LAKE BASIN DEVELOPMENT AUTHORITY
Proposal for the
Feasibility Study of
Webuye Falls Hydropower Project.
MAY 2008
1.0 Introduction
Lake Basin Development Authority was established under the Act of Parliament as a
statutory organization in 1979 for promoting regional development and domestic resources
for equitable development. The authority undertakes overall planning, co-ordination and
implementation of development projects and programmes in the region. Among the
development options that have been proposed include hydropower harnessing from identified
sites within the jurisdiction of the authority.
Nzoia River falls within the jurisdiction of Lake Basin Development Authority and flows
within a valley exhibiting fairly gentle slopes, an exception to this being where the river
descends the Nandi Escarpment so forming the Webuye falls. Though many possible dam
sites exist, the available head for generation of hydroelectric power is generally limited to
that provided by the dams themselves. The individual potential of hydroelectric project at
Webuye Falls is examined within this proposal for a feasibility study. The study encompasses
the possibility of construction of intake structure, embankment, tunnel, spillway, and surge
chamber, diversion and outlet works, powerhouse and switchgear, access road and railway
diversion
2.0 Problem statement
Even though the Lake Basin region is endowed with abundant water resources with potential
sites for hydropower generation, the region still suffers from inadequate power supply from
the national grid, which would otherwise promote accelerated industrial development
especially in rural areas. There have been proposals for small-scale industries e.g. proposed
pineapple-processing plants but the development of such can be accelerated with an
increased pace of rural electrification programme.The rural population would also benefit
from improved lighting in homes. The rate of destruction of forests would also reduce, as
electrical energy would be available for use in small-scale industries in the rural areas.
Currently, Kenya’s energy production and consumption are well below the levels needed to
support not only a satisfactory standard of living but also the country’s vision of
industrialized economy by the year 2030. In addition, frequent droughts experienced from
major hydropower generation reservoirs have meant power rationing so as to meet the high
demand. The development of other power services will therefore be an important element of
the regional development policy as it will stimulate industrial and agricultural development
as well as promote general welfare in the rural areas.
3.0 Background Information
Energy Sector
Kenya’s energy sector is largely dominated by imported petroleum for modern sector and
wood fuel for rural communities. The current domestic demand for petroleum fuels account
for 25% of the total import bill. In terms energy supply, wood fuel provides about 68% of the
total energy requirements, petroleum energy 20%, electricity 10% and other alternative
sources account for 2%. The above statistics indicates that Kenya’s current electricity
generation capacity is inadequate, with demand regularly exceeding supply during peak
periods. This normally leads to rationing which obviously affects the performance of the
economy. This reflects the requirements for developing other power services to deliver
adequate supplies to the large urban centres, fast growing towns and small urban centres in
rural areas. With increased pace of modernization and limited supply of electrical energy, it’s
obvious that Kenya’s electricity generation capacity will be inadequate with demand
regularly exceeding supply during peak periods.
4.0 Literature Review
Previously in 1985, C Lotti and Associates completed and submitted a report on the ‘Lake
Basin River Regulation and Hydropower Development Options’. In their report they
identified potential hydropower sites on six major river basins namely, Sio, Nzoia, Yala,
Nyando, Sondu and Kuja. Two major hydropower development options were identified in
Nzoia basin namely; Webuye falls dam and the Hemsted Bridge-Kerio transfer scheme. The
river flow availability in the Nzoia Basin is entirely sufficient to meet projected consumptive
demands. Table 4.1 shows development options on the basis of the benefit-cost ratios. On
this basis it is seen that only two options namely Webuye Falls dam scheme and Hemsted
Bridge-Kerio transfer scheme show benefit-cost ratios close to unity.
Webuye Falls Dam
The Nzoia River cascades waterfalls some 40m in height at Webuye. Various alternatives
were examined by Lotti and Associates to exploit this natural feature for the purpose of
hydropower generation. Fundamental to these alternatives is the need to provide regulatory
storage to enhance the otherwise low dry season flows. Combined developments of either
Rongai or Lugari storage reservoirs together with a run-of-river scheme at Webuye have
been examined. However, these schemes were found to be uneconomical. The favored
arrangement would comprise a 54m high dam some 2.5 km up the stream of the falls
supplying a single 30MW power station by means of a 3000m long 3.4m diameter concrete
lined tunnel. The reservoir with a full supply level of 1555m would provide a live storage of
200x106m3, equivalent to 14% of the mean annual flow. The firm yields of this reservoir; net
evaporation and anticipated future public water supply requirements would be 17.1 m 3/s. A
low ridge on the left bank of the river appears to limit the height of the dam and therefore the
storage capacity.
