Chilenje Rural Water Supply Scheme-Design Report

WORLD VISION MALAWINKHOMA AREA DEVELOPMENT PROGRAMMETuesday, January 07, 2014CHILENJE RURAL PIPED WATER SCHEMEVOLUME 1DESIGN REPORTSubmitted for Registration withMALAWI BOARD OF ENGINEERSAUTHOR: WELTON EDDIE MTONGA

CHILENJE RURAL PIPED WATER SCHEME

DECLARATION BY THE CANDIDATE

I, the undersigned declare that I personally carried out the design of Chilenje Water Supply Scheme and that the work contained in this report for registration with the Malawi Board of Engineers is my own work._______________________

W. E. Mtonga

(GRADUATE ENGINEER)

Tuesday, January 07, 2014CERTIFICATION BY THE SUPERVISOR

I, the undersigned certify that I have read the professional report for registration with the Malawi Board of Engineers and hereby recommend for acceptance by the Malawi Board of Engineers, in partial fulfillment of the requirements of the professional registration with the Malawi Board of Engineers._______________________

Eng. B.B. Nkhoma

(SELECTED REGISTERED ENGINEER)

Date: July, 2014EXECUTIVE SUMMARY

World Vision Malawi through Nkhoma Area Development Programme is providing water to rural communities in the area where it renders its services and ensures that people have convenient access to water in sufficient quantity and adequate quality for basic use. In view of the above objective, World Vision Malawi planned to upgrade and extend a small existing scheme with intakes arising from spring capping structures in Ngala Hills in Lilongwe District. This scheme was previously implemented by Africare. Africare is no longer operating in the area at the moment.

Field investigations revealed that the springs had sufficient flows especially if the design was in an augmented arrangement. In October 2011 very few communities located along the foot of the mountain benefited from the scheme.

Flow observations coupled with the terrain of the area indicated that the scheme can be extended to benefit more people living in the Chilenje Plain. Chilenje is part of the area where World Vision Malawis Nkhoma Area Development Programme offers its services. This influenced World Vision to engage an engineer to provide consultancy services to carry out detailed analysis and design of the scheme. The main tasks of the Engineer were to confirm the previously identified potential of the flows, to assess the possibility of extending the scheme and to design all the components of scheme so that the people living in the technically feasible area can benefit from it.

Project Objectives

The main objective of the project was to carry out hydraulic analysis for all extension lines of the scheme and to design the entire infrastructure necessary for the transmission of water to the beneficiaries.

The scope of works was as follows:-a) To take an inventory of what was in the field in October 2011.b) To assess the functionality of the existing infrastructure and their conformity to design standards.c) To make recommendations on whether the existing infrastructure could still be incorporated in the new design to ensure that the scheme performs to its intended design capacity.d) To conduct demographic survey to establish the baseline number of beneficiaries and to determine the levels of service for the scheme over the design period.e) To conduct detailed topographic survey for the intended water supply system including distribution networks.f) To conduct detailed engineering design of the entire scheme.g) To compile drawings for the designed scheme.h) To compile bills of quantities including engineers estimates for the designed scheme.i) To provide specifications for the schemeProject Findings

The project analysis revealed that it is possible to extend the scheme southwards to supply more areas under Group Village Headmen Chauwa and Gwenembe. The source had a collective discharge capacity of 5.2l/s which is adequate to accommodate the demand for the target villages over a design period of 20 years.

Conclusions and RecommendationsField investigations revealed that it is possible to upgrade Chilenje Rural Piped Water Scheme and extend it to reach more people residing in the Lithipe River Valley. This conclusion led to detailed design for upgrading and extension.

The following recommendations were proposed:- In view of the growing population against a constant yield from the springs, all the available waters should be trapped using the same technology. Two additional spring capping structures were proposed to augment the existing supply. There was an additional spring that showed potential of yielding 1.2l/s at the time of field investigations and this flow was considered reasonable for augmenting the scheme. It was therefore recommended to tap this spring as well. Since the upper area was already supplied from other springs or from alternative sources no storage tank was proposed for that spring. All the water was expected to flow directly to the proposed common tank. Field interviews with the community revealed that most communities were previously living close to the hill. As a result the upper area was encroached and cultivation was still observed at the time of field investigations. It was therefore recommended that cultivation in the area should be stopped and the communities should engage in preserving the catchment area. It was recommended to lay 75mm Galvanized Steel (GS) pipes between Spring Capping 1 and the common storage tank and between Spring Capping 2 and the common storage tank. It was recommended to install 50m Galvanized Steel (GS) pipes from Spring Capping 3 and 4 to the proposed common storage tank. It was recommended to construct a reinforced concrete storage tank of 119m3 in volume. The storage tank was expected to serve as a sedimentation tank as well. The dimensions of the proposed tank were specified to be 8.9mx7.4mx2m. To allow continuous circulation of water, the tank was specified to be baffled with reinforced concrete walls. It was recommended to lay class 10 pipes throughout the scheme except in gully crossings and community connections. This was done to ensure that the communities do not make mistakes in sourcing pipes of different classes during maintenance. It was recommended to install end caps at the end of each main line to allow for minor extensions in future.

Acknowledgement

I would like to accord special thanks to the staff of World Vision International that worked tirelessly and contributed to the development of this report. Special thanks are also extended to Mr Peter Matipwiri, Water and Infrastructure Manager for his support during and after field visit. I would like to thank field staff for their support and providing population head counts for the area.

I would like to thank Eng. B.B. Nkhoma , my supervisor for his guidance in the development of this report. His contribution is highly commended.

Acronyms and Abbreviations

ADPArea Development ProgramCBMCommunity Based ManagementCWPCommunal Water PointCDACommunity Development AssistantsGSGalvanized SteelGVHGroup Village HeadmanHDPEHigh Density Polyethylene ToRTerms of ReferenceVHVillage HeadmanVDC Village Development CommitteeVHWCVillage Health and Water CommitteePVCPolyvinyl ChlorideWMAWater Monitoring AssistantWPWater Point WPCWater Point Committee

Foreword

This report is one of the four documents that were produced in partial fulfillment for the requirements for registration with Malawi Board of Engineers. The brief outline of all the documents is indicated below.1) Volume 1Design Report2) Volume 2Bills of Quantities3) Volume 3Drawings4) Volume 4Specifications

The Design Report gives design information. The Bills of quantities give an outline of quantities of works taken off from the drawings according to standard methods of measurements. The drawings specify the dimensions of the structures while Specifications indicate the standards of performance in the execution of works.

