Water supply infrastructure design reports are essential documents that communicate the technical specifications, construction requirements, and operational considerations of water distribution systems. In Kenya, civil engineers must prepare these reports with precision to ensure compliance with regulatory standards and to facilitate the efficient delivery of potable water to communities. This chapter focuses on the critical construction appurtenances that must be included and detailed in such reports, providing a comprehensive understanding of their functions, design considerations, and applications within Kenyan water supply projects.

5.1 Construction appurtenances

Construction appurtenances are the auxiliary devices and structures integrated into water supply systems to control flow, enable maintenance, and ensure system safety. These components play a vital role in the operational efficiency, reliability, and resilience of water distribution networks. In Kenya, where water infrastructure often faces challenges such as variable demand and environmental stresses, appurtenances like valves, fire hydrants, and surge tanks must be carefully designed and documented in infrastructure reports to support sustainable water management.

5.1.1 Valves

Valves regulate, control, and isolate the flow of water within the distribution network. Their inclusion in design reports is critical for operational flexibility and emergency management in water supply systems.

Kenyan water engineers commonly specify several valve types, each serving distinct purposes, as described under the headings below.

Design Considerations for Valves

Designing valves requires attention to pressure ratings, material compatibility, and accessibility:

• Pressure rating: Valves must match the system’s maximum operating pressure; for instance, a valve in a high-pressure urban distribution line in Mombasa must withstand pressures above 10 bar.
• Material selection: Corrosion resistance is paramount; valves in coastal regions often use stainless steel or ductile iron with protective coatings.
• Accessibility: Valves should be located for easy operation and maintenance, with clear signage in public utility facilities such as those managed by Nairobi City Water and Sewerage Company.

Installation and Maintenance Practices

Proper installation ensures valve longevity and system reliability:

• Installation: Valves should be installed with adequate support and alignment to prevent stress on pipelines; thrust blocks are often used to counteract operational forces.
• Maintenance: Regular inspection and lubrication prevent valve seizure; maintenance logs at county water offices help track valve conditions.
• Testing: Hydrostatic pressure testing post-installation verifies valve integrity before commissioning.

5.1.1.1 Gate

• Gate valves: Used primarily for isolation, gate valves provide a full bore when open, minimizing pressure loss. They are suitable for sections requiring infrequent operation, such as isolating a pipeline segment during maintenance at a county water supply system.

Large industrial gate valve outdoors (Source: Wikimedia Commons)

A gate valve closes the flow by lowering a flat or wedge-shaped gate across the pipe bore, operated by a handwheel or key turning a threaded stem. When fully open, the gate is lifted completely out of the flow path, so the valve causes very little head loss, which makes it the standard isolating (sluice) valve in water mains. Gate valves should be used fully open or fully closed only, because partly open gates vibrate, wear and erode. Example: a water and sanitation company in Nakuru installed resilient-seated gate valves at every branch of its distribution network so that sections could be shut off for repairs without cutting supply to the whole town.

Parts of a Gate Valve

• Body: The main casing, usually ductile iron, connected to the pipeline by flanges or spigots.
• Gate (wedge or disc): The closing element that slides across the bore.
• Stem (spindle): The threaded rod that raises and lowers the gate; it may be rising or non-rising.
• Bonnet and gland: The cover and seal that prevent leakage around the stem.
• Handwheel or cap: The operating device, with buried valves operated by a key through a surface box.

Guidelines for Using Gate Valves

• Use for isolation only: Operate fully open or fully closed and do not use for throttling.
• Close slowly: Close large valves gradually to avoid water hammer.
• Exercise regularly: Open and close valves periodically to prevent seizure.
• Provide surface boxes and markers: Mark buried valves so they can be found and operated.
• Support and anchor: Support valves independently so pipes do not carry their weight.

5.1.1.2 Globe

• Globe valves: Designed for precise flow regulation, globe valves are preferred in treatment plants where flow adjustments impact water quality.

