14. ASSIGNMENT TOPICS WITH MATERIALSkgr.ac.in/beta/wp-content/uploads/2018/09/WRE-II.pdfCH. Hari...

CH. Hari Prasad, ASST PROFESSOR

14. ASSIGNMENT TOPICS WITH MATERIALS UNIT 1

1. Give the classification of reservoirs. 2 Discuss the steps involved in selecting a site for reservoir construction. 3 Write brief notes on reservoir yield. 4 Explain various levels of a reservoir with neat sketch. 5 Write short notes on mass curve and demand curve 1. Give the classification of reservoirs.

Ans: The data and information required for fixing the various components of the design capacity of a reservoir are as follows:

a) Precipitation, run-off and silt records available in the region;

b) Erodibility of catchment upstream of reservoir for estimating sediment yield;

c) Area capacity curves at the proposed location;

d) Trap efficiency;

e) Losses in the reservoir;

f) Water demand from the reservoir for different uses;

g) Committed and future upstream uses;

h) Criteria for assessing the success of the project;

i) Density current aspects and location of outlets;

j) Data required for economic analysis; and

k) Data on engineering and geological aspects

2. Discuss the steps involved in selecting a site for reservoir construction.

Ans: This method is also known as the Rippl mass curve method after the developer of this method. This is a simple method which is commonly used to estimate the required storage capacity of a reservoir in project planning stage. The method uses the most critical period of recorded flow to compute storage. The critical period is defined as the duration in which initially full reservoir depletes and passing through various states empties without spilling. In the methods based on critical period concept, a sequence of stream flows containing a critical period is routed through an initially full reservoir in presence of specified demands. The


reservoir capacity is obtained by finding the maximum difference between cumulative inflows and cumulative demand curves. Let x(t) be the inflows to a reservoir in volumetric units. We define a function X(t): X(t) = Σt x(t) dt then the graph of X(t) versus time is known as the mass curve. The mass curve technique, proposed by Rippl in 1883 to determine storage capacity of a reservoir, is a graphical technique.

3. Write brief notes on reservoir yield.

Ans: Sedimentation of a reservoir is a natural phenomenon and is a matter of vital concern for storage projects in meeting various demands, like irrigation, hydroelectric power, flood control, etc. Since it affects the useful capacity of the reservoir based on which projects are expected to be productive for a design period. Further, the deposited sediment adds to the forces on structures in dams, spillways, etc. The rate of sedimentation will depend largely on the annual sediment load carried by the stream and the extent to which the same will be retained in the reservoir. This, in turn, depends upon a number of factors such as the area and nature of the catchment, level use pattern (cultivation practices, grazing, logging, construction activities and conservation practices), rainfall pattern, storage capacity, period of storage in relation to the sediment load of the stream, particle size distribution in the suspended sediment, channel hydraulics, location and size of sluices, outlet works, configuration of the reservoir, and the method and purpose of releases through the dam. Therefore, attention is required to each one of these factors for the efficient control of sedimentation of reservoirs with a view to enhancing their useful life and some of these methods are discussed in the Bureau of Indian Standard code IS: 6518-1992 “Code of practice for control of sediment in reservoirs”. In this section, these factors are briefly discussed. There are different techniques of controlling sedimentation in reservoirs which may broadly be classified as follows:

• Adequate design of reservoir

• Control of sediment inflow

• Control of sediment deposition

• Removal of deposited sediment.

4. Explain various levels of a reservoir with neat sketch.

Ans: The capacity of reservoirs is governed by a number of factors which are covered in IS: 5477 (Parts 1 to 4). From the point of view of sediment deposition, the following points may be given due consideration:

a) The sediment yield which depends on the topographical, geological and geomorphological set up,meteorological factors, land use/land cover, intercepting tanks, etc;

b) Sediment delivery characteristics of the channel system;

c) The efficiency of the reservoir as sediment trap;


d) The ratio of capacity of reservoir to the inflow;

e) Configuration of reservoir;

f) Method of operation of reservoir;

g) Provisions for silt exclusion.

5. Write short notes on mass curve and demand curve

Ans: A reservoir exists for a long time and the period of its operation should normally check large technological and socio-economic changes. The planning assumptions about the exact socio-economic outputs are, therefore, likely to be changed during operation, and similarly, the implication of socioeconomic differences in the output due to sedimentation are difficult to access. The ever increasing demands due to both increase of population and increases in per capita needs are of a larger magnitude than the reductions in outputs, if any, of existing reservoirs. Thus effects of sedimentation, obsolescence, structural deterioration, etc. of reservoirs may require adjustments in future developmental plans and not simply replacement projects to bring back the lost potential. On a regional or national scale, it is the sufficiency of the total economic outputs, and not outputs of a particular project which is relevant. However, from local considerations, the reduction of outputs of reservoir like irrigation and flood control may cause a much greater degree of distress to the population which has got used to better socioeconomic conditions because of the reservoir. „Life‟ strictly is a term which may be used for system having two functional states „ON‟ and „OFF‟.


UNIT 2 1 Explain the forces acting on a gravity dam. 2 Draw an elementary profile of a gravity dam. 3 Draw the practical profile of a gravity dam. 4 Write the effects of earthquake forces on a gravity dam. 5 Explain the failure of a gravity dam due to overturning.

1. Explain the forces acting on a gravity dam.

Ans: Dead Load

Reservoir and Tail-water Loads (Ww , Ww′, W1, and W1′)

Uplift Forces

Ice Pressure

Earthquake

Other Miscellaneous Loads

2. Draw an elementary profile of a gravity dam.

Ans: (i) The gravity method, (ii) The trial-load method, and (iii) The finite element method

3. Draw the practical profile of a gravity dam.

Ans: Require costly foundation treatment. The entire loose overburden over the area of the foundation To be occupied by the base of the dam should be removed. The dam itself must be based on the Firm material which can withstand the loads imposed by the dam, reservoir, and other Appurtenant structures.

4. Write the effects of earthquake forces on a gravity dam.

Ans: The behaviour of concrete gravity dam as well as its foundation is observed through suitable instruments during the periods of construction, reservoir filling, and operation of the reservoir. Instruments are employed for measurements of strain, temperature, stress, deflection, and deformation of the foundation.

5. Explain the failure of a gravity dam due to overturning.

Ans: An outlet in a dam is a combination of structures and equipment required for the safe operation and control of water released from a reservoir to serve different objectives. Outlets are classified According to the purpose they serve. River outlets regulate flows to the river and control the Water level in the reservoir. Besides, the river outlets may be useful for increasing the flow downstream of the dam alongwith the normal spillway discharge.


UNIT 3 1 What are the types of embankment dams? 2 Explain various earth dams classified based on the materials used 3 Explain various types of earth dams classified based on methods of construction. 4 Explain the hydraulic failures of earth dams. 5 Explain seepage failures of earth dams. 1. What are the types of embankment dams?

Ans: Embankment dams come in two types: the earth-filled dam (also called an earthen dam or

terrain dam) made of compacted earth, and the rock-filled dam. A cross-section of an embankment

dam shows a shape like a bank, or hill. Most have a central section or core composed of an

impermeable material to stop water from seeping through the dam. The core can be of clay,

concrete, or asphalt concrete. This dam type is a good choice for sites with wide valleys. They can

be built on hard rock or softer soils. For a rock-fill dam, rock-fill is blasted using explosives to break

the rock. Additionally, the rock pieces may need to be crushed into smaller grades to get the right

range of size for use in an embankment dam.

