Designing a Water Feature_Tech Bulletin

8/2/2019 Designing a Water Feature_Tech Bulletin

1/24

Hydrotechnology

Technical Bulletin

DESIGNING A WATER FEATURE

CI/SfB 998


2/24

1 INTRODUCTION

Few designers have the time that is necessary to master the intricacies of designingwater features and so they have to rely upon performance specifications to convey theirwishes. Unfortunately these are of little value as they are almost impossible to enforce.This bulletin is intended to help designers and end users to define their requirementswith precision. This is a briefing document and should be treated as such. Each topiccovered in this bulletin is a complex subject in itself. All technical matters, particularlythose of an electrical nature, need to be resolved by a qualified person in a way thatreflects local regulations. However, with the aid of this publication nozzles, spillways,

flow rates, and pipe sizes can be accurately defined.

When designing a water feature it is important to anticipate maintenance problems, touse high quality materials, and not to be overly complex. If a feature is not welldesigned and constructed it will become a burden rather than an asset. An adequatebudget is important as good quality materials are always expensive. Experimentationis an important part of any creative design process. The feasibility of all key compo-nents should be demonstrated before construction commences.

The factors which need to be considered when designing a feature are:-

the climate the setting the scale the nature of the required effect

the maximum acceptable noise level the standard of cleanliness that is required the accuracy required of the water level control system the problems that wind will cause the availability of water the risk of vandalism the budget

2 SETTING AND SCALE

When designing a water feature it is important to pay attention to all aspects of theenvironment in which it is to be placed. For example, sun angles are particularlyimportant in urban areas as water in permanent shade can appear very cold. Close to

tall buildings turbulent down-draughts can lift water directly from an unbroken surface.These down-draughts usually preclude the use of reflective pools in urban locations.A feature should always be in scale with its surroundings. Often the desire not to losedevelopment space overrides the need to create a feature of adequate size. It is bet-ter not to have a feature than one which is too small. It is also important to anticipatethe activities that are to take place adjacent to any feature. For example, in a crowdedshopping mall a feature has to either cover a large area or be well over two meters(6 ft 6 in) tall if it is to be seen from a distance.

The water spray from a vertical jet will usually spread outwards by at least half thedistance that it travels upwards (fig 1). This is a rule which can only be improved uponby employing a very short burst effect in which the rising water does not collide withthe falling water. In external locations the radius of a pool should at least equal theheight of the effect which it is to contain. In exposed locations the display will need to

be lowered or the pool size increased by 20% for every 1m/s (2.2mph) increase in theprevailing wind speed above 2.5m/s (5.5mph). An external feature should alwayshave a wind activated control system, particularly if it is close to a building.Anemometers should be mounted in a representative location as close to the featureas possible e.g. on top of an adjacent lamp post or flag pole.

When water runs down a vertical surface the amount of spray which it createsdepends upon the physical characteristics of that surface. Water which passes downa very rough surface can spread forward almost half the height of the wall (fig 2). Thiscontrasts with polished stone or glass, both of which will hold water in close contactwith their surface. The spread of water is surprisingly small when it is dropped as afree falling curtain in a sheltered location. However, any curtain or wall of water issusceptible to the effect of wind so an anemometer and / or a remote switch shouldalways be provided in external locations.

Around natural lakes the ground should slope gently to the water particularly if thearea is to be used for storm water balancing. Paving should fall away from formalpools so that rain does not wash debris into the feature. The paving should fall todrainage channels so that any water which is accidentally lost from the system can besafely disposed of. During very cold weather some pools will need to be draineddown. Such features must be designed to be vandal proof and attractive when empty.

Fig 1 In still conditions water willspread outwards by half the distancethat it travels upwards

Fig 2 Water will splash forward by aquarter to a half the height of a roughwall depending upon its angle andsurface characteristics

Fig 3 Circular pools can surge upand down if nozzles are used whichdischarge below water

Fig 4 If the water is to be flush withits surroundings then a tankedrecessed channel is needed to avoidtracking under finishes


3/24

3 NOISE

Water will generate white noise when it is agitated. This can be useful if it masksconversations or mechanical noise. In most retail locations the background noise levelis so high that the sound of water is seldom noticed and may even be welcomed.However, in a quiet reception area even a small amount of noise can be disturbing. Insuch locations features need to be designed carefully with fine low volume displays.Noise levels can be reduced by placing energy absorbing mats just above the water toreduce splashing. Alternatively, air can be mechanically entrained to reduce thedensity of the water both in the effect and within the feature itself, which in turn serves

to reduce noise levels.

4 FREEBOARD

High winds can produce waves over 300mm (1 ft) high on a lake only one hundredmetres (110 yds) across. Powerful fountain nozzles can also produce waves. Circularpools may surge up and down if nozzles are used which initially discharge below thesurface (fig 3). If pools at different levels are linked together then the lowest pool willreceive any water which runs back when the feature is shut down. If the lowest pool isnot large enough to receive all the water then a hidden tank must be provided. Whencalculating the size of a fall back tank, or the lowest pool in a series, it is prudent toassume that any non-return valves in the pumping system will fail to close. Positioningthe inlets to the higher pools above the surface avoids the problem of water draining

back through the supply pipework when the pumps are turned off.

