Volume II
FEASIBILITY REPORT
FOR PHASE I OF DEVELOPMENT
PROJECT 1: POGOLLA DIVERSION
1. General Scheme of Water Distribution
The Water supply is derived from the
how of the Mahaweli Ganga and Amban
Ganga in their upper reaches and also from the
local yield which is regulated in the reservoirs and smaller tanks in
the systems D-l and Ii.
The main water source is the Mahaweli
Ganga, from which a maximum discharge of 2,000
cusecs is diverted through the Sudu Ganga into the Amban Ganga by the diversion structure and tunnel at Polgolla.
The diverted Mahaweli flow, supplemented
by runoff in the catchments of Amban Ganga itself, is bifurcated as described hereunder
A discharge of 1,300 cusecs (maximum)
is sent farther down the Amban Ganga
and diverted at the Elahera anicut
through Elahera – Minneriya
- Kantalai-Yoda Ela
(EMYE) canal to Minneriya and from there to
Kaudulla and Kantalai tanks, which
supply water to system D-l (system C is irrigated directly from the EMYE
canal).
The remaining 700 cusecs is transferred
through the Polgolla-Kala Oya
canal (P.K.) to Kalawewa and Kandalama
tanks, from which 70 percent of system H is irrigated.
The irrigation water supply is assured
for 85 percent of years as determined from the 20-year runoff records.
2. Polgolla
Hydraulic Unit
The Polgolla
hydraulic unit includes a barrage across the Mahaweli Ganga,
a tunnel connecting the Mahaweli to the Sudu
Ganga, and a hydro-electric power station.
Geological conditions at th3 proposed
sites can be rated as favourable. At the dam site, at a depth of 20-30
feet below the surface sand and highly-weathered formation, there are
hard quartz-biotite granulites which can serve
as a reliable .foundation for the hydraulic structure. The tunnel axis
is laid through fresh quartzitic and quartz-biotite
gneisses, granulites. and quartzites,
in which layers occur at an angle of 20-60 degrees to the tunnel axis
and dip at 70-90 degrees. There is the possibility of crossing several
closed faults which date as far back as the age of the geologic formation.
The slope in the Sudu Ganga valley, where the tunnel
has its outlet, is covered to a depth of 80 feet by loosely fragmented
sediments and layers consisting of granulites and crystalline limestone
of decomposed and crushed texture. These layers are under laid by slightly
weathered and fresh rocks.
The alternative studied for the structural
arrangements of the unit were
(i) A free-flow tunnel
and an underground hydro-electric station at the beginning of the tunnel,
producing an energy output of 18.3 million kWh at a cost of Rs.
83 million (pre-devaluation rate).
(ii) A pressure tunnel with a ‘surface’ hydro-electric
station at its end, on the bank of the Sudu
Ganga, giving an energy output of 192 million
kWh at a cost of Rs. S8 million.
The alternatives are very similar in
benefits, and the first is cheaper by Rs. 5
million, which is less than 10 percent of the cost and within the range
of tolerance. The economic appraisal in this report favours the first
alternative. but since the alternatives do not differ in principle, the
final selection car. be left; for the final stage
of designs. when detailed investigations will
permit a more accurate assessment. If the costs and benefits are still
found to be very similar, the second alternative is to be preferred.
The items contained in the hydraulic
unit are described briefly below
(i) The barrage will be a concrete dam with sector
gates and have a maximum head of 25 feet. It will be 530 feet long at crest
level and will be capable of coping with a discharge of 203,000 cusecs this being a flood of 1,000
years frequency. This discharge can pass through the barrage, when the gates
are open, without causing any change in the normal conditions upstream.
(ii)
The underground hydro-electric station, which will have four installations
with a total capacity of 35.8 megawatts, will be located at the bottom of
vertical shaft 230 feet below the normal water surface elevation. The net
guaranteed head is 256 feet. The discharge taken through turbines is variable.
Thus, for 40 percent of the time the operating flow will be at its maximum
of 2,000 cusecs; for 70 percent of the time the discharge will be over 1,000
cusecs.
The
average annual firm power capacity at a flow of 90 percent frequency will
be 21 megawatts, with an energy output of 183 million kWh per year. In the
dry months (January to May) the monthly firm power capacity will be reduced
to 10-14 megawatts. While in the wet months (October to December) it will
reach the maximum of 35.8 megawatts. The seasonal fluctuation in firm power
capacity should be taken into account when. Establishing the consolidated
operation graph of the available power system., After 1976, decline in power
generation at Polgolla hydro-electric station during
the dry months will he compensated for in great measure by a controlled regime
of operation during this period at Victoria hydro-electric station.
(iii)
The tunnel will be of horse-shoe section, 18 feet in diameter, and
lined with concrete; its length will be 26,150 feet.
The total cost of the hydro-unit will amount to Rs.
97.44 million (post-devaluation), of which the foreign currency allocation
will be Rs. 56.44 million leaving 41.04
million required in local currency. Distribution of costs by utilization
criteria allows Rs. 68.4 million for irrigation and Rs.
29.0 million for power production. Annual cost of operation and maintenance
adds up to Rs. 974,400 estimated
at one percent of corresponding capital expenditures. The sales value
of one kWh at the bus bars of the hydro-electric station has been estimated
at 5.9 Ceylon
cents (pre-devaluation)
and 6.0 cent (post-devaluation).
