GUIDELINES FOR TANK CASCADE DEVELOPMENT

TANK CASCADE DEVELOPMENT





CONCEPT PAPER























P.B. Dharmasena








August 2008












GUIDELINES FOR

TANK CASCADE DEVELOPMENT



1. INTRODUCTION

Role of Small Tanks (Cascades) in the Dry Zone Agriculture

Dry zone civilization might have first emerged around natural lakes (vil)
and streams (Oya) in varying sizes. Subsequently man could find rainwater-
harvesting methods to make living possible in other areas of the dry zone.
Intrinsic networks of minor tanks and streams have evolved with the
formation of organized communities. More logical water use systems have
formed when farming societies were developed. Culture, customs,
agriculture, traditions and all sort of life styles have evolved on this
landscape on the basis of several phenomena. One is the bimodality of
rainfall. Migration and invasion from Northern side of the island might
have influenced to accelerate this evolutionary process of civilization.
However, later this had been the basis for development of the well-known
hydrologic civilization in the dry zone.

Dry zone watersheds exist as composites of smaller watersheds in varying
sizes because of the topographical formation. Natural dendretic drainage
system in a watershed blocked by earth bunds at appropriate locations to
store water has led to form a series of tanks along the drainage. This
ramifying nature of the drainage system leads to create clusters of small
tanks found in series, which are connected to form a system known as 'tank
cascades'.

Existence of small tanks in a cascade pattern is an advantageous feature in
many ways. Surface water bodies spread over an area can maintain the
groundwater level closer to the land surface at least in lower portions of
the minor basins. It can be stipulated that absence of such a branched
system of tanks could lead to rapid depletion of groundwater due to natural
gradient of the drainage system. Therefore, in the absence of tank cascade
systems natural vegetation seeing now would have not been in the same
composition with deep-rooted large tree species found in the various
positions along the catenary slope.

Upper tanks in a tank cascade system act as buffer reservoirs to absorb
flood-generating rainfall, which would otherwise bring the risk of
breaching lower tanks. Similarly, these upper tanks are buffer reservoirs
to supply water to the lower tanks when they are in short of water to save
the crop. The flood events taken place in maha 1957/58 season beginning
from upper small tanks down to lower large tanks such as Huruluwewa,
Manankattiya etc. have demonstrated the extreme situation due to abnormally
high rainfall occurred in that season.

There are about 12,000 small tanks and anicuts found in Sri Lanka, feeding
an extent of about 185,000 ha. This is 35 percent of the total irrigable
area in the country, and small irrigation schemes produce 191,000 mt
annually accounting for 20 percent of the national irrigated rice
production. Even though the rice yields of small irrigation systems are
relatively low their production capacity should not be overlooked from the
national economic point of view.


The Agrarian Services Act No. 58 of 1979 defines small tank or anicut as an
irrigation work serving up to 80 ha. of irrigable land. There are about
2,000 small tanks in the Anuradhapura district and 70 percent of them bear
the capacity of irrigating less than 40 ha of land. The command area is as
small as less than 20 ha in 50 percent of the total number of tanks in the
Anuradhapura District. Highest number of small tanks is found in
Kurunegala District and it is more than 4,200 in number.


Tank density is high in Anuradhapura and Vavunia Districts. Existence of
large number of tanks in an area depends on favourable climate, soil and
topographical factors. It can be observed that the optimum density of
tanks is found around the iso-hyet of 1,500 mm of annual rainfall, and a
decreasing trend is observed either side of this line. Low density of
tanks is found in certain dry zone areas where Red yellow Latasols and
regosols are found. Percolation rates are relatively high in these soils;
therefore, water-storing ability is low in these areas. Nature of
undulation of the landscape is also a factor controlling the tank density.

