• Head work is constructed at the head of canal to divert the river water towards canal.

Types:

1. Storage head work:

• Headwork capable of seasonal regulation of water.
• Dam is constructed to use during time of deficit.

2. Diversion headwork:

• Headwork can regulate water daily, weekly or monthly.
• Consist of weir or barrage.

Types of diversion headwork:

• Temporary diversion headwork
• Permanent diversion headwork

Function of diversion headwork:

• Helps to raise the water level in upstream side.
• Regulates supply of water into canal.
• Creates pond on upstream to store water.
• Control silt entry into canal.
• Reduce fluctuation in the level of supply in river.

Components of headwork:

1. Weir or barrage:

Weir:

• Solid construction across the river to raise water level.
• Less costly.
• After long time it becomes ineffective due to silt deposition.

Barrage:

• Water is collected in upstream mainly due to large gates constructed over concrete weir.
• More costly.
• Quantity of water can be controlled.

2. Under sluice:

• To control the entry of silt into canal.
• To ensure easy diversion of water even during low flow.

3. Divide wall:

• To separate the under sluice portion from the weir portion.
• Increase effectiveness of under sluice portion.

4. Fish ladder:

• Provide just by side of divide wall for free movement of fishes.

5. Canal head regulator:

• Regulates the supply of water entering the canal.
• Prevent river flooding from entering into the canal.

Difference between silt excluder and silt extractor:

1.2 Condition and cause of failure of hydraulic structure in alluvial formation:

1. Failure by piping or undermining:

• When the seepage water retains sufficient residual force at the emerging downstream end of work it may lift up the soil particle. This leads to increased porosity of soil by progressive removal of soil from beneath the foundation. The structure may ultimately subside into the hollow so formed resulting in the failure of the structure.

2. Failure by direct uplift:

• The water seeping below the structure exerts an uplift on the floor of structure. If the force is not counterbalanced by the weight of the concrete or masonry floor, the structure will fail by a rapture of a part of the floor.

1.3 Bligh’s, Lanes and Khosla’s seepage theory:

Bligh’s seepage theory:

Assumption:

• Loss of head is proportional to the length of creep.
• Hydraulic gradient is constant throughout seepage path.

Let, there be level difference between upstream and downstream.

Creep length (L) = d₁ + d₁ + L₁ + d₂ + d₂ + L₂ + d₃ + d₃

or, L = (L₁ + L₂) + 2 (d₁ + d₂ + d₃)

or, L = b + 2 (d₁ + d₂ + d₃)

Hydraulic gradient = H_L/ [b + 2 (d₁ + d₂ + d₃)] = H_L / L

Lane’s weighted creep theory:

• Improvement of Bligh’s theory.

Lane creep length (L) = d₁ + d₁ + L₁ / 3+ d₂ + d₂ + L₂ /3+ d₃ + d₃

or, L = (L₁ + L₂)/3 + 2 (d₁ + d₂ + d₃)

or, L = b/3 + 2 (d₁ + d₂ + d₃)

Hydraulic gradient = H_L/ [b/3 + 2 (d₁ + d₂ + d₃)] = H_L / L

Khosla’s theory:

• Khosla’s theory states that “seeping water doesn’t creep along the bottom contour of hydraulic structure.”
• Water moves along a set of stream lines.
• Seepage is governed by Laplacian equation:

d² Φ / dx² + d² Φ / dz²  = 0

1.4 Cross drainage structure, condition for their application and design:

• Cross drainage is constructed at crossing of canal and natural drain to dispose drainage water without interrupting the continuous canal supplies.

Types:

1. Passing canal over drainage:

• Aqueduct
• Syphon aqueduct

2. Passing canal below drainage:

• Super passage
• Syphon

3. Passing drain through the canal:

• Level crossing
• Inlet and outlet

1.5 Canal Escape:

• Canal escape is a side channel constructed to remove surplus water from an irrigated channel into natural drain.

Types:

1. Weir type:

• Reduce level is equal to full supply level.

2. Regulator type:

• Better control.
• Used for completely emptying the canal.

1.6  Canal drops:

• Canal drop is used to bring down the canal bed line.

Types of fall:

1. Ogee fall:

• Used in old days.

2. Rapid fall:

• Provide with long sloping floor.

3. Steeped fall:

• Provided long stepped floor.

4. Trapezoidal notch fall:

• Consist of number of trapezoidal notch.

5. Vertical drop fall:

• Crest wall created to create vertical drop.

1.7 Function of head and cross regulator:

Head regulator:

Function:

• Structure provided at head of canal to control flow of water entering into different branch canal.
• Control or regulate supply of water entering different branch canal.
• To control silt entry.
• Used as meter to measure discharge.

Cross regulator:

Function:

• Used to raise the water level.
• Effectively control the entire canal irrigation system.
• Raise the water level if parent channel is low.

1.8 Canal Outlet:

• Canal outlet is a small structure built at the head of water course to connect minor or distributary.

Requirement of good outlet (module):

• Should be simple which can be constructed easily.
• Should work effectively with small working head.
• Should be cheap.
• Any interference by local people should be made difficult and easily detectable.
• Should be strong and durable.