Commissioning of Polgolla hydro-electric station
in the National electric-power grid will require construction of 2.5
miles of DC 132 kilovolts transmission, at a total cost of Rs. 456,000. This expenditure is classified as indirect and
is included in the economic evaluation.
3. Stabilisation of the Sudu Ganga Channel
Stabilisation of the Sudu Ganga
channel will prevent its erosion and active silting of the reservoir
proposed at Bowatenna. The stabilisation will
be done by removing irregularities from the river gradient in the reaches
where scouring is possible. This will be achieved by building drop structures,
straightening sharp bends in the river, and training the bed and the banks
suitably with river profiles of masonry and rip-rap protection.
Its proposed to carry out the river training in two steps, the
first step to include straightening and stabilisation of the channel to take
the design discharge; and the second, with further improvements, to be undertaken
after three to five years of operation under the new conditions.
The
cost of the first step is estimated at Rs. 5,700,000
and the second step is expected to cost l(s. 4,901,000,
making a total cost of Rs. 10,610,000. The operation
and maintenance cost is estimated at Rs. 106,100
per year.
4. Elahera-Minneriya-Kantalai-Yoda
Ela (E.M.Y.E.) Canal
The
Elahera.Minneriya.Kantalai-Yoda Ela
canal, constructed several centuries ago, has been restored and partly remodelled
in the, past twenty years. The canal begins at the Elahera anicut, on the Amban Ganga, and flows along a contour
to the existing Minneriya tank Issuing again from
the Minneriya tank, it
passes above the Kaudulla tank, augmenting the latter
through a special feeder, and spills into the Yoda Ela
canal, which leads to the Kantalai tank.
The
present conveyance capacity of the canal is 1,000 cusecs in the first
4.9 miles.1,250 cusecs from mile 4.9 to mile
6.3, 1,500 cusecs from mile 6.3 up to the Minneriya
tank. In the first 1,000 feet of its run, the
canal crosses rock structure and is lined. Farther on it goes through
earth soils and is guide by an earth bund on the downhill side. On the
uphill side, the canal is open for intercepting the flow of the streams
that drain its catchment area. Floods occurring
in these streams are discharged from the canal through spillways constructed
at suitable intervals.
The E. M.Y.E canal will be utilized
for he following restricted purpose when the
scheme is fully developed: irrigation of system G, And augmentation of
the Minneriya tank from the Kalu Ganga reservoir, Amban Ganga, and the canal catchment itself. In the reach from Minneriya
to Kantalai, the canal will serve as a waterway
for the spill flood discharges from Minneriya
to Kantalai, and, by suitable connections, from Kaudulla.
However, in the first phase of development
– that is, before water is diverted to the N.C.P – the Elahera
canal will also be used to augment the tanks in system D – 1 from the
Amban Ganga. For this purpose, a minor improvement is proposed in
the head sluice and the initial section of the canal (from mile 0 to mile
6) : the increasing of its conveyance capacity to 1.500 cusecs.
This improvement involves the construction of an additional head regulator
to discharge 500 cusecs, and increase in height of the lining of the canal,
and the raising of the crest of its spillway by 2 – 3 feet. Apart from
this only local improvements of the canal bunds and construction
of suitable approaches at entrances of the cross – drainage streams need to be done.
- Polgolla – Kala Oya
(P.K) Canal
The alternatives considered for the
canal are:
(i)
diversion at Diggala site and total length of the trace 19.07 miles;
(ii)
diversion at Bowatenne site and total length of the trace 9.25 miles;
The first alternative requires an open
- out lined canal which, through difficult topographic and geological
conditions, will need, in addition, four short tunnels and 10 major structures
(6 syphones, 1 energy dissipater, 2 regulators
at the spillways, and I fall structures).
The total cost is estimated at Rs.
97.4 million (pre – devaluation), a good part of excavation cost being
for machine work. When estimated on the basis of using manual work as
far as possible, the cost is Rs. 84 million
(pre – devaluation), Rs. 57.0 million of which
is local expenditure, the balance being required in foreign exchange.
Annual operation an maintenance expenditure comes
to Rs. 840,000 (pre – devaluation)
The chief advantages of the first alternative
is that it can be implemented with a minimum foreign exchange and be carried
out simultaneously with the construction of Polgolla,
thus permitting the operation of the required part of system G as early
as in the fourth and fifth year after the commencement of the project.
The disadvantages are the high capital
and operation costs of maintaining the canal to withstand floods and landslides.
In the second alternative, the canal
runs for the greater part of its length through a tunnel 4.25 miles long
which crosses the water divide between the catchments of the Amban
Ganga and Kala Oya. There after it coincides with the tail reach of the first
alternative.
The cost, all apportioned for irrigation
purpose, is estimated at Rs. 56.3 million (pre-devaluation)
When the possibility of developing
hydropower in two directions from Bowatenna
(toward Moragahakanda and toward Dambulu
Oya) was considered, positive advantages were
found in raising the height of
Bowatenne dam by 20 feet thus creating a reserve storage of
20,00 acre – feet and giving greater assurance of water to systems H,
D and 0. This also permits the installation of a turbine of 3.7 megawatts
capacity (of which 2.2 megawatts is firm power) at the Dambulu
Oya and the construction of a hydro-electric station at the
Amban Ganga end with
firm power capacity of 15.4 megawatts.