Past Efforts to Develop Small Tank Agriculture

Research Efforts


One of the facts that exists as the crux of the scenario of the dry zone
settlement is that maintenance of the groundwater table close to the land
surface gave the life to living environment of the people. Water table
behaviour was studied by Panabokke (1958) at the Research Station,
Mahailluppallama by conducting a water table monitoring program from 1951
to 1957. This could be considered as the earliest investigation on surface
and groundwater hydrology at Mahailluppallama. However, need for such
studies had emerged with some failures experienced from soil conservation
and crop rotation programs conducted at Kurundankulama Rotational Farming
Scheme initiated in 1938. At the beginning of the scheme land lots had
been conserved by constructing earth bunds along the perimeters of each
acre plot irrespective of the land slope, drainage and surface runoff
characteristics. During the heavy rains runoff water from the higher-lying
allotments as accumulated in the lower allotments due to absence of surface
drainage caused swamp conditions leading to crop failures. Subsequently
broad-based, graded bunds with a shallow drain were constructed as soil
conservation measures.


Tank water use
Water balance of a small tank in the dry zone was studied by Somasiri
(1979) during the period from 1976 to 1978. This preliminary information
on the hydrology of village tanks filled a wide gap in the knowledge found
in the development of the dry zone. Several objectives were considered in
the study; an important aspect being to focus attention on the need for new
technology in the management and utilization of tank water along with other
available water resources. Considering the wide variation in the nature of
the tank water supply several models of water use were considered, with the
possibility of choosing any one model that may suit the available water in
the tank.


Land use
A land and water resource survey was conducted by Dharmasena (1991) in
Mahakanumulla cascade and found that more than 70 % of the study area is
occupied by well drained uplands. The upland included mainly of
homesteads, chena and scrub vegetation. About 10 % of the upland area was
used as settlement sites and the rest was used for chena farming. The
irrigable lowland under village tank has been seriously fragmented with
respect to the ownership, so that any introduction of better water
management method would be challenging. The traditional shifting
cultivation has exploited almost all catchment areas of village tanks.


Tank water loss
Water losses from small tanks are very high. Within a period of 2 – 3
months since the seasonal rains cease, most of the tanks appear as somewhat
marshy lands infested with aquatic weeds. A tank water balance study
carried out in selected tanks in the Siwalakulama tank cascade showed that
contribution of direct rainfall to the storage varies from 25 to 40 percent
(Dharmasena and Goodwill, 1999) . Higher contribution from direct rainfall
was recorded in tanks with relatively larger water spread area. Total tank
water loss through evaporation and percolation varies from 35 to 90 percent
depending upon geometry of the water body. Water losses are higher from
tanks with shallower water bodies than those with deep water. Therefore,
it is clear that tank bed geometry determines more the water storing
efficiency of a tank than other factors do. These results indicate that
about half the storage in a tank would not remain to irrigate the
downstream command area. It indicates that if the tank geometry could be
altered to form a high capacity: area ratio, water loss would be reduced to
a very satisfactory level.


Catchment runoff
A case study was carried out at Paindikulama (Anuradhapura District) to
study the hydrological behaviour of village tanks during the period from
1985 to 1989. It showed that catchment needs sufficient amount of rainfall
for the initial saturation before it produces any effective runoff
(Dharmasena, 1989). This prerequisite is 140 mm in yala season and 220 mm
in maha season. It also showed that the percent runoff from the tank
catchment varied widely depending upon the seasonal rainfall. It was
evident that once the initial requirement for moisture replenishment is
met, 20 percent of maha rains and 15 percent of yala rains would flow into
the tank. The direct rainfall contribution to the tank is about 25 percent
in maha season and 50 percent in yala season. Rainfall probability
analysis shows that the tank would gain 80 percent of the storage only once
in 5 years. One third of the storage is expected once in 3 years. Analysis
further showed that the storage half life of village tanks is in the range
of 12-17 weeks indicating the inefficiency of storing water in village
tanks for the successive seasons. Only about 40 percent of the total
outflow moves into the command area through irrigation sluices while 60
percent is lost from tank seepage and evaporation.



At present, tank and well-irrigated cultivations are practised separately
although these water sources are hydrologically inter-connected. The
situation can be improved if a proper integrated approach is adopted for
water resource management. Studies have indicated that it is possible to
develop an integrated surface and groundwater management model. Components
such as runoff, percolation, evaporation, groundwater availability, crop
water use etc. can be estimated by using the present knowledge at
reasonable accuracy. Integrated water management plan needs to be
implemented with farmers' participation, aiming to increase water use
efficiency and farmer income.


