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CHAPTER 6

SLBC COMMAND AREA DEVELOPMENT

6.1 GENERAL

The potential of the agriculture sector and the country‘s

development depends on the effective utilization of water. Efficient

utilization and optimum development of water resources, assume

great significance. The Ministry of water resources, New Delhi lays

down policies and programmes for regulation and development of the

country‘s water resources. It covers sectoral planning, policy

guidelines, technical examination and techno-economic appraisal of

projects, coordination, facilitation of external assistance and

assistance in resolution of inter-state water disputes, planning and

guidance in respect of minor irrigation, command area development

and development of ground water resources. It provides Central

assistance to specific projects, policy formulation and others. Water is

a main natural resource as per National Water Policy 1987 , and a

basic human need and a invaluable national asset. In 1998 National

Water Board, in its meeting reviewed and updated the existing

National Water Policy 1987 and placed before the National Water

Resources Council for its consideration and adoption.

6.1.1 Water Resources Potential

In India the average runoff the river system has been estimated

as 1869 3km , out of which, 690 3km is the useful portion and 432 3km is

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the ground water potential. The availability of water has reduced due

to the increasing water scarcity in the river basins.

6.1.2 Command Area Development Programme

In 1974-75 centrally sponsored Command Area Development

Programme was started to shift the management paradigm from fully

state managed systems to farmer managed systems by encouraging

farmer‘s participation in the management of irrigation with the

following objectives.

Improving utilization of irrigation potential involves construction

of field channels, field drains, land leveling, land shaping,

conjunctive use of surface and ground water.

Optimizing agricultural productivity involves rotational system

of water distribution, timely supply of water, establishing

suitable cropping patterns.

Integrating agricultural practices encourages and motivates

farmers, with demonstrations and training for improving

farming practices.

Reclamation of waterlogged areas in irrigated command is also

an important component of this programme.

6.1.3 Irrigation Requirement of Crops

Irrigation is an artificial application of water for the cultivation

of crops, trees, grasses and so on. For the urban Indian, the word

‗irrigation‘ conjures up the image of the first Prime Minister of India,

Jawaharlal Nehru, and the Bhakra Nangal Dam (Temples of Modern

India) and images of Medha Patkar, Aamir Khan, and the tribal

126

oustees of the Narmada Dam. These are diverse perspectives on the

story of large irrigation infrastructure in India. In fact, in popular

public perception, irrigation connotes ‗large irrigation infrastructure‘

rather than provision of irrigation services.

Irrigation means a wide range of interventions at the farm level,

ranging from a couple of support watering(s) during the kharif season

from a small check dam/pond/tank well to assured year-round water

supply from canals or tube wells to farmers cultivating three crops a

year. The method of application has also evolved, from traditional

gravity flow and farm flooding to micro-irrigation where water is

applied close to the root zone of the plant.

Indian farmers gain access to irrigation from two sources—

surface water (i.e. flow of water on the surface or water storage

reservoirs) and groundwater (i.e. water extracted by pumps from the

groundwater aquifers through wells, tube wells and so on). Surface

irrigation is largely provided through large and small dams and canal

networks, run-off from river lift irrigation schemes and small tanks

and ponds. Canal networks are largely gravity-fed while lift irrigation

schemes require electrical power. Groundwater for irrigation is

accessed by dug wells, bore wells, tube wells and is powered by

electric pumps or diesel engines. To meet the growing needs of

irrigation, the government and farmers have largely focused on a

supply side approach rather than improving the efficiency of existing

irrigation systems.

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The terms used by the Ministry of Water Resources, Ministry of

Rural Development, and the Ministry of Agriculture and the three

ministries within the government are responsible for irrigation in the

following way:

Major irrigation (cultivable command area above 10,000 ha ).

Medium irrigation (cultivable command area between 2000 ha

to 10,000 ha ).

Minor irrigation (cultivable command area less than 2000 ha )

The irrigation requirements of the various crops may be

expressed in different ways as indicated below.

Consumptive Irrigation Requirement CIR

It is defined as the amount of irrigation water that is required to

meet the evapotranspiration needs of a crop during its full growth.

However, if during the growth period of a crop, rain occurs, a part of it

will be retained by the soil in the root zone and the same will be

available to meet a part of the evapotranspiration requirements of the

crop and hence the quantity of irrigation water required to be applied

will be correspondingly reduced. This part of the rainfall is known as

effective rainfall and its value may be determined as indicated later.

Thus if cET or Cu is the evapotranspiration or consumptive use of

water for a crop and Re is the effective rainfall during the growth

period of the crop then

ReRe CuorETCIR c

128

Net Irrigation Requirement (NIR)

It is defined as the amount of irrigation water required to be

delivered at the field to meet the evapotranspiration needs of a crop as

well as the other needs such as leaching, presowing requirement and

nursery water requirement (if any). Thus we have

NWRPSRLRCIRNIR

Where LR = leaching requirements, PSR = presowing requirement

NWR = nursery water requirement

In this thesis, NIR is considered as equal to CIR

Field Irrigation Requirement (FIR)

The amount of water required to meet the Net Irrigation

Requirements (NIR) in addition to the amount of water lost as surface

run-off and through deep percolation is known as FIR . The water

application efficiency a accounts for the loss of irrigation water by

surface runoff and through deep percolation and hence

a

NIRFIR

Gross Irrigation Requirement (GIR)

The amount of water required meeting the filed irrigation

requirements (FIR) in addition to the amount of irrigation water lost in

conveyance through the canal system by evaporation and seepage is

known asGIR . The water conveyance efficiency c accounts for the

conveyance losses and hence

c

FIRGIR

129

Integration of the existing system along with expansion of

irrigation facilities has been the main strategy for increasing

production of food grains. Major, medium and minor irrigation

projects and development of command area supports the Irrigation

system. With sustained and systematic development of irrigation, the

potential has been increased from 22.6 haM. in 1951 to about 89.56

haM. by the end of 1997, as per the statistics relating to irrigation

potential created and utilized under major, medium and minor

irrigation during the various Five Year Plans.

