Water Budgeting for Integrated
Management and Introducing Watershed Concept for Coastal Ecosystem in India:
Future Vision
H.S.SENa, ANIL KUMAR SINGHb
and J.S.P.YADAVc
aFormer Director, Central Research Institute for Jute &
Allied Fibres (ICAR), WB, India, 91-33-700120, Email: hssen.india@gmail.com; bDeputy
Director General (NRM), Indian Council of Agricultural Research, New Delhi, India,
91-11-110012, Email: aksingh.icar@gmail.com; cFormer Chairman, Agricultural
Scientists Recruitment Board, New Delhi, India, 91-11-110 012, now deceased
ABSTRACT With a vision on source-wise water
allocation for irrigation for higher productivity and stability of the coastal irrigated
plains in India, an analysis shows need
for stepwise increase in water use under different modes along with
suggested increase in cropping intensity from 150 % to 225 % during 2020 to
2050. A Field Water Balance model has been utilized to estimate surface water
storage opportunities, which should gradually dominate over under ground water use
for stability of the coastal plain. It is suggested to introduce coastal watersheds
having multiple components for computation of overall water balance of the
ecosystem through integrated approach. Creation of new cadres is necessary for
appropriate planning through participatory approach and technology
dissemination in systems mode.
Key words.
Coastal ecosystem India, Water source-wise budgeting, Field water balance,
Watershed approach, Participatory appraisal
Introduction
‘Coastal
plain’ is the landward extension of the continental shelf or the sea and commonly
used for agriculture and allied activities as well as for few other
occupational purposes, but
aCorrespondence Address: Present
address 2/74 Naktala, Kolkata, West Bengal, India, 91-33-700047
is
generally distinctly differentiated from other ‘main’ components, viz. estuaries, coral reefs, salt marshes, mangrove swamps,
macrophyte dominated regions, continental shelves, etc. (Yadav et al., 2009;
Encyclopedia of Earth, 2007). Rather, coastal plains may, in
some cases, include few such main components within its spatial boundary, and
are in dynamic equilibrium with each other, together present a ‘coastal ecosystem’.
In other words, though at a given time the area under each component is well
demarcated and thus may be estimated with some degree of precision, it may
alter, even considerably, over a long time from one component to another or
vice versa because of geomorphologic changes due either to
or a combination
of natural, hydrological and anthropogenic factors, in
support of which there are plenty of examples all over the globe. This suggests
its vulnerable nature, extent of which is much more in this ecosystem than in any
other. While there should be practically no control
on the natural factors affecting stability of ecosystem, the other two deserve
attention.
It
has been observed, based on a study by Spanish researchers, how an
inappropriately planned coastal development could lead to increasing water
consumption to unsustainable levels in Europe
(European Commission, 2007). They inferred that future
planning for sustainable development, based particularly on water resources,
should be such as not to disturb the ecosystem in the long run. Potential
threat for unplanned use of Ganga river water to destabilize the coastal
ecosystem across both India and Bangladesh has been highlighted by Sen (2010). In
spite of the coastal ecosystem presenting a delicate equilibrium among
different components there is, however, no firm strategy, as of now, for
exploitation of water resources for irrigation and other purposes for long term
solution in any sector in most countries including India. There is thus always
an utmost need for laying maximum emphasis on technological developments on
conservation and efficient utilization of the available water resources as well
as their management aspects including capacity building in any ecosystem.
The paper utilizes
a Field Water Balance approach, for source-wise water allocation for
irrigation, which may form the basis, in the first hand, for working out
strategies for future planning for irrigation during the coming four decades
for the coastal plains in India. Concept of coastal watersheds, on the other
hand, with due consideration to multiple components under it has been
introduced in this paper for computation of overall water balance, being the
main component other than climate, towards stability of the ecosystem through an integrated approach.