2. Explain various earth dams classified based on the materials used

Ans: Hydraulic-fill dams are constructed by using water for transporting the material to its final position in the dam. The material is discharged from pipes along the outside edges of the fill, and the coarse materials are deposited soon after discharge, While the lines are carried into the central pool. The result is a zoned embankment with a relatively impermeable core. This type of construction originated in the western United States as a result of experience with hydraulic mining. Recent improvements in equipment for transporting and compacting dry fill have tended to discourage use of the hydraulic method. Hydraulic fill is best suited for placing well-graded soils containing a considerable amount of coarse sand and gravel. Adequate water supply is necessary, although some of the water may be recirculate

3. Explain various types of earth dams classified based on methods of construction.

Ans: The change in storage of a reservoir depends on the difference between the amount of inflow and outflow and can be expressed by the equation, s = Qit – Qot (17.1) where, s is the change in storage during time interval t, and Qi and Qo are, respectively, the average rates of inflow and outflow during the time interval t. The rate of inflow at any time is obtained from the inflow flood hydrograph selected for the purpose (Fig. 17.1). The rate of outflow (which should, strictly speaking, include outflow from the river outlets, irrigation outlets, and power turbines) is obtained from the outflow discharge versus reservoir water surface elevation curve (Fig. 17.2). Similarly, the storage is obtained by the reservoir storage versus reservoir water surface elevation curve


5. Broad crested weirs

Ans: The hydraulc characteristics of flow over rectangular broad-crested weirs with varying

upstream slopes were experimentally studied. A series of laboratory experiments was performed

to investigate the effects of changing upstream slopes from 90° to 75°, 60°, 45°, 30°, 22.5°, 15°,

and 10° on the flow surface pattern, discharge coefficient values, approach velocity profile and

flow separation zone. In addition, a new mathematical relationship for water surface profile and

a new correction factor to estimate discharge coefficient over weirs with various upstream slopes

were introduced. The results showed decreasing upstream slopes from 90° to 10° leading to

increasing discharge coefficient values and dissipation of the separation zone.


UNIT 4 1. Give a brief note on diversion headwork. 2 Distinguish between weir and a barrage. 3 Give the classification of weirs. 4 Draw a neat sketch of layout of a diversion headwork. 5 Mention various components of a diversion headwork. 1. Give a brief note on diversion headwork.

Ans: A diversion head-works is a structure constructed across a river for the purpose of raising water level in the river so that it can be diverted into the off taking canals. It is also known as canal head works.

2. Distinguish between weir and a barrage.

Ans: It raises the water level on its upstream side so that commanded area can be increased. It regulates the supply of water into canals. It controls the entry of silt into the canals. It provides some storage of water for a short period. It reduces fluctuations in the level of supply in the river.

3. Give the classification of weirs.

Ans: There are two types of diversion headworks; Temporary: They are temporary in nature and required to be constructed after flood. Permanent. It consists of permanent concrete (masonry) structure. E.g Weir and Barrage

4. Draw a neat sketch of layout of a diversion headwork.

Ans: Weir or barrage 2. Scouring sluices or Under sluices 3. Divide wall 4. fish ladder 5. Canal head regulator 6. Silt excluder 7. Marginal bunds and Guide banks

5. Mention various components of a diversion headwork.

Ans: The weir is a solid construction placed across the river to raise the water level in the river and divert the water into the canal.


UNIT 5 1 What are the different types of cross drainage works necessary on canal alignment? 2 What do you understand by the term level crossing? 3 Explain the necessity of cross drainage structure. 4 Explain various types of cross drainage works. 5 What is a cross drainage work? 1. What are the different types of cross drainage works necessary on canal alignment?

Ans: Include the cross regulator and the distributary head regulator structures for controlling the flow through a parent canal and its off-taking distributary . help to maintain the water level in the canal on the upstream of the regulator.angle at which a distributary canal off-takes from the parent canal has to be decided carefully. The best angle is when the distributary takes off smoothly. Another alternative is to provide both channels (off-taking and parent) at an angle to the original direction of the parent canal. When it becomes necessary for the parent canal to follow a straight alignment, the edge of the canal rather than the centre line should be considered in deciding the angle of off-take.

2. What do you understand by the term level crossing?

Ans: are thin, vertical, curved parallel walled structures constructed of plain or reinforced concrete on the floor of the parent canal, just upstream of the off-taking canal. height of the vanes may be about one-fourth to one-third of the depth of flow in the parent canal. thickness of the vanes should be as small as possible and the spacing of the vanes may be kept about 1.5 times the vane height. To minimize silting tendency, the pitched floor on which the vanes are built should be about 0.15 m above the normal bed of the parent channel.

3. Explain the necessity of cross drainage structure.

Ans: project out in to the parent canal from the downstream abutment of the off-taking canal. it

divides the discharge of the parent canal in proportion of the discharge requirement of the off-

taking canal with respect to the flow in the downstream parent canal. The groyne wall extends

upstream in to the parent canal to cover ¾ to full width of the off-take. proportional

distribution of flow in to the off-taking canal is expected to divert proportional amount of

sediment. The height of the groyne wall should be at least 0.3m above the full supply level of

the parent canal.

4. Explain various types of cross drainage works.

Ans: A skimming platform is an RCC slab resting on low height piers on the bed of the parent canal, and in front of the off-taking canal. creates a kind of low tunnel at the bed of the parent canal, which allows the sediment moving along its bed to pass through downstream.


floor of the off-taking canal being above the level of the platform thus only takes suspended sediment load coming along with the main flow in the parent canal.

5. What is a cross drainage work? Ans: structures meant to release excess water from a canal, which could be main canal, branch canal, distributary, minors etc. usually an irrigation system suffers from deficit supply in later years of its life situations that might suddenly lead to accumulation of excess water in a certain reach of a canal network may occur due to the following reasons: Wrong operation of head works in trying to regulate flow in a long channel resulting in release


15. TUTORIAL TOPICS AND QUESTIONS (NIL)


16 UNIT WISE-QUESTION BANK

UNIT –I

TWO MARK QUESTIONS WITH ANSWERS

1. what are the methods of capacities of a reservoirs?

Ans. The data and information required for fixing the various components of the design capacity of a reservoir are as follows:

a) Precipitation, run-off and silt records available in the region;

b) Erodibility of catchment upstream of reservoir for estimating sediment yield;

c) Area capacity curves at the proposed location;

d) Trap efficiency;

e) Losses in the reservoir;

f) Water demand from the reservoir for different uses;

g) Committed and future upstream uses;

h) Criteria for assessing the success of the project;

i) Density current aspects and location of outlets;

j) Data required for economic analysis; and

k) Data on engineering and geological aspects

2. Briefly explain the mass curve method ?

Ans. This method is also known as the Rippl mass curve method after the developer of this method. This is a simple method which is commonly used to estimate the required storage capacity of a reservoir in project planning stage. The method uses the most critical period of recorded flow to compute storage. The critical period is defined as the duration in which initially full reservoir depletes and passing through various states empties without spilling. In the methods based on critical period concept, a sequence of stream flows containing a critical period is routed through an initially full reservoir in presence of specified demands. The reservoir capacity is obtained by finding the maximum difference between cumulative inflows


and cumulative demand curves. Let x(t) be the inflows to a reservoir in volumetric units. We define a function X(t): X(t) = Σt x(t) dt then the graph of X(t) versus time is known as the mass curve. The mass curve technique, proposed by Rippl in 1883 to determine storage capacity of a reservoir, is a graphical technique.