Types:

1. Non – modular outlet:

• Minimum head loss.
• Easy to construct.
• Cheap.
• Unequal distribution of water.

2. Semi – modular outlet:

• Equal distribution of water.
• Easy to construct.
• Expensive.

3. Rigid modular outlet:

• Equal distribution of water.
• Costly.
• Requires skilled manpower.

References:

• WECS (1998), Design Guidelines for Surface Irrigation in Terai and Hills of Nepal, (Vol. I and II)
• Michael, A.M.(2011). Irrigation theory and practice
• FAO(1977). Guidelines for Predicting Crop Water Requirements. FAO Irrigation and Drainage Paper No. 24.

The post Hydraulic Structure in Surface Gravity Irrigation System: Bligh’s, Lanes and Khosla’s seepage theory appeared first on OnlineEngineeringNotes.

1. Head work:

• Consist of all the works to store, divert and control river water and regulate supplies into canal.

2. Canal network:

a. Main canal:

• Large capacity canal which supplies water to branch canals and the major distributaries.

b. Branch canal:

• Supply water to major and minor distributaries.

c. Major distributaries:

• Use for direct irrigation.
• Supply water to minor distributaries.

d. Minor distributaries:

• Discharge is less than 0.25 cumec.
• Supply water through outlet to water course for irrigation.

e. Water course:

• Small channel managed by farmers to take water from minor to the field.

3. Structure in canal:

a. Cross drainage structure:

• Structure constructed at the crossing of canal and natural drainage.
• Use to disposal of drainage water without interrupting the continuous canal supply.

b. Canal fall:

• Use to carry canal water below stream or drainage.

c. Cross regulator:

• Constructed across a canal to regulate the water level in canal.

d. Canal escape:

• Constructed to escape extra water from the canal into natural drain.

1.2 Classification of canal:

A. Based on their function:

1. Irrigation canal:

• Canal used to fulfill irrigation water requirement.

2. Navigation canal:

• Canal used for transportation through water.

3. Hydropower canal / power canal:

• Canal use to supply water to power house to generate electricity.

4. Feeder canal:

• Canal that supplies water to two or more canals.

5. Link canal:

• Canal that link one river with the other.

B. Based on carrying capacity:

• Main canal
• Branch canal
• Major distributary
• Minor distributary
• Water course

C. Based on alignment:

• Watershed or ridge canal
• Contour canal
• Side slope canal

D. Based on financial output:

1. Protective canal:

• To protect particular area from famine.

2. Productive canal:

• To generate revenue to the nation.

E. Based on canal surface:

1. Lined canal:

• Canal with their surface lined by impervious material like concrete, brick etc.

2. Unlined canal:

• Canal with their surface in natural condition.

F. Based on nature of source:

1. Permanent canal:

• Canal that have continuous supply from the source like lake or perennial river or  ice.

2. Inundation canal:

• Canal in which flows occurs only during the high stage of river.

1.3 Components of canal cross- section:

1. Side slope:

• Used  for stable canal.
• Depends upon type of soil.
• Steeper slope is provided in cutting.

2. Berm:

• Used for deposition of silt which acts as a lining.
• Reduce seepage.
• Protect bank from erosion.

3. Free- board:

• Margin between full supply level (FSL) and bank level.
• Depends upon size of canal:

4. Canal banks:

• Primary purpose is to retain water.
• Used for inspection and as means of communication.

5. Service road:

• Roads provided on canal for inspection purpose.
• Provided 0.4 m to 1 m above FSL (Full supply level) depending upon canal size.

6. Spoil bank:

• Constructed when earth work in excavation exceed earthwork in filling.
• Disposal of such soil may be uneconomical by mechanical means.

1.4 Alignment canal:

1. Watershed or ridge canal:

• Line separating the catchment of two streams is ridge line.
• No drainage can intersect watershed.

2. Contour canal:

• Economical than ridge canal.
• Suitable for contour farming.
• Irrigation only one side so serves small area.

3. Side slope canal:

• Canal aligned perpendicular to contour line.
• Doesn’t require cross drainage structure.

Consideration during alignment of canal:

• Alignment should not pass through valuable land, religious site, village etc.
• Alignment should be short as possible.
• Alignment should be straight as possible.
• Alignment should not involve heavy cutting or filling.
• Alignment should done such way minimum number of cross drainage are required.
• Alignment should cross natural drainage.
• Ridge or watershed is preferred so both side can be irrigated.

4.5 Canal seepage and evaporation and other losses:

1. Evaporation:

• Evaporation losses are about 2% to 3 % of total losses.
• Depeds upon meteorological factors like temperature, wind velocity and humidity.

2. Seepage:

a. Percolation:

• In percolation there exits a continuous zone of saturation from the canal to the water table.
• A direct flow is established between canal and ground water reservoir.

b. Absorption:

• In absorption a small saturated zone exits round the canal section.
• A small zone above water table is also saturated by capillary action.
• An unsaturated zone exits between these two saturated zone.