Water Budget
IWMI analysed that globally, out of 110,000 cubic kilometers
rainfall received annually, about 56 % is evapotranspired by various landscape
uses including bioenergy, forest products, livestock grazing lands and other
forms of biodiversity, and 4.5 % by rainfed agriculture including crops and
livestock, in addition to another 2 % utilized for irrigated agriculture,
aquaculture and livestock either directly from rainwater or through withdrawal
from the ground water. The balance about 38 % comprises of evapotranspiration
losses from open surface sources like rivers, wetlands, lakes, etc. for supporting
aquaculture, other forms of biodiversity (1.3 %), cities and industries (0.1
%), and run-off losses (36 %) to the ocean (Molden, 2007). The
colossal loss of 36 % water holds the key to create higher storage
opportunities by reducing the run-off losses. In the coastal watershed being at
the lowest topographical elevation the scope for intervention of run-off amount
received from the upper reaches should be much higher, and thus the scope for
higher storage.
On the other hand, in view of the susceptibility of the
coastal plains to seawater intrusion and its adverse impact on soil and plant
growth the practice for use of ground water, even if in small quantity, for
irrigation should be very carefully exercised, for which suitable optimization
model may be used (Da Silva et al.). In India, sufficient evidences are by now
available of seawater intrusion due to over-extraction of under ground water in
coastal areas (Talati, 2007), and therefore it becomes imperative to restrict use of under ground water
in this region by increasing the surface storage of water through either direct
interception or run-off from upper catchments by an equivalent amount or more. A
field water balance approach is therefore proposed for source-wise water
budgeting as road map for the coming four decades for India with main
consideration that the water management in the coastal plains should
principally revolve round creating fresh surface water sources to their
potential limits and their proper management with minimal dependence on the
subsurface source in order to maintain stability of the ecosystem.
Field Water Balance
Equations
The agricultural field water balance for storage during wet
season and recycling may be computed from the following equations.
neglecting
and
, the equation (1) becomes
which may be re-written as,
In equation (1) through (3)
is the annual
precipitation (average 1200 mm for the whole country) and
is the precipitation received through direct
interception during wet season only, which is at least 80 % of the annual (Sen
et al., 2000), over the whole catchment in the coastal plain,
is the contribution due to capillary rise, which may
be neglected during the wet season under consideration,
is the run-off contribution from upstream, which may
also be neglected, being site specific and highly variable depending on the
hydrological characteristics of the adjoining catchment areas, for the purpose
of this estimation,
is the deep
percolation (vertical) loss of water,
is the
evapotranspiration loss, and
represents all
other forms of loss including biological need of the aqua species, etc. The
losses (
+
+
) referred above are computed for the entire year from
the areas under storage reservoir (recommended to use one-fifth of the holding)
only (Ambast et al., 1998), since the corresponding losses from the cropped area,
especially during dry season, may be considered as relatively negligible.
is the net
change in moisture storage in the soil
profile, which is taken as negligible (no net loss or gain), at the end of the
wet season after meeting above components of the equation, and allowing excess
water,
, being the amount of run-off, to be stored at the
appropriate locations down the slope.
is the gross cropped area in the catchment (total area
x cropping intensity factor), and
is the
irrigation efficiency factor after meeting conveyance loss, etc., which is
expected to improve with increase in area should irrigation system become more
efficient along with improvement in related infrastructural arrangement with
time. Irrigation efficiencies of surface systems may range
between about 30 and 60 %, conservatively estimated for the rice-oriented
cropping system. Sprinkler systems generally achieve efficiencies in the range
of 60–85 %, and drip systems commonly operate at 85–95 % efficiency (Rawitz,
2008), when considered alone for the upland non-rice crops, for
example.
We have, however, assumed in our calculation irrigation efficiency (
) to increase from 60 – 75 % during the
period.
Source-wise Water Allocation
Based on average soil hydrological and meteorological data for
the coastal areas in India (Sen et al., 2000; Bandyopadhyay et al., 1988; Sen,
1992) different components of the Field Water Balance have been
computed approximately using equation 3 and shown in Tables 1 and 2. The first
term of the LHS in equation 3 designates the net total (potential) storable
amount in the surface reservoir based on rains received during rainy season and
the second term of the LHS designates annual loss of water from the reservoir under
different processes throughout the year. Neglecting the scanty rainfall during
post-monsoon period, being insignificant relative to
towards contribution to storage of water, the
difference between the LHS and RHS of equation 3 becomes the net surface amount
(
) stored during rainy season (Table 2). This (
) is a conservative estimate mainly for reasons, viz.