Development efforts

Government investment on irrigation during latter half of the last century
was mainly made to new construction and rehabilitation of major and medium
schemes, and the investment on minor irrigation was smaller than 10
percent. The emphasis in recent years has directed more towards
rehabilitation of small irrigation schemes after completing major river
diversions in the country. A significant government intervention and
investments were made during 1970-77 period when a major emphasis was given
for the improvement of the small tank irrigation sector. A development
project on village tank rehabilitation launched in 1982 has spent 670
million Rs to renovate 200 tanks, improving irrigation facilities for about
6,000 ha. Since then various development projects have spent considerable
amount of money to improve physical infrastructure of small tanks.

Under the decentralized government budget, substantial financial
allocations were made to political authorities in every district to utilize
local labour to the maximum in small tank repair and maintenance. The
approach was attempted by many projects such as Village Irrigation
Rehabilitation Project (VIRP), National Irrigation Rehabilitation Project
(NIRP) etc. Further, the Asian Development Bank (ADB), International Fund
for Agricultural Development (IF AD) and NORAD have also given significant
assistance to the different provinces on infrastructure improvement for
small tank systems. In these programs investments have been made primarily
on hardware, namely construction of infrastructure and repair, maintenance
and rehabilitation.

On an average most tanks have been able to benefit by rehabilitation on
various aspects. This has helped to extend the life of most of the small
tank cascade systems but not to increase their productivity in a
significant manner. Three important reasons could be traced to answer the
question of less impact of tank rehabilitation programs. They are: 1).
limiting the development program to repairs of structures and
infrastructure development such as access roads, community centers etc.;
2). rehabilitation of individual tanks without considering the entire
cascade; and 3). less attention paid to restore the tank bed and its
surrounding eco-system. As the village tank cascades developed over
centuries appear to be time-tested land and water management systems with a
remarkable degree of harmony with their natural environment, it is
essential to consider a broad approach for development rather confining to
engineering aspects of rehabilitation.

Land Degradation: Threat to Dry Zone Agriculture

Severe erosion taking place in rainfed upland farming areas of low country
dry zone is the most acute problem associated with the crop production.
During last five decades, the dry zone primary forest has drastically
declined due to colonization and shifting cultivation (chena). Removal of
topsoil due to soil erosion in chena lands and use of heavy machinery in
colonization schemes has left behind agriculturally unproductive lands in
these areas. At present, rainfed farming lands produce about 80 percent of
Sri Lanka's coarse grains, pulses and vegetables, but actual farm yields
are far below the potential yields. As a result poverty level of dry zone
farmers is rising and the production of field crops is in a gradual
declining trend. This degraded land resource at present is not capable of
performing any productive farming under rainfed situation mainly due to
soil moisture deficit and deterioration of physical, chemical and
biological properties of soil.

The reduction of forest cover from half to less than quarter in Sri Lanka
during last fifty years more than anything else contributes to land
degradation. This is primarily due to colonization and rice land
development under major irrigation schemes and opening of new lands for
chena cultivation in the dry and intermediate zones.

Soil erosion is a real threat for agricultural production mainly due to two
reasons. First, it took longer period of time even for scientists to
recognize that the land is being degraded due to soil erosion. For
example, the work reported by Joachim and Kandiah in 1948, indicated that
chena cultivation would not lead to reduction of soil fertility
significantly and farmers abandon chena lands because of increased weed
problem. This conclusion was based on data of few seasons. It is
important to note that one of the indicators of land degradation is the
resurgence of obnoxious weeds. Second reason is that the soil erosion
problem is usually addressed by looking at the consequences rather
investigating and treating the real cause of problem. Two well known
examples are that the low soil fertility and soil compaction due to soil
erosion are treated with application of inorganic fertilizer and tillage
operation respectively, rather attempting to control the technical and non-
technical factors of soil erosion process. Although the nature of the soil
erosion problem is well understood, its hazardous effects are not properly
recognized.

