REPUBLIC OF KENYA COAST WATER MINISTRY OF WATER SERVICES BOARD AND IRRIGATION (CWSB)
Water and Sanitation Service Improvement Project (WaSSIP) Loan Nos.: IDA 4376-KE and CKE3010-1
Consultancy Services for Water Supply Master Plan for Mombasa and Other Towns within Coast Province
Final Full Feasibility Study
May 2013 (modified ver. 4 November 2013)
in association with Contents Page
Executive Summary 1. INTRODUCTION ...... 1 1.1 Background ...... 1 1.2 Objectives of the Present Report ...... 1 1.3 Previous Reports and Related Studies ...... 2 1.4 Structure of the Present Report...... 3 2. POPULATION AND WATER DEMAND PROJECTIONS ...... 5 2.1 General ...... 5 2.2 Population Projections ...... 5 2.3 Water Demand Projections ...... 7 2.4 Water Demand – Urban and Rural ...... 8 2.4.1 Water Demand of the 20 Main Urban Centres ...... 8 2.4.2 Water Demand of Rural Bulk Consumers...... 9 2.4.3 Target Water Demand for CWSB ...... 10 2.4.4 Demand Management ...... 10 3. CURRENT AND POTENTIAL WATER RESOURCES ...... 13 3.1 Current Water Resources ...... 13 3.1.1 Mzima Springs ...... 13 3.1.2 Baricho Wellfield ...... 14 3.1.3 Total Production of the Current Water Systems ...... 18 3.2 Water Resources Management ...... 18 3.2.1 Overview ...... 18 3.2.2 Existing Situation ...... 19 3.2.3 WRMA Catchment Strategies ...... 26 3.2.4 Principles of Water Resources Management ...... 28 3.2.5 Proposed Actions ...... 30 3.3 Potential of Surface Water Resources ...... 31 3.3.1 Mkurumudzi Dam ...... 31 3.3.2 Tana River ...... 32 3.3.3 Mwache Dam ...... 33 3.3.4 Rare Dam ...... 41 3.4 Potential of Groundwater Resources ...... 45 3.5 Potential of Deep Groundwater ...... 46 3.5.1 Overview and Preliminary Analysis ...... 46 3.5.2 Recommendations: General Exploratory Plan ...... 49 3.6 Total Potential of Water Resources ...... 50 4. PROPOSED STRATEGIES AND SCENARIOS ...... 52 4.1 Defining Strategies for Development ...... 52 4.2 Coverage of the Master Plan ...... 53 4.3 Meeting the Potential Demand ...... 53 4.4 Water Supply Scenarios for the Interconnected Bulk System...... 56 4.4.1 Scenario B1 ...... 58 4.4.2 Scenario B1.1 ...... 62 4.4.3 Scenario B3 ...... 66 4.4.4 Scenario B5 ...... 71 4.4.5 Scenario C2 ...... 75 4.5 Water Supply to Lamu and Tana Counties...... 79
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Contents (cont.)
4.5.1 General ...... 79 4.5.2 Supply Alternatives ...... 79 4.5.3 Discussion ...... 80 4.6 Water Supply to Taveta Area ...... 81 4.6.1 Overview ...... 81 4.6.2 Water Supply Alternatives ...... 82 4.6.3 Discussion ...... 85 4.7 Water Supply to Remote Rural Areas ...... 86 4.7.1 General ...... 86 4.7.2 Rainfall Roof Harvesting ...... 86 4.7.3 Surface Catchment Systems ...... 88 4.7.4 Water Pan for Runoff Water Harvesting ...... 88 4.7.5 Sand Dam ...... 90 5. FINANCIAL AND ECONOMIC ANALYSIS ...... 92 5.1 Introduction ...... 92 5.2 Methodology ...... 92 5.3 General Assumptions for the Evaluation ...... 94 5.4 Cost Estimates ...... 95 5.5 Stand-Alone Analyses of Projects ...... 98 5.6 Financial Analysis ...... 100 5.6.1 General ...... 100 5.6.2 Total Investment ...... 100 5.6.3 Average Capital Cost per m3 ...... 100 5.6.4 Cost of Energy per m3 ...... 101 5.6.5 Cost of O&M per m3 ...... 101 5.6.6 Total Cost of Water per m3 ...... 101 5.6.7 NPV and IRR ...... 102 5.7 Economic Analysis ...... 103 5.7.1 General ...... 103 5.7.2 Cost of Energy per m3 ...... 104 5.7.3 Cost of O&M per m3 ...... 104 5.7.4 Total Cost of Water per m3 ...... 104 5.7.5 ENPV and EIRR ...... 105 5.8 Financial & Economic Analysis for Lamu Area ...... 106 5.9 Analysis of Supply Options for Taita-Voi Area ...... 109 6. MULTI-CRITERIA ANALYSIS ...... 111 6.1 Background ...... 111 6.2 Results ...... 112 7. ADDITIONAL DEVELOPMENT CONSIDERATIONS ...... 115 7.1 Significance of the Development of the Bulk Water Supply System on the WSP's Water Distribution Networks ...... 115 7.1.1 Overview ...... 115 7.1.2 Impact on Water Pressures ...... 115 7.1.3 Impact on Water Losses ...... 116 7.1.4 Effect of Pressure on Pipe Bursts ...... 116 7.1.5 Effect on the Mode of Water Supply ...... 117 7.1.6 System Operation ...... 117 7.2 Significance of the Bulk Water Supply System on the Negative Effect of Sewage Volumes ...... 118
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Contents (cont.)
7.2.1 Increase in Generated Wastewater Quantities ...... 118 7.2.2 Long-Term Planning of the Wastewater Collection System ...... 118 8. DISCUSSION AND CONCLUSIONS ...... 120
List of Annexes
Annex 1 – The MRS Model Annex 2 – Financial and Economic Analysis Annex 3 – Basic Unit Costs Annex 4 – Geotechnical Survey of Proposed Dams Annex 5 – Summary of Groundwater Model Runs Annex 6 – Mwache Reservoir Operation Model Annex 7 – Mwache Reservoir Operation Model (considering climate change) Annex 8 – Mwache Reservoir Filling Probability
List of Tables
Table 6-2: Multi-Criteria Analysis for Bulk Water Supply ...... 14 Table 2-1: Coast Province – Past Population Data and Projections to 2035 ...... 5 Table 2-2: Coast Province Population Projections, by District ...... 6 Table 2-3: Kenya MWI Standards for Per Capita Water Use ...... 7 Table 2-4: Total Water Demand Based on MWI Standards ...... 7 Table 2-5: Water Demand Projections for the Target Urban Centres...... 8 Table 3-1: Daily Flows on Monthly and Annual Basis Having Probability of 50, 90, 95 and 100% (m3/s) ...... 17 Table 3-2: Current Water Supply Capacity in the Coast Province ...... 18 Table 3-3: List of River Gauging Stations, Available Data and Condition ...... 20 Table 3-4: Tana River at Garsen Hydrometric Station 4G02 – Flow Duration Curves Fractiles of All Measured Daily Flows (1950–1998) ...... 33 Table 3-5: Averages and Standard Deviations of Precipitations for 14 and 50 years ...... 34 Table 3-6: Measured Mean Monthly Flows at 3MA03 Hydrometric Station (m3/s) ...... 35 Table 3-7: Major Characteristics of the Rainfall Stations ...... 36 Table 3-8: Mwache Reservoir Site – Simulated Monthly Flows (MCM), 1958/59– 2007/08 ...... 38 Table 3-9: Reliability Levels of Different Reservoir Volumes ...... 39 Table 3-10: Reliability Levels of Different Reservoir Volumes (Climate Change Considerations) ...... 39 Table 3-11: General and Model Parameters of the Rare River...... 42
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Contents (cont.)
Table 3-12: Rare Reservoir Site – Simulated Monthly Flows (MCM), 1958/59–2007/08 ...... 42 Table 3-13: Installed Capacity and Potential of Water Resources in the Coast Province ...... 51 Table 4-1: Water Resources Development by Phases – 5 Development Scenarios ...... 57 Table 4-2: TAVEVO Water Supply (2008–2010) ...... 81 Table 4-3: Water Demand Projection for Taita Taveta County ...... 82 Table 4-4: Development Scenarios for Taita Taveta County ...... 84 Table 4-5: Construction Cost of Roof Rainwater Harvesting ...... 87 Table 4-6: Cost of Building a Sand Dam for Average Volume of 100,000 m3 ...... 90 Table 5-1: Cost Estimates for the Various Systems ...... 96 Table 5-2: Basic Financial Indicators by Scheme ...... 98 Table 5-3: Basic Financial Indicators by Scenario ...... 100 Table 5-3: Calculated Indicators – Financial ...... 103 Table 5-4: Basic Economic Indicators by Scenario ...... 103 Table 5-5: Calculated Indicators – Economic ...... 106 Table 5-7: Lamu Area – Basic Financial Indicators by Scenario ...... 106 Table 5-8: Lamu Area – Basic Economic Indicators by Scenario ...... 107 Table 5-9: Lamu Area Calculated Indicators – Financial ...... 109 Table 5-10: Lamu Area Calculated Indicators – Economic ...... 109 Table 6-1: Classification and Weighting of Parameters and Indicators for ...... 111 Table 6-2: Multi-Criteria Analysis for Bulk Water Supply ...... 112 Table 6-3: Multi-Criteria Analysis for Bulk Water Supply (Engineering priority) ...... 112 Table 6-4: Multi-Criteria Analysis for Bulk Water Supply (Environmental priority) ...... 113 Table 6-5: Multi-Criteria Analysis for Bulk Water Supply (Social & Political priority) ...... 113 Table 6-6: Multi-Criteria Analysis for the Lamu Area ...... 114
List of Figures
Fig. 2-1: Daily water demand in the horizon year (2035) ...... 12 Fig. 3-1: Map showing geology of the area near Baricho ...... 15 Fig. 3-2: General map showing location of paleochannel near Baricho ...... 16 Fig. 3-3: Duration Curve of the Sabaki River Near Baricho ...... 17 Fig. 3-4: River gauging stations in Athi Catchment area ...... 22 Fig. 3-5: Tana River at Garsen Hydrometric Station 4G02 – flow duration curve of all measured daily flows (1950–1998) ...... 33 Fig. 3-6: Mwache Hydrometric Station 3MA03 – comparison between observed and simulated monthly hydrographs ...... 36 Fig. 3-7: Mwache Hydrometric Station 3MA03 – comparison between observed and simulated monthly flow duration curves (1976/77–1989/90) ...... 37 Fig. 3-8: Volume – Area – Elevation Curve for the proposed Mwache Reservoir ...... 40 Fig. 3-9: Layout Map of the proposed Flooded Area of Mwache Reservoir ...... 41 Fig. 3-10: Volume – Area – Elevation Curve for the proposed Rare Reservoir ...... 44 Fig. 3-11: Layout Map of the proposed Flooded Area of Rare Reservoir ...... 45
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Contents (cont.)
Fig. 3-12: Alternative locations for deep exploratory/production wells for the Neogene Aquifer ...... 48 Fig. 3-13: Schematic cross-section of the Neogene Sequence between Garissa and Kipini wells ...... 49 Fig. 4-1: Calculated demand curves, current (2012) consumption and actual curve ...... 54 Fig. 4-2: Development of water resources vs. demand – Scenario B1 ...... 58 Fig. 4-3: Block Diagram – Scenario B1 ...... 60 Fig. 4-4: Layout Map of Sequential Development – Scenario B1 ...... 61 Fig. 4-5: Development of water resources vs. demand – Scenario B1.1 ...... 62 Fig. 4-6: Block Diagram – Scenario B1.1 ...... 64 Fig. 4-7: Layout Map of Sequential Development – Scenario B1.1 ...... 65 Fig. 4-8: Development of water resources vs. demand – Scenario B3 ...... 66 Fig. 4-9: Block Diagram – Scenario B3 ...... 68 Fig. 4-10: Layout Map of Sequential Development – Scenario B3 ...... 69 Fig. 4-11: Development of water resources vs. demand – Scenario B5 ...... 71 Fig. 4-12: Block Diagram – Scenario B5 ...... 73 Fig. 4-13: Layout Map of Sequential Development – Scenario B5 ...... 74 Fig. 4-14: Development of Water Resources vs. Demand – Scenario C2 ...... 75 Fig. 4-15: Block Diagram – Scenario C2 ...... 77 Fig. 4-16: Layout Map of Sequential Development – Scenario C2 ...... 78 Fig. 4-17: Development of water resources vs. demand – Lamu area ...... 81 Fig. 4-18: Circular pan (left) and rectangular pan (right) ...... 89 Fig. 4-19: Typical Sand-Storage Dam with Sand Reservoir Upstream ...... 91 Fig. 5-1: Total Water Costs – Financial ...... 102 Fig. 5-2: Cost and Composition per m3 – Financial Costs ...... 102 Fig. 5-3: Total water costs – economic costs ...... 105 Fig. 5-4: Cost and composition per m3 – economic costs ...... 105 Fig. 5-5: Lamu area total water costs – financial costs ...... 106 Fig. 5-6: Lamu area cost and composition per m3 – financial costs...... 107 Fig. 5-7: Lamu area total water costs – economic costs...... 108 Fig. 5-8: Lamu area cost and composition per m3 – economic costs ...... 108
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Contents (cont.)
List of Abbreviations
AFD Agence Française de Développement CBO Community-Based Organization CWSB Coast Water Services Board DAC District Area Coordinator Dia. Diameter DN Nominal diameter EIA Environmental Impact Assessment GoK Government of Kenya HTH High Test Hypochlorite HQ Headquarters JV Joint venture KIMAWASCO Kilifi-Mariakani Water and Sewerage Company KWAWASCO Kwale Water and Sewerage Company LAWASCO Lamu Water and Sewerage Company MALWASCO Malindi Water and Sewerage Company MDG Millennium Development Goals MOWASCO Mombasa Water and Sewerage Company MWI Ministry of Water and Irrigation NGO Non-governmental organizations NWCPC National Water Conservation and Pipeline Corporation NWSS National Water Services Strategy O&M Operations and maintenance PN Nominal pressure PPT Project preparation team RC Reinforced concrete TAWASCO Tana Water and Sewerage Company TAVEVO Taveta Voi Water and Sewerage Company ToR Terms of Reference UfW Unaccounted-for Water WRMA Water Resources Management Authority WAB Water Appeal Board WaSSIP Water and Sanitation Service Improvement Project () WSB Water Services Board WSMP Water Supply Master Plan WSP Water Services Provider WSRB Water Services Regulatory Board WSTF Water Services Trust Fund WSS Water Supply and Sanitation WB World Bank
Units BCM billion cubic metres km kilometres lpcd litres per capita per day m metres masl metres above sea level MCM million cubic metres mm millimetres m3 cubic metres m3/d cubic metres per day m3/h cubic metres per hour m3/s cubic metres per second y year
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Executive Summary Water Supply Master Plan for Mombasa and Other Towns within Coast Province: Final Full Feasibility Study
The contract for providing consultancy services for preparation of the Water Supply Master Plan for Mombasa and Other Towns within the Coast Province for the Coast Water Services Board (CWSB) under the Water and Sanitation Service Improvement Project (WaSSIP) was awarded to TAHAL Consulting Engineers Ltd. in association with Bhundia Associates. The Contract was signed on 19 October 2011 and contains two main phases:
The first includes a Water resources study: it identifies all the water resources in the region and assess their magnitude, future potential and their feasibility for development. The second phase includes the preparation of a regional water demand projection for the year 2035; it consists of the regional water balance, the water supply master plan and and the proposed sequence of development and action plans.
The master plan's coverage includes the entire province of the Kenyan coast, and also covers remote areas like the northern shores of Lamu, Garsen in Tana River county, Taveta town in Taveta County, Mwatate, Wudanyi and others. Previous reports for this assignement were submitted to the CWSB during the past year. Among them were the water demand and the supply assessment, full water resources study and the final pre-feasibility report. Eight scenarios were analysed during the pre-feasibility stage and five scenarios were selected for further study in the full-feasibility stage. The main objective of the full feasibility report is to present a comprehensive engineering and financial analysis and prioritization of the water supply scenarios. The evaluation of the five scenarios forms the basis for the discussion and the selection of the leading feasible option. Following several meetings with CWSB, WB, AfD & PPT and stakeholder meeting, the current report presents the analyses of the scenarios and recommends the selected one. Comprehensive considerations were given to the comments put forward by the client and donors during this period, such as availability of water, availability of resources, environmental aspects and so. The major tasks performed by the consultant include:
Assessment of current water resources based on a review of previous reports, studies and field visits: From the outset of the study on the CWSB-WSMP, dozens of reports and documents related to the development of water resources in the region were made available to the Consultant by CWSB and other consultants. The reports were prepared by a number of different stakeholders, companies and consultants, and cover a spectrum of future resources for the region. The reports lack, however, a comprehensive view of water resources for the region as a whole. Indeed, the TOR for the project emphasized the need to review all the papers and documents and "filter out" the main concepts from each to contribute to the WSMP. Assessment of new water resources potential: In accordance with the previous assignment, a study was conducted to locate new water resources that could be part of the
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Water Supply Master Plan for Mombasa and Other Towns within Coast Province Final Full Feasibility Study – Executive Summary
bulk water supply system, contributing additional sustainable water. In this context, the work activities, divided into three groups, investigated different types of resources: – Initially, overall review of the potential of all water resources in the Coast Province was conducted. Due to the magnitude of the resources, it was decided to focus on three main groups, which shows the highest potential for the bulk water supply. – The first group conducted a preliminary analysis of 11 seasonal rivers draining to the Indian Ocean, and quantified the annual potential water volumes to be collected in dams. This group also prepared a preliminary assessment of the available water quantities in the Sabaki River near Baricho. – The second group focused on regional aquifers: a groundwater model was applied in order to estimate the annual potential without affecting the aquifer by causing seawater intrusion or rapidly declining water levels, mainly in the south; This group, led by TAHAL’s hydro geologist team, was deeply involved in the investigation of the deep aquifer potential along the coast, namely the Neognic layers. Initial results indicate that this source is probably available only in the north area of Lamu. – The third group analysed the potential to add desalinated water to the water balance of the region, emphasizing local constraints such as availability of electricity, location on the shores and reliability. Desalination plants were considered due to their flexibility in terms of modular development. The main disadvantages of implementing this technology are its extensive energy utilization costs and environmental considerations.
Determination of a methodology for creation of the supply option: A methodology was defined in order to identify supply alternatives, and compared on the basis of a multi-criteria analysis. Three major development strategies were presented, each strategy based on a firm concept regarding water resources development, and containing one or more alternatives derived from the strategy, referred to as scenarios. The scenarios defer mainly by the sequence of development which affects water balance, bulk system topology and investments. Multi criteria analyses: In order to reflect the different aspects of the development plan a Multi criteria methodology was established. The methodology applies and ranks five main parameters to each scenario. They are: Engineering, economic, environmental and social & political. For the sensitivity analyses, different percentile weights were given to the each parameter.
The main objective of the CWSB-WSMP is to develop a highly reliable water supply system that will provide local residents with an uninterrupted water supply (i.e. 24/7). The financing, design and construction required for the utilization of the new sources (storage tanks, new transmission mains, booster, pumps etc), requires defined sequential development phasing Development of the system will be implemented in four main phases: Emergency Immediate Works for Water Supply Improvements Phase I: 2020, Midterm phase (Phase II 2025) Horizon (Phase III2035). For each one of the phase content of work see below
Two basic principles were set as a key rule of each phase:
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A water balance must be fulfilled so that the total water demand will be met by appropriate resources, in terms of supply, reliability, quality and sustainability Specific implementation steps should be determent for each one of the development phases.
Current Water Resources
General
Water demand in the Coast Province depends mostly on a bulk water supply system comprising of the Mzima Pipeline, Marere Pipeline, Tiwi Boreholes and Sabaki Pipeline.
Taveta Township and the surrounding villages are supplied with water from the high-yielding Njoro Kubwa Springs (separate from the bulk system). It is suggested that this scheme will be connected only to Taveta town, following major rehabilitation and expansion. The township of Lamu depends on the local Shella aquifer. Hola town abstracts water directly from the Tana River. All are relatively small water schemes. With regards to Taveta, extensive analysis was conducted and the most economically viable option would be to utilize local sources, mainly from the Tana River.
Table Exec-1 presents the installed capacity of water resources in the Coast Province.
Table Exec-1: Current Water Supply Capacity in the Coast Province
Installed Capacity Year Water Source (m3/d) developed Mzima Springs 35,000 1957 Marere Springs (with Pemba) 12,000* 1923 Baricho Wellfield 90,000* 1980 Tiwi Aquifer 13,000* 1980 Njoro Kubwa Springs 3,000 1990 Tana River 1,400** 1965 Shella Aquifer 1,800 Unknown Total 149,200 * Capacities expected for Marere Springs, Baricho Wellfield and Tiwi Aquifer following completion of ongoing rehabilitation projects by WaSSIP.
Future Water Resources
Surface Water Potential
The analysis of surface water includes five main assignments, namely:
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Review of previous and on-going studies on dams and direct river intakes in the Coast Province. Field surveys to various rivers and river basins Analysis of monthly and annual flows of 11 seasonal rivers draining to the Indian Ocean, including Mwache, Kombeni and Rare. Analysis of low flows in the Sabaki River near Baricho site. Analysis of low flows in the Tana River near Garsen site.
The Coast Province has a high potential for development of surface water sources. Analysis of seasonal rivers shows that the mean annual flows in Mwache River and Rare River are 120 MCM/y and 190 MCM/y (average daily flow of 330,000 m3/d and 520,000 m3/d), respectively. These rivers have very high potential for dam construction.
Analysis of the Sabaki River near the Baricho site shows a minimum flow (100%) of 2.6 m3/s and a sustainable flow (95%) of 3.58 m3/s (309,000m3/d). Current abstraction at the Baricho Waterworks is 1 m3/s (86,000m3/d). Additional abstraction from Baricho or adjacent new sites is possible from the resources point of view. Adding an additional 1 m3/s (86,000m3/d) to the current pumping will double the supply potential, and will enable minimum flow of 1.58 m3/s ( 136,000m3/d) to the Sabaki River Delta.
Tana River is the longest river in Kenya. Analysis indicates a minimum flow (100%) of 8.5 m3/s(734,000m3/d) and sustainable flow (95%) of 44.7 m3/s (3,862,000m3/d). Since the High Grand Falls project is expected to reduce turbidity and sediment loads in the river and moderate floods, the Tana River can constitute a highly viable resource. Due to the distance between the river and Mombasa, it is recommended to abstract water from this source only for Lamu and Tana counties.
Groundwater Potential
Analysis of groundwater potential in the South Coast included the following stages:
Review of previous studies and available data for the hydrogeology of the study area. Field surveys to various potential areas for groundwater. Identification of data gaps. Construction of a regional flow model based on the existing data, with simplifying assumptions. Model calibration and assessment of seawater intrusion according to different pumping scenarios.
Stage 1 model runs studied the general flow regime and the parameters affecting seawater intrusion for the Tiwi and Msambweni areas as part of the South Coast. The parameters affecting seawater intrusion were analyzed specifically for Tiwi area and included:
Amount of recharge to the aquifer (high and low scenarios). Amount of pumping (high and low scenarios).
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Water Supply Master Plan for Mombasa and Other Towns within Coast Province Final Full Feasibility Study – Executive Summary
Distance from the ocean.
Stage 2 model runs studied the flow regime in the Tiwi and Msambweni areas assuming conservative conditions: lower topography and lower recharge. A transient run simulated the effect of high pumping and seawater intrusion rate for a period of 20 years, both in Tiwi and Msambweni.
The conclusions regarding groundwater potential in the South Coast include:
Groundwater potential determined for Tiwi and Msambweni areas is approximately 20,000 m3/d (7.5 MCM) and 30,000 m3/d (11 MCM), respectively. The analysis indicates that additional well-fields may be developed south of Msambweni. Major data gaps were identified and plans for required actions and further investigation are outlined. It is emphasized that the required actions are mandatory before any new wellfields are developed, or any significant changes in pumping policy are decided on. The most critical parts of the required actions include: – Drilling of deep exploratory/monitoring wells for detecting the seawater-freshwater interface location and depth. – Performance of an accurate well survey. – Performance of water level measurements – long-term, regular records. – Performance of water quality measurements – long-term, regular records. – Survey of pollution sources.
Deep Groundwater
Data from deep oil and gas exploration wells in Kenya were reviewed in order to assess whether potential deep groundwater exists. This analysis is based on the assumption that Kenya's Coast Province may share the same hydrogeological characteristics with Tanzania's coastal area (the area of Dar es Salaam), where a deep and highly productive aquifer of immense volume and excellent water quality was recently discovered and investigated.
General and detailed geological information was collected from the data reviewed for 13 of the deep wells in Kenya. Information included stratigraphy, top and base of the Neogene Sequence, thickness and depth to the Neogene Sequence, etc.
A cross-section along four deep wells located along the Tana River from inland to the coast adjacent to the Lamu area revealed a Neogene Sequence of 400–500 m thickness inland increasing to 1,000–1,500 m close to the coastline. The depth to this potential aquifer varies from several metres (about 5–30 m) in Pandangua 1 and Walu 2 wells (near Tana River) to 150–200 m in other locations.
The lateral continuity of the Neogene Aquifer is mapped and related to the location of the Lamu Rift Basin. The potential aquifer units extend into the Lamu area to the north, and narrow southwards towards Mombasa.
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Potential recharge of freshwater to this aquifer should be thoroughly investigated. However, the location near Tana River is promising, as the river may serve as a source of recharge to the aquifer in this area.
Further investigation of this potential aquifer is suggested by drilling of deep wells to a depth of about 600 m. Three alternative locations are suggested, two in the Lamu area and one along the Tana River between Pandangua 1 and Walu 2 wells. The counties of Mombasa, Kilifi, Kwale and Taita-Taveta appear to be less promising with regards to the existence of a deep aquifer. This is mainly due to the dearth of Neogene formations south of Malindi. The TAHAL/Bhundia Team has conducted thorough examination of the possibilities of conveying water from Lamu and Tana towards Malindi and Mombasa. Inter basin transfer of water from Tana and Lamu area will be recommended if the potential of the neogenic aquifer will prove to be feasible and only after the full development of local sources (Baricho, Mwache etc.).
In view of the future water demand in the Lamu area, the existence of water potential in the Neogene layer presents an opportunity not to be missed. Inherent in Lamu Port and the future project of the corridor to the Ethiopian border present a massive demand for water, in a semi- arid zone where water is scare. Desalinated water may be found too expensive to afford by localities. Thus, the Neogene water potential must be further investigated from the geological viewpoint and by adding exploration drills to clarify the nature of this water source.
Desalination
Desalinating sea water for potable water supply can be a reliable source. Among its advantages is the option for gradual development (and investment) concurrent with the master plan development phases and projected increase in the regional demand for water..
The major constraints of desalination are environmental impacts and high energy costs. The Kenyan coastline is rich in marine life and marine reserves, and the large number of eco-sensitive areas allows very few potential locations for desalination plants. Energy costs and availability in Kenya depend on rainfall, as a large proportion of energy production in the country is based on hydropower. The cost-benefit of desalination plants in the Kenyan coast will be subject to electricity costs and reliability.
The wide range of environmental impacts can constitute serious obstacles and need to be carefully investigated.
Recycled Water
Initiation, design and establishment of a recycling system in CWSB's area of jurisdiction can be considered only in the later stages of the Master Plan mid-term phase, after 2025.
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Water Supply Master Plan for Mombasa and Other Towns within Coast Province Final Full Feasibility Study – Executive Summary
A prerequisite for any recycling efforts should be an efficiently operating gravity sewage system, a treatment plant and a recycling plant, none of which will be in operation during the first development phase of the Master Plan.
Within Mombasa and some other neighbouring towns, recycled water can be used for gardening within the urban/domestic sector (in addition to agriculture in the rural areas). This will have a positive effect on the per capita water demand, reducing the total urban water demand. For the purpose of determining the water balance, only in horizon year 2035 is recycled water introduced to the extent of 50 lpcd in the greater Mombasa area.
Rainfall Roof Harvesting
Promotion and construction of rainfall harvesting technology is deemed suitable in the coastal areas and recommended as a means of augmenting the amount of water available. In public buildings (offices, schools, clinics, etc.), where harvested water uses can be controlled, it is recommended to consider government support. This water will serve the needs of flushing and gardening, resulting in a decrease in the use of potable water for those facilities.
In rural households, under appropriate guidance and training in the correct use and maintenance of the facilities, rooftop harvesting can be viable and effective.
Estimating the potential of this source is traditionally complex and inaccurate. That said, analysis of previous studies in eastern Africa and augmented by onsite interviews has indicated that between 2.5% to 10% of the rural water demand can be supplied from rooftop harvesting, the average ratio of 5% had been adopted.
It should be borne in mind that the possibility of controlling the use of water collected in rooftop tanks and its quality is very limited. Water will inevitably be used also for drinking without means of quality control, raising the probability of water-related illnesses. Only a backing in the form of appropriate education programs will lead to efficient use of this water without affecting the health of the population.
Population and Water Demand Projection
Population
An estimated total population of 7.5 million inhabitants will live in the area by target year.
Table Exec-2: Summary of the Coast Province Population County 2009* 2,012 2,015 2,020 2,025 2,030 2,035 Mombasa 939,470 1,051,268 1,163,066 1,386,173 1,624,076 1,902,809 2,229,380 Kwale 649,931 709,981 770,030 888,091 1,040,510 1,219,088 1,428,315 Kilifi 1,100,674 1,220,103 1,339,532 1,569,430 1,838,784 2,154,367 2,524,112 Lamu 101,539 113,270 125,000 287,500 437,500 600,000 750,000 Tana River 240,075 262,413 284,751 328,922 385,374 451,514 529,006
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Taita Taveta 284,657 304,757 324,856 375,911 440,427 516,016 604,578 Total Population 3,316,346 3,661,791 4,007,235 4,836,027 5,766,671 6,843,794 8,065,391 *census 2009
Water Demand
The region’s total water demand was calculated using two different scales: A. The coast region total urban demand considers all water consumers including those which are disconnected to the bulk water supply today and in the future. B. The total urban water demand in the 20 main urban centres, according to the TOR and the clarification letter defining the scope of the Master Plan
Each major town is comprised of the township and adjacent settlements. The final water demand projection for the 20 urban centres for the horizon year is presented in the table below.