A globe valve controls flow by moving a disc or plug towards or away from a seat inside a roughly spherical body, and the water changes direction as it passes through the valve. This design gives fine, accurate control of flow and seals tightly, so globe valves are used for throttling and regulating flow, for example on chemical dosing lines, sampling points and small bypasses. Because of the change in flow direction, globe valves cause much higher head loss than gate valves and are rarely used on large mains. Example: the chlorine dosing line at a water treatment works for a girls’ school in Kericho used small globe valves to set the dose accurately.

Gate and Globe Valves Compared

5.1.1.3 Check

• Check valves: These valves prevent backflow, protecting pumps and maintaining system integrity, especially important in rural water schemes where gravity-fed systems are common.

A check valve (non-return valve) allows water to flow in one direction only and closes automatically when flow tries to reverse. It is fitted on pump delivery lines to stop water flowing back through the pump when it stops, at connections to storage tanks and at consumer connections to protect the public supply from contamination by backflow. The valve operates without any outside control, using the force of the flowing water to open and gravity, a spring or reverse flow to close. Example: on a borehole supply for a dispensary in Turkana, a check valve on the pump rising main prevented the rising main from draining back into the borehole each time the solar pump stopped.

Types of Check Valves

• Swing check valve: A hinged disc swings open with flow and closes against the seat when flow reverses.
• Lift check valve: A disc or ball lifts off the seat with flow and drops back when flow stops.
• Dual-plate (wafer) check valve: Two spring-loaded half-plates close quickly, reducing slam and water hammer.
• Ball check valve: A ball moves off and onto the seat, suitable for small pipes and sewage.
• Foot valve: A check valve with a strainer at the bottom of a pump suction pipe, keeping the pump primed.

5.1.1.4 Air relief

• Air release valves: Installed at high points to expel trapped air, preventing airlocks that can disrupt flow in hilly regions like the Rift Valley.

Air release valve on pipeline (Source: Wikimedia Commons)

Air relief valves remove air from pipelines and, in some types, admit air to prevent vacuum, keeping water flowing smoothly and protecting pipes. Air collects at high points in pipelines and reduces their carrying capacity, causes inaccurate metering and can lead to surges, while vacuum formed when a pipe drains can collapse thin-walled pipes or draw in contaminated water. Air valves are therefore installed at high points, at changes of gradient, after pumps and at regular intervals along long flat runs. Example: a gravity main supplying a market centre in Murang’a stopped flowing at one hill crest until an air valve was installed there, after which full flow was restored.

Types of Air Valves

5.1.1.5 Pressure reducing

A pressure reducing valve (PRV) automatically lowers a high, varying upstream pressure to a lower, steady downstream pressure, regardless of changes in flow or upstream pressure. In hilly areas, water supplied from high reservoirs can reach low-lying zones at pressures high enough to burst pipes, damage fittings and increase leakage, so PRVs divide the network into pressure zones. A PRV uses a spring-loaded or pilot-operated mechanism that opens and closes in response to downstream pressure, and it is normally installed with isolating valves, a strainer, pressure gauges and a bypass for maintenance. Example: a water company serving a hilly town in Kisii installed PRVs on mains feeding the lower suburbs, reducing pipe bursts and leakage after pressure was cut from over 10 bar to about 4 bar.

Worked Example: Pressure from Static Head

A distribution point lies 120 m below the reservoir water level. Find the static pressure and state the effect of a PRV set at 4 bar.

p = ρ × g × h

p = 1,000 × 9.81 × 120

p = 1,177,200 Pa = 11.8 bar

A PRV set at 4 bar reduces the downstream pressure from about 11.8 bar to 4 bar, protecting pipes and fittings in the low-lying zone.

Steps for Installing a Pressure Reducing Valve Assembly

1. Select the PRV: Choose the size, pressure rating and setting range to suit the flow and pressures.
2. Construct the chamber: Build a chamber large enough for the valve, fittings and maintenance access.
3. Install upstream isolating valve and strainer: Fit an isolating valve and strainer to protect the PRV from debris.
4. Install the PRV: Fit the valve in the correct flow direction, supported independently of the pipe.
5. Install gauges: Fit pressure gauges upstream and downstream to monitor performance.
6. Install downstream isolating valve and bypass: Provide a bypass with a valve to maintain supply during servicing.
7. Set and test: Adjust the PRV to the required downstream pressure and check its response to varying flow.

