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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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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
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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
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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 ).