6.2 IDENTIFICATION OF PROBLEMS IN THE SLBC COMMAND

AREA

Physical

No significant physical problems are anticipated in the

command area. The suitable crops for the soils in the command area

are proposed. As the area is well drained by the existing natural

drainages and as the ground water table fluctuates sufficiently below

the root zone of the crops, the drainage and water logging problems

were not anticipated after the introduction of canal irrigation.

Financial problems

No financial problems could be foreseen. The farmers are

already in the field of agriculture. The present policy of the

government both at central and state levels is aimed at growing more

food and achieving self sufficiency by providing every conceivable

assistance to the farmers, the locally available banks and other

130

financial institutions could be expected to be geared up to provide the

increased timely financial assistance to the farmers.

6.3 SLBC COMMAND AREA DEVELOPMENT WORKS

Land Development

The land of the proposed command area is partly uneven and

partly plane. The land leveling and its preparation to receive the

irrigation supplies may have to be taken up with active participation

of the beneficiary farmers. The cost of leveling and the preparation of

land could be made to be borne by the farmers themselves, and land

development banks can provide the required loans to be recovered in

easy installments. Distributory channels on high level canal for 1,

57,100 acres command area were completed and remaining

distributory channel work is in progress.

Field Channels

Irrigation supplies to the fields are the primary function of field

channels, constructed through the entire command area of the canals.

On the high level canals, the field channel work is completed for only

83,111 acres command area. For remaining 2, 29,813 acres field

channel work on high level canal has to be completed. On the low level

canals field channel work is not yet started. Again active participation

of the farmers for the work is called for, which could be planned

simultaneously with the land leveling works.

Field Drainage to Prevent Water Logging

The introduction of canal irrigation does not create water

logging because the command area is already on higher elevations and

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the post monsoon ground water is below 5 m or more. The topography

is undulating with several small local streams, finally joining bigger

streams. Hence it forms good field drainage system, which would allow

the excess water, if any, to flow without causing stagnation of water,

avoiding possibilities of water logging in the command area. So, the

ground water level would be well below the root zone of crops.

Farm Roads

The existing roads to reach various parts of the command area

are sufficient. However, after introduction of irrigation, some new farm

roads are to be constructed and old village roads will have to be

realigned for better accessibility to the villages and agricultural fields.

Other Facilities

In addition to the above development works, credit facilities

from banks, marketing and ware housing facilities, easy availability of

agriculture inputs, and consolidation of land holdings will have to be

thoroughly planned and developed and should be well organized for

proper command area development. It is also pertinent to develop

other facilities concerning health, education, protected drinking water

supply, communications and others for the general betterment of the

living standards of the population of the command area.

6.4 SIMULATION OF ID CROPS UNDER SLBC COMMAND AREA

WITH CROPWAT MODEL.

Computer model simulation is an emerging trend in the field of

water management. CROPWAT is a powerful simulation tool which

analyzes complex relationships of on-farm parameters such as the

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crop, climate, and soil, for assisting in irrigation management and

planning. Water managers, irrigation agronomists, engineers and

researchers are taking keen interest in model simulation for the easier

solution of problems faced by them. CROPWAT is one of the models

extensively used in the field of water management throughout the

world. CROPWAT facilitates the estimation of the crop

evapotranspiration, irrigation schedule and agricultural water

requirements with different cropping patterns for irrigation planning.

6.4.1 CROPWAT model Input data

The basic input data for CROPWAT model are the climatic

parameters which are required for calculating Reference

Evapotranspiration 0ET . Researchers proposed several methods to

determine 0ET , of which the Penman-Monteith Method (FAO 1998) has

been recommended as the appropriate combination method to

determine 0ET from climatic data on temperature, humidity, sunshine

and wind speed.

The FAO Penman-Monteith method to estimate 0ET is:

)34.01(

)(408.0

2

2273900

0u

eeuGRET asTn

0ET = reference evapotranspiration [ 1daymm ]

nR = net radiation at the crop surface 12 daymMJ

G = soil heat flux density 12 daymMJ

T = mean daily air temperature at 2 m heights [ C0 ]

2u = wind speed at 2 m height 1sm

133

se = saturation vapour pressure kPa

as ee = saturation vapour pressure deficit kPa

= slope vapour pressure curve 10 CkPa

a = psychrometric constant 10 CkPa

Climate Data

The monthly average climatic data of Nalgonda region was

collected from Bureau of Statistics, Hyderabad. The average climate

data and simulated reference evapotranspiration 0ET calculated by

using Penman-Monteith model is shown in Table 6.1.