2. What is the control of sedimentation of a reservoir ?

Ans. Sedimentation of a reservoir is a natural phenomenon and is a matter of vital concern for storage projects in meeting various demands, like irrigation, hydroelectric power, flood control, etc. Since it affects the useful capacity of the reservoir based on which projects are expected to be productive for a design period. Further, the deposited sediment adds to the forces on structures in dams, spillways, etc. The rate of sedimentation will depend largely on the annual sediment load carried by the stream and the extent to which the same will be retained in the reservoir. This, in turn, depends upon a number of factors such as the area and nature of the catchment, level use pattern (cultivation practices, grazing, logging, construction activities and conservation practices), rainfall pattern, storage capacity, period of storage in relation to the sediment load of the stream, particle size distribution in the suspended sediment, channel hydraulics, location and size of sluices, outlet works, configuration of the reservoir, and the method and purpose of releases through the dam. Therefore, attention is required to each one of these factors for the efficient control of sedimentation of reservoirs with a view to enhancing their useful life and some of these methods are discussed in the Bureau of Indian Standard code IS: 6518-1992 “Code of practice for control of sediment in reservoirs”. In this section, these factors are briefly discussed. There are different techniques of controlling sedimentation in reservoirs which may broadly be classified as follows:

• Adequate design of reservoir

• Control of sediment inflow

• Control of sediment deposition

• Removal of deposited sediment.

3. Explain the design procedure of reservoir?

Ans. The capacity of reservoirs is governed by a number of factors which are covered in IS: 5477 (Parts 1 to 4). From the point of view of sediment deposition, the following points may be given due consideration:

a) The sediment yield which depends on the topographical, geological and geomorphological set up,meteorological factors, land use/land cover, intercepting tanks, etc;

b) Sediment delivery characteristics of the channel system;

c) The efficiency of the reservoir as sediment trap;

d) The ratio of capacity of reservoir to the inflow;


e) Configuration of reservoir;

f) Method of operation of reservoir;

g) Provisions for silt exclusion.

5. Explain Life of reservoir and design criteria ?

Ans. A reservoir exists for a long time and the period of its operation should normally check large technological and socio-economic changes. The planning assumptions about the exact socio-economic outputs are, therefore, likely to be changed during operation, and similarly, the implication of socioeconomic differences in the output due to sedimentation are difficult to access. The ever increasing demands due to both increase of population and increases in per capita needs are of a larger magnitude than the reductions in outputs, if any, of existing reservoirs. Thus effects of sedimentation, obsolescence, structural deterioration, etc. of reservoirs may require adjustments in future developmental plans and not simply replacement projects to bring back the lost potential. On a regional or national scale, it is the sufficiency of the total economic outputs, and not outputs of a particular project which is relevant. However, from local considerations, the reduction of outputs of reservoir like irrigation and flood control may cause a much greater degree of distress to the population which has got used to better socioeconomic conditions because of the reservoir. „Life‟ strictly is a term which may be used for system having two functional states „ON‟ and „OFF‟.


THREE MARK QUESTIONS

1. Explain types of reservoirs?

Ans. Storage / conservation reservoir Flood control reservoir Multipurpose reservoir Distribution reservoir

2. Explain the flood control reservoir?

Ans. A flood control reservoir , generally called a flood-mitigation reservoir , stores a portions of the flood flows in such a way as to minimise the flood peaks at the areas be protected downstream.” The entire inflow entering the reservoir is discharged till the out flow reaches the safe capacity of the channel downstream. The inflow in excess of this rate is stored in the reservoir , which is then gradually released , so as to recover the storage capacity for the next flood. 3. Explain the types of flood control reservoir?

Ans. Storage reservoir: A reservoir having gates and valves installation at its spillway and at its sluice outlets is known as storage reservoir. Retarding reservoir: A reservoir with uncontrolled and ungated outlets is known as a retarding basin or retarding reservoirs. 4. Explain multiple reservoir?

Ans. A reservoir planned and constructed to serve not only one purpose but various purpose together is called a multipurpose reservoir.” 5. What are the uses of multiple reservoir?

Ans. Multipurpose reservoirs may be managed to balance some or all of the following activities: Water supply Flood control Soil erosion Environmental management Hydroelectric power generation Navigation Recreation Irrigation


FIVE MARK QUESTIONS

1. Explain the distribution of reservoir?

Ans. A distribution reservoir connected with the conduits of a primary water supply; used to supply water to consumers according to fluctuations in demand over short time periods and serves for local storage in case of emergency.” Such a reservoir can be filled by pumping water at a certain rate and can be used to supply water even at rate higher than inflow rate during period of maximum demands called critical periods of demand. Such reservoirs are, therefore, helpful in permitting the pumps or the water treatment plants to work at a uniform rate, and they store water during the hours of no demand or less demand, and supply water from their storage during the critical periods of maximum demand… 2. What type of investigation for selection of a reservoir? Ans. Engineering surveys

Geological investigations Hydrological investigations

Engineering surveys: Conducted for dam, reservoir and other associated work. Topographic survey of the area is carried out and the contour plan is prepared The horizontal control is usually provided by triangulation survey, and the vertical control by precise leveling. Geological investigation: Geological investigations of the dam and reservoir site are done for the following purposes. (i) Suitability of foundation for the dam. (ii) Watertightness of the reservoir basin (iii) Location of the quarry sites for the construction materials. 3. Explain the site selection reservoir? Ans. Large storage capacity River valley should be narrow, length of dam to constructed is less. Water tightness of reservoir. Good hydrological conditions Deep reservoir Small submerged area Low silt inflow No objectionable minerals Low cost of real estate Site easily accessible

4. Explain the capacity of reservoir?

Ans. depends upon the inflow available and demand inflow in the river is always greater than the demand, there is no storage required if the inflow in the river is small but the demand is high, a large reservoir capacity is required. The required capacity for a reservoir can be determined by the following methods: 1. Graphical method, using mass curves. 2. Analytical method


5. Explan graphical method? Ans. Prepare a mass inflow curve from the flow hydrograph of the site for a number of consecutive years including the most critical years (or the driest years) when the discharge is low. 2. Prepare the mass demand curve corresponding to the given rate of demand. If the rate of demand is constant, the mass demand curve is a straight line. The scale of the mass demand curve should be the same as that of the mass inflow curve. Draw the lines AB, FG, etc. such that (i) They are parallel to the mass demand curve, and (ii) They are tangential to the crests A, F, etc. of the mass curve. 4. Determine the vertical intercepts CD. HJ, etc. between the tangential lines and the mass inflow curve. These intercepts indicate the volumes by which the inflow volumes fall short of demand. Assuming that the reservoir is full at point A, the inflow volume during the period AE is equal to ordinate DE and the demand is equal to ordinate CE. Thus the storage required is equal to the volume indicated by the intercept CD. 5. Determine the largest of the vertical intercepts found in Step (4). The largest vertical intercept represents the storage capacity required.


OBJECTIVE QUESTION WITH ANSWERS

1. The optimum depth of kor watering for a rice crop is A. 23 cm B. 17.5 cm C. 25 cm D. 19 cm 2. The duty of water at the inlet of canals is D1 and infield is D2 then A. D1=D2 B.D1>D2 C. D1<D2 D. D12=D2 3. The delta for a crop having a base period 120 days is 700 mm. Its duty is (in hect/cumecs) A. 2400 B. 1481 C. 148 D. 1.481 4. Field capacity of a soil depends upon A. Porosity of soil B. Capillary tension in soil C. Both a ,b D. None 5. The crop among the following which is expected to have the maximum duty A. Wheat B. Rice C. Sugarcane D. Cotton 6.The optimum depth of kor watering period for rice is about A. 26 cm B.19 cm C. 13.5 cm D. 9 cm 7. The water which can be utilized by crops from soil is called A. Field capacity water B. hygroscopic water C. Capillary water D. Water of adhesion 8. If the irrigation water applied to a field penetrates uniformly throughout then water distribution efficiency is A. 1

B. 0


C. 0.5

D. Data is insufficient 9.The crop period with in which a crop must receive its first major weathering will be A. Paleo watering B. Kor - watering C. Crop watering D. All the above 10. The crop out of the following which is not a cash crop A. Jute B. Tea C. Rice D. Sugar cane KEY Q.NO 1 2 3 4 5 6 7 8 9 10

Ans d c d c a b c a b c


FILL IN THE BLANKS 1. 2. ____________________

3. Effluent irrigation is the name given to________________

4. Effluent irrigation indicates _______

5. The duty of crops requiring 1.08 m of water over 120 days is __________________ Kharif season generally extends from __________

6. A crop requires a total depth of 9.2 cm of water for a base period of 120 days.The duty water is

____________________________

7. The study of moisture is soils comes under the category of _________________________

8. The delta for a crop having base period 120 days is 70 cm then the duty is ______________________________

9. The total depth of water required by a crop during the entire period the crop is in the field is know as _________________________________

10. . Sprinkler irrigation is not suitable to ______________________________________

KEY

Q.NO 1 2 3 4 5 6 7 8 9 10

Ans treated

sewage

water

meant

for

irrigati

on

Irrigat

ion by

treated

sewag

e

960.0

hect/cum

e

june -

octomb

er

1130

0 ha/

cume

c

Osmos

is

hydrol

ogy

481

hect /

cume

c

Delta Rice.


