| Divundu hydro power plant | Units |
Alt. A | Alt. B |
| Total capacity at mean head | MW | 19 | 20 |
| Total energy production | GWh | 150 | 160 |
| Total cost primo 1999 | mill. N$ | 297 | 345 |
| Unit Investment cost 1) | Ncent/kWh | 23 | 25 |
1) Annually distributed investment cost plus cost of operation and maintenance divided by the average annual production. 10% discount rate, 40 year lifetime, annual maintenance/operating cost 0.03 N$/kWh.
4.2 Project Description
4.2.1A Description of Alternative A
Appendix 1: Alt A; Map 1:50 000
The weir will be located approximately 2 000 m upstream of the "Popa Falls" in Okavango River close to Divundu village in Caprivi. A gross head of 9 m in the wet season and 10 m in the dry season will be obtained by construction of the 6 m high weir (from surface riverbed to to the highest regulated water level, HRWL). The weir will be 930 m long. The reservoir inundates 1.4 km2 of land. The water surface will normally be kept close to HRWL with option of 0.5 m regulation. The scheme will not affect Angola (inundation of land), and only marginally affect Botswana due to approximately 1.5 mill m3 annually increased evaporation. The power plant will be located at the outlet in the river downstream of the "Popa Falls". The total length of the waterway is 2 500 m. The access to the plant will be from the existing road, B 8. The plant will be connected to the local grid by a short transmission line.
4. 2.1B Description of the Alternative B
Appendix 2: Alt B; Map 1:50 000
The weir is located on the Popa Falls. The power station is located downstream of the rapids similar to alt. A. The gross head is approximately 9 m. The weir is 6 m high and the length is 2 150 m. The reservoir will inundate 2.1 km2 of land, and evaporation will be approximately 2 mill m3 annually.
4.2.2 Catchment Area - Runoff
| Part
of Catchment Area |
Identification | Area km2 |
Specific runoff l/s/km2 |
Mean inflow |
|
| m3/s |
mill m3/year | ||||
| 1 | Okavango at Divundu |
Approx 203 000 | 1.8 | 365 | 11500 |
4.2.3 Reservoirs
| Alternative | Name of Reservoir |
Before regulation |
After regulation |
Active Reservoir |
|||
| Area at NWL km2 |
NWL masl |
Area at HRWL km2 |
HRWL masl |
LRWL masl |
mill. m3 | ||
| A | 1.5 | 1001 | 2.9 | 1006 | 1005.5 | 1.1 | |
| B | 2.4 | 1001 | 4.5 | 1006 | 1005.5 | 1.7 | |
The inundated area is measured to 1.4 km2 in alt A, and 2.1 km2 in alt B. The transport of sediments in the river is unknown, but arrangement for flushing is assumed. A gravity-concrete weir is assumed (rockfill can be used as an alternative at both sides).
Alt. A:
The weir will be 8 m high (from cleaned damfoot to HRWL) and the crest
930 m long. The total volume will be 6 000 m3.
Alt B:
The weir will be 8 m high (from cleaned damfoot to HRWL) and the crest
2 150 m long. The total volume will be 35 650 m3.
Rock is exposed at the damsites. Some excavation and grouting are necassary to obtain a watertight and stable damfoot.
Diversion during construction will be obtained by means of cofferdams, culvert(s) and gates. It is assumed that some overflow during construction will be accepted.
The spillway is calculated as a fixed concrete weir. The alternative could be fixed labyrinth weir or with inflatable rubber gates. The Q1000 flood is estimated to be 8 000 m3/s with a max flood level up to HRWL+2,5 m in alternative A, and HRWL + 2 m in alternative B. The alternative with inflatable rubber gates will reduce the increase of water level during floods, and give an option for increased head during low flow periods.
4.2.4 Waterways
Section (from – to)
Type
Length, m
Cross-section
(m2 )
Diameter (m)
Alternative
Inntake – cone
Headrace tunnel / canal
2 000
150 m2
A
Cone-turbine
Steel
10
(2 x 5) m
A
Turbine – outlet
Tailrace canal
500
150 m2
A
Intake-turbine
Steel
10
(2 x 5) m
B
Turbine – outlet
Tailrace canal
500
150 m2
B
4.2.5 Power Station
The station will be located downstream of the "Popa Falls" on the
left river bank.