Table 6.1 Basic Climate data and simulated 0ET values

Month

Max

Temp

C0

Min

Temp

C0

Humidity

(%)

Wind Speed

daykm/

Sun Shine

hours

Solar Rad.

daymMj // 2

0ET

daymm /

Jun 35.1 23.7 62 381 3.1 14.3 6.10

Jul 30.8 22.8 75 350 1.9 12.5 4.18

Aug 29.1 21.7 79 292 2.4 13.2 3.62

Sep 30.3 21.6 79 180 3.0 13.6 3.41

Oct 30.4 21.0 71 141 4.7 14.9 3.67

Nov 28.8 19.8 64 156 6.0 15.3 3.76

Dec 27.8 16.3 59 148 7.2 16.1 3.67

Avg 32.0 20.8 59 227 5.5 16.5 4.94

Jan 28.4 15.1 58 177 7.6 17.1 4.00

Feb 31.7 17.3 48 194 7.9 19.1 5.12

Mar 35.3 20.5 41 201 8.6 21.8 6.37

Apr 37.8 24.6 38 218 7.5 21.0 7.17

May 39.0 24.9 36 285 6.4 19.4 8.22

Rainfall data

The rainfall contributes greater/lesser extent in satisfying crop water

requirement, depending on the location. During monsoon in tropical &

some semi-tropical regions, a great part of the crop's water needs are

covered by rainfall, while during the dry season, the major supply of

water should come from irrigation. It is difficult to predict the

134

contribution of rainfall and contribution of irrigated water as rainfall

varies greatly from season to season. Statistical analysis of long term

rainfall record is required to estimate the rainfall deficit for irrigation

water requirement. Rainfall used by the crop varies from year to year,

due to surface runoff and deep percolation below the root zone. To

determine the portion of the rainfall which effectively contributes to

cover crop water requirement, 10 average annual series of monthly

rainfall records are processed, by taking weighted average from 4 rain

gauge stations namely Devarakonda, Nalgonda, Miryalaguda and

Suryapet to represent average climatic conditions of SLBC command

area. Average rainfall of 10 series records of SLBC command area is

657 mm .

The amount of dependable rainfall corresponding to 80%

probability of exceedance represent a dry year, commonly used for

design of the irrigation system capacity. The dependable rain fall

corresponding to 20%, 50% and 80% probability of exceedance

indicates wet, normal and dry years respectively. The rainfall in

normal years is nearly equal to the average rainfall (657 mm ).

The rainfall data of dry year is used for the designing of

irrigation system capacity. Processed rainfall data for dry, wet and

normal can be obtained by computing and plotting probabilities from

the rainfall records. The various steps involved are:

i. Yearly rainfall data for 10 years are tabulated

ii. Data is arranged in descending order of magnitude.

iii. Plotting position is tabulated as

135

1

*100

N

mFa

Where: N = number of records

m = rank number

Fa = plotting position

iv. Values are plotted on log normal scale to obtain logarithmic

regression equation.

v. Year values at 20%, 50% and 80% probabilities are calculated

as wet ( 20P ) =876 mm , normal ( 50P ) =595 mm and dry ( 80P )

=451 mm .

vi. Monthly values of dry year are determined according to the

relationship av

dry

iavidryP

PPP *

Where: iavP = average monthly rainfall for month i

idryP = monthly rainfall dry year for month i

avP = average yearly rainfall

dryP = yearly rainfall at 80% probability of

exceedance

Similarly values for normal and wet years can be determined.

Processed rainfall records is shown in Table.6.2

Table 6.2 Processed rain fall record

Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Total

Avg.

mm 99 100 109 154 110 33 7 5 4 7 13 16 657

Dry

mm 68 69 75 106 75 22 5 3 3 5 9 11 451

Wet

mm 133 134 145 205 147 44 9 7 5 9 17 21 876

136

Effective rain fall

In order to account for the losses due to runoff or percolation, effective

rain fall is calculated by empirical method. Dependable rain empirical

formula according to Food and Agriculture Organization of United

Nations/Water Resources Development Management Service

(FAO/AGLW) is

Effective rain fall = 10*6.0 P for rain fall 70 mm .

Effective rain fall = 24*8.0 P for rain fall 70 .mm

Effective rain fall calculations for precipitation data of a year with

rainfall of 80% probability of exceedance (dry) are shown in Table. 6.3.

Table 6.3 Effective rain fall

Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Total

Rain fall

(dry year)

mm

68.0 69.0 75.0 106 75.0 22.0 5.0 3.0 3.0 5.0 9.0 11.0 451.0

Effective

rain fall

mm

30.8 31.4 36 60.8 36 3.2 0.0 0.0 0.0 0.0 0.0 0.0 198.2

Crop & Cropping pattern

The CROPWAT software allows unto maximum of 30 crops‘

data. It has some predefined crops and one can modify or edit the

properties of the crop which are inbuilt and can define new crops also

which are not present in the software. The crop properties include

name of the crop, first planting date, first harvesting, crop factors,

rooting depth, yield response factors, percentage of total area planted

and others are collected agricultural research station, Hyderabad, AP.

137

The CROPWAT model requires crop data over the different

development stages and defined as follow:

1. Initial Stage: It starts from planting data to approximately 10%

ground cover.

2. Development stage: It runs from 10% ground cover to initiation

of flowering

3. Mid season stage: It runs from initiation of flowering to the start

of maturity. The start of maturity is often indicated by the

beginning of ageing, yellowing or senescence of leaves, leaf

drop, or the browning of fruit to the degree that the crop

evapotranspiration is reduced relative to the 0ET

4. Late season stage: It runs from the start of maturity to harvest

or full senescence.

Data required for calculation of crop water requirement for non-rice

crops are crop name, planting date, crop coefficient cK , stages length,

rooting depth, Critical depletion fraction p and Yield response

factor ky .

6.5 CROP WATER REQUIREMENT

Estimation of the crop water requirement is derived from crop

evapotranspiration (crop water use) which is the product of the

reference evapotranspiration 0ET and the crop coefficient cK . The

reference evapotranspiration 0ET is estimated based on the FAO

Penman-Monteith method, using climatic data (FAO, 1977; 1998).