Table of Contents

DECLARATION BY THE CANDIDATEiiCERTIFICATION BY THE SUPERVISORiiEXECUTIVE SUMMARYiiiProject ObjectivesiiiProject FindingsivConclusions and RecommendationsivAcknowledgementviAcronyms and AbbreviationsviiForewordviiiTable of ContentsixList of FiguresxiiCHAPTER ONE PROJECT BACKGROUND11.1Introduction11.2Intakes Location21.3Sources of Information31.4Purpose of the Report41.5Structure of the Report4CHAPTER TWO GENERAL DESCRIPTION OF PROJECT AREA52.1Introduction52.1.1Topography of the area62.1.2Weather62.1.3Political Boundaries72.2Benefiting Villages in 201172.3Benefiting Population in 201172.4Access to the Area82.5Socio-economic Activities92.6Infrastructure92.7Sources of Drinking Water in 201192.8Drinking Water Related Problems in 2011102.9Proposed Solution10CHAPTER THREEDESIGN CONSIDERATIONS123.1Introduction123.2Water Quality Considerations123.2.1Water Quality Criteria123.2.2Field Observations123.3Water Quantity Considerations133.4Basic Design Criteria143.4.1Per Capita Demand143.4.2Design Period143.4.3Design Flow at the tap143.4.4Night Storage Factor143.4.5Peak Factor143.4.6Number of Persons per tap143.4.7Maximum Walking Distance143.4.8Level of Service143.4.9Population Growth Rate153.4.10Roughness factor for PVC153.4.11Residential Head153.4.12Flow Velocities in pipes153.5Population in 2011153.6Water Demand in 2011183.7Water Supply (Quantity)183.7.1Supply Criteria183.7.2Field Observations183.8Population Growth Rate193.8.1Assumptions on Growth Rate193.9Population Projection and Projected Water Demand19CHAPTER FOUR FIELD SURVEY214.1General Reconnaissance of the Area214.2Detailed Survey work214.3Key Points based on Survey Work214.3.1Distribution Line to Chauwa Primary School234.3.1Distribution Line to Gwenembe Village23CHAPTER FIVE DETAILED DESIGN OF SCHEME COMPONENTS255.1Introduction255.2Design Criteria255.3Design Population255.4Water demand calculations275.5Design of Transmission Lines285.5.1Design Criteria285.6Review for the Design of storage tanks and Spring Capping Structures305.6.1Design Criteria for the Intake Structure315.7Design of Service Reservoir/Sedimentation Tank335.7.1Design Criteria335.7.2Tank Location335.7.3Tank Volume345.7.3.1Case 1: Sedimentation Tank345.7.3.2Case 2: Storage Tank365.7.4Tank Dimensioning385.7.5General Arrangement of the Tank395.7.6Tank Site Conditions395.7.7Structural Design of the Tank395.7.7.1Design Assumptions and Conditions395.7.7.2Top Slab405.7.7.3Concrete Wall405.7.7.4Raft Concrete Base405.7.7.5Design Standards and Codes415.8Design of Distribution Lines415.8.1Design Criteria415.8.2Alignment of Pipelines425.8.3Pipe Materials435.8.4Hydraulic Design of Pipelines435.8.5Hydraulic Design of the Distribution Line between the Storage Tank and Chauwa Primary School455.8.6Hydraulic Design of the Distribution Line between the Storage Tank and Gwenembe465.8.7Design of Small branches to the Communities465.7.9Hydraulic Design of Branch Line to Mkhalala475.8Relocated Villages475.9Profiles485.10Tap Locations495.11Valves and Fittings495.12Thrust Blocks505.13Aprons, Washing Slabs and Drainage50CHAPTER SIXCONCLUSION AND RECOMMENDATIONS516.1Introduction516.2Conclusion516.3Recommendations51APPENDICES53References59

List of Figures

Figure 1: Aerial view of the area where springs are located3Figure 2: Aerial view of the project supply area6Figure 3: Chilenje Project Area8Figure 4: Borehole in use in the project area9Figure 5: Schematic Arrangement for the project(not to scale)24Figure 6: Shallow well with Elephant Pump26Figure 7: Side view of Storage Tank31Figure 8: Top view of Storage Tank32Figure 9: Spring Capping Structure32Figure 10: Position of the storage tank34Figure 11: Project area indicating communities close to hills and Linthipe River but empty in between48

List of TablesTable 1: Villages that utilized taps from springs in 20117Table 2: Water Quality Results13Table 3: Villages in the upper part of GVH Chauwa.16Table 4: Villages in the Lower part of GVH Chauwa17Table 5: Villages in the upper part of GVH Madzumbi17Table 6:Villages located in the lower part of GVH Madzumbi18Table 7: Yields of springs19Table 8: Target Population27Table 9: Water Demand Calculations based on projected Population27Table 10: Water Demand based on number of taps28Table 11: Balancing Requirements for the tank37Table 12: Required flow (l/s) for respective No of Taps42Table 13: C values for pipe materials44

Chilenje Rural Water Supply Scheme-Design Report2014

Chilenje Rural Water Supply Scheme-Design Report2014

Welton Eddie Mtonga Page 57

Welton Eddie Mtonga Page vi

CHAPTER ONEPROJECT BACKGROUND1.1Introduction

World Vision Malawi through Nkhoma Area Development Programme is providing water to rural communities in the area where it renders its services and ensures that people have convenient access to water in sufficient quantity and adequate quality for basic use. In view of the above objective World Vision Malawi planned to upgrade and extend a small existing scheme with intakes arising from spring capping structures in Ngala Hills in Lilongwe District. This scheme was originally implemented by Africare. However, Africare is no longer operating in the area at the moment.

Field investigations revealed that the springs had sufficient flows especially if the design was in an augmented arrangement. In October 2011 very few communities located along the foot of the mountain benefited from the scheme.

Flow observations coupled with the terrain of the area indicated that the scheme could be extended to benefit more people living in the Chilenje Plain. Chilenje is part of the area where World Vision Malawis Nkhoma Area Development Programme provides its services. This influenced World Vision to engage an engineer to provide consultancy services to carry out detailed analysis and design of the scheme. The main tasks of the Engineer were to confirm the previously identified potential of the flows, to assess the possibility of extending the scheme and to design all the components of scheme so that the people living in the technically feasible area could benefit from it.

The scope of works included the following:-a) To take an inventory of what was in the field in October 2011.b) To assess the functionality of the existing infrastructure and their conformity to design standards.c) To make recommendations on whether the existing infrastructure could still be incorporated in the new design to ensure that the scheme performs to its intended design capacity.d) To conduct demographic survey to establish the baseline number of beneficiaries and to determine the levels of service for the scheme over the design period.e) To conduct detailed topographic survey for the intended water supply system including distribution networks.f) To conduct detailed engineering design of the entire scheme.g) To compile drawings for the designed scheme.h) To compile bills of quantities including engineers estimates for the designed scheme.i) To provide specifications for the scheme1.2Intakes Location

Chilenje Gravity Fed Water Supply scheme was a proposed upgrading and extension to the existing small schemes arising from springs on the southern side of Ngamba hills. Field investigations revealed that there were five (5No) springs. Four springs had brick wall storage tanks, one for each spring. At the time of carrying out field investigations the fifth spring had not been developed yet. The developed springs supplied few communities located close to them. Figure 1 below shows the aerial view of the area where springs are located.

Area for springsFigure 1: Aerial view of the area where springs are located1.3Sources of Information

In order to successfully carry out the assignment, the following information was utilized;-a) Topographic maps of the area with scale 1:50,000 produced by the Department of Surveys.b) Aerial photographs from Google earthc) Population figures from National statistical office and head count by World vision Malawi.d) Related development information of the project area was sourced from World Vision Malawi and field observations.e) Hydrological data was collected by World Vision Malawi and confirmed through field measurements.f) Water quality testing was carried out in the laboratory at Lilongwe Water Board and the results were utilized in the report.g) Reference Literature

1.4Purpose of the Report

The purpose of the report include summarizing the findings in the field investigations and detailed design of the facilities necessary for upgrading and extension of Chilenje Rural Piped Water Scheme. It also includes Design Calculations for Hydraulic Analysis and Structural Design of the storage tank.1.5Structure of the Report

The report is divided into six chapters. Chapter one is introduction which gives the background of the project, its location, purpose of the report and structure of the report. Chapter two gives the general description of the project area. Chapter three gives design considerations. Chapter four gives details of field survey. Chapter five gives detailed design information and finally Chapter six gives conclusion and recommendations.

CHAPTER TWOGENERAL DESCRIPTION OF PROJECT AREA

2.1Introduction

Chilenje Gravity Fed Water supply Scheme is located in Traditional Authority Mazengera in Lilongwe District. The service area covers the escarpments on the southern side of Ngamba Hills extending down all the way to the Valley of Linthipe River. The area is located between easting 844200 and 844450 and between northing 617000 and 620500. In terms of area the scheme covers approximately six square kilometres. Figure 2 below shows an aerial view of the area.

The supply area falls within the Linthipe Valley that is commonly referred to as Chilenje. According to field investigations the supply area was limited by the combined capacity of the spring discharges and the topography of the area since water conveyance was designed to be through gravitational potential energy.

The scheme was designed to allow water to be flowing in the southward direction targeting some of the villages under Group Village Headman Madzumbi and others under Group Village Headman Chauwa including Chauwa Primary School.

Figure 2: Aerial view of the project supply area

2.1.1Topography of the area

The average altitude ranges between 900m and 1000m above sea level. However, there are some hills which rise as high as 1400m above sea level.

The Supply area is located to the south of Ngamba Hills. In figure 2 above the area is covered under the blue line. The area has a mild slope southwards and towards Linthipe River with another slope eastwards, following the direction of flow for Linthipe River.