Process of land degradation in the dry zone agriculture is in a vicious
cycle. Land does not make any productive out put due to its declined
fertility. Farmers do not manage the land to sustain the fertility due to
risk involved and the poverty. They can not gain an adequate income from
agriculture and resort to other possible income generation activity eking
out an existence. At this juncture any external intervention to support the
resource system to maintain its sustainability is the key element in
overwhelming the vicious cycle of dry zone agriculture.





PART ONE

2. Problems in Small Tank Based Agriculture

Problems Associated with Tanks

Cultivable extent from small tanks decreases gradually due to tank
sedimentation and high tank water losses. Investigations carried out in
1990 showed that small tanks in the Nachchaduwa major watershed are filled
with sediments due to soil erosion from tank catchments in the range of 23-
35 percent of their original capacity (Dharmasena, 1992). Sedimentation of
tanks not only causes reduction of storage capacity but also leads to alter
the tank bed geometry. Subsequent rehabilitation works where the capacity
was improved by raising the spill and the tank bund have created shallow
water body spreading over a larger surface area. This makes the situation
more complicated creating several additional problems. They are: a)
inundation of upstream paddy lands; b) development of salinity conditions
in the upper area; c) increase of tank water losses; d) disappearance of
the tree strips in the high flood region (Gasgommana) and the grass cover
(Perahana) underneath; and e) disappearance of some indigenous fish
species, due to diminishing favourable breeding and living environment
created by shallow waters.

In irrigated lowland farming, sometimes even in major rainy seasons, the
cultivation goes abandoned due to low rainfall. Very often the full extent
is not cultivated and crop losses or complete crop failures occur because
of inadequate water supply from tank. Although traditionally, rice is
cultivated in these lowlands, tendency for cultivating other field crops at
least in yala season has emerged as an alternative. Dug well irrigation
also has been introduced recently for food crop cultivation (agro-well
farming) in certain areas due to inadequacy of water. One of the main
reasons for water shortage problem is that the silted tanks fail to store
adequate storage due to low capacity and high losses caused from
sedimentation.

Cropping intensity is very low in small tank systems. In a study carried
out for Anuradhapura District using rice cultivation statistics recorded
from 1970 to 2003, it was observed that the cropping intensity had never
exceeded one, and it fluctuated according to the rainfall received during
maha season. With all efforts made to renovate small tanks under various
tank rehabilitation projects implemented during this period in Anuradhapura
District, no significant improvement in cropping intensity could be
achieved. This would drive us to make serious thoughts on present tank
rehabilitation strategies and their impact on water storage efficiency of
tanks.

Problems Associated with Lands

Degraded Lands

Many seasonal food crops are grown under rainfed conditions in the tank
catchments, from which runoff water flows into the tank below. This
continuous cultivation without adequate soil conservation measures has
caused deterioration of the soil resource leading to low moisture holding
capacity, low infiltration and fast evaporation due to soil compaction.
Thus, crops are frequently affected with soil moisture deficit resulting in
low yields or complete crop failures.

Comparative studies have revealed that rice yields are always lower in
small irrigation schemes, when compared with those major irrigation
schemes. This situation arose due to several factors. Degradation of paddy
lands due to poor soil and water management practices such as deep tillage,
lack of drainage, disposal of top soil in land preparation, non addition of
micro-nutrients and use of petroleum based chemicals.

Depletion of Soil Fertility

Soil fertility in paddy lands has declined in both major and minor
irrigation schemes. The traditional farmers in the past could manage soil
fertility of paddy fields in the dry zone without applying mineral
fertilizer. It has been found that traditional practices such as long
fallowing period, planting trees on paddy field bunds, application of green
manure, animal waste from buffalo and cattle grazing on the stubble,
utilization of relatively large quantities of nutrients (eg: K2O, Ca, Mg)
present in water from upper areas have contributed to the sustainability of
soil fertility. These practices preserved the natural biological processes,
which led to the restoration of soil fertility. However, these practices
have ceased to exist with the introduction and promotion of modern farming
practices.