5.1.1.6 Butterfly Valves

• Butterfly valves: These are quarter-turn valves that regulate flow and can be used for throttling. Their compact design makes them ideal for urban water networks with space constraints, such as those in Nairobi’s metropolitan area.

5.1.2 Fire hydrants

Fire hydrants are critical safety features in water distribution systems, providing accessible water sources for firefighting.

Placement and Design Criteria

Strategic placement ensures effective firefighting coverage:

• Spacing: Hydrants are typically spaced 100 to 200 meters apart in urban settings to allow rapid access, as per Kenya Bureau of Standards (KEBS) guidelines.
• Accessibility: Hydrants must be unobstructed and clearly visible; in Nairobi’s central business district, this involves coordination with municipal authorities to prevent illegal parking.
• Flow capacity: Hydrants should deliver minimum flow rates of 10 liters per second to meet firefighting demands.

Maintenance and Operational Challenges

Maintaining hydrants is essential for emergency readiness:

• Inspection schedules: County governments often mandate biannual inspections to ensure operability.
• Common issues: Blockages, corrosion, and vandalism are frequent problems in informal settlements, requiring community engagement for protection.
• Testing: Flow tests verify hydrant performance and are documented in fire safety compliance reports for institutions like Kenyatta National Hospital.

5.1.2.1 Wet barrel

• Wet barrel hydrants: Common in warmer regions like Nairobi, where water remains in the barrel, allowing immediate flow.

Red wet barrel fire hydrant on pavement (Source: Wikipedia (Fire hydrant))

A wet barrel hydrant is a fire hydrant whose barrel (upright body) is always full of water under pressure, with a separate valve behind each outlet. Because water is already in the barrel, firefighters can open any outlet immediately and connect hoses independently, which gives fast response. Wet barrel hydrants are suited to warm climates where there is no risk of freezing, which covers most of Kenya, but they must be robust and well protected because damage above ground can cause water loss. Example: a business park in Kisumu installed wet barrel hydrants along its internal roads so that fire crews could connect hoses within seconds of arrival.

Features of Wet Barrel Hydrants

• Barrel always charged: Water stands in the barrel at mains pressure.
• Individual outlet valves: Each outlet has its own valve, allowing hoses to be connected and operated separately.
• Quick operation: Water is available immediately when an outlet valve is opened.
• Suited to frost-free climates: There is no risk of freezing damage in warm areas.
• Need for impact protection: Damage to the barrel releases water, so bollards may be needed in traffic areas.

5.1.2.2 Dry barrel

• Dry barrel hydrants: Suitable for colder areas such as Eldoret, designed to prevent water freezing by keeping water below ground level.

A dry barrel hydrant keeps its main valve below ground at the base of the hydrant, so the barrel above ground is empty when the hydrant is closed and drains automatically through a drain hole after use. The valve is opened by turning an operating nut on top of the hydrant, which fills the barrel and supplies all outlets together. This design prevents freezing in cold climates and limits water loss if the hydrant is knocked over, which is also useful in areas exposed to vehicle damage or vandalism. Example: a county water department supplying a high-altitude town near Mount Kenya chose dry barrel hydrants for exposed roadside locations, where cold nights and vehicle impacts were both concerns.

Steps for Operating a Dry Barrel Hydrant

1. Remove the outlet cap: Remove the cap from the outlet to be used and check the outlet thread.
2. Connect the hose: Connect the fire hose securely to the outlet.
3. Open the main valve fully: Turn the operating nut slowly until the valve is fully open, so the drain hole closes.
4. Supply water: Allow water to flow to the fire appliance or hose.
5. Close the valve slowly: Turn the nut slowly to close the valve and avoid water hammer.
6. Allow the barrel to drain: Leave the outlet open briefly so the barrel drains through the drain hole.
7. Replace the cap: Replace the outlet cap and report any faults.

5.1.2.3 Wall Hydrants

• Wall hydrants: Installed on building walls for localized firefighting needs, often in commercial complexes.

Red wall hydrant with two outlets (Source: Wikimedia Commons)

5.1.3 Meters

Water meters measure consumption, enabling billing and demand management within water supply systems.