(i)
has been neglected, in other words, only direct interception
has been considered, (ii) precipitation has been considered for wet season
only, while (iii) losses have been
considered for the whole year. The cropping intensity, which varied from 125 –
134 % only in 1994 (Sen et al., 2000; Subba Rao et al., 1994) in the coastal
areas of the country, has been assumed to reach a value of 150 % in 2020,
200 % in 2030, and 225 % in 2050. In the coastal areas of Orissa, the cropping
intensity at present was worked out to be 150 % (Singhandhupe et al., 2007). The
corresponding annual water requirement of the cropping system (assuming entire
area under rainfed rice during monsoon with 1 m water requirement and non-rice
crop in the post-monsoon period with 0.3 m irrigation requirement) is thus expected
to increase with time with creation of more water resources, as advised by Government
of India (Planning Commission, 1981), from 1.15 m in 2020 to 1.375 m in 2050
(Table 3).
, when multiplied with total water requirement for the
cropping system, gives rise to total irrigation
amount required (Table 3).
In our calculation, the net storable amount at the surface
(col. 4, Table 3) has been drawn from Table 2 (
, col. 6). Difference in annual irrigation
water volume and the surface storable amount is the total annual deficit, which
should be met from other sources, viz. sub-surface, conjunctive use of mild
saline water, and other sources, say desalinated saline water, etc. Apportions
of the deficit water among the last three sources (Table 3) mentioned, though
strictly not based on rigid calculation, have its basis on the current trend in
limited data available and their desired projections suggested by a few.
The data in
Table 3 provide source-wise water allocation for irrigation for the coastal
areas. The trend suggests increase in water storage for each source with
increase in gross cropped area over time (Figure 1). Although, initially there
may be possibility for higher use of sub-surface water for irrigation than for
the surface (
) the latter has the scope to gradually dominate over
the former in due course, since the surface water storage opportunity has increased more rapidly in our
calculation than the annual volume of irrigation water
required with increase
in cropping intensity assumed over the period.
Planning may
be made accordingly. It is especially for the reason that the under ground
water use should be discouraged particularly for the coastal region for
ecological reasons as explained earlier (section 1). It may be borne in mind that in the
estimation of surface water storage (
) only direct interception of rainwater was considered
and the run-off water from the upper catchments, which may be substantial in many
cases, was not considered, suggesting much larger scope for surface water
storage in actual (Gupta & Deshpande, 2004), than that projected here, in
future planning.
According to Government of India, the ground water irrigation has
been developing for the whole country (available
resource is 399 bcm) at an explosive rate, while tank irrigation has declined
fast and surface water irrigation grew much more slowly in the recent times. Over the last two decades, 84 %
of the total addition to net irrigated area came from ground water, and only
16% from canals (Ministry of Water Resources, 2006). According to World Bank
assessment (World Bank, 2005) in 2005 ground water supplies support 70 % of the
irrigated area. Discussion on ground water management for coastal areas has
been made by Dhiman & Thambi of CGWB, though the issue was not adequately addressed.
Appropriate planning should, therefore, be made, based on location-specific
considerations, to reverse the trend for under ground water use, if not, arrest
the same immediately for the coastal areas. The suggested trends have been
projected in Table 3 and Figure 1.
Among
other sources, suitability for use of marginally saline water in rivers,
canals, etc., available in plenty in coastal areas, is judged based on potential
severity of the problem following its long term use (Ayers & Westcot, 1994). Details of such works with special reference to
India have been discussed (Minhas & Rao, 2007 and Gupta, 2008). The former
workers emphasized the use of fresh water layer floating on the denser (saline)
under ground water through skimming, while both suggested conjunctive use
through judicial combination of saline and fresh water available at the surface
and at subsurface depths. The scope for conjunctive use for improvement of crop
yield has been considered to be a useful way for vegetable production, in
particular, in other countries, particularly in coastal areas having limited
fresh water resources, notable among which are Hanoi (Viet Nam) and Kumasi
(Ghana) (Molden, 2007). The data provided (Table 3 and Figure
1) suggest increasing scope of conjunctive use of saline water with time, and should
hold considerable promise in India, if properly planned.