Poor Drainage

One of the major issues with respect to sustainability of minor tank
systems in the dry zone is increasing trend of salinity development in the
paddy fields. Main drainage of almost all paddy tracts has been encroached
by farmers to increase their cultivable extent. This has blocked the
disposal of excess water from the paddy field allowing to gradual increase
of salt content of soil. Farmers in many small tanks have acquired the land
reservation found immediately below the tank bund (kattakaduwa) for
cultivation. This area had been maintained in the past to prevent entering
cations such as Na, Mg, K, Fe etc. into the paddy field. Further,
expansion of tank capacity by raising the tank bund caused inundation of
upstream area, which could be the paddy area of the upper tank. As a result
drainage of the upper paddy tract is affected by poor drainage encouraging
the salinity problem.

Land Tenure

In most of the minor tanks the land ownership fragmentation has become so
serious that farmers abandon cultivation because of its non-profitability
and management difficulties. The need for land consolidation has hence
emerged under these circumstances, but high expenses for land survey and re-
blocking can not be justified by its beneficial impact. However, it has
been understood by various development agencies that the success of the
tank irrigation rehabilitation would ultimately be determined by the degree
of land fragmentation in the command area. Therefore, a low cost and cost
effective land consolidation strategy must be developed and amalgamated to
the rehabilitation program.

Land ownership and its distribution make a complex situation in the minor
tank farming system. A particular community can have one relatively large
tank and few other tanks. Most of the farmers own land in more than one
tank. Farmers cultivate a portion in one lowland and move to the other. In
some seasons they find hardly any time to cultivate some lands and it was
found that only few farmers cultivate a yaya in ad-hoc manner. This
practice creates a very difficult situation in water management and crop
protection activities.

Traditionally almost all command areas had at least three phases of land,
and according to the availability of tank water farmers start cultivation
in one portion and move to the other. Most critical situation found at
present is that the number of owners is larger than that was in the past so
that the consolidation process also has certain limitations.

Land fragmentation means geographical scattering of holdings and it is a
common feature in the dry zone minor irrigation systems. This leads to low
cropping intensity and complete abandonment of the severely fragmented
lands without undergoing any productive farming. Land fragmentation is a
typical character of the old paddy land (puranawela). It is not much
distinct in the recently developed land (akkarawela). The reasons for
fragmentation of puranawela are the high demand for such lands located
close to the tank which assures proper irrigation and the prestigious value
attached to it. Both these reasons prevent the farmers from selling what
they have inherited. It must be distinguished between fragmentation of
actually cultivated and owned lands. Farmers have over-estimated the extent
and provided information to the Land Register of Agrarian Services
Department, which is used as the document to grant cultivation loan.

Lack of Off-farm Income

Communities in small tank villages, dependant merely on agriculture have
been gradually resorted to other income generating activities due to low
income from agriculture and high household needs under present lifestyle
situation. Young generation both male and female left the village seeking
for employment opportunities in security forces and trade industries. This
has led to create a vacuum in labour availability for agriculture in rural
sector. At present, there is hardly any opportunity within the village to
fill the income gap through earning opportunities outside the agriculture
such as cottage industry, small entrepreneur, fishery, livestock etc. This
aspect needs due consideration in planning village level development
programs.

In brief, there are three major issues pertaining to the sustainability of
functions of major reservoir watersheds:
Degradation of land resource due to severe soil erosion, leading to
loss of agricultural productivity
Heavy sedimentation of small tanks causing loss of their capacity and
storability
Salinity development in the lower portion of the micro-basins leaving
unproductive lands for agriculture.


PART TWO

3. Strategic Approach

1. Strategy

With the above background the Expert Committee of the Ministry of
Environment and Forestry has developed a concept document to propose the
strategies to develop major reservoir watersheds in the dry zone of Sri
Lanka. The document highlighted following strategies stressing the
importance following the cascade approach for the water resources
development in the dry zone.

Further, poverty of the farming communities living in these watersheds is
the ultimate consequence of the above issues, Therefore, strategies should
be focused on poverty alleviation and sustainability of the community.
Focusing towards these objectives the document suggested the following
strategies to restore the land and water resources potential in these
watersheds.
Formulate integrated development master plan for each major reservoir
watershed.
Rehabilitate all small tanks in the watershed considering cascade as
the smallest planning unit.
Develop tank catchments allocating most appropriate and productive
land uses (forestry, agro-forestry, wind barriers, rainfed farming,
pasture etc.)
Launch soil and water conservation program in all types of
agricultural lands.
Establish strong institutional mechanisms and inter-institutional
linkages to manage the entire watershed through formulation of village
management committees, cascade management committees and the watershed
management committee.

