Water Management
under Rainfed Ecology: Rainwater harvesting technologies for crop and water
productivity
A. Zaman
Emeritus Professor
Centurion
University of Technology and Management
MSSSoA,
Paralakhemundi-761 211, Odisha
Former Head,
Irrigation Expatriate Team, The Government of Uganda, East Africa
INTRODUCTION
Water in
the ground is stored in the interstices (inter-particulate spaces) of the soil
or rock that usually forms earth. Rainfall occurs on the surface of the earth
that of a portion percolates through soil and moves downwards under effect of
gravity, said to be infiltration, gets filtered in the process of passing through
the pores. Thus groundwater aquifers are formed over many years. Indiscriminate
use of ground water that caused a drastic depletion of the ground water table
and which resulted a lot of serious problems. Ground water reservoir was
primarily replenished by the annual precipitation received in a particular
area. The rate of entering water to ground water reservoir was depended on
pattern of rainfall, run-off, stream flow, permeability of the soils and earth
materials present prior to reach the water up to the zone of saturation.
Introduction high
yielding irrigation-responsive cultivars of rice and intensive cropping system
three to four crops in a year in the same land required huge amount of water.
This water was supplied from ground water resources. The deep and shallow tube
wells were dug indiscriminately. As a resulted the ground water is depleted
rapidly and creating severe health and environmental hazards. The objectives of the papers dealt with
efficient harvesting of rainwater, its conservation and utilization for
sustainable agriculture.
The situations prevail
Water became a
serious concern in urban as well as rural India. In Maharasthra, only at Aurangabad,
more than 30 million of people or every third person in the state, reportedly had
been depended on tankers for their daily water supply. In Surendranagar, six
out of ten bore well yielded no water even at at the depth of 1,200 feet and
over 2.5 crore of people are in distress. In Rajasthan, at least four trains
fetch 6 million litres of water from Jodhpur for four lakhs people in only Pali
district, become designated as desert state of the country. The drying up of
Usman Sagar in Hyderabad, one of the main sources of drinking water in the city
has become news to push the people to brink. It has been reported that only 34
of 116 municipalities in Andhra Pradesh get regular water for one hour twice a
week. 100 million people in 35 big cities face at least 30 per cent cut in
supply of fresh drinking water. In Bangalore, water is rationed twice a week,
in Bhopal, 30 minutes a day, 250 tankers make 2250 trips to quench Chennai
thirst. In rural India is far away from water tap-culture, the situation is
worse off as groundwater level plunged in at least 220 out of 593 districts.
Villagers used to trek water from miles. 15 million people are affected by
arsenic poisoning, 66 million people in 200 districts become at the risk of
fluoride and heavy metals contamination. The situation aggravated with heavy
uses of chemicals (inorganic fertilizers, pesticides, fungicides and
herbicides) in agriculture, its residual toxicity that come though food chain
resulted diarrhea, dysentery, kidney problems like thousands of health hazards
apart from severe water borne diseases.
Thus water became biggest crisis in terms of spread and
severity. This became the serious concern of the researchers, policy makers and
other stakeholders.
Table 1: World Water Availability Pattern:
Forms
of water
|
%
of availability
|
1.
Sea and Ocean
|
97.208
|
2.
Ice and Iceland
|
2.150
|
3.
Atmospheric water
|
0.006
|
4.
Ground water (Under the ground)
|
0.625
|
5.
Surface water (Lake, River, Pond)
|
0.001
|
Source: MoWR, 2011
Status of Groundwater
Bouwer (1978), a
renowned hydrologist first reported that nature’s way of storing water is under
ground, where about 98% of the entire world’s liquid and fresh water occurs.
And mostly 2% occurs in streams and lakes, which often are fed by groundwater
as a dependable source, less affected by the vagaries of climate.
Indiscriminate use of groundwater particularly with introduction high
irrigation responsive photo-insensitive short duration rice varieties
throughout the year caused a drastic depletion of the ground water table and resulted
to have been complicated problems. Ground water reservoir was primarily
replenished by the annual precipitation received in a particular area. The rate
of entering water to ground water reservoir was depended on pattern of
rainfall, run-off, stream flow, permeability of the soils and earth materials
present prior to reach the water up to the zone of saturation. The total water
resource of the country comes about 400 million ham and total amount of surface
flow throughout the year in our country is estimated as about 180 mham, out of
which about 105m ham comes from annual rainfall. And estimated ground water
recharge per year is about 67 mham, out of which about 50 m ham comes from
rainfall. So there was enough scope to increase the amount of rechargeable
ground water adopting ways and means. Introduction high yielding
irrigation-responsive varieties of rice and intensive cropping system three to
four crops in a year in the same peace of land required huge amount of water.