Factors on which seepage loss depends:

• Types of seepage (Percolation loss is more)
• Soil permeability (More permeable soil more seepage loss)
• Seepage through silted canal is more than from a new canal.
• More amount of silt less loss.
• More velocity less loss.
• Cross-section and wetted perimeter.

4.6 Tractive force approach in canal:

• The movement of sediment at bed is caused by a force exerted on its grains by the flowing water. The force is known as tractive force.
• Consider a grain of weight ‘w’  represented by dotted circle on the side slope and hollow circle on a horizontal bed of channel as shown in figure below.

Critical shear stress at horizontal loads = τ_L = τ_C = wtanΦ

Critical shear stress at slopping surface = τ_S

Angle of repose of soil = Φ

We know,

      (τ_S)² + (wsinθ)² = (wcosθ*tan Φ)²

or, (τ_S)² + ((τ_L * sinθ)/ tan Φ)² = ((τ_L* cosθ*tan Φ)/ tan Φ)²

or, (τ_S)² + ((τ_L * sinθ)/ tan Φ)² = (τ_L* cosθ)²

or, (τ_S / τ_L)² = cos²θ – sin²θ / tan² Φ

or, (τ_S / τ_L)² = (1- sin² θ – sin² θ / tan² Φ)

or, (τ_S / τ_L)² = (1- sin² θ (1+1/tan² Φ)

or, (τ_S / τ_L)² = (1- sin² θ (1+cot² Φ)

or, (τ_S / τ_L)² = (1- sin² θ *cosec² Φ)

or, (τ_S / τ_L)² = (1- sin² θ/sin² Φ)

∴ τ_S / τ_L = (1- sin² θ/sin² Φ)^1/2

Above equation is the required expression.

4.7 Silt theories:

Kennedy’s silt theory:

• According to Kennedy’s “regime channel” are those channels in which neither silting nor scouring takes place.
• This condition is not possible in natural channel.
• Expression of critical velocity.

V_o = 0.55y^0.64

Lacey’s regime theory:

• According to lacey a canal showing no silting and no scouring may not be in regime.
• He defined three regime condition:

1. True regime:

• Discharge is constant.
• Flow is uniform.
• Silt discharge is constant.
• Silt grade i.e. type and size of silt is constant.
• Practically not possible.

2. Initial regime:

• Bed slope of a channel varies.
• Cross- section or wetted perimeter remains unaffected.

3. Final regime:

• All variables such as perimeter, depth, slope etc. are equally free to vary and achieve permanent stability called final regime.

In such a channel:

• The coarse the silt, the flatter is the semi-ellipse.
• The finer the silt the more the section attains a semi circle.

Design of canal according to Lacey’s theory:

• Based on final regime.
• The empirical equation is:

V = (2FR/5)^1/2 ————-(i)

AF² = 140V⁵ —————-(ii)

V = 10.8 R^2/3 S^1/3————(iii)

Where,

V = Mean velocity of flow in m/s

F = Silt factor = 1.76(D_mm)^1/2

D_mm = Average size of particle in mm

A = Cross section area in m²

S = Bed slope

Relation derived from Lacey’s formula:

1. Perimeter discharge relation:

P = 4.75 (Q)^1/2

Proof:

From equation (i)

   V = (2FR/5)^1/2

or, V⁴ = 4F²R² / 25

From equation (ii)

AF² = 140V⁵

Eliminating F² from the equation and substituting R = A/P

   V⁴ = (4*140V⁵ *R²)/25A

or, V⁴ = (560V⁵ *A²)/(25*A*P²)   [∴R = A/P]

or, P² = 22.4Q

∴ P = 4.75 (Q)^1/2

2. Regime slope equation:

S = F^5/3/(3340*Q^1/6)

Proof:

From equation (iii)

V = 10.8 R^2/3 S^1/3

Cubing on both side

V³ = 1259.712 R² S

We have,

   R = 5 V² / 2F

or, R² = 25 V⁴ /4F²

Now,

      V³ = 1259.712S [(25 V⁴)/4F²]

or, S = F² / 78732V ———(iv)

Again,

V = (QF²/140)^1/6

Now, equation (iv) becomes

S = F²/[7873.2*(QF²/140)^1/6]

On simplifying we get

∴ S = F^5/3/(3340*Q^1/6)

3. Hydraulic Radius:

R = 5V²/2F

Proof:

From equation (i)

V = (2FR/5)^1/2

Squaring on both side

V² = 2FR/#

∴ R = 5V²/2F

Difference between Lacey’s theory and Kennedy’s theory:

4.8 Advantage and economics of canal lining:

Advantage of canal lining:

• Seepage control. (Treated with less permeable material)
• Prevention of water logging.
• Increase channel capacity.(Less resistance to flow of water)
• Reduction in maintenance cost.
• Elimination of flood risk.

Types of lining:

1. Hard surface lining:

• Cement concrete lining
• Brick lining
• Boulder lining

2. Earth type lining:

• Soil cement lining
• Compacted earth lining

References:

• WECS (1998), Design Guidelines for Surface Irrigation in Terai and Hills of Nepal, (Vol. I and II)
• Michael, A.M.(2011). Irrigation theory and practice
• FAO(1977). Guidelines for Predicting Crop Water Requirements. FAO Irrigation and Drainage Paper No. 24.

