Irrigation & Soil and Water Conservation Engineering

a. Surveying is a process which determines positions of points on the surface of earth, in horizontal distance.

Objective: to prepare a plan or map

Uses:

(1) To prepare road

(2) To make irrigation channel

(3) To make channels

(4) To make railway lines

(5) In soil conservation etc.

b. Soil Surveying helps in getting and collecting information’s about soils and preparing an inventory of soil resources of an area.

c. Types of surveying:

1. Reconnaissance soil survey (RSS): helps to identify benchmark soils for delineating problem and potential areas and providing information’s useful for making land use plants and agriculture development.

Scale: 1:50,000 -> 1cm = 0.5km (for state and district level survey)

1:2, 50,000 1cm = 2.5km (for national survey)

2. Detailed soil survey (DSS): helps to understand the soil and land problems and for different conservation measures to control soil erosion, to fix irrigation scheduled, in agriculture and watershed development.

Scale: 1:8,000 1cm = 80mm or 0.08km

1:20,0001cm = 0.2km

1:10,000 for Arial photos

a. Cadastral survey (land survey): determines land boundaries and areas.

b. Topographic survey: determines the shape or relief of the ground and the location of various natural and artificial features.

f. Instruments used in Surveying:

A. Instruments Used for Measuring Distance:

1. Chain: The chain is composed of 100 or 150 pieces of galvanized mild steel wire 4mm in diameter called links.

a. Metric chains: The chains are made in lengths of 20 and 30 meters.

b. Giinter’s Chain: It is 66 fit long and is divided into 100 links. Each link is 0.66 ft. long.

c. Revenue Chain: It is 33 ft. long and divided into 16 links. Each link is 2.0625 ft. long. It is commonly used for measuring fields in cadastral survey.

d. Engineer’s chain: It is 100 ft. long and it is divided into 100 links. Each link is 1 ft. in a length. Used in all Engineering surveys.

2. Arrows (chain pins): also called as marking or chaining pins and are used to mark the end of chain during the process of chaining. The arrows are made 400 mm in length. They are pointed at one end of inserting in to the ground.

3. Tape: Metric, cloth and steel tape.

B. Instruments for marking stations:

1. Wooden Pegs: These are used to mark the positions.

2. Ranging rods: Used for making the positions of stations and for ranging.

3. Ranging Poles: Used in the case of very long lines.

4. Offset Rod: It is used for aligning short offsets.

5. Plumb Bob: It is also used for testing the verticality of ranging poles.

g. Contour line: an imaginary line of constant elevation on the surface of the ground.

h. Contour interval: the vertical distance between two consecutive contours.

i. Theodolite is a device used for measuring horizontal and vertical angles.

j. Hydrology is the earth science dealing with the occurrence and movement of water upon and beneath the land areas of globe.

k. The average & annual rainfall of India is about 119.4 cm.

l. Gross Command Area (G.C. A): total area which can be irrigated by a certain channel or a project.

m. Culturable Command Area (C.C. A): it is the portion of the G.C. A which is Culturable or cultivable.

n. C.C. A. = G.C.A. – uncultivable area in the G.C. A.

o. The common practice in northern India for distribution of water through canal to farmer is Warabandi (numbers of turns).

p. Aquifer: A porous soil or geological formation which will yield significant quantity of water.

q. Unconfined aquifer is also known as a free, phreatic or non-artesian aquifer, is one overlying an impervious stratum, in which the water is not under pressure.

r. Confined aquifers: also known as artesian or pressure aquifers lie below an impervious layer and the water in them is under pressure.

s. Manually operated water lifting devices: Swing basket (lift – 1 to 1.2m), Counter poise lift (2-3 m), don (1.2m), Archimedean screw (lift 0.5-1.2 m). Paddle wheel (lift <1.2 m).

t. Animal powered operated water lifting devices: Rope and bucket lift (15m), Persian wheel (lift <10 111), Chain pump (lift<6 m).

Types of pumps for Irrigation:

1. Displacement pumps (reciprocating pumps and rotary pump): operating pressure (atm pressure i.e. 1 kg/cm^ water lift <10m, best result-7mi

2. Centrifugal pump (suction Iift<4.5m, Maximum suction head is taken as 6 m, but beyond about 4 m the efficiency of pump drop down substantially.). Impeller and casing are two parts of centrifugal pumps.

3. Turbine pumps (Deep well turbine pumps and submersible pump) – suction lift >7.5 meters.

4. Propeller pumps (axial flow and mixed flow) -Suction lift 1-2.5 meters.

5. Airlift pumps

6. Jet pump (suction lift 12-18m)

a) The interrelationship of capacity, head, power and efficiency – are best shown graphically and these curves are called the “characteristics of the pumps”.

b) Priming is the process of removing air from pump casing and suction pipe by filling water in the suction pipe.

c) Static bead = Static suction head + Static discharge head

d) Total head = Static head + Friction head + Velocity head

e) Water is measured under two conditions: at rest and in motion. Hence, the s commonly used in measuring water is in unit flow and unit of volume.

f) The commonly used units of water at rest are the litre, cubic meter and hectare- centimeter.

g) The commonly used units of water in motion are in m3/s and It/s.

h) Orifices, Weirs, Notches and Parshall flumes are used to measure the rates of flow (discharge) of water.

i) The basic formula for calculating the discharge through a weirs is Q = CLHm

Where, C = a coefficient, depending on the nature of the crest and approach conditions

L = length of crest cm,

H = head of the crest cm,

m = exponent depends on the type weir opening

j). Types of weir based on their shape:

1. Rectangular weir

(a) Suppressed Rectangular Weir (Francis formula)- Q = 0.0184LH-”^2

(b) Contracted Rectangular Weir Q = 0.0184(L-0.1nH) H^/^ zvhere, n= numbers of end contractions

2. Cipolletti weir – trapezoidal weir (slope H: V=l:4) Q=0.0186LH 3/2

3. 90″V notch weir (triangular shape) Q = 0.0138 H’-‘^

k) Bernoulli’s theorem is application of the law of conservation of energy to fluid flow.

l) Total energy (head) = Pressure energy (head) + Velocity energy (head) + Elevation head energy

m) Darcy’s law is applicable to groundwater flow and drainage problems,

n). Hydraulic radius is ratio between the cross-section (a) of the stream and its wetted perimeter (p).

o). Soil texture refers to the relative proportion of the various size groups of mineral particles in a given.

p). Soil structure refers to the manner in which the soil particles are arranged in groups or aggregates.

q). A typical Si.t loam soil contains about 50% solids, 30% water and 20% air.

r). Clay soils contain more than 40% of clay particles and 45% sand or silt.

s). Hygroscopic water: water held tightly to the surface of soil particles by adsorption forces.

t). Capillary water: water held by forces of surface tension in continuous films around soil particles and capillary space.

u). Gravitational water: water that moves freely in response to gravity and drains out of the soil.

v). Percolation is the downward movement of water through the soil profile.

w). Seepage is the lateral movements of water from water sources such as a reservoir or irrigation canal.

x).Tensiometers, electrical resistance measuring devices and neutron moisture meter are used for measurement of soil moisture.

y). Evaporation is the process of vaporization by which water is transferred into the atmosphere.

z). Transpiration is the discharged of water as vapour into the atmosphere by the leaves and stems of living plants.

Irrigation efficiency is the ratio usually expressed as per cent, of the volume of the irrigation water transpired by plants, plus that evaporated from the soil, plus that necessary to regulate the salt concentration in the soil solution, and that used by the plant tissue to the volume of water diverted, stored, or pumped for irrigation