The water was supplied from ground water resources. The deep and shallow tube
wells were dug indiscriminately. As results, the depletion of water table
occurred to be severe.
In this context, it was very much important to have the
access as much as the excess water could be added to underground reservoir
during the period high to medium rainfall, the possibilities of occurrence of
flood would be drastically reduced. And as the water table would come to rise,
the re-cycling of water during the period of drought would become easier and
safer. There was clear indication that several soil conservation and
water-harvesting measures could increase the ground water recharge up to a
certain limit. In India, groundwater recharge from open wells and pits are very
common practices in Orissa, Gujrat and Rajasthan. That’s why greater
exploitation of ground water prior to rainy season provided scope of greater
quantity to infiltrate during high rainfall period. The use of surface water
would become also to be more effective and helpful to mitigate the arsenic like
problems. As the possibility of contamination of arsenic are very less in
surface water; only the flowing surface water is the safest source that is free
from arsenic. In this context, it is essential to add ground water as much as
possible taking all possible measures for its purification (avoiding all sorts
of contamination following de-germs chambers to be constructed for the purpose)
and taking off water at need without hampering the water table depletion.
Table 2: Demand and
Supply of Water Resources in India
Demand and supply
|
Km3
|
1. Amount of surface
water resources
|
1880
|
2. Amount of
usable surface water
|
690
|
3. Amount of
usable ground water
|
418
|
4. Total usable
water
|
1108
|
5. Water demand
in 2002
|
780
|
6. Water demand
in 2025 (Estimated)
|
1200
|
Source: MoWR, 2011
Table 3: The water
resources scenario in India
Annual Average
Precipitation
|
1140 mm
|
Total Available
water
|
400 million ha
|
Net area sown
|
145 million ha
|
Gross cropped
area
|
175 million ha
|
Irrigated area
|
70 million ha
|
Water demand for
irrigation
|
46 million ha
|
Source:
CGWB Annon, 2014
Groundwater vis-Ã -vis Rainwater harvesting
Over extraction of
groundwater leads to an imbalance in reserve as the withdrawal of water exceeds
recharge. Agriculture, as largest stakeholder of water use sector might be
responsible for this alarming situation prevailed. The monsoon usually breaks
in the month of June-July and ends by October confined to few months only. The
heavy amount of rainfall within a shortened time causes maximum river flows
during this period. Thus the available water resources are ill-distributed
resulting seasonal abundances. As the
flows could not be utilized fully, it sometimes causes devastated flood in some
areas that resulted wastage of the water resources. Ironically, Cherrapunji
receives about 11,000 mm annual average rainfalls that also suffer from acute
shortage of drinking water. Hence, it has got prime important to store such
excess water during the period of heavy rainfall in the reservoirs for its
subsequent uses.
Water harvesting is
the activity of direct collection of rainwater that could either be used
directly or could be recharged in to the ground. The activities of water
harvesting not only involved collection and storage of excess rainwater but
also harvesting surface and groundwater, prevention of losses through
evaporation and seepage with all possible hydrological studies and engineering
interventions, aimed at conservation and efficient utilization of this limited
water endowment of physiographic unit termed as watershed.
India is fortunate enough to receive an average
rainfall of at least 1170 mm, higher as compared to global average of 800 mm.
The amount of water
received in the form of rainfall over an area is called rainwater endowment of
that area. The amount of water could be effectively harvested is called as
water-harvesting potential. That could be computed with multiplying amount of
rainfalls and collection efficiency.
Under these stated
conditions, ground water recharge to be increased substantially assuring the
greater recharge of the aquifers. It could only be possible by larger
exploitation of ground water that might be resulted lowering down pre-monsoon
ground water table. The upper limit of the groundwater extraction should not be
extended more that annual amount of recharge. But actually, introduction of
intensive agriculture with high yielding fertilizer and irrigation responsive
photo-insensitive short duration rice cultivars that grow three/four times a
year that required high volume of water which is being extracted from the
ground water. Its crossed its upper limit and posed severe problems lowering
the water table. The problem of arsenic, iron concentration increased severely.