The post Canal Design: Components of surface gravity irrigation system & Classification of canal appeared first on OnlineEngineeringNotes.

Exploration of groundwater:

• Objective is to locate aquifier capable of yielding water of suitable quality, for irrigation, drinking water, agricultural and industrail purpose.
• Done by geophysical drilling.

Methods:

1. Surface exploration:

• Geological method.
• Remote sensing.
• Surface geophysical method.

2. Sub- surface exploration:

• Test drilling.
• Geophysical logging.

Aquifer:

• Aquifer is underground water bearing layer of permeable rock.
• Types:

a. Confined aquifer: Presence of underground water.

b. Unconfined aquifer: Open to atmospher.

• Advantage of ground water:
• Less investment required.
• No channel required.

1.2 Types of well:

• Well are vertical holes driven below the ground surface to extract water from ground.

a. Shallow well:

• Hole which has been dug, bored, driven or drilled into ground for purpose of extracting water.

        b. Deep well:

• Well drilled to an aquifer below an impervious strata.
• Water is hard and contains dissolved salt.

1.3 Components of tube well:

• A tube well consist of 100 to 200 mm wide stainless steel tube or pipe which is bored into underground aquifer.

Components:

a. Temporary reservoir:

• Small reservoir of water made at outlet of tube well.

b. Casing:

• Support to the well.
• Protect borehole from collapse.

c. Screening:

• Help to maintain good water supply from aquifer.
• Allow for long term satisfactory operation of well.

1.4 Design consideration of shallow and deep well:

• Determining location of well.
• Water well design and installation.
• Well drilling.
• Well development (includes well screen, well casing is developed and borehole is cleaned).
• Well head protection (construction of well seal and use of backflow prevention device).

1.5 Type and selection of pump:

Types of pump:

1. Centrifugal pump:

• Mechanical device designed to move a fluid by means of transfer of rotational energy from one or more driven rotors called impeller.
• Simple design and produce high flow rate and high efficiency.

2. Reciprocating pump:

• Pump which uses backward and forward movement to move a fluid.
• Provide steady, unchanging flow rate.
• Better than centrifugal pump.

Selection of pump:

• Should be capable of pumping required quantity of water.
• Intial cost should be cheap.
• Maintenance cost should be cheap.
• Should be reliable.
• Should be high efficeient.
• Should have long life and depreciation cost should be small.
• Cost of labour should be low.

1.6 Conveyance and distribution system in ground water irrigation schemes:

• Water is conveyed from ground water source to cropped field using network of open channel or pipe line.
• Pipe line have more advantage than open channel because it save water and energy consumption.
• Though underground pipe distribution system is expensive it have many advantage such as:
  • Farmers receive water near the field.
  • Seepage, evaporation loss are avoided.
  • Quantity of water delivered is same in each outlet.
  • Maintenance cost is low.
  • Full control of water supply.

1.7 Conjunctive use of surface and ground water:

• Conjuctive use is the combined use of surface water and ground water resource in a unified way to optimize water use and minimize adverse effect of using a single source.
• Efficient and ecnomic way to maximize agricultural production.

Advantage:

• Problem of water logging is reduced.
• Promotes sustainable water management.
• Improves environmental condition of irrigated area.
• Enhance water use efficiency.

Limitation:

• Reduce pump efficiency due to large fluctuation of water level.
• Active participation of people required for proper conduction.
• Construction of ground water recharge structure required.

References:

• WECS (1998), Design Guidelines for Surface Irrigation in Terai and Hills of Nepal, (Vol. I and II)
• Michael, A.M.(2011). Irrigation theory and practice
• FAO(1977). Guidelines for Predicting Crop Water Requirements. FAO Irrigation and Drainage Paper No. 24.

The post Planning & Conveyance and distribution systems in groundwater irrigation schemes: Conjunctive use of surface and ground water, components of tube-wells appeared first on OnlineEngineeringNotes.

• An agricultural land is said to be water logged if productivity gets affected by high water table.
• Due to high water in root zone, oxygen gets removed and bacteria cannot get enough air to produce sufficient food for plant.
• Cause:
  • Over irrigation.
  • Seepage of water through canal.
  • Excessive rain.
  • Irregular or flat topography.
  • Inadequate surface and natural drainage.
• Effects:
  • Hamper’s nitrification.
  • Cultivation operation becomes difficult.
  • Restricted root growth.
  • Leads to salinity (presence of salt).
• Control:
  • Lining of canal and water course.
  • Reduce intensity of irrigation.
  • Crop rotation.
  • Increase natural drain.
  • Optimum use of water.

1.2  Consideration in the design of surface and sub-surface drainage system:

Drainage:

• Process of taking out excess water from irrigated land to minimize water logging.

Types:

1. Open or surface drainage:

• Constructed at land surface having open channel flow in drain.
• Types of open or surface drainage:

a. Shallow drain:

• Depth of drain is small.
• Used to accelerate storm water removal.

b. Deep open drain:

• Depth of drain is large.
• Used to discharge collected rain and seepage water safely to natural drain.