2.1.2Weather

The area is cool with average temperatures ranging from 180 C to 210 C. Average annual rainfall ranges between 900mm and 1000mm.

The rainy season runs from December to April while the dry season runs from May to November with some months shared between the rainy season and the dry season. Minimum flows are observed in the months of October and November.

2.1.3Political Boundaries

The scheme is in Traditional Authority Mazengera and particularly in Group Village Headmen Chauwa and Madzumbi. The location of the scheme is such that it does not cross the boundaries of these two group village headmen.2.2Benefiting Villages in 2011

Table 1 below shows a list of villages that utilized taps from the developed springs in 2011.

NoGVH MADZUMBIGVH CHAUWA

1KhokoMyowe

2NdindiGalanga 1

3KulandiraGalanga 2

4ChimwenjeZukutu 1

5NkhonoZukutu 2

6Kuntheta

7Andevu

8Kuselikwambiya

Table 1: Villages that utilized taps from springs in 20112.3Benefiting Population in 2011

Not all the people living in the villages listed above were connected to the scheme due to limitations in topographic location. Some people used alternative sources such as boreholes and shallow wells. The connected people were about 750. The connections were through communal water points. There were 6 communal water points and an additional water point that served a maize mill.

Figure 3 below shows a scanned topographic map of the project area indicating the Linthipe Valley relative to Ngamba Hills.

Proposed GwenembeLineProposed Chauwa LineProposed Sedimentation/Storage TankSpringsFigure 3: Chilenje Project Area2.4Access to the AreaThe area can be accessed using a gravel road that passes through Kaundama Primary School from M1 to Nkhoma Mission. Just before Nkhoma Mission there are two small roads leading into the area. One road runs through the edge of the hills while the other runs closer to Linthipe River through to Chauwa Primary School. There are also some interlinks between the upper road and the lower road. Alternatively one can use a tarmac road from Kamphata on M1 to Nkhoma Mission and then connect to the area through Madetsa Village.2.5Socio-economic ActivitiesChilenje is generally an agricultural area with most people engaged in subsistence farming. Maize is a staple food crop. Other crops include groundnuts, beans, sugarcanes, vegetables etc. They also rare animals like cattle, goats, chickens, pigeons etc. 2.6InfrastructureThe major infrastructures in the area include gravel roads, school blocks, play grounds, churches and water points like shallow wells and boreholes 2.7Sources of Drinking Water in 2011

In 2011 the residents of the area sourced water from unprotected shallow wells, protected shallow wells that used elephant pumps, Linthipe River and some boreholes. The people who lived along the foot of Ngamba Hills used taps from the springs. Figure 4 below shows one of the water sources in the area.

Figure 4: Borehole in use in the project area

2.8Drinking Water Related Problems in 2011

The major problem was that the residents of the lower areas close to Linthipe River did not have access to sustainable adequate supply of safe water. Field observations revealed that water from the Linthipe River required treatment facilities to make it potable. There was also need to install high lift pumps to pump water to the target areas. These facilities demand high levels of capital investments. The other option was to drill a number of boreholes to supply the target areas. There were already some few boreholes in the area but some of them were not functioning due to drying up. Generally boreholes need to be separated by an adequate margin because rapid draw-down in one borehole affects the water level in the other if they share the same aquifer. This paused to be a challenge as well. Finally the hydrogeology of the area makes some boreholes produce salty water which is not palatable. Interviews with the community revealed that some residents were not comfortable with the water. They therefore resorted to be drawing unsafe raw water from Linthipe River.2.9Proposed Solution

From the studies conducted, the feasible option was to tap excess water from the existing springs and gravitate it to the target areas. It was further observed that the springs that had not been developed could also be tapped to augment the existing supply. It was therefore proposed that water from all the springs should be transmitted to a common storage tank that would also act as a sedimentation tank. The outline of the scheme was as follows;-1) Five (5No) Spring Capping Structures.2) Five (5No) transmission lines to a common reservoir.3) Existing storage tanks for individual springs were to be maintained in the scheme but control of their operations was proposed through introduction of new outlets and valves.4) Common storage/sedimentation tank was proposed at reduced level 1219.2m above sea level.5) One (1 No) Distribution main to Chauwa was proposed with a branch to Mkhalala Village.6) One (1 No) Distribution main to Gwenembe.

CHAPTER THREEDESIGN CONSIDERATIONS3.1IntroductionThe proposed solution outlined in 2.9 provided the basis for the design of the scheme. According to the design, the existing lines that supplied water to 7No taps including the one at the maize mill were not supposed to be disturbed. As such the new design concentrated on the structures that facilitated upgrading and extension to the target villages3.2Water Quality ConsiderationsWater quality is very critical in the design of water supply systems. There are many organisms that cause diseases and disorders when consumed through water. However, not all of them can be tested individually due to tedious procedures and number of samples required. As a result only few indicators were tested and monitored in the pre-design phase whose data guided in the determination and design of treatment facilities.

3.2.1Water Quality Criteria

Chilenje Rural Piped Water Scheme was designed to supply drinking water only. The water quality criteria were therefore focused on drinking water quality standards for rural areas in Malawi.

3.2.2Field Observations

As indicated in the introductory passages, Chilenje Water Supply Scheme was already operational in the areas close to the hills in 2011. The existing set up was that there were small storage tanks that also acted as sedimentation tanks.

Samples were taken from taps at random and were taken to the laboratory at Lilongwe Water Board. In order to assess the treatability of water, some chlorine was injected into the existing system and residuals were monitored at strategic points of the existing system. Table 2 below shows the parameters that were analyzed, unit of measurement, test results and acceptable range.

Table 2: Water Quality ResultsThe results revealed that water was not contaminated and hence no complicated treatment facilities were required. A simple tank that acts as balancing tank for water demand and also as a sedimentation tank was adequate. The only change required to the existing facilities design was reservoir sizing to accommodate the projected demand in 2031

3.3Water Quantity Considerations

The scheme has to have enough water to meet the demand from existing consumers as well as that from proposed new consumers. Both demands will grow to maximum limit over the design period. The growth in demand is generated from the growing population that will be utilizing the water from the scheme.3.4Basic Design Criteria3.4.1Per Capita DemandThe scheme was designed for a per capita demand of 36lcd.3.4.2Design PeriodAccording to terms of reference the design period was 20 years commencing in 2011. This means that the scheme has been designed for parameters for the end of 2031.3.4.3Design Flow at the tapThe scheme was been designed for a 16 hour design flow. This means that the design flow at the tap was 0.075l/s.3.4.4Night Storage FactorIn this scheme the service time was assumed to be between 4.00am and 8.00pm translating into 16hours service.

3.4.5Peak Factor

The peak factor for a line with one tap was 2 while the peak factor for a line with more than or equal to 10 taps was 1.3.4.6Number of Persons per tapIn this scheme each tap was anticipated to have a maximum of 120 persons drawing the water from it or being served.3.4.7Maximum Walking Distance

According to the Malawi Government Guidelines each consumer should walk not more than 500m to draw water. The same was adopted for this scheme.3.4.8Level of Service

The scheme was designed to provide water to public taps or communal water points and not for individual connections inside dwelling houses.3.4.9Population Growth Rate

According to information sourced from National Statistical Office, Nkhoma Area had a population growth rate of 2.5% per annum.3.4.10Roughness factor for PVC

For the application of Colebrook White formula PVC pipes have a roughness factor of 0.01mm. For Hazen Williamss formula PVC pipes have a C value of 145. These were adopted in the design of this scheme.3.4.11Residential Head

The scheme was designed for an ideal head of between 5m and 10m at the tap. However, heads between 10m and 15m were also acceptable.

3.4.12Flow Velocities in pipes

In the design of this scheme flow velocity was limited to values between 0.5m/s and 2.5m/s for the transmission and distribution lines. In special circumstances velocities of up to 3m/s were also acceptable.3.5Population in 2011

According to Nkhoma Area Development Area Project Design Report (World Vision Malawi), the target population comprised 4,155 people in 2011. This population was basically made up of indigenous people of the area. There were no records of migration or emigration. This data was based on Population and Housing Census 2008 Main Report and Analytical Report Volume 7(National Statistical Office 2009). There was also head count carried out by World Vision Malawi.