Table Exec-3: Water Demand Projections for the Target Urban Centres (by county) Urban Water Demand (m3/day) Urban Centre 2,012 2,015 2,020 2,025 2,030 2,035 Mombasa 140,999 155,840 188,236 243,288 280,501 317,715 Kwale 23,396 25,764 31,096 39,775 48,956 58,136 Kilifi 37,723 41,516 51,616 65,090 79,823 94,555 Taita Taveta 14,778 16,615 19,554 23,494 28,261 33,028 Lamu 4,300 18,568 37,462 62,068 89,314 116,560 Tana River 3,597 4,340 5,207 6,036 7,629 9,222 Total Population 224,793 262,643 333,171 439,751 534,483 629,216
Development Phases
The entire development program for the bulk water supply system was divided into 4 distinct phases.
Emergency immediate phase: Under the additional finance awarded to the CWSB (total additional investment of approximately 30 million US$ for emergency actions to improve supply to Mombasa), includes two new boreholes within Baricho site, pipe segment rehabilitation along the Baricho-Nguu Tatu pipe, thus allowing to increase the supply to Mombasa by 20,000 m3/day. Phase 1, targeting year 2020. The importance of this phase lies in the major changes it will effect with respect to the water supply situation in the region, mainly in Mombasa city and vicinity, where water shortages are severe (as stated in Report No. 2, less than 30% of the water demand in the city was met in 2011). Taking into consideration the duration it takes to develop water resources and the supply scheme to supply the water – it may take 3–5 years from commencement to final operation. In some cases, one must consider that after the water works construction period has ended, it may take additional
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time to fulfil the dam/reservoir to its minimum capacity that will yield the daily desired water volume. Phase 2 will be devoted to enlarging the bulk water supply system and improving supply reliability. This phase will include both the development of new resources for the region as well as extension of the supply network to new areas, some of which are not connected to the existing bulk water system. The target year has been set to 2025. According to the phase of development suggested, additional water resources will be deployed during the 2020–2030 period, and new water supply pipes will be constructed to connect more consumers to the main supply network. Phase 3 refers to the horizon year of 2035. In order to cope with the increasing water demand in the Coast Province, additional water resources will be introduced, some possibly consisting of artificial sources such as desalination. At the end of this phase, all the region's resources will meet the region's water demand. The master plan suggests that future water resources for the region will not be limited to the "conventional" resources such as springs, rivers and groundwater. New types will be promoted in order to support the regional demand for water. At this time, various on-going activities include evaluation of the potential of water abstraction from the Neogene Aquifer along the coast, desalination water plants along the coast (with alternatives to be centralized near the centre of demand or separate plants, as suggested in Lamu), etc. Additional "other" water resources considered for utilization by the horizon year include utilizing grey water within the urban sector (considered for the city of Mombasa, high class residence only), recycled treated wastewater to public gardening in the urban sector (again, probably only to Mombasa) and roof top rainwater harvesting. Unlike grey water or recycled wastewater resources, the water potential of roof harvesting is relatively limited. Moreover, water quality issues and the functionality of water storage tanks during the dry season must be considered.
Development Strategies and Scenarios for the Interconnected Bulk Water Supply
Three main strategies were drafted for the supply Scenarios, The strategies were briefly presented to the client and the donors and were discussed in various meetings at the WB office in Nairobi, these are:
Priority expansion of existing resources Priority development according to financial considerations Differentiation of coastal consumers from inland consumers.
The pre-feasibility report presented eight different water supply scenarios. The feasibility stage analysed 4 of the more promising ones (B1, B3, B5, C2). The current report contains one sub scenario referred to as B1.1. It differs from B1 only by the development of the Rare system in the horizon year. The different scenarios within each group do not reflect different options of development, rather the development of the same resources but in different sequences. The region’s distinguishing geographic and topographic features clearly indicate that different development
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Water Supply Master Plan for Mombasa and Other Towns within Coast Province Final Full Feasibility Study – Executive Summary sequences may lead to dissimilar costs in terms of Capex and Opex, Thereby changing the results regarding the total cost of the projects and the cost of water production per cubic meter. The sequence of development for each of the development scenarios is: B1: Baricho Small expansion 22,000 m3/day; Mwache Dam 186,000m3/day; Baricho full development 63,000m3/day and Mzima II 105,000m3/day. B1.1: Baricho 22,000 m3/day; Mwache Dam 186,000m3/day; Baricho full development 63,000m3/day and Rare Dam 100,000m3/day. B3: Baricho full development 85,000 m3/day; Mwache Dam 186,000m3/day and small Rare Dam 100,000m3/day.
B5: Mwache Dam 186,000m3/day and Rare Dam 180,000m3/day (No development of Baricho).
C2: Baricho Small expansion 22,000 m3/day; Mwache Dam 186,000m3/day; Baricho full development 63,000m3/day and gradual development of desalination plants 2x50,000 m3/day.
Financial & Economic Analysis
A full financial and economic analysis was conducted for each of the 5 development scenarios found to be technically feasible during the Pre-Feasibility Study; five in the Mombasa area and three within the Lamu region. Moreover, computations were conducted for both the financial indicators expressing the point of view of the CWSB and the utility and the economic indicators which articulate the financial outlook of the region and national economy. Since the projects shall be of public nature and based on historical facts that such projects have not in the past been financed through commercial bank loans; donor funded project interest rates were used for the economic and financial analysis. The rates applied were donor rates of 1% p/a for 10 years grace period and 3% p/a for additional 30 years period.
The investment indicators included: Total Investment required for the development of each scenario. Investment per m3 supplied. Annual Operations and Maintenance expenditures for each scenario (including specific consideration for energy costs). Total cost of m3 water supplied.
Financial indicators included: Net present value (NPV). Internal rate of return (IRR). Economic net present value (ENPV). Economic internal rate of return (EIRR). Sensitivity and risk analysis.
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Tables Ecec-2 and Exec-3 presents the main investment indicators (Financial and Economic respectively) for each of the scenarios for development of the Bulk supply (Mombasa Area). Total investments set out in the following sections and within the Master Plan documents do not include and do not cover the investments that will be required for water distribution for the various areas of the WSPs.
Table Exec-4: Main Financial Indicators
Financial Indicators Average Financial Total Total Scenario Capital Energy O&M Water Water Investment Cost Cost Cost Cost Volume (million US$) (US$/m3) (US$/m3) (US$/m3) (US$/m3) (m3/day) Scenario B1 681.6 0.112 0.122 0.057 0.29 396,000 Scenario B1.1 516.2 0.098 0.130 0.062 0.29 391,000 Scenario B3 516.2 0.137 0.211 0.056 0.40 391,000 Scenario B5 463.9 0.159 0.123 0.047 0.33 386,000 Scenario C2 699.6 0.108 0.114 0.154* 0.38 391,000 * Energy for desalination was calculated as part of the O&M costs.
Total investment varies substantially, from US$ 465 million for Scenario B5 to over US$ 700 million for Scenario C2. As expected, the large and diverse water sources programmed for development in this scenario (both Mwache and Mzima 2) and the early stage of heavy investment (during Phase 1) generate a substantial capital investment amount
Table Exec-5: Main Economic Indicators
Economic Indicators Average Economic Total Total Scenario Capital Energy O&M Water Water Investment Cost Cost Cost Cost Volume (million US$) 3 (US$/m3) (US$/m3) (US$/m3) (US$/m3) (m /day) Scenario B1 681.64 0.473 0.110 0.051 0.63 396,000 Scenario B1.1 516.23 0.519 0.117 0.056 0.69 391,000 Scenario B3 516.23 0.463 0.190 0.050 0.70 391,000 Scenario B5 463.90 0.392 0.111 0.042 0.55 386,000 Scenario C2 699.59 0.450 0.102 0.139 0.69 391,000
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The total cost and composition of each m3 supplied, by scenario is set out in fig. Exec 1 below. It is important to note that the cost per m3 present is the cost for the bulk water supply system, i.e. the rate of water for the delivery from the CWSB to the WSP's.
Figure Exec-1: Composition of Calculated Financial Water Costs
Figure Exec-2: Composition of Calculated Economic Water Costs
NPV and IRR
Table Exec-4 presents the financial net present value (NPV) and the internal rate of return (IRR) of each scenario (at a 10% discount rate).
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Table Exec-6: Financial Indicators
NPV IRR Scenario (million US$) (%) B1 20.41 35.42% B1.1 21.08 35.05% B3 -41.60 -5.65% B5 0.27 10.26% C2 -23.70 ND
Four of the main scenarios exhibit a positive NPV ranging between US$ 2.60 million (B1) to US$ 24.67 million (B5), with IRRs of 12.06% to 18.08%, respectively.
The Economic Net Present Value and the Economic Internal Rate of Return are set out in the following tables
Table Exec-7: Economic Indicators
ENPV EIRR Scenario (million US$) (%) B1 -180.19 2.64% B1.1 -215.35 1.04% B3 -229.30 0.64% B5 -125.67 3.31% C2 -201.87 ND
Lamu area – Financial analysis of Scenarios The Lamu system is separate from the rest of the CWSB's basins and water source options. Additional scenarios were therefore developed, and their financial and economic implications are presented in Table Exec-6.
Table Exec-8: Lamu Area – Basic Financial Indicators by Scenario
Average Total Capital Energy O&M NPV IRR Water Scenario Investment Cost Cost Cost (million US$) (%) Cost (million US$) (US$/m3) (US$/m3) (US$/m3) (US$/m3) L1: (Nanighi Barrage) 549.00 0.95 – 0.30 -82.89 0.44% 1.257 L2: (Garsen Barrage) 152.71 0.26 0.21 0.08 20.31 18.03% 0.564 L3: (Desalination) 136.38 0.16 0.84 0.26 -48.05 N/A 1.263
The total cost and composition of each m3 supplied in the Lamu area, by scenarios is set out in figure Exec-3 below.
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Figure Exec-3: Composition of Calculated Water Costs (Lamu Area)
Multi Criteria Analysis
Four main parameters were identified and classified as the range of parameters for the multi criteria analysis; they include engineering, economics, environmental aspects and social & politics. A grade (in 100 scale) was linked to each scenario and associated with the indicators in each field of significance. The economic grading was based on the computed differences in ratios between the scenarios; grades for the other indicators were assigned according to similar projects as well as the consultant experience. Each parameter was classified with a percentile weight, reflecting the importance of the specific parameters for decision making.
Summary results of the basic multi criteria analyses are shown in table Exec-5 below.
Table Exec-9: Multi-Criteria Analysis for Bulk Water Supply
Inner Scenario Item Criteria / Parameter Classification Weighting B1 B1.1 B3 B5 C1 1.0 Engineering Sustainability 30% 1.1 Feasibility of implementation 40% 80 70 50 65 50 1.2 Reliability of Resources 30% 90 70 70 60 90 1.3 Diversity of Resources 30% 90 80 80 20 100 Engineering Summary 86 73 65 50 77 2.0 Economic Considerations 40% 2.1 NPV 20% 47 13 0 100 26 2.2 IRR 35% 80 31 19 100 0 2.3 O&M Costs 10% 83 76 85 100 31 2.4 Calculated Water Cost 35% 86 79 78 100 79
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Economic Summary 76 49 42 100 36 3.0 Environmental Issues 15% 3.1 Water Quality 30% 90 70 70 50 95 3.2 Downstream Impact 30% 60 60 70 50 60 3.3 Energy Consumption 30% 90 70 70 80 50 3.4 Construction Effects 10% 60 60 70 80 50 Environmental Summary 78 66 70 62 67 4.0 Social & Political Aspects 15% 4.1 Supply Coverage 30% 100 80 80 80 80 4.2 Resettlement / Income Loss 40% 80 70 70 50 60 4.3 Political acceptability 30% 100 90 50 50 30 Social Summary 60 51 39 39 33 Total 100% 76.8 59.0 52.8 70.2 52.4 Rank 1 3 4 2 5
Three different options were examined: A 30/40 percent weighting between engineering/economic parameters A 40/30 percent weighting between engineering/economic parameters A 40% for the economic and 25% for environmental The results clearly indicate that the leading scenario B1 maintains its prominent position in each of the three cases. It is followed by B5. Both are strong in the economic and environmental breakdowns but lag within the engineering parameters
Conclusions and Recommendations
a. The recommendation of the consultant is to implement the design laid out in scenario B1. Namely sequential development commencing with the expansion of "Baricho small" through immediate investments, followed by construction and operation of Mwache dam (supplying bulk to Mombasa and the southern coast areas), full development of the Baricho well field (supplying Malindi, Kilifi and the surrounding areas) and culminating in the phase III development of the Mzima II pipeline and replacing the current obsolete system. b. This option delivers the most efficient engineering solution while maintaining reasonable financial values and minimizing social and political bottlenecks. The primacy of this option is also evident from the multi criteria analysis results. c. Another feasible source is the Rare River. NWC&PC is currently conducting a feasibility study on this dam. This can also serve as a potential source for phase III as detailed in scenario B1.1.
d. In order to meet the water demand of the new Lamu port, it was found that the Garsen option is the best development practice, however, desalination plants is a viable option for future supply mainly depends on the availability of electricity and its prices.
e. The supply to Settlements along the Tana River and the Taveta township are relatively simple due to the proximity of large and reliable water sources. In both
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cases the magnitude of the source is far above the demand, although quality may be an issue.
f. The area of Taita Hills (Wundanyi and Mwatate) will be supplied with water from Mzima springs through a conveyance pipeline from Voi.
List of Projects According to Development Phases
Immediate phase: Drilling two new boreholes in Baricho Wellfield; connecting to the treatment tank, Upgrading a 12 km 600 mm pipeline at the upstream section of Nguu Tatu to 800 mm Connecting Gongoni to the Malindi water supply line (20Km, 300 mm) Construction of the Kakuyuni-Kilifi pipeline (50Km) Construction of the new Kakuyuni water tank and Kilifi water tank Expansion of the source works and transmission system of Njoro Kubwa springs to increase supply to Taveta town
Phase 1: Completing the Mwache dam, the treatment facilitates and the water tank under the CDA project (not part of the CWSB development plan) , Constructing a new pumping facility at the downstream of the treatment outfall Constructing 3 pump arrays from the Mwache dam: To +120 new water tank; to Changamwe water tank, and to the southern area supply. Laying new water mains to supply water for Mombasa and the southern area: - Connecting Mwache P.S. to the new elevated water tank +120, - Connecting Mwache P.S. to the Changamwe water tank - Connecting Mwache P.S. to the south supply by connecting to Likoni and to the Kaya Bombo water tank - New water tank at +120 elevation (12,000 m3) - Upgrading of the water tank at Kaya Bombo. - Connecting the new +120 tank to Nguu Tatu water tank by 30Km pipe of 800 mm. - Connecting Likoni to Tiwi pipe line in the south region. - Analyzing the capacities of the Mombasa and Malindi water distribution networks to receive more water (as proposed in Phase 2). Expansion of the source works and transmission system of Njoro Kubwa springs to increase supply to Taveta town
Phase 2 Extension of the Baricho abstraction capacity to a total of 175,000 m3/day by adding five new boreholes of HCG type to enable abstraction of 900 m3/h each. Analyzing the existing equipment to test its productivity and performance, Interchanging the existing boreholes with new HCG type ones. Augmenting the pumping house at Baricho with 2 new delivery pumps to Mombasa and 3 new pumps to Malindi (2+1)
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Constructing the second Baricho Nguu Tatu pipe line (800 mm, 107km) Constructing the second Baricho Kakuyuni pipe line ( 600mm, 45km) Upgrading water tanks at Kisimini, kiugani. Constructing the new Marafa supply line (30km 300mm) Extension of the Kakuyuni water tank Constructing a new booster pump to supply Marafa Constructing the new Marafa water tank. Extension of the electric production facility at the Baricho site For Lamu: Constructing the Garsen-Lamu off-take structure and the main pumping station(alternately when the Lamu port construction commences, desalination can be considered Constructing the new Garsen-Lamu supply line 75km 1000mm
Phase 3 Construction of the second Mzima pipe line at 1200mm from the spring to Voi junction and 1000 mm down to Mombasa until Mazeras tank Supplement the development of the south coast supply branch from Mwache including the supply line to Msambweni (500mm) and further south to Lunga Lunga (300 mm) Constructing the new Msambweni water tank (10,000 m3) and the attached booster pump to deliver water to Lunga Lunga Development of the Msambweni well field with a target capacity of 20,000 m3/day and connecting to the Msambweni water tank. Adding two pump units to the pumping house at Baricho for the supply to Malindi Connecting Mwatate and Wudanyi to the bulk water supply from Voi junction by new Pipe line (400mm) and booster pump to Wudanyi (250mm)
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Fig. Exec-3: Water systems, demand centres and potential sources for the main towns of the Master Plan
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1. Introduction
1.1 Background
The contract for providing consultancy services for preparation of the Water Supply Master Plan for Mombasa and Other Towns within the Coast Province for the Coast Water Services Board (CWSB) under the Water and Sanitation Service Improvement Project (WaSSIP) was awarded to TAHAL Consulting Engineers Ltd. in association with Bhundia Associates. The Contract was signed on 19 October 2011.
Funding for the consultancy services is being provided by the Government of Kenya (GoK) with the assistance of the International Development Association (IDA) and Agence Française de Développement (AFD).
Preparation of a water supply master plan requires the Consultant to map and scan all aspects of the water systems. This starts with investigation of the resources and their sustainability over time, the search for and estimation of new water resources, including both surface water and groundwater, as well as water quality aspects, financial aspects in terms of capital cost and operation cost of the system, and the manner in which the main pipelines will be connected to current water distribution systems and water consumers.
According to the ToR and a clarifying letter dated 28 May 2012, the Master Plan will cover the city of Mombasa and the towns of Lamu, Malindi, Watamu, Hola, Kilifi, Mtwapa, Garsen, Kwale, Ukunda/Diani, Voi/Maungu, Taveta, Mwatate, Wundanyi, Mpeketoni, Mariakani, Msambweni, Lunga-Lunga and Kinango.
1.2 Objectives of the Present Report
The aim of the Final Full Feasibility Report is to focus on the scenarios that were defined and briefly compared in the pre-feasibility study. For the four selected scenarios in the pre-feasibility study, the consultant added one more (B1.1.) in order to cover more options of the development sequences. These five scenarios for the feasibility stage are the subject in this report.
The following objectives have been set out in the framework of the feasibility study:
Use of water demand forecasts and water balance to allocate the water resources in the Coast Province for 20 townships and rural areas. Review and analyse the previous reports and documents on existing and proposed water resources, and their contribution to the future bulk water supply system.
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Identification and investigation of new potential water resources – including surface water, groundwater and desalinated water – and estimation of their future sustainable yield. Definition of supply alternatives in the framework of defined strategies based on demand projections over time and resources availability. To present the Capex and the Opex of the suggested scenarios. To present the financial considerations of the suggested scenarios, in order to support the selection of the desired development scenarios To define the methodology for multi criteria analysis, in defined areas of interest, indicators (under areas of interest), percentile weights and rank. Recommendation of preferred development scenario for consideration into the preliminary design report.
The aim of the current report is to present the entire work done on the selected scenarios, for the purpose of deeper evaluation. This is done by applying multi criteria decision variables, as a tool to present wider aspects on the development plan. The multi-criteria decision tool is presented with its four main areas of interest, namely:
Engineering feasibility. Financial aspects, in terms of annual cost, comprising both Capex and Opex. Primary environmental aspects, irrespective of the EIA of the desired scenario. Social and political considerations.
1.3 Previous Reports and Related Studies
As of December 2012, the following reports have been submitted by the Consultant to the client:
Inception Report, December 2011. Low Flow Analysis of Major Rivers (Athi, Tsavo, Tana), March 2012. Draft Water Demand and Supply Assessment Report, April 2012. Revised Water Demand and Supply Assessment Report, August 2012. Draft Pre-Feasibility Study for all Options Report, August 2012. Final Pre-Feasibility Study for all Options Report, October 2012. Draft Water Resources Report, October 2012. Final Water Resources Report, December 2012. Feasibility Study – key issues for discussions, December 2012. Draft Full Feasibility Study Report, December 2012.
In addition to the Water Supply Master Plan for the Coast Province, four important studies impacting the Coast Province are in the process of preparation under different stakeholders in the water sector in Kenya. These are:
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National Water Master Plan 2030 (NWMP) – The Japan International Cooperation Agency (JICA) study team is preparing the NWMP for year 2030. Work on the NWMP began in 2010, covering the entire area of Kenya. The plan will indicate water resources to be developed, some of which will influence the availability of water for the Coast Province. The JICA study team presented their Interim Report on 3 August 2012. The final report is expected at the beginning of 2013. Chyulu Hills Aquifer Study – The World Bank is funding a hydrological study to investigate the groundwater system of the Chyulu Hills. This aquifer is the source for Mzima Springs and other smaller springs (Umani, Mtito Andei, Kiboko, Makindu, Mangelete and others). The Water Resources Management Authority (WRMA) published a request for Expressions of Interest for this contract in August 2012. Mwache Multipurpose Dam – The Coast development Authority (CDA) is promoting the design of Mwache Dam for domestic water supply and irrigation. Pre-feasibility study by Samez (2008) indicated that the dam is feasible. Full feasibility and the detailed design are being carried out by CES/APEC, the final design is expected April 2013.
The Consultant is in coordination with the JICA study team, CES/APEC, CDA, WRMA and the World Bank to share the data and findings from these studies.
1.4 Structure of the Present Report
Chapter 2 Population and Water Demand Projections This chapter summarizes the population projections and the water demand forecasts, which were thoroughly presented in the Water Demand and Supply Assessment Report.
Chapter 3 Current and Future Water Resources This chapter presents the current and future water resources of the region. The current water resources in terms of yield are presented in the first part and potential expansion of the resources is discussed. In the second part, a review of several reports on local water resources is presented and examined. In the third part the future potential of the current resources is demonstrated. The fourth part gives a preliminary analysis of surface water potential in the region. The last part is dedicated to the groundwater of the region and presents the groundwater model that was developed in order to estimate the annual sustainable yield from the main aquifers.
Chapter 4 Proposed Strategies and Scenarios This chapter is the core of this report and it consists of a description of the three main strategies to develop water resources and presents the scenario defined within each strategy. Each development strategy and scenario is presented in both tabular form showing the resources to be implemented in each phase and in narrative form which describes the development sequence.
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Chapter 5, Financial and Economic Analysis The chapter presents the principles, assumptions and results of the financial and economic analysis of the selected development scenarios.
Chapter 6 Multi Criteria Analysis This will define the methodology, application results and several runs of the multi criteria analyses perform to each one of the 5 scenarios in the light of the main 4 parameters and indicators.
Chapter 7 Further Recommendations This chapter highlights further aspects that should be considered currently when the development plan of the bulk water supply system is implemented. Issues such as the rehabilitation of the water distribution network, coordination between the bulk water supply systems and local distribution networks as well as the need of sewer gravity systems – are all considered in this chapter.
Chapter 8 Discussion and Conclusions Finally, discussion of the 5 scenarios emphasises each scenario strength and weaknesses and the opportunity to the region bulk water supply is summarized in this chapter. It is intended in this chapter to indicate the leading development scenario recommended by the consultant to form the focus of the preliminary design stage of this study.
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2. Population and Water Demand Projections
2.1 General
The following activities have been carried out in the framework of the water demand and supply assessment task:
Demographic analysis, with three growth rate scenarios, to derive population growth rates and population forecasts for the five target years – 2015, 2020, 2025, 2030 and 2035 – based on past population censuses of the Coast Province, the latest being the 2009 census. Identification of the existing water supply situation in the Coast Province. Determination of level of services and the willingness/ability of consumers to pay for the services. Projection of water demand for the target years.
2.2 Population Projections
The database for the population projections for the Coast Province comprised the five census datasets (sub-location-wise) for the years 1969, 1979, 1989, 1999 and 2009.
Table 2 -1: Coast Province – Past Population Data and Projections to 2035
Low Medium High Linear Geometric Exponential 1969 745,877 745,877 745,877 1979 1,108,974 1,108,974 1,108,974 1989 1,653,429 1,653,429 1,653,429 1999 2,415,917 2,415,917 2,415,917 2009 3,316,346 3,316,346 3,316,346 2015 3,792,231 4,010,574 4,293,595 2020 4,207,960 4,698,892 5,182,370 2025 4,623,689 5,505,343 6,255,121 2030 5,039,419 6,450,201 7,549,931 2035 5,455,148 7,557,222 9,112,768
For each of the districts of the Coast Province, the projected population (for each year and model) was estimated as a proportion of the province population. The percentage proportion of population of each district was estimated after analyzing the current and historic percentage, as follows:
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Districts for which the percentage proportion of population (population out of the province population) showed a constant trend during the period 1989– 2009 were assumed to exhibit this behaviour up to 2035. For districts whose population dynamics showed a positive trend as compared with the population of the province (i.e. the population within the district increased more than the province average), it was assumed that the trend will continue in the same manner and with about the same rate of change up to 2025, and will then remain constant up to 2035.
Table 2 -2: Coast Province Population Projections, by District
District Scenario 2009 2015 2020 2025 2030 2035 Low 523,283 599,172 664,858 730,543 796,228 861,913 Mombasa Medium 523,283 633,671 742,425 869,844 1,019,132 1,194,041 High 523,283 678,388 818,814 988,309 1,192,889 1,439,817 Low 416,187 500,574 576,491 633,445 690,400 747,355 Kilindini Medium 416,187 529,396 643,748 754,232 883,678 1,035,339 High 416,187 566,755 709,985 856,952 1,034,341 1,248,449 Low 151,978 170,650 185,150 203,442 221,734 240,027 Kwale Medium 151,978 180,476 206,751 242,235 283,809 332,518 High 151,978 193,212 228,024 275,225 332,197 400,962 Low 209,560 227,534 244,062 268,174 292,286 316,399 Kinango Medium 209,560 240,634 272,536 319,310 374,112 438,319 High 209,560 257,616 300,577 362,797 437,896 528,541 Low 288,393 329,924 366,093 402,261 438,429 474,598 Msambweni Medium 288,393 348,920 408,804 478,965 561,168 657,478 High 288,393 373,543 450,866 544,196 656,844 792,811 Low 456,297 523,328 580,699 638,069 695,440 752,810 Kilifi Medium 456,297 553,459 648,447 759,737 890,128 1,042,897 High 456,297 592,516 715,167 863,207 1,041,891 1,257,562 Low 243,825 273,041 294,557 323,658 352,759 381,860 Kaloleni Medium 243,825 288,761 328,922 385,374 451,514 529,006 High 243,825 309,139 362,766 437,858 528,495 637,894 Low 400,552 470,237 530,203 582,585 634,967 687,349 Malindi Medium 400,552 497,311 592,060 693,673 812,725 952,210 High 400,552 532,406 652,979 788,145 951,291 1,148,209 Low 143,411 155,481 168,318 184,948 201,577 218,206 Tana River Medium 143,411 164,434 187,956 220,214 258,008 302,289 High 143,411 176,037 207,295 250,205 301,997 364,511 Low 96,664 113,767 126,239 138,711 151,183 163,654 Tana River Medium 96,664 120,317 140,967 165,160 193,506 226,717 Delta High 96,664 128,808 155,471 187,654 226,498 273,383 Low 101,539 121,351 134,655 147,958 161,261 174,565 Lamu Medium 101,539 128,338 150,365 176,171 206,406 241,831 High 101,539 137,395 165,836 200,164 241,598 291,609 Low 216,992 235,118 256,686 282,045 307,405 332,764 Taita Medium 216,992 248,656 286,632 335,826 393,462 460,991 High 216,992 266,203 316,125 381,562 460,546 555,879 Taveta Low 67,665 72,052 79,951 87,850 95,749 103,648
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District Scenario 2009 2015 2020 2025 2030 2035 Medium 67,665 76,201 89,279 104,602 122,554 143,587 High 67,665 81,578 98,465 118,847 143,449 173,143 Low 3,316,346 3,792,231 4,207,960 4,623,689 5,039,419 5,455,148 Total Medium 3,316,346 4,010,574 4,698,892 5,505,343 6,450,201 7,557,222 High 3,316,346 4,293,595 5,182,370 6,255,121 7,549,931 9,112,768
From the Coast Province population projections, it should be noted that an estimated total population of 7,557,222 inhabitants will live in the area and will demand water supply services at different levels in their locations. This figure represents the medium model for projected population for the horizon year of 2035.
2.3 Water Demand Projections
Water demand projections were calculated in several different ways in order to identify the most adequate forecast for the region's future water demand. Therefore, the total water demand is the sum of the following:
Population water demand, or domestic forecast, including water loss. Institutional and other public institutions water demand. Industrial demand – The Consultant collected data from the WSPs of all major industrial and commercial consumers. The industrial demand was updated in September 2012 after discussions with WSPs. Livestock water demand in the rural sector. Water demand of mega-projects, as reflected in the development documents. Separation of urban and rural settlements.
Table 2 -3: Kenya MWI Standards for Per Capita Water Use
Socioeconomic Level Home Type as MWI lpcd Remarks Class H Home Type 1 250 * % by division Class M Home Type 2/3 150 % by division Class L (IC) Home Type 4/5 75 % by division Class L (non-IC) Home Type 4/5 40 % by division Note: The figure for lpcd includes domestic water use plus water losses. * In the year 2035, it has been assumed that Mombasa will use a dual system for utilization of grey water, reducing lpcd to 180.