Design consideration of surface drainage:

• If ground has good natural slope no drain required.
• Drain are required for area having very mild slope and heavy rainfall.
• Alignment should follow natural slope.
• Strom water should drain with 3 to 5 days.

2. Subsurface irrigation:

• Drainage of water through underground drains.
• Subsurface irrigation:
• Also known as drip irrigation.
• Effective for coarse texural soil.
• Cultivable land loss is minimum.

1.3 Objective of river training:

River training work:

• River training work is known as all engineering work which are constructed to guide, controll or regulate river.

Objective of river training work:

• To prevent river from changing it course.
• To provide safe passage of flood.
• To protect river bank.
• To ensure effective disposal of sediment load.
• To control and regulate river.

1.4 Types of river training work:

1. High water training:

• Purpose to control flood.
• Protect land from flood.

2. Low water training:

• Provide sufficient water depth for navigation.
• Groyne’s are constructed to contact the width of channel and increase the depth.

3. Mean water training:

• Effeciently dispose suspended and bed load.
• Example: Check dam.

1.5 Specific design consideration in hill irrigation:

• The length of canal should kept short as possible.
• Local manpower and locally available material should be utilized.
• Proper design should be adopted so that farmers can easily maintain and repair.
• Non-modular and semi- modular outlet are used.
• Slope should be cut to maintain uniform gentle gradient.
• Manning’s equation is used to design canal.
• Narrow canal is used to reduce risk of erosion and seepage.

1.6 Choice of intake, control and regulation structure:

Intake:

• Used for collecting water from the surface source such as river, lake and conveying it for irrigation purpose.

Selection criteria of intake:

• Sufficient flow is available in both monsoon and dry season.
• Sufficient availabiluty of head of water.

Sedimentation control of river:

• By construction of intake outside the river bank.
• Afforestation.
• Use of divide wall.
• Construction of setting basin.

1.7 Environmental protection measure in hill irrigation:

Problem:

• Mass movement.
• Weathering due to high velocity.
• Cutting of river.

Solution:

• Construction of small dams.
• Construction of retaining wall.
• Construction of surface and sub-surface drainage.
• Bamboo planting can be used for soil erosion on slope.
• Use of stone pitching to reduce velocity of water.

References:

• WECS (1998), Design Guidelines for Surface Irrigation in Terai and Hills of Nepal, (Vol. I and II)
• Michael, A.M.(2011). Irrigation theory and practice
• FAO(1977). Guidelines for Predicting Crop Water Requirements. FAO Irrigation and Drainage Paper No. 24.

The post River Control & Drainage and Hill Irrigation: Objective of river training and environmental protection measures appeared first on OnlineEngineeringNotes.

1. Free flooding:

• Ditches are excavated on field and water is allowed to flow across the field with no control mechanics.
• Suitable for irregular land.
• Inefficient method of irrigation.

 2. Border flooding:

• Land is divided into a number of strips with the help of low levees.
• Each strip has 10 to 20 meter width and 100 to 400 meter length.
• Supply of water is stopped once it reduce lower end.
• Suitable for close crops.

3. Check flooding:

• Similar to ordinary flooding except water is controlled with help of low and flat levees.
• Reduce percolation loss.

4. Basin Flooding:

• Special type of check flooding which is adopted specially for orchard tree.
• One or more tree are placed in basin and surface is flooded.

5. Furrow irrigation:

• Narrow ditches excavated between rows of plants and carry water through them.
• Spacing of furrow depends upon spacing of plants.

6. Sprinkler irrigation:

• Water is applied to soil in the form of spray through network of pipes and pumps.
• Suitable:
  • Topography is irregular.
  • Land gradient is steeper.
  • Crop water requirement is low.
  • Classified as:
  • Permanent system
  • Semi- permanent system
  • Portable system
• Advantage:
  • Seepage losses is completely eliminated.
  • Land levelling is not required.
  • No extra land required for ditches.
  • High efficiency.
• Disadvantage:
  • Affected by high wind.
  • Not suitable for crops with high water requirement.
  • Not suitable for high temperature area.

1.2 Hydraulics of irrigation distribution:

1. Advance phase:

• Time interval between the start of irrigation and arrival of the advancing (wetting) front at the lower end of the field.

2. Ponding phase:

• Irrigation time extending between the end of advance and inflow cut-off.

3. Depletion phase:

• Time interval between supply cutoff and the time that water dries up at the inlet boundary.

4. Recession phase:

• Time required for the water to recede from all points in the channel starting from the end of the depletion phase.

1.3 Efficiency irrigation method:

1. Efficiency of water conveyance:

• Ratio of water delivered into the field from the outlet point to the water entering into the channel at its starting point.

2. Efficiency of water application:

• Ratio of quantity of water stored into the roof zone of the crops to the quantity of water actually delivered into the field.

3. Efficiency of water storage:

• Ratio of quantity of water stored into the root zone during irrigation to the water needed in the root zone.

4. Efficiency of water use:

• Ratio of water beneficially used including leaching water to the quantity of water delivered.