According to the design the target population was located in the areas with altitude lower than the altitude of the source. Administratively there were two group village headmen sharing the supply area. These are GVH Chauwa and GVH Madzumbi. Each GVH had a number of villages. The spatial distribution of these villages was that some were located along the foot of Ngamba Hills while others were located in the Linthipe Valley. There were 1045 people under GVH Chauwa that were living in the foot of Ngamba Hills in 2011. Table 3 below shows 8No villages located in the upper part of Chauwa that had the potential to utilize taps from springs. Note that some of these people already had the service from 4No existing taps. Further to the villages under GVH Chauwa there were 6No villages with a total population of 810 people under Madzumbi within the same belt that had the potential of utilizing the water from the scheme. Amongst these people some already had the service from 3No taps.

Table 3: Villages in the upper part of GVH Chauwa.The table shows that there were 1045 people in 2011.

Table 4 below indicates the villages located in Chilenje Valley but under GVH Chuwa

Table 4: Villages in the Lower part of GVH ChauwaThe table indicates that there were 1000 people in 2011. A combination of data in table 3 and table 4 gives the total population under GVH Chauwa that had the potential of benefiting from the project. The population was 2,045 people.

Table 5 below indicates the villages located in the upper part of GVH Madzumbi that were utilizing taps from springs in 2011. There was a total population of 810 people in the area.

Table 5: Villages in the upper part of GVH Madzumbi

Table 7 below shows the villages under GVH Madzumbi located in the Chilenje Valley close to Linthipe River.

Table 6:Villages located in the lower part of GVH Madzumbi

By combining the data from all the tables, it is noted that there was a total population of 4155 people in 2011.3.6Water Demand in 2011

Using the per capita demand of 36lpcd the above population translates to a total water demand of =1.73l/s in 2011. 3.7Water Supply (Quantity)

3.7.1Supply Criteria

Chilenje Rural Piped Water Scheme was designed to ensure adequate of water throughout the design period of 20 years.

3.7.2Field Observations

Flow measurements were taken at the outlets of all the springs. Table 7 below indicates the flows that were observed from the five springs that had potential for development.Field Observations on flows

Spring NoTime to fill 20l BucketsDischarge Rate (l/s)

1141.43

2102.0

3400.5

4210.95

5630.32

Total5.20

Table 7: Yields of springs

From the supply point of view, it was observed that there was plenty of water for meeting future demand. It was also noted that some of the houses within the list of villages outlined above are restrained from relying on the scheme due to topographic location and distance to the nearest tap.

3.8Population Growth Rate

As indicated in 3.4.9 the information from Population and Housing Census of 2008, Main Report by National Statistical Office indicated that the population in the project area was growing at the rate of 2.5% per annum by 2011.

3.8.1Assumptions on Growth Rate

The socio-economic activities of the area were assumed that they would remain constant throughout the design period as such population growth rate was also been assumed to remain constant throughout the design period3.9Population Projection and Projected Water Demand

Generally, population growth in rural areas follows a geometric trend due to availability of land and other resources that sustain human activities. Chilenje is rural as well. Geometric increase in population is given by the following formula;-where

Po=Initial population in 2011r =Growth rate in percentagen =number of years in the projection periodIn 20 years time the population of Chilenje was projected to grow to 4,155x (1+2.5%)20 =6,808 people by 2031. This population translated to a water demand of =2.84l/s by the end of the design period.

It was noted that this demand level was still far much less than the supply of 5.2l/s. Even if the scheme was extended as required, it would supply enough water up to the design period. 30% of unaccounted for water was added to the demand and the ultimate figure was 3.69l/s. It was observed that the figure was still very safe compared to the supply of 5.2l/s.

CHAPTER FOURFIELD SURVEY4.1General Reconnaissance of the Area

Generally most of area is flat as it lies in the Valley of Linthipe River even though some communities live on the edge of Ngamba Hills. The word Chilenje is vernacular and it means flat land of the valley. Some parts are swampy. The general land use is for crop cultivation as described in 2.5 above.

The area is rural. There are no telephone lines. There are no sewer lines. There are no electricity lines. In this regard the construction of this scheme was considered not to impinge on the provision of other services.

In some parts the area has gullies which may hinder movement or installation of pipelines. There are some gravel roads and foot paths. These were considered to be possible routes for pipe alignment.

The areas close to the hills are rocky. Rock blasting was considered to be necessary for possible pipeline installation. Diversion of the pipeline was considered to be an alternative.

4.2Detailed Survey work

Topographic survey was carried out using a Dumpy Level and staff. Control points were established within close proximity of the project area. A hand-held GPS was utilized to establish the coordinates of control points and for tracing way points. Before taking readings on the Dump Level, the machine was set firmly on the ground after establishing visibility of the staff.

Booking was recorded on an especially designed table. Data and the calculations are indicated in the appendices.

4.3Key Points based on Survey Work

The approximate reduced levels for the proposed intakes and the existing spring capping sites were at 1250m, 1245m, 1247m, 1252m, and 1254m respectively above sea level for each.

The reduced level for the proposed storage/sedimentation tank was approximately at 1219.00m above sea level.

The distances from the existing storage tanks to the proposed storage tank vary significantly. Naming spring capping sites with numbers from west to east, the arrangement was as follows:-i. Spring Capping 1 was located to the far west. The estimated distance from the storage tank for this spring to the proposed common storage tank was 500m. It was proposed to construct an additional spring capping at this site to ensure that all the water from this source was directed towards the common storage tank. There was untapped water flowing by the side of this spring. This water was used for irrigating vegetables nearby.ii. Spring capping 2 was located near Spring Capping 1 but to the eastern side. The estimated distance from this spring to the proposed common tank was about 450m. There were two spring capping structures which were poorly located. As a result flows from the two structures were inadequate. One capping structure was observed to have very small quantity of water that was stagnant and muddy. However, it was noted that there was a point nearby that had flows of at least 2l/s. It was observed that this point could be capped and the flows would rise significantly. It was therefore proposed that a capping structure should be constructed at this point.iii. Spring Capping 3 was not developed by 2011 but was proposed for development to augment the supply at the proposed storage tank. There was no need for a separate storage tank for this spring. The distance from the proposed spring capping to the proposed common storage tank was about 400m.iv. Spring Capping 4 was located to the east of Spring Capping 3 but to the west of Spring Capping 5. The distance from the existing storage tank for this spring to the proposed common storage tank was about 500m. It was proposed to develop an additional spring capping for this site. There was some water flowing below Nkuyu tree located about 10m away from the existing spring capping structure.v. Spring Capping 5 was located to the east of Spring Capping 4. The distance from the storage tank for this spring to the proposed common tank was about 900m.

4.3.1Distribution Line to Chauwa Primary School

Two distribution lines were proposed from the common storage tank. One line was designed to go to Chauwa Primary School and a nearby village. At the time of designing this scheme the nearby village was the headquarters of GVH Chauwa. The line was designed from chinage 0+00 at the proposed common tank site to chainage 1+600 at Chauwa. Reduced levels varied from 1219.20 m above sea level at the proposed common tank down to 1199.471m above sea level at the end of the line. Static head at the end of the line was 43.303m. This line was designed to have a branch to Mkhalala Village. The branch was located at chainage 0+960m and at reduced level 1180.73m. At the end of the branch the chainage was 1+240m while the reduced level was 1173m above sea level. Static head at the end of the branch was 45.739m.

4.3.1Distribution Line to Gwenembe Village

The second line was designed to go to Gwenembe Village. According to the design, the alignment for this line crossed a gully, and then it passed through Dimba gardens close to Njovu Village before approaching Gwenembe Village. It was 2.94 km. Fig 5 below shows the schematic arrangement for the scheme. In the schematic diagram the line to Gwenembe is in the north-eastern direction.