The total cost of the second alternative
in this arrangement is estimated at Rs. 62.5
million (pre-devaluation), excluding the cost of the Amban
Ganga tunnel and power plant. Of this sum, Rs. 32.5 million are required in local currency, and
the balance has to be obtained from foreign sources. Annual operation
and maintenance costs will amount to Rs. 400,000.
With the increased height of Bowatenne bariage,
the second alternative is cheaper than the first by Rs.. 21.5 million in capital expenditure
and by Rs. 440,000 (pre-devaluation) in annual
operation and maintenance costs. The foreign exchange requirement in the
second alternative is, however, greater (by the equivalent of Rs. 3.0 million). This amount could be saved if the tunnels
were constructed after completion of the Polgolla
tunnel, the same machinery and equipment being used. But then the required
part of system 1-I could be put into operation only after a delay of two
years and an income of Rs. 20 million from this
area would have to be foregone.
The total cost of the second alternative,
if the height of Bowatenne dam is raised and
the tunnel as constructed after completion of the Polgolla
tunnel, can thus be considered as Rs.
62.5 million+ Rs. 20 million. This cost of Rs. 82.5 million is very close to the Rs.
84 million of the first alternatives. Preference was given to the second
alternative, since its operation cost is less than half that of the first
alternative and since income losses from delay in bringing into operation
the required part of system H are theoretical.
The Polgolla-Kala
Oya canal, as adopted to this second alternative,
will be as follows
The dam at Bowatenne
will serve as a bifurcation structure. It will be 107 feet high and 804)
feet long along the crest and designed to cope with a flood discharge
of up to 124,500 cusecs (occurrence of once in 1,000 years).
The tunnel intake towards the Dambulu Oya will be located in the
bay of the proposed reservoir. A pressure tunnel, 16 feet in diameter
and 21,500 feet long, will be designed to convey a maximum discharge
of 750 cusecs. A small hydro-electric station will be installed at its
outlet to produce 16 million kWh firm energy
annually.
The open-cut canal beyond the station will
be 4.89 miles long and have concrete lining in a part of the first mile.
A 266 feet long syphon,
a drop structure, and a regulator at the spill to the Dambulu
Oya will be provided en route.
Geologic conditions at the sites for
construction of the barrage and the tunnel are favourable for a darn)
with adequate grouting. The foundation consists of gneisses and crystalline
limestone at 5-20 feet below the loosely fragmented and weathered formation.
The tunnel trace will be driven at
a depth of 100-600 feet in practically fresh metamorphic rocks (gneisses,
granulites, quartzites, and crystalline limestone)
in which layers occur at an angle of 200 -600 to the tunnel axis. It is only at the tunnel
inlet and outlet that loosely fragmented and weathered material will be
encountered.
The total post-devaluation cost of
Bowatenne amicus and the P. K. canal is Rs.
73,050,000, of which Rs. 35,940,000 are required
in foreign exchange, and Rs. 37,110,000 locally.
6. Irrigation Systems D-1 and
C
General
Conditions of irrigation
(a)
Available land resources
Systems D-l and C, which cover
a total area of 100,500 net acres, are adjacent, and are supplied with
water from the same trunk canal, the Elahera-Minneriya-Kantalai-Yoda
Ela.
System G is irrigated directly
from the trunk canal, and system D-l is irrigated
from the Minneriya, Kaudulla,
and Kautalai tanks. Available land resources
include the following areas.
System G 4,900 acres of existing
paddy fields
7,440 acres of undeveloped
lands
Total
12,340 acres
System D-1 43,400 acres
of existing paddy fields
7,700 acres of existing sugar-cane plantation
37,060 acres of undeveloped lands
Total
88,160 acres
Total of D-1 and G 100,500 acres
Natural conditions and homogeneous
in the two systems and they can be considered together.
(b) Effective precipitation and
irrigation duties
The effective precipitation was estimated for three critical years, 1947148,
1956/57 and 1958/59, when there was respectively
81 percent, 75 percent, and 76 percent frequency of occurrence. The average
effective precipitation during these three years is tabulated below.
TABLE
3
Average
Effective Precipitation for Three Critical Years, 1947/48, 1956/59 in
Systems D-1 and G.
Average
Percentage of Crop
Crops Effective
precipitation requirements
-----------------------------
-------------------------
Maha YaIa Annual Maha Yala
feet
Paddy ..
.. 1.98
0.64 2.62
72 20
Dry
crops ..
..
1.52
0.53 2.05
84 — 71
30 — 24
The Table above shows the effective precipitation in both seasons to be
insufficient for the growth of paddy and the majority of dry crops. In Maha, only some types of dry crops get almost all the moisture
they need, provided the distribution of effective precipitation during the
period is favourable. Consequently, this region requires guaranteed year-round
irrigation.
Average
gross irrigation duties for the main types of cropping pattern are as follows :-
TABLE 4
Average
Gross irrigation Duties for Main Crops
Type
of cropping pattern
Maha YaIa Annual
(0
(2) (3) (4)
Paddy . .
-.
..