This document suggests a methodology for the development of a tank cascade
on the basis of above strategies.

2. Development Components

Cascade development includes following components

1. Tank rehabilitation - Removal of excess sediment through partial
desilting method, structural repairs (sluices, spills, canals,
waterways, drainage, field culverts etc.), tank ecosystem
development (gasgommana, perahana, godawala, iswetiya, wekanda,
kattakaduwa, thisbambe, kiul ela etc.), low land cultivation
(land consolidation, cultivation scheduling, crop diversification
etc.)
2. Tank catchment (upper areas) development – Reforestation, rainfed
conservation farming, agro-forestry (fruit-forest gardens)
development, community pasture land development, establishment of
wind barriers, home garden development (tree planting, vegetable
plot, medicinal garden,
composting, rainwater harvesting, soil conservation etc.)
3. Promoting other development activities – Infrastructure (access
roads, community centers, community wells, road culverts etc.),
livestock, fishery, agro-based industry, cottage industry.
4. Institutional development - Social mobilization, establishment of
a watershed based institutional network, linkage development for
agricultural inputs, marketing (collection centers, community
storage, processing, forward agreement), technology services etc.


PART THREE

4. Prioritizing Tanks/ Cascades for Intervention

a. Criteria

Rural communities are scattered in the dry zone but gathered into tank
cascade systems of various state of physical, economic and social
conditions, which need improvements. Priority setting for intervention
needs to be considered as it involves a huge attempt and inputs for the
entire development. Following general and specific criteria are suggested
to identify tank cascades, which need immediate improvements.

General criteria
Relatively higher population increase during last three decades
(population factor),
Neglected areas in recent development programs and project
interventions (development factor),.
People are more dependant on agriculture (livelihood factor),
Family income levels are relatively low (poverty factor).

Specific criteria
Average irrigable extent per family is small
Cropping intensity (cultivated area / total command area) is low
Tank water supply potential (total capacity/ total command area) is
low
Catchment water supply potential (Catchment area/ command area) low
Average tank water depth (Capacity/ water spread area) is low


2. Need Assessment

At the outset in identifying the rehabilitation needs it is felt essential
to focus on the apparent problem of the tank irrigated farming as the low
cropping intensity. Situation has to be analyzed to exercise the need
assessment as follows.




Problem: Low cropping intensity
Possible Reasons:
Inadequate tank capacity
Low tank water storage
High tank water losses
Poor management of tank storage
Socio-economic issues


Causal Factors:
Inadequate tank capacity
Tank is silted (weed infestation, shallow water depth, large
water spread, upstream salinity patches, lack of trees around)
Present capacity is lower than the potential (frequent spilling,
water shortage for irrigation)


Low tank water storage
Limited catchment area (low runoff, rare spilling)
Blocking! diversion of streams
Newly constructed tanks/ anicuts
Land use changes


High tank water losses
Tank is silted
Structural failures (downstream water stagnation, water leakage,
rapid
storage reduction)
Absence of wind barriers (kattakaduwa, gasgommana)
Piping (rapid water level drop)


Poor management of tank storage
Unplanned cultivation (staggered cultivation, continuous
irrigation, late
cultivation)
Poor maintenance of downstream canals/ structures (water wasting
in
canals, unwanted water stagnation)
Socio-economic issues
Collapse of institutional mechanism (disorganized cultivation,
marketing
problems)
Low profitability of paddy cultivation (high cost of
cultivation, unnecessary operations and management practices,
low yield, post harvest
losses, frequent fallowing)
Land fragmentation (ad-hoc fallowing, crop protection failures,
irrigation
difficulties)
Off farm employments (Low interest in group works, frequent
abandonment)