S. TankSpringsGwenembe LineLine to ChauwaLinthipe RiverFigure 5: Schematic Arrangement for the project(not to scale)In this schematic arrangement dots represent concentration of houses. During desk study all the concentrations were allocated communal water points. However, this map is a bit old and outdated in the sense that some communities that appear on the map were not available on the ground. Field observations revealed that other communities that were noted on the ground were not seen on the map. This was treated to be a sign of relocation.

CHAPTER FIVEDETAILED DESIGN OF SCHEME COMPONENTS

5.1Introduction

This chapter looks at detailed design of the individual components of the scheme except those that were considered to function without disturbance in the upgrading and extension. The components that were considered in this chapter comprised the following;-a) 1No Spring Capping Structureb) 5No Transmission linesc) 1No Storage tank which should also serve as a sedimentation tank.d) 2No Distribution lines with their branches.e) Locating Taps and their demands5.2Design CriteriaThe general design criteria outlined in chapter three still applied in this chapter. However, each component had its own design criteria based on the principles that were supposed to be satisfied. At each stage a particular component was under design, specific design criteria applicable to that component were considered in depth.

5.3Design Population

The population in 2011 was based on the data collected by World Vision in the target villages. According to Nkhoma Area Development Programme, Project Design Report,(World Vision Malawi) this data was collected in March 2011.The data was synthesized using information contained in Population and Housing Census 2008, Main Report (National Statistical Office).

It was noted that the target villages for the components in this chapter were located in the lower areas. The villages located along the foot of Ngamba Hills were already supplied using either the existing taps from the springs or from alternative sources such as shallow wells that use elephant pumps or boreholes.

Figure 6 below shows a shallow well with an Elephant Pump providing water to residents along the foot of Ngamba Hills.

Figure 6: Shallow well with Elephant Pump

It was observed that villages located in upper areas but far away from the hills could not access water from this scheme due to their topographic locations and hence were not considered for design purposes of the proposed improvements. However, villages that use existing taps were accounted for in evaluating adequacy of flows from the springs in chapter three.

The design population in 2011 for these components was 2,300 people i.e. a combination of the new target population from GVH Chauwa and the new target population from GVH Madzumbi.

Table 8 below shows the villages and their respective 2011 population. Design population was derived by projecting the 2011 population over the design horizon using the existing growth rates. In this case the population was projected to 2031 using 20yrs as design period.

As explained in section 3.9, population growth in rural areas follows a geometric trend due to availability of land and other resources that sustain human activities. Geometric increase in population is given by the following formula which has already been described above;-where

Po=Initial populationr =Growth rate in percentagen =number of years in the projection period

Group VillageCurrent populationGroth RatePopulation in 20yrs

Madzumbi13002.5%2130

Chauwa10002.5%1639

Total2,3003,769

Table 8: Target Population5.4Water demand calculations

(a) Water demand calculations based on projected population

Table 9 below shows the calculations and the parameters involved. A per capita demand of 36l per day was adopted in this calculation

YearEstimated populationPer capita per day consumption in litresDaily water demand m/d

Flow rate required l/s

20112300365.1751.4375

20212944366.6241.84

20313769368.482.356

Table 9: Water Demand Calculations based on projected PopulationIt was noted that a total demand of 2.356l/s will be required by 2031.

(b) Water demand based on taps in the schemeThe major difference from the first approach is that a parameter related to distance walked to access water was incorporated. According to guidelines provided by the Malawi Government an individual should not walk more than 500m to access safe water as indicated in section 3.4.7. Additional taps were therefore provided in a locality even if the number of people per tap was less than 120 people. Where the number of people exceeded 120 an additional tap is provided also.

Table 10 below shows the calculations and the parameters involved.

Table 10: Water Demand based on number of tapsIt was observed that the required flow rate in 2031 would be 3.1l/s

5.5Design of Transmission Lines

5.5.1Design Criteria

The transmission lines were designed for constant flow rate from either the existing tanks or from the proposed springs to the common storage tank. They were designed for 24hour flow since they were to operate 24hours continuously.

The transmission lines were designed to be as straight and as short as possible to reduce frictional losses. However, minor diversions were allowed for due to presence of rocks and other obstacles in the area.

Transmission lines were designed to carry uniform flows.

The structure of the scheme was arranged in such a manner that five small transmission mains from springs lead to a common reservoir. The summation of flows from all the springs must add up to two thirds of 3.1l/s at the reservoir which was equal to 2.067l/s.

The limiting factor was the yield of each spring and the requirements from the population already under service i.e. demand from the villages already being supplied by each spring. The transmission lines were therefore designed to ensure that only excess water over and above the existing design demand would be taken to the common storage tank. For the newly proposed springs all the available yield was available for new demand downstream. The diameter of the transmission lines was determined by applying the Colebrook White Equation adopted from Sharme et al.

The two equations are the same only that there is rearrangement to make the required item subject. The following are the descriptions of parameters in the equations;- Q=flow either in m3/s or l/s. D=pipe diameter in m or in mm G=acceleration due to gravity =9.81 H1=Height of the initial position in m above a datum H2=Height of the second point of consideration in m above datum. L=length of pipe under consideration. Ln = natural logarithm e =average roughness of pipe material in mm =viscosity of water at a given temperature.Application of the above yielded the following results;-a) Transmission Line No1-75mm of Galvanized Steel pipeb) Transmission Line No2-75mm of Galvanized Steel pipec) Transmission Line No3-75mm of Galvanized Steel piped) Transmission Line No4-50mm of Galvanized Steel pipee) Transmission Line No 5-50mm of Galvanized Steel pipeIn addition to manual calculations, a software Civil Calculator was used to compute the required pipe diameter as shown in the results.

5.6Review for the Design of storage tanks and Spring Capping Structures

Field observations revealed that the storage tanks were stable. There were no visible cracks. There was no excessive or differential settlement. Figures 7 and 8 show how one of the storage tanks looked like from the side and from the top respectively. In like manner the spring capping structures were also stable. Figure 9 below shows how one of the spring-capping structures looked like from side view. All structures were intact. Interviews with the community revealed that there had not been any problem since the time they were commissioned. They only needed cleaning to remove some dirt that accumulated on the floor due to sedimentation process.

The design life for these types of structures is usually above 30 years. It was therefore assumed that these structures would be stable throughout the design horizon of 20 years. Therefore the proposed improvements would utilize these structures without any modification.

For new springs the same technological design for spring capping structure as shown in figure 9 was adopted. It was in brickwork with some rocks fitted in such a way that there was no disturbance to water discharge that was finally being collected by a pipe underneath downstream.5.6.1Design Criteria for the Intake Structure

The spring intake structure was designed to ensure free flow of the water but at the same time securely protecting it. A wall extending a little above the maximum level to which the water rises under static conditions should surround the seepage area. The seepage area was designed to be filled with stones with enough pore space to allow free flow of water. The lower area was designed to be cleared to create a pool where water could collect and get tapped using a strained ended pipe. A V notch was added for flow measurements.

Figure 7: Side view of Storage Tank

Figure 8: Top view of Storage Tank

Figure 9: Spring Capping Structure

5.7Design of Service Reservoir/Sedimentation Tank

5.7.1Design Criteria

This tank was designed to serve the following purposed amongst others;-i. To balance the fluctuating demands from the distribution system permitting the source to give a steady or different phased output.ii. To give suitable pressure for the distribution system and reduce pressure fluctuations therein.iii. Increasing detention time for settling out the sediments and other foreign matter.

5.7.2Tank Location

For a floating tank, the location to should ensure that the distribution system has adequate pressures even at times when water level in the tank is low. The location should also ensure that the system does not have extra-ordinarily high pressures that can lead to pipe bursts and failure of taps and other facilities. The tank was proposed to be located at contour 1219.20m above sea level which was located about 30m south of the dusty road from Nkhoma Mission. Using this contour, it was possible to let the water flow from all the five source points by gravity. Besides the above mentioned fact about using this position, it was also possible to let the water flow to all target villages by gravity. Figure 10 below indicates the position of the tank and is marked Storage Tank. The tank was positioned at a point that could not disturb or force relocation of the existing dwelling houses.

The critical elements of this tank were that it should balance the fluctuating demand from the distribution system and that it should allow enough detention time for trapping and effectively settling out the sediments. These determined the design shape and the sizing.