5. Uniformity coefficient or water distribution efficiency:

• Represents the extent to which water has penetrated to a uniform depth throughout the field.

η = (1 – d/D)

where,

d = Average absolute value

D = Mean depth

1.4 Operation and management needs of surface and ground water irrigation schemes:

Operation of irrigation system:

• Operation of irrigation system is a package of organisational, economical and technical arrangement that ensure planned distribution and full use of water resource for heavy yield of agricultural crops of good quality under irrigation conditions.
• Operation measure includes:
  • Implementation of schedule water use practice to provide the irrigation regime required under specific meteorological condition on certain land areas under efficient water use.
  • Keeping irrigation, drain and other canal in working state by proper supervision and maintenance.
  • Prevention of excess water.
  • Control water loss of canal.
  • Organization of irrigation water accounting.

1.5 Canal operation plan:

• Method of organizing water delivery in a planned way by releasing, conveying and dividing water in canal system.
• It includes:
  • Starting and closure of season.
  • Starting storage.
  • Irrigation release schedule.
  • Responding to specific situation.

Data required for operation plan:

1. Water resource:

• Availability
• Storage status
• Inflow

2. Water demand:

• Cropping plan
• Rainfall

3. Canal status:

• Discharge
• Water level
• Losses

4. Irrigation schedule:

• Timing
• Duration

1.6 Participatory management:

• Participatory management is the participation of irrigation users in the management of irrigation system.
• Recognised all over world as tool of improving irrigation management along with sustainability of the system.

Objective participatory management:

• To promote and secure distribution of water among user and economic utilisation of water in agriculture.
• To protect environment and to ensure ecological balance inculcating sense of ownership of irrigation system.
• Users are directly involve in design process which will ensure better understanding of design and management of system.
• Farmers will have better idea of accounting, budgeting, planning and organizing techniques.
• Farmers can manage and operate the system more cheaply than government agencies.

References:

• WECS (1998), Design Guidelines for Surface Irrigation in Terai and Hills of Nepal, (Vol. I and II)
• Michael, A.M.(2011). Irrigation theory and practice
• FAO(1977). Guidelines for Predicting Crop Water Requirements. FAO Irrigation and Drainage Paper No. 24.

The post Method of Irrigation and Planning & Management of Irrigation System: Hydraulics of irrigation distribution appeared first on OnlineEngineeringNotes.

• Saturation capacity:

Water content of soil when all pores are filled with water.

• Field capacity:

Water content of soil after free drainage has taken place for sufficient period.

• Gravity water:

Rainfall or irrigated water flow down to water table under gravity.

• Capillary water:

Water held by surface tension against gravity.

• Hygroscopic water:

Water that cannot be extracted by plants.

• Soil moisture:

Water above water table.

• Permanent wilting point (PWP):

The water content at which plant can no longer extract sufficient water for growth and wilts up.

• Available moisture content (AMC):

Difference of water content between field capacity and permanent wilting point.

• Readily available moisture content (RAM):

Portion of AMC that is easily extracted by plants.

• Optimum moisture content (OMC):

The water content soil is not allowed to deplete below a certain value.

• Soil moisture deficiency:

Water required to bring soil at a given water content to its field capacity.

Soil moisture irrigation relationship:

Let,

d = Effective depth of root zone

FC = Field capacity

From definition of field capacity,

FC = Weight of water retained in certain volume of soil / Weight of dry soil of same volume

Considering unit area of soil

Weight of dry soil = γ_d * d

Weight of water retained = FC * γ_d * d

So, volume of water retained is,

V = (FC * γ_d * d) / γ_w

Where,

γ_w = Unit weight of water

γ_d  = Dry unit weight of soil

1.2 Soil moisture regime: Crop water requirement

• Consumptive use (Cu) or Evapotranspiration:

Defined as the total amount of water used by the plants in transpiration and evaporation from adjacent soil in specified time.

• Potential evapotranspiration (PET):

If sufficient moisture is available to completely meet need of plant.

• Actual evapotranspiration (AET):

Real evapotranspiration occurring in a specific situation.

• Estimation of consumptive use:

Consumptive use is estimated by penman’s equation.

PET = ( A* H_n + E_a * γ) / (A + γ)

Where,

H_n =  Net incoming solar radiation or energy expressed in mm of evaporable water per day

A = Slope of saturation vapor pressure versus temperature curve at mean air temperature

E_a = Parameter including wind velocity and saturation deficit in mm/day.

γ = Psychrometric constant = 0.49 mm of Hg/^oC

1.3 Factors affecting crop water requirement:

• Crop factor:
  • Variety
  • Growth stage
  • Duration
  • Plant population
  • Crop growing season
• Soil factor:
  • Structure
  • Texture
  • Depth
  • Topography
  • Soil chemical composition
• Climate factor:
  • Temperature
  • Sunshine hour
  • Relative humidity
  • Wind velocity
  • Rainfall
• Agronomic management factor:
  • Irrigation method use
  • Frequency of irrigation and its efficiency

1.4 Base period, kor period, duty, delta and their relationship.

• Crop period:

Time period that elapses from the instant of its sowing to the instant of its harvesting.

