Explanation:

Components of Head Works

Following are parts/components of headworks

• Weir
• Under Sluices
• Canal Head Regulators
• Fish Ladder.
• Divide Wall.
• River Control Works

Concept-

The elementary profile of a dam

• An elementary profile of a gravity dam is oretical shape of its cross-section when it is subjected to only three main forces,i.e self-weight, water pressure, and uplift pressure.
• But when reservoir is empty, water pressure and uplift pressure will be zero, so only weight will be acting.
• Moreover, elementary profile has zero top width and no freeboard.
• The right angle triangle is most suitable section for oretical profile.
• The elementary profile is hypotical because an actual gravity dam has some minimum top width and freeboard, and it will also be subjected to forces or than three main forces considered in elementary profile. 

Concept:

Groynes or Spurs:

• A groyne is a rigid hydraulic structure built eir from shore (in case of seas) or bank (in case of rivers) in order to dissipate wave energy or to protect banks from erosion by trapping sediments.
• They are perpendicular or slightly oblique to shoreline.

Guide banks:

• Guide banks are meant for guiding and confining flow in a reasonable waterway at site of structure.
• The design of guide banks is based on ory developed by Mr. Bells. Hence, guide banks are also known as Bell’s bunds.
• The guide banks are constructed parallel or approximately parallel to direction of flow. They extend both upstream and downstream of abutments of hydraulic structure.
• The guide banks may be provided on eir side of hydraulic structure or on one side as required.

Levees:

• It is a low ridge or earn embankment built along edges of a stream or river channel to prevent flooding of  adjacent land. 
• Levees are usually embankments of dirt built wide enough so that y will not collapse or be eroded when saturated with moisture from rivers running at unusually high levels.

Flood walls:

• When no space is available for construction of a levee or when it is not suitable to construct levee due to local site conditions, n a flood wall is constructed as local flood hazard prevention for some important area situated at a low level.
• There are masonry or concrete walls constructed just on river bank.

Explanation:

Lacey’s Silt Theory of Canals

Lacey stated that a channel may not be in regime condition even if it is flowing with non-scouring and non-silting velocity. Therefore, he distinguished three regime conditions as follows :

1. True regime
2. Initial Regime
3. Final Regime

1. True regime

A channel is said to be in regime condition if it is transporting water and sediment in equilibrium such that re is neir silting nor scouring of channel.  But according to Lacey, channel should satisfy following conditions to be in regime condition.

• Canal discharge should be constant.
• The channel should flow through incoherent alluvium soil, which can be scoured as easily as it can be deposited and this sediment should be of  same grade as is transported.
• Silt grade should be constant.
• Silt charge, which is minimum transported load should be constant.

If  above conditions are satisfied, n channel is said to be in true regime condition. But this is not possible in actual practice. Hence lacey defined two or conditions which are initial and final regime conditions.

2. Initial Regime

A channel is said to be in initial regime condition when only bed slope of channel gets affected by silting and scouring and or parameters are independent even in non-silting and non-scouring velocity condition. It may be due to absence of incoherent alluvium. According to Lacey’s, regime ory is not applicable to initial regime condition.

3. Final Regime

If channel parameters such as sides, bed slope, depth etc. are changing according to flow rate and silt grade n it is said to be in final regime condition. The channel shape may vary according to silt grade as shown in figure below :

Note:

Lacey’s specified that regime ory is valid for final regime condition only and he also specified that semi-ellipse is ideal shape of regime channels.

Explanation:

Glacis fall:

• It consists of a straight-sloping glacis provided with a crest. A water cushion is provided on downstream side to dissipate energy of flowing water.
• The sloping glacis is constructed with cement concrete.
• Curtain walls and toe walls are provided on upstream and downstream sides.
• The space between toe walls and curtain walls is protected by stone pitching.
• This type of fall is suitable for drops up to 1.5 m and discharge up to 60 cumecs.

Hence, Glacis or Straight Glacis fall is used for moderate discharge of 40 - 50 cumecs (up to 60 cumecs) and low fall height of 1 to 1.5 m.

Additional Information

Vertical drop fall:

• It consists of vertical drop walls which are constructed with masonry work. The water flows over crest of wall.
• It is provided on downstream side which acts as a water cushion to dissipate energy of falling water.
• A concrete floor is provided on downstream side to control scouring effect of flowing water.
• Curtain walls are provided on upstream and downstream sides.
• Stone pitching with cement grouting is provided on upstream and downstream sides of fall to protect it from scouring.
• This type of fall is suitable for drops up to 1.5 m and discharge up to 15 cumecs.