Pipeline to GwenembePipeline to ChauwaStorage TankFigure 10: Position of the storage tank

5.7.3Tank Volume

Tank volume was determined by fulfilling the requirements of the critical functions of the tank. As a storage tank, the tank must satisfy balancing requirements. As a sedimentation tank, it must satisfy the requirements for surface loading rate and detention time.

5.7.3.1Case 1: Sedimentation Tank

Sedimentation tanks are designed to reduce the velocity of water so as to permit suspended solids to settle out of the water by gravity if possible. There are several design approaches which depend on water treatability and whether the system is to use chemically aided settlement or not. The success of the design is judged on its ability to maintain the required throughput and the required effluent water quality under adverse raw water quality conditions which generally occur at the end of the dry season or during the first flood of the wet season when riverside pollutants are flushed downstream. In rural water supply systems the approach is simplified due to lack of capacity to handle chemicals. At the same time the water is assumed to be of substantially good quality due to natural treatment processes in the aquifer. In this scheme there were two advantages.i. The water comes from springs which are natural screening devices.ii. The water passes through other storage tanks that are located immediately after spring capping structures. These settle out sediments before the water comes to the tank under consideration.

The tank design was restricted to plain settling. In plain settling, the critical parameter is surface lading. The surface loading rate is given by. This criteria ensures that particles with falling velocity of more than or equal to surface loading rate will be effectively removed by the tank. Looking at the environment the most likely type of suspended solid were soil particles. Area of the tank was evaluated from other requirements and then it was checked if surface loading removes the desired particles.

The other parameter considered in the design of a sedimentation tank is detention time. This depends on several factors and amongst them are the following:-a. Quantity of flow.b. Amount of suspended particles.c. Size of suspended particles.d. Surface area of water in the tanke. Presence of a reservoir downstream.

According to rural water scheme requirements, the minimum detention time is 60 minutes. This assumes that water does not pass through pre-treatment process. From this requirement the minimum capacity of the tank is given by the formula where V is the volume in m3, Q is the flow rate in m3/s and t is the detention time. The design flow was 3.1l/s. Therefore the minimum volume of the tank should be 0.0031x60x60 m3=10.8m3.

5.7.3.2Case 2:Storage Tank

In order to assess the adequacy of the tank in terms of evening out hourly demand there is need to look at demand variations across the day. There is a typical trend where by the demand reaches the peak between 6.00am and 9.00am. It falls slightly thereafter and rises again to another peak between 5.00pm and 8.00pm. There is generally no water drawing between 8.00pm and 4.00am. This leads to a simple assumption that water is collected over 16hrs in a day and hence the 16hr demand.

There are typical factors based on long-term observations on how people draw water in rural areas of Malawi and indeed nearby countries. These factors are applied to find the amount of water that is needed in each hour of the day based on total daily demand. The cumulative amount is evaluated for each hour. Balancing requirement is found by subtracting the lowest accumulated value from the highest accumulative value (Ref: Santiago Alnararch, Gravity Flow Water Supply.

Table 11 below shows a summary of calculations carried out in an excel spreadsheet based on demand of 3.1l/s which translates to a total demand of 267.84m3 per day.

Table 11: Balancing Requirements for the tank

Looking at the setting of the supply area, there were no critical items requiring water for fire- fighting. This component was therefore neglected. An additional volume of 5% of the balancing requirement was added for emergency cases. This led to a total volume of 107.31m3.

The other approach for calculating the volume of the tank is stipulated by Design Manual for Piped Water Supply Systems, Ministry of Works, Malawi Government by Carl Bro International, which states that as a minimum requirement tank size must be 2 times the difference between the 16hour flow and 24 hour flow.

Tap demand was taken to be 3.1l/s as evaluated above. The 24 hour flow was calculated by multiplying by 2/3. The result was 2.067l/s. The difference between the two was 1.033l/s. Thus minimum tank volume was evaluated as 1.033x16x3.6x2=119m3.

The required tank volume was the higher between the two values evaluated above. This was 119m3.

5.7.4Tank Dimensioning

A rectangular tank was chosen for two reasons namely:-a) It is easy to construct.b) The tank was designed to serve as a sedimentation tank as well. A circular tank would bring complications since water has to flow upwards.

The major forces in a tank are the hydrostatic forces which are evaluated by the product of water density, acceleration due to gravity and the height. The only variable is the height. It was therefore important to limit height in order to reduce hydrostatic forces. Taking height H=2m then the product of width and length should help to determine volume i.e. L x B=59.5. Take L=8.5 then B=7.0The tanks internal dimensions were found to be as follows;-L=8.5mB=7.0mH=2.0mThis gave a volume of 119m3.

5.7.5General Arrangement of the Tank

Tank partitioning was noted to be necessary and this was designed in concrete work. Walls were introduced dividing the length and breadth in half each. That means that there were four compartments with baffle walls inside.

The outside dimensions of the tank were as follows;-Length=9.1mWidth=7.6m.

5.7.6Tank Site Conditions

The geology of the proposed tank site revealed that the area was underlain by a mature granitic rock that protruded in some places. This granitic rock was considered to be strong enough to support the foundation of the proposed tank. The same rock structure supports the existing infrastructures. The rock was found at an average depth of about 500mm.

The average slope of the tank site was found to be about 1:7. The upper side of the tank site would require considerable cutting to reach the required formation.

5.7.7Structural Design of the Tank

The general layout of the tank revealed that the following were the components.a) Reinforced concrete top slab.b) Reinforced concrete wallsc) Reinforced concrete Raft Base /foundation5.7.7.1Design Assumptions and Conditions

The following assumptions have been applied in the design of the tank. Concrete grade was taken to be 35N/mm2. Concrete weight was taken to be 24KN/m3 Water density was taken to be 10.0KN/m3. Screed weight was taken to be 0.3KN/m3 Strength of high yield steel was taken to be 460N/mm2 Critical Steel ratio was taken to be 0.0035. Partial safety factor for concrete was taken to be 1.25 Partial safety factor for steel was taken to be 1.155.7.7.2Top Slab

The top slab was designed to carry self-weight of concrete including screed. Looking at the arrangement, the slab was two way spanning because effective. Bending moments and shearing forces were determined using appropriate coefficients from Table 3.14 of BS 8110 part one. Deflection and cracking were checked at the centre of the spans. Even though shear was not critical, it was also checked at supports. Reinforcement for torsion was provided at the edges of the slab.

Design Calculations are found in appendix five.

5.7.7.3Concrete Wall

The wall was designed to resist bending moments and shearing forces generated by hydrostatic forces of water. The bending moments and shearing forces were determined from relevant coefficients. Moment Distribution method was applied to determine member moments in the lateral direction.

The wall was designed for hoop forces and bending moments. Deflections, shear and cracking were checked at appropriate critical sections.

Design calculations are found in appendix five.

5.7.7.4Raft Concrete Base

Reinforced concrete raft slab/floor system was adopted in order to satisfy both the architectural and structural requirements of the tank. The design approach for solid rafts is to treat them as inverted slabs. Punching shear and cracking were checked.

Design calculations are found in appendix five.

5.7.7.5Design Standards and Codes

Design of reinforced concrete members have been designed in accordance with British Standard BS 8110: 1997, Structural Use of Concrete. Design of water sections have been designed in accordance with British Standard BS 8007, Design of Concrete Structures for Retaining Aqueous Liquids. Loading categories have been adopted in accordance with British Standard BS 6399: Part 1 Loading for Buildings: Code of practice for dead and imposed loads and Part 2 Loading for Buildings: Code of Practice for Wind Loads. Hydrodynamic effects on the wall have been determined according to the Indian Codes of Practice, IS: 456-2000, Principles and Practice.

Design calculations are found in appendix five.

5.8Design of Distribution Lines

5.8.1Design CriteriaThe distribution lines were designed for 16 hour flow requirements from the taps. The 16 hour flow requirement was 0.075l/s for the tap serving a maximum of 120 people.