The wide valley favors an embankment type dam with a reinforced concrete chute spillway
situated on the left flank. A spillway design flood of 1525m3/s has tentatively been assumed
for the purpose of estimating construction costs. The site topography lends itself to a general
arrangement of the power system with a surface powerhouse fed by a long headrace tunnel; a
surge chamber located on a knoll some 300m from the powerhouse. A reinforced concrete
intake structure would house control gates and trash removal facilities at the head of the
tunnel system.
Access to site would require the construction of some 4km of access roads while it has bee
assumed that construction personnel would be housed in Webuye township, thereby
benefiting from the existing infrastructure and minimizing project cost. The existing NairobiKampala railway line traverses the impoundment area of the reservoir. It will therefore be
necessary that the railway is diverted to a new alignment crossing downstream of the
proposed dam and hence passing to the south of the reservoir. The need for diversion is
therefore included in the feasibility study and cost of the project.
More detailed studies will be required to finalize scheme details. In particular, an increase in
the reservoir storage, should topographical and geological conditions be satisfactory, would
sustain an increased firm yield. Alternative power system layouts including underground
power houses may also require consideration in view of the limited area available for
construction of surface works within the gauge downstream of the falls. The benefit-cost
ratio of 0.94 indicates that the cost effectiveness of the project is marginal at present cost and
benefit levels. Table 4.1 below shows the development options that can be considered on
Webuye falls.
Table 4.1 Webuye falls development options
Description
Unit
Development option
Webuye fall
Webuye falls
Webuye falls
Webuye falls
Run-of-river
Supported by
Plus Lugari
Dam
Lugari
Dam fill volume
MCM
0.1
0.1
0.1+ 6.37
3.88
Reservoir storage
MCM
-
-
234
200
Head (gross)
M
60
60
60 + 55
105
Head (mean/min)
M
55/55
55
50/25 +55
92/72
MW
16
16
15 + 16
30
Ksh. (million)
249
249
2481
1264
3
m /s
2.0
17.8
17.8
17.1
Firm energy
GWh/year
7.7
68.61
130.98
113.45
Secondary energy
GWh/year
92.5
23.89
78.79
54.00
Firm energy
Ksh. (million)
69.38
617.47
1178.81
1020.92
Secondary energy
Ksh. (million)
277.60
71.67
144.15
162.02
Total
Ksh. (million)
346.98
689.14
1322.96
1182.94
1.39
2.77
0.89
0.94
(live)
Installed power
Capital cost
Firm flow
Capitalized power
benefits
Benefit-cost ratio
5.0 Project Description
According to Lotti and Associates the proposed project will comprise a 54m-earth
embankment dam located at 2.5 km upstream of Webuye falls. A reservoir with a full supply
level would supply a live storage of 200x106 m3. The dam is expected to supply a single
30MW power station by means of a 3000m long 3.4m diameter concrete lined tunnel with a
reinforced concrete intake structure with control gates and trash removal facilities. There
would also be a surge chamber located on a knoll 300m from the powerhouse. Access to site
would also require construction of 5 km access roads. It is also proposed that the existing
Nairobi-Kampala railway line traversing the impounded be diverted to a new alignment.
Table 5.1 below shows the project work summary while table 5.2 shows the cost estimate
breakdown of the proposed works.
Table 5.1 Webuye falls dam project work summary
Description
Reservoir
Dam crest level
Full supply level
Gross storage
Live storage
Mean annual runoff (M. A. R)
Live storage (% M. A. R.)
Gross storage (% M. A. R.)