Table 2 -4: Total Water Demand Based on MWI Standards
County 2015 2020 2025 2030 2035
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Mombasa 152,302 184,372 238,874 288,918 312,554 Kwale 50,535 59,566 76,769 90,701 119,910 Kilifi 84,597 103,160 133,443 159,856 210,047 Lamu 22,204 41,681 67,556 104,763 125,186 Tana River 25,194 29,492 36,981 43,486 55,739 Taita Taveta 29,411 34,430 42,789 50,366 63,817 Total (m3/d) 364,243 452,701 596,413 738,090 887,253 Total (MCM/y) 132.9 165.2 217.7 269.4 323.8
In terms of the annual water demand (relevant for the water supply deficit calculation), the total water demand was estimated to be:
132.9 MCM/y in the year 2015. 165.2 MCM/y in the year 2020. 217.7 MCM/y in the year 2025. 269.4 MCM/y in the year 2030. 323.8 MCM/y in the horizon year of 2035.
2.4 Water Demand – Urban and Rural
2.4.1 Water Demand of the 20 Main Urban Centres
The various scenarios and alternatives take into consideration the 20 main urban centres, according to the TOR and the clarification letter defining the scope of the Master Plan.
Each major town is comprised of the township and adjacent settlements. The final water demand projections for the 20 urban centres for the horizon yearare shown in Table 2-5 and Fig. 2-1.
Table 2 -5: Water Demand Projections for the Target Urban Centres
Urban Water Demand (m3/d) County Urban Centre 2012 2015 2020 2025 2035 Mombasa 137,611 152,302 184,372 238,874 312,554 Mombasa Total Mombasa 137,611 152,302 184,372 238,874 312,554 Kwale 3,786 4,162 4,945 6,000 8,676 Kinango 1,775 1,951 2,365 2,949 4,489 Msambweni 1,976 2,171 2,665 3,252 4,809 Kwale Ukunda/Tiwi 11,098 12,250 14,676 19,671 28,453
Southern Area Southern Area L. Lunga/Vanga 4,761 5,230 6,445 7,903 11,709 Total Kwale 23,397 25,764 31,097 39,776 58,136 Kilifi Mariakani 4,036 4,441 5,421 6,884 10,150
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Kilifi 5,167 5,686 7,090 9,014 13,240 Malindi/Watamu 18,694 20,574 25,616 32,067 46,064 Marafa 1,287 1,417 1,803 2,303 3,402 Mtwapa 8,539 9,398 11,686 14,822 21,699 Total Kilifi 37,723 41,515 51,615 65,090 94,555 Taveta 2,972 3,573 4,265 5,121 7,228 Mwatate 2,127 2,350 2,758 3,332 4,665 Taita Taveta Wundanyi 2,178 2,406 2,823 3,411 4,777 Voi/Maungu 7,501 8,286 9,708 11,630 16,358 Total Taita Taveta 14,778 16,615 19,554 23,493 33,028 Mpeketoni 1,800 2,753 3,272 4,263 6,749 Lamu Lamu Island/Port 2,500 15,815 34,190 57,805 109,811 Total Lamu 4,300 18,568 37,462 62,068 116,559 Garsen 1,456 1,567 1,866 2,269 3,302 Hola 750 1,246 1,524 1,558 2,707 Tana River Northern Area Area Northern Bura 1,391 1,527 1,817 2,209 3,213 Total Tana River 3,597 4,340 5,206 6,036 9,222 Total Urban Water Demand: 213,509 236,196 286,637 367,233 498,273 Southern Region Total Urban Water Demand: 7,897 22,908 42,668 68,103 125,781 Northern Region
Total Urban Water Demand 221,406 259,104 329,306 435,336 624,053
It is important to indicate the differences between the figures for the total water demand in the coast region for the horizon year (projection summary): For the whole cost province – 887,250 m3/day, equal 323.8 MCM/y. (table 2-4) For Mombasa + 19 townships in the mainland – 498,273 m3/day. The balance for the main land includes 40,000 m3/day for rural supply out of the main lines, to total of 538,273 m3/day. For Lamu region 125,782 m3/day not include rural supply.
2.4.2 Water Demand of Rural Bulk Consumers
The various scenarios and alternatives take into consideration the 20 main urban centres.
In order to best calculate the portion of the water demand in the rural areas that will be supplied from the bulk system, an adequate methodology was assumed as follows:
This is based on the basic distance that people will be ready to walk in order to reach a standpipe or a water kiosk for the need of water (to be filled in plastic container). Assuming two main factors:
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High reliability – Abstracting water from a bulk water pipe ensures high reliability (i.e., each time a residence will go to the standpipe to fill water, water will be available). High quality – The water quality in the bulk water pipe is very high, results from the high standards of treatment plants for the bulk system.
According to this, it was assumed that a distance of 5 km, roughly equivalent to one hour of walking, is the maximum distance that people will consider to walk in order to get water of adequate quality and high reliability. Thus, the total area served by 1 km of main pipeline is 10 km2.
In the calculation process, the population density is determined in each one of the districts/divisions. The density is then multiplied with the length of the bulk water supply systems (existing + proposed) in each district, as was measured using GIS database. The result is the total population in each area that are located (by calculation) near the main pipeline and should be considered as water demand population. In order to determine the water demand, the total population was multiplied by the lpcd for the rural sector. The results – by districts – finally are added to the water demand table and to the water balance, increasing the total urban demand in the Coast Province by 8%.
2.4.3 Target Water Demand for CWSB
The total water demand for the development of the master plan includes the main townships and the rural bulk consumers. The computed water balance calls for 95% supply from the bulk water system augmented with 5% supply from small local water sources that will not be part of the bulk system such as small boreholes, small desalination plants. Table 2-6 presents the total and targeted demand.
Table 2 -6: Target Water Demand for CWSB
Year 2012 2015 2020 2025 2030 2035 Population Projection [Capita] 2,907,067 3,521,284 4,130,325 4,839,196 5,669,727 6,642,798 Total Water Demand [m3/day] 213,509 242,696 299,637 394,233 465,753 538,273 Target Water Demand * [m3/day] 202,834 230,561 284,655 374,521 442,465 511,359 * (Less 5% local sources)
2.4.4 Demand Management
The demand for water is the most important factor behind production activities, i.e., pumping, treatment to potable (or other) level and supply.
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In many regions of the world experiencing water crises and a significant gap between supply and demand, the main cause is uncontrolled and unrestrained water demand and usage. Various development processes – such as high population growth and other demographic changes; rural-urban migration; unplanned urban development; and improved sanitation, hygiene and health – cause higher and frequently unpredictable demand for water.
Therefore, management of water demand is the most efficient instrument for monitoring and regulating the stress on water resources.
Several countries in which demand has increased substantially above the supply capacity of local natural sources are now shifting to desalination. At first glance, desalinated water is a product that is within the grasp of commercial traders or brokers, and the state has an option to buy any amount required at an agreed upon price from the producer. However, the total dependence of the desalination process on energy, coupled with the level of global energy costs, has given rise to an understanding that desalination is not a universal panacea and that artificial water production is just one element in the entire scheme of augmenting water quantities while reducing demand. In Israel for example, the National Authority for Water and Sewage includes a special department (called "effectiveness of water use") whose role is to highlight (to decision-makers) inefficient uses of water, initiating campaigns for water conservation and educational programs.
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Fig. 2-1: Daily water demand in the horizon year (2035)
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3. Current and Potential Water Resources
3.1 Current Water Resources
Current water resources comprise of the water resources within in the Coast province areas that are currently developed either partially or fully to their maximum yield for water supply within the jurisdiction of the CWSB.
3.1.1 Mzima Springs
Mzima Springs are located in a protected area – Tsavo National Park, at the foot of Chyulu Hills. The main spring emerges to surface at an elevation of 700 m, at a distance of 220 km from Mombasa city.
The springs are connected to Mazeras Water Tanks by a pipeline totalling 215 km in length. Together with the 3 km source works tunnel, the distance along the pipeline to Mazeras Water Tanks is 218 km. Half of the pipeline lies within the Tsavo National Park.
The current rate of abstraction is only about 0.4 m3/s. According to documents recently presented to CWSB under the Bulk Water Service Consultancy Program, this flow rate is limited by the capacity of the Mzima Pipeline. A recent hydraulic study showed that the gravitational flow along the pipeline is limited to the slope in one section that can convey only up to 35,000 m3/d. In addition, some of the water does not reach the Mazeras Water Tanks (for Mombasa) as water is lost through leakage along the way, as well as abstraction by other consumers: according to a study on the bulk water supply system, only 70% of the total potential daily volume from the pipeline reaches the Mazeras Water Tanks due to the above reasons.
The initial works in the 1950s were designed to enable laying of a parallel pipeline at a later date, thus doubling the flow to 0.9 m3/s (78,000 m3/d). Taking into consideration the environmental impacts, earlier studies proposed that the upper limit that can be abstracted from Mzima Springs should be 1.2 m3/s (103,000 m3/d).
The need for a second Mzima Pipeline has been raised several times in the past two decades. China Machinery Engineering Corporation has recently (April 2012) delivered a proposal to CWSB for a "Second Mzima Pipeline", the proposed capacity of the new pipeline being 100,000 m3/d (1.15 m3/s).
Surpluses from Mzima Springs flow to the Tsavo River, which subsequently meets the Athi River to form the Sabaki River.
WRMA has recently invited consultancy contract (supported by WB) for the study of the Chiulu hills Aquifer in order to ascertain the sustainable yield of
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Mzima and other springs (Umani, Mtito Andei, Kiboko, Makindu, Mangelete and others) originates from the Chiulu hills, in light of the climatic changes in the region. (WRMA) published a request for Expressions of Interest for this contract in August 2012, this study will play a major role in understanding the real potential of this source as well as other sources. The actual potential of Mzima Springs will be determined following this in-depth study.
3.1.2 Baricho Wellfield
The Baricho Wellfield consists of eight boreholes on the southern bank of the Sabaki River. The boreholes abstract water from the paleochannel, and have a total capacity of approximately 96,000 m3/d. Two bulk supply systems from Baricho exist, one to Malindi and Watamu, and the other to Kilifi and Mombasa. According to the site visit conducted in June 2012, current water supply from the Baricho Waterworks is about 62,000 m3/d (50,000 m3/d via the Mombasa Pipeline, and 12,000 m3/d via the Malindi Pipeline). Latest data received 02.2013 indicates a total production of 67,000-68,000 m3/d as an average dailyproduction.When the ongoing improvement works – rehabilitation of pumps and electric components under WaSSIP at the site – are completed, it is assumed that the overall capacity of this water source will be around 90,000 m3/d, equal to 3,800 m3/h. This new installed capacity will bring the two conveyance systems to their full capacity; thus any further abstraction of water to Mombasa from this source will have to include not only wells (boreholes) and booster pump expansion, but also a water conveyance or transmission system.
Baricho was first developed as a surface water intake site during the 1980 and used to supply water to Mombasa. The intake site included full conventional water treatment works and a pumping station. Baricho was abandoned as a surface source in the early 1990s after a few years of operation, largely because of excessive O&M costs related to high silt loads: the amount of chemicals for flocculation and coagulation tripled, while daily desilting of the intake apron had to be performed manually, and rapid breakdown of the pump impellers took place due to the abrasive action of silt and sediments.
After the abandonment of Baricho as a surface water option, groundwater from the paleochannel was explored and developed as a source with highly productive boreholes on the south bank of the Sabaki River. The boreholes make use of the existing pumping and transmission systems. Except for the high electricity costs, groundwater has proved to be successful.
H.P. Gauff conducted two studies on the paleochannel:
Seismic & Resistivity Survey (1993, with the assistance of Groundwater Survey Kenya). Modular three-dimensional finite difference groundwater flow model of the Sabaki Aquifer (1995).
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These studies were aimed at investigating the boundaries and potential of groundwater in the paleochannel. The following findings were obtained:
The survey covered an area 8.5 km in length along the river. The depth of the coarse sediments ("the paleochannel") is 50–60 m. Aquifer transmissivity in the paleochannel is of the order of 10,000 m2/d. The model covered the area of the eight boreholes. Expansion to 220,000 m3/d is feasible, under limitations of low flows. Figs. 3-1 and 3-2 depict the geology structures and the general location of the paleochannel near Baricho.
Source: Seismic & Resistivity Survey, H.P. Gauff 1993)
Fig. 3-1: Map showing geology of the area near Baricho
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Source: Seismic & Resistivity Survey, H.P. Gauff 1993)
Fig. 3-2: General map showing location of paleochannel near Baricho
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Low Flow Study The hydrology of the Sabaki River had been studied and presented in the Water Resources Report. Fig 3-3 and table 3-1 summarizes the results of the study.
Fig. 3-3: Duration Curve of the Sabaki River Near Baricho
Table 3 -1: Daily Flows on Monthly and Annual Basis Having Probability of 50, 90, 95 and 100% (m3/s)
% JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Total 50 8.42 8.42 8842 8242 572 7242 .244 .242 8547 5248 2445 2242 7.83 90 444 .44 .4. 584. 8447 8842 554. 842 24. 745 5847 5448 .88 95 242 .45 .48 748 5248 5.45 847 245 748 248 247 5847 387 100 844 .42 .42 .4. 24. 744 248 245 242 .48 .42 245 683
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3.1.3 Total Production of the Current Water Systems
The Coast Province mostly depends on a bulk water supply system comprising Mzima Pipeline, Marere Pipeline, Tiwi Boreholes and Sabaki Pipeline, supplying Mombasa and other counties such as Kwale, Kilifi and Taita Taveta. Taveta township and the surrounding villages are supplied with water from the high-yield Njoro Kubwa Springs. The settlement of Lamu depends on the local Shella Aquifer. Hola town abstracts water directly from the Tana River.
Table 3-1 summarizes the capacity of the main water supply systems in the Coast Province.
Table 3 -2: Current Water Supply Capacity in the Coast Province
Installed Capacity Year Water Source (m3/d) Developed Mzima Springs 35,000 1957 Marere Springs (with Pemba) 12,000* 1923 Baricho Wellfield 90,000* 1980 Tiwi Aquifer 13,000* 1980 Njoro Kubwa Springs 3,000 1990 Tana River 1,400 1965 Shella Aquifer 1,800 unknown Total 149,200 * Capacities expected for Marere Springs, Baricho Wellfield and Tiwi Aquifer following completion of ongoing rehabilitation projects.
The area of the Coast Province falls under two catchment areas managed by WRMA – Tana Catchment Area and Athi Catchment Area. The Coast Province is located downstream of both catchments, and, therefore, it is essential to understand the development strategies for the catchment as a whole.
The WRMA Catchment Management Strategies (2008) established the short- and medium-term strategies for water resources development.
3.2 Water Resources Management
3.2.1 Overview
Three key institutional players are currently involved in Water Resources Management in Kenya – the Ministry of Water and Irrigation (MWI); the Water Resources Management Authority (WRMA), exercising jurisdiction over water uses and flood control; and the National Environmental Management Authority (NEMA), responsible for management of the water environment (water quality
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and aquatic ecology), including watershed management under the authority of the Ministry of Environment.
Responsibility for flood control is not completely clear according to the Water Act 2002 (i.e., whether under the authority of MWI or WRMA). Catchment protection is under the authority of WRMA, although it is not clear if catchment protection includes flood control. Watershed management is part of catchment protection while water quality management is also conducted to a partial extent by WRMA.
In the future, the water resources management framework will have to consider present and future needs of various water-related sectors, policy and non-policy measures and requirements, alternative measures, and an appropriate balance between policies and measures.
3.2.2 Existing Situation
The Coast Water Services Board relies on both ground water and surface water resources for its water supply in its area of jurisdiction. The surface water resources comprise largely of spring water resources. The two largest river resources in the area namely the Sabaki River and Tana River have not been fully exploited to their full potential. The Sabaki has been largely exploited in the form of subsurface abstraction at Baricho. Tana River, except for Bura irrigation scheme in Bura and water supply abstraction in Hola, largely remains untapped and has a huge potential for exploitation as a water supply resource in the northern part of the province. The sections that follow look at the systems in place for the management of water resources in the Coast Province
3.2.2.1 Existing Groundwater Management
Aquifers in Kenya in general and the Coast Province in particular, are managed on an ad hoc basis. Water allocation is not based on a formal system of assessment or with an allocation plan in mind.
Groundwater management decision-making is sector-based and ad hoc in nature, with no mechanism for coordination or encouragement of multi-sector linkages. Management of groundwater resources is carried out independently of land management and other land based resources. Decision-making in connection with groundwater management is largely centralized, with minimum involvement, if any, on the part of stakeholder water resources management units.
Despite provision for groundwater conservation zones in the Water Act 2002, no ground conservation zones have been gazetted for the Coast Province or Kenya as a whole. A majority of the numerous groundwater users do not have abstraction
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permits and hence essentially they are not documented. Groundwater management is therefore weak and largely lacking in any strategic focus.
3.2.2.2 Existing Surface Water Management
Existing surface water management is limited to flow gauging stations along the major rivers and springs found within the Coast Province. There is no evidence of any catchment conservation or environmental flow management efforts for these rivers.
Table 3-3 presents a list of the gauging stations, their locations and data availability.
Table 3 -3: List of River Gauging Stations, Available Data and Condition
Station Location Status Period of available data 3F02 Athi River Active in the past 1952–1995, with gaps 3HA01 Sabaki River Not active 3HA02 Sabaki River Not active 3HA03 Sabaki River Not active 3HA04 Sabaki River Not active 3HA05 Sabaki River Not active 3HA08 Sabaki River Active in the past 1973–1982, with gaps 3HA09 Sabaki River Not active 3HA10 Sabaki River Not active 3HA11 Sabaki River Not active 3HA12 Sabaki River Active in the past 1980–1987, with gaps 3HA13 Sabaki River Not active 4G01 Lower Tana Active in the past 1941–1994, with gaps 4G02 Lower Tana Active in the past 1950–1998, with gaps 4G03 Lower Tana Active in the past 1962–1993, with gaps 3MH01 Marere Springs Not active 3MH02 Marere Springs Not active 3MH03 Marere Springs Not active 3MH09 Marere Springs Not active 3MH11 Marere Springs Not active 3MH16 Marere Springs Not active 3MH25 Marere Springs Not active 3MH26 Marere Springs Not active 3MH08 Mwadabara/Mkomba Springs Not active (Marere Springs) 3MH17 Mwadabara/Mkomba Springs Not active (Marere Springs) 3MH21 Mwadabara/Mkomba Springs Not active (Marere Springs) 3MH23 Kitanzi Springs (Marere Springs) Not active 3KD04 Mkurumudzi River Not active 3KD05 Mkurumudzi River Not active 3G03 Mzima Springs Active in the past 1951–1990, with gaps 3G02 Tsavo River Active in the past 1949–1991, with gaps
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Station Location Status Period of available data 3G04 Tsavo River Active in the past 1949–1997, with gaps 3G05 Tsavo River Active in the past 1951–1979, with gaps 3G06 Tsavo River Active in the past 1951–1989, with gaps 3G12 Tsavo River Not active 3G13 Tsavo River Not active 3G14 Tsavo River Not active 3J01 Lumi River Not active 3J04 Lumi River Not active 3J06 Lumi River Not active 3J07 Lumi River Not active 3J15 Lumi River Active in the past 1961–1994, with gaps 3J05 Njoro Kubwa Springs Not active 3J02 Rovu River (drains to Lake Jibe) Not active 3KC04 Mwachema River Active in the past 1978–1991, with gaps 3KB01 Ramisi River Active in the past 1961–1991, with gaps 3KC01 Ramisi River Not active 3KC03 Ramisi River Not active 3KC04 Ramisi River Active in the past 1978–1991, with gaps 3LA01 Rare River Not active 3LA02 Rare River Not active 3MH10 Pemba River Active in the past 1947–1978, with gaps 3MA02 Mwache River Not active 3MA03 Mwache River Active in the past 1976–1990, with gaps 3LA03 Voi River Active in the past 1961–1981, with gaps 3LA04 Voi River Not active 3LA05 Voi River Active in the past 1969–199,2 with gaps 3KG01 Umba River Active in the past 1966–1968, with gaps
The table presents data received from WRMA, clarifications regarding the stations is not available. The consultant had made effort to achieve the most updated data.
3.2.2.3 Main rivers: Athi Catchment Area
The following are the main rivers found in the Athi Catchment Area.
A map showing the river gauging stations in the Athi catchment area is presented in Fig. 3-3.
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Fig. 3-4: River gauging stations in Athi Catchment area
1. Athi & Sabaki Rivers
The catchment area for the Athi/Sabaki River is 37,836 km2. There are numerous regular river gauging stations on the river, namely, 3F02, 3HA01, 3HA02, 3HA03, HA05, 3HA06, 3HA08, 3HA09, 3HA010, 3HA011, 3HA012 and 3HA013. Data for gauging station 3F02, located at about 200 km upstream of the confluence of the Sabaki and Tsavo rivers, is available for the period 1952–1995, albeit with significant gaps. The other stations for which data are partly available are 3HA08, with data for the period 1973–1982, and 3HA12, with data for the period 1980–1987. For the rest of the stations data are not available.
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2. Mwache River
The Mwache River basin covers an area of approximately 2,000 km2. Two regular gauging stations exist on the Mwache River, namely, 3MA02 and 3MA03. Data for 3MA03 are partly available for the period 1961–1981. Data are not available for station 3MA02.
3. Rare River
The Rare River, located in Kilifi District, is a seasonal river with a catchment area of about 7,729 km2. The river has two regular gauging stations, 3LA01 and 3LA02. Data are not available.
4. Pemba River
The Pemba River is located in the east part of Shimba hills and drains an area of about 637 km2. The river has only one gauging station, namely, 3MH10. Data available for the river relate to the period 1947–1978 (with gaps corresponding to periods when data were not recorded).
5. Ramisi River
The Ramisi River, draining an area of about 1,610 km2, has four regular gauging stations: 3KB01 on the river itself; and 3KC01 on Ndoro, 3KC03 on Cheruka and 3KC04 on Mwachema tributaries. Data are available only for station 3KB01 for the period 1978–1991 (with gaps).
6. Mwachema River
The Mwachema River flows along the eastern side of the Shimba hills. The catchment area is about 2,000 km2 and borders the catchments of Pemba and Mkurumuji rivers. The river drains into Mombasa Bay near Port Reitz, south of Mombasa Island. The data available from the one gauging station, 3KC04, relates to the period 1978–1991 (with gaps).
7. Lumi River
The main water resource in Taita Taveta District, the Lumi River originates in the southern slopes of Mt. Kilimanjaro. It drains an area of approximately 590 km2
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and drains into the swamps of Lake Jipe. The river has five regular gauging stations: 3J01, 3J04, 3J06, 3J07 and 3J15. Data are available only for station 3J15 for the period 1961–1994 (with gaps).
8. Tsavo River
The Tsavo River has its origin in the Mzima Springs area and flows eastward from the foothills of Mt. Kilimanajro, draining an area of 7,140 km2. It is the largest tributary of the Athi River. The Tsavo River basin has seven regular river gauging stations on its several tributaries (Mzima, Nolturesh Springs, Ngong Naroko, Kitendeni and Simeki streams). The gauging stations are 3G02, 3G04, 3G05, 3G06, 3G012, 3G013 and 3G014. Data are available for gauging stations 3G02 (for the period 1949–1991), 3G04 (for the period 1949–1997), 3G05 (for the period 1951–1979) and 3G06 (for the period 1951–1989). All data for these stations have gaps when no records were taken.
9. Mkurumudzi River
The Mkurumudzi River originates in the Shimba Hills and drains a catchment area of about 200 km2. It has three gauging stations, 3KD04, 3KD05 and 3KD05. However, data for the stations are not available.
10. Voi River
The Voi River originates in the Taita hills and drains into Rare River. It is a seasonal river with three gauging stations: 3LA03, 3LA04 and 3LA05. Data are available at 3LA03 for the period 1961–1981and at 3LA05 for the period 1969– 1992 (data for both stations having gaps).
11. Umba River
The Umba River originates in Tanzania. It has one gauging station on the Kenya side namely 3KG01 with data available spanning the period 1966–1968 when it was not recorded throughout the year.
3.2.2.4 Main rivers: Tana Catchment Area
The Tana Basin, with a catchment area of about 94,700 km2, can be divided into three sections: the upper 9,520 km2 area, consisting of streams from Mt. Kenya and the Aberdares, the middle 15,480 km2 area, and the Lower Tana 69,700 km2 area. While the master plan is based on the Lower Tana, it is also affected by
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activities in the entire catchment. The Tana River has several gauging stations, among them 4G01 (Garissa), 4G02 (just upstream of Garsen) and 4G04 (just upstream of Hola). Station 4G01 has data for the period 1941–1994, 4G02 for the period 1950–1998 and 4G04 for the period 1962–1993, all displaying some gaps corresponding to periods when data were not recorded.
In addition to the Tana River itself, there are several seasonal rivers in the area, found in the area west of the Tana River, in the northeastern part of the Tana River Delta. These rivers, popularly known as "lagas", flow in a west-east direction from Kitui, Makueni and Mwingi districts, draining into the Tana River and eventually into the Indian Ocean.
3.2.2.5 Spring Water Resources
In addition to river resources, spring-water resources are also found in the Coast Province. They are listed below:
1. Mzima Springs
The Mzima Springs basin lies 220 km to the northwest of Mombasa, with the source located on the fringes of Chyulu Hills. The springs are located west of Chyulu Hills in Tsavo West National Park, at an elevation of about +680 masl at the spring intake works and at the pipeline haedworks at an elevation of 673masl. Mzima Springs comprise a group of four springs – Hippo Pools, Bathing Pools, Cataract Swamp and Banana Swamp. Water from Mzima Springs is measured in gauging station 3G03 before discharging into the Tsavo River. Data available for this station relate to the period 1951–1990, with gaps corresponding to periods when data were not recorded.
2. Marere Springs
Marere Springs originate from Shimba Hills and are the source of the oldest piped water supply to Mombasa. They are located in Kwale District, southwest of Mombasa. The sources of Marere Springs are three springs in Shimba Hills – Marere, Votia and Mwaluganje. The springs have seven regular gauging stations – 3MH01, 3MH02, 3MH03, 3MH09, 3MH25, 3MH26 and 3MH14. Votia Spring, a tributary of the Mwalolo River, has three gauging stations – 3MH06, 3MH15 and 3MH16. Mwadabara and Mkomba streams/springs have three gauging stations – 3MH17, 3MH08 and 3MH21 – while Kitanzi Spring has one gauging station, 3MH23. Data are not available for any of these stations.
3. Njoro Kubwa Springs
The Njoro Kubwa Springs emerge in a pool beside the right bank of the Lumi River, about 3 km southeast of Taveta township. The group of springs includes
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two other springs – Njoro Ndogo 1 and Njoro Ndogo – emerging 100 m upstream. The Njoro Kubwa Springs are utilized for irrigation water supply to sisal estates. They have one gauging station, 3J05, for which data are not available.
3.2.2.6 Lake Water Resources
Additional water resources available in the Coast Province include the following fresh water lakes:
1. Lake Jipe
Lake Jipe is a shallow water body located on the Kenya-Tanzania border, with about one-quarter of it lying within Tsavo West National Park. Lake Jipe is fed mainly by rainfall from the slopes of Mt. Kilimanjaro, perennially by runoff from the Lumi River and ephemerally by the Mbaro River to the south. The lake is drained by the Rovu River, which flows out from the northwestern corner of the lake. The Rovu River has one gauging station, 3J02, for which data are not available.
2. Lake Challa
Lake Challa occupies the site of an old volcanic caldera, with the Kenya- Tanzania border passing through its middle. The surface area of the lake is 4.21 km2, the volume of water stored is in excess of 400 MCM and the crater is some 140 m deep. Water depth ranges from 85 m to 91 m. Data are not available from the one gauging station, 3J03.
3.2.3 WRMA Catchment Strategies
3.2.3.1 General
The area of the Coast Province falls under two catchment areas managed by WRMA – Tana Catchment Area and Athi Catchment Area. The Coast Province is located downstream of both catchments, and, therefore, it is essential to understand the development strategies for the catchment as a whole.
The WRMA Catchment Management Strategies (2008) set short- and medium- term strategies for water resources development.
3.2.3.2 Athi Catchment Area Strategies
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WRMA management strategies for the Athi Catchment Area, with an annual average rainfall of 739 mm, include development of surface water storage, in the framework of which the region will adopt a micro (household level) and macro (state level) strategy, promoting:
Construction of large dams. Rehabilitation of small dams/pans. Construction of water harvesting facilities.
Water storage can be improved through the enhancement of groundwater storage, performed by encouraging development of groundwater recharge infrastructure.
Targets in terms of water resources development include:
Development of plans to meet 150,000 m3 capacity groundwater storage. Development of 1.9 MCM storage in small-scale reservoirs by 2013. Promotion of 1.62 BCM storage on the Athi River by 2013, as well as at Munyu, Fourteen Falls, Site A13, Mavindini and Yatta Bridge.
3.2.3.3 Tana Catchment Area Strategies
The Tana Catchment Area is home to the largest dam and reservoir capacity in Kenya. The existing dams are Kindaruma (1968), Kamburu (1975), Gitaru (1978), Masinga (1981), Kiambere (1988), Sasumua (1956) and Ndakaini (Thika, 1993). There is a need to construct the High Grand Falls Dam. In addition, many small dams/pans have been constructed by private individuals, institutions and communities.
WRMA management strategies for the Tana Catchment Area, with an annual average rainfall of 679 mm, include the utilization of underexploited natural aquifers. In considering the development of additional groundwater storage, artificial groundwater recharge techniques will be one way to ensure better use of water resources.
The region expects to carry out planned activities during the next 10 years, including:
Two dams, each of 1 MCM capacity. A dam of 4–5 BCM capacity. Five small dams, each of 0.2 MCM capacity. Five sand dams / check dams / pans / rock catchments, each of 100–1,000 m3 capacity. Groundwater survey and mapping. Rainwater harvesting in 1,000 households/institutions.
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3.2.4 Principles of Water Resources Management
Water supply systems are based mostly on natural water resources. The increasing awareness of the environment and natural resources, the rising global demand for water (especially since the 1990s) and the decline in water availability from natural resources intensify the need for consistent, rational and integrative water use management.
The increasing emphasis on environmental and ecological approaches, the role of water in preserving natural resources and the several regional catastrophes that took place during the 1990s due to unplanned utilization of natural resources (or flawed management of resources, such as mines and sewage, causing contamination of water sources) have resulted in a pressing need for effective water resources management.