Installation Guidelines

Correct installation affects meter accuracy and lifespan:

• Orientation: Meters should be installed horizontally or vertically as specified by manufacturers; improper orientation can cause measurement errors.

• Straight pipe lengths: Upstream and downstream straight pipe sections prevent turbulence, improving accuracy, this is critical in installations at Nairobi Water Company.

• Protection: Meter chambers shield meters from environmental damage and unauthorized access.

Meter Reading and Data Management

Efficient meter reading supports revenue collection and water conservation:

• Manual reading: Traditional method involving periodic site visits, common in rural water schemes.
• Automated reading: Smart meters transmit data to central databases, facilitating real-time monitoring.
• Data analysis: Patterns in consumption help detect leaks and unauthorized use, essential for SACCO-managed water projects.

5.1.3.1 Domestic

• Positive displacement meters: Suitable for low flow rates in residential connections, providing accurate measurements for household billing.

Domestic water meters are small meters, typically 15 mm to 25 mm in size, installed on individual customer connections to measure water used by homes, small shops and offices for billing. The most common types are positive displacement meters, which measure by filling and emptying a chamber of known volume, and multi-jet or single-jet velocity meters, which measure by the speed of a rotating impeller. Domestic meters must be accurate at low flows, robust, tamper-resistant and easy to read. Example: a housing SACCO in Kitengela installed individual 15 mm meters for every house, so that each member paid only for the water used, which reduced disputes and wastage.

Domestic Meter Assembly

Features of Good Domestic Meters

• Accuracy at low flow: Measures small flows such as dripping taps.
• Durability: Withstands water quality, pressure and outdoor conditions.
• Tamper resistance: Has seals and magnetic protection to prevent interference.
• Readability: Has a clear register readable without opening the meter.
• Compatibility with remote reading: Can be fitted with pulse outputs or smart modules.

5.1.3.2 Bulk

• Velocity meters: Including turbine and electromagnetic types, these are used in larger pipelines, such as those feeding industrial parks.

Bulk meters are large meters, usually 50 mm and above, installed on transmission mains, reservoir outlets, zone inlets and large consumers such as factories, hospitals and institutions to measure large volumes of water. They allow water utilities to measure water produced and supplied to each zone, calculate non-revenue water (water lost through leaks, theft and errors) and bill large consumers accurately. Common types include Woltmann (turbine) meters and electromagnetic meters, often with data loggers for continuous recording. Example: a water company in Eldoret installed bulk meters at the inlets of each supply zone and found that one zone was losing over 40% of its water, leading to targeted leak repairs.

Uses of Bulk Meters

• Production metering: Measuring water leaving treatment works and boreholes.
• Zone (district) metering: Measuring water entering each distribution zone to detect losses.
• Large consumer billing: Measuring supply to factories, institutions and estates.
• Non-revenue water analysis: Comparing water supplied with water billed.
• Network management: Providing flow data for planning and operation.

5.1.3.3 electromagnetic

An electromagnetic (magnetic flow) meter measures the velocity of water using Faraday’s law of electromagnetic induction: water, which conducts electricity, flowing through a magnetic field created by coils around the pipe produces a small voltage proportional to its velocity, which electrodes measure and convert into flow rate. Because it has no moving parts and no obstruction in the pipe, it causes no head loss, does not wear and remains accurate over a wide range of flows, which makes it ideal for bulk metering of treated and raw water. It requires an electrical power supply or long-life battery and is more expensive than mechanical meters. Example: the treatment works serving a county water project in Embu used electromagnetic meters on its outlet mains to provide accurate continuous flow data to its control room.

Advantages and Limitations of Electromagnetic Meters

• Advantage, no moving parts: No wear, low maintenance and long life.
• Advantage, no head loss: The full bore causes no obstruction to flow.
• Advantage, wide flow range: Accurate at low and high flows and in both directions.
• Limitation, needs conductive liquid: Works only with liquids that conduct electricity, such as water.
• Limitation, power supply: Requires mains power or batteries.
• Limitation, cost: Higher initial cost than mechanical meters.