There is also scope to use highly saline seawater through use
of desalination plants, though no attempt has been made so far for its significant
use for irrigation in India, mainly for economic reason and for lack of
infrastructure. The large energy reserves of many Middle Eastern countries,
along with their relative water scarcity, have led to extensive construction of
desalination in this region up to 75 % of total world capacity. Other countries
for potential use of this technology are USA and Australia (Wikipedia, 2009 and
State Government of Victoria, 2009). In India, since 1970, there
has been significant development using various desalination technologies at Kalpakkam
with production cost at about Rs. 50 m-3 (Kumar et al., 2005).
Desalination, as currently practised, mostly uses fossil fuels. Solar and wind
energy are available in abundance in coastal India and may be explored as
alternative sources for this purpose. It is expected that if the cost comes
down and alternate energy sources are used, desalinization might become
commercially viable in due course (Kumar et al., 2005). We have suggested scope
for increasing use of this technology for irrigation (Table 3, Figure 1).
Coastal zone, Management
Issues and Capacity Building
The
law (Ministry of Environment and Forestry, 1991) on Integrated Coastal Zone
Management was passed by the Government of India in 1991 restricting activities
up to 500 m from the High Tide Line (HTL) and declaring the land between the
Low Tide Line (LTL) and the HTL as “Coastal Regulation Zone” (CRZ)”.
Potentiality of increase in water productivity in the low
productivity areas was classically shown (Zwart &
Bastiaanssen, 2004) for maize, wheat,
cotton and rice. Potentiality for such increase does still exist in South Asia
and in the Sub-Sahara African countries under rainfed agriculture. Coastal
plains represent in general typically low productivity areas. It has been
emphasized to develop a new paradigm of soil and water management based on a
holistic approach with focus on natural resource conservation, in the line
suggested in the earlier section, to reach for the desired productivity level
under rainfed agriculture (Wani et al., 2008), and for coastal areas (Sen et al., 2000) through multiple-use
approach, like introduction of aquaculture, livestock, and allied activities
available in abundance.
Capacity building should be viewed in systems perspectives in
terms of various commodities and levels of environmental management aspects in
use. Education, research, capacity building, and awareness creation are the
integral steps. It is also suggested that a new cadre of policy makers,
managers and extension providers is needed for appropriate planning through
farmers’ participatory appraisal and technology dissemination along with power
for governance. Under certain circumstances, collective water rights might be
preferred to individual rights. A hierarchy of management staff should thus be
created at basin, regional, state and national levels, and the plans should
invariably be integrated in systems mode with other issues for coastal area
development.
Watershed Approach
Because watersheds
are defined by natural hydrology and ultimately drain to coastal waters, they
are a good focal point for managing coastal resources. For India and other
countries with significant coastline having high degree of vulnerability, either
the regions should be clearly identified as ‘coastal sub-watersheds’, as practiced in USA and a few other developed
countries, or the regions within the existing watersheds should be delineated
with separate mandates.
Hydrology of the Coastal Watershed:
A Model
It
is desirable, therefore, to delineate the coastal area within each unit of the
watershed identified. It may be worth attempting to estimate the surface water
balance for coastal sub-watershed with integrated approach for precision in the
management of water which forms the key component for development. It is proposed that the following model
may be used for the computation of net surface water storage over a long time.
We assume, at this stage, that prior steps have been taken for effective
control of seawater surge during climatic disaster, etc. or its intrusion into
subsurface aquifer due to human interferences or other reasons. The model is described below:
where,
represents time varying from
to
;
represents the space or location within the sub-watershed;
and
represents any
single component, varying from
to
.
is the total water storage, to be computed with the
help of Field Water Balance approach at a given time, and thereafter integrating
over the entire sub-watershed area comprising of different components for the entire
time period.
is the (direct)
precipitation at a given time;
is the net
recharge from or to the adjoining catchment at a given time;
represents function of water storage, as expressed
below, with respect to each coastal ecosystem component, like estuaries, coral
reefs, salt marshes, mangrove swamps, macrophyte dominated regions, continental
shelves, etc., at a given time; and
, equivalent to
(used in equation
3), is the balance amount of water lost
as run-off, depending on the intensity and distribution of rainfall and other
soil and sub-watershed characteristics, from each component, over the entire
period.