This activity includes principally:
Judicious management of water consumption, utilizing tools and techniques that are outside the sphere of engineering (education, promotion campaigns, economic policy, etc.). Long-term study of water source features, as well as ways to ensure sustainability. Balancing of volumes used vis-à-vis replaceable amounts. Introduction and implementation of metering and monitoring systems. Incorporation of sophisticated tools and techniques adopted from statistical disciplines, operations research and natural resources management, as a basis for the preparation of activity/work programs – both short-term programs with an operational orientation (answering the question "how?"), as well as long-term programs with an infrastructure orientation (answering the question "what?").
Integration of the above activities will form the basis for a water resources management plan that takes into consideration all elements within a single holistic system, including consumers, ecological conservation and environmental protection.
3.2.4.1 Study of Water Source Features
Often, the unique characteristics of the sources are not sufficiently understood. Most countries keep regular records of water resources data. Experience has shown that a long-term study and understanding of the diversity and quality of natural water sources, together with effective monitoring and measurement, is a prerequisite for effective and sustainable water source management. Many instances exist in which natural water sources have been utilized without an adequate knowledge or understanding of recharge processes, aquifer characteristics, surface water features, etc. Uses that do not preserve a sustainable
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balance can cause ecological catastrophes. Resource management that is not backed by reliable and accurate measurements and understanding of trends can lead to erroneous decisions regarding pumping policies and overexploitation.
It should also be noted that the evaluation of water volumes, assessment of the impact of climate change on rainfall and hydrological conditions, and the drafting of appropriate natural resources policies have become pressing issues in the past decade. At this early stage, it is very difficult to quantify future water availability and hydrological potential based on climate change models.
3.2.4.2 Introduction and Implementation of Measurement and Monitoring Systems
In order to apply decision support systems based on real and accurate data, there is a need for multiannual recording, documentation, monitoring and analysis of data on water production and usage.
The main variables that should be rigorously monitored include the following:
Amounts pumped and quality. Drilling, analysis of new water sources and inspection of aquifers. Examination of surface water and groundwater levels. Changes in ecological environments in the vicinity of pumping sites. Measurement of water demand on the part of large consumers. Multiannual flows, rainfall, number of precipitation days and other events. Other measurements – atmospheric water, soil moisture, etc.
Progressive forward thinking, coupled with initiation and application of monitoring and measurement systems, is an essential precondition for water resources management. This approach can be summed up in the saying "What is not measureable is not manageable".
Sufficient information that is both relevant and accurate should be made available to decision-makers in order to enable them to make well-informed choices. Moreover, in addition to data, tools and instruments for analysis and evaluation should also be utilized.
3.2.4.3 Application of Management Tools and Models
All too frequently it is the abundance of available data that challenges system engineers to develop tools to predict variables that characterize water systems. These include available water quantity, general engineering variables, meteorological prediction models and surface water modelling. The environment of uncertainty gives rise to the dire need to develop and apply appropriate tools to manage and coordinate natural water systems and promote decision-making.
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Conditions of uncertainty are the main factor influencing decision-making in natural water management. Adaptation of risk management models from diverse disciplines such as finance, insurance and demography have been found to be the most suitable for management of natural resources and water. Analysis of historical data, understanding of trends and preparation of predictions based on statistical values enable decision-making at differing risk levels, each involving different financial costs and engineering variables.
In addition to statistical models, other models may include hydraulic models of water conveyance and pumping systems (for energy efficiency), models for the location of seepages and water losses from regional and local systems, and hydraulic models for the assessment of surface water flows, to name just a few.
In general, operations analysis within the sphere of water supply systems demands regular hands-on activities by trained engineering staff.
3.2.5 Proposed Actions
3.2.5.1 Proposed Groundwater Management Plan
Institution of urgent aquifer management and protection / conservation programs with focus on the following aspects:
Incorporation of the subject of groundwater management into policy and planning. Improvement of the knowledge base on aquifers within the Coast Province by improving both institutional and human resources in the relevant institutions responsible for water resources management. Implementation of suitable monitoring programs for aquifers within the Coast Province. Improvement in data collection, management, storage and dissemination. Enhancement of active involvement by groundwater users in aquifer management. Encouragement of and campaigning for concerted public support for groundwater resources management. Managed aquifer recharge: the "Kenya Groundwater governance case study" (November 2010) indicates that this a major issue for WRMA. The recommendation indicates that WRMA shall incorporate Groundwater recharge as a policy.
3.2.5.2 Proposed Surface Water Management Plan
The following measures are proposed for surface water resources management in CWSB's area of jurisdiction:
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Enhancement of hydrometric measurements of the river and stream systems within the Coast Province, including establishment of new gauging stations where necessary, and ensuring that measurements are taken in the existing stations at the required frequency in order to eliminate gaps in the data collected. Establishment of environmental flows for all perennial rivers and streams in the province in order to protect the aquatic environment both inland and in the delta region. Determination in accordance with Water Resources Management Rules, 2006, the reserve for each of the water resources in order to guarantee equitable utilization between the various competing demands. Ensuring viable programs are in place for conservation of each catchment against degradation. A comprehensive catchment programme should be implemented. The programme should include: sedimentation reduction strategies, community land use limitations.
3.3 Potential of Surface Water Resources
Future water resources' are presented as 'potential water resources' which shall be developed for water supply in the Coast province
3.3.1 Mkurumudzi Dam
Mkurumudzi River originates in the Shimba Hills and flows southeast to the Indian Ocean. Mkurumudzi Dam is being developed to supply water for the new titanium mine by the Australian company Base Titanium. The quantity of titanium in the mine is assumed to suffice for 15 years of mining operations.
After mining operations are terminated, the source can be used for Msambweni District. Hence, it is suggested that CWSB make appropriate arrangements to take over management of the dam once the mining operations end. However it should be emphasized that the dam will not be available in the near future.
The main parameters of Mkurumudzi Dam are as follows: (Source: Borehole and Completion Report, Msambweni Area, Kwale, South Coast, by Tiomin Resources Inc., June 2005). Dam height was not definitely established at the time of preparing this report (the mining company is still exploring possibilities of the dam expansion)
Purpose: Mining Catchment area 125 km2 Gross storage 8.0 MCM Flooded area 140 ha Daily yield, min/max 19,000/28,000 m3/d Annual yield, min/max 6.94/10.22 MCM/y
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3.3.2 Tana River
3.3.2.1 General
The Tana River originates in the area of Aberdare Mountains and is the longest river in Kenya. According to the current study by TAHAL/Bhundia (see Water Resources Report, December 2012), the lowest measured flow (frequency of 100%) in the past 60 years is 8.5 m3/s; the sustainable flow is 43 m3/s (frequency of 95%).
This source has been proposed for various water supply, irrigation and hydropower projects, as mentioned in the Catchment Management Plan and Vision 2030. The main projects involve increasing storage capacity in upstream areas and are expected to reduce available water in the downstream area and moderate fluctuations between the rainy and dry seasons.
Under the jurisdiction of CWSB, there are only a few large abstractions around the towns of Hola and Bura.
The river was indicated as a possible source in the LAPPSET Master Plan by JPC & BAC /GKA. Two intake sites are considered for water abstraction for supply to Lamu town from the Tana River. The first intake site is in the Nanighi area near Hola Town at an estimated distance of 180 km from Lamu. The second intake site is near Garsen Bridge, further downstream at a distance of about 80 km from Lamu.
3.3.2.2 Current Study
Available daily streamflows measured at the 4G02 hydrometric station were organized in descending order in order to create monthly and total flow duration curves. Streamflow values at various frequencies were read from these curves to serve as a basis for formulating recommendations regarding water abstraction from the Tana River.
Fig. 3-4 presents the flow duration curve of all daily measured data at hydrometric station 4G02 – Tana River at Garsen. Table 3-3 presents the daily flow duration curves fractiles on a monthly and total period basis.
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4G02-Tana Garsen-Discharge [m^3/s]Final Full Feasibility Study
300 120
90 250 60
30 200 0 Average Daily Daily Flow (cumecs) Average 50 60 70 80 90 100 % of Time 150
100
Average Daily Flow (cumecs) Average Flow Daily
50
0 0 10 20 30 40 50 60 70 80 90 100 % of Time
Fig. 3-5: Tana River at Garsen Hydrometric Station 4G02 – flow duration curve of all measured daily flows (1950–1998)
Table 3 -4: Tana River at Garsen Hydrometric Station 4G02 – Flow Duration Curves Fractiles of All Measured Daily Flows (1950–1998)
% JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Total 50 108.7 74.8 66.4 107.9 154.7 143.2 96.3 72.9 66.9 62.7 118.4 147.1 101.0 90 67.7 40.3 29.6 48.0 95.4 80.9 63.6 54.8 45.2 44.9 67.0 92.0 55.7 95 56.3 33.0 27.8 35.5 78.4 73.3 58.4 50.9 41.5 37.4 58.8 86.2 44.7 100 33.0 23.1 16.0 16.0 37.9 57.1 46.0 27.2 19.4 8.5 44.5 62.5 8.5
3.3.3 Mwache Dam
3.3.3.1 General
The Mwache River was identified by JICA in the National Water Master Plan 1992 (NWMP 1992) as a possible river for damming. The JICA study team suggested the river as a viable source for urban water supply, mainly to Mombasa city. The location suggested in NWMP 1992 is 5 km from Mazeras tanks and a few kilometres before the river debouches to the sea at Port Reitz.
The Government of Kenya selected Mwache Dam to be a flagship project as part of Vision 2030.
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3.3.3.2 CES/APEC Study
The Ministry of Regional Development Authorities (MoRDA) awarded Consulting Engineering Services (India) Private Limited (CES), in association with APEC Consortium Ltd., the assignment of carrying out the feasibility study and detailed design for the Mwache Multipurpose Dam Development Project on the Mwache River. The study commenced in June 2010 and is currently in its final stages.
CES/APEC initially designed the dam height 85 m above ground level, with a gross capacity of 200 MCM and dead storage of 4 MCM. After discussions with World Bank experts, CES/APEC lowered the dam height to 65 m above ground level, with a gross capacity of 120 MCM and dead storage of 20 MCM. Dead storage volumes were increased following the sedimentation analysis.
The only available records of the Mwache are from river gauging station 3MA03, which was active for 14 years (1976–1990). The minimum and maximum annual (June to May) flow during these 14 years were 75 MCM and 186 MCM, respectively.
A measurement period of 14 years is insufficient for designing big dams like Mwache, because it usually cannot capture extreme flows during droughts and floods.
CES/APEC used the STOMSA (Stochastic Model of South Africa) method to generate 50 years of flows. The results of the hydrological analysis by CES/APEC are as follows:
Average annual water availability: 112.54 MCM. 75% dependable annual water availability: 88.4 MCM. 90% dependable annual water availability: 77.1 MCM. 99% dependable annual water availability: 69.6 MCM.
Table 3-5 presents a comparison between measured rainfall in the period 1976– 1989 (corresponding to the 14 years of gauged flow) and measured rainfall over a 50-year period.
Table 3 -5: Averages and Standard Deviations of Precipitations for 14 and 50 years
Period Average St. dev. Station Ratio (years) (mm/y) (mm/y) 1961–2009 1081.3 292.0 Malindi 1.17 1976–1989 1082.0 249.3
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1957–2011 1165.8 375.5 Msabaha 1.55 1976–1989 1166.3 242.9 1959–2010 1308.8 367.6 Mtwapa 1.42 1976–1989 1321.1 258.6
Table 3-5 shows that:
The average annual rainfall is consistent for both the short period (14 years) and the long period. The standard deviation is greater by 45–50% in the long period.
Based on the above comparison, the low flows of the Mwache River may be expected to be lower than those calculated by CES/APEC (70 MCM/y).
3.3.3.3 Current Study
The available monthly streamflows measured at the Mwache River hydrometric station 3MA03 were applied using the MRS monthly rainfall-runoff model1 calibrated for the period of available records, 1976/77–1989/90. The monthly rainfall used as input to the model input was based on the Theissen procedure as related to five rainfall stations having monthly data for the period 1958/59– 2008/2009. Following completion of calibration, the model was applied to simulate monthly flows for the latter period.
Table 3 -6: Measured Mean Monthly Flows at 3MA03 Hydrometric Station (m3/s)
YEAR JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY 1976/77 4.474 2.457 1.225 4.423 1.871 3.786 6.481 5.464 2.743 5.050 8.882 2.091 1977/78 1.669 3.687 2.471 4.439 8.768 10.826 11.455 5.004 3.859 7.016 6.776 9.222 1978/79 2.357 1.708 1.370 1.390 0.000 6.366 7.319 4.759 3.415 6.320 4.129 8.514 1979/80 8.225 2.010 1.769 1.810 1.941 4.528 2.746 1.777 1.500 1.700 3.346 1.852 1980/81 1.357 2.400 16.752 1.754 0.420 6.372 5.975 1.815 0.000 14.259 6.765 3.115 1981/82 2.433 1.492 0.689 2.764 3.726 3.676 5.321 1.940 1.193 0.017 4.056 20.333 1982/83 3.175 2.901 1.728 1.733 4.191 3.764 4.872 1.038 0.000 3.500 2.343 5.989 1983/84 4.585 2.108 1.525 1.954 1.092 0.969 1.564 1.318 0.000 1.600 6.769 3.470 1984/85 1.819 1.781 0.736 0.750 1.578 6.283 4.056 3.522 4.563 1.299 2.178 5.238 1985/86 1.055 3.782 1.840 0.750 0.690 2.989 3.803 1.301 1.265 5.418 6.746 11.082 1986/87 5.645 1.323 1.500 0.000 1.498 4.876 6.086 2.645 1.016 0.000 3.882 12.179 1987/88 1.753 1.650 2.754 1.510 1.800 0.510 1.867 4.378 1.128 7.574 8.279 2.409 1988/89 7.141 1.281 0.893 1.147 1.300 3.614 3.796 4.320 0.000 3.861 4.463 4.760 1989/90 1.974 1.970 0.940 4.200 5.800 2.606 3.632 2.399 1.067 8.400 4.064 2.292
1 MRS is a rainfall-runoff model developed by TAHAL, which is described in Annex 1.
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Table 3 -7: Major Characteristics of the Rainfall Stations
Available Data Area of Mean Mwache Annual Rainfall Name Code Base Station Original Completed Basin (mm) (km2) Voi 9338001 1960–1988 1959–2009 Msabaha 101 556 Mackinnon 9339002 1963–1994(1) 1959–2009 Maji, Kayafungo 1,895 494 Makamini 9339049 1971–1985 1959–2009 Maji, Mackinnon 953 630 Mariakani 9339057 1977–2009 1959–2009 Maji, Kayafungo 575 772 Mazeras 9339048 1971–1995 1959–2009 Port Reitz, Mariakani 81 987 1 Data include records relating to the 1926–1947 period, not used in the present study.
Completion of missing data was done based on monthly linear regressions (with correlation coefficient equal to at least 0.7). Some gaps were filled in by the mean multi-annual value.
90.0
80.0 OBS 70.0 SIM
60.0
50.0
40.0
Monthly Volume (MCM) 30.0
20.0
10.0
0.0 1/6/76 26/2/79 22/11/81 18/8/84 15/5/87 8/2/90
Fig. 3-6: Mwache Hydrometric Station 3MA03 – comparison between observed and simulated monthly hydrographs
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90.0
80.0 OBS 70.0 SIM
60.0
50.0
40.0
Monthly Volume (MCM) 30.0
20.0
10.0
0.0 0 10 20 30 40 50 60 70 80 90 100 % of Time
Fig. 3-7: Mwache Hydrometric Station 3MA03 – comparison between observed and simulated monthly flow duration curves (1976/77–1989/90)
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Table 3 -8: Mwache Reservoir Site – Simulated Monthly Flows (MCM), 1958/59–2007/08
YEAR JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY ANNUAL 1958/59 9.0 8.0 7.0 7.0 6.0 5.0 5.0 4.0 4.0 3.0 31.0 23.0 112.0 1959/60 9.0 4.0 3.0 2.0 6.0 3.0 2.0 2.0 3.0 2.0 2.0 1.0 39.0 1960/61 1.0 14.0 11.0 118.0 232.0 303.0 156.0 120.0 106.0 95.0 86.0 77.0 1319.0 1961/62 69.0 62.0 56.0 51.0 45.0 41.0 37.0 33.0 30.0 27.0 38.0 38.0 527.0 1962/63 31.0 24.0 17.0 15.0 13.0 14.0 25.0 14.0 9.0 8.0 11.0 18.0 199.0 1963/64 8.0 6.0 5.0 4.0 4.0 3.0 57.0 17.0 4.0 3.0 3.0 5.0 119.0 1964/65 4.0 2.0 2.0 2.0 1.0 37.0 9.0 2.0 1.0 44.0 20.0 27.0 151.0 1965/66 22.0 7.0 3.0 1.0 2.0 1.0 1.0 1.0 6.0 1.0 17.0 16.0 78.0 1966/67 6.0 3.0 4.0 28.0 88.0 54.0 14.0 11.0 13.0 16.0 24.0 20.0 281.0 1967/68 26.0 11.0 9.0 7.0 6.0 14.0 9.0 5.0 33.0 12.0 9.0 10.0 151.0 1968/69 8.0 6.0 7.0 5.0 5.0 11.0 6.0 4.0 4.0 4.0 3.0 3.0 66.0 1969/70 3.0 2.0 2.0 2.0 2.0 1.0 1.0 1.0 1.0 1.0 1.0 3.0 20.0 1970/71 2.0 1.0 1.0 0.0 0.0 0.0 8.0 1.0 0.0 0.0 0.0 21.0 34.0 1971/72 2.0 2.0 1.0 11.0 7.0 6.0 8.0 1.0 1.0 1.0 24.0 24.0 88.0 1972/73 9.0 2.0 2.0 1.0 1.0 2.0 1.0 1.0 2.0 1.0 2.0 2.0 26.0 1973/74 3.0 4.0 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.0 3.0 12.0 1974/75 1.0 2.0 0.0 0.0 0.0 0.0 0.0 8.0 1.0 0.0 0.0 1.0 13.0 1975/76 1.0 1.0 0.0 0.0 0.0 3.0 2.0 0.0 0.0 0.0 1.0 1.0 9.0 1976/77 1.0 1.0 3.0 17.0 20.0 24.0 22.0 9.0 4.0 9.0 18.0 12.0 140.0 1977/78 6.0 3.0 3.0 2.0 4.0 24.0 26.0 19.0 4.0 2.0 23.0 39.0 155.0 1978/79 20.0 12.0 9.0 8.0 7.0 6.0 7.0 5.0 4.0 4.0 5.0 3.0 90.0 1979/80 3.0 10.0 9.0 25.0 16.0 17.0 9.0 5.0 5.0 7.0 5.0 4.0 115.0 1980/81 3.0 4.0 3.0 2.0 2.0 4.0 5.0 2.0 2.0 3.0 47.0 87.0 164.0 1981/82 30.0 25.0 20.0 19.0 16.0 16.0 11.0 8.0 8.0 7.0 23.0 24.0 207.0 1982/83 20.0 12.0 9.0 8.0 7.0 6.0 5.0 5.0 4.0 7.0 18.0 11.0 112.0 1983/84 6.0 4.0 3.0 2.0 2.0 11.0 15.0 28.0 16.0 6.0 4.0 4.0 101.0 1984/85 8.0 4.0 3.0 2.0 2.0 9.0 3.0 2.0 1.0 7.0 50.0 35.0 126.0 1985/86 8.0 7.0 6.0 5.0 6.0 34.0 20.0 13.0 12.0 11.0 18.0 22.0 162.0 1986/87 10.0 13.0 11.0 7.0 6.0 5.0 5.0 4.0 4.0 5.0 5.0 6.0 81.0 1987/88 4.0 3.0 2.0 2.0 2.0 4.0 7.0 3.0 1.0 9.0 20.0 9.0 66.0 1988/89 2.0 1.0 1.0 1.0 1.0 5.0 4.0 1.0 0.0 24.0 28.0 2.0 70.0 1989/90 0.0 0.0 0.0 0.0 1.0 3.0 3.0 1.0 1.0 1.0 15.0 21.0 46.0 1990/91 16.0 11.0 4.0 3.0 2.0 3.0 3.0 2.0 2.0 1.0 2.0 2.0 51.0 1991/92 1.0 1.0 1.0 1.0 1.0 1.0 1.0 4.0 1.0 1.0 1.0 1.0 15.0 1992/93 1.0 1.0 1.0 0.0 0.0 0.0 2.0 0.0 0.0 0.0 0.0 7.0 12.0 1993/94 2.0 2.0 1.0 1.0 1.0 8.0 3.0 1.0 1.0 0.0 11.0 13.0 44.0 1994/95 2.0 2.0 1.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 12.0 8.0 26.0 1995/96 1.0 1.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 5.0 7.0 15.0 1996/97 4.0 2.0 1.0 13.0 30.0 33.0 25.0 47.0 10.0 7.0 7.0 7.0 186.0 1997/98 7.0 5.0 5.0 4.0 3.0 3.0 3.0 2.0 2.0 2.0 6.0 4.0 46.0 1998/99 3.0 3.0 2.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 2.0 3.0 20.0 1999/00 2.0 1.0 1.0 1.0 1.0 1.0 1.0 0.0 0.0 0.0 0.0 2.0 10.0 2000/01 2.0 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.0 4.0 2001/02 0.0 0.0 2.0 16.0 7.0 5.0 2.0 2.0 1.0 1.0 6.0 5.0 47.0 2002/03 2.0 1.0 1.0 1.0 1.0 1.0 2.0 25.0 3.0 0.0 5.0 1.0 43.0 2003/04 0.0 0.0 0.0 5.0 2.0 1.0 0.0 0.0 0.0 0.0 1.0 1.0 10.0 2004/05 2.0 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 15.0 79.0 39.0 136.0 2005/06 20.0 14.0 13.0 34.0 58.0 65.0 46.0 22.0 16.0 15.0 13.0 14.0 330.0 2006/07 12.0 11.0 10.0 9.0 8.0 7.0 6.0 5.0 5.0 4.0 4.0 5.0 86.0 2007/08 5.0 4.0 4.0 3.0 2.0 2.0 2.0 2.0 1.0 1.0 1.0 1.0 28.0 Average 8.3 6.4 5.2 8.9 12.5 16.0 11.6 8.9 6.5 7.4 14.1 13.9 119.8
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3.3.3.4 Reservoir operation
After discussions with WB experts and client staff it was decided that TAHAL/Bhundia will continue with a deterministic approach as opposed to the stochastic approach of CES/APEC. Reservoir operation calculated on the basis of continuous sequence where the initial boundary for the calculation of the total availability of water to the T year is based on the result of the remaining water in the reservoir to the T-1 year. In the case of Mwache dam where there is a data series of the annual rainfall and the rainfall-runoff model was calibrated there is no advantages to run the simulation on probabilistic approach but to do it on the simulation approach as done.
Two series of flows were analysed, the first with a coefficient of variance 0.3 that reflects the common figure in the Kenyan rivers, the second with coefficient of variance 0.5 that reflects climate change severe affects. The results of the reservoir operation model shows that the reliability of water supply from Mwache Dam can increase from 90.9% to 95.5% by increasing the reservoir volume to 150MCM. The climate change affects severely on the reliability levels, mainly due to four consecutive years of droughts in the model.
Table 3 -9: Reliability Levels of Different Reservoir Volumes
Annual Reliability Monthly Reliability Volume [MCM] Urban Irrigation Urban Irrigation 120 90.9% 90.9% 97.6% 96.4% 150 95.5% 95.5% 99.3% 98.7% 180 100.0% 100.0% 100.0% 100.0%
Table 3 -10: Reliability Levels of Different Reservoir Volumes (Climate Change Considerations)
Annual Reliability Monthly Reliability Volume [MCM] Urban Irrigation Urban Irrigation 120 80.0% 80.0% 90.7% 85.4% 150 86.7% 83.3% 92.1% 87.5% 180 86.7% 83.3% 92.7% 88.6% 200 90.0% 86.7% 93.2% 88.8%
3.3.3.5 Geotechnical Feasibility
A rockfill dam can be constructed at the proposed location on the Mwache River.
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Excavation of rock layers from the flooded area can provide the required construction materials for the dam: the rock layer, the shale, gravel and sand for filters. The relatively thin cover of clay above the local sandstone may be used as core fill. Otherwise clay should be imported.
According to the feasibility study and detailed design for the Mwache dam by CES it is suggested that the dam will be a concrete dam instead of a rock fill dam as previously suggested by both team. On a meeting held with the WB and CES team it was concluded that the detailed design made by CES will be the major design document, and that the master plan will adopt the conclusions of the design.
The layer of the lower Taru grits is a good foundation layer for the dam.
It seems as if this layer is massive and has low permeability. The upper Mariakani and especially Mazeras layers have open fissures, horizontal and vertical. Thus the contact between the dam and the riverbanks should be treated to prevent flow and erosion.
For further details regarding geotechnical issues, see Annex 5.
Fig. 3-8: Volume – Area – Elevation Curve for the proposed Mwache Reservoir
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548,000 550,000 552,000 554,000 556,000 558,000 560,000
!P
9,568,000
9,568,000
9,566,000
9,566,000
!(
9,564,000
9,564,000
9,562,000 9,562,000
!( sarezaM
9,560,000
9,560,000 !P Mwache Dam Base Elevation: 25m
Dam length: 570m
9,558,000 9,558,000 Flooding Elev.: 105m
!( ognajaM
9,556,000
9,556,000
548,000 550,000 552,000 554,000 556,000 558,000 560,000
9,554,000
9,554,000 !(
Fig. 3-9: Layout Map of the proposed Flooded Area of Mwache Reservoir
3.3.4 Rare Dam
3.3.4.1 General
The Rare River was identified in NWMP 1992 by JICA as a possible river for damming. The JICA study team suggested the seasonal river as a viable source for urban water supply for the growing urban centres of Kilifi and Malindi. The location suggested in NWMP 1992 is 3 km upstream of the crossing of the Rare River and the Sabaki Pipeline.
NWMP 1992 indicated a dam with a gross storage capacity of 37 MCM and annual yield of 15.7 MCM.
The Kenyan Government chose the Rare Dam to be a flagship project as part of Vision 2030.
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NWCPC is in the process of selecting consultants to carry out a feasibility study and detailed design for a dam on the Rare River.
3.3.4.2 Current Study
Conversion of the simulated Mwache River monthly streamflows to the other rivers was performed by using transfer coefficients based on the ratios of basin areas, basin mean annual rainfalls, basin mean runoff coefficients (being a function of soils and soil cover) and basin mean contribution to surface runoff (being a function of lithological and geological characteristics) to their corresponding values in the 3MA03 hydrometric station basin.