Steps for Installing an Electromagnetic Meter

1. Choose the location: Select a position with full pipe flow and enough straight pipe upstream and downstream.
2. Prepare the chamber: Construct a chamber with drainage and access for the meter and electronics.
3. Install the meter body: Fit the meter between flanges in the correct flow direction, with the pipe always full.
4. Earth the meter: Connect earthing rings or electrodes as specified to avoid electrical interference.
5. Connect power and signal cables: Connect the converter to power and data logging or telemetry.
6. Configure the converter: Enter the pipe size, units and output settings.
7. Test and commission: Check the readings against a reference flow and record the installation details.

5.1.3.4 Compound Meters

• Compound meters: Combine features to measure varying flow rates, ideal for mixed-use developments.

5.1.3.5 Smart Meters

• Smart meters: Increasingly adopted in Kenyan urban centers for remote reading and leak detection.

5.1.4 Chambers

Chambers are underground enclosures that house valves, connections, or other appurtenances, facilitating operation and maintenance.

Design and Construction Requirements

Chamber design ensures durability and safety:

• Material selection: Reinforced concrete is standard for robustness; polymer-based chambers are used in areas with corrosive soils.
• Dimensions: Chambers must accommodate personnel access and equipment handling, with minimum internal dimensions per KEBS standards.
• Waterproofing and drainage: Essential to prevent flooding and ingress of contaminants, particularly in flood-prone areas of Kisumu County.

Safety and Operational Considerations

Ensuring safe and effective chamber use involves:

• Access covers: Must be load-rated and lockable to prevent unauthorized entry and accidents.

Open access cover on concrete surface (Source: Wikipedia (Manhole cover))

• Ventilation: Chambers require ventilation to avoid hazardous gas buildup.
• Signage: Clear labeling aids maintenance teams during emergencies.

5.1.4.1 Meter

• Meter chambers: Specialized chambers protecting water meters, detailed separately.

A meter chamber is a small underground or partly buried enclosure that houses a water meter and its associated fittings, protecting it from damage, tampering and weather while allowing it to be read and maintained. For domestic connections, a small precast or masonry box is usually enough, while bulk meters need larger reinforced concrete chambers with space for the meter, valves, strainer and dismantling joint, and room for a person to work. The chamber must be sited where it is accessible to the meter reader, usually at the property boundary. Example: a hotel in Nanyuki had its bulk meter housed in a reinforced concrete chamber at the gate, with a lockable cover so that utility staff could read it without entering the hotel premises.

Steps for Constructing a Bulk Meter Chamber

1. Set out the chamber: Mark the position and internal dimensions to suit the meter assembly and working space.
2. Excavate: Excavate to the required depth and compact the base.
3. Cast the base slab: Cast a concrete base with a sump or drain to remove water.
4. Build the walls: Construct masonry or reinforced concrete walls with openings for the pipes.
5. Install the meter assembly: Fit the isolating valves, strainer, meter and dismantling joint on supports.
6. Seal pipe openings: Seal around pipes to prevent soil and water entering.
7. Fit the cover slab and cover: Cast or place the roof slab and fit a lockable, load-rated access cover.
8. Backfill and finish: Backfill around the chamber, finish the surface and label the chamber.

5.1.4.2 valve

• Valve chambers: Provide access to valves for operation and repair.

A valve chamber is an underground enclosure built around a valve, such as a gate valve, air valve, washout or pressure reducing valve, to protect it and allow operators to reach and maintain it. Small buried valves may only need a surface box for the operating key, but larger valves and valve assemblies need a chamber with enough space to operate, inspect and remove the valve. Chambers must be built so that the pipeline does not rest on the chamber walls, preventing damage from settlement, and must drain or be pumped to stay dry. Example: on a transmission main supplying a sugar factory in Mumias, each large isolating valve was housed in a reinforced concrete chamber with step irons and a lockable cover.

Requirements for Valve Chambers

• Adequate size: Internal space must allow operation and removal of the valve and fittings.
• Independent pipe support: The pipe passes through openings with flexible seals so chamber movement does not stress it.
• Drainage: A sump or drain prevents water accumulation around the valve.
• Safe access: Step irons or ladders and a secure, load-rated cover are provided.
• Identification: Chambers are labelled and marked with marker posts for easy location.