UNIT II


1. What are the forces acting in the gravity dam ?

Ans. Dead Load

Reservoir and Tail-water Loads (Ww , Ww′, W1, and W1′)

Uplift Forces

Ice Pressure

Earthquake

Other Miscellaneous Loads

2. Stress analysis of gravity dams

Ans. (i) The gravity method, (ii) The trial-load method, and (iii) The finite element method

3. What is foundation treatment ?

Ans. Require costly foundation treatment. The entire loose overburden over the area of the foundation To be occupied by the base of the dam should be removed. The dam itself must be based on the Firm material which can withstand the loads imposed by the dam, reservoir, and other

Appurtenant structures.

4. what is instrumentation ?

Ans. The behaviour of concrete gravity dam as well as its foundation is observed through suitable instruments during the periods of construction, reservoir filling, and operation of the reservoir. Instruments are employed for measurements of strain, temperature, stress, deflection, and deformation of the foundation.

5. what is outlets ?

Ans. An outlet in a dam is a combination of structures and equipment required for the safe operation and control of water released from a reservoir to serve different objectives. Outlets are classified According to the purpose they serve. River outlets regulate flows to the river and control the Water level in the reservoir. Besides, the river outlets may be useful for increasing the flow downstream of the dam alongwith the normal spillway discharge.


THREE MARK QUESTION WITH ANSWER

1. Explain design of a gravity dam?

Ans. An elementary profile is only an ideal profile which needs to be modified for adoption in actual practice. Modifications would include provision of a finite crest width, suitable freeboard, batter in the lower part of the upstream face, and a flatter downstream face. The design of a gravity dam involves assuming its tentative profile and then dividing it into a number of zones by horizontal planes for stability analysis at the level of each dividing horizontal plane. The analysis can be either two-dimensional or three-dimensional. The following example illustrates the two-dimensional method of analysis of gravity dams.

2. Explain causes of failure of a gravity dam ?

Ans. A gravity dam may fail on account of overturning. For a gravity dam to be safe against overturning, the dimensions of the dam should be such that the resultant of all the forces intersects the base of the dam within its middle-third portion. Consider any horizontal section (including the base) of a gravity dam and the resultant of all the forces acting on the dam above the section. If the line of action of this resultant passes outside the downstream edge of the section, the dam would overturn.

3. Explain Uplift pressure

Ans. Uplift forces (U) occur due to internal hydraulic pressures in pores, cracks, and seams within the body of a dam, at the contact between the dam and its foundation, and within the foundation. The distribution of internal hydrostatic pressure along a horizontal section through a gravity dam is assumed to vary linearly from full reservoir pressure at the upstream face to zero or tail-water pressure at the downstream face, and to act over the entire area of the section. The pressure distribution is also adjusted depending upon the size, location, and spacing of internal drains. Experimental and analytical studies indicate that the drains set in from the upstream face at 5 per cent of the maximum reservoir depth and spaced laterally twice that distance will reduce the average pressure at the drains to approximately tail-water pressure plus one-third the difference between reservoir water and tail-water pressures

4. Explain Silt load ?

Ans. The construction of a dam across a river carrying sediment invariably results in reservoir sedimentation which causes an additional force (Ws) on the upstream face of the dam. The


horizontal silt pressure is assumed equivalent to a hydrostatic load exerted by a fluid with a mass density of 1360 kg/m3. The vertical silt pressure is assumed equivalent to that exerted by a soil with a wet density of 1925 kg/m3.

5. Explain Ice pressure ?

Ans. If the designer anticipates the formation of an ice sheet of appreciable thickness and its remaining on the reservoir water surface for a long duration, the ice pressures must be computed using a suitable method of their estimation. In the absence of such a method, ice pressure may be taken as 250 kPa (250 kN/m2) applied over the anticipated area of contact of ice with the face of the dam (2).


FIVE MARK QUESTION WITH ANSWER

1. ELEMENTARY PROFILE OF A GRAVITY DAM

Ans. The stability conditions required to be met for a gravity dam, subjected only to its self-weight W, force due to water pressure P, and uplift force U can be satisfied by a simple right-angled triangular section (Fig. 16.7) with its apex at the reservoir water level, and which is adequately wide at the base where the water pressure is maximum. Such a section is said to be an elementary profile of a gravity dam. For the empty-reservoir condition the only force acting on the dam is its self-weight whose line of action will meet the base at b/3 from the heel of the dam and thus satisfy the stability requirement of no tension. The base width of the elementary profile is determined for satisfying no tension and no sliding criteria as given below, and the higher of the two base widths is chosen for the elementary profile. For the elementary profile shown in Fig. 16.7, if one considers that the resultant R of all the three forces Wc (= 0.5 s gbh), W1 (= 0.5 gh2), and U (= 0.5 ghbc′) (here, s = specific gravity of concrete and c′ is a correction factor for uplift force) passes through the downstream middle third point, one gets

b2 (s – c′) = h2


OBJECTIVE QUESTION WITH ANSWERS

1. The reservoir capacity for a given demand is obtained from

A. Double mass curve

B. Mass inflow curve

C. Hydrograph

D. Hyetograph

2. The requirement of water is the highest for

A. Live stock

B. Irrigation

C. Domestic needs

D. Nuclear power plants

3. A balancing reservoir is one which

A. Balances the peak and min flows

B. Balances the distribution

C. Balances the flow rates of supply and demand

D. Stores water for emergencies

4. A detention dam stores water

A. And release water at a safe rate

B. And diverts to another stream

C. Permanently

D. Raises ground water level

5. Retarding reservoirs are located


A. Downstream of confluence

B. Upstream of confluence

C. Away from the confluence down stream

D. Downstream of a city

6. Silt storage is same as

A. Dead sorage

B. Garbage storage

C. Effective storage

D. Live storage

7. The trap efficiency of a reservoir is a function of

A. Age of the reservoir

B. Thee reservoir capacity

C. Total inflow

D. Reservoir capacity or Total inflow

8. The elementary profile of a dam is

A. A rectangle

B. Trapezoidal

C. An equilateral triangle

D. Right angle triangle

9. Clover leaf coffer dam belongs to

A. Cellular type

B. Diaphragm type


C. Sheet pile type

D. Braced type

10. Dead storage in a reservoir is provided

A. To meet emergency needs

B. To mitigation floods

C. To accommodate the sill-trapped in the reservoir

D. To increase the useful life period

KEY

Q.NO 1 2 3 4 5 6 7 8 9 10

Ans b b c a b a d d a c


FILL IN THE BLANK QUESTIONS WITH ANSWERS

1. The net free board is ------------------------

2. What is middle third base rule is ------------------------------

3. A gravity dam is subjected to hydrodynamic pressure caused by -----------------

4. Axis of dam is

A. The line of upstream face

B. The line of crown of dam

5. Leakage through the transverse joints in a gravity dam is prevented by ------------

6. The top line of an ogee spillways is which is kept at R.L equal to the fully reservoir level----------------------

7. Spillways is least suited to earthen dams------------------

8. The hydrolic jump is widely used for dissipation of energy in-----------------

9. A check dam is a -----------------------------

10. To prevent leakage through pores , cracks , fissures the process adapted is called -----

KEY

Q.