Table 3 -11: General and Model Parameters of the Rare River
Parameter Value
Area (A) 6,138 Rainfall (R) 690.1 CN 74.9 Contribution to surface runoff (SR) 93.8 Ai/Ah 1.703 Ri/Rh 0.957 CNi/CNh 0.99 SRi/SRh 1.00 Combined transfer coefficient 1.600
Table 3 -12: Rare Reservoir Site – Simulated Monthly Flows (MCM), 1958/59–2007/08
YEAR JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY ANNUAL 1958/59 14.4 12.8 11.2 11.2 9.6 8.0 8.0 6.4 6.4 4.8 49.6 36.8 179.2 1959/60 14.4 6.4 4.8 3.2 9.6 4.8 3.2 3.2 4.8 3.2 3.2 1.6 62.4 1960/61 1.6 22.4 17.6 188.8 371.3 484.9 249.6 192.0 169.6 152.0 137.6 123.2 2110.8 1961/62 110.4 99.2 89.6 81.6 72.0 65.6 59.2 52.8 48.0 43.2 60.8 60.8 843.4 1962/63 49.6 38.4 27.2 24.0 20.8 22.4 40.0 22.4 14.4 12.8 17.6 28.8 318.5 1963/64 12.8 9.6 8.0 6.4 6.4 4.8 91.2 27.2 6.4 4.8 4.8 8.0 190.4 1964/65 6.4 3.2 3.2 3.2 1.6 59.2 14.4 3.2 1.6 70.4 32.0 43.2 241.6 1965/66 35.2 11.2 4.8 1.6 3.2 1.6 1.6 1.6 9.6 1.6 27.2 25.6 124.8 1966/67 9.6 4.8 6.4 44.8 140.8 86.4 22.4 17.6 20.8 25.6 38.4 32.0 449.7 1967/68 41.6 17.6 14.4 11.2 9.6 22.4 14.4 8.0 52.8 19.2 14.4 16.0 241.6 1968/69 12.8 9.6 11.2 8.0 8.0 17.6 9.6 6.4 6.4 6.4 4.8 4.8 105.6 1969/70 4.8 3.2 3.2 3.2 3.2 1.6 1.6 1.6 1.6 1.6 1.6 4.8 32.0 1970/71 3.2 1.6 1.6 0.0 0.0 0.0 12.8 1.6 0.0 0.0 0.0 33.6 54.4
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1971/72 3.2 3.2 1.6 17.6 11.2 9.6 12.8 1.6 1.6 1.6 38.4 38.4 140.8 1972/73 14.4 3.2 3.2 1.6 1.6 3.2 1.6 1.6 3.2 1.6 3.2 3.2 41.6 1973/74 4.8 6.4 1.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.6 4.8 19.2 1974/75 1.6 3.2 0.0 0.0 0.0 0.0 0.0 12.8 1.6 0.0 0.0 1.6 20.8 1975/76 1.6 1.6 0.0 0.0 0.0 4.8 3.2 0.0 0.0 0.0 1.6 1.6 14.4 1976/77 1.6 1.6 4.8 27.2 32.0 38.4 35.2 14.4 6.4 14.4 28.8 19.2 224.0 1977/78 9.6 4.8 4.8 3.2 6.4 38.4 41.6 30.4 6.4 3.2 36.8 62.4 248.0 1978/79 32.0 19.2 14.4 12.8 11.2 9.6 11.2 8.0 6.4 6.4 8.0 4.8 144.0 1979/80 4.8 16.0 14.4 40.0 25.6 27.2 14.4 8.0 8.0 11.2 8.0 6.4 184.0 1980/81 4.8 6.4 4.8 3.2 3.2 6.4 8.0 3.2 3.2 4.8 75.2 139.2 262.4 1981/82 48.0 40.0 32.0 30.4 25.6 25.6 17.6 12.8 12.8 11.2 36.8 38.4 331.3 1982/83 32.0 19.2 14.4 12.8 11.2 9.6 8.0 8.0 6.4 11.2 28.8 17.6 179.2 1983/84 9.6 6.4 4.8 3.2 3.2 17.6 24.0 44.8 25.6 9.6 6.4 6.4 161.6 1984/85 12.8 6.4 4.8 3.2 3.2 14.4 4.8 3.2 1.6 11.2 80.0 56.0 201.6 1985/86 12.8 11.2 9.6 8.0 9.6 54.4 32.0 20.8 19.2 17.6 28.8 35.2 259.2 1986/87 16.0 20.8 17.6 11.2 9.6 8.0 8.0 6.4 6.4 8.0 8.0 9.6 129.6 1987/88 6.4 4.8 3.2 3.2 3.2 6.4 11.2 4.8 1.6 14.4 32.0 14.4 105.6 1988/89 3.2 1.6 1.6 1.6 1.6 8.0 6.4 1.6 0.0 38.4 44.8 3.2 112.0 1989/90 0.0 0.0 0.0 0.0 1.6 4.8 4.8 1.6 1.6 1.6 24.0 33.6 73.6 1990/91 25.6 17.6 6.4 4.8 3.2 4.8 4.8 3.2 3.2 1.6 3.2 3.2 81.6 1991/92 1.6 1.6 1.6 1.6 1.6 1.6 1.6 6.4 1.6 1.6 1.6 1.6 24.0 1992/93 1.6 1.6 1.6 0.0 0.0 0.0 3.2 0.0 0.0 0.0 0.0 11.2 19.2 1993/94 3.2 3.2 1.6 1.6 1.6 12.8 4.8 1.6 1.6 0.0 17.6 20.8 70.4 1994/95 3.2 3.2 1.6 0.0 0.0 0.0 1.6 0.0 0.0 0.0 19.2 12.8 41.6 1995/96 1.6 1.6 0.0 0.0 0.0 1.6 0.0 0.0 0.0 0.0 8.0 11.2 24.0 1996/97 6.4 3.2 1.6 20.8 48.0 52.8 40.0 75.2 16.0 11.2 11.2 11.2 297.7 1997/98 11.2 8.0 8.0 6.4 4.8 4.8 4.8 3.2 3.2 3.2 9.6 6.4 73.6 1998/99 4.8 4.8 3.2 1.6 1.6 1.6 1.6 1.6 1.6 1.6 3.2 4.8 32.0 1999/00 3.2 1.6 1.6 1.6 1.6 1.6 1.6 0.0 0.0 0.0 0.0 3.2 16.0 2000/01 3.2 1.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.6 6.4 2001/02 0.0 0.0 3.2 25.6 11.2 8.0 3.2 3.2 1.6 1.6 9.6 8.0 75.2 2002/03 3.2 1.6 1.6 1.6 1.6 1.6 3.2 40.0 4.8 0.0 8.0 1.6 68.8 2003/04 0.0 0.0 0.0 8.0 3.2 1.6 0.0 0.0 0.0 0.0 1.6 1.6 16.0 2004/05 3.2 1.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 24.0 126.4 62.4 217.6 2005/06 32.0 22.4 20.8 54.4 92.8 104.0 73.6 35.2 25.6 24.0 20.8 22.4 528.1 2006/07 19.2 17.6 16.0 14.4 12.8 11.2 9.6 8.0 8.0 6.4 6.4 8.0 137.6 2007/08 8.0 6.4 6.4 4.8 3.2 3.2 3.2 3.2 1.6 1.6 1.6 1.6 44.8 Average 13.3 10.3 8.3 14.3 20.1 25.5 18.6 14.2 10.5 11.8 22.6 22.2 191.7
3.3.4.3 Geotechnical Feasibility
Three sites were studied:
"Rare School" at 582100/9617030, close to the local school. "Rare Mangndo" at 581200/9620200, close to the Mangndo Irrigation Project. "Rare Pipe" at 583860/9617710, close to the river crossing of the water pipe.
The "Rare Pipe" site was found to be the most appropriate for the required dam. A rockfill dam can be constructed at this location.
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Local materials are available for dam construction:
The local black sandstone is the main source for construction materials for the rockfill layer of the dam. Local shale, gravel and sand are available for filters. Clay for the core is available in the highlands north of the river.
The existing black sandstone could also be a good foundation layer for the dam.
The riverbanks and their contact to the dam should be treated to prevent flow and erosion.
For further details regarding geotechnical issues, see Annex 5.
Fig. 3-10: Volume – Area – Elevation Curve for the proposed Rare Reservoir
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574,000 576,000 578,000 580,000 582,000 584,000 586,000
9,626,000 9,626,000
9,624,000
9,624,000
9,622,000
9,622,000
9,620,000
9,620,000
!P
9,618,000 Rare 9,618,000 Dam Base Elevation: 44m
Dam length: 220m Flooding Elev.: 84m
9,616,000 9,616,000
9,614,000
9,614,000
574,000 576,000 578,000 580,000 582,000 584,000 586,000
Fig. 3-11: Layout Map of the proposed Flooded Area of Rare Reservoir
3.4 Potential of Groundwater Resources
The analysis of groundwater potential in the South Coast included the following stages:
Review of previous studies and available data for the hydrogeology of the study area. Identification of data gaps. Construction of a regional flow model based on the existing data, with simplifying assumptions. Model calibration and assessment of seawater intrusion according to different pumping scenarios.
The Stage 1 model runs studied the general flow regime and the parameters affecting seawater intrusion for the Tiwi and Msambweni areas as part of the
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South Coast. The parameters affecting seawater intrusion were analyzed specifically for Tiwi area and included:
Amount of recharge to the aquifer (two scenarios – high and low). Amount of pumping (two scenarios – high and low). Distance from the ocean.
The Stage 2 model runs studied the flow regime in the Tiwi and Msambweni areas assuming conservative conditions: lower topography and lower recharge. A transient run simulated the effect of high pumping and seawater intrusion rate for a 20-year period, both in Tiwi and Msambweni.
The conclusions regarding groundwater potential in the South Coast include:
Groundwater potential determined for Tiwi and Msambweni areas is approximately 20,000 m3/d (7.5 MCM) and 30,000 m3/d (11 MCM), respectively. The analysis indicates that additional wellfields may be developed south of Msambweni. Major data gaps were identified and a plan of required actions and further investigation is outlined. It is emphasized that the required actions are mandatory before any new wellfield is developed, or any significant changes in pumping policy are decided on. The most critical parts of the required actions include: Drilling of deep exploratory/monitoring wells for detecting the seawater- freshwater interface location and depth. Performance of an accurate well survey. Performance of water level measurements – long-term, regular records. Performance of water quality measurements – long-term, regular records. Survey of pollution sources.
See Annex 6 for additional data regarding the model runs.
3.5 Potential of Deep Groundwater
3.5.1 Overview and Preliminary Analysis
Data from deep oil and gas exploration wells in Kenya were reviewed in order to assess whether potential deep groundwater exists. This analysis is based on the assumption that the Coast Province in Kenya may share the same hydrogeological characteristics with the Tanzania Coast area (the area of Dar es Salaam), where a deep and highly productive aquifer of immense volume and excellent water quality was recently discovered and investigated.
General and detailed geological information was collected from the data reviewed for 13 of the deep wells in Kenya. Information included: stratigraphy, top and
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base of the Neogene Sequence, thickness and depth to the Neogene Sequence, etc.
The Consultant reviewed data from deep oil and gas exploration wells, including reports and well logs.
Information gathered from the reports and well logs included:
Well depth. Stratigraphy – geological units found in the well logs. Top and base of the Neogene Sequence (specifically Miocene). Thickness of the Neogene Sequence. Depth of the Neogene Sequence. Spatial extent of the Neogene Sequence based on well locations. Lithology – geological materials composing the relevant Neogene units.
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Fig. 3-12: Alternative locations for deep exploratory/production wells for the Neogene Aquifer
A cross-section along four deep wells located along the Tana River from inland to the coast adjacent to the Lamu area revealed a Neogene Sequence of 400– 500 m thickness inland, increasing to 1,000–1,500 m close to the coastline. The depth to this potential aquifer varies from several metres (about 5–30 m) in Pandangua 1 and Walu 2 wells (near Tana River) to 150–200 m in other locations.
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Water Supply Master Plan for Mombasa and Other Towns within Coast Province Final Full Feasibility Study Correlation of Top and Bottom Neogene in Deep wells in Lamu Area, coastal Kenya Garissa 1 Walu 2 Pandangua 1 Kipini 1 1000 758
500 132 92 51 23 0 86 -154 23
-281 -500 -385
-1000
Top Formation Elevation Elevation Formation Top -1006
-1500
-1678 -2000 0 50 100 150 200 250 300 Distance (Km)
Top Neogene Top Oligocene Surface Elevation
Fig. 3-13: Schematic cross-section of the Neogene Sequence between Garissa and Kipini wells
The lateral continuity of the Neogene Aquifer is mapped and related to the location of the Lamu Rift Basin. The potential aquifer units extend into the Lamu area to the north, and narrow southwards, towards Mombasa.
Potential recharge of freshwater to this aquifer should be thoroughly investigated. However, the location near Tana River is promising, as the river may serve as a source of recharge to the aquifer in this area.
Further investigation of this potential aquifer is suggested by drilling of deep wells to a depth of about 600 m. Three alternative locations are suggested, two in the Lamu area and one along the Tana River between Pandangua 1 and Walu 2 wells. The Mombasa area appears to be less promising regarding the existence of a deep aquifer due to the limited presence of Neogene formations south of Malindi.
3.5.2 Recommendations: General Exploratory Plan
The neogenic aquifer should be further investigated by drilling exploratory boreholes, performing pumping tests and study the replenishment mechanism of the aquifer.
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General exploratory plan: Two wells to a depth of about 600 m are proposed for each of the abovementioned areas, located within a distance of 300–500 m from each other. In all proposed areas this depth covers a significant thickness of the Neogene Sequence and will enable a study of both shallow and deep aquifer properties and hydraulic relationships.
The wells will be opened to the potential Neogene Aquifer while the Pleistocene Sequence (recent) will be separated by cementing the upper part of the well to ensure that the target aquifer is explored and tapped.
3.6 Total Potential of Water Resources
The demand for water in the Coast Province is much above the supply. Despite the high supply deficit, however, large and viable water sources exist in the province that is yet to be developed (see Table 3-13).
The major sources of water in the Coast Province are:
Tana River – minimum flow (100%) 8.5 m3/s and sustainable flow (95%) 44.7 m3/s. Mzima springs – minimum flow (100%) 2.6m3/s and sustainable flow (95%) 5.9m3/s Njoro Kubwa – safe yield is 4.5m3/s and sustainable flow (95%) 5.6m3/s Sabaki River – minimum flow (100%) 2.6 m3/s and sustainable flow (95%) 6.3 m3/s. Mwache River – mean annual flow 120 MCM/y. Rare River – mean annual flow 190 MCM/y. Tiwi Aquifer – 7.5 MCM/y. Msambweni Aquifer – 11 MCM/y. Desalination – this artificial source can cover the gap between supply from natural resources and demand. Environmental impacts and energy costs should in this context be investigated carefully.
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Table 3 -13: Installed Capacity and Potential of Water Resources in the Coast Province
Current Potential Resource / Status capacity yield Comments System (m3/d) (m3/d) Mzima Existing 35,000 105,000 Surpluses of Mzima reach Baricho Baricho Existing 90,000 180,000 Low flow is Sabaki river 3.5 m3/s Tiwi Existing 10,000 15,000 Marere Existing 8,000 12,000 Njoro Kubwa Springs Existing 2,700 100,000 Surpluses used for irrigation Shella Wellfield Existing 1,800 Tana River Existing 1,400 Low flow is 8 m3/s Mkanda Dam Existing 2,000 5,900 Used by local communities
Mwache Dam D/D – 220,000 Only 186,000 are dedicated to urban supply Rare Dam F/S – 200,000 Initial figures Mkurumudzi Dam D/D – 19,000 Will be used by Base Titanium Msambweni Aquifer – – 20,000 Will be used by Base Titanium
Desalination – Economic and environmental limitations Deep groundwater – Without desalination, Tana River, and Total 876,900 deep groundwater
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4. Proposed Strategies and Scenarios
4.1 Defining Strategies for Development
In accordance with the national goals for the water sector, the various meetings held with CWSB, WB and AFD, and the current study, the Master Plan team identified three main strategies for development of water resources in the Coast Province. Each strategy represents a firm concept regarding supply alternatives.
Development of the bulk water supply system consists in the development of several water sources, water transmission mains, as well as other water works components such as, inter alia, pumping stations and water treatment plants. Where a single water supply scheme is developed it can be analysed as standalone project with respect to its technical feasibility, economic viability and other aspects. However, where development of a bulk water supply system is involved, a different methodology must be adopted, allowing the system to be investigated as a whole rather than examining each scheme separately. This is essential because, strictly speaking, a bulk water supply scheme is not the sum of its individual schemes. Apart from the water balance, where it is possible to add up water production from each source to give the total water production, in all others aspects – such as hydraulics, energy consumption, pipe diameters and infrastructure layout – the various options in combination (scenarios) do not produce the same results as a simple aggregation of the separate schemes.
For the above reason the methodology used for creation of the scenarios was based on the following process:
The water resources of the region were identified and analysed for water production potential and sustainability. This was carried out mainly in the Water Resources Report. Once the water resources were quantified with respect to their potential, rationality was introduced in order to create a group of options for the development plan. These groups were referred to as strategies for development. Under each strategy a number of alternatives were created, all sharing a common concept. Each one of the alternatives was referred to as a scenario. The term alternative will be used later in the design report phase when several physical options will be considered for the selected scenario, each physical option being referred to as an alternative. A total of 8 scenarios were found and subjected to primary analysis in the Pre-Feasibility Report. Of these, 4 scenarios were introduced in the feasibility stage of the work. All the above 4 scenarios are based on the results of the water resources study, water abstraction from them is feasible and no constraints exist that could cause unavailability of water. The scenarios then focus on the bulk water supply options (under each scenario) and on the main delivery pipelines (layout, diameters, pressure) and pumping (installed
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capacity, operation, energy) and economic considerations (both CAPEX and OPEX).
The methodology used to create scenarios was described in detail in the Pre- Feasibility Report dated August 2012. It is important to note that each scheme was validated before being included in a scenario. As explained earlier, each water resource was analysed as a standalone component in terms of its water potential and future abstraction, following which it was merged into schemes and scenarios.
It is for this reason that the Consultant insisted that the Water Resources Report precede the feasibility study, preventing a situation in which the feasibility study will contain scenarios based on unfeasible sources or schemes. On completion of the water resources study, the scenarios created based on the Water Resources Report ensure all resources are viable.
Two main guiding principles were defined with respect to the core concept of the scenarios, namely:
Each scenario must be balanced (i.e. water resources >= demand) in each phase of development; Sequence of development must be such that high capital investment schemes will be postponed to the future.
4.2 Coverage of the Master Plan
The water supply master plan covers the whole area of the Coast Province in terms of water resources development. The master plan separates the coast province to four different areas: Interconnected bulk system Lamu and Tana counties Taveta area Remote rural areas
Adequate solutions are analysed and proposed each of the distinct areas.
4.3 Meeting the Potential Demand
The initial phase of the water supply master plan study included demand assessment. When calculating the demand for the immediate term of the plan – namely 2020 – it was clear that the difference in the demand projection for the year 2015 and the overall water consumption is huge. The total water demand calculated for 2015 (roughly 150 MCM/y for the entire region) is nearly triple then current water supply (some 150K–165K m/.d, equivalent to 55–58 MCM/y), Yet the actual demand is much less due to the high rate of inefficiency
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of the network and its extreme water loss percentage .In other words, according to the estimation, the water demands will double itself in a very short period of 3 years. This is unrealistic, as we know that the initiative for the increase in water demand is the development of new water resources, including their infrastructure, to supply water to the WSPs. Therefore, the following question arose: What will be the actual water demand during the first phase of implementation, and should the water supply master plan consider more conservative demand figures (i.e., less demand) regarding development of water resources in the immediate phase.
Fig. 4-1 shows the projection of water demand as calculated in the Water Demand and Supply Assessment Report in several scenarios and the average. The red dash-dot line shows the actual demand curve for the region starting with the current 2012 water consumption, as reflected in CWSB data, up to the demand calculated for horizon year 2035.
One may see that for the immediate phase of the development – 2020 – the total project demand is 225 MCM/y while the actual assumed water demand curve shows only 125 MCM/y. It is important to indicate that the actual water consumption in CWSB's urban sector is less than the supply, as the current water demand is assumed to be the overall supply less the water loss. Since the TWL (total water loss) consists of both leakage and administrative losses, one cannot calculate the portion of the TWL that is actually being consumed, and is not metered or billed.
Fig. 4-1: Calculated demand curves, current (2012) consumption and actual curve
The development of new water resources is a time-consuming process and may take several years. This refers not only to design and construction, but in the case of new surface water resources also the time span it takes to fill the reservoir/dam and thus make water supply available.
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Mapping the resources for the region and their future potential (as done in the water resources study) shows that 4-5 "big" water sources exist which are relevant for development. Some other resources are relevant as well; however their total yield is not significant in light of overall demand. Due to a lack of financial resources, it is not reasonable to assume that all resources will be developed concurrently (indeed, such a situation would render the master plan redundant). The sequence of development is a key issue in the CWSB master plan and was introduced as a core aspect for analysis from the pre-feasibility stage. Hence, it is reasonable to assume that each of the major resources will be developed in a separate phase. In parallel with the phases of development, the main resources will be deployed for 2–3 mega-projects during the development period. The water production curve will have the shape of a "step", with 2–3 steps. In this case, it is clear that following completion of the first water source and actual production of water for the bulk system (from Mwache for example) the total water potential will be greater than the ability of the network to receive the new water. Thus the brown curve in fig 4-1 represent the actual proposed demand curve.
As the region's resources are limited, once water resources are subjected to ongoing development, the system will be constructed to 100% capacity, including all required infrastructures (water treatment plant, pumping stations and water main). At the same time, the local distribution networks will not be able to absorb all the additional water; hence operation of the new system will be accordance with the capacity of the WSP network. Only extension of the local networks and reduction of losses will enable the supply and distribution of additional water, works that are beyond the scope of the master plan. It is clear that the option to develop sources gradually in accordance with the increase in demand does not exist. That is why, in the final analysis, the master plan phases are coherent with the stages of new water resources development, i.e. in every phase one big source will be developed. This is reflected in all the scenarios.
New water resources will be developed to their capacity from Day 1 of the construction period. However, due to the low demand at the time of completion, actual supply will meet consumption and will therefore be lower than the projected demand.
This situation will end in a relatively short period after supply increases. As water losses will increase in the first year (due to the increase in pressure), and demand will grow rapidly as water becomes more available and reliable, it is expected that the actual demand curve will close the gap with the calculated curve.
For this reason, the master plan strategy is that the total available water should meet the calculated demand curve in every phase of the development plan.
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4.4 Water Supply Scenarios for the Interconnected Bulk System
Three main strategies for development were defined to guide the creation of scenarios. Eight scenarios were created and studied during the Pre-Feasibility phase, 5 scenarios were studied during the feasibility phase. All scenarios were formulated according to guiding principles. Water balance must be achieved. Small scale sources (boreholes, small desalination systems, usage of saline water) will continue to exist in the future, therefore allow 5% decrease in supply. High capital investments schemes should postponed to future phases Robustness of the system must be achieved. The bulk water system will the demand of the twenty main townships and the bulk rural consumers. 5% of the demand will be supplied from small local sources.
Water balances and development scenarios are presented in Table 4-1.
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Table 4 -1: Water Resources Development by Phases – 5 Development Scenarios
Year 2012 2015 2020 2025 2030 2035 Projected Population 2,907,067 3,521,284 4,130,325 4,839,196 5,669,727 6,642,798 Target Water Demand (incl. 25% NRW) 213,509 242,696 299,637 394,233 465,753 538,273
Target Water Demand (Less 5% local) 202,834 230,561 284,655 374,521 442,465 511,359 sources)
Existing capacity of water resources [m3/day] 2012 2015 2020 2025 2030 2035 Tiwi Bh (existing) 13,000 13,000 13,000 13,000 13,000 13,000 13,000 Marere (existing) 12,000 12,000 12,000 12,000 12,000 12,000 12,000 Mzima 1 (existing) 35,000 35,000 35,000 35,000 35,000 0 0 Baricho 1 (existing) 90,000 90,000 90,000 90,000 90,000 90,000 90,000 Others (locals) (existing) 12,000 12,000 12,000 12,000 12,000 12,000 12,000 Total Existing Water Resources 162,000 162,000 162,000 162,000 127,000 127,000 Expected Water Deficit -40,834 -68,561 -122,655 -212,521 -315,465 -384,359
Development Scenarios Scenario B1 Supply Year [m3/day] 2012 2015 2020 2025 2030 2035 Baricho Immediate Expansion 2015 22,000 0 22,000 22,000 22,000 22,000 22,000 Mwache Dam 2020 186,000 0 0 186,000 186,000 186,000 186,000 Baricho II - Full Expansion 2024 63,000 0 0 0 63,000 63,000 63,000 Mzima II * 2030 105,000 0 0 0 0 105,000 105,000 Msambweni Aquifer / Mkurumudzi Dam 2035 20,000 0 0 0 0 0 20,000 Total Available Water Resources 162,000 184,000 370,000 433,000 503,000 523,000 Surplus / Deficit -40,834 -46,561 85,345 58,479 60,535 11,641 *: The Mzima Scenario B1.1 Supply Year [m3/day] II 2012 scheme 2015 2020 2025 2030 2035 Baricho Immediate Expansion 2015 22,000 will 0 supply 22,000 22,000 22,000 22,000 22,000 Mwache Dam 2020 186,000 105,0000 0 186,000 186,000 186,000 186,000 m3/day and 2024 63,000 0 0 0 63,000 63,000 63,000 Baricho II will replace Rare Dam 2030 100,000 the 0 old 0 0 0 100,000 100,000 Msambweni Aquifer / Mkurumudzi Dam 2035 20,000 scheme0 0 0 0 0 20,000 Total Available Water Resources 162,000 184,000 370,000 433,000 498,000 518,000 Surplus / Deficit -40,834 -46,561 85,345 58,479 55,535 6,641
Scenario B3 Supply Year [m3/day] 2012 2015 2020 2025 2030 2035 Baricho II 2016 85,000 0 0 85,000 85,000 85,000 85,000 Mwache Dam 2020 186,000 0 0 186,000 186,000 186,000 186,000 Rare Dam 2031 100,000 0 0 0 0 100,000 100,000 Msambweni Aquifer / Mkurumudzi Dam 2035 20,000 0 0 0 0 0 20,000 Total Available Water Resources 162,000 162,000 433,000 433,000 498,000 518,000 Surplus / Deficit -40,834 -68,561 148,345 58,479 55,535 6,641
Scenario B5 Supply Year [m3/day] 2012 2015 2020 2025 2030 2035 Mwache Dam 2020 186,000 0 0 186,000 186,000 186,000 186,000 Rare Dam 2024 180,000 0 0 0 180,000 180,000 180,000 Msambweni Aquifer / Mkurumudzi Dam 2035 20,000 0 0 0 0 0 20,000 Total Available Water Resources 162,000 162,000 348,000 528,000 493,000 513,000 Surplus / Deficit -40,834 -68,561 63,345 153,479 50,535 1,641
Scenario C2 Supply Year [m3/day] 2012 2015 2020 2025 2030 2035 Baricho Immediate Expansion 2015 22,000 0 22,000 22,000 22,000 22,000 22,000 Mwache Dam 2020 186,000 0 0 186,000 186,000 186,000 186,000 Baricho II 2026 63,000 0 0 0 0 63,000 63,000 Desalination Plant I 2030 50,000 0 0 0 0 50,000 50,000 Desalination Plant II 2033 50,000 0 0 0 0 0 50,000 Msambweni Aquifer / Mkurumudzi Dam 2035 20,000 0 0 0 0 0 20,000 Total Available Water Resources 162,000 184,000 370,000 370,000 448,000 518,000 Surplus / Deficit -40,834 -46,561 85,345 -4,521 5,535 6,641
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4.4.1 Scenario B1
4.4.1.1 Overview
The sequence of resources development according to Scenario B1 is presented in Table 4-1 above. The presented information clearly indicates that three new water resources will be developed in order to meet future water demand in the region, commencing with Mwache at 84% of the total future dam yield to be abstracted in Phase 1 to meet the mainland water demand (all urban water demand, except for Lamu Region and the Tana River Delta). Subsequent development (Phase 2 and continuing to the development horizon) will include the extension of Baricho Wellfield to sustain an additional 85,000 m3/d of water. This will bring the total abstraction of water from the Baricho site to 175,000 m3/d, this being about 90- 95% of its maximum yield.
Fig. 4.2 shows the potential of water resources in the region in accordance with the sequence suggested in Scenario B1. It is clear that in each one of the phases – I, II – the total potential of resources is above the calculated demand, i.e. if the actual demand is consistent with projections, the total available water from resources at the end of each phase will be sufficient to meet the demand. Only at the horizon stage will there be a deficit of 15,000 m3/day, which is about 2.5% of the projected demand.
Fig. 4-2: Development of water resources vs. demand – Scenario B1
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4.4.1.2 Phasing:
Emergency Immediate Works for Water Supply – small expansion of Baricho water works. Two new boreholes. Improvements of the Sabaki pipeline New Kakuyuni – Kilifi pipeline.. Phase 1 (2020) – For the development of Mwache Dam, the entire reservoir to conveyance system will be deployed, including the water treatment plant downstream of the dam. The main pumping station will lift the water through a 40"/48" main pipeline to the new water tank at elevation +100. No water will be pumped to Mazeras tank. This tank will enable conveyance of water to both the Changamwe Water Tank at +70 masl, and, as planned by the Mwache Dam designers, to the +70 existing water tank at Nguu-Tatu. Implementation period of Mwache Dam: 2014 – 2018. Phase 2 (2025) – Full development of Baricho Wellfield, 85,000 m3/d. This phase will require implementation of the second Baricho Pipeline, parallel to the existing one, with a 1,200 mm diameter, as well as extension of the Baricho site itself. This may include activities along the southern shore of the Sabaki River to locate new sites for pumping facilities in order to add the required water volumes to the bulk water supply system. Moreover, an additional pipeline to Malindi will be needed. Implementation period for wellfield and pipelines: 2021 – 2023. Phase 3 (2035) – Development of Mzima Pipeline, which will deliver 105,000 m3/d via a new 220 km pipeline (abstraction of an additional 70,000 m3/d from this source). Msambweni Aquifer (Gongoni Forest) and Mkurumudzi Dam will be available after the completion of mining works, and the development of transmission works will add 20,000 m3/d. Implementation period of Mzima II: 2026 – 2029. Implementation period for South coast sources: 2035.
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-
416.67
904.14
551.66
575.79
141.75
9,053.88
5,120.33
1,343.54
7,291.67
3,541.67
3,750.00
m^3/h
m^3/h
3,402
-8,045
21,699
13,240
13,819
32,245
122,888
10,000.00
85,000.00
90,000.00
m^3/d
m^3/d
217,293.07
175,000.00
1
B
Baricho
Z=20
Z=20
Z=20
Z=20
Z=90
Main land north land Main
Mezarestank
Main land north Balance Balance north land Main
Total demad demad Total
Along the road (rural) road the Along
Mavueni
Kisanui (Mom) Kisanui
Matwapa
Klifi
Watamu
Malindi
Marafa
Demand summary summary Demand
Total resources Total
Rare Dam RareDam
Baricho 2 Baricho
Baricho 1 Baricho
Resources Summary Resources
Main land north land Main
tank
Nguu Tatu Tatu Nguu
PhaseIII
PhaseII
PhaseI
Development Legend
Existing
34,248
5,688.83
2,007.83
3,681.00
m^3/h
tank
Bckup from Bckupfrom
Mwache to Kisauni to Mwache
Chang
423
625
199
2,123
4,375
2,917
1,458
194.38
681.57
54,050
48,188.0
88,344.0
tank
136,532.0
m^3/d
m^3/h
m^3/h
0.0
tank
Tank
e e
Mwache
Mezares
88,344
4,777.00
4,665.16
m^3/d
m^3/d
50,949.76
10,150.00
15,000.00
16,357.60
70,000.00
35,000.00
105,000.00
69,270
34,294
34,248
122,592
186,000
186,000
48,188.0
Total demad demad Total
Mombasa (Island) Mombasa
West mainland West
Demand summary summary Demand
Mombasa (Island & West M.L) West & (Island Mombasa
48,188
Actual Supply Actual
Total allocated Total
to South to
to West Mlnd&Is West to
to North to
to Island to
Mwache
Mombasa Is & West M.L Balance M.L West & Is Mombasa
Total demad demad Total
Mariakani Mariakani
Along the road (rural) road the Along
Wundanyi
Mwatate
Voi
Demand summary summary Demand
Taita
Total resources Total
Mzima 2 Mzima
Mzima 1 Mzima
Resources Summary Resources
69,270
625
-
-69,270.11
187.060344
m^3/h
m^3/h
5261.254677
361.4874037
2213.916667
1185.536916
200.3911481
487.8621989
-0.11
8,676
4,489
4,809
53,134
15,000
28,453
11,709
126,270
57,000.00
12,000.00
12,000.00
13,000.00
20,000.00
m^3/d
m^3/d
Tiwi
Marere
Checked 7th February 2013 February 7th Checked
312,554.0
Mesambweni
Total demad demad Total
Kwale
Kinango
likoni
Along the road the Along
Ukunda/Tiwi
Msambweni
Lunga Lunga/Vanga Lunga
Demand summary summary Demand
Main land south land Main
Total resources Total
0thers 0thers
Marere
Tiwi Tiwi
Msambweni Msambweni
Resources Summary Resources South Net balance Incl. from Mwache from Incl. Net balance South Main land south Balance Excl from mwache from Excl Balance south land Main
Fig. 4-3: Block Diagram – Scenario B1
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Fig. 4-4: Layout Map of Sequential Development – Scenario B1
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4.4.2 Scenario B1.1
4.4.2.1 Overview
The sequence of resources development according to Scenario B1.1 is presented in Table 4-1 above. The presented information clearly indicates that three new water resources will be developed in order to meet future water demand in the region, commencing with Mwache at 78% of the total future dam yield to be abstracted in Phase 1 to meet the mainland water demand (all urban water demand except for Lamu Region and the Tana River Delta). Subsequent development (Phase 2 and continuing to the development horizon) will include the extension of Baricho Wellfield to sustain an additional 85,000 m3/d of water. This will bring the total abstraction of water from the Baricho site to 175,000 m3/d, some 95% of its maximum capacity.