Gross yield
Net yield
Dam
Dam type
Dam height
Fill volume
Power system
Gross head
Net head
Installed capacity
Power tunnel length
Spillway
Spillway type
Spillway capacity
Hydrologic data
Mean annual Eo
80% probability rainfall
Drought year losses
Quantity
1560m
1555m
220*103 m3
200*103 m3
1437*103 m3
14%
41%
18.6m3/s
17.1m3/s
Earth fill embankment
54m
3.81*103 m3
105m
102m
30MW
2.7 km
Free overflow chute
1525m3/s
1800 mm
1320 mm
480 mm
Table 5.2 Webuye falls dam (Cost estimate breakdown)
Description
Access roads
Camp and sit facilities
Embankment
Sub-total
Spillway
Excavation (soft)
Excavation (hard)
Concrete
Formwork
Reinforcement
Sub-total
Intake
Excavation (soft)
Excavation (hard)
Concrete
Formwork
Reinforcement
Structural steel
Gates, screens, etc
Sub-total
Tunnel
Excavation (soft)
Excavation (hard)
Excavation (tunnel)
Excavation (shaft)
Concrete
Formwork
Reinforcement
Over break
Shot Crete
Rock bolts
Steel pipes
Sub-total
Surge chamber
Excavation (soft)
Concrete
Formwork
Quantity Unit Rate
(Kshs)
5
Km 85.25
Sum
3
3880000 M
213.273
Amount
(millions)
42.625
50
827.5
924.125
64950
60000
27078
16800
1800
M3
M3
M3
M2
t
116.4
583.3
5191.7
851.2
50377.8
7.56
35
140.58
14.3
90.68
288.12
3000
2000
5670
7315
638
120
M3
M3
M3
M2
t
t
116.7
580
5194
853.04
50313.5
193750
Sum
0.35
1.16
29.45
6.24
32.1
23.25
32.16
124.71
2000
2000
37700
707
10788
28840
359.6
38641
18848
28266
98.6
M3
M3
M3
M3
M3
M2
t
M2
M2
m
t
115
580
2557.3
5799.5
5193.7
851.6
28086.8
1394.89
13959
1394.3
232657.2
0.23
1.16
96.41
41
56.03
24.56
10.1
53.9
26.31
39.41
22.94
372.05
3141
1130
1005
M3
M3
M2
5810.3
5212.39
848.26
18.25
5.89
0.8525
Reinforcement
Sub total
Diversion and outlet works
Excavation
Concrete
Formwork
Reinforcement
Cofferdams
Sub total
Power house and switch yard
Excavation (soft)
Excavation (rock)
Concrete
Formwork
Reinforcement
Structural steel
Finishes, services etc
Sub total
Railway diversion
Grand total
113
t
50442.4
5.7
30.6925
4800
2100
3600
180
M3
M3
M2
t
581.25
5190.5
850
50388.9
sum
2.79
10.9
3.06
9.07
7.75
33.57
2000
1100
10520
16160
745
20
M3
M3
M3
M2
t
t
116.25
5809.09
5193.9
853.96
50402.68
193750
Sum
15
km
2121.5m
0.2325
6.39
54.64
13.8
37.55
3.875
96.875
535.96
322.6
2631.83
5.1 Project Location Characteristics
The proposed hydropower project is located in Nzoia river basin in Bungoma east district of
western province. The River Basin measures 12, 843 km2, the length of the mainstream is
275 km and the average elevation is 1,917m above sea level while the maximum elevation on
top of mount Elgon is about 4,300m above sea level. The mean slope of the river is 0.01,
while that of the basin is 0.071. The mean annual rainfall of the whole basin varies from
about 1000 mm at the mouth to more than 2100 mm east of Kakamega. The project dam site
is located in Bungoma East district in Western Province of Kenya.
6.0 Objectives
Under the rural Electrification programme, the main objective of the government is to
provide electricity to as many parts of the country as possible and reduce demand on wood
fuel and petroleum for industry. The objectives of this project would therefore be:
To increase the supply of energy in the region.
To reduce the country’s dependence on imported petroleum energy.
To stimulate industrial development in the region.
To reduce demand on wood fuel and conserve forests.
To alleviate poverty in the region and raise standards of living.
To encourage the development of agro-business and agricultural processing plants.
7.0 Scope Of Work
Webuye falls scheme has a potential of generating 30MW. The scope of work comprises
collection and analysis of all relevant data and carrying out detailed studies to determine the
technical and economic feasibility as well as social and environmental acceptability of the
project. The study will make use of earlier studies, and where appropriate will recommend
new alternatives which would lead to an optimal development of the river potential. The
accepted alternative will be advanced to full feasibility study with emphasis laid on the
optimum development of the power potential. This will entail detailed site investigations and
design studies leading to confirmation of the engineering viability of the scheme and
improved assessment of construction costs.
7.1 Exploring and Inception phase
The inception phase of the project shall include the following activities by the consultant:
Provide consolidated review of data and information from all relevant previous studies.
Undertake topographic surveys of all relevant areas and provide mapping to appropriate
scales and contour intervals as agreed with the client.
Provide review of the alternatives that exist for river regulation and hydropower
development at Webuye falls dam and demonstrate that the selection of the same as a site
for hydropower generation is economically viable.