Table 1 shows analysis matrix to identify intervention needs.
Table 1. Determination of Rehabilitation Activities
Major issue: Low cropping intensity
"Possible reason"Causal factors "Factor indicators "Quantification "Recommendation "
"1.Inadequate "Tank is silted "Capacity/water spread "Sedimentation survey"Partial desilting "
"tank capacity "Low structural "is low "Inflow estimation "Investigate for "
" "capacity "Capacity/ command is " "capacity increase "
" " "low " " "
"2. Low tank "Limited catchment area"Catchment/command is "Inflow estimation "Catchment "
"water storage "Blocking/diversion of "low "Inflow estimation "development "
" "streams "Rare spilling "Inflow estimation "Catchment "
" "Newly constructed "Observations " "development "
" "tanks/ anicuts " "Land use "Catchment "
" "Land use changes "Land use mapping "interpretation "development "
" " " " " "
" " " " "Land use mapping "
"3.High tank "Tank is silted "Capacity/water spread "Sedimentation survey"Partial desilting "
"water losses "Structural failures "is low "Preliminary "Structural repairs "
" "Absence of wind "Catchment/ command is "investigation "Eco-system "
" "barriers "high "Land use "development "
" "Piping "Land use mapping "interpretation "Tank bed "
" " "Capacity/command is "Preliminary "improvements "
" " "high "investigation " "
"4. Poor "Unplanned cultivation "Irrigation water "Preliminary "Cultivation "
"management of " "demand is high "investigation "scheduling "
"tank storage "Poor maintenance of "Observations " " "
" "downstream canals/ " "Preliminary "Downstream "
" "structures " "investigation "development "
"5. "Collapse of "Disorganized "Socio-economic "Social mobilization "
"Socio-economic "institutional "cultivation "survey " "
"issues "mechanism " " "Crop diversification"
" "Low profitability of "Frequent fallowing "Socio-economic " "
" "paddy cultivation " "survey "Land consolidation "
" "Land fragmentation "High land " " "
" " "fragmentation index "Socio-economic "Crop diversification"
" "Off farm employments "Ad-hoc abandonment "survey " "
" " " " " "
" " " "Socio-economic " "
" " " "survey " "






Data sheet for factor identification

1. Tank name:
2. Catchment area (ha):
3. Capacity (ha.m):
4. Water spread area (ha.):
5. Command area (ha):
6. No. of families:
7. Year of last rehabilitation:
8. Maha cropping intensity:
9. Remarks:

5. Anticipated Impact


The proposed project is expected to bring following improvements to the
watershed

Favourable water resource situation in the watershed area and in the
major reservoir below.
Productive utilization of land resource in the watershed
Arrested soil erosion status over the entire watershed
Tank sedimentation reduced to the lowest
Reduced water losses and efficient water use in reservoirs within the
watershed
Improved living standards of villagers.
Strengthened institutional network in the watershed


REFERENCES

DHARMASENA, P.B., 1989. OPTIMUM UTILIZATION OF THE STORAGE IN VILLAGE
TANKS. TROPICAL AGRICULTURIST. DEPT. OF AGRICULTURE, PERADENIYA, SRI
LANKA 145:1-11.
Dharmasena, P.B., 1991. Present use of land and water resources in village
tank farming. J. Soil. Sci. Soc. Sri Lanka 7:1-17.
Dharmasena, P.B., 1992. Magnitude of sedimentation in village tanks.
Trop. Agric., Dept. of Agriculture, Peradeniya, Sri Lanka. 148:97-110.
Dharmasena, P. B. and I.M. Goodwill, 1999. Use of groundwater in minor tank
irrigation schemes of Sri Lanka. In ICID, 17th Congress on Irrigation and
Drainage, Granada, Spain, 1999. 'Water for Agriculture in the Next
Millenium, Transactions, Vol. 1D, Q. Irrigation under conditions of water
scarcity pp 175-194.
Panabokke, C.R., 1958. A pedologic study of dry zone soils. Trop. Agric.
Vol. CXIV:151-174.
Somasiri, S., 1979. Village tank as an agricultural resource in the dry
zone of Sri Lanka. Trop. Gric. Vol. CXXXV:33-46