3.4
5.1 8.5
Mixed (Paddy and
subsidiary crops) 2.8 2.7
5.5
Sugar-cane ..
..
2.6
4.6 7.2
High value crops ..
..
1.7
2.8 4.5
(c) Relief and soils
The relief of the region as a whole can be rated as suitable for gravity
irrigation. System C and the upper part of system 0-I have slightly undulating
relief with differences in elevation of 20-30 feet and slopes of 2 - 3 degrees.
The lower part of system D-1, bordering upon the Mahaweli Delta. is flatter with relatively moderate slopes of I - 1.5 degrees.
The soil cover consists of four major varieties, Reddish Brown Earth (RBE),
which has good drainage conditions and forms 40 percent of the total useful
area; reddish brown earth (RBE) imperfectly drained (10 percent); Low Humic Gley soils (LHG) and Alluvial
soils (Al), poorly drained (CO percent). The Reddish Brown Earth (RBE) is
the most fertile, and is capable of producing all o~ Le high value dry crops
and sugar-cane. The Red Brown Earth (RBE) with imperfect drainage conditions
is suitable for rice and for several other dry crops cultivated during Yala. I he gley soils can be used
for paddy rotations.
(d) Reclamation of low-lying areas from periodical floods
The reclamation of lands affected by the periodic inundating of the alluvial
plains and low-lying areas of system D-l must be considered.
The
settlement of new territory in system 0-1 required a new, though not very
large. infrastructure.
Existing
irrigation
The existing irrigated lands of system 0 stretch along the Elahera trunk canal and merge with the area proposed for new
development, forming one block.
In system 0-I, the existing irrigated lands are under command of the four
tanks augmented by the Elahera canal (Giritale,
Minneriya, Kaudulla, and Kantalai see general layout plan, Drawing No. 1). Information
on areas irrigated under these tanks is given in Table 5.
TABLE 5
Characteristics of Existing Irrigation Tanks
of System DI
Name of Tank
Irrigated Area
Catchment Average Yield
Active -----------------------------
Area
yield P-75%
storage Paddy Sugar
Total
cane
(1) Sq. (3) (4) (5) (6) (7) (8)
mile ac/ft (thousands) acres
Giritale
..
..
9
5 3 19 4,400 — 4,400
Minneriya ..
..
93
50 27
109 14,300 — 14,300
Kaudulla
..
..
32
32.5 18
94 10,200 — 10,200
Kantalai and Vendarasan ..
81
81 46.4 130 14,500 7,700
22,200
Total ..
..
215
171.5 94.4 352 43,400 7,700
51,100
All the existing irrigation systems
were reconstructed in the last 15—20 years, the most recent being the
Kaudulla and Kantalai systems. The
common disadvantages of the existing systems are insufficiency of the
irrigation network, unsatisfactory drainage conditions, and the very widely
spaced system of field canals.
Watering of paddy is maintained by transference from one ‘liyadda’ or small paddy tract to another. Water use is not
economical and considerable losses occur.
Statistics taken over the last 14 years
reveal that the irrigated area has been adequately supplied with water
only during Maha season. In Yala,
watering was-provided for the whole area under irrigation in seven years
only ; one dry year had almost no irrigation during both seasons, and
in the remaining six years water was supplied for only 80— 90 percent
of the area during Yala.
In order to determine the extent of
assured irrigation in the existing irrigation systems, a study was made
of the present scheme of water supply in a critical year with 75 percent
frequency of occurrence. A comparison between the estimated and statistical
data is shown in Table 6.
TABLE
6
Present
Irrigation Intensity of (lie Existing Areas in System D
Area with Crop acreage Crop Coefficient
Data irrigation ------------------ acreage of
network Maha Yala total intensity
Acres ( thousands)
Estimated for
the year of
75 percent
frequency
..
56.0
56.0 27.0 83.0 1.48
Statistical ..
..
56.0
56.0 42.6 98.6 1.78
Thus it can be seen that the irrigated area, according to the statistical
data, exceeds that estimated in the operation study by 15,600 crop acres.
Obviously, its frequency of irrigation is less than 75 percent. in the agro-economic estimates, to be on the safe side, the
greater extent of the irrigated area was adopted; this gives a somewhat lower
‘value added’ after the existing irrigation systems are completely satisfied
with water.
The operation study data were used to determine the equivalency coefficient
(ratio) of the additional water supply for the existing irrigated lands to
the requirements of the areas new to irrigation. In this case, the partial
augmentation of the 56,000 acres of existing systems will permit the sure
irrigation of an additional 29,000 acres in Yala,
which is equivalent to the year-round irrigation of new lands amounting to
14,500 acres (29,000+2). In other words, the augmentation of the 56,003 acres
of existing lands is equivalent to 14,500 acres of new irrigation; the equivalency
coefficient is around 14,500: 56,000.
The planned augmentation of the Amban Ganga will improve the assured water supply to the irrigation
systems up to 85 percent.
With the aim of having a properly arranged irrigation network and a more
productive use of irrigated lands, it is proposed to improve the existing
systems by the following means
(i) Modernisation of the head sluices and regulators
on the main and branch canals, including the installation of water measuring
devices, at a cost of Rs. 9.7 million.