Make recommendations for the development concepts to be considered in the full
feasibility studies.
Provide detailed recommendations for the scope of work to be undertaken in the
feasibility studies.
Provide detailed description of the impact of the project on the environment and on
public health and make recommendations on catchments conservation measures to be
considered in full feasibility study.
Provide detailed recommendations on how the local community would participate in
project implementation.
All findings of the phase I work will be presented to the client (within ten months of the start
of the work) in form of an inception report. The report should have a proposed table of
contents for the final feasibility study report.
7.2 Feasibility studies
7.2.1 Field Investigations and Project formulation
Field investigations shall be carried out in sufficient detail to allow for international project
appraisal and subsequent preparation of tender designs and tender documents. The
following activities shall be included in this phase of the study:
(a)
Complete any necessary action, administrative and physical, to facilitate site
access and establish any necessary on site working facilities.
(b) Develop and carry out complete geotechnical and geological field program.
(c) Establish an agreed flow record for project design purposes. Establish flood estimates
suitable for decision and spillway designs; establish probable maximum flood estimate.
(d) Prepare alternative hydropower layouts and scopes of development.
(e) Conduct environmental impact assessment.
(f) Provide preliminary estimates for alternative layouts established in (d) above.
(g) Provide an interim report to the client within eight months of the start of the study,
including detailed recommendations on the project layout(s) to be taken to full feasibility
level. Discuss conclusions with the client and funding agency.
7.2.2 Feasibility studies
(a) Taking into consideration the comments on the interim report and having regard for
the findings of the field investigations, prepare a recommended project layout on the basis
of the further studies including:
- Finalize dam/diversion/spillway design and optimization of dam crest elevation.
- Select installed generating capacity, and number type of turbine generator units.
- Optimize water passage design and sizing, having regard for the likely operating
modes of station.
- Finalize powerhouse, switch house, switchgears and interconnection arrangements,
having regard for KENGEN design and operation standards.
(b) Finalize assessment of socio-economic and environmental impacts and compensation
costs.
(c) Prepare detailed cost estimates; capital and recurring for all works including
construction costs, engineering, project management and owner costs operation and
maintenance.
(d) Prepare time schedules for project appraisal, financing and contract award,
construction and commissioning through to full production.
(e) Prepare cash flows to a quarter-annual disbursement schedule, separating major
items/contracts into foreign and local cost components and showing separate allowances
for physical and price contingencies.
(f) Undertake detailed economic analysis of the ‘with’ and ‘without ‘ project scenarios to
determine the economic viability of the proposed hydropower generation. The analysis
should be based on economic pricing including shadow pricing of all costs and benefits,
with presentation of results including:
- Net benefits and benefits/costs ratios versus discount rate.
- Internal rates of return.
- Sensitivity analysis against all significant variables, costs, benefits or demerits that
have been omitted from the economic analysis, including benefits derived from
environmental improvements.
7.3 Phase III Project Preparations, Design And Tender Documentation.
The consultant shall also prepare the following final tender documents:
(a) Tender documents for civil works.
(b) Tender documents for metal works.
(c) Tender documents for generating equipment, transmission lines and sub-station
equipment.
(d) Prepare final estimates of the financing requirements for all contracts, including separate
allowances for physical and price contingencies, showing foreign and local costs components
separately; and showing disbursement schedules.
(e) The consultant will be expected to provide draft tender documents and discuss with the
client within twenty-one months of the start of the study.
(f) The consultant will be expected to provide final tender documents within six weeks of
receiving the client’s comments.
8.0 Reporting
The consultant shall prepare and provide the following reports during the study as shown in
the time schedule in Annex I.
(a) Inception report
(b) Interim report
(c) Draft feasibility report
(d) Final feasibility report.
(e) Draft Tender Design/documents
(f) Final Tender Design/documents
(g) Progress reports.
9.0 Training Provisions
Training is an important part of the feasibility study and the consultant shall offer facilities to
be agreed with the client for both on-the-job training and short courses at the consultant’s
head offices and approved institutions of higher learning.
Annex I Time Schedule (Months)
Month
Phase I INCEPTION
Inception Report
Client/financier comments
Phase II FEASIBILTY
STUDIES
Interim Report
Client/financier comments
Draft Feasibility Report
Client/financier comments
Final Feasibility Report
Phase III TENDER
DESIGN AND TENDER
DOCUMENTATIO N
Draft Tender
documentation
Client Comments
Final Tender Documents
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