where, say,
is function of
water status in cropped field depending on type of crop grown along with crop
coefficient value, its stage of growth, extent of vegetative cover, status of
soil salinity and other hydraulic properties,
is function of
potential evaporation from free water surface in the reservoirs and other water
bodies depending on climatic parameters;
is function of
evapotranspiration loss of water from forest and other wetland vegetation
depending on the nature of vegetation and stage of growth along with crop
coefficient value for each, extent of cover, soil moisture and salinity status;
is the function of biological water need for animal
species and aquatic flora and fauna; while
represents change in hydrological properties as a
function of sedimentation received from the upstream; and so on. There could be
many other location specific considerations, like toxic concentration of
nutrients, eutrophications, etc., and above all the effect due to global climatic
change on each parameter to affect plant growth and hydrological balance in the
long run. Coastal sub-watershed thus represents an extremely complex situation
comprising of a variety of parameters, for many of which we have no proper
knowledge of the various biotic and abiotic factors and their interrelations.
Yet, one needs to make an attempt, to the least, for computation of overall water
balance based on this integrated approach, although its success depends upon
the methodologies used for the estimation of different parameters along with accuracy
of the functional relationships developed for each, their nature and extent of
variation, both spatially and temporally, and the initial and boundary
conditions assumed in close proximity to the actual.
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Table 1. Different components of loss
from the water storage reservoir computed with the help of Field Water Balance
equation 3
Evaoptranspiration
loss (
|
Deep
percolation loss (
|
Other forms of loss
(
|
Total lossc
0.2 (
|
||
Average
daily
|
Average annual
|
Average daily
|
Average annual
|
||
(1)
|
(2)
|
(3)
|
(4)
|
(5)
|
(6)
|
0.005
|
1.83
|
0.03
|
11.0
|
3.5
|
3.27
|
aSen et al., 2000; Bandyopadhyay et al., 1988;
Sen, 1992; bMolden (2007);
cStorage reservoir is assumed to occupy
one-fifth of the total cropped area (Ambast et al., 1998)
Table 2. Computation
of net storable amount (projected) from different components with the help of
equation 3 in different years
Year
|
Cropping intensitya
(%)
|
Gross cropped area (
|
Irrigation efficiency factor (
%
|
Potential storable amount (
|
Net storable amount
(Col. 5─Total loss of stored waterc) (
Mha-m
|
(1)
|
(2)
|
(3)
|
(4)
|
(5)
|
(6)
|
2020
|
150
|
16.17
|
60
|
9.22
|
5.95
|
2030
|
175
|
18.86
|
65
|
11.65`
|
8.38
|
2040
|
200
|
21.56
|
70
|
14.34
|
11.07
|
2050
|
225
|
24.26
|
75
|
17.29
|
14.02
|
aSen et al., 2000;
Subba Rao et al. 1994; bTotal rainfall during monsoon (
) = 0.95m (Sen et al., 2000); cTotal loss
of stored water = Col. 6 of Table 1
Total coastal area in India = 10.78 Mha (Velayutham et
al., 1998)
Table 3. Projected source-wise
allocation of water in different years based on Field Water Balance (equation 3)
Year
|
Annual water require-ment for
the cropping system,
m
|
Annual volume of irrigation
water for the cropping system
(
Mha-m
|
Source-wise allocation of water, Mha-m
|
|||
Surfacea
(
|
Sub-surface
|
Conjunctive use
|
Other sources (viz., desalinated
seawater)
|
|||
(1)
|
(2)
|
(3)
|
(4)
|
(5)
|
(6)
|
(7)
|
2020
|
1.150
|
18.60
|
5.95(31.99)
|
8.0(43.01)
|
3.0(16.13)
|
1.65(8.87)
|
2030
|
1.225
|
23.10
|
8.38(36.30)
|
9.0(38.96)
|
4.0(17.32)
|
1.72(7.45)
|
2040
|
1.300
|
28.02
|
11.07(39.50)
|
10.0(35.69)
|
5.0(17.84)
|
1.95(6.96)
|
2050
|
1.375
|
33.36
|
14.02(42.03)
|
10.5(31.47)
|
6.5(19.48)
|
2.34(7.01)
|
aCol. 6 of Table 2; Data in parentheses
suggest percent allocation with respect to annual water required under Col. 3.
|
Fig. 1. Percent water allocation
source-wise with respect to total amount of irrigation water of the
cropping system and gross cropped area per year during coming four decades
in the coastal areas of India
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