Rare surface water reservoir will be included in the development plan to meet the horizon year demand.
Fig. 4-5: Development of water resources vs. demand – Scenario B1.1
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4.4.2.2 Phasing:
Emergency Immediate Works for Water Supply – small expansion of Baricho water works. Two new boreholes. Improvements of the Sabaki pipeline New Kakuyuni – Kilifi pipeline.. Phase 1 (2020) – For the development of Mwache Dam the entire reservoir to conveyance system will be deployed, including the water treatment plant downstream of the dam. The main pumping station will lift the water through a 40"/48" main pipeline to the new water tank at elevation +100. No water will be pumped to Mazeras tank. This tank will enable conveyance of water to both the Changamwe Water Tank at +70 masl, and, as planned by the Mwache Dam designers, to the +70 existing water tank at Nguu-Tatu. Implementation period of Mwache Dam: 2014 – 2018. Phase 2 (2025) – Full development of Baricho Wellfield, 85,000 m3/d. This phase will require implementation of the second Baricho Pipeline, parallel to the existing one with 1,200 mm diameter, as well as extension of the Baricho site itself. This may include activities along the southern shore of the Sabaki River to locate new sites for pumping facilities in order to add the required water volumes to the water bulk supply system. Moreover, an additional pipeline to Malindi will be needed. Implementation period for wellfield and pipelines: 2021 – 2023. Phase 3 (2035) – Development of Rare Dam to supply 80,000 m3/d to Kilifi and Mombasa. Msambweni Aquifer (Gongoni Forest) and Mkurumudzi Dam will be available after the completion of mining works, and the development of transmission works will add 20,000 m3/d. Implementation period of Rare Dam: 2026 – 2029. Implementation period for South coast sources: 2035.
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416.67
904.14
551.66
575.79
141.75
9,053.88
5,120.33
1,343.54
7,291.67
4,166.67
3,541.67
3,750.00
m^3/h
m^3/h
3,402
57,707
21,699
13,240
13,819
32,245
122,888
m^3/d
m^3/d
10,000.00
85,000.00
90,000.00
217,293.07
275,000.00
100,000.00
1.1
B
Z=20
Z=20
Z=20
Z=20
Z=90
Main land north Balance Balance north land Main
Total demad demad Total
Along the road (rural) road the Along
Mavueni
Kisanui (Mom) Kisanui
Matwapa
Klifi
Watamu
Malindi
Marafa
Demand summary summary Demand
Main land north land Main
Total resources Total
Rare Dam RareDam
Baricho 2 Baricho
Baricho 1 Baricho
Resources Summary Resources
Main land north land Main
57,707
15,950
PhaseIII
PhaseII
PhaseI
Existing
-15,950
5,688.83
2,007.83
3,681.00
m^3/h
Supply from Mwace to Mezares to Mwace from Supply
0
-
422.92
625.00
199.04
194.38
681.57
48,188.0
88,344.0
2,122.91
1,458.33
1,458.33
tank
136,532.0
m^3/d
m^3/h
m^3/h
Tank
Mezares
tank
30,637
4,777.00
4,665.16
e e
m^3/d
m^3/d
50,949.76
10,150.00
15,000.00
16,357.60
35,000.00
35,000.00
Mwache
15,950
Total demad demad Total
Mombasa (Island) Mombasa
West mainland West
Demand summary summary Demand
Mombasa (Island & West M.L) West & (Island Mombasa
48,188
69,270
78,825
31,905
164,045
186,000
Actual Supply Actual
Total Mwache Total
to South to
to Mombasa to
to Mariakani to
Mwache
Mombasa Is & West M.L) Balance M.L) West & Is Mombasa
Total demad demad Total
Mariakani Mariakani
Along the road (rural) road the Along
Wundanyi
Mwatate
Voi
Demand summary summary Demand
Taita
Total resources Total
Mzima 2 Mzima
Mzima 1 Mzima
Resources Summary Resources
69,270
625
-
m^3/h
m^3/h
5261.255
361.4874
187.0603
2213.917
1185.537
200.3911
487.8622
-0.11
8,676
4,489
4,809
53,134
15,000
28,453
11,709
126,270
57,000.00
12,000.00
12,000.00
13,000.00
20,000.00
m^3/d
m^3/d
Tiwi
Marere
Checked 7th Feb 2013 Feb 7th Checked
Main land south Balance Balance south land Main
Total demad demad Total
Kwale
Kinango
likoni
Along the road the Along
Ukunda/Tiwi
Msambweni
Lunga Lunga/Vanga Lunga
Demand summary summary Demand
Main land south land Main
Mesambweni
Total resources Total
0thers 0thers
Marere
Tiwi Tiwi
Msambweni Msambweni Resources Summary Resources Main land south land Main
Fig. 4-6: Block Diagram – Scenario B1.1
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Fig. 4-7: Layout Map of Sequential Development – Scenario B1.1
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4.4.3 Scenario B3
4.4.3.1 Overview
The sequence of resources development according to Scenario B3 is presented in Table 4-1 above. During Phase 1, the Mwache dam will be constructed as in the B1 and B1.1 options. From the discussion held in CWSB on the availability of water from Mwache only by 2022 or thereabouts, it was concluded that development of Baricho will be advanced to Phase I as well in order to ensure supply even in the case of a lack of availability of water from Mwache. Baricho Pipeline and the extension of the well fields and abstraction capacity from the Sabaki River will be developed in Phase I. Only Rare Waterworks (including the dam, water treatment facility and low-lift pumping station) will be established in Phase III. Both the Rare and the Baricho pipelines will be constructed within a single corridor. Mwache Dam and related infrastructures will be developed during Phase 1, and will include the force main pipeline to pump water to the proposed tank at +100 masl and water conveyance to Mombasa Island and to the north Kisauni area. Development in this scenario will be in two main phases.
The sequence of development of this scenario has changed during the full- feasibility stage. Originally, Rare Dam was in phase II and Mwache Dam in phase III.
Fig. 4-8: Development of water resources vs. demand – Scenario B3
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4.4.3.2 Phasing:
Phase 1 (2020) – Full development of Baricho Wellfield, with additional 85,000 m3/d to achieve full daily abstraction of 175,000 m3/d. This will require two pipelines: - The first will be parallel to the existing one (Baricho-Nguu-Tatu Pipeline) to Mombasa. - The second will be parallel to the 600 mm Baricho-Malindi Pipeline. The Baricho-Nguu-Tatu Pipeline will be designed with an adequate diameter to meet the development of Rare Dam and supply 80,000 m3/d to Kilifi and Mombasa. Implementation period for wellfield and pipelines: 2014 – 2016. Implementation period of Rare Dam: 2014 – 2017. Phase 2 (2025) – Development of Mwache Dam, initially supplying 140,000 m3/d. Implementation period of Mwache Dam: 2018 – 2021. Phase 3 (2035) – Increase water abstraction from Mwache Dam to a full daily yield from the reservoir of 180,000 m3/d Msambweni Aquifer (Gongoni Forest) and Mkurumudzi Dam will be available after the completion of mining works, and the development of transmission works will add 20,000 m3/d. Implementation period for South coast sources: 2035.
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-
416.67
904.14
551.66
575.79
141.75
833.33
9,053.88
5,120.33
1,343.54
7,291.67
3,333.33
3,541.67
3,750.00
m^3/h
m^3/h
3,402
10,000
21,699
13,240
13,819
32,245
217,293
122,888
3
20,000.00
80,000.00
85,000.00
90,000.00
57,707
m^3/d
m^3/d
275,000.00
B
Main land north land Main
Z=20
Z=20
Z=20
Z=20
Z=90
Main land north Balance Balance north land Main
Total demad demad Total
Along the road (rural) road the Along
Mavueni
Kisanui (Mom) Kisanui
Matwapa
Klifi
Watamu
Malindi
Marafa
Demand summary summary Demand
Total resources Total
Rare Dam RareDam
Rare Dam RareDam
Baricho 2 Baricho
Baricho 1 Baricho
Resources Summary Resources
Main land north land Main
57,707
-15,950
PhaseIII
PhaseII
PhaseI
to mombasa mombasa to
Existing
5,688.83
2,007.83
3,681.00
m^3/h
Supply from Mwace to Mezares to Mwace from Supply
-
-
422.92
625.00
199.04
194.38
681.57
-15,950
tank
48,188.0
88,344.0
2,122.91
1,458.33
1,458.33
m^3/d
m^3/h
m^3/h
136,532.0
Tank
Mazeras
30,637
4,777.00
4,665.16
m^3/d
m^3/d
50,949.76
10,150.00
15,000.00
16,357.60
35,000.00
35,000.00
Mwache
15,950
Total demad demad Total
Mombasa (Island) Mombasa
West mainland West
Demand summary summary Demand
Mombasa (Island & West M.L) West & (Island Mombasa
30,637
69,270
78,825
31,905
48,188.0
164,050
186,000
Main land north Balance Balance north land Main
Actual Supply Actual
Total allocated Total
to South to
to Mombasa to
to Mariakani to
Mwache
Total demad demad Total
Mariakani Mariakani
Along the road (rural) road the Along
Wundanyi
Mwatate
Voi
Demand summary summary Demand
Taita
Total resources Total
Mzima 2 Mzima
Mzima 1 Mzima
Resources Summary Resources
69,270
625
-
m^3/h
m^3/h
5261.255
361.4874
187.0603
2213.917
1185.537
200.3911
487.8622
8,676
4,489
4,809
53,134
15,000
28,453
11,709
-0.11
126,270
57,000.00
12,000.00
12,000.00
13,000.00
20,000.00
m^3/d
m^3/d
Tiwi
Marere
Main land south Balance Balance south land Main
Total demad demad Total
Kwale
Kinango
likoni
Along the road the Along
Ukunda/Tiwi
Msambweni
Lunga Lunga/Vanga Lunga
Demand summary summary Demand
Main land south land Main
Mesambweni
Total resources Total
0thers 0thers
Marere
Tiwi Tiwi
Msambweni Msambweni Resources Summary Resources Main land south land Main
Fig. 4-9: Block Diagram – Scenario B3
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Fig. 4-10: Layout Map of Sequential Development – Scenario B3
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4.4.4 Scenario B5
4.4.4.1 Overview
Table 4-1 summarizes the total projected available water according to Scenario B5 and the balance between abstraction and supply for each phase, i.e. 2020, 2025 and the horizon year (2035).
In this, the "surface water reservoir" scenario, only two major water resources are scheduled for development in the region. During Phase 1, Mwache Dam will be constructed to its full capacity. Due to the fact that water availability during the initial years after dam completion is not yet clear, this scenario suggests abstracting only 75% of the dam's full yield. However, all required infrastructure downstream of the dam will be constructed to full capacity from Day 1.
During Phase 2, gradual development of the Rare Waterworks will commence. In this scenario, supply of water to the bulk water system will be implemented within two main phases. In the first phase 140,000 m3/d will be added to the system. This water will be conveyed to Mombasa, where the main pipeline will be approximately 1,200–1,250 mm in diameter. During Phase 2, only Module 1 will be implemented at the Rare Pumping Station and, as a result, the hydraulic load on the pipe will be low.
By the horizon year of 2035, extension of the pumping station and the treatment works downstream of the reservoir will be required in order to supply the full capacity of this source. Additional water (40,000 m3/d) will be contributed by Mwache Dam to the bulk water supply, giving a total yield of 180,000 m3/d.
Fig. 4-11: Development of water resources vs. demand – Scenario B5
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4.4.4.2 Phasing
Phase 1 (2020): Full development of Mwache Dam in terms of both dam construction and water works facilities. The dam will supply 140,000 m3/d during this phase. Implementation period of Mwache Dam: 2013 – 2017. Phase 2 (2025): Augmentation of 40,000 m3/d from Mwache Dam to a total supply of 180,000 m3/d. Development of Rare Dam to supply 80,000 m3/d to Mombasa. Implementation period of Rare Dam: 2021 – 2023. Phase 3 (2035): Augmentation of 80,000 m3/d from Rare Dam to a total supply of 180,000 m3/d Msambweni Aquifer (Gongoni forest) and Mkurumudzi Dam will be available after the completion of mining works, and the development of transmission works will add 20,000 m3/d. Total available water by 2035 year will be 530,000 m3/d. Implementation period for South coast sources: 2035.
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-
-
416.67
904.14
551.66
575.79
141.75
9,053.88
5,120.33
1,343.54
4,166.67
3,333.33
3,750.00
m^3/h
m^3/h
11,250.00
3,402
52,707
21,699
13,240
13,819
32,245
122,888
5
m^3/d
m^3/d
10,000.00
80,000.00
90,000.00
217,293.07
270,000.00
100,000.00
B
Z=20
Z=20
Z=20
Z=20
Z=90
big Rare) big
big Rare) big
Main land north Balance Balance north land Main
Total demad demad Total
Along the road (rural) road the Along
Mavueni
Kisanui (Mom) Kisanui
Matwapa
Klifi
Watamu
Malindi
Marafa
Demand summary summary Demand
Main land north land Main
Total resources Total
Rare Dam ( RareDam
Rare Dam ( RareDam
Baricho 2 Baricho
Baricho 1 Baricho
Resources Summary Resources
Main land north land Main
-15,950
PhaseIII
PhaseII
PhaseI
Existing
52,707
5,688.83
2,007.83
3,681.00
m^3/h
Supply from Mwace to Mezares to Mwace from Supply
to mombasa mombasa to
-
-
422.92
625.00
199.04
194.38
681.57
-15,950
tank
48,188.0
88,344.0
2,122.91
1,458.33
1,458.33
m^3/d
m^3/h
m^3/h
136,532.0
Tank
Mezares
35,637
tank
4,777.00
4,665.16
50,949.76
10,150.00
15,000.00
16,357.60
35,000.00
35,000.00
e e
m^3/d
m^3/d
Mwache
15,950
Main land north Balance Balance north land Main
Total demad demad Total
Mombasa (Island) Mombasa
West mainland West
Demand summary summary Demand
Mombasa (Island & West M.L) West & (Island Mombasa
35,637
69,270
83,825
15,950
169,045
186,000
48,188.0
Total demad demad Total
Mariakani Mariakani
Along the road (rural) road the Along
Wundanyi
Mwatate
Voi
Demand summary summary Demand
Taita
Total resources Total
Mzima 2 Mzima
Mzima 1 Mzima
Resources Summary Resources
Actual Supply Actual
Total allocated Total
to South South to
to Mombasa to
to Mariakani to
Mwache
69,270
625
-
m^3/h
m^3/h
5261.255
361.4874
187.0603
2213.917
1185.537
200.3911
487.8622
-0.11
8,676
4,489
4,809
53,134
15,000
28,453
11,709
126,270
57,000.00
12,000.00
12,000.00
13,000.00
20,000.00
m^3/d
m^3/d
Tiwi
Marere
Checked 7th Feb 2013 Feb 7th Checked
Main land south Balance Balance south land Main
Total demad demad Total
Kwale
Kinango
likoni
Along the road the Along
Ukunda/Tiwi
Msambweni
Lunga Lunga/Vanga Lunga
Demand summary summary Demand
Main land south land Main
Mesambweni
Total resources Total
0thers 0thers
Marere
Tiwi Tiwi
Msambweni Msambweni Resources Summary Resources Main land south land Main
Fig. 4-12: Block Diagram – Scenario B5
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Fig. 4-13: Layout Map of Sequential Development – Scenario B5
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4.4.5 Scenario C2
4.4.5.1 Overview
Table 4-1 presents the total projected available water as set out in Scenario C2 and the balance between abstraction and supply for each phase, i.e., 2020, 2025 and the horizon year (2035). Green highlights represent water resources to be developed during the various phases.
This scenario generally corresponds to Scenario B1 with regard to development activities to be conducted during Phases 1 and 2. In Phase 3, it is proposed to develop a desalination plant as a source of water that is not dependent on precipitation.
Fig. 4-14: Development of Water Resources vs. Demand – Scenario C2
4.4.5.2 Phasing:
Emergency Immediate Works for Water Supply – small expansion of Baricho water works. Two new boreholes. Improvements of the Sabaki pipeline New Kakuyuni – Kilifi pipeline.. Phase 1 (2020) – Development of Mwache Dam.
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During Phase I, the dam will supply 140,000 m3/d (see also Scenario B1). Implementation period of Mwache Dam: 2013 – 2017. Phase 2 (2025) – Augmentation of 40,000 m3/d from Mwache Dam to a total supply of 180,000 m3/d, and full development of Baricho Wellfield to 85,000 m3/d with a new pipeline to Mombasa and Malindi. Implementation period for Baricho wellfield and pipelines: 2023 – 2025. Phase 3 (2035) – Supply of an additional 60,000 m3/d from a coastal desalination plant in the vicinity of Mombasa in order to cope with the projected increase in urban water demand. Msambweni Aquifer (Gongoni Forest) and Mkurumudzi Dam will be available after the completion of mining works, and the development of transmission works will add 20,000 m3/d. Implementation period for Desalination Plant I: 2031 – 2033. Implementation period for Desalination Plant II: 2033 – 2035.
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-
-
416.67
904.14
551.66
575.79
141.75
9,053.88
5,120.33
1,343.54
7,291.67
3,541.67
3,750.00
m^3/h
m^3/h
0
3,402
10,000
21,699
13,240
13,819
32,245
217,293
122,888
m^3/d
m^3/d
85,000.00
90,000.00
2
175,000.00
C
Z=20
Z=20
Z=20
Z=20
Z=90
PhaseIII
PhaseII
PhaseI
42293
Main land north Balance Balance north land Main
Total demad demad Total
Along the road (rural) road the Along
Mavueni
Kisanui (Mom) Kisanui
Matwapa
Klifi
Watamu
Malindi
Marafa
Demand summary summary Demand
Main land north land Main
Total resources Total
Rare Dam RareDam
Baricho 2 Baricho
Baricho 1 Baricho
Resources Summary Resources
Main land north land Main
Existing
supply to head +70 head to supply
From desalination toward Kisauni Kisauni toward desalination From
4167
5,688.83
2,007.83
3,681.00
m^3/h
m^3/h
0
-
422.92
625.00
199.04
194.38
681.57
100,000
-15,950
tank
48,188.0
88,344.0
2,122.91
1,458.33
1,458.33
136,532.0
m^3/d
m^3/d
m^3/h
m^3/h
Tank
Mazeras
Mwache
57707
78,825
4,777.00
4,665.16
m^3/d
m^3/d
50,949.76
10,150.00
15,000.00
16,357.60
35,000.00
35,000.00
15,950
Desalination plant - Mom - plant Desalination
Resources Summary Resources
Desalination Desalination
Main land north Balance Balance north land Main
Total demad demad Total
Mombasa (Island) Mombasa
West mainland West
Demand summary summary Demand
Mombasa (Island & West M.L) West & (Island Mombasa
78,825
69,270
78,825
15,950
164,045
186,000
Total demad demad Total
Mariakani Mariakani
Along the road (rural) road the Along
Wundanyi
Mwatate
Voi
Demand summary summary Demand
Taita
Total resources Total
Mzima 2 Mzima
Mzima 1 Mzima
Resources Summary Resources
69,270
From desalination toward Island Island toward From desalination
Actual Supply Actual
Total allocated Total
to South South to
to Mombasa to
to Mariakani to
Mwache
625
-
m^3/h
m^3/h
5261.255
361.4874
187.0603
2213.917
1185.537
200.3911
487.8622
8,676
4,489
4,809
-0.11
53,134
15,000
28,453
11,709
126,270
57,000.00
12,000.00
12,000.00
13,000.00
20,000.00
m^3/d
m^3/d
Tiwi
Marere
Main land south Balance Balance south land Main
Total demad demad Total
Kwale
Kinango
likoni
Along the road the Along
Ukunda/Tiwi
Msambweni
Lunga Lunga/Vanga Lunga
Demand summary summary Demand
Main land south land Main
Mesambweni
Total resources Total
0thers 0thers
Marere
Tiwi Tiwi
Msambweni Msambweni Resources Summary Resources Main land south land Main
Fig. 4-15: Block Diagram – Scenario C2
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Fig. 4-16: Layout Map of Sequential Development – Scenario C2
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4.5 Water Supply to Lamu and Tana Counties
4.5.1 General
Lamu and Tana counties, the two northern counties in the Coast Province, are remote from the main urban centres of the coast and from the bulk water supply. Only a few small aquifers exist within these two counties, and they cannot sustain the growing demand.
The Tana River is the longest river in Kenya and sustains a minimum flow of 8 m3/s. As of 2012, only small water supply and irrigation schemes use this mighty source downstream of Garissa. The flow regime in this river suffers from high fluctuations, while severe floods occur frequently every few years. It therefore poses an obstacle for simple river intakes.
According to Vision 2030 and WRMA management plans, a few medium to large size reservoirs are to be built upstream of Garissa [i.e., High Grand Falls (HGF)]. These reservoirs are expected to moderate the floods and siltation in the downstream areas.
4.5.2 Supply Alternatives
The major development in this area is expected around the new Lamu Port and the LAPPSET Corridor.
In Tana County, most of the population and all of the towns are located along the banks of the Tana River.
The potential sources and supply options identified for Tana and Lamu counties are as follows:
Barrage near the settlement of Nanighi, and gravitational supply with a 180 km pipeline to Lamu. Barrage near the Garsen Bridge, and pumping to Lamu via an 80 km pipeline. Additional small/local intakes along the Tana River, for the towns of Tana County. Expanding the small aquifers near Lamu. Desalination plants.
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4.5.3 Discussion
Nanighi Barrage – Although it involves a very long pipeline, this option will consume very little energy, as most of the topography from Nanighi to Lamu is plain.
Garsen Bridge Barrage – While this location is closer to Lamu than Nanighi (75 km vs. 180 km), a pumping head of about 20 bars (200 m) will be needed in order to supply water to Lamu.
Garsen Bridge Barrage (two phases) – implementing the Garsen option in two phases, each consisting of 75km / 40" pipeline. This option is not recommended due to the requirement of the construction of two parallel pipes within a very short period. The complexity of this venture may create a situation which initial delays may cause the overlapping in the construction period of both pipes.
Small intakes – This option appears to be feasible, especially after the flow in the Tana River is moderated.
Expanding small aquifers around Lamu – This option appears to be feasible only for the immediate term. The capacity of expansion of the Hindi, Mpeketoni and Shella aquifers is limited, and can sustain only the immediate phase of building the new Lamu Port.
Seasonal river damming – This option appears to be less feasible than the others, as most of the soil in this location is sandy and seepage will be high.
Desalination plant – As Lamu Port is expected to grow rapidly, the desalination option appears to be feasible. The desalination option can be developed in stages: Initially a primary module will be introduced to meet the current demand for constructing the new port. Additional modules will be built with development of the area.
Deep groundwater – Preliminary analysis indicates the possible existence of groundwater in the Neogene layers in the area of Lamu and Tana counties. Further study is recommended in order to verify the potential of this source.
Inter basin transfers – conveying water from the Tana River towards Malindi, Kilifi & Mombasa is feasible, but will require long transmission mains and high pumping costs. Therefore, Inter basin transfer of water from Tana and Lamu area are recommended beyond the horizon of the master plan, after full
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development of closer sources.
Fig. 4-17: Development of water resources vs. demand – Lamu area
4.6 Water Supply to Taveta Area
4.6.1 Overview
The Water Supply Master Plan for the Coast Province includes six counties. Among them is Taita Taveta County, comprising four townships – Voi, Taveta, Mwatate and Wundanyi. Currently, only the town of Voi is connected to the bulk water supply system via the connection from the Mzima Pipeline. Taveta Township is supplied from the Njoro Kubwa Springs, which are located near the township, at an elevation of +730 masl. Both Mwatate (+806 masl) and Wundanyi (+1,450 masl) are disconnected from the bulk water supply today. A summary of water production was presented in the Water Demand and Supply Assessment Report, and is summarized in Table 4-2.
Table 4 -2: TAVEVO Water Supply (2008–2010)
Production Daily Year volumes Production (m3) (m3 /d) July 2008 to June 2009 2,420,755 6,632
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July 2009 to June 2010 3,026,418 8,292
July 2010 to June 2011 2,370,592 6,495
According to the demand projection, the entire water demand for Taita Taveta County was presented in the Water Demand and Supply Assessment Report, and is summarized in Table 4-3.
Table 4 -3: Water Demand Projection for Taita Taveta County
Total Demand 2015 2020 2025 2035 (m3/d) Taveta 3,573 4,265 5,121 7,228 Mwatate 2,350 2,758 3,332 4,665 Wundanyi 2,406 2,823 3,411 4,777 Voi/Maungu 8,286 9,708 11,630 16,358 Total – Taita Taveta County 16,615 19,554 23,493 33,028 Future / Current Demand (%) 233% 274% 329% 463%
It is clear that the demand for water in the region will increase sharply, and that current water supply is far lower than the current water demand.
Taita Taveta County is characterized by long distances between the small villages and townships in the region. Of the 20 cities in the scope of the Water Supply Master Plan, only four townships fall within Taita Taveta County. A separate analysis was carried out to seek the best possible solution for water supply to that area, without connecting to the water bulk supply system. It is important to note that the area has a huge water resource, the Njoro Kubwa Springs, which emerge from the Kilimanjaro Aquifer. The water flows down the stream and reaches Challa Lake. Only sparse data on the spring yield are available. It is known that minimal flows in the spring can drop down to 4.5 m3/s (>300,000 m3/d) where overall abstraction of water in the last year was 3,000 m3/d, to meet the actual water demand of Taveta township and some villages around the township.
4.6.2 Water Supply Alternatives
For the case of Taveta Taita County, four alternatives were examined:
Alternative 1 – Supply Taveta, Mwatate and Wundanyi from the Njoro Kubwa Springs, and leave Voi connected to the Mzima Pipeline.
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Alternative 2 – Supply Mwatate and Wundanyi from the Mzima Pipeline by abstracting water through pumping from Voi, leaving Taveta to being supplied from the Njoro Kubwa Springs. Alternative 3 – Supply Taveta, Mwatate, Wundanyi and Voi from the Njoro Kubwa Springs, taking no water from Mzima Pipeline. Alternative 4 – Maintain current situation – supply Voi from the Mzima Pipeline, supply Taveta from the Njoro Kubwa Springs and rely on local springs and boreholes for water supply to Mwatate and Wundanyi.
Additional details for each of the proposed alternatives are as follows:
Abstraction from the Njoro Kubwa Springs will be increased by pumping 393 m3/h for the Taveta, Mwatate and Wundanyi supply. A 75 km pipeline will be laid along the main road up to Mwatate in order to convey the water for use. For the transmission of the water it will be required to lay a 400 mm pipeline. Due to the elevation difference and the length of the pipe, a total dynamic head (TDH) of 298 m (30 bars) will be needed. Water supply to Wundanyi will be from a second stage pump from the Mwatate location to an elevation of +1,430 masl. It is suggested that this supply "arm" be postponed to the last stage of development – see economic calculation later in this section. Abstraction from the Mzima Pipeline and pumping of the water to Mwatate and Wundanyi. The pumping rate will be the same (393 m3/h) while the Taveta location will be supplied from the Njoro Kubwa Springs. The TDH to lift the water to Mwatate will be 335 m as the line to Mwatate is only 30 km. but the elevation difference is 260 m. Supply of all the Taveta county water demand from the Njoro Kubwa Springs, i.e. no water will be abstracted from the Mzima Pipeline to the Taveta customers. In that case, the system will comprise a 500 mm pipeline from the spring in Taveta to Mwatate. This pipeline will deliver 1,075 m3/h, equal to the daily demand of the three townships. The water lift from the spring will be 298 m to Mwatate. Supply to Voi will be via a force main gravity pipeline, 600 mm in diameter and 30 km in length. Water will be delivered from Mwatate at +850 masl to Voi at +600 masl. The flow gradient will be 260 m/30 km – 8.66 m/km on average. The scheme of supply will be remain as at present: Abstraction of water to Voi will be from the Mzima Pipeline (and only to Voi). Taveta will utilize water from the local intake near the Njoro Kubwa Springs, and both Mwatate and Wundanyi will be left disconnected from the bulk water supply system, and will rely on small boreholes, local springs at Wundanyi Mountain, etc.
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CWSB will invest in efforts to increase the production of these small schemes to improve reliability.
Table 4-4 summarizes the comparison of alternatives for supply for Taveta County.