• Base period (B):
  • Time period that elapses between first watering of crop after sowing to last watering of crop before harvesting.
  • Crop period and base period are taken equal.
• Delta (Δ):
  • Total quantity of water required by a crop for full maturity.
  • Expressed in mm or cm.
• Duty (D):
  • Number of hectares of land irrigated for full growth of a given crop by the supply of 1 cumec water continously during base period.
  • Expressed in hectare/cumec.
  • Design discharge (Q) = Area (A) / Duty (D)
• Kor watering:
  • First watering which is given to a crop when crop is few centimeter high.
  • Maximum watering is done.
• Kor period:

Kor watering must be applied within the fixed limited period.

• Kor depth:

Depth of water supplied in the Kor period.

Relationship between duty, delta and base period.

Let, there be a crop of base period B days. Let 1 cumec of water be applied to this crop for B days.

Now, volume of water applied to this crop during base period.

    V = ( 1 cumec * B days)

or, V = 1 * 60 * 60 * 24 * B days

or, V = 86400B m³

The quantity of water mature D hectare of land.

So, area irrigated A = 10⁴ D, ha

Total depth of water applied to the field is given by

  Δ = Volume / Area = 86400B / 10⁴ D

or, Δ = 8.64B / D , m

or, , Δ = 864B / D , cm

Since design discharge is calculated based on kor depth and kor period.

Kor depth = (864 * Kor period) / Duty , cm

1.5 Command area of irrigation system – GCA, CCA and NCA.

• Gross commanded area ( GCA) :
  • Total area bounded within irrigation boundary which can be irrigated without considering the limitation of quality of water available.
  • Includes cultivable and uncultivable area like road, ponds, residential area etc.
• Cultural  or cultivable commanded area (CCA):
  • Includes  only cultivable area.
  • Divided into:

a. Cultural cultivated area

b. Cultural uncultivated area

• Net commanded area (NCA):
  • Cultivable commanded area deducting the area of canal network, supply ditches, bunds constructed in the field.

1.6 Principal crops, their season and water requirement

In irrigation a year is divided into two cropping season:

• Kharif season (Summer)
  • Starts from April 1 and ends on 30^th September.
  • Kharif crops: rice, bajra, maize, cotton, tobacco etc.
  • Rice is the most important kharif crop.
• Rabi season (Winter)
  • Starts from October 1 and ends on 31^st March.
  • Rabi crops: wheat, barley, mustard, potatoes etc.
  • Wheat is the most important rabi crops.

References:

• WECS (1998), Design Guidelines for Surface Irrigation in Terai and Hills of Nepal, (Vol. I and II)
• Michael, A.M.(2011). Irrigation theory and practice
• FAO(1977). Guidelines for Predicting Crop Water Requirements. FAO Irrigation and Drainage Paper No. 24.

The post Soil Moisture and Crop Relation: Command area of irrigation system-GCA,CCA and NCA appeared first on OnlineEngineeringNotes.

Different places in the earth have different climatic conditions. Some places may get frequent rainfall throughout the year while some may avail them- selves with scanty rainfall. The regions in earth which receive very scanty rainfall are called ”Arid regions”. Some regions in earth may receive precipitation below potential evapotranspiration. These regions are called ”Semi- Arid regions”. Meanwhile ”Tropical wet regions” that lie near the equator receive continuous rainfall throughout the year.

If the natural rainfall is not sufficient to meet the water needs of the plants, water has to be supplied to the plants artificially.

1.1 Definition of irrigation

The artificial application of water to the land throughout the certain du- ration according to the water requirement of a particular crop for its full development is called irrigation. It means if effective rainfall in a particular place is 50 mm and plant water requirement is 80 mm, then 30 mm has to be supplied artificially. Only the water that has been applied to plants artificially comes under irrigation.

Necessity of irrigation

⋆ Diversity of climate and topography

Due to climate and topography, different crops are grown in different parts of the country. Different crops have different requirements of water. Irrigation is necessary to fulfill this requirement.

⋆ Uneven distribution of rainfall

Since the distribution of rainfall is not uniform throughout the country, irrigation is necessary to supplement the deficit water to the plants.

⋆ Inadequate rainfall

Some part of crop water requirement is fulfilled by the rainwater. How- ever, if the rainfall is inadequate, irrigation is necessary to fulfill the deficit water.

⋆ Growing more number of crops                 

More number of crops can be grown if irrigation is available to meet their needs.

⋆ Increase in production

Sufficient irrigation is necessary to increase crop production.

1.2 Classification/ types of irrigation systems

Irrigation systems are broadly classified into two types:

1. Surface irrigation

The process of irrigation in which water is supplied to the soil surface is called surface irrigation.

