Accepted Papers - 3.pdf - UNESCO

INTRODUCTION
Indian water sector is confronted with the
controversies of inter-state disputes vs. integrated
basin development, reliance on water-shed
development vs. reservoir projects, government
owned vs. private utilities and large vs. small
projects. On one side, the technological advances in
the fields of meteorology, hydrology, geology,
seismology and the techniques of investigation,
planning, construction and operation of the projects
are making possible the optimisation of scarce
national resources. On the other hand, a fear
syndrome has been created against river valley and
hydro projects by exaggerated likely or assumed
adverse environmental impacts and by ignoring or
suppressing their need and tremendous benefits by
few non-credible NGOs like NBA and novelists self
styled activists. As a result, many potential economic
developmental activities, which could generate
wealth and employment in India have been blocked
in large cities, towns and villages due to acute
shortage of water especially during the dry season.
At the same time, fury of floods routinely continue
to affect the economic activities causing large scale
loss of life, properties and flora & fauna.
Widely prevalent beliefs about the role of land
use and its relation to hydrology must be critically
examined in the light of scientific evidence. Simplistic
views have created a mindset which not only links
degradation with less forest but also rehabilitation &
conservation with more forest. Most of the people
imply the inevitable link between the absence of
forests and ‘degradation’ of water resources. Same
is the situation about relation to forestry, agro forestry
and various hydrological elements; even though
claims by enthusiastic agro foresters and nonprofessional
ecologists are often not valid. When
scrutinized, many of the mother statements relating
to forestry and the environmental processes are seen
to be either exaggerated or untenable. It is highly
relevant and crucial to know what can be attached
to these statements for the proper management of
water resources and land use. This article presents
basic facts on limitations and efficacy of large water
storage versus small dams & popularly known as
rain water harvesting structures and suggests serious
examination of mother statements about relation of
forests and hydrologic elements - Whether Forests
increase rainfall, Forests increase runoff, Forests
regulate flows, Forests reduce erosion, Forests
reduce floods, Forests ‘sterilize’ water supplies and
improve water quality and Agro forestry systems
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increase productivity?
CAN SMALL DAMS & RWH REPLACE
LARGE DAMS?
The former captures rain in-situ and
supplements/conserves soil moisture for a longer
period, whereas the latter holds the run-off in
storages of surface waters and make it available
through canals for irrigation. The former has a crucial
role in treatment of catchment area and noncommand
areas of irrigation schemes. It recharges
ground water for use in local drinking water needs.
Also, it provides soil moisture to replace may be one
or two irrigation watering, in kharif season. Its main
role therefore is important for the vast rainfed areas
of the country, which will not be irrigated through
surface storages even in ultimate stage of
development.
Small dams and RWHS successfully operate
within a narrow band of meteorological phenomena
of intensity, duration, antecedent rainfall, potential
evaporation, infiltration capacity dictated by
topography, geology, slope, vegetative cover etc. Its
contribution in increase in productivity of cropped
land is rather limited. It is also essential that adequate
investigations & foundation testing, detailed
hydrologic analysis, hydraulic & structural designs,
proper construction supervision are given needed
attention even for small water projects, check dams
and rain water harvesting structures. Large number
of incidences have been noticed for washing away
of too many check dams within a year or two due to
structural, hydrologic, seismic and hydraulic failures.
Both therefore are considered as
complementary and not adversarial. Sediment
generation is reduced in the former case. Erosion
and deposition in downstream will continues due to
hydraulic phenomena. Dams hold bed load of
sediment in the designed pockets. Economic analysis
on dams accounts for such siltation. Peak flood is
reduced for local watersheds but does not have
significant impact on generation of floods. Available
data shows that when numerous small projects are
constructed to substitute a single large storage project
the cost per unit storage, relative submergence and
relative evaporation losses are invariably many times
more. Evaporation loss would obviously be more
because of larger water spread. Claims that only
small size (or some claim only large) of dams be
adopted are wrong. Only small dams can not capture
required quantity of water. In each basin, even if
one wants, all dams can’t be of only large or only