0*ETKET cc

138

Where:

cET = Crop Evapotranspiration

cK = Crop Coefficient

0ET = Reference Evapotranspiration

cET is computed for crops grown under optimal management

and environmental conditions. However, given that in most instances

crops are not under optimal conditions. aET is calculated by using a

water stress coefficient or by adjusting cK for different stress and

environmental constraints.

csa ETKET *

Where:

aET = Actual Crop Evapotranspiration, sK = Water stress coefficient

Yield response to Water Deficit

If crop water requirements are completely met from the available

water supply, then actual evapotranspiration aET takes place which

is equal to the rate of maximum mET . When the water supply is

insufficient, aET is less than mET (Doorenbos and Kassam, 1979) and

the yield reduction with the water deficit is expressed as

m

a

yET

ETK

Ym

Ya11

Where Ya = actual yield with the available water;

Ym= maximum yield that can be obtained where there is

no limitation of water; and

139

yK = yield factor.

It is economical to irrigate from the date of sowing when the

ratio of actual evapotranspiration to the maximum evapotranspiration

m

a

ET

ET is 100%.

6.6 IRRIGATION SCHEDULING

Irrigation scheduling is made, to predict the timing and amount

of irrigation at the farm level. Its main objective is to develop

indicative irrigation schedules, for the agricultural extension service to

promote better irrigation practices and for the irrigation service to

establish improved rotational delivery schedules. The calculations of

the irrigation schedules are based on a soil water budget, where on a

daily basis, the soil moisture status is determined, accounting for

incoming and outgoing water in the root zone. For the irrigation

scheduling, the data of climate/ 0ET , rainfall, crop and soil are

required.

6.6.1 Soil Type information

This is very much useful for knowing soil water storage capacity

and available soil moisture storage. For irrigation the soil water

storage capacity is defined as the total amount of water that is stored

in the soil within the plant‘s root zone. The soil texture and the crop

rooting depth determine this. A deeper rooting depth means there is a

larger volume of water stored in the soil and therefore a larger

reservoir of water for the crop to draw upon between irrigations.

Knowing the soil water storage capacity, allows the farmer to

140

determine quantity of water to apply at one time and how long to wait

for other irrigation. For example, the amount of water applied at one

time on a sandy soil, which has a low soil water storage capacity,

would be less than for a loam soil, which has a higher soil water

storage capacity. This is assuming that crop‘s rooting depth is the

same for both soils. Applying more water to the soil than can be stored

results in a loss of water to deep percolation and leaching of nutrients

beyond the root zone. Only a portion of the total soil water is readily

available for plant use. Plants can only extract a portion of the stored

water without being stressed. An availability coefficient is used to

calculate the percentage of water that is readily available to the plant.

The maximum soil water deficit is the amount of water stored in the

soil that is readily available to the plant. The crop should be irrigated

once when there is depletion of soil moisture. Once depleted this is

the amount that must be replenished by irrigation. It is also the

maximum amount that can be applied at one time, before the risk of

deep percolation occurs. However, in some cases leaching of salts is

desirable and extra irrigation would be desired.

Total available moisture in root zone (TAM) mm = (water content at field

capacity ( 33 / mm ) – water content at wilting point ( 33 / mm ))*rooting

depth. Readily available moisture (RAM) = TAM *fraction of TAM that

a crop can extract without suffering water stress. Depletion = Soil

moisture deficiency =Depth of Irrigation. Soil information for different

soils is collected from command area development office, AP, and is

shown in table 6.4.

141

Table 6.4 Soils information

S. No

Soil Type

Total

available moisture

mmm /

Max. infiltration

rate

daymm /

Max. rooting depth

cm

Initial

available moisture

mmm /

1 Light soil (FAO) 60 40 90 60

2 Medium soil (FAO) 290 40 90 290

3 Heavy soil (FAO) 200 40 90 200

4 Red Sandy 100 30 90 100

5 Red loamy 180 30 90 180

6 Red Sandy loam 140 30 90 140

6.6.2 Scheduling Criteria Options.

Optimal irrigation can be defined as the amount of irrigation

required from the first planting date of the crop to the date at which

readily available soil moisture had been used. The irrigation amount

will be equal to the soil moisture deficit, so that the soil moisture

deficit returns to zero after the irrigation and no water is wasted.

Application Timing: Watering or irrigation is done when entire

readily available moisture has been used up, so that the crop never

becomes stressed (Irrigation at critical depletion).

Application Depth: This is the irrigation amount calculated to

refill the soil moisture i.e. irrigate to return the soil to field capacity

(Refill soil to filed capacity).

Start of scheduling: It may be of any date during the growing

season of the crop but the default is to begin from the earliest planting

date of each crop

142

Initial soil moisture conditions: It is the date pertaining to initial

soil moisture deficit. The example soil files provided are all set to zero

moisture deficit. To avoid crop stress, calculated soil moisture deficit

should not fall below the readily available moisture content.

Development of irrigation schedule which fit our requirements

needs a systematic procedure in which several runs are made with

different timing and application options.

Run 1 (Optimal Condition)

Timing option : Irrigation at critical depletion

Application option : Refill soil to filed capacity

Evaluation Criteria : Interval variance

Application variance

Run 2

Timing option : Irrigation at fixed depletion [40 mm)

Application option : Fixed application depth (40 mm)

Evaluation Criteria : Interval variance

Run 3

Timing option : -

Application option : -

Evaluation Criteria : No irrigation (rain fed)

6.7 Results & Discussion

The simulated values of Crop water requirement cET , Net

Irrigation Requirement NIR and Gross Irrigation Requirements GIR

for the crops (Cotton, Chilies, Ground nut Kharif, Ground nut Rabi

143

and Pulses) under SLBC command area are estimated using

CROPWAT.