NO

1 2 3 4 5 6 7 8 9 10

Ans Differ

ence

betwe

en the

top of

the

dan

and

MWL

The

resultant

of all

forces

increas

e

A&B Water

Ways

Crest Ogee

spillwa

y

Ogee

spillway

Fl

oo

d

co

ntr

ol

str

uc

tur

e

Press

ure

tech

niqu

e


UNIT III TWO MARK QUESTIONS WITH ANSWERS

1. Explain types of earth dams?

Ans. Embankment dams come in two types: the earth-filled dam (also called an earthen dam or

terrain dam) made of compacted earth, and the rock-filled dam. A cross-section of an embankment

dam shows a shape like a bank, or hill. Most have a central section or core composed of an

impermeable material to stop water from seeping through the dam. The core can be of clay, concrete, or asphalt concrete. This dam type is a good choice for sites with wide valleys. They can

be built on hard rock or softer soils. For a rock-fill dam, rock-fill is blasted using explosives to break the rock. Additionally, the rock pieces may need to be crushed into smaller grades to get the right

range of size for use in an embankment dam.

2. Explain Methods of construction of Earth Dam ?

Ans. Hydraulic-fill dams are constructed by using water for transporting the material to its final position in the dam. The material is discharged from pipes along the outside edges of the fill, and the coarse materials are deposited soon after discharge, While the lines are carried into the central pool. The result is a zoned embankment with a relatively impermeable core. This type of construction originated in the western United States as a result of experience with hydraulic mining. Recent improvements in equipment for transporting and compacting dry fill have tended to discourage use of the hydraulic method. Hydraulic fill is best suited for placing well-graded soils containing a considerable amount of coarse sand and gravel. Adequate water supply is necessary, although some of the water may be recirculate.

3.What is flood routing ?

Ans. The change in storage of a reservoir depends on the difference between the amount of inflow and outflow and can be expressed by the equation, s = Qit – Qot (17.1) where, s is the change in storage during time interval t, and Qi and Qo are, respectively, the average rates of inflow and outflow during the time interval t. The rate of inflow at any time is obtained from the inflow flood hydrograph selected for the purpose (Fig. 17.1). The rate of outflow (which should, strictly speaking, include outflow from the river outlets, irrigation outlets, and power turbines) is obtained from the outflow discharge versus reservoir water surface elevation curve (Fig. 17.2). Similarly, the storage is obtained by the reservoir storage versus reservoir water surface elevation curve


3 MARK QUESTIONS WITH ANSWER

1. What are the consideration of selection of embankment of a dam?

Ans. (i) Significant thickness of soil deposits overlying bedrock, (ii) Weak or soft bedrock which would not be able to resist high stresses from a concrete dam, (iii) Abutments of either deep soil deposits or weak rock, (iv) Availability of a suitable location for a spillway, and (v) Availability of sufficient and suitable soils from required excavation or nearby borrow areas. 2. What are the types of a Embankment dams? Ans. Embankment dams are mainly of two types: (i) Earth-fill or earth dams, and (ii) Rock-fill or earth-rock dams.

2. Explain the selection of a rock-fill dam ? Ans. The upstream impervious membrane, with a suitable drain behind it, prevents seepage from entering the embankment. This reduces pore pressures and prevents the embankment mass from being submerged. Both these effects result in greater stability of the embankment. (ii) The upstream impervious membrane is accessible for inspection and repair. (iii) The upstream impervious membrane also serves a secondary function of wave protection. (iv) The upstream impervious membrane can be built after completion of the embankment. This would permit initial settlement of the embankment without affecting the membrane adversely. 3. Design consideration of a embankment dam? Ans. The design of an embankment dam is based on analytical considerations as well as on experience. The main steps in the design of an embankment dam are as follows (4): (i) A thorough exploration of the foundation and abutments. (ii) Evaluation of the quantities and characteristics of all the embankment construction materials available within a reasonable distance of the dam site. (iii) A study of all the factors which may influence the design. (iv) The selection of trial designs. (v) Analysis of the safety of the trial designs. (vi) The modification of the designs to satisfy the minimum stability requirements. (vii) The preparation of detailed cost estimates. (viii) The final selection of the design which seems to offer the best combination of economy, safety, and convenience in construction. 4. Explain General Design Criteria for Embankment Dams? Ans. There is no danger of overtopping. For this purpose, spillway of adequate capacity and sufficient freeboard must be provided. (ii) The seepage line is well within the downstream face so that horizontal piping may not occur. (iii) The upstream and downstream slopes are flat enough to be stable with the materials used for the construction of embankment for all conditions during construction, operation, and sudden drawdown.


(iv) The shear stress induced in the foundation is less than the shear strength of the foundation material. For this purpose, the embankment slopes should be sufficiently flat. (v) The upstream and downstream faces are properly protected against wave action and the action of rain water, respectively. (vi) There should not be any possibility of free passage of water through the embankment. (vii) Foundation seepage should not result in piping at the downstream toe of the dam. (viii) The top of the dam must be high enough to allow for the settlement of the dam and its foundation. (ix) The foundations, abutments, and embankment must be stable for all conditions of operation (steady seepage and sudden drawdown) and construction.


5 MARK QUESTIONS WITH ANSWER

2. What is the Design Requirement for Gravity walls

Ans. Gravity Retaining walls are designed to resist earth pressure by their weight. They are constructed of the mass, concrete, brick or stone masonry. Since these materials can not resist appreciable tension, the design aims at preventing tension in the wall. The wall must be safe against sliding and overturning. Also the maximum pressure exerted on the foundation soil should exceed the safe bearing capacity of the soil.

So before the actual design, the soil parameters that influence the earth pressure and the

bearing capacity of the soil must be evaluated. These include the unit weight of the soil,

the angle of the shearing resistance, the cohesion intercept and the angle of wall friction.

Knowing these parameters, the lateral earth pressure and bearing capacity of the soil

determined.

3. Example 17.2 The pond upstream of a power house may be approximated as a rectangular channel of width 80 m and length 2.0 km. The inflow as well as outflow into the pond at the beginning was 100 m3/s. The inflow increases gradually to 200 m3/s in two hours. Assuming that the outflow is through a sluice gate and discharge through which is expressed as Q = 80 H (in which, H is the head of water above the sill of the sluice gate in the pond),


4. Explain types of spillways ?

Ans. Spillway is usually referred to as controlled or uncontrolled depending on whether spillway gates for controlling the flow have been provided or not. A free or uncontrolled spillway automatically releases water whenever the reservoir level rises above the overflow crest level. The main advantage of an uncontrolled spillway is that it does not require constant attendance and operation of the regulating devices by an operator. Besides, there are no problems related to the maintenance and repair of the devices. If it is not possible to provide a sufficiently long uncontrolled spillway crest or obtain a large enough surcharge head to meet the requirements of spillway capacity, one has to provide regulating gates. Such gates enable release of water, if required, even when the reservoir level is below the normal reservoir water surface level. Most common types of spillway are as follows: (i) Free overfall (straight drop) spillway, (ii) Ogee (overflow) spillway, (iii) Side-channel spillway, (iv) Chute (or open channel or trough) spillway, (v) Shaft (or morning glory) spillway, (vi) Siphon spillway, (vii) Cascade spillway, and (viii) Tunnel (conduit) spillway. 5. Explain shaft spill ways?