Alt. A
Alt. B
Dry
season
Wet
season
Dry
season
Wet
season
Underground / open powerhouse
Open
Open
Access tunnel
m
None
None
Capasity at max head
MW
20
21
Maximum flow
m3/s
250
250
Type of turbine
Kaplan
Kaplan
Number of units
2
2
Tailwater (Dry/wet season)
masl
996 / 998
996 / 998
Voltage
kV
33
33
4.2.6 Peak Power
The future value of peak power will probably give a higher optimum
capacity. The plant can be operated to meet daily peak power
demand.
4.2.7 Data on the powerplant (with restrictions; 20 m3/s water release
during 5 months)
Divundu Hydro Power Plant
Dry / wet
season1)
Dry / wet
season1)
Alt. A
Alt. B
1
Hydrological data
Catchment area
km2
?200 000
?200 000
Mean annual inflow
mill m3
11 500
11 500
Reservoir volume as % of annual
inflow
mill m3 / %
1.1/0
1.7/0
2
Power Station data
Mean gross head
m
10/9
10/9
Mean energy equivalent
kWh/m3
0.023/0.020 2)
0.024 / 0.022 2)
Max flow at mean head
m3/s
250
250
Max capacity at mean head
MW
19/16 3)
20/18 3)
Utilization time
hours
~6 500
~6 500
3
Energy, average
Energy production, firm
GWh
126
135
Energy production, surplus
GWh
24
25
Energy production annual
GWh
150
160
4
Cost estimate/Economy
Construction period
years
3
3
Cost estimate primo 1999
mill N$
297
345
Specific cost
N$ /kWh
1.98
2.16
Unit investmentcost 4)
Ncent/kWh
23
25
1) 60 % of the year is estimated as dry season and 40 % as wet season.
2) The energy equivalent is based on the net head, which is lower
in Alt A than B due to energy loss in a longer waterway.
3) The output during the dry season will be 15 - 19 MW and 16 - 20
MW in the wet season.
4) 10% discount rate, 40 years lifetime, annual maintenance / operating
cost 0.03 N$/kWh.
4.2.8 Access roads
The power plant will be located close to the existing infrastructure,
which are: roads, grid, restcamps, shops, hospital, airport (small
aircrafts) etc. The need is only to build short access roads to the powerstation
and the weir.
Section (from – to)
Type
Length, km
Temporary/Permanent
Exist. road-station
Upgrad./new tarred road
2
Permanent
Exist. road- weir
Gravel surfaced
2
Permanent
4.2.9 Grid
The powerplant is located close to the local 33 kV-grid, which also
connects Divundu to Rundu through a 200 km 33 kV-line The connection
to the local 33 kV-grid will be permanent. The power from Divundu will
mainly be used in the Caprivi area, but will also be a supplement
to national demand. The need for upgrading the transmission line
to Rundu has not been evaluated. However, the Divundu scheme will enhance
connection of the Eastern Caprivi (Catima Mulilo) to the Namibian
transmission network.
Section (from-to)
Lenght, km
Voltage, kV
Capacity existing transmission line
(assumed)
Powerstation - grid
2
33
30 MW
4.2.10 Tele Communication
Local grid will be used.
4.2.11 Location of (Tunnel) Masses
The tunnel/canal masses will be placed near the power station. As
an alternative the masses can be used for construction of roads
or for other purposes.
4.2.12 Borrow pit - Mass – Quarry
It is assumed that the aggregates for the concrete work can be taken
from suitable places in the neighbour-hood.
4.2.13 Costs
Costs (mill N$) pr 01.01.99 (10% pa interest during construction period)
Divundu Alt. A
(Dam wall above the rapids)
Divundu Alt. B
(Dam wall on the rapids)
1
Reservoir, weir cost
39
117
2
Diversion 1)
0
0
3
Waterway (Penstock included)
61
17
4
Power station (civil works)
14
14
5a
Power station (mechanical)
39
39
5b
Power station (electrical)
41
41
6
Access roads, Temporary lines, Transportation
4
4
6b
Permanent transmission lines
1
1
7
Housing. Workshop. Admin. block. Storage, etc.