Irrigation schedules are also prepared using CROPWAT for the

crops of SLBC for different soils (Light soil, Medium soil, Heavy soil,

Red sandy soil, Red Loamy soil and Red sandy Loamy soil). The

results are tabulated and plotted in this section.

6.7.1 Crop water requirement for SLBC command area

Calculation of Crop water requirement can be carried out by

calling up successively the appropriate climate and rainfall data sets,

together with the crop files and corresponding planting dates. Crop

water requirements of different crops of SLBC are presented and

shown in Table 6.5 to 6.9

Table 6.5 Crop water requirements of Cotton

1. Crop: Cotton

Month 10

days Stage

Kc

coeff cET

daymm /

cET

daysmm 10/

Eff rain

daysmm 10/

Irr. Req.

daysmm 10/

Aug 1 1 0.35 1.33 13.3 10.9 2.4

Aug 2 1 0.35 1.27 12.7 11.1 1.6

Aug 3 2 0.35 1.25 13.7 14.2 0.0

Sep 1 2 0.46 1.58 15.8 19.0 0.0

Sep 2 2 0.62 2.11 21.1 22.6 0.0

Sep 3 2 0.78 2.72 27.2 19.0 8.2

Oct 1 2 0.94 3.37 33.7 15.0 18.7

Oct 2 3 1.10 4.04 40.4 12.4 28.0

Oct 3 3 1.16 4.29 47.2 8.6 38.6

Nov 1 3 1.16 4.32 43.2 3.3 39.9

Nov 2 3 1.16 4.36 43.6 0.0 43.6

Nov 3 3 1.16 4.32 43.2 0.0 43.2

Dec 1 3 1.16 4.28 42.8 0.1 42.7

Dec 2 4 1.15 4.22 42.2 0.0 42.2

Dec 3 4 1.05 3.95 43.5 0.0 43.5

Jan 1 4 0.91 3.56 35.6 0.0 35.6

Jan 2 4 0.79 3.16 31.6 0.0 31.6

Jan 3 4 0.66 2.88 31.6 0.0 31.6

582.4 136.2 451.3

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Table 6.6 Crop water requirements of Chillies

2. Crop: Chillies

Month 10

days Stage

Kc

coeff cET

daymm /

cET

daysmm 10/

Eff rain

daysmm 10/

Irr. Req.

daysmm 10/

Aug 1 1 0.60 2.28 22.8 10.9 11.9

Aug 2 1 0.60 2.17 21.7 11.1 10.6

Aug 3 2 0.60 2.13 23.5 14.2 9.3

Sep 1 2 0.68 2.35 23.5 19.0 4.5

Sep 2 2 0.79 2.71 27.1 22.6 4.5

Sep 3 2 0.91 3.18 31.8 19.0 12.8

Oct 1 3 1.00 3.59 35.9 15.0 20.9

Oct 2 3 1.01 3.70 37.0 12.4 24.7

Oct 3 3 1.01 3.73 41.1 8.6 32.5

Nov 1 3 1.01 3.76 37.6 3.3 34.3

Nov 2 4 1.00 3.76 37.6 0.0 37.6

Nov 3 4 0.97 3.63 36.3 0.0 36.3

Dec 1 4 0.95 3.50 35.0 0.1 34.9

Dec 2 4 0.92 3.36 33.6 0.0 33.6

Dec 3 4 0.89 3.35 36.9 0.0 36.9

481.5 136.2 345.3

Table 6.7 Crop water requirements of Groundnut Kharif

3. Crop: Ground Nut Kharif

Month 10

days Stage

Kc coeff

cET

daymm /

cET

daysmm 10/

Eff rain

daysmm 10/

Irr. Req.

daysmm 10/

Jul 1 1 0.40 1.90 19.0 10.3 8.7

Jul 2 1 0.40 1.63 16.3 10.3 6.0

Jul 3 2 0.44 1.72 19.0 10.9 8.1

Aug 1 2 0.64 2.42 24.2 10.9 13.3

Aug 2 2 0.84 3.05 30.5 11.1 19.4

Aug 3 3 1.05 3.73 41.1 14.2 26.9

Sep 1 3 1.12 3.90 39.0 19.0 19.9

Sep 2 3 1.12 3.82 38.2 22.6 15.6

Sep 3 3 1.12 3.92 39.2 19.0 20.1

Oct 1 3 1.12 4.01 40.1 15.0 25.1

Oct 2 4 0.99 3.65 36.5 12.4 24.1

Oct 3 4 0.70 2.60 28.6 8.6 20.0

371.6 164.2 207.4

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Table 6.8 Crop water requirements of Groundnut Rabi

4. Crop: Ground Nut Rabi

Month 10

days Stage

Kc

coeff cET

daymm /

cET

daysmm 10/

Eff rain

daysmm 10/

Irr. Req.

daysmm 10/

Oct 1 1 0.40 1.43 14.3 15.0 0.0

Oct 2 1 0.40 1.47 14.7 12.4 2.3

Oct 3 2 0.44 1.63 17.9 8.6 9.3

Nov 1 2 0.64 2.40 24.0 3.3 20.6

Nov 2 2 0.85 3.21 32.1 0.0 32.1

Nov 3 3 1.06 3.96 39.6 0.0 39.6

Dec 1 3 1.14 4.21 42.1 0.1 42.0

Dec 2 3 1.14 4.17 41.7 0.0 41.7

Dec 3 3 1.14 4.30 47.3 0.0 47.3

Jan 1 3 1.14 4.42 44.2 0.0 44.2

Jan 2 4 1.02 4.07 40.7 0.0 40.7

Jan 3 4 0.74 3.22 35.4 0.0 35.4

394.0 39.4 355.3

Table 6.9 Crop water requirements of Pulses

5. Crop: Pulses

Month 10

days Stage

Kc

coeff cET

daymm /

cET

daysmm 10/

Eff rain

daysmm 10/

Irr. Req.