5.1.4.3 Junction Chambers

• Junction chambers: Facilitate pipeline connections and branching.

5.1.4.4 Inspection Chambers

• Inspection chambers: Allow visual inspection and cleaning of pipelines.

5.1.5 Meter chambers

Meter chambers are specialized enclosures designed to protect water meters from environmental damage and unauthorized interference.

Design Features of Meter Chambers

Meter chambers incorporate design elements that safeguard meters:

• Structural integrity: Chambers are constructed to resist soil pressure and surface loads, especially in urban areas with vehicular traffic.
• Accessibility: Chambers have removable covers and sufficient space for meter reading and maintenance.
• Protection from elements: Chambers prevent water ingress and temperature extremes that could affect meter performance.

Installation and Positioning

Proper installation is crucial for meter accuracy and longevity:

• Location: Chambers are typically placed near property boundaries to facilitate access by water service providers without disturbing customers.
• Leveling: Chambers must be level to ensure meters function correctly and to prevent sediment accumulation.
• Connection points: Inlet and outlet pipes are aligned to minimize flow disturbances.

Maintenance and Security

Maintaining meter chambers enhances system reliability:

• Routine inspection: Regular checks prevent blockages and detect leaks early.
• Security measures: Lockable covers deter tampering and theft, a concern in informal settlements.
• Cleaning: Chambers should be kept free of debris and standing water to protect meters.

5.1.6 Surge tanks

Surge tanks mitigate pressure fluctuations in water supply systems, protecting pipelines and equipment from water hammer effects.

Purpose and Function of Surge Tanks

Surge tanks serve as protective devices in pressurized systems:

• Pressure stabilization: They absorb sudden changes in pressure caused by rapid valve closures or pump failures.
• Water hammer prevention: By providing a cushion of air or water, surge tanks reduce the risk of pipeline bursts.
• Flow regulation: Surge tanks help maintain steady flow rates during transient events.

Types and Design Parameters

Different surge tank designs suit varied system requirements:

• Simple surge tanks: Open to atmosphere, located at high points to allow water level fluctuations.
• Differential surge tanks: Equipped with air cushions to control pressure variations more effectively.
• Surge vessels: Closed tanks with compressed air, used in confined spaces.

Design parameters include tank volume, height, and placement relative to pipelines, calculated based on system pressure and flow characteristics common in Kenyan water supply projects.

Worked Example: Pressure Rise from Water Hammer

Water flowing at 1.5 m/s in a pipeline is stopped suddenly by a fast-closing valve. Taking the pressure wave speed as 1,000 m/s, estimate the pressure rise.

Δp = ρ × c × Δv

Δp = 1,000 × 1,000 × 1.5

Δp = 1,500,000 Pa = 15 bar

A pressure rise of this size could burst the pipe, which is why surge tanks, surge vessels and slow-closing valves are provided.

Installation and Operational Considerations

Proper integration of surge tanks ensures system longevity:

• Location: Surge tanks are installed at strategic points, such as pump discharge lines near Mombasa’s water treatment plants.
• Structural design: Tanks must withstand internal pressures and external loads.
• Maintenance: Periodic inspection of air cushions and water levels prevents malfunction.

Chapter Summary

This chapter covers the preparation of a water supply infrastructure design report, beginning with an overview of construction appurtenances such as various types of valves including gate, globe, check, air relief, and pressure reducing valves. It then discusses fire hydrants, distinguishing between wet barrel and dry barrel types, as well as different meters including domestic, bulk, and electromagnetic meters. The chapter also addresses chambers used for meters and valves along with surge tanks that help regulate pressure fluctuations. Technical specifications for materials and equipment are outlined to ensure quality and suitability for water supply systems. The bill of quantities section explains the measurement of works and cost estimations necessary for budgeting and project planning. The technical design report section delves into structural analysis topics such as moments in beams, shear forces, bending moments, graphical representations, section properties, and the theory of simple bending. It further examines forces in frames, deflection in beams, and the design of reinforced concrete, timber, and steel structures, including welded connections. The chapter concludes with guidance on technical report writing and assembling the comprehensive design report.