(ii)
Reconstruction of the main drainage lines, by deepening and widening
their channels and construction of embankments in the lower reaches of the
streams, at a cost of Rs. 14.1 million.
(iii)
Intensification of the field irrigation and drainage network so that
the space between the feeders is not more than 600 feet, with adequate
improvements to field canals, at a cost of Rs. 11.6
million.
The
total cost of improvements to the existing amounts to Rs.
35.6 million.
New Irrigation
(a)
System D-1
The newly irrigated lands of system fl-I will be under the command of the
Kaudulla and Kantalai
tanks. To create a consolidated system of water supply, it is proposed to
connect these tanks by a link canal, which will simultaneously irrigate lands
en route from the Kaudulla tank. In the third
phase of development, when the Kaudulla
tank will be augmented from the Mahaweli Ganga through
the L. B. transbain canal, the above link canal
will permit augmentation of the Kantalai tank with
waters from the Nlahaweli.
The lands to be irrigated under the Kaudulla tank
cover 30,530 acres, generally isolated from the existing irrigation system.
New conveyance canals 28 miles in length will be constructed here to cater
for blocks of 5,000 or more acres.
The lands proposed for irrigation under the Kantalai
tank (6,480 acres) are under command of existing canals in the adjacent irrigation
systems. This permits the use of part of these conveyance canals for irrigation
of the new lands.
A narrow strip of land covering 9,100 acres of system A and lying along
the eastern boundary of system 0-1 is proposed for irrigation, also from the
Kantalai tank., in Project 3 of the
first phase. This strip shares a common water conveyance network with system
0-1, which lies at higher elevations.
To summarise, the irrigation of all lands under command of the Kantalai tank, a total of 15,580 acres (6,480 + 9,100), requires
16.8 miles of water conveyance canals, of which & miles involve the construction
of existing canals, and 8.8 miles must be of new construction.
Two methods of irrigation have been proposed furrow irrigation for 18,380
acres, and border irrigation for 18,680 acres.
To control water usage, the irrigation network will be equipped with accurate
automatic water measuring devices at the head of blocks of 200— 250 acres.
Within these blocks the discharge will be measured by farmers through
calibrated outlets or portable syphons.
The main drainage lines of system D-l, will be
deepened and widened as necessary in the upstream reaches and trained
in the lower reaches. Drainage channels serving blocks of 5,000 acres
in the upper part of the system are generally led to the existing streams,
where usually no improvements will be required. In the lower part of the
system, where the conveyance capacity of the natural streams is insufficient,
trenching of artificial drainage lines is proposed.
(b) System G
The new irrigated lands in system G (7,440 acres) are adjacent to the existing
irrigation systems and will use the same network of distribution and drainage.
The entire area in this system will be under border irrigation.
(0
Cost of new irrigation in systems D-l and G
The cost of the main irrigation and drainage system was estimated for each
canal. The cost of the irrigation and drainage network, and of levelling and
jungle clearing, was determined by applying the unit cost of these works
derived from the standard plot. The total cost is estimated to be
Rs. 1 10,590,000.
The total estimated cost, comprising improvement of the existing schemes,
construction of new systems arid land development, is Rs.
146.19 million. Operation and maintenance costs are estimated at Rs. 3.3 million per year.
7.
Irrigation System H
Conditions of Irrigation
System 1-1 is located in the Kala Oya basin. Its total net area is 103,100 acres, of which 46,200
acres are already irrigated and 56,900 acres are proposed for new
irrigation.
The
existing systems are fed by seven tanks, the more important of which are
Kandalama, Kalawewa, LJsgala and Rajangana; the undeveloped
lands are in the zone of command of the Kandalama
and Kalawewa tanks, for which water will be
supplied from the Mahaweli Ganga through the
P. K. canal. All tanks located below Kandalama
are connected by natural streams or canals.
The climate of the Kala
Ova basin is slightly more arid than that of the Mahaweli Ganga
basin. Cultivation of rice and dry crops under rainfed
conditions is possible only in Maha, in the
wet sears. The distribution of effective precipitation is critical years
and the corresponding average values of irrigation duties; are given in
Table 7.
TABLE
7
Effective
Precipitation for Critical years and water Duties in System H
Percentage of
Crops Maha Yala Annual Consumptive
use Irrigation duties
---------------------- ----------------------------
Maha Yala Maha vala
Feet
Fed
Paddy 1.45 1.00
2.45 53
32
3.5
5
Dry crops 1.15
0.83 1.98
62 - 46 41 - 28 0.8 - 2.2 2.2 -2.8
Soil conditions of the area are favourable
for growing value crops. Fertile and well drained Reddish brown Earth
(RBE) soils prevail in 66 percent of the irrigable area. The Reddish Brown
Earth (RBE) with imperfect external drainage occurs on 8 percent of the
lands, and the gley soils (suitable for rice)
and alluvial soils cover the remaining 26 percent.
The relief of the water divides is
slightly undulating. with moderate slopes varying
front I 3 de2rees the terrain
is flatter in the river valleys, where slopes are smoother.
The greater part of this area has favourable
conditions for land reclamation, there being no swamps or danger of salinisation. Only the river valleys are subject to periodic
flooding in brief spells: hence, sonic flood protection is necessary.