daysmm 10/

Nov 1 1 0.40 1.49 14.9 3.3 11.6

Nov 2 1 0.40 1.50 15.0 0.0 15.0

Nov 3 2 0.54 2.00 20.0 0.0 20.0

Dec 1 2 0.79 2.90 29.0 0.1 28.9

Dec 2 2 1.03 3.79 37.9 0.0 37.9

Dec 3 3 1.15 4.33 47.6 0.0 47.6

Jan 1 3 1.15 4.45 44.5 0.0 44.5

Jan 2 4 1.14 4.55 45.5 0.0 45.5

Jan 3 4 0.68 2.98 32.8 0.0 32.8

287.3 3.4 283.9

146

Table 6.10 SLBC command area Crop Water requirements

S No

Crop Plant Date

Harvest Date

Area %

cET

mm

Eff. Rain

mm

Irr Req mm

1 Cotton 01/08 31/01 10 582.4 136.2 451.3

2 Chillies 01/08 31/12 30 481.5 136.2 345.3

3 Groundnut

Kharif 01/07 31/10 15 371.6 164.2 207.4

4 Groundnut

rabi 01/10 31/01 30 394.0 39.4 355.3

5 Pulses 01/11 31/01 15 287.3 3.4 283.9

From the Table 6.10 it is observed that Net Irrigation

Requirement for the crops Cotton, Chilies, Ground nut Kharif, Ground

nut Rabi and Pulses under SLBC command area using CROPWAT for

dry year are 451.3 mm , 345.3 mm , 207.4 mm , 355.3 mm and 283.9 mm

respectively.

6.7.2 Gross Irrigation Requirement for SLBC command area

Gross irrigation requirements of crops under command area of

SLBC, for crop wise and month wise are shown in Table 6.11 and

6.12.

Table 6.11 Gross Irrigation requirement for SLBC

S.No.

Crop Area in Acres.

Base period in

Days

NIR

cm

FIR= (NIR/0.65)

cm

GIR= FIR/0.7

cm

TMCft /

Lakh Acres

TMCft

1 Cotton 30000 184 45.13 69.44 99.2 14.17 4.25

2 Chillies 90000 153 34.53 53.14 75.91 10.81 9.78

3

Ground

nut Kharif 45000 123 20.74 31.91 45.59 6.51 2.94

4

Ground

nut Rabi 90000 123 35.53 54.65 78.07 11.15 10.04

5 Pulses 45000 92 28.39 43.66 62.37 8.19 4.03

Total requirement 31.04

147

From the Table 6.11 it is observed that Gross Irrigation

Requirement for the crops Cotton, Chillies, Ground nut Kharif,

Ground nut Rabi and Pulses under SLBC command area using

CROPWAT for dry year are 4.25TMCft , 9.78TMCft , 2.94TMCft ,

10.04TMCft and 4.03TMCft respectively.

Table.6.12 Monthly gross irrigation requirement of SLBC

S. No.

Month Cotton Chillies

Ground

nut Kharif

Ground

nut Rabi

Pulses Total gross

Requirement

TMCft TMCft TMCft TMCft TMCft TMCft 3Mm

1 Jul 0 0 0.32 0 0 0.32 9.06

2 Aug 0.04 0.9 0.84 0 0 1.78 50.40

3 Sep 0.08 0.62 0.79 0 0 1.49 42.19

4 Oct 0.8 2.21 0.98 0.33 0 4.32 122.33

5 Nov 1.19 3.06 0 2.61 0.66 7.52 212.94

6 Dec 1.21 2.98 0 3.7 1.62 9.51 269.29

7 Jan 0.93 0 0 3.4 1.74 6.1 172.73

Total 4.25 9.77 2.93 10.04 4.02 31.04 878.96

From the Table 6.12, Gross irrigation requirements for SLBC

command area using CROPWAT for dry year during July, August,

September, October, November, December and January are

0.32TMCft , 1.78 TMCft , 1.49TMCft , 4.32TMCft , 7.52TMCft , 9.51TMCft ,

6.1TMCft respectively. It is found that Gross Irrigation Requirement

for dry year is 878.96 3Mm (31.04TMCft ).

Gross irrigation requirements for SLBC command area using

CROPWAT run for an average year (cotton - 3.79TMCft , chillies -

7.43TMCft , groundnut kharif - 1.63TMCft , groundnut rabi -

148

9.11TMCft , pulses- 3.7TMCft ) is 25.66TMCft (726.61 3Mm ). Water

requirement for SLBC varies from 25.66TMCft to 31.04TMCft .

CROPWAT results are checked with manual calculation in every step

and found to be satisfactory.

6.7.3 Irrigation Scheduling for SLBC command area

Irrigation scheduling can be defined as a process by which the

timing and amounts of irrigation water applications are determined.

When irrigation water is insufficient appropriate schedule can

increase crop yields. It is a ―Management Tool‖ used to help farmers to

get their share of water supplied between different fields of crops, and

by the project manager to allocate water to canals and project area.