Ogee fall:

• In this type of fall, an ogee curve (a combination of a convex curve and a concave curve) is provided for carrying canal water from a higher level to a lower level.
• This fall is recommended when natural ground surface suddenly changes to a steeper slope along alignment of canal.
• The fall consists of a concrete vertical wall and a concrete bed.
• Over concrete bed, rubble masonry is provided in shape of an ogee curve.
• The surface of masonry is finished with rich cement mortar (1:3).
• The upstream and downstream side of fall is protected by stone pitching with cement grouting.
• The design consideration of ogee fall depends on site condition.

Baffle or Inglis fall:

• In this type of fall, gracis is straight and sloping, but baffle walls are provided on downstream floor to dissipate energy of flowing water.
• The height of baffle depends on head of water on upstream side.
• The main body of fall is constructed with cement concrete.
• The toe walls and curtain walls are same as straight glacis.
• The protection works with stone pitching are also same. Sometimes, this fall is known as a baffle fall.
• It is suitable for all discharges and drop/fall height greater than 1.5 m.

Explanation:

Lacey's ory

• Lacey followed Lindley’s hyposis, which states that “dimensions and slope of a channel to carry a given discharge and silt load in easily erodible soil are uniquely determined by nature”. Lacey’s ory is applicable to flow in alluvial rivers and canal

According to Lacey:

“Silt is kept in suspension by vertical component of eddies generated at all points of forces normal to wetted perimeter”. So eddies are generated from  bottom as well as side of  channel.

Regime Channel: “A channel is said to in regime if re is neir silting nor scouring”.

According to Lacey, re may be three regime conditions:

(i) True regime; (ii) Initial regime; and (iii) Final regime.

Kennedy's ory

• R.G. Kennedy studied a number of sites at Upper Baro Doab System (now in Punjab) for carrying out investigations about velocity and depth of channels.
• According to him, Critical velocity (Vo) is mean velocity that will just keep  channel free from sitting and scouring and related it to depth.
• Modified critical Velocity, $V_o=0.55m{d}^{0.64}$
• Where, d = depth of channel (m), m = Critical velocity ratio (V / Vo) (For sand m = 1.1 to 1.2, for finer sand or than standard m = 0.9 to 0.8)
• For calculating velocity, He used Kutter's formula and Manning's formula.

Important Points 

According to  Kennedy’s ory Silt carried by flowing water is kept in suspension by vertical

component of eddies which are generated from bed of channel.

Concept:

For an irrigation land:

SC = Saturation capacity, FC = Field capacity, OMC = Optimum moisture content, PWP = Permanent welting point and UWP = Ultimate welting point

1. Equivalent depth of water held at field capacity (x) = S × d × Fc

2. Equivalent depth of water held at PWP (x’) = S × d × (PWP)

3. Available moisture/storage capacity of soil (y) = S × d × (Fc - PWP)

4. Readily available moisture content (dw) = S × d × (Fc - OMC)

Given:

Field capacity (F. C) = 25 % = 0.25

Permanent willing point (PWP) = 15 % = 0.15

Depth of root zone (d) = 80 cm

Dry Unit weight of soil (γ_d) = 1.5 g/cc

Calculations:

The storage capacity $=\frac{{\gamma }_d\times d\times \left(F.C-PWP\right)}{{\gamma }_w}$

The storage capacity $=\frac{1.5\times 80\times \left(0.25-0.15\right)}{1}=12cm$

Hence, storage capacity of soil is 12 cm.

Concept:

Aggrading Rivers:

• These rivers collect sediments and build up its bed by silting.
• As silting process goes on, bed slope of aggrading rivers get increased, which is shown below.
  
• Aggrading rivers also known as Accreting Rivers.

Important Points

• The rivers which displaces sediment and carry on scouring are known as degrading rivers.
• The river which curves and bends back and forth across landscape and swings from side to side is called meandering rivers and this process is known as meandering.
• In absence of rain, many seasonal rivers show depletion in flow in dry season because source of water starts depleting. 

Concept:

The drainage water intercepting canal can be classified in following ways:

i) By passing canal over drainage

a) Aqueduct

b) Syphon aqueduct

ii) By passing canal below drainage

a) Superpassage

b) Syphon

iii) By drain through canal ⇒ a) level crossing b) inlets and outlets

Computation:

Bed level of Canal = + 131.3 m;

Full Supply depth of Canal = 1.6 m;

Bed level of Drain = + 129.5 m;

High Flood Level of drain = + 131.6 m

From given data,

We can conclude that HFL of drain is higher than bed level of canal and bed level of canal is higher than bed level of drain, so suitable type of cross drainage structure is syphon aqueduct.

Explanation:

Components of Head Works

Following are parts/components of headworks

• Weir
• Under Sluices
• Canal Head Regulators
• Fish Ladder.
• Divide Wall.
• River Control Works