It is further divided into two types:

a. Flow irrigation

When the water available at higher location is supplied to the lower level under the action of gravity, it is called flow irrigation.

i. Perennial irrigation

The system of irrigation in which constant and continuous water supply is assured to the crops in accordance with the crop water requirement throughout the crop period is called perennial irrigation.

ii. Direct irrigation

When irrigation is done by diverting the river runoff into the main canal by constructing a diversion weir or barrage across the river, then it is called direct irrigation.

iii. Storage irrigation

When a dam is constructed to store the monsoon water and use it for irrigation during period of low flow, it is called storage irrigation.

iv. Flood irrigation

The type of irrigation in which soil is kept submerged and thoroughly flooded with water so as to cause thorough saturation of the land is called flood irrigation. This soaked moisture supplemented by the natural rain brings the crop to maturity.

b. Lift irrigation

If the water is lifted up by some manual or mechanical means such as pumps and then supplied for irrigation, it is called lift irrigation. Wells and tube wells are used for this purpose.

2. Sub surface irrigation

In sub surface irrigation, water is not supplied to the soil surface. In- stead it is provided beneath the soil surface and this water is extracted by the plant by capillary.

a. Natural sub irrigation

Leakages of water from channels and passage through the sub soil may irrigate crops by capillarity. When underground irrigation is achieved simply without extra efforts, it is called natural sub irrigation.

b. Artificial sub irrigation

When a system of open jointed drains is artificially laid below the soil to supply water to the crops, it is known as artificial sub irrigation. It is costly process and hence applied in small scale for crops with high return.

1.3 Functions and advantages of irrigation

Advantages of irrigation

• Increase in food production

Fulfillment of crop water requirement by irrigation increases crop yield.

• Elimination of mixed cropping

Mixed cropping means sowing together two or more crops in the same field. This process is suitable where irrigation facilities are lacking. Thus, if irrigation is assured, mixed cropping can be elimated.

• Prosperity of the nation

Revenue returns from irrigation projects is high which helps in overall development and prosperity of nation.

• Elimination of famine

Irrigation fulfills crop water requirement and increases crop production eliminating the possible famine.

• Domestic water supply

Though the main purpose of irrigation is to provide water to the fields, this water can be used by local people for washing, bathing and as drinking water for animals.

• Facilities of communication

Development of irrigation project provides access to the embankments and roads which provide facilities of communication and transportation of people and goods.

• Navigation

Large scale irrigation projects can be used for navigation and recreational purposes.

Disadvantages of irrigation

• Irrigation may contribute to the water pollution.

Different chemical fertilizers and pesticides are used in field. These are poisonous to health. When these chemicals get mixed with water and reach the water sources, they may cause water pollution thus affecting aquatic lives and human health.

• Irrigation may result in damp and marshy area causing breeding of mosquitoes

• Over irrigation may lead to water logging and may reduce crop yields

• Development of irrigation projects is costly and complex

• Loss of valuable land:

If case of storage irrigation system, valuable land may get submerged directly or due to rise in water table thus reducing its value.

1.4 Irrigation development in Nepal

History of irrigation development

• Before 1922, only FMIS famer managed irrigation systems prevailed in Nepal.
• The minor irrigation program was introduced in second three-year development plan (1962-1965)
• After 1970, large scale irrigation system were initiated in the Terai.
• “Chandra Nahar” was the first irrigation canal of Nepal.
• Water resource act and Irrigation Policy were promulgated in 1992 with the vision of irrigation development.
•  Irrigation master plan 1990, Agriculture perspective plan 1995, Water resource strategy 2002 and National water plan 2005 are other documents which guide irrigation development in Nepal.
•  Department of irrigation was established in 2009

Present status of irrigation in Nepal

• Total area:14.718 million ha
• Cultivable area: 2.641 million ha
• Irrigable area: 1.766 million ha
• 76% of potential irrigable area lies in the Terai region

At the end of fiscal year 2071/72, the area covered by three different methods are:

• Surface irrigation: 813067 ha
• Sub-surface irrigation:443365 ha
• Farmers channel:167925 ha

Challenges of irrigation development in Nepal

The various challenges of irrigation development in Nepal are:

• Most of the irrigation projects are Runoff River type.
• Non availability of water during lean period in the source of existing irrigation systems.
• Resource constraint to develop irrigation systems through intra-basin transfer for year round irrigation.
• Unsatisfactory people’s participation in sharing operation and maintenance (O&M) and capital cost of system.
• Insufficient budget allocation for O&M.
• Low water use efficiencies.
• High operating cost of tube well due to price hike of fuels.
• Non-availability of electricity due to limited generation capacity.
• Weak institutional capability of agencies.
• High land acquisition cost.
• Weak linkages between agriculture and irrigation.

Major irrigation projects of Nepal

Irrigation projects enlisted as the project of nation pride are:

• Sikta Irrigation Project
• Babai Irrigation Project
• Rani-Jamariya-Kularia Irrigation Project

Some major irrigation projects are enlisted in table below:

References:

• WECS (1998), Design Guidelines for Surface Irrigation in Terai and Hills of Nepal, (Vol. I and II)
• Michael, A.M.(2011). Irrigation theory and practice
• FAO(1977). Guidelines for Predicting Crop Water Requirements. FAO Irrigation and Drainage Paper No. 24.

The post Introduction to Irrigation: Classification/types of irrigation system appeared first on OnlineEngineeringNotes.