The schedule module essentially includes, producing soil water

balance on a daily step. The parameters used for the calculation of

soil water balance on a daily step are effective rainfall for dry year,

water stress coefficient ( sk ), actual Crop evapotranspiration ( aET ), root

zone depletion, net irrigation, deficit and irrigation losses. Irrigation

schedules for the crops of SLBC are prepared for different soil

conditions and different runs are shown in Tables 6.13 to 6.17.

Irrigation scheduling graphs are also shown for the crops of SLBC and

shown in Figs. 6.1 to 6.5.

149

Table 6.13 Summarized results scheduling runs for cotton

Run Net irrigation

mm

No of

irrigations

Total net

irrigation

(mm)

Schedule

efficiency

%

Yield

Reduction

%

Rain

Efficiency

%

Light soil

1 Variable 6 362 100 0 69

2 40 9 360 100 0 65

3 - - - - 43.6 69

Medium Soil

1 309 1 309 100 0 69

2 40 9 360 100 0 65

3 - - - - 1 69

Heavy Soil

1 185 1 185 100 0 69

2 40 9 360 100 0 65

3 - - - - 15.6 69

Red Sandy

1 Variable 3 289 100 0 69

2 40 9 360 100 0 65

3 - - - - 35.5 69

Red Loamy

1 165 1 165 100 0 69

2 40 9 360 100 0 65

3 - - - - 19.4 69

Red Sandy Loam

1 Variable 2 269 100 0 69

2 40 9 360 100 0 65

3 - - - - 27.3 69

150

Table 6.14 Summarized results scheduling runs for chillies

Run Net irrigation

mm

No of

irrigations

Total net

irrigation

(mm)

Schedule

efficiency

%

Yield

Reduction

%

Rain

Efficiency

%

Light soil

1 Variable 33 408 100 0 25

2 40 3 120 100 21.8 83

3 - - - - 45.3 83

Medium Soil

1 Variable 2 163 100 0 85

2 40 6 240 100 0 83

3 - - - - 45 83

Heavy Soil

1 Variable 3 170 100 0 85

2 40 6 240 100 0 82

3 - - - - 22.2 85

Red Sandy

1 Varibale 14 294 100 0 56

2 40 5 200 100 3 84

3 - - - - 37.2 84

Red Loamy

1 Variable 5 226 100 0 80

2 40 6 240 100 0 82

3 - - - - 24.7 85

Red Sandy Loam

1 Variable 8 235 100 0 70

2 40 6 240 100 0.2 82

3 - - - - 30.5 85

151

Table 6.15 Summarized results scheduling runs for Groundnut Kharif

Run Net irrigation

mm

No of

irrigations

Total net

irrigation

(mm)

Schedule

efficiency

%

Yield

Reduction

%

Rain

Efficiency

%

Light soil

1 Variable 7 149 100 0 61

2 - - - - 6.6 93

3 - - - - 6.6 93

Medium Soil

1 - - - - 0 93

2 40 2 80 100 0 83

3 - - - - 0 93

Heavy Soil

1 - - - - 0 93

2 40 2 80 100 0 83

3 - - - - 0 93

Red Sandy

1 Variable 2 77 100 0 83

2 40 2 80 100 0 83

3 - - - - 3.1 93

Red Loamy

1 - - - - 0 93

2 40 2 80 100 0 83

3 - - - - 0 93

Red Sandy Loam

1 51 1 51 100 0 91

2 40 2 80 100 0 83

3 - - - - 0.6 93

152

Table 6.16 Summarized results scheduling runs for Groundnut Rabi

Run Net irrigation

mm

No of

irrigations

Total net

irrigation

(mm)

Schedule

efficiency

%

Yield

Reduction

%

Rain

Efficiency

%

Light soil

1 Variable 14 323 100 0 58

2 40 5 200 100 15.3 64

3 - - - - 49.1 66

Medium Soil

1 Variable 2 214 100 0 64

2 40 8 320 100 0 66

3 - - - - 20.3 66

Heavy Soil

1 Variable 4 303 100 0 66

2 40 8 320 100 0 66

3 - - - - 30.1 66

Red Sandy

1 Variable 8 298 100 0 64

2 40 7 280 100 0.5 66

3 - - - - 43.5 66

Red Loamy

1 Variable 4 263 100 0 65

2 40 8 320 100 0 66

3 - - - - 32.6 66

Red Sandy Loam

1 Variable 6 312 100 0 66

2 40 8 320 100 0 66

3 - - - - 37.9 66

153

Table 6.17 Summarized results scheduling runs for Pulses

Run Net irrigation

mm

No of

irrigations

Total net

irrigation

(mm)

Schedule

efficiency

%

Yield

Reduction

%

Rain

Efficiency

%

Light soil

1 Variable 7 254 100 0 81

2 40 6 240 100 2.9 90

3 - - - - 55.6 90

Medium Soil

1 175 1 175 100 0 90

2 40 6 240 100 0 90

3 - - - - 5 90

Heavy Soil

1 123 1 123 100 0 90

2 40 6 240 100 0 90

3 - - - - 19.6 90

Red Sandy

1 - 30 179 100 0 90

2 40 6 240 100 0 90

3 - - - - 44.5 90

Red Loamy

1 Variable 2 219 100 0 90

2 40 6 240 100 0 90

3 - - - - 24 90

Red Sandy Loam

1 Variable 2 167 100 0 88

2 40 6 240 100 0 90

3 - - - - 33.7 90

154

6.7.3.1 Irrigation Schedule graphs for SLBC command area

The predominant soils in the SLBC command area are Red soils.

Under this group, loamy sands, sandy loams, sandy clay, loamy and

silt soils are covered. From the results of tables 6.13 to 6.17,

Irrigation scheduling graphs are prepared for optimal condition (Run

1) and Red Sandy loam soil condition.