The main lines were designed for flow rates based on demand from each direction. This means that the initial flow rate was divided into two according to the demands. In like manner flow in each direction was reduced to remove the demand allocated to each smaller branch until the last branch. However, where the number of taps reduced to less than 10 a peak factor was applied to evaluate the flow requirements. A maximum peak factor of 2 was applied when there was one tap only. This peak factor reduced to 1 when the number of taps reached 10 and above.

Table 12 below shows how peak factors were varied in assigning flow requirements for branches.No of TapsRequired Flow in l/s

10.15

20.28

30.40

40.50

50.58

60.65

70.70

80.73

90.74

100.75

>100.075X No of Taps

Table 12: Required flow (l/s) for respective No of Taps

This implies that the figure indicated in the draw off column of the design calculations was related to the projected number of taps that could be connected by 2031. The actual number of taps in the year of project implementation was dependent on the current set up of communities and their respective population.

5.8.2Alignment of PipelinesThe criterion used to align pipelines in this scheme was based on the following factors:-i. Pipe lengths were minimized to reduce hydraulic losses and costs.ii. Pipelines were located close to the road unless there were no roads.iii. River crossings were avoided as much as possible but where it was not evitable galvanized steel was specified for the crossing.

In this scheme roads from the source to the target communities were generally absent. Since the flow was designed to be by gravity the terrain of the area and proximity of the target communities dictated the alignment of lines. In some cases the existing physical features prohibited accessibility and as such the proposed lines were diverted to proper locations. The plan for pipe alignment is shown in figure10 above.5.8.3Pipe MaterialsIn this scheme PVC class 10 was specified for all pipelines except in areas where the lines crossed gullies and rocky areas. HDPE was proposed for community connections.

5.8.4Hydraulic Design of Pipelines

Pipe sizing is a key element of hydraulic analysis. The objective is to minimize hydraulic loses so that the available potential energy can enable water reach the target points at an adequate pressure. At the same time the flow velocity must be controlled so that pressure surges are reduced or avoided and stagnation is also prevented. The procedure employed in the design was as follows. Select pipe size from the list of commercially available pipes. Estimate frictional losses based on pipe characteristics and the difference in head between the end points of the pipeline. Estimate form losses from pipe fittings bends and other obstructions. Find total losses. Subtract total losses from total head. This gives the available head at the end point. Please note that the acceptable available head at the end point must also be controlled to suit the standards according to functionality. From the design flow and the selected pipe size calculate flow velocity. Check the velocity compliance with standards. Calculate static head. Establish the class of the pipe required from the list of commercially available pipe class against the static head. Check the economics of the pipe material and class. Check technical possibility of breaking the pressure if there is need and incorporate the effects in the analysis.

In this exercise Hazen Williams Formula was utilized to calculate pipe losses. The formula is indicated as follows:= where=Head loss in mQ=Flow rate in l/sL=Pipe length in kilometresC=Constant and is dimensionless and is dependent on pipe materialsD=Pipe diameter in mmTable 13 below shows the values of C for different materials that were applied in the analysis.Pipe MaterialValue of C

PVC or HDPE145

GS120

Table 13: C values for pipe materialsVelocity of water was limited to values between 0.5 to 2.0 m/s. This was applied to ensure that stagnation due to low velocities is prevented while at the same time pressure surges that cause water hammer, due to high velocities are also prevented. The formula for velocity is as follows.whereV=flow velocity in m/sQ=flow rate in m3/sA=cross-sectional area of the pipe in m2 where;-

The calculations also ensured that the hydraulic losses are reduced to minimal so that adequate pressure is available at the taps. In general hydraulic gradient was designed to descend to the tap pressure of not less than 5m but not more than 15m at the required flow rate of 0.075l/s. This applied to the service line where the end point is a tap. For the distribution main, the scenario is different. The end of the line was encased by an end cap which indicated that the line may be extended in future within limits of service lines. Therefore the head at the end of the distribution main was between 20 and 30m.

Design charts were also used to check the findings from the above procedure. The design charts were based on the Colebrook-White Method of calculating head loss. In this procedure pipe diameter leads to the determination of losses which were later subtracted from the available head to determine working head. In the Design Calculation Tables;-Hydraulic Gradient Level (HGL) =Static Head Head lossWorking Pressure (WP) =HGL-Ground Level.

5.8.5Hydraulic Design of the Distribution Line between the Storage Tank and Chauwa Primary School

The hydraulic calculations revealed that 50mm PVC pipe was adequate to deliver the required flow from chainage 0+0.00m to chainage 0+960m. It was recommended to reduce this diameter to 40m at this chainage and a further reduction to 32mm at chainage 1+520m which should be maintained until the end of the pipeline at chainage 1+600m. Hydraulic analysis also revealed that there was a working pressure of about 23m at the end of the line. This pressure was adequate to make a minor extension on it hence a provision of an end cap at the far end.

There was a draw off of 0.58l/s at Mkhalala profile junction. This was the flow requirement for Mkhala Village. The total number of taps for Chauwa line was 14. Subtracting 5 taps for Mkhala line from 14, 9 taps remained for the rest of the pipe. The second draw off of 0.4l/s was lumped at this point for design purposes. The actual points for draw-offs would depend on the communitys requirements as the village was concentrated. In other words the actual connections were expected to be distributed along the main line.

For Design Calculations refer to Appendix 2

5.8.6Hydraulic Design of the Distribution Line between the Storage Tank and Gwenembe

Hydraulic calculations revealed that 63mm PVC pipe was adequate to deliver the required flow from chainage 0+0.00m to 1+260m. At this chainage the pipe diameter was reduced to 50mm. The 50mm diameter run to a chainage of 2+660m where further reduction to 40mm was recommended. Like in the line to Chauwa, hydraulic analysis revealed that there was a working pressure of about 27m at the end of the line.

This line passed through a place that was very close to Njovu Village. This village was relatively big and required at least three taps in 2011. The connections could be directly installed at chainage 1+260m. There was a projection of 5taps by 2031 and hence a draw of 0.58l/s. This demand was lumped at this point because the set-up of villages demanded that one pipe of at least 32mm be connected at one point. The demand would be distributed to the rest of the nearby villages using this line.

Again the draw off of 0.4l/s towards the end of the line was just for design purposes so that the line did not have to continue with a constant diameter. The actual set up would depend on community requirements which essentially meant that the demand would be distributed.

5.8.7Design of Small branches to the Communities

Apart from the two main lines explained above there are smaller branches that supply the communities directly. These have been considered to be community connections or service lines of not more than 25m. Further analysis for these has not been carried out because they are generally small and their actual locations are determined by the communities. However there is one line that is relatively long (280m). This branch is projected to have 5 taps. Its analysis is indicated under the following heading.

5.7.9Hydraulic Design of Branch Line to Mkhalala

This line branches at chainage 0+960m along Chauwa Line. It has a design flow of 0.58l/s. A 32mm PVC pipe is recommended up to chainage 1+100m where the diameter is reduced to 25mm. This diameter should be used up to the end of the line at chainage 1+240m.Hydraulic analysis indicates that the above arrangement produce a working pressure of 28.5m at the end of the line. This working pressure is adequate to make minor extension to the line. In this regard an end cap is recommended at the end of the line.

5.8Relocated Villages

During desk study it was observed from the map (produced in 1972) that there were some villages that needed separate profiles as branches from the two main lines. These villages included Mjolo and Kasadwa. However, these villages were not observed in their expected places during field survey. They got relocated either closer to the hills or closer to Linthipe River. One distinct observation was that Gwenembe looked a bit extended compared to what is presented on the map. Interviews with villagers revealed that the area has three villages namely Kasinje, Gwenembe and Julius.

Figure 11 below shows some of the areas that appear to have communities on the map but there is an empty space in the field.

Figure 11: Project area indicating communities close to hills and Linthipe River but empty in between

5.9Profiles

Profiles have been drawn to the following scales:- 1:50,000 for horizontal. 1:1,000 for verticalThe invert level of the pipe is dictated by pipe size, soil conditions, expected loading on top of the pipeline and risk to vandalism. In this scheme the community expressed willingness to have the facility and to contribute towards its implementation. In this case it was assumed that the risk of vandalism from the communities is minimal. However, the area is not closed up. It can be accessed by outsiders who may vandalize the facilities.