Existing irrigation
Two types of irrigation systems exist
in the Kala Oya basin:
major schemes involving engineering works and minor village schemes.
Major irrigation schemes are similar
to those described earlier under, the Kaudulla
and Kantalai tanks. The chief defects of these systems are the
lack of proper devices to control the water issues, insufficiency of the
field irrigation network, and inadequacy of drainage. Most of the irrigated
lands are at present tinder paddy cultivation, the few exceptions being
under mixed rotation of crops. Distribution of the irrigated areas under
the existing feeder tanks is given in Table 8.
TABLE
8
Characteristics of Existing Irrigation Tanks
in System H
Averace Active Active Existing Acreage
Name of Work
Catchnient yield
P—75t, Storage -
------------------------------------------------------_
Area
1,000 1,000 1.000 Major
Minor
Schemes Schemes
Sq. miles
acre feel acres
Kandalama ..
.. 38
26 12 25.6 4,000 3,280
Kalawewa..
260
180 82 72.7 13.020 6,900
Usgala
Sivambalagamuwa ..
71
49 23 20.7 1.500 -
Rajangana
..
.. 177
123
54 76.5 17.500
-
36,020 +
10,180
Total = 46.200
There
is no assurance of continuous water supply to the above areas and, according
to statistics collected over 14 years, an average of only 30 percent of lands
irrigated in Maha were irrigated during Yala season. In some years the water supply was even less,
and in one of the 14 years there was no irrigation at all in Yala.
The
adequacy of water supply to the existing areas in system U was measured from
estimates similar to those made for systems D-l and 0. The results of the
processed statistical data and the operation estimates for the critical year
of 75 percent frequency of recurrence are tabulated in Table 9.
TABLE 9
Present irrigation intensity of the Existing Area in System H (1,000 acres)
Area with Total Coefficient of
Data irrigation Maha YaIa crop intensity
network
average
Estimated .. 46.2 42.2 22.4 64.6 1.53
Statistical .
. 46.2 42.2 19.0 61.2 1.45
Although
the areas of crop acreage obtained by different methods are closely similar,
a discrepancy in the intensity coefficients
is seen. However, since the estimation of ‘value added’ is based on the statistically
determined total crop-acreage, the difference in the intensity coefficients
does not affect the economic estimate. The equivalency coefficient’ of the
existing irrigated lands is around 0.3 as in system D-I and 0.
The
same basis is used for the proposed improvement to the engineering systems
as for the existing schemes in system D-l.
Village
irrigation schemes are dependent on small tanks which provide for watering
of paddy during Maha season only. These schemes
vary in size from 5 to 50 acres and total 10,180 acres. The tanks are
created by low bunds (sometimes 3-4 feet high) across shallow valleys of small
streams. The water surface area of the tanks sometimes exceeds the area; irrigated.
Spilling of flood waters is normally through shallow excavations, the head
sluices are primitive and a concentrated irrigation network is lacking. in several instances there are cascades of bunds barring water
flow along the natural streams: this leads to over-moistening of the whole
stream valley.
It
is proposed to reconstruct the village irrigation works which will be absorbed
in the new irrigation systems and to use some of the existing tanks as water
regulators to irrigate the paddy fields lying below them. Where the village
irrigation scheme is excluded from the new systems, or where its area is not
convenient for expansion, some improvement to the irrigation and drainage
network, as well as augmentation with return waters available from the new
irrigation, is contemplated.
The
cost of the improvement and reconstruction of the existing irrigation schemes
under system H is estimated at Its. 27,440.000.
New Irrigation
The
greater part (85 percent) of the new irrigation area, covering 48,205
acres, is located in the zone under command of the Kalawewa
tank; only 8,695 acres will be irrigated from the Kandalama
tank.
For reasons explained in the next section (Water Supply to the
Irrigation System), only 31.300 acres, or about 70 percent of the 48,205 acres
of new irrigated area commanded by Kalawewa Tank
in system H, will form part of Project I. The balance of 16,900 acres will form
part of Project 3.
I, Coefficient
expressing the relationship between the water consumption of an already irrigated
area and an area proposed for irrigation.
The allocation of the new
irrigated area for Kite whole system,
to projects and by method of irrigation, is shown in Table 10. The remark which follows, except the details of costs,
apply to system H as a whole.
TABLE 10
Allocation of New Irrigation Area in system H
Area in 1,000
Total Project I Project 2
Existing ..
46.2 46.2
New
.. 56.9 (31
300—8 695) 16.9
Border irrigation 19.3 13.7 5.6
Furrow irrigation 36.5 25.6 10.9
Sprinkler irrigation
1.1 0.7 0.4
The newly developed lands of various systems under Kalawewa tank will exceed by almost 2.5 times its existing irrigated area, thus calling for considerably
greater use of the local water yield. Under present conditions, the tank fills
up as a rule in the middle of the Maha season; after
which, until the beginning of Yala, it is generally
full and spills off the extra inflow. With the increase of the irrigated area,
the spilling off can be reduced to a minimum by gradual controlled filling
of the tank with water released from the Mahaweli. Thus the available active
storage of Kalawewa, when augmented from the Mahaweli
Ganga, will be sufficient to irrigate the proposed
area. It should be emphasized, however, that an increase in active capacity
of Kalawewa is desirable, as this would appreciably
improve water distribution.