Table 4 -4: Development Scenarios for Taita Taveta County
Sub Scenario 1: Supply water from the Njoro Kubwa Springs to Mwatate & Wundanyi only Sub Scenario 2: Supply water from Mzima Pipeline to Mwatate & Wundanyi only Sub Scenario 3: Supply water from the Njoro Kubwa Springs to Mwatate +Wundanyi + Voi Total water demand Units Scenario 1 Scenario 2 Scenario 3 Total water demand, 2035 m3/d 9,442 9,442 25,800 Total water demand, 2035 m3/h 393 393 1,075 Elevations Taveta m 750 750 750 Mwatate m 860 860 860 Wundanyi m 1,450 1,450 1,450 Voi/Maungu m 600 600 600 Distances Taveta-Mwatate km 75 75 75 Voi-Mwatate km 30 30 30 Taveta-Voi km Elevation difference Taveta-Mwatate m 110 110 110 Voi-Mwatate m 260 260 260 Taveta-Voi Head Loss Taveta-Mwatate m 187.5 187.5 187.5 Head Loss Voi-Mwatate m 75 75 Total dynamic head (TDH) Taveta-Mwatate m 298 298 298 Voi-Mwatate m 335 335 Mwatate-Voi m gravity Diameter Taveta-Mwatate mm 400 400 1,000 Voi-Mwatate mm 400 400 600 Capital cost Pipe per km US$/km 250,000 250,000 450,000 Pump per km US$/km 250,000 250,000 350,000 Pumps (US$ per Q/H) 100 100 70 Total cost Pipes US$ x 106 18,750,000 7,500,000 41,250,000 Pumps US$ x 106 11,704,443 13,179,793 22,386,734 Energy Total operating US$/y 1,281,636 1,443,187 3,501,925 Annual costs NPV US$ Rate % 10% 10% Lifespan of pipes years 50 50 Lifespan of pumps years 15 15
Total annual costs
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Taveta-Mwatate Capital US$/y 3,250,773 6,761,029 Voi-Mwatate Capital US$/y 2,287,494 Taveta-Mwatate Energy US$/y 1,281,636 3,501,925 Voi-Mwatate Energy US$/y 1,443,18 Total annual costs US$/y 4,532,410 3,730,681 10,262,954 Total annual volume m3/y 3,446,417 3,446,417 9,416,941 Specific cost (per m3) US$/m3 1.32 1.08 1.09
Note: Calculations do not include the additional cost needed to pump the water to Wundanyi town. It should be noted that additional pumping of 500 m (from +860 masl at Mwatate to +1,350 masl at Wundanyi) is essential in order to supply water.
4.6.3 Discussion
The remote location of the Taita Taveta townships, the distance between the settlements and the elevation of the region cause the water supply schemes to be relatively complex compared to other water supply schemes in the Coast Province.
Scenario 1 shows the highest water production cost as it demands the development of large infrastructures and high operating cost allocated relative to the small annual volume of water. In Scenario 2, since the length of the Voi-Mwatate Pipeline is only 30 km, the total annual cost per m3 is less than Scenario 1. Scenario 3 shows the production cost is US$ 1.09/m3, similar to Scenario 2. The advantage of Scenario 2 is mainly in the lower usage of the bulk water supply system, as supplying water to Voi from the Njoro Kubwa Springs will ease the stress of water demand from the Mzima Pipeline, enabling Mombasa to receive more water from the Mzima Pipeline compared to the current situation. Considering the future water demand at Voi town (16,500 m3/d) some 45% of all water from the Mzima Pipeline will be needed. Yet, it is important to note that Voi has more than one option of supplying water, whereas Mwatate, Taveta and Wundanyi are much more limited with regard to supply options.
Thus, two strategies for connection between Taita Taveta townships and the bulk water supply are recommended, as follows:
Only in the case of Scenario B1, where Mzima 2 Pipeline will be implemented, it is suggested to connect Mwatate and Wundanyi to the bulk water supply system by constructing a pipeline and pump to deliver water from Voi Junction to Mwatate. The scheme will be able to supply 9,432 m3/d, the total daily flow to meet the demand of Mwatate and Wundanyi. Taveta town will be supplied from the local intake in the Njoro Kubwa Springs.
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In all other cases where additional new resources to the bulk water supply will not include the Mzima 2 Pipeline, only Voi town will be supplied from the current Mzima Pipeline, and water supply to Mwatate, and Wundanyi will remain as at present, based on local and private schemes. It is recommended to enhance local solutions for the area of Wundanyi and Taita. Taveta town will be supplied from the local intake in the Njoro Kubwa Springs.
4.7 Water Supply to Remote Rural Areas
4.7.1 General
The rural areas within the Coast Province area of jurisdiction cover more than 95% of the land area, but host less than 20% of the region's population. Due to the dispersed nature of the rural population, sustainable water supply to the remote areas via the bulk water supply system is a complex task. Thus, the considered appropriate ways to supply water to the rural sector are as discussed in sections 4.7.2 to 4.7.5.
4.7.2 Rainfall Roof Harvesting
4.7.2.1 Overview
Rainwater harvesting has not been promoted in a systematic manner in urban areas in the Coast Region, although it is practiced and is found to be practical in rural communities. Given the high variability of rainfall, this can be a useful option in the rural sector for schools, remote communities, informal settlements and individual households. Galvanized corrugated iron sheets, corrugated plastic and tiles all make good roof catchment surfaces. Tanks are built from a wide range of materials including metal, wood, plastic, fibreglass, bricks, interlocking blocks, compressed-soil or rubble-stone blocks, ferrocement and concrete.
This form of water supply is useful in areas with rainfall between 500 mm and 1,000 mm, and is especially favourable in areas with two separate rainy seasons.
This method can constitute a cheap and efficient solution for rural settlements, and can be promoted by CWSB and various NGOs active in the region. Above-ground tanks with capacities ranging from 1 m3 to more than 40 m3 for homes, and 40 m3 to more than 100 m3 for institutions, can be constructed.
4.7.2.2 Advantages
The water can be of good quality in terms of colour, taste and bacteriological quality if adequate precautions can be taken, with the roof being made of suitable materials.
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4.7.2.3 Disadvantages
The cost of tanks is often beyond the reach of many poor households. The cost of this technology varies considerably depending on location, type of materials used and degree of implementation. Table 4-5 presents costs associated with the implementation of roof rainwater harvesting systems.
Table 4 -5: Construction Cost of Roof Rainwater Harvesting
Tank Size (including additional materials) Cost (Ksh) 1 m3 of plastic 13,300 3 m3 of plastic 42,900 4 m3 of plastic 59,600 5 m3 of plastic 74,500 6 m3 of plastic 85,000 8 m3 of plastic 123,700 10 m3 of plastic 160,700 15 m3 of plastic 272,500 24 m3 of plastic 406,000 Source: Prices have been adopted and adjusted to the present from the Manual Water from the Roofs by Erik Nissen-Petersen for Danish International Development Assistance (Danida), 2007
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4.7.3 Surface Catchment Systems
4.7.3.1 Overview
Harvesting of rainwater can be performed from rock outcrops/slopes, concrete surfaces, plastic sheets or treated ground surfaces. It consists of a catchment area, retention and conveyance structures, and storage tank/reservoir. This type of system is useful in regions with rainfall between 200 and 750 mm. The water is mainly used for domestic and livestock consumption.
4.7.3.2 Advantages
Advantages of rock surface catchment system:
Economical and reliable sources for water in water scarce areas. Can be built and used by self-help groups. Can be constructed during drought periods when the demand for water is highest and work in the fields is lowest. Maintenance involves only cleaning of the catchment and the reservoir. Even small rain showers falling on the rock catchment area produce large volumes of runoff that can be drawn off from the reservoir. Rock catchment dams do not occupy farmland but only rocks that are in no man's land.
4.7.3.3 Disadvantages
Disadvantages of rock surface catchment system are:
The quality of the water might be low if the catchment and the reservoir are not cleaned. It provides a breeding ground for disease-causing organisms. It has high evaporation rates.
4.7.4 Water Pan for Runoff Water Harvesting
4.7.4.1 Characteristics
A pan, also called a pond, is an excavated earth reservoir that is easy to construct in relatively flat terrain and harvest runoff for livestock utilization and small-scale irrigation. Pans are preferably located in topographically low areas where runoff from infrastructures such as roads can easily be harvested, and where impervious soils prevail to reduce seepage losses.
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The capacity is variable and depends on site conditions and investment capabilities. While common pans are 1,500–5,000 m3, the capacity can be increased with time to hold more water.
Source: Cash-Food for Assets by GoK and WFP
Fig. 4-18: Circular pan (left) and rectangular pan (right)
4.7.4.2 Advantages
Water pans are highly functional in arid and semi-arid region (rainfall between 200 mm and 750 mm) – even in semi-desert (<200 mm) areas, depending on water availability (scarcity) and available catchment area (suitable landscape).
4.7.4.3 Disadvantages
Low and erratic rainfall and prolonged droughts over several years of below average rainfall may lead to reservoirs failing to fill. High evaporation rates leading to significant losses from any water stored in open reservoirs or ponds. Siltation due to large amounts of sediment washed into reservoirs during severe storms, especially at the end of the dry season, which also make the water turbid. Siltation can be avoided by trapping inflowing silt in silt traps and utilizing it for fertilizing garden plots. Contamination of water in open reservoirs can be caused by livestock entering reservoirs, resulting in poor water quality. Livestock should therefore be watered downstream of dam reservoirs, where water can be drawn from a hand-dug well sunk in an area with seepage from the dam reservoir. Clean water for domestic use can also be drawn from such a well. The risk exists of small children and livestock falling into ponds or reservoirs. Small water reservoirs should therefore always be fenced.
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4.7.5 Sand Dam
4.7.5.1 Characteristics
A sand dam is a reinforced concrete wall built across a seasonal river to hold groundwater in sand. It is initially built one metre high and up to 90 m across. During heavy and erratic seasonal rains, water and silt flow over the dam while the heavier sand settles to the bottom. Over one to three seasons of rain, the dam fills up with sand, which acts as a storage tank for water. In good quality sand, the sand dam volume is approximately 35% water (Beimers, et al., 2001)
4.7.5.2 Advantages
It provides a year-round source of water near community-member homes so they do not have to spend hours walking and queuing to fetch water. Saline water becomes less salty over time as less evaporation occurs: as more water comes into the sand dam, the concentration of salt lessens. The water is cleaner, having been filtered through the sand. The water is protected from parasites and people are less likely to become ill. Increased water capacity allows communities to set up tree nurseries in semi- arid areas where tree planting is otherwise very difficult.
Each sand dam has the potential to provide a clean supply of water for up to 1,200 people, animals, tree nurseries and vegetable gardens. The increased water availability within a 10 km radius means that a sand dam may indirectly benefit up to thousands of people, as the use of the stored water is never restricted to the people who built the sand dam. Sand dams change the lives of people by providing water for their needs:
4.7.5.3 Disadvantages
According to calculations performed in 2010 by Utooni Development Organization, Kola, Kenya, the cost of building a sand dam by adding (a) the average cost of the dam including all staff and materials and (b) the community self-help group contribution is as detailed in Table 4-6, the volume of water in an average dam being 100,000 m3.
Table 4 -6: Cost of Building a Sand Dam for Average Volume of 100,000 m3
Cost in 2010 Cost in 2010 Cost in 2012 Cost Items (Ksh) (US$) (US$) Dam 575,184 7,669 8,691 Self-help contribution 640,000 8,533 9,670 Total 1,215,184 16,202 18,361 Note: To get cost in 2012, an escalation factor of 85/75 = 1.13 was used, based on US$ 1= Ksh 75 in 2010, and US$ 1= Ksh 85 in 2012.
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On average, the cost to the community is about US$ 0.20–0.30/m3 for each cubic metre of water from a sand dam (Nissen-Peterssen, 2000).
Source: Two waterfalls do not hear each other, sand-storage dams, science and sustainability development in Kenya by Maurits Ertsen and Rolf Hut
Fig. 4-19: Typical Sand-Storage Dam with Sand Reservoir Upstream
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5. Financial and Economic Analysis
5.1 Introduction
The main objective of the financial and economic analysis is to provide CWSB and other policymakers and stakeholders with all necessary information needed for informed decision-making regarding the potential water development scenarios in the region, as well as other promising programs and projects.
Initial economic analysis of the seven water supply scenarios – four scenarios for the bulk water supply and three scenarios for the Lamu area – was presented in the Pre-Feasibility Study Report. At this point, each of the scenarios is analyzed with regard to more stringent financial and economic indicators
The final outcome of this chapter is to present the financial and economic indicators of each scenario, and identify the preferred ones. The outcomes will also serve to upgrade the multi-criteria analysis.
5.2 Methodology
The financial and economic analysis of the CWSB-WSMP scenarios is based on a comparison between the net benefit flows from water delivery and income to the cost of developing and operating the systems that will supply the water.
The initial financial evaluation was presented during the pre-feasibility phase, and included the drafting of detailed cash flows for each alternative. These included discounted investments, O&M costs and energy costs.
Moreover, additional analysis included computations of basic indicators per supplied m3 of water – total investment per m3, energy and O&M costs per m3 and the total water cost per m3 delivered to the utility firm.
These indicators enabled the Consultant to rank each of the scenarios according to multi-criteria ranking, and identify the scenarios that are viable for further examination. At this stage, the full feasibility study, discounted cash flow techniques have been applied to the recommended scenarios to further refine the analysis and identify the most promising scenarios.
The distinction made between the financial and economic analysis in the master plan computations are based on the traditional differences between the two economic indicators as well as the project-specific variables identified by the consultant during preparations of the cost estimates, cash flows and economic evaluations.
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The financial analysis compares the revenues and expenses (investment, maintenance and operation costs, energy) of the concerned agent (in this case CWSB) in each scenario alternative and then computing the corresponding financial returns and indicators. The economic analysis aims at identifying and comparing economic and social benefits accruing to the national, regional and community economies as a whole.
Several key factors are instrumental in explaining the distinctive and significant differences between financial and economic analysis results in the Master Plan computations. First and foremost are the subsidized terms and conditions of the long term loans for investments. These are the donor funds supporting the CWSB and the other investment agencies (WRMA, CDA etc). The subsidized terms of these attractive loans consist of a 10 year grace period, 1% interest per annum and an additional 30 years maturity with 3% per annum.
In the financial cash flow analysis, only the annual share of invested funds and the corresponding (very low) interest payments is included as expenses in the cash flow calculations. The major share of the capital investments is deferred to latter years. Concurrently, the cash flow is discounted at 12 percent per annum. These factors produce an attractive investment environment with high IRRs and NPVs. Due to the discounting effects, postponed expenses (especially 20 years into the future), entail low present outlays. These considerations also explain the relatively substantial influence of the O&M components (operations, maintenance, energy) on the ranking of the different scenarios. The low capital expenditures in the present (due to the soft loans and high annual discounts) are dwarfed by the annual O&M costs.
In contrast, in the economic analysis computations, the total capital investments are recorded in the same year as implemented. Hence annual expenses are much higher and their relative significance in the total annual expenditure ratio is increased.
This clarifies the fact that a comparison between alternative scenarios will show that very often the relationship between the financial and economic scores have a nonlinear relationship. Meaning one scenario may be the least-cost one from the economic point of view (for example B5 with 463.9 $ million investment costs and the lowest also on water prices) whereas in the financial analysis scenario B1.1 has the lowest water costs but much higher capital investments.
The indicators analyzed at this stage include:
Net present value (NPV). Internal rate of return (IRR). Economic net present value (ENPV). Economic internal rate of return (EIRR). Sensitivity and risk analysis.
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Financial and economic evaluation of the scenarios is divided into two distinct phases.
Analysis indicators: NPV and IRR In economic and financial analysis there are a number of different approaches that can be used to evaluate any given project. The Internal Rate of Return (IRR) and the Net Present Value (NPV) are among the most widely accepted, accurate and relevant. The net present value approach is considered the most accurate valuation approach to capital budgeting issues. Discounting the cash flows by the weighted average cost of capital allows economists and decision makers to determine whether a project will be profitable or not and, more importantly, it will reveal exactly how profitable a project will be in comparison to alternatives. Generally, all projects which have a positive net present value should be accepted while those that are negative should be rejected. When funds are limited the projects/alternatives with the highest NPV should be selected. The main advantage of the NPV method is that it provides a direct measure/amount of the contribution or income of the project to the investor/initiator. The discount rate selected in the financial analysis of the projects in the Master Plan is 12% (As stipulated by the World Bank for WB funded ventures). This means that any alternative with a positive NPV generates a profit above and beyond the 12% discount rate. The Internal Rate of Return (IRR) is the rate of growth a project is expected to generate. It is the interest rate (or discount rate) that makes the net present value of all cash flows of the project equal to zero. Generally, the higher a project’s IRR the more desirable it is to the investors or decision makers. Assuming all other factors are equal among various projects, the IRR can be used to rank prospective projects and to select the most feasible. The main advantage of the IRR method is that it clearly displays the return (in percentage) on the original investment. This can be then compared to alternate investment opportunities. Although, as a rule, projects with higher NPVs and IRRs should be selected for implementation and ones with negative indicators rejected, at times more detailed analysis is required. For example, both NPV and IRR of the immediate emergency investment are negative; this project is not a stand-alone project and cannot be evaluated as such. Rather, it is an initial (and emergency) investment in the overall Baricho project which exhibits robust and positive cash flows and rates of return at plan horizon.
5.3 General Assumptions for the Evaluation
Costs are expressed at September 2012 costs, and are constant. Project lifespan is set at 50 years. Investments relate only to the additional infrastructure needed to be developed, regardless of any existing facilities.
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An annual discount factor of 10% has been tentatively set for the analysis. Investments relate to development from the water source and up to the final connection point at the water utility company. Average capital costs and average O&M and energy costs are calculated for each scenario's additional costs only (without existing facilities), and are determined as a constant rate set at 1% per annum of the total accumulated investments. O&M expenditures reflect an annual investment of 0.5% of accumulated investments for rehabilitation purposes. In the event of an incompatibility between the total water capacity and the total water demand (in certain years), the lower between the two is set as a constraint in the calculations. Government policies regarding water prices will remain unchanged. Policy shifts may cause corresponding changes in the analysis results. Different water prices have been set for the Mombasa area and the Lamu area, reflecting the differing costs of water production and supply between the two areas. Investments for each phase are divided equally by the anticipated number of years of the component implementation (relevant for economic analysis). Total investments do not include and do not cover the investments that will be required for water distribution for the various areas of the WSPs. Total investments do not include and do not cover the investments that will be required for water distribution for the various areas of the WSPs. A standard conversion factor (SCF) of 0.9 was determined in order to reflect additional (or decreased) benefits (or costs) to the economy (relevant for economic analysis). Funding costs are computed according to the terms of loans of the water utilities – 10-year grace period with annual interest rate of 1%, and additional 30 years of loans' refund with an annual interest rate of 3% (relevant for financial analysis).
5.4 Cost Estimates Comment [J1]: Comment was: Why use projects outside Kenya? Wouldn’t it be prudent to use local similar projects? Unit costs for the engineers cost estimates are presented in Annex 4, the The response to the comment was: following documents have been used to determine reasonable unit prices: Cost estimates based mostly on other projects in Kenya generally and coast province in particular. Projects from Various WaSSIP reports (EGISBCEOM/MIPB, IGIP/TCE, BRL/GIBB, H.P. neighbor countries (e.g. Tanzania and Uganda) are used for verifications. GAUFF) Detailed Design and Tender Documents for Musoma Bukoba Water Supply, Engineers Costs Estimate, Poyry Environment December 2010 (Tanzania) MAMADO (Maji na Maendeleo Dodoma), NGO, Information from Susan Workshop, Mtwara, September 2010 (Tanzania) Costs Optimisation of UDDT’s in Kenya, Steffen Blume, 2009 (Kenya) Mwanza Sewerage Works Project Phase 2, Implementation of Works, 2010 (Tanzania)
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Update of the 2003 Feasibility Study – Kampala Water Supply, Poyry Environment GmbH, June 2010 (Uganda)
Table 5-1 presents preliminary cost estimates for the development of each source. It should be emphasized that these estimates are general; diameters, powers and volumes will be more accurate in the preliminary design stage
Table 5 -1: Cost Estimates for the Various Systems Comment [J2]: Comment was: In table 5-1, the quantities here differ from those in chapter 4, Mwache is now 200,000m3/day Capital instead of 180,000m3/day. The same applies to Rare Dam. Any explanation for this? No. Source/Project Cost Again how can 180,000m3/day be supplied (US$) as per scenario B1 yet the pumping capacity 1 Baricho Immediate Expansion (22,000 m3/day, 2 years impl.) is only 6000m3/hr (144,000m3/day) Recheck this table to ensure justifiable 3 Boreholes (3 BH, 10,000m /d each) 3,200,000 costs, pressure ratings etc. Pumping Units to Kakuyuni,800 m3/hr,100m 1,300,000 What does rehab of Mkurumudzi Dam 3 entail? Pumping Units to Nguu Tatu,800 m /hr,240m 2,250,000 New Kakuyuni Tank 2,500m3 800,000 The response was: Quantities were New Kilifi Tank 5,000m3 1,000,000 revised. Mkurumudzi dam and Msambweni Gravity Main Kakuyuni-kilifi, 20"/50km, PN10 16,889,167 Aquifer (Gongoni) are being utilized by Gravity Main Malindi-Gongoni, 12"/20km, PN10 4,556,500 Base Titanium for limited time. It is suggested that CWSB will ensure Parallel Force Main Lower Ribe - Nguu Tatu ,32"/12km,PN16 7,830,225 secure this source for the future of the 1.1 Total 37,825,892 Coast province in the end of the mining works. 2 Mwache Dam (186,000 m3/day, 4 years implementation) CWSB will have invest in rehabilitation of this sources. Dam, 75 m high, Rockfill type 109,764,706 Treatment works 35,000,000 Comment [J3]: Comment was: Cost for Weir 23,529,412 treatment works for both Mwache & Rare for 200,000m3/d is different at 35mUSD 3 Pumping Station, 3000 m /hr, 40m 9,333,331 and 22.5 mUSD, why? Check rows 4 and Transmission Mains, 32"/13km, PN10 8,482,744 21 of the table. 2.1 Sub-Total Changamwe Scheme 17,816,075 -Cost of 3 boreholes for Baricho is different for item 4& 5 at 350,000USD and 4.8 mUSD, why? Check also for 5 boreholes. Pumping station, 4,000 m3/h, 140 m 8,666,665 The response is: Cost estimates were Transmission Mains, 40"/4km, PN25 5,512,000 revised after reviewing recent projects of New Tank-Nguu Tatu 40"/17km, PN10 18,740,800 CWSB.
2.2 Sub-Total Transmission to New Reservoir 32,919,465 Comment [J4]: Comment was: -Split Pumping Station to Kaya Bombo, 2,500 m3/hr, 40m 4,333,332 the Baricho scheme into stand-alone contracts, one to be financed by the Transmission Mains Mwache - Kaya Bombo 28"/22km, PN10 11,711,700 available funds from WaSSIP-AF and the Transmission Mains Kaya Bombo - Likoni 20"/11km, PN10 3,715,617 other contract by other funds to be sought. Transmission Mains Kaya Bombo - Tiwi, 20"/11km, PN10 3,715,617 -Consider adding Kakuyuni water tank and also Kilifi town water tank. Transmission Mains Tiwi - Ukunda 16"/6km, PN10 1,667,250 Response is: Stand-alone analyses are Transmission Mains Ukunda - Msambweni 12"/22km, PN10 5,012,150 presented, the immediate expansion Transmission Mains Msambweni - L. Lunga 12"/46km, PN10 10,479,950 includes the new reservoirs. 2.3 Sub-Total Transmission to South Coast 40,635,616
2.4 Total Mwache Dam Project (Without Changamwe) 241,849,198
3 Rare Dam (180,000 m3/day, 3 years implementation) Dam, 60m High, Rockfill type 80,000,000
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Capital No. Source/Project Cost (US$) Treatment works 33,500,000 Pumping Station, 7500m3/hr, 150m 8,333,331 Transmission Mains to Nguu Tatu, 48"/70Km, PN16 (Partly PN25) 102,636,625 3.1 Total 213,469,956
4 Rare Dam (100,000 m3/day, 3 years implementation) Dam, 50m High, Rockfill type 60,000,000 Treatment works 20,000,000 Pumping Station,3500m3/hr, 150m 2,333,333 Transmission Mains to Nguu Tatu, 32"/70Km, PN16 (Partly PN25) 45,676,313 4.1 Total 128,009,645
5 Mzima II (100,000 m3/day, 4 years implementation) Intake 450,000 Tunnel,3.2mØ-1.5mØ,3km 11,250,000 Pipeline Mzima - Voi,48"/98.6km,PN16 144,571,018 Pipeline Voi - Mazeras, 40"/121.4km, PN 16 133,831,360 Pipeline Voi - Taita Hills,16"/30km, PN40 2,946,450 Pumping Station to Taita Hills, 400m3/hr, 300m 379,535 5.1 Total 293,428,362
6 Baricho II Malindi Expansion (22,000 m3/day, 2 year impl.) Boreholes (2 BH, 10,500m3/d each) 3,200,000 Pumping Units,1300 m3/hr,100m 2,250,000 Transmission Mains Baricho Kakuyuni,28"/27km,PN16 14,373,450 Transmission Mains Kakuyuni Marafa,28"/27km, PN12.5 14,373,450 6.1 Total 19,823,450
7 Baricho II Mombasa Expansion (41,000 m3/day, 2 years impl.) For Mombasa Boreholes (3 BH, 10,500m3/d each) 4,800,000 Pumping Units,2200m3/hr, 240m 3,750,000 Baricho - Mombasa Transmission Mains,32"/50km,(Mostly PN40) 40,782,422 Baricho - Mombasa Transmission Mains,32"/31km,PN25 20,880,600 7.1 Total 70,213,022
8 Nanighi Barrage and Pipeline (130,000 m3/day, 4 years impl.) Barrage at Nanighi 90,000,000 Gravity Transmission Mains, 80"/180km/PN16 459,000,000 8.1 Total 549,000,000
9 Garsen Barrage and Pipeline (130,000 m3/day, 3 years impl.) Barrage at Garsen 2,000,000 Pumping Station, 6000 m3/hr, 220m 4,795,546 Transmission Mains, 48"/75km, PN25 137,459,766 9.1 Total 144,255,312
10 Msambweni Aquifer / Mkurumudzi Dam (20,000 m3/day)
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Capital No. Source/Project Cost (US$) Rehabilitation of Well field 4,000,000 Pumping station for Lunga Lunga, 200 m3/hr,120m 200,000 Rehabilitation of Mkurumudzi Dam 4,000,000 Pumping station to Ukunda, 500 m3/hr, 80m 379,535 10.1 Total 8,579,535
11 Kakuyuni Marafa Scheme new transmission main10"/20km 4,161,083 Pumping station for Marafa at Kakuyuni 200 m3/hr,50m 300,000 New Marafa Tank 1,000m3 300,000 11.1 Total 4,761,083
12 Hola Scheme water intake and pumping station 750,000 transmission mains 650,000 12.1 Total 1,400,000
13 Bura Scheme water intake and pumping station 750,000 transmission mains 850,000 13.1 Total 1,600,000
14 Njoro Kubwa intake works 450,000 new transmission main 1,050,000 Pumping station 500,000 14.1 Total 2,000,000
5.5 Stand-Alone Analyses of Projects
In order to ease the funding of new water projects, under these two foundations, the consultant formed 8 scenarios in the pre-feasibility report and later with the approval of the WB, AFD and the client minimize it to 4 in the draft full feasibility report. Since at the full pre-feasibility a comment were given by WB that one realistic option is missing, we add the fifth scenario (B1.1) in order to cover more options. Table 5 -2: Basic Financial Indicators by Scheme Comment [J5]: Comment was: In table 5.2, are we having the same volumes in all the scenarios? No explanation given regarding the comment Michael look at this
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Average item Total Average Average NPV Capital IRR Water Cost Project / Indicator Investment energy O&M (us$ 3 Cost (%) (US$ /m ) (us$ Million) (US$/m3) (US$/m3) Million) (US$/m3) 1 Baricho Immediate Finance 47.75 0.188 0.25 0.07 -5.262 -6.79% 0.5101 2 Mwache Dam 241.85 0.141 0.08 0.05 71.564 54.99% 0.2685 3 Large Rare Dam 213.47 0.113 0.14 0.04 65.248 74.66% 0.2963 5 Mzima II 293.43 0.308 0.02 0.10 25.165 46.38% 0.4307 6 Baricho II (Mal. Expansion) 19.82 0.078 0.09 0.03 16.890 268.44% 0.2014 4 Small Rare Dam 128.00 0.122 0.10 0.04 43.885 78.34% 0.2681 7 Baricho II (Mom. Expansion) 70.20 0.148 0.23 0.05 -0.051 10.16% 0.4304 8 Nanighi Barrage and Pipeline 549.00 0.443 - 0.15 -51.564 - 0.5911 9 Garsen Barrage and Pipeline 142.26 0.104 0.20 0.04 30.276 64.64% 0.3441 10 Msambweni Aquifer / Mkurumudzi Dam 8.58 0.037 0.07 0.01 19.222 452.73% 0.1217
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5.6 Financial Analysis
5.6.1 General
Financial analysis was conducted from the perspective of the water utilities firm, namely CWSB.
For each of the selected scenarios, Table 5-3 presents the financial figures of the main indicators – total investment per scenario; average capital, energy and O&M expenditures per m3 supplied; and the final water cost per m3 supplied
Table 5 -3: Basic Financial Indicators by Scenario
Financial Indicators Average Total Total Scenario Capital Energy O&M Water Water Investment Cost Cost Cost Cost Volume (million US$) (US$/m3) (US$/m3) (US$/m3) (US$/m3) (m3/day) Scenario B1 681.642 0.112 0.122 0.057 0.29 396,000 Scenario B1.1 516.230 0.098 0.130 0.062 0.29 391,000 Scenario B3 516.227 0.137 0.211 0.056 0.40 391,000 Scenario B5 463.897 0.159 0.123 0.047 0.33 386,000 Scenario C2 699.591 0.108 0.114 0.154 0.38 391,000
5.6.2 Total Investment Comment [J6]: Comment was: What would be the effect of having loans on commercial terms? Does it mean that Total investment varies substantially, from US$ 465 million for Scenario B5 to without donor loans the projects may turn over US$ 680 million for Scenario B1. As expected, the large and diverse water out to be less feasible? Response was: Without donor's loans, the sources programmed for development in this scenario (both Mwache and financial cost per unit of water will Mzima 2) and the early stage of heavy investment (during Phase 1) generate a increase. However, The economic cost will substantial capital investment amount. Scenario B5, on the other hand, relies remain the same. mainly on the gradual development of the adjacent Baricho 2 source, with augmentation of desalination steadily developed throughout the three phases.