5
5
8
Landscape design, etc
5
5
9
Contingency
17
20
10
National taxes
0
0
11
Planning. Administration)*
23
26
12
Compensation. etc.**
8
9
13
Financing costs (I of 1-12)***
40
47
Total estimate cost
297
345
1) Included in reservoir costs.
Specific cost: Alt A: 1.98 N$/kWh, Alt. B: 2.16 N$/kWh,
Based on mean annual production.
* Planning/administration are calculated with 10% for civil work,
and 5% for electrical and mechanical work.
** 4% of 1 – 6 is used, which is normal according to experiences from
other hydropower scehemes.
The mitigation for each scheme will decide the actual level.
*** Calculation formula:
I = (1.05(1.10 t - 1))/(0.10 t) - 1, "t" is construction period in
years
"I" is to be multiplied with the sum of 1 – 12
Unit investment cost with different discount rate (Ncent/kWh)
Alt
7 %
10 %
15 %
A
17.2
23.2
37.9
B
18.5
25.1
35.0
4.3 Hydrology, Consequenses
4.3.1 Use of reservoir
The level of the reservoir will be held close to HRWL most of the
year. (If peak power is needed, a small regulation (0.5 m) can
be used. The length of the reservoir at HRWL will be approximately
4 km in alt. A, the surface area is 2.9 km2, and the inundated
land area is 1.4 km2. The length of the reservoir at HRWL is 6 km
in alt. B, the surface area is 4.5 km2, and the inundated land area
is 2.1 km2.
4.3.2. Discharge
The capasity of the plant is 68 % of Q mean. This means that in approximately
70 % of the year there will be water over the weir and so in
Popa Falls. The rest of the year at least 20 m3/s compensation water
is included in the calculations. This is released through the
weir.
4.3.3 Flood
Implementing the reservoir will not make any influence on the floods
or waterlevel in the river downstream of the plant. Upstream
of the weir a certain backwater will occur, but in this case the effect will
be small and will not affect Angola.
4.4 Compensated Initiatives
4.4.1 Planned Compensation
Resettlement of directly affected people is included in the costs.
This cost will depend on the local situation. In this case we
have used 4% of 1 – 6 in the cost to come up with a general figure.
The 4% is normal according to experiences from other hydropower
schemes. The mitigation for each scheme will decide the actual
level. In the cost estimate 8 mill N$ for alt A, and 9 mill N$ for
alt B is assumed to be used for compensation.
The minimum amount of water release is assumed to be 20 m3 / s in
approximately 5 months.
4.4.2 Possible Compensation
Peak power operation is possible during the day, and should be discussed
in later studies in order to highlight possible negative environmental
impacts and actions to reduce them.
5 Socio-economic and Environmental Considerations
The plant will have a long utilization time, and be in operation nearly
all the year. The reservoir created by the weir is not big enough
to manipulate the river flow, therefore it will always be water in
the river downstream of the scheme.
The inundated area is approximately 1.4 km2 in alt A, and 2.1 km2
in alt B. The scheme will not affect Angola. Approximately 75
huts, 15 houses and 4 campsites around Divundu will be affected by
the increased water level. A socio-economic programme must therefore
be established to secure new land and improved life for the people
directly affected. Due to the increased water surface, the annual
evaporation will increase by approximately 1.5 mill m3 (alt A)
and 2 mill m3 (alt B), and thereby have a minor impact on the
flow into the Okavango Swamps. However this flow is 11 500 mill m3
annually at Divundu.
The rapids inhabit a small-sized rare fish species, which could be
negatively affected during construction, and later operation
of the plant. The biological life in the river between the dam and
the outlet from the powerstation must be thoroughly studied and
measures taken to prevent severe impacts.
The scheme will enhance the connection of the Caprivi to the main
grid in Namibia. Secured electricity supply is a prerequisite
to develop the agriculture potential in Caprivi. This added value
to the local society should be investigated.
6 Other alternatives
The plant has not been optimised. In addition to the two described
alternatives there are several alternative heads, capasities,
damsites, spillways and combinations that should be investigated at
later stages of the planning.
1
2
01.09.00
ABBREVIATIONS:
NWL Normal Water Level
HRWL Highest Regulated Water Level
LRWL Lowest Regulated Water Level
masl meter above sea-level
UNITS
Output 1 MW = 1000 kW
Energy 1 GWh = 1 mill kWh
Voltage 1 kV = 1000 V