The
main canals in system H were designed to obtain maximum use of the existing
channels by including the existing left and right-bank channels of the Kandalama tank, and the right-bank channel of the Kalawewa tank. These channels will be reconstructed suitably,
a new trace being proposed for the left-hank channel of Kalawewa. The total length of the main canals and their branches
is about 96 miles.
The
main drainage line will be the Kala Oya itself Its conveyance capacity
and the level regime satisfy the requirements of the water intake for the
drainage and spill flows. However, during floods.
the river overflows its banks and inundates a part of the developed
area. For protection, the lower areas will have embankments and the river
channel discharge capacity will be improved by excavation. Branch drainage
lines will follow the natural streams their channels will be deepened and
widened wherever necessary and the reaches at the confluence will be trained.
The total length of the main drainage lines and their branches is about 80
miles.
The
cost of irrigation in the 70 percent of new land for irrigation in system
H which is being included in Project I is estimated at Rs.90,210,000.
Since, as reported above, the cost of improving and reconstructing the existing
irrigated land of the system is Rs.27,440,000, the total cost of system I-I
in Project I is Its. 117,650,000. The operation and maintenance expenditure
is Its. 2,600,000.
8. Water Supply to the Irrigation
Systems
The
principle of water supply to the irrigation systems included in Project I
consists of regulating the diverted water of the Mahaweli Ganga
into tanks of the irrigation systems and issuing it to the irrigation network
as required. The tanks can provide seasonal regulation for the yield from
both the local catchments and the augmenting system but effective use becomes
possible only under a certain regime of water supply. Two main rules of water
operation must be followed
(i) In Maha, full discharge
is to be conveyed until the tanks are filled to NWSEL,1 or 3-5 feet beIow NWSE
L thereafter, the discharge conveyed from Polgolla
should not exceed current water consumption, with care being taken to reduce
conveyance to nil if the tanks spill.
1.
NWSEL =
Normal
Water Surface Elevation.
(ii) At
the beginning of Yala, the augmentation is to
be carried out by maximum flows in order to fill the tanks to NWSEL before
peak use, which occurs in July.
Operational
studies performed in accordance with these rules over a 20-year period,
considering 5-day discharges
at Polgolla and daily discharges at Elahera, showed that the augmentation from the Mahaweli needs
quite a regular regime, which can he maintained in practice.
These
operational studies, performed for the whole area tinder system H. revealed
that there was a deficit in water supply for 7 years out of 20 in the
Kalawewa tank and that the assurance of irrigation of lands
under its command did not exceed 65 percent, which is lower than the adopted
rate. After reducing the new area wider command of the tank from 48,200
to 31,300 acres (i. e. by 16,900 acres, or about
30 percent of the area in system H), the assurance of irrigation reaches
85 percent which is the standard for all lands under Project 1.
The
regime of water supply was determined by the design rates of water consumption
and was later checked at the higher duties for existing paddy and sugar
cane cultivation. The increase in duties affected water supply to the
lands under command of the Kalawewa tank only;
for other tanks in system H, D-l and G. this increase can generally be
met, without adversely affecting irrigation of the new lands.
Results
of the water control estimate for the Kalawewa
tank are tabulated below
TABLE II
Kalawewa — Water Control Estimate
Years of deficit
in the 20 years
45/45 45/46 47/48 49/50 52/53
55/56
58/59 Notes
series
Amount of deli-
Water
consump-
cit in the critical
tion Pot 48,200
months (June,
acres: June 43,800
July) 100 ac. ft.
ac.ft. July,
for area of 48,200
33,800 ac.ft.
acres.
12.7
9.2 31.5 15.7
42.0 22.7
8.0
Area assured
Water consump—
with irrigation
tion for 31.300
(% of given area) 62 73
25 54
0 32 76 acres: June 28,000
ac. ft.
July
21.800
ac. ft.
Amount of defl-
Increase in duty
cit for reduced
for existing pad
area of 31,300
over design duty
acres. — — 17.0
3.7 27.0
10.7 — 0.1
acre feet per
acre in critical
month.
It
can be seen from Table 11 that with the reduction of the area to 31,300 acres,
the deficit occurs in four years out of 20 ; in one
year of the four the deficit is only 16.5 percent of the consumptive use and
this can practically be ignored. It may be considered that the assured water
supplies to the area of 31,300 acres will be approximately 85 percent. The
reduction of the area will also offset the insecurity of considerable deficits
in the three consecutive years, occurring in the case of the full irrigated
area tinder the Kalawewa tank.
The
above considerations dictated the deferment of the development of 16,900 acres
within the new lands of system H until the third phase of development, by
which time an additional water source will give 100 percent assurance of water
issues to the entire area in this system.
9. Settlement and Agricultural
Use of Lands
Development
of the newly irrigated lands is based on the settlement of farmers
transferred from overpopulated regions of the country. The main contingent
of the relocated population will be farmers on small holdings (5 acres) whose
production will be based on the labour output of the family, using
animals and small machines to assist with the most laborious tasks. A smaller
number of farmers is proposed for medium-sized farms (I 5 acres) on which
specialized cultivation of high value crops, with a higher level of mechanisation
and hired labour, is envisaged. Urge plantations (200 acres) are proposed
for growing cotton and sugar-cane; they will be highly mechanised.