In all cases pipe diameters are 110mm or less. Generally minimum cover over the top of the pipe should be as follows:- 450mm for light loading. 600mm for medium loading. 900mm for heavy loadingThe lines from the spring boxes will cross the road. Therefore they will be subjected to heavy loading from passing vehicles.Considering all these factors the invert level for all main lines is taken to be at 900mm below the surface while the smaller branches are put at 600mm.5.10Tap Locations

Taps are located in all areas where the population is concentrated. In the Chauwa Distribution Line there is Chauwa Primary School which needs a tap of 20mm because it is an institution. In general each tap is designed to serve a maximum of 120 people. Where communities have more than 120 people additional taps are provided. The other limiting factor is that people should not walk more than 500m to access water. Therefore isolated communities with more than 500m radius will have taps allocated to each of the communities.

According to the information gathered during field visits and surveys, taps supplying communities close to the springs will be maintained. 5.11Valves and Fittings

In general all PVC pipes are jointed using rubber-rings located at one end of each pipe. The end without a rubber-ring is carefully inserted into the end with a rubber-ring. Where the PVC pipe is jointed to a GI pipe like in case of stream crossings, an appropriate size of VJ coupling or CI Joint may be used.

HDPE pipes are jointed using couplings of appropriate sizes determined by the pipe size.

Y fittings will be installed at all places where there are branches. The size of the fittings will be dictated by the diameter of the branch. Please refer to the profiles for specifications of each fitting.

Sluice Valves will be located in each line just after the branch. Air valves will be installed on all high spots to prevent air-locks. Wash-out valves and drains will be provided on all lower spots to ensure that water is flushed out during maintenance.

Gate valves will be installed to all smaller lines immediately after branches to ensure that they are isolated when need arises. In like manner gate valves or stopcocks will be installed just before taps.

A section of about 5m to the stand pipe including the stand pipe itself will utilize GI pipes. The GI pipes will be fitted to HDPE using couplings of appropriate size. Bends, elbows and bib taps will be of GI.Isolation valves have been proposed in section which are more than 2.5Km long

Adaptors or reducers will be installed where a smaller pipe is joined to a larger pipe.5.12Thrust Blocks

Thrust blocks have been proposed for all valves (but not gate valves), bends, tees and reducers. The general requirement is that thrust blocks must be strong enough to resist the maximum expected pressure.5.13Aprons, Washing Slabs and DrainageIt has been proposed to construct aprons and washing slabs at each tap to ensure that tap premises are kept clean, sanitary well and without mud. It has equally been proposed to construct brick wall drains so that all water wastes can be discharged into soak pits. However this is at the discretion of the community.

CHAPTER SIXCONCLUSION AND RECOMMENDATIONS6.1IntroductionThe conclusion and recommendations provided hereunder were based on the conditions observed at the time of field investigations and design of the scheme in September 2011. 6.2Conclusion

Field investigations revealed that it is possible to upgrade and extent Chilenje Rural Piped Water Scheme to serve more people residing in the Linthipe Valley. There is adequate water to meet the demand over the design period. The terrain of the area permits water transmission by gravity from the sources to the storage reservoir and from the reservoir to all water points.6.3Recommendations

The following recommendations were proposed:- In view of the growing population against a constant yield from the springs, all the available waters should be trapped using the same technology. Two spring capping structures are proposed to augment the present supply. There is an additional spring that shows some potential of yielding a reasonable amount of water. It is recommended to tap this spring as well. Since the upper area is already supplied from other springs or from alternative sources no storage tank is proposed for this spring. All the water is expected to flow directly to the proposed common tank. Field interviews revealed that most communities were previously living up hill. As a result the upper area is encroached and cultivation is still taking place. It is recommended that cultivation in the area stops and that the communities should engage in preserving the catchment area. This will assist aquifer recharge but at the same time will prevent contamination of the source. It is recommended to lay 75mm Galvanized Steel (GS) pipes between Spring Capping 1 and the common storage tank and between Spring Capping 2 and the common storage tank. It is recommended to install 50mm Galvanized Steel (GS) pipes from Spring Capping 3 and 4 to the proposed common storage tank. It is recommended to construct a common storage tank of 119m3 in volume. The tank should be constructed in concrete. The dimensions of the tank should be 8.9m x 7.4m x 2.4m. To allow for continuous circulation of water, the tank is baffled with walls inside. It is recommended to lay class 10 pipes throughout the scheme apart from rocky areas gully crossings and community connections. This is done to ensure that the communities do not make mistakes in sourcing pipes of different classes during repairs. Experience has also shown that class 6 pipes cause problems in most schemes. It is recommended to install end caps at the end of each profile to allow for minor extensions in future.

APPENDICES

Population Projections, Design Calculations

APPENDIX 1

POPULATION PROJECTIONS, DEMAND PROJECTIONS, SPRING DISCHARGES

AND TANK VOLUME

APPENDIX 2

CHAUWA PROFILE

SURVEY DATA, DESIGN CALCULATIONS AND HYDRAULIC CHART

APPENDIX 3

GWENEMBE PROFILE

SURVEY DATA, DESIGN CALCULATIONS AND HYDRAULIC CHART

APPENDIX 4

MKHALALA PROFILE

SURVEY DATA, DESIGN CALCULATIONS AND HYDRAULIC CHART

APPENDIX 5

STORAGE TANK STRUCTURAL, DESIGN CALCULATIONS

References1. American Water works association, PVC Pipe-Design and Installation, AWWA Manual M23.2. American Water Works Association, Principles of Water Supply Operations, Water Transmission and Distribution, Third Edition3. B. Mosley, J.Bungey and R. Hulse, Reinforced Concrete Design to Eurocode 2, sixth edition.4. British Standards, Code of Practice for Design of Concrete Structures for Retaining Aqueous Liquids, BS8007.5. Concrete Society, Standard Method of Detailing Structural Concrete, Third Edition.6. David Stephenson, Pipeline Design for Water Engineers.7. D. Butler and B.R.C. Pinkerton, Gravity Flow Pipe Design Charts8. Government of Malawi, Ministry of Works, Water Department, Design Manual for Piped Water Supply Schemes, {Carl Bro International AS, Consulting Engineers and Planners}9. Government of the Republic of Malawi, Ministry of Irrigation and Water Development, Implementation Manual for Piped and Point Water Supply Systems.10. Ian Batty and Roger Westbrook, The Design of Water Retaining Structures.11. Indian Standard, Code of Practice for Concrete Structures for the Storage of Liquids, Part IV, Design Tables.12. IRC, Small Community Water Supplies.13. Mackenzie L.D., Water and Wastewater Engineering, Design Principles and Practice.14. Malawi Government, Department of Lands, Valuation and Water, Gravity-Fed Rural Piped Water Schemes.15. Mays L., Water Distribution Systems Handbook.16. Mays L. W. Hydraulic Design Handbook.17. M. Mohitpour, H. Golshan and A. Murray, Pipeline Design and construction, A Practical Approach, 2nd Edition.18. Mosley W.H., Reinforced Concrete Design, Fifth Edition.19. National Statistical Office, Population and Housing Census, Analytical Report Volume 7, 2009.20. National Statistical Office, Population and Housing Census, Main Report, 2008.21. N. Krishnan Raju and R.N. Pranesh, Reinforced Concrete Design, IS 456-200, Principles and Practice.22. N. Trifunovic, Introduction to Urban Water Distribution.23. P. K. Swamee and A.K Sharme, Design of Water Supply Pipe Networks.24. R. Cheng, Design Tables to BS 8007, Design of Concrete Structures for Retaining Aqueous Liquids.25. R. D. Anchor, Design of Liquid Retaining Concrete Structures.26. Republic of Malawi, Gravity Fed Rural Piped Water Schemes, Rural Water Operators Handbook.27. T.D. Jordan Jr. Handbook of Gravity Flow Water Systems for Small Communities28. T.M. Walski, D.V. Chase, D.A. Savie, W. Grayman, S. Beckwith and E. Kelle, Advanced Water Distribution Modeling and Management29. Santiago Alnarach, Gravity Flow Water Supply.30. UNHABITAT, Gravity Water Supply System Design Tools.