Fig. 6.1 Irrigation scheduling graph for crop Cotton

Fig 6.1 represents 2 irrigations of variable depth on 113th day,

148th day after planting with a total net irrigation of 269 mm , where

schedule efficiency is 100%, yield reduction 0% and rain efficiency

69%.

155

Fig. 6.2 Irrigation scheduling graph for crop Chilies

Fig 6.2 represents 8 irrigations of variable depth on 6th day, 11th

day, 22nd day, 82nd day, 97th day, 109th day, 122nd day and 138th day

after planting with a total net irrigation of 235 mm , where schedule

efficiency is 100%, yield reduction 0% and rain efficiency 70%.

Fig. 6.3 Irrigation scheduling graph for crop Groundnut Kharif

Fig 6.3 represents 1 irrigation of 51 mm depth on 102nd day after

planting with a total net irrigation of 51 mm , where schedule efficiency

is 100%, yield reduction 0% and rain efficiency 91%.

156

Fig. 6.4 Irrigation scheduling graph for crop Groundnut Rabi

Fig 6.4 represents 6 irrigations of variable depth on 51st day,

65th day, 78th day, 91st day, 103rd and 119th day after planting with a

total net irrigation of 312 mm , where schedule efficiency is 100%, yield

reduction 0% and rain efficiency 66%.

Fig. 6.5 Irrigation scheduling graph for crop Pulses

Fig 6.5 represents 2 irrigations of variable depth on 47th day,

67th day after planting with a total net irrigation of 167 mm , where

schedule efficiency is 100%, yield reduction 0% and rain efficiency

88%.

157

6.8 DRINKING WATER DEMAND FOR SLBC COMMAND AREA

The much-delayed Srisailam Left Bank Canal (SLBC) Tunnel

Scheme of Alimineti Madhava Reddy Project (AMRP) is finally close to

becoming a reality. It would be a great relief for people of Nalgonda

region, the poorest and most drought prone district of Andhra

Pradesh. Presently, people of Nalgonda district are affected not only by

scarcity of water but also excess fluoride in groundwater, causing slow

poisoning. Today, the district is characterized by thousands of people

with paralyzing bone diseases, stooped backs, crooked hands and

legs, deformed teeth, blindness and other handicaps. Ground water in

the district has 10 parts per million (ppm) of fluoride in contrast to a

maximum permitted level of just 1.5 ppm.

In India on average the domestic consumption of water under

normal conditions for town population of 2 to 5 lakhs as per IS: 1172-

1971 is about 180 ltrs per head per day Population benefited by the

scheme in Nalgonda district are 4.5 lakhs.

Yearly drinking water demand = 29.45 3Mm

= 1.04 TMCft

= 1.6 TMCft

(Considering evaporation Losses, Percolation loses etc.,)

Drinking water demand can be drawn from Srisailam Reservoir

only in monsoon season (July-0.4TMCft , August-0.4TMCft ,

September-0.4TMCft and October-0.4TMCft ) and same can be stored

for remaining months.

158

Yearly total demand of water for SLBC gravity scheme is equal

to Crop Water demand (Gross Irrigation Requirement) and drinking

water demand, which is tabulated and shown in Table 6.18.

Yearly total water demand = 31.04 + 1.6 = 32.64 TMCft (924.26 3Mm )

Table.6.18 Monthly demand of water for SLBC gravity scheme

Month Crop Water

demand )(TMCft Drinking water demand )(TMCft

Total Demand )(TMCft

Jun 0 0 0

Jul 0.32 0.4 0.72

Aug 1.78 0.4 2.18

Sep 1.49 0.4 1.89

Oct 4.32 0.4 4.72

Nov 7.52 0 7.52

Dec 9.51 0 9.51

Jan 6.1 0 6.1

Feb 0 0 0

Mar 0 0 0

Apr 0 0 0

May 0 0 0

Total 31.04 1.6 32.64

From the table 6.18, the peak demand of water found to be in

the month of December is 269.29 3Mm (9.51TMCft ) which works out to

be a canal discharge of 100 cumecs . The duty at the head of the Dindi

Balancing Reservoir of SLBC gravity scheme is 10258.4 cumecha /

(88 sec/ cuacres ).

6.9 CONCLUSIONS

The above study provides a basis for the timing of irrigations

required under the given agro-climatic conditions and the system

capacity and in the preparation of project operation plans for the

optimal use of water both from seasonal incident rainfall as well as

project water. During the actual implementation of schedules ever,

159

these results will be quite helpful, if the climatic data on short term

and medium term basis could be forecast. The model CROPWAT can

appropriately estimate the yield reduction caused by water stress and

climatic impacts, which makes this model as a best tool for irrigation

planning and management. It is economical to irrigate from the first

day of sowing when the ratio of actual crop evapotranspiration to the

maximum crop evapotranspiration

m

a

ET

ET is 100%. Through timely

supply of water to SLBC command area, agricultural productivity

could be optimized and therefore development can be achieved.

Monthly demand of water includes crop water requirement and

drinking facility for SLBC gravity scheme are needed outflow from

Dindi Balancing Reservoir. Water demand of SLBC gravity scheme in

the months of July, August, September, October, November,

December and January are respectively 20.39 3Mm (0.72 TMCft ), 61.73

3Mm (2.18 TMCft ), 53.52 3Mm (1.89 TMCft ), 133.65 3Mm (4.72 TMCft ),

212.94 3Mm (7.52 TMCft ), 269.29 3Mm (9.51 TMCft ), 172.73 3Mm

(6.10TMCft ).