The
data of farm organisation is summarized in Table 12.
TABLE 12
Farm Organisation
Medium
Large
Systems Small farms
size farms Plantations Total
number area number
area number area number area
acres acres acres acres
(l,000s) (l,000s) (l,000s) (l,000s)
D and G
6,520 32.6
460 6.9
— 5.0
6,980 44.5
H 6.059 30.3
368 5.5
21 4.2
6,448 40.0
Total 12,579 62.9 828 12.5 21 9.2 13,428 84.5
Of
the total number of 12,579 small farms, 9,615 will be established by new settlers,
each farm representing a family. The other 2.964 farms will be provided by
enlarging” the present holdings. On the medium-sized farms and large plantations,
in addition to the farmers, 1,832 families of agricultural labourers will
be settled.
To
create proper conditions for providing community services, the settlements
will be set u p as villages containing 400 — 500 families ; a consolidated
system of water supply and electrification, administrative services, hospitals,
schools, and other public Institutions will be located in ‘townships’.
To render services in the field of administration and management,
medicine, education. etc., 2,100 families of service personnel will be required
in the townships and villages. There will be 26 new villages, and 8 new townships,
and the total number of families to be resettled is 14,396.
The total costs (‘post-devaluation’
rates) of settlements for the development area are given in Table 13.
Agricultural use of the irrigated
lands was designed by applying the following cropping patterns.
Paddy (paddy + paddy + legume)
(1)
Mixed rotation (paddy + high
value crops + legume) (2)
High value
crop rotation (cotton, chillies, groundnut, vegetables, etc.) (3)
Sugar-cane (5)
It is proposed that the existing
paddy lands be used for paddy rotation, while other lands presently irrigated
will preserve their existing pattern of crops.
The estimated yield of the
crops was based on the average level of farming practice which can’ he achieved
through moderate improvements to the existing practice. Below are given the
estimated yields of the main crops per acre:
Paddy (Maha
and Yala) – 56 and 61 bushels.
Cotton (one season)
– 10 cwt.
Groundnuts (one season) – 12 cwt
Maize (one season) – 20 cwt
Onions (one season)
– 80 – 90 cwt.
Sugar cane (one serason) – 25 tons
Distribution of the irrigated lands
by cropping pattern and the expected benefits are shown in Table 14.
TABLE 13
Project 1: Land Settlement Costs (post
– devaluation rates)
System D G
System H
Foreign Project
Net allo-
Project Net allo-
Exchange Proper cation to Proper
cation to
Project Project
Rs. (100s) Rs. (100s) Rs. (100s) Rs. (100s)
-
Health
.. 30% 1,800
2,450 800 1,080
-
Education
.. - 7,263 -
3,676
-
Water Supply
.. 40% 9,500
1,588 5,300 887
-
Electricity
.. - 6,930 -
3,867
-
Settlement Roads 10% 1,600
248 900 131
-
Farmers Cottages 10% 23,700 -
11,100 -
-
Extension services 60% 4,500 -
3,600 -
-
Irrigation Department 10% 1,300 -
1,500 -
-
Paddy stores
- 3,266 -
1,707
-
Farm working capital
-
New acreas 25% 17,800 - 20,000 -
-
Existing area 100% 5,300 - 3,300 -
-
Experimental Farm 60% 200 - 800 -
-
Postal services
- 819 - 492
-
Police
- 428 - 257
-
Veterinary services
- 185 - 11
-
Civic center - 625 - 345
-
Land Com. Department 10% 1,100 -
600 -
-
Social services
10% 100 - 100 -
-
Co – op
- 625 - 345
Totals by system
66,900 24,427 48,000 12,898
Total Project proper
114,900
Apart frown these costs, which are
allocated to the project proper, certain additional costs which cannot
be directly allocated 10 the project will be incurred. These will include
a part of the cost of land settlement. Transmission lines, and also a
part of overhead charges; all amounting to Rs.
46.9 million.
The current expenditure required to
operate the hydro-electric station and the irrigation systems, as well
as service to be rendered for the farmers, is estimated at Rs.
10 million (operation and maintenance of the irrigation systems, Rs. 7.3 million: operation and maintenance of the H ES. Rs. 0.4 million;
on extension services. Rs. 2.3 million).
Based on the ‘value added’ from production
and benefits with minor improvements in present agricultural methods,
and considering the duration of construction and development, the following
‘post-devaluation’ indexes of economic efficiency were obtained
Capital cost—Net benefit ratio 4.4 : 1 (market
prices)
Internal rate of return 17
percent at market prices
21
percent at accounting prices
As has already been pointed out, the
release of water from Bowatenne toward N4oragahakanda
can be used for power generation. The hydro-electric station
at Bowatenne is designed to have an installed capacity of 40
megawatts and firm power production of 135 million kWh. The cost of the
conveyance and hydropower plant is estimated at Rs.
42 million.
The value added’ from the power at
bus bars of the station provides, according to the estimation, an internal
rate of return of 15 percent.
Bowatenne hydra-electric station may be considered as quite independent; in
order that more electricity can be provided when it is required (which
depends on the actual power consumption in the next five years), it is
expedient to construct this station in the first phase simultaneously
with the P.K canal.