Ans. In a shaft spillway (Fig. 17.12) water enters a horizontal crest, drops through a vertical or sloping shaft, and then flows to the downstream river channel through a horizontal or nearly Horizontal conduit or tunnel. A rock outcrop projecting into the reservoir slightly upstream of the dam would be an ideal site for shaft spillway. Depending upon the level of the rock outcrop and the required crest level, a spillway may have to be either constructed or excavated. The diversion tunnels, if used for river diversion purposes during construction, can be utilized for discharge tunnels of the spillway. Radial piers provided on the spillway crest ensure radial flow towards the spillway and also provide support to the bridge which would connect the spillway with the dam or the surrounding hill. A shaft spillway with a funnel-shaped inlet is called a


“morning glory” or “glory hole” spillway. One of its distinguishing characteristics is that near maximum capacity of the spillway is attained at relatively low heads. Therefore, a shaft spillway is ideal when maximum spillway discharge is not likely to be exceeded. Because of this feature, however, the spillway becomes unsuitable when a flow larger than the selected design flow occurs. This disadvantage can be got rid of by providing an auxiliary or emergency spillway and using the shaft spillway as service spillway.


OBJECTIVE QUESTIONS WITH ANSWERS

1. Which of the below is the earliest known dam?

A) Sadd-el-Kafara dam B) Dam of Marib C) Jawa Dam D) Ha-ilar Dam 2. Portion of dam in contact with ground at downstream side is

A) Crest B) Toe C) Foot D) Heel 3. Based on function of dam, it can be classified into:

A) 5 B) 10 C) 8 D) 6 4. Which of the below is example for earth dam?

A) Bhakra Nangal Dam B) Banasura Sagar Dam C) Idukki Dam D) Bisalpur Dam 5. ___________ is the arrangement made near top of dam for passage of excess water from reservoir.

A) Sluice way B) Spillway C) Gallery D) Abutments 6. Hydroelectric power plants at dam supplies about _________ of world’s electricity.

A) 19%

B) 25%


C) 42%

D) 50%

7. Natural dam is not created usually by: A) Glacial activity

B) Volcanic activity C) River meandering D) Moraine deposit 8. Arch-gravity dams are thinner dams and save resources.

A) True B) False 9. Buttress dams are of __________ types.

A) 6 B) 4 C) 8 D) 3 10. Hydraulic head for a small dam is:

A) 5-7.5m B) 7.5-12m C) 12-13m D) 5-10m

KEY

Q.NO 1 2 3 4 5 6 7 8 9 10

Ans c d a b b a c a d B


FILL IN THE BLANK QUESTIONS WITH ANSWERS

1. Earth dams are _________ in shape.

2. Based on material of construction, ___________ types are there.

3. _________ is a temporary dam constructed to exclude water from a specific area.

4. The obstruction or a barrier built across the stream or river is called as____

5. FTL Stands for ________

6. _______ is openings extending from upstream to downstream of dam.

7. Water stored in dam is expressed in _______

8. MDDL Stands for ________

9. _____ dam which resists are the external forces by virtue of its self weight.

10. The factor of safety against overturning should not be less than ______


Q.N

O

1 2 3 4 5 6 7 8 9 10

Ans Trape

zoida

l

2 Coffer dam Dam Full

tank

level

Slui

ces

Milli

on

cubi

c

metr

es

Minimum

draw

down level

Grav

ity

dam

1.5


UNIT IV


1. What is the Defination of Diversion Head works?

Ans. A diversion head-works is a structure constructed across a river for the purpose of raising water level in the river so that it can be diverted into the off taking canals. It is also known as canal head works.

2. What is the Purposes of diversion head works? Ans. It raises the water level on its upstream side so that commanded area can be increased. It regulates the supply of water into canals. It controls the entry of silt into the canals. It provides some storage of water for a short period. It reduces fluctuations in the level of supply in the river.

3. What are the types of diversion head works ? Ans. There are two types of diversion headworks; Temporary: They are temporary in nature and required to be constructed after flood. Permanent. It consists of permanent concrete (masonry) structure. E.g Weir and Barrage

4. What are the components of diversion head works? Ans. 1. Weir or barrage 2. Scouring sluices or Under sluices 3. Divide wall 4. fish ladder 5. Canal head regulator 6. Silt excluder 7. Marginal bunds and Guide banks

5. What is Weir? Ans. The weir is a solid construction placed across the river to raise the water level in the river and divert the water into the canal.


THREE MARK QUESTIONS WITH ANSWER

1. What are the types of weirs in diversion head works?

Ans. Based on materials of construction, design features and types of soil foundation the weir may be of different types. Such as: 1. Vertical drop weir 2. Rock fill weirs 3. Concrete weir with sloping glacis

2. Briefly explain vertical drop weir?

Ans. A vertical drop weir consists of a masonry wall with a vertical (or nearly vertical) downstream face and a horizontal concrete floor. The shutters are provided at the crest, which are dropped during flood so as to reduce afflux. The water is pounded up to the shutters during the rest of the period. The weir floor is designed as gravity section. Immediately at the upstream end of the floor a block protection and at the downstream end a graded inverted filter are provided. Launching aprons are provided at the u/s and d/s ends of floor to safeguard against scouring action. This type of weir is suitable for hard clay foundation as well as consolidated gravel foundation, and where the drop is small.. Such weirs are obsolete now a days.

2. Briefly explain rock fill weir?

Ans. It consists of a main masonry weir wall and a number of core walls. The space between the core walls is filled with the fragments of rock called rock fill. The rock fill is usually given a slope of 1 in 4 on u/s and a slope of 1 in 20 on d/s. A rock fill weir requires a lot of rock fragments and is economical only when a huge quantity of rock fill is easily available near the weir site. It is suitable for fine sand foundation. Such weirs are more or less obsolete now a days.


3. Briefly explain Concrete weir with sloping glacis?

Ans. Concrete weir with sloping glacis are of relatively recent origin. The crest has glacis (sloping floors) in u/s as well as d/s. There are sheet piles (or cut off walls) driven up to the maximum scour depth at the u/s and d/s end of the concrete floor. Some times an intermediate pile is also driven at the beginning of the u/s glacis or at the end of the d/s glacis. There is a concrete block protection in the continuation of the concrete floor both at the u/s and d/s side. On the u/s of the u/s concrete block protection as well as on the d/s of the d/s block protection, there is talus. This type of weir may be constructed in pervious foundations and are commonly adopted these days.

4. Briefly explain barrage?

Ans. The function of barrage is similar to that of weir, but the heading up of water is effected by the gates alone. During the floods, the gates are raised to clear off the high flood level. When the flood recedes, the gates are lowered and the flow is obstructed, thus raising the water level at the u/s of the barrage.


FIVE MARKS QUESITIONS WITH ANSWER

1. What is under sluices. Explain the functions of under sluices?

Ans. The under sluices are the openings provided in the weir wall with their crest at lower level.. These openings are provided with adjustable gates. The weir proper is constructed in the middle portion of the diversion headworks an at the ends under sluices are provided adjacent to the canal head regulators. If canal takes off only from one side, the under sluice section is provided near that end only. There is a divide wall between the weir proper and the under sluice section to separate the two portions and to avoid cross flows. The under sluice section is similar to the sloping weir section, but its crest is at a lower level. Most of the dry weather flow passes through the under sluices because of the lower bed level. Since relatively clear water is supplied to the canal, some silt gets deposited in the pocket just u/s of the head regulator near the under sluice. The deposited silt is periodically washed through the under sluices. Functions of under sluices:

They maintain a clear and well defined river channel in front of the head regulator.

They are used to scour away the silt deposited in front of the head regulator. They pass low floods without dropping the weir crest shutters. They control the silt entry into the canal They provide greater waterway for floods, thus lowering the flood levels.