The natural springs abolished from the farmers’ field. The hand pumps are not
workable at various places. The sands are coming with ground water extraction
through submersible pumps. The deep tube wells are being inaction at several
places. This is the serious concern of the farmers.
There was clear
indication that several soil conservation and water-harvesting measures could
increase the ground water recharge up to a certain limit. Ground water recharge
from open wells and pits are very common practices in Orissa, Gujrat and
Rajasthan. That’s why greater exploitation of ground water prior to rainy
season provided scope of greater quantity to infiltrate during high rainfall
period. The use of surface water would become also to be more effective and
helpful to mitigate the arsenic like problems. As the possibility of
contamination of arsenic are very less in surface water; only the flowing
surface water is the safest source that is free from arsenic. So there was an
endeavor to add the ground water as much as possible taking all possible
measures for its purification (avoiding all sorts of contamination following
de-germs chambers to be constructed for the purpose) and taking off water at
need without hampering the water table depletion.
Efficient
Rainwater Management
The amount and
pattern of annual rainfall in India is clearing indicating the necessity of
tapping excess runoff water during medium to heavy rainfall period for it’s
recycling and its effective utilization for crop cultivation during rainless
period. As water harvested by these means are expensive and limited, a careful
planning in installation of such structures as well as its proper utilization
is very much essential. The objective of rainwater management is mostly to
provide life saving irrigation to crop to obtain as much as possible yield per
unit of water used where water is usually applied at specific physiological
growth stages of crop to improve its quality and yield. Hence, rainwater
management needs more careful observations pertinent to specific land
situations and crops to be grown.
Water Harvesting Structures
To take
protection and prevention against undependable and erratic rainfall, it is
essential to collect excess rainwater, which usually flows unused and waste
through runoff. Depending upon the soil, climate, amount of runoff available,
land situation and crop choice, a number of water harvesting structures is
popular throughout the World. Such as farm ponds (lined and unlined), small
water tanks, small earthen dams, water harvesting bundhis and stop dams.
On-farm
Water Management
Adoption of proven
and efficient water management technologies are essential to maximize crop
production and minimizing gap between irrigation potential created and
utilized. Application losses due to conveyance, methods and scheduling of
irrigation also are effective in this direction. Selection of crop(s) and crop
sequence(s) also played an important role for enhancement of water use
efficiency through crop cultivation and related agronomic practices.
Conservation, distribution and utilization of irrigation water are the basic
parameters of on-farm water management. Optimum scheduling of irrigation,
suitable method adoption, conjunctive use of rain, surface and ground water for
crop cultivation having improved agro-technology adoption and provision of
drainage. Application of proper amount of water at proper time increased the
water use efficiency and crop yield maximization with given amount of water
reducing evaporation and deep percolation. Scheduling of irrigation with
limited water availability is a big challenge to the irrigation experts that
needs rigorous research.
The possible
solutions and recommendations
(1)
Development of micro-level water resources
(tank-well system, small springs, perennial and seasonal streams) with a
command of 2-10 ha to reduce dependency on major and medium irrigation projects
through R & D projects should be explored;
(2)
Effective harvesting of excess rainwater
during heavy to medium rainfall period as well as artificial recharge of groundwater
should fully be exploited wherever possible through participatory research and
development along with mass awareness program;
(3)
Planned intervention is required to reduce
the negative effects of surplus groundwater exploitation by two-fold actions: (1)
to control excessive draw down and (2) to prevent water quality deterioration
and degradation.
(4)
The gap between technology generation and
adoption in the farmers’ field is to be minimized; The methods, systems,
scheduling of irrigation based on different approaches, its transformation in
farmers’ language, water-harvesting structures and water-lifting devices, water
measurement should come into farmers’ practices.
(5)
An action plan should be prepared to
address the problem of water logging during monsoon period to increase the
water productivity, alternate/multiple use of water, crop diversifications and
by other suitable measures for which assistance from State Department of
Agriculture, Government of West Bengal may be called for;
(6)
Coordination amongst all the water related
ministries in national and state levels are very much important that could only
ensure proper and efficient water resource utilization.
(7)
The problems and prospect of major and
medium irrigation command should be studied in depth and participatory water
management research as well as on-farm research on adoption of irrigation
scheduling to be conducted through on-farm water management approaches;
