening the under sluices from time to time. Low floods can be passed through them without…

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Method of independent variables
METHOD OF INDEPENDENT VARIABLES

Method of independent variables

METHOD OF INDEPENDENT VARIABLES Break up of a complex profile of a weir to simple three elementary. This break up shows the theoretical profiles. Actually, the usual weir section consists of a combination of all the three elementary profiles. In addition to this, the floor also has some thickness. Khosla solve the actual profile of the weir by an empirical method know the method of independent variables. According to this method, the actual complex profile is broken into a number of simple profiles know elementary profiles. Each elementary profile is then treat independently of the others. Each elementary profile is independently amenable to mathematical treatment. The pressures at key points are read from Khosla’s curves. The key points are the junction points of the floor and pile and bottom points of different piles. The pressures read from Khosla’s curves are true for individual elementary profiles. But when all the profiles…

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Weir
WEIRS

Weir

WEIRS Weir is a solid obstruction, put across the river to store water on its U/S. The store water is divert to the off-taking canal. Depending upon the criterion of design, the weirs may be gravity type or non-gravity type. The gravity weir is the weir in which uplift pressure below the weir due to seepage is fully resist by the self weight of the weir. In the case of non-gravity weirs the thickness of the floor is kept relatively small and uplift pressure is largely resist by the bending action of the reinforc concrete floor.   Depending upon the design features and available construction materials gravity weirs or simply, weirs can be further subdivide into the following three categories. Vertical drop weirs. Rockfill weirs. Concrete weirs with sloping glacis. 1. Vertical drop weirs. This weir consists of a vertical drop wall or crest wall, rectangular or nearly rectangular in shape.…

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Failure of weirs on permeable foundation
CAUSES OF FAILURE OF WEIRS ON PERMEABLE SOILS AND THEIR REMEDIES

Failure of weirs on permeable foundation

CAUSES OF FAILURE OF WEIRS ON PERMEABLE SOILS AND THEIR REMEDIES The weir failure may take place due to the following reasons 1. Piping or undermining. 2. By uplift pressure. 3. By suction due to standing wave. 4. By scour on the U/S and D/S of the weir. 1. Piping or undermining. When water seeping through the permeable foundation emerges out at the D/S end of the impervious floor of the weir, at hydraulic gradient or exit gradient greater than the critical value for the foundation soil, the soil starts boiling at the exit point. Boiling of the soil indicates lifting of the soil against gravity and it happens only when exist gradient of seeping water is greater than the safe limit for the foundation soil. The soil gets wash out with boiling water. With washing out of some soil from D/S side, the exit gradient increase and boiling of…

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