Note: All investments are considered loans taken at the following terms: 10 year grace period with an annual interest rate of 1% Additional 30 years of refund with an annual interest rate of 3%. The loan is considered to be taken at the year of implementation).
5.6.3 Average Capital Cost per m3
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The share of the capital cost along with the funding costs which are attributed to the price (cost) of each m3 of water supplied. As expected, and since the total amount of water supply is similar in all scenarios, this indicator corresponds to the previous. Capital costs per m3 range between US$ 0.098 and US$ 0.159 for scenarios B1.1 and B5, respectively.
5.6.4 Cost of Energy per m3
Variations are also evident when analyzing this indicator:
Scenarios C2 and B3, with energy expenses of 0.21 US$/m3, have the highest energy cost per m3 supplied. As expected, the energy-intensive scenarios – C2 ("desalination-based") and B3 ("Baricho first") – have the higher energy expenses. Since Baricho is a significant project in each scenario, the energy expenses are similar. Scenarios B1 with energy expenses of 0.12 US$/m3, has the lowest energy cost per m3 supplied.
5.6.5 Cost of O&M per m3
Within the scenarios that do not utilize desalination to a significant degree – B1, B1.1, B3 and B5 – the amount attributed to each m3 supplied varies between US$ 0.06 and US$ 0.07. Since O&M (without the energy component) is calculated as a fixed percentage of total investment costs (1% in all projects, an additional 3% for desalination units and 14% for membranes replacement), the deviation between scenarios is mostly attributed to the desalination component in each. By and large, the water supply alternatives that utilize desalination (even for a relatively small amount of water) exhibit a significantly higher ratio of O&M in the final cost of each m3 supplied.
For Scenario C2, which is "desalination-dependent", the O&M cost is significantly higher, at 0.15 US$/m3.
5.6.6 Total Cost of Water per m3
This factor is an aggregation of all expenses attributed to the development of the water resources, conveyance, treatment and desalination in each scenario per m3 supplied. Therefore, it is a key indicator in the comparison between the alternatives and gauging the ones that merit additional and more detailed analysis.
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This indicator varies as follows:
Scenarios B1 and B1.1 have the lowest cost, at 0.29 US$/m3. Scenarios B3 has the highest water cost of 0.40 US$/m3.
Fig. 5-1: Total Water Costs – Financial
Fig. 5-2: Cost and Composition per m3 – Financial Costs
5.6.7 NPV and IRR
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Table 5-4 presents the financial net present value (NPV) and the internal rate of return (IRR) of each scenario.
At 10% discount rate, three of the scenarios (except B3 and C2) exhibit a positive NPV ranging between US$ 0.3 million (B5) to US$ 21 million (B1 and B1.1), with IRRs of 10 % to 35%, respectively.
Table 5 -4: Calculated Indicators – Financial
NPV IRR Scenario (million US$) (%) B1 20.41 35.42% B1.1 21.08 35.05% B3 -41.60 -5.65% B5 0.27 10.26% C2 -23.70 ND
5.7 Economic Analysis
5.7.1 General
Economic analysis examines the feasibility and viability of each scenario from the perspective of the entire regional and national economy.
For each of the selected scenarios, Table 5-5 presents the economic figures of the main indicators – total investment per scenario; average capital, energy and O&M expenditures per m3 supplied; and the final water cost per m3 supplied
Table 5 -5: Basic Economic Indicators by Scenario
Economic Indicators Average Economic Total Total Scenario Capital Energy O&M Water Water Investment Cost Cost Cost Cost Volume (million US$) 3 (US$/m3) (US$/m3) (US$/m3) (US$/m3) (m /day) Scenario B1 681.64 0.473 0.110 0.051 0.63 396,000 Scenario B1.1 516.23 0.519 0.117 0.056 0.69 391,000 Scenario B3 516.23 0.463 0.190 0.050 0.70 391,000 Scenario B5 463.90 0.392 0.111 0.042 0.55 386,000 Scenario C2 699.59 0.450 0.102 0.139 0.69 391,000
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5.7.2 Cost of Energy per m3
Costs exhibit negligible variations – between 0.10 US$/m3 and 0.19 US$/m3.
It should be noted again that energy costs include pumping and conveyance, and do not include desalination needs. Hence, Scenario C2 is competitive at this level.
5.7.3 Cost of O&M per m3
Within the scenarios that do not utilize desalination to a significant degree – B1, B1.1, B3 and B5 – the amount attributed to each m3 supplied varies between US$ 0.05 and US$ 0.06. Since O&M (without the energy component) is calculated as a percentage of total investment costs (1% in all projects, an additional 3% for desalination units and 14% for membranes replacement), the deviation between scenarios is mostly attributed to the desalination component in each. By and large, the water supply alternatives that utilize desalination (even for a relatively small amount of water) exhibit a significantly higher ratio of O&M in the final cost of each m3 supplied.
For Scenario C2, which is "desalination-dependent", the O&M cost is significantly higher, at 0.14 US$/m3.
5.7.4 Total Cost of Water per m3
This factor is an aggregation of all expenses attributed to the development of the water resources, conveyance, treatment and desalination in each scenario per m3 supplied. Therefore, it is a key indicator in the comparison between the alternatives and gauging the ones that merit additional and more detailed analysis.
This indicator varies as follows:
Scenario B5 has the lowest cost, at 0.55 US$/m3. This is due mostly to the low total investment required and corresponding average capital cost per unit supplied. The water costs for the other scenarios – B1, B1.1, B3 and C2 – range between 0.63 US$/m3 (B1) and 0.70 US$/m3 (B3).
The relative cost composition of each m3 supplied is presented in Fig. 5-3.
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Fig. 5-3: Total water costs – economic costs
Fig. 5-4: Cost and composition per m3 – economic costs
5.7.5 ENPV and EIRR
Table 5-6 presents the economic net present value (ENPV) and the economic internal rate of return (EIRR) of each scenario.
For all five scenarios, the ENPV is negative. However, Scenarios B1, B1.1, B3 and B5 have a positive EIRR, ranging between 0.64% (B3) and 3.31% (B5).
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Table 5 -6: Calculated Indicators – Economic
ENPV EIRR Scenario (million US$) (%) B1 -180.19 2.64% B1.1 -215.35 1.04% B3 -229.30 0.64% B5 -125.67 3.31% C2 -201.87 ND
5.8 Financial & Economic Analysis for Lamu Area
The financial and economic analysis for the Water Supply Development scenarios for the Lamu area is presented in Tables 5-6 and 5-7
Table 5 -7: Lamu Area – Basic Financial Indicators by Scenario
Average Total Capital Energy O&M NPV IRR Water Scenario Investment Cost Cost Cost (million US$) (%) Cost (million US$) (US$/m3) (US$/m3) (US$/m3) (US$/m3) L1: (Nanighi Barrage) 549.00 0.95 – 0.30 -82.89 0.44% 1.257 L2: (Garsen Barrage) 152.71 0.26 0.21 0.08 20.31 18.03% 0.564 L3: (Desalination) 136.38 0.16 0.84 0.26 -48.05 N/A 1.263
Fig. 5-5: Lamu area total water costs – financial costs
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Fig. 5-6: Lamu area cost and composition per m3 – financial costs
Table 5 -8: Lamu Area – Basic Economic Indicators by Scenario
Average Economic Total Capital EIRR Water Scenario Investment Cost Energy O&M ENPV (%) Cost (million US$) (US$/m3) (US$/m3) (US$/m3) (million US$) (US$/m3) L1: (Nanighi Barrage) 549.00 2.52 – 0.27 -321.59 1.64% 2.79 L2: (Garsen Barrage) 152.71 0.70 0.19 0.08 -50.42 6.39% 0.97 L3: (Desalination) 136.38 0.41 0.74 0.17 -82.79 N/A 1.33
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Fig. 5-7: Lamu area total water costs – economic costs
Fig. 5-8: Lamu area cost and composition per m3 – economic costs
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Table 5 -9: Lamu Area Calculated Indicators – Financial
NPV IRR Scenario (million US$) (%) L1: (Nanighi Barrage) -123.09 -5.58% L2: (Garsen Barrage) -19.89 1.83% L3: (Desalination) -85.15 ND Note: ND = not defined
Table 5 -10: Lamu Area Calculated Indicators – Economic
ENPV EIRR Scenario (million US$) (%) L1: (Nanighi Barrage) -357.77 -0.70% L2: (Garsen Barrage) -86.60 2.15% L3: (Desalination) -127.62 ND Note: ND = not defined
5.9 Analysis of Supply Options for Taita-Voi Area
Table 4-4 summarizes the comparison of alternatives for supply for Taveta County.
Table 5 -11: Development Scenarios for Taita – Voi Area
Sub Scenario 1: Supply water from the Njoro Kubwa Springs to Mwatate & Wundanyi only Sub Scenario 2: Supply water from Mzima Pipeline to Mwatate & Wundanyi only Sub Scenario 3: Supply water from the Njoro Kubwa Springs to Mwatate +Wundanyi + Voi Total water demand Units Scenario 1 Scenario 2 Scenario 3 Total water demand, 2035 m3/d 9,442 9,442 25,800 Total water demand, 2035 m3/d 393 393 1,075 Elevations Taveta m 750 750 750 Mwatate m 860 860 860 Wundanyi m 1,450 1,450 1,450 Voi/Maungu m 600 600 600 Distances Taveta-Mwatate km 75 75 75 Voi-Mwatate km 30 30 30 Taveta-Voi km Elevation difference Taveta-Mwatate m 110 110 110 Voi-Mwatate m 260 260 260 Taveta-Voi Head Loss Taveta-Mwatate m 187.5 187.5 187.5 Head Loss Voi-Mwatate m 75 75
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Total dynamic head (TDH) Taveta-Mwatate m 298 298 298 Voi-Mwatate m 335 335 Mwatate-Voi m gravity Diameter Taveta-Mwatate mm 400 400 1,000 Voi-Mwatate mm 400 400 600 Capital cost Pipe per km US$/km 250,000 250,000 450,000 Pump per km US$/km 250,000 250,000 350,000 Pumps (US$ per Q/H) 100 100 70 Total cost Pipes US$ x 106 18,750,000 7,500,000 41,250,000 Pumps US$ x 106 11,704,443 13,179,793 22,386,734 Energy Total operating US$/y 1,281,636 1,443,187 3,501,925 Annual costs NPV US$ Rate % 10% 10% Lifespan of pipes years 50 50 Lifespan of pumps years 15 15
Total annual costs Taveta-Mwatate Capital US$/y 3,250,773 6,761,029 Voi-Mwatate Capital US$/y 2,287,494 Taveta-Mwatate Energy US$/y 1,281,636 3,501,925 Voi-Mwatate Energy US$/y 1,443,18 Total annual costs US$/y 4,532,410 3,730,681 10,262,954 Total annual volume m3/y 3,446,417 3,446,417 9,416,941 Specific cost (per m3) US$/m3 1.32 1.08 1.09
Note: Calculations do not include the additional cost needed to pump the water to Wundanyi town. It should be noted that additional pumping of 500 m (from +860 masl at Mwatate to +1,350 masl at Wundanyi) is essential in order to supply water.
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6. Multi-Criteria Analysis
6.1 Background
Selection of the optimal water supply solution entails issues which are beyond the traditional engineering and economic considerations. The Multi Criteria analysis provides a systematic approach that enables a more objective evaluation of the scenarios on disciplines which are not quantitative such as environmental or social parameters. In recent years, multi-criteria analysis has become an invaluable tool for the evaluation of different scenarios. Each indicator of the design is allocated a different weight that reflects the importance that the stakeholder or the expert assigns to it.
Four main filed of interests (also called "parameters") were selected for comparison and weighting. They are deemed the most appropriate by the stakeholders and the experts: variables within each one of the parameters are named indicators:
Engineering aspects. Financial and economic considerations. Environmental considerations. Social & Political aspects.
Table 6 -1: Classification and Weighting of Parameters and Indicators for
Assigned Criteria / Parameter Weights A. Engineering Sustainability 30% Feasibility of implementation 40% Reliability of Resources 30% Diversity of Resources 30% B. Economic Considerations 40% NPV 20% IRR 35% O&M Costs 10% Calculated Water Cost 35% C. Environmental Issues 15% Water Quality 30% Downstream Impact 30% Energy Consumption 30% Construction Effects 10% D. Social & Political aspects 15% Supply Coverage 30% Resettlement / Income Loss 40% Political acceptability 30%
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6.2 Results Comment [J7]: Comment was: By this criteria B1 is the best option! Ecofin criteria shows B5 is the best! Which do we follow? Table 6-2 presents the final results and the weighted average of each scenario. -Can the multi-criteria be simulated from Scenario B1 has the highest overall score of 76.8, followed by B5. the current schemes at Baricho, Mzima etc and the classification weights realistically established? Response was: The multi criteria methodology is used to simulate all Table 6 -2: Multi-Criteria Analysis for Bulk Water Supply aspects in order to identify the best scenario Inner Scenario Item Criteria / Parameter Classification Weighting B1 B1.1 B3 B5 C1 1.0 Engineering Sustainability 30% 1.1 Feasibility of implementation 40% 80 70 50 65 50 1.2 Reliability of Resources 30% 90 70 70 60 90 1.3 Diversity of Resources 30% 90 80 80 20 100 Engineering Summary 86 73 65 50 77 2.0 Economic Considerations 40% 2.1 NPV 20% 47 13 0 100 26 2.2 IRR 35% 80 31 19 100 0 2.3 O&M Costs 10% 83 76 85 100 31 2.4 Calculated Water Cost 35% 86 79 78 100 79 Economic Summary 76 49 42 100 36 3.0 Environmental Issues 15% 3.1 Water Quality 30% 90 70 70 50 95 3.2 Downstream Impact 30% 60 60 70 50 60 3.3 Energy Consumption 30% 90 70 70 80 50 3.4 Construction Effects 10% 60 60 70 80 50 Environmental Summary 78 66 70 62 67 4.0 Social & Political Aspects 15% 4.1 Supply Coverage 30% 100 80 80 80 80 4.2 Resettlement / Income Loss 40% 80 70 70 50 60 4.3 Political acceptability 30% 100 90 50 50 30 Social Summary 60 51 39 39 33 Total 100% 76.8 59.0 52.8 70.2 52.4 Rank 1 3 4 2 5
Scenario B5 has the highest score regarding financial & economic aspects (lowest investment and lowest O&M costs), but the lowest engineering and environmental score.
Table 6 -3: Multi-Criteria Analysis for Bulk Water Supply (Engineering priority)
Scenario Scenario Scenario Scenario Scenario Criteria Classification B1 B1.1 B3 B5 C2 Engineering Sustainability 45% 86 73 65 50 77 Economic Considerations 25% 76 49 42 100 36 Environmental Issues 15% 78 66 70 62 66.5 Social & Political Issues 15% 60 51 39 39 33 Total 100% 78.4 62.6 56.2 62.7 58.6
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Rank 1 3 5 2 4
Table 6 -4: Multi-Criteria Analysis for Bulk Water Supply (Environmental priority)
Scenario Scenario Scenario Scenario Scenario Criteria Classification B1 B1.1 B3 B5 C2 Engineering Sustainability 20% 86 73 65 50 77 Economic Considerations 30% 76 49 42 100 36 Environmental Issues 40% 78 66 70 62 66.5 Social & Political Issues 10% 60 51 39 39 33 Total 100% 77.1 60.8 57.6 68.7 56.1 Rank 1 3 4 2 5
Table 6 -5: Multi-Criteria Analysis for Bulk Water Supply (Social & Political priority)
Scenario Scenario Scenario Scenario Scenario Criteria Classification B1 B1.1 B3 B5 C2 Engineering Sustainability 20% 86 73 65 50 77 Economic Considerations 30% 76 49 42 100 36 Environmental Issues 10% 78 66 70 62 66.5 Social & Political Issues 40% 60 51 39 39 33 Total 100% 71.7 56.3 48.3 61.8 46.1 Rank 1 3 4 2 5
Table 6.6 presents the final results and the weighted average of the development scenarios for the Lamu area. The Garsen scenario has the highest overall score of 64.6, followed by the Nanighi scenario with an overall score of 49.4.
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Table 6 -6: Multi-Criteria Analysis for the Lamu Area
Inner Nanighi Garsen Desalination Item Criteria Classification Weighting Scenario Scenario Scenario 1.0 Engineering Sustainability 30% 1.1 Feasibility of implementation 40% 40 60 100 1.3 Reliability of resources 30% 80 70 100 1.4 Diversity of resources 30% 0 0 0 Engineering Summary 100% 40 45 70 2.0 Economic Considerations 40% 2.1 NPV 20% 32 100 0 2.2 IRR 35% 86 100 0 2.3 O&M costs 10% 36 100 47 2.4 Calculated water cost 35% 95 100 57 Economic Summary 100% 40 65 5 3.0 Environmental Issues 15% 3.1 Water quality 30% 80 70 100 3.2 Downstream impact 30% 50 70 70 3.3 Energy consumption 30% 100 60 40 3.4 Construction period 10% 60 60 50 Environmental Summary 100% 75 66 68 4.0 Social Issues 15% 4.1 Supply coverage 30% 100 90 70 4.2 Resettlement / income loss 40% 80 70 70 4.3 Political acceptability 30% 90 80 50 Social Summary 100% 90 86 56 Total 100% 52.8 62.3 41.5 Rank 2 1 3
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7. Additional Development Considerations
7.1 Significance of the Development of the Bulk Water Supply System on the WSP's Water Distribution Networks
7.1.1 Overview
Development of the bulk water supply system will improve supply of water via the main system to storage reservoirs and to distribution systems managed by WSP's.
A change in the mode of water supply, enhanced water availability and operation of the system to provide water 24 hours a day, seven days a week (24/7) will result in improved reliability of water supply, with its inherent potential for better billing of water consumers for use of water (by raising their willingness to pay). At the same time, attention must be paid to the impact of augmented water supply from the main system to the local systems, a fact that will only emphasize the need for preparing a multiannual program for rehabilitation of the water distribution pipelines. Preparation of such a program will take into consideration the expected changes in the water supply system as well as the age of the pipelines, frequency of pipe bursts along the lines, past data vis-à-vis present pipe failures, construction materials, type of soil, and other factors.
Attention must be given to the following factors, as described below:
Impact on water pressures Impact on water losses Effect of pressure on pipe bursts Effect on the mode of water supply System operation
7.1.2 Impact on Water Pressures
Augmentation of water supply and filling of the pipelines in which the current water pressure is low or in which there is no water at all for several hours of the day will result in a rise in water pressure in these lines. Apart from the implications with respect to bursts (see following item), it should be borne in mind that open taps, distribution points without valves and similar deficiencies exist in certain parts of the system, with water flowing out from these points for a limited number of hours a day (corresponding to the number of hours in which water reaches these points).
Local water companies must map all demand points lacking in taps or valves and take the necessary action to close these points in order to prevent uncontrolled flow of water for several hours a day.
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7.1.3 Impact on Water Losses
Water losses may be defined as a phenomenon involving leakage of water from small cracks and holes in the system, generally caused by corrosion inside the pipe. Cracks are also caused by fatigue at welded joints or by stresses exerted by the ground on the pipe. All of the above cause leakage of water from the pipes, with the extent of leakage depending on three factors:
The size of the hole or crack. The water pressure prevailing in the pipeline, affecting flow. The period of time elapsed from the start of leakage.
The size of the hole or crack is an independent variable and is principally a function of the pipe "history" (i.e. age, mode of laying, quality of material, workmanship, type of soil).
The expected water pressure in the local water supply systems will increase with an improvement in water supply in the main system. At the present stage, it is difficult to quantify the expected increase in losses as a result of the existing leakages in the system and the expected total losses. At the same time, it is known that a non-linear relationship exists between water pressure and general losses from cracks and holes. The exponent in this mathematical relationship is 1.2–1.3 in water supply systems of medium size, and up to 1.5 in small systems. This means that an additional pressure of 30% (e.g., raising the water supply pressure from an average of 2 bar to 2.6 bar) will cause an increase of 301.2 units in leakage flow, i.e. an increase of 60% in local losses vis-à-vis the original value. If we add to this the fact that water supply will be continuous and not just for a few hours a day, it may be concluded that the potential increase in water losses is up to 2–3 times the existing figure.
This issue calls for immediate attention and for definition of courses of action to be followed by water supply providers. In the Consultant's estimation, CWSB should be regarded as responsible for the main water supply system, being the technical entity governing all matters relating, inter alia, to improvement of water loss management, reduction of leakages in the existing system, and performance of water surveys for identification of additional sources of loss.
7.1.4 Effect of Pressure on Pipe Bursts
Increasing the water pressure will bring about an increase in the number of pipe bursts in the old systems. A rise in the supply pressure following the higher quantity of available water that will be conveyed from the main lines to the distribution lines will result in local water hammer. This will cause instantaneous water pressure (lasting from fractions of a second to 2–3 seconds) that is 4–5
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times the nominal water pressure. The intensity of water hammer depends mainly on the volume of the water supply system upstream of the burst.
Over time, water hammer causes a weakening of the joints between the pipes, thus reducing the resistance of the joints to additional leakage. When the joints undergo fatigue, the probability of a failure and subsequent burst increases and the number of bursts rises. The volume of water lost from these bursts depends primarily on the water pressure prevailing in the pipeline and the response time of the maintenance crew responsible for repairing the fault.
7.1.5 Effect on the Mode of Water Supply
A change in the water sources feeding the local supply system (with particular reference to the Mombasa system) necessitates adaptation of the supply systems to the change in the supply mode.
At present, for some of the water supply providers, water is supplied to the existing system via a main feed pipeline from the regional system. The increase in the quantities of water necessitates adaptation of the local system. This will have to be done by increasing the size or by extending/adding to the main feed pipeline and/or adding branches to the distribution network as required, enabling it to provide a solution for the higher demand downstream and higher supply upstream.
The most common and well-known means of examining the most suitable alternatives in each system is by running a hydraulic simulation program that simulates flows in the various system pipelines, from the feed point to the consumers. This will allow identification of the pipelines having the highest load and requiring enlargement and/or examination with respect to development and construction of new feed lines for water supply.
7.1.6 System Operation
Revised conceptualization is required in the context of the upgraded local water supply systems with regard to operation of the networks and distribution and allocation of water to the various consumers.
The switch from intermittent to continuous supply (24/7) could necessitate additional work on operation and maintenance of the system, additional manpower for this purpose, training of the operators in troubleshooting, etc.
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7.2 Significance of the Bulk Water Supply System on the Negative Effect of Sewage Volumes
7.2.1 Increase in Generated Wastewater Quantities
Enhanced water supply to the city and consumption by urban users will, in a short time (1–2 years), lead to an increase in the quantities of wastewater generated. This increase will be phased, in accordance with the phased increase in water demand.
Initially, the increased water use will be attributed mainly to drinking and cooking – uses that produce relatively small quantities of wastewater. Once the convenience of water use is established and the level of system reliability rises, water use will spread to include washing, as a result of which the quantities of wastewater produced will increase.
In considering full use of water (domestic use for all purposes, including sanitary use) it is customary to assume that about 60–70% of the water enters the wastewater system. The part that does not end up as wastewater is assumed to be water that does not result in flows to the wastewater system. Even if a minimum contribution to wastewater is assumed in the initial years of main system development – of the order of magnitude of 10–20 lpcd – the total contribution to wastewater is expected to be thousands of cubic metres per day in small communities, to tens and hundreds of thousands of cubic metres per day in large communities, not to mention Mombasa and neighbouring towns.
7.2.2 Long-Term Planning of the Wastewater Collection System
Due attention must be given at present to the need for long-term planning of the wastewater collection system, as follows:
In the absence of a proper wastewater collection system, most of the wastewater will continue to flow to percolating pits, causing contamination of the groundwater and aquifer systems. There are already areas where the groundwater underlying urban areas is experiencing increased levels of pollution, precluding its use. The absence of wastewater collection systems creates a potential for the outbreak of diseases and epidemics in built-up areas. The lack of proper wastewater removal systems as an underlying cause of diseases and epidemics worldwide is well known. Based on the common assumption that discharge of wastewater to percolating pits in the ground is not a solution, there is an increasingly acute need for preparing and implementing a plan for collection of wastewater in parallel with the increase in use of water by the population. Collection of wastewater by means of gravity systems constitutes merely the first link in a wastewater recycling system for reuse in agriculture in Kenya.
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For this purpose it is necessary to prepare a plan that takes a holistic view of the issue of water recycling: Design and construction of gravity wastewater collection systems in the urban domain. Preparation of a general regional plan with respect to the location of wastewater treatment plants and discharge of all the wastewater to these plants. Determination of criteria and standards for recycled water quality and recognition of this water as a resource. Planning of recycled water supply systems for agriculture, ensuring congruity between the quality of the water and the end uses.
Preparation of a regional plan for collection, treatment, reclamation and reuse of wastewater in the area of jurisdiction of the Coast Province in Kenya has become a cardinal need and all the necessary resources must be directed towards this end. Failure to prepare such a plan will not only result in continued pressure on water sources and abstraction of fresh water from natural sources for agricultural use but will also cause further contamination of groundwater due to the rise in water use and increased contribution to wastewater.
Collection and treatment of wastewater serving no useful purpose in order to reuse it in agriculture will allow greater quantities of water to be made available for the agricultural sector, improve cultivation conditions for the farmers by supplying additional quantities of water that are not rainfall-dependent, and at the same time raise sanitary levels in the urban sector.
The distance between the main population centres in the area will call for preparation of a regional master plan for wastewater treatment centres and transfer points for diversion of water to the agricultural sector, including weighting of the costs of wastewater conveyance over long distances (it is not customary to pump wastewater over distances exceeding 10–12 km). On the other hand, due consideration must also be given to the number of wastewater treatment plants planned as they entail high operating costs in addition to the initial investments.
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Comment [J8]: Comment was 8. Discussion and Conclusions regarding the last paragraph: The phasing of development is not clear and this should be The coastal areas of Kenya are characterized by a limited number of suitable substantiated further. This section has been re-written water sources. Approximately six major sources can be utilized for a comprehensive program of the magnitude of the Master Plan. These are Mwache River, Baricho well field, Mzima springs, Rare River, Tana River and Njoro Kubwa springs.
Any bulk water solutions for this area for the horizon period will need to utilize at least three of these (Tana River for the northern coastal area). Therefore all of the assessed scenarios will consist of a sequential development of a combination of these sources.
Other sources such as deep groundwater may be feasible. The consultant proposes more detailed studies to verify the potential of the neogene aquifer. The CWSB jurisdiction area includes isolated rural settlements which are characterized by low population densities and low demand for water. These villages are also distant from any of the potential bulk water supply systems. The proposed solutions will be based on the development of small and local water sources.
As mentioned above, the bulk water supply will be based on several large sources.
The basic assumptions of the consultant were to select a scenario that is technically feasible, economically viable, environmentally sound and socially desirable. An option that provides diversified sources regarding both spatial origin and source type. Hence, a combination of groundwater and surface water. The consultant recommends the following development:
The proposed Mwache dam is located near to the Mombasa demand centre, has sufficient annual flows and can be utilized as a long term sustainable source. Baricho well field is already a major source for Mombasa and Malindi. Plans for its expansion (Baricho II) can augment Mwache and provide all of the water requirements for the region up and including phase II (2025).
The population projections and water demand assessments conducted by the consultant indicate that both Mwache and Baricho will be able to supply the demand until approximately 2030. Analysis of the Mzima springs indicates that it is a reliable source and has been supplying the Mombasa area since the 1950s. The suggested Mzima II project can be developed at a later stage to increase the supply by phase III.
The final Water Supply scenario for Mombasa and the other coastal towns has been designed and recommended by the consultant and then reviewed, evaluated and approved by the client (CWSB) and by the donors (WB and AFD).
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This is scenario B1 which includes the sequential and gradual development of the following segments. 1. Early expansion of Baricho that will add approximately 22,000 m3 by 2015 (through immediate investments). 2. Design, construction and operation of the Mwache dam. This will add an estimated 186,000 m3 by 2020. 3. Full expansion of Baricho to add 63,000 m3 by 2024 4. And finally development of the Mzima II source that will add approximately 105,000 m3 towards phase III horizon of the Master Plan, 2030. This Water Supply scheme has the advantages of providing a gradually increasing supply of water concurrent to the increase and spatial patterns of the regional population, its future agricultural and industrial composition and the expected expansion of economic capabilities of individuals and firms within the coastal areas. Moreover, this scheme optimizes water availability, development deadlines, financial considerations and environmental impacts.
Extensive analysis by the consultant (see table 4-2) indicates that initial development of Mwache dam is an essential precondition for the timely supply of water during phase I that will ensure the required amount at feasible costs/prices. Postponing the development of Mwache or deferring it to a later stage (say after Mzima II) may result in a gap between demand and supply towards 2020. It is the consultant's judgment that the development of Mzima as a major water supply source during phase I will result in a lengthy construction period, high investment costs, high water prices and insufficient amounts of water to cover expanding demand towards 2020. Mzima II source should and will be developed during phase III, after the final development and operation of Mwache and Baricho.
This option delivers the most efficient engineering solution while maintaining reasonable financial values and minimizing social and political obstacles. The primacy of this option is also evident from the multi criteria analysis results. Another feasible source is the Rare River. NWC&PC is currently conducting a feasibility study on this dam. This can also serve as a potential source for phase III as detailed in scenario B1.1.
The development of the LAPSSET Corridor and especially the Lamu port requires drastic increase in water demand and supply. The lead alternative for the Lamu port and surroundings is supply water from the Tana River near Garsen. Gradual development of medium size desalination plants, to meet the growing demand over the time, is also an attractive option. The expedience of desalination plants will mainly depends on the availability of electricity and its prices.
Small and medium settlements along the Tana River will be able to augment the water supply directly from the Tana River.
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Taveta Township will rely mainly on gradual development of Njoro Kubwa Springs which is located 3km from the town. It was clearly found that it will not be economically viable to connect Taveta to the bulk water supply.
Availability of deep groundwater from the neogenic aquifer is yet to be verified, hence it is the consultant opinion that further studies should be conducted prior to further development of this source. This is the reason that deep groundwater has not been used in the water balance calculations.
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