2. Briefly explain the Divide wall?

Ans. A Divide wall is a long masonry or concrete wall protected on all sides by stone or concrete blocks, constructed at right angles to the axis of the weir to separate the weir proper section and the under sluices section. If there are under sluices at both the sides, there are two divide walls. The divide wall extends on the u/s side up to a distance little beyond the beginning of the


canal head regulator and on the down stream side up to the end of the launching apron of under sluices. Functions of divide wall: It separates the floor of the scouring sluices from that of the weir proper which is at a higher level. It provides a silt pocket in front of the canal head regulator so that silt gets deposited in it and relatively clear water enters the canal. It isolates the pocket upstream of the head regulator to facilitate scouring operation. It prevents formation of cross currents and the flow parallel to the weir axis. It provides a straight approach through the pocket and thus helps to concentrate scouring action of the under sluices for washing out the silt deposited in the pocket. It serves as one side of the fish ladder.

3. Briefly Explain the fish ladder?

Ans. A fish ladder is a passage provided adjacent to the divide wall, on the weir side, for the

fish to travel from the upstream to the down stream of the weir and also in the reverse

direction.

In north Indian rivers, the fish generally travel from the cold water in hills to warmer water in plains during winter. In the months of May and June, they move in the reverse direction in search of clear water. It has been established that most types of fish can travel upstream against a flow velocity of about 3 to 3.5 m/s. If no fish ladder is provided at the weir site and only a gap is left, even the strongest fish will not be able to travel upstream. In a fish ladder, the head is gradually dissipated so as to provide smooth flow at sufficient low velocity. Suitable baffles ( or Staggering devices) are provided in the fish passage to reduce the flow velocity.


4. Explain Silt Excluder?

Ans. Silt excluder is a device by which silt is excluded from water entering the canal. It is constructed in the bed in front of the head regulator at right angles to the axis of canal (or parallel to the axis of head regulator) A silt excluder is consists of a number of rectangular tunnels resting on the floor of the under sluice pocket. The bottom of the tunnels is formed by the floor of the under sluice pocket. The top level of the roof of the tunnels is kept same as the level of the crest (or sill) of the canal head regulator. The tunnels are of different lengths. The tunnel nearest to the crest of the canal head regulator is of the same length as the width of the canal head regulator. The length of the tunnels gradually decreases as the distance of the head regulator increases. This arrangement separates the water into two clear layers. The top layer (above the roof of the under tunnels) enters the head regulator while the bottom layer, containing relatively heavier silt charge goes to the under sluices and discharges to the d/s of the river. The capacity of these tunnels is kept about 20% of the canal discharge, and the tunnels are so designed that a minimum velocity of 2 to 3 m/s is maintained. Thus the required cross sectional area can be obtained by dividing the discharge by the velocity.

5. Explain canal regulator? Ans. A structure which is constructed at the head of the canal to regulate flow of water in the off taking canal is known as canal head regulator. It consists of a number of piers which divide the total width of the canal into a number of spans which are known as bays. They are operated by gates provided for regulation of flow into the canal. The crest level is usually kept about 1.2 to 1.5 m higher than that of the under sluices. However, if a silt excluder is provided, the crest level is further raised by at least 0.75 m. The span between the piers is usually kept between 8 to 12 m for large canal. Functions of Canal Head Regulator: It regulates the supply of water entering the canal It prevents the river-floods from entering the canal The entry of silt into the canal is controlled by keeping the crest of the head regulator higher than the crest of the under-sluices. Silt gets deposited in the pocket, and only the clear water enters the regulator bays. The deposited silt can be easily scoured out periodically, and removed through the under-sluice openings.


OBJECTIVE QUESTIONS WITH ANSWERS

1. The following is not a component part of a diversion headwork

A. Spillway B. Weir C. Fish ladder D. Canal head regulator

2. The under sluices in diversion head works are provided

A. To control silt entry into the channel B. To avoid parallel flow to the weir C. To prevent hydraulic jump

3. The most suitable location for canal head work is

A. Free flow of river B. Rocky stage of river C. Trough stage of river D. Silting stage of river

4. The difference between the level of the top of the bank and the F.S.L is known as

A. Safe margin depths B. Beam C. Free board D. None of the above

5. According to khoslas theory the undermining of the floor starts from the

A. Foundation beds B. Starting end C. Intermediate point D. Tail end

6. A divide wall is constructed for the purpose of

A. Controlling seepage B. Scouring the silt C. Creating a still pond


D. Providing a fish passage

7. The escape of earth from underneath the foundation of a weir along with the percolated water results in a phenomenon called

A. Piping B. Creep C. Uplift D. Scour

8. In the design of impervious apron by khoslas theory for weirs the horizontal length of the apron is found by the consideration of

A. Scouring depth B. Design discharge C. Velocity of flow over the weir D. Permissible exit gradient

9. If the R is the normal depth of scour by lacey equation the depths below HFL up to the which the up strem and downstream sheet piles in a weir are usually provided to protect against the effect of scour are

A. 1.5 R and 2.0 R B. 2.0 R and 1.5 R C. 2 R to 3 R D. 1.0 R to 1.5 R

10. A weir on permeable foundation has the following elements

A. Impervious floor B. Block protection C. Block protection over inverted filter D. Launching apron

KEY

Q.NO 1 2 3 4 5 6 7 8 9 10

Ans a a d c d c a d a D


FILL IN THE BLANKS

1. Silt excluders are constructed ----------------------- 2. A canal head works has nothing to do with a ----------------------------- 3. The silt exclusion device constructed on the bed of the dam of the main taking of from head work is called------------------------------ 4. In divertion head project the canel head regulator is usually aligined-------------------------- 5. The back water effect of a weir is best called ------------- 6. Blighs theory as applied to the design of weirs and barrages on permeable foundations account for ---------------------------- 7. The value of khoslas safe exit gradient for usually met alluvial river soils of our country is --------------------------- 8. The minimum thickness of downstream floor as required in the design of weirs can be expressed as -------------------------- 9. While designing floor thickness of a weir in its upstream length. The average head causing uplift is 2.8 m the provided floor thickness here with a suitable factor is ----------------- 10. While desiging a hydraulic structure the piezometric head at the bottom of the floor is computed as 10m the dam is 3m below floor bottom. The assured standing water above the floor is 2m the specific gravity of floor material is 2.5. the floor thickness should be ----------

KEY

Q.NO 1 2 3 4 5 6 7 8 9 10

Ans On the

river bed

upstream

of head

regulator

Safety

regulator

Silt

ejector

Parallel

to

divide

wall

Afflux

Hydroststic

forces only

¼

to

1/6

4/3(h/g-

1)

0.8m

2m


UNIT V


1. What is canal head regulator?

Ans. canal obtains its share of water from the pool behind a barrage through a structure called the canal head regulator also a regulation structure for controlling the amount of water passing into the canal .

2. Explain the structures of canal head regulator?

Ans. These structures may be described as follows: 1. Drops and falls, to lower the water level of the canal 2. Cross regulators, to head up water in the parent channel to divert some of it through an off take channel, like a distributary. 3. Distributary head regulator, to control the amount of water flowing in to off take channel. 4. Escapes, to allow release of excess water from the canal system.

3. Explain the canal drops and falls?

Ans. canal has a designed longitudinal slope but has to pass through an undulating terrain. When a canal crosses an area that has a larger natural surface slope, a canal drop, also called fall in India, has to be provided suitably at certain intervals.

4. What are the necessities of canal falls? Ans. When slope of ground suddenly changes to steeper slope, permissible bed slope cannot be maintained. Slope of ground is more or less uniform and slope is greater than permissible bed slope of canal. In cross drainage work, when difference between level of canal and that of drainage is small or when F.S.L of canal is above bed level. 5. Explain types of canal falls? Ans.

1. Ogee fall

2. Rapid fall

3. Trapezoidal notch fall

4. Vertical drop fall


THREE MARK QUESTION WITH ANSWER

1. Explain canal regulators?

Ans. include the cross regulator and the distributary head regulator structures for controlling the flow through a parent canal and its off-taking distributary . help to maintain the water level in the canal on the upstream of the regulator. angle at which a distributary canal off-takes from the parent canal has to be decided carefully. The best angle is when the distributary takes off smoothly. Another alternative is to provide both channels (off-taking and parent) at an angle to the original direction of the parent canal. When it becomes necessary for the parent canal to follow a straight alignment, the edge of the canal rather than the centre line should be considered in deciding the angle of off-take. 2. Explain Silt vanes? Ans. Are thin, vertical, curved parallel walled structures constructed of plain or reinforced concrete on the floor of the parent canal, just upstream of the off-taking canal. height of the vanes may be about one-fourth to one-third of the depth of flow in the parent canal. thickness of the vanes should be as small as possible and the spacing of the vanes may be kept about 1.5 times the vane height. To minimize silting tendency, the pitched floor on which the vanes are built should be about 0.15 m above the normal bed of the parent channel. 3. Explain Groyne walls or curved wings? Ans. project out in to the parent canal from the downstream abutment of the off-taking canal. it divides the discharge of the parent canal in proportion of the discharge requirement of the off-taking canal with respect to the flow in the downstream parent canal. The groyne wall extends upstream in to the parent canal to cover ¾ to full width of the off-take. proportional distribution of flow in to the off-taking canal is expected to divert proportional amount of sediment. The height of the groyne wall should be at least 0.3m above the full supply level of the parent canal. 4. Explain Skimming platforms? Ans. A skimming platform is an RCC slab resting on low height piers on the bed of the parent canal, and in front of the off-taking canal. creates a kind of low tunnel at the bed of the parent canal, which allows the sediment moving along its bed to pass through downstream. floor of the off-taking canal being above the level of the platform thus only takes suspended sediment load coming along with the main flow in the parent canal. suitable where the parent channel is deep (about 2m or more) and the off-take is comparatively small.

5. Explain canal escapes? Ans. structures meant to release excess water from a canal, which could be main canal, branch canal, distributary, minors etc. usually an irrigation system suffers from deficit supply in later years of its life situations that might suddenly lead to accumulation of excess water in a certain reach of a canal network may occur due to the following reasons: Wrong operation of head works in trying to regulate flow in a long channel resulting in release of excess water than the total demand in the canal system downstream.


FIVE MARK QUESTIONS WITH ANSWER

1. Explain Weir or surface escapes? Ans. are constructed in the form of weirs, without any gate or shutter and spills over when the water level of the canal goes above its crest level.

2. Briefly Explain the sluice? Ans. gated escapes with a very low crest height. these sluices can empty the canal much below its full supply level and at a very fast rate.

In some cases, these escapes act as scouring sluices to facilitate removal of sediment. The locations for providing escapes are often determined on the availability of suitable drains, depressions or rivers with their bed level at or below the canal bed level. Escapes may be necessary upstream of points where canals takeoff from a main canal branch. Escape upstream of major aqueducts is usually provided. Canal escapes may be provided at intervals of 15 to 20km for main canal and at 10 to 15km intervals for other


canals.

3. Explain cross regulator? Ans. Cross Regulator • A Regulator Constructed in the main canal or parent canal downstream of an off take canal is called crossregulator. • It is generally constructed at a distance of 9 to 12 km along the main canal and 6 to 10 km along branch canal. • Functions: • (i) To Control the flow of water in canal system • (ii) To feed the off taking Canals • (iii) To enable closing of the canal breaches on the d/s (iv) To provide roadway for vehicular traffic.


4. Explain Silt control device? Ans. Scouring Sluices or Under sluices, silt pocket and silt Excluders The above three components are employed for silt control at the head work. Divide wall creates a silt pocket. Silt excluder consists of a number under tunnels resting on the floor pocket. Top floor of the tunnel is at the level of sill of the head regulator. Various tunnels of different lengths are made. The tunnel near the head regulator is of same length of head regulator and successive tunnels towards the divide wall are short. Velocity near the silt laden water is disposed downstream through tunnels and under sluices. Silt Excluder: The silt excluder is located on the u/s of diversion weir and in front of the head regulator. The object is to remove silt that has entered in the stilling basin through scouring sluices. • Silt Ejector: Silt Ejector is located in the canal take off from the diversion weir at 6 to 10 km in the canal reach. It ejects the silt that has entered in the canal.

5. What are the requirements of a good outlet? Ans. It should be simple in design ,construction and maintenance. It should be quite strong and durable. It should not be easily tampered with by the cultivators, but if tampered with it should be easily detected It should be worked efficiently with a small working load. It should not be expensive. It design should be such that it can be easily constructed by the local workers.


OBJECTIVE QUESTIONS WITH ANSWERS 1. Laceys scour depth for stream carrying a discharge of 3 cumecs per meter width and

having a silt factor of 1.2 is

A. 1.32m

B. 2.64m

C. 3.96m

D. 4.32m

2. If silt factor F used in laceys theory in upper – baridoab alluvium is adjusted to 1 , then

what is the average size of silt grain

A. 0.28m

B. 0.32m

C. 0.4m

D. 0.5m

3. The depths of flow in an open alluvium channel is 1.5m if critical velocity ratio is 1.1

and mannings n is 0.018 , the critical velocity as per kennedys theory

A. 0.713 m/s

B. 0.784 m/s

C. 0.879 m/s

D. 1.108 m/s

4. If D10 and D50 of a certain silt grade in keel canal region are 0.5 and 0.16 respetively

then the silt factor f is

A. 0.704


B. 1024

C. 1

D. 2

5. Laceys silt factor of silt having D50 as 0.1 cm

A. 0.176

B. 1.76

C. 17.6

D. 0.0176

6. If the flow velocity and depth in a channel are given as 2 m/ s and 0.5 m respectively

then scour depth according to laceys silt theory is

A. 2.7m

B. 1.35m

C. 1m

D. None

7. A stream carrying a discharge of 4 cumecs per meter width is having a silt factor 2 , then

the laceys scour depth will be

A. 1.35 m

B. 2.7 m

C. 3.4 m

D. 5.4m

8. The velocity of flow will be least in case of a channel which is

A. Alluvial


B. Clean and straight

C. Natural stream with weeds

D. Cement lined

9. If the silt factor is 1 and the discharge is 30 m3/s , then the canel bed slope according to

laceys method of canel design is

A. 1/5000

B. 1/5100

C. 1/5900

D. 1/6100

10. Garrets diagram is used in the design of a

A. Dam

B. Canal

C. Weir

D. Spillway

Q.NO 1 2 3 4 5 6 7 8 9 10

Ans b b b a b b b c c b


FILL IN THE BLANKS WITH ANSWERS

1. Channel in alluvial soils are designed by -------------------------------

2. The regime scour depth for a channel in soil with silt factor of unity and carrying 8 m3/s

of discharge intensity in accordance with laceys regime theory is ---------------------------

3. The total number of independent equations that from the laceys regime theory is --------

4. The slope of canal for a discharge of 300 cumecs is ---------------------

5. The channel where silting and scouring needs no special attention is called as ----------

6. A channel designed by lacys theory has a mean velocity of 1 m/s the silt factor is unity .

the hydraulic mean radius is ----------------------------

7. For medium silt whose average grain size is 0.16 mm laceys silt factor is likely to be -----

------------

8. The depth of flow in an alluvial channel is 1.5 m. if critical velocity ratio is 1.1 and

mannings n is 0.018 the critical velocity of the channel as per kennedys method is ---------------

9. If the regime velocity of flow in a laceys channel having hydraulic mean radius of 1 m is

0.4 m/s , the silt factor is -------------------------------------

10. Laceys concept of design of design of chanals is based on the -----------------------

KEY

Q.NO 1 2 3 4 5 6 7 8 9 10

Ans Silt

theory

5.4

m

4 1 in

8000

Critical

flow

channel

2.5 m 0.70 0.784

m/ s

0.4 Unlined

channels

only.

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