To ensure that water does not escape over the top of a membrane a minimumfreeboard of 150mm (6 in) is to be recommended. With a quiet feature this can bereduced to 75mm (3 in). The risk of capillary action behind decorative finishes can beavoided by close bonding. If water is to appear flush with an adjacent surface then adrained channel needs to be recessed into the floor around the feature to avoid watertracking back under the finishes (fig 4).

5 RIGID STRUCTURES

Water bodies are inherently stable and only circulate slowly of their own volition.Water will always take the shortest route and this fact must be reflected in the overallplumbing configuration. Water should be introduced and drawn off in a way that en-

sures full turnover (fig 5 & 6). Underwater jets pointing towards or away from the outerwalls will help to minimise the accumulation of floating debris and greasy deposits,particularly in corners (fig 7). The base of a pool should always be laid to a fall of atleast 2 to a drainage point or sump to facilitate sweeping. Channel bottoms can alsobe laid to falls to keep debris moving (table 1).

In urban locations it is advisable to minimise the depth of water so as to shorten main-tenance periods and for reasons of safety. The industry standard water depth for adecorative pool is 400mm (16 in). This depth is sufficient to cover most lights andnozzles. With a freeboard of 150mm the base of a pool will still be less than 600mmbelow its surroundings. It is not usual to provide safety rails for a drop of less than600mm (2 ft) so this establishes the normal edge profile. If there is a requirement forlarge nozzles then sumps can be formed in the base of a pool (fig 8). To avoid clutterand the possibility of vandalism cable ducts and supply pipes should be set into the

base of the pool, below the finishes, and not left exposed on the surface.

As water freezes so it expands. This force can crack rigid structures, lift finishes andsplit pipework. Water trapped behind decorative finishes may force them away fromtheir backing as it freezes so full bonding is necessary. If water is to remain in a poolduring freezing conditions it may be necessary to have gently sloping sides which willallow the ice to slide upwards. A feature must be designed so that it looks attractivewhen it is switched off or drained down. A simple bed of cobbles can make an emptypool look attractive in the middle of Winter. Alternatively a pool can be covered withpaving so that it looks like a piazza when it is out of commission.

When a feature is close to or within a building it must be completely watertight. If apool consists of a single concrete structure it may not need lining but this is seldom thecase. Day work joints usually mean that a membrane is required. Liquid rubber orbitumen based paints can be used to seal small cracks. Liquid applied systems are

cheap but they usually fail within a few years. Some liquid systems are reinforced in-situ with fibreglass, polypropylene or polyethylene mat to increase their resilience.There are a range of sheet materials which are good for tanking but these cannotsupport a decorative finish without a rigid internal structure. GRP (glass reinforcedplastic) or fibreglass is a useful material as it has structural properties of its own. It isexpensive but can carry decorative finishes particularly if the surface is textured with

Fig 5 Complete circulation isimportant if the water is to remainclean (option 1)

Fig 6 Complete circulation isimportant if the water is to remainclean (option 2)

Fig 7 Water can be bled out below anozzle to keep the corners clean

Fig 8 A sump can be formed toaccommodate large nozzles

Table 1 Silt movement over aflat concrete bed

flow rate silt movement

0.075m/s no silt movement

0.125m/s slight movement whendisturbed but settling later

0.150m/s big conglomerations ofalgae starting to move

0.300m/s silt moving well, largeinorganic materialstationary

1.000m/s usual speed required formass flow in sewers


4/24

crushed flint or silver sand. All membranes should be electronically and / or floodtested before decorative finishes are applied. All penetrations need to be carefully de-tailed as most leaks occur at these points.

6 APPLIED FINISHES

The surfaces within a feature must be easy to clean and not affected by water. In ex-ternal locations sunlight and freeze thaw cycles put an additional stress on finishes. Atthe waterline they must be particularly durable as this is where environmental condi-

tions are at their most extreme and where deposits accumulate. Pool walls should befinished with smooth materials which are easy to clean. Horizontal surfaces may ben-efit from having some texture as it will improve traction, although rough surfaces willpresent maintenance problems.

Historically marble was used for water features because it was widely available andeasy to work. Unfortunately, its surface dissolves quickly particularly when the waterhas a low pH or is treated with aggressive chemicals such as chlorine. Sandstone andlimestone should be avoided as they absorb water. If natural stone is to be used thenthe best material is granite. Terrazo should never be used as the pigments, whichprovide much of its colour, are denatured by halogens and acids. High quality glazedceramic tiles are durable and much cheaper than stone.

It is important to select the right colour for a feature. Dark blues, dark greys and blackare usually best as they give the water an illusion of depth, and contrast with the

effects on the surface. Browns and yellows should be avoided as they tend to makethe water look dirty. Greens should be approached with caution as they often lookartificial and clash with adjacent vegetation. Uniform colours highlight imperfectionsand make debris more apparent so patterned or dappled finishes are to be preferred.

Fixing through membranes, for example to support natural stone slabs, is not to berecommended. Thoughtful detailing often allows vertical stone panels to be fixed atthe top whilst the bottoms are retained by the floor. If large, complex or heavy panelsare to be used then an engineering brick wall can be built in front of the membrane toreceive mechanical fixings (fig 9). All mechanical fixings must be made from stainlesssteel. Bedding layers under finishes should either be pure epoxy based (not epoxy ce-ment) and preferably flexible rubber compounds. Under no circumstances shouldconventional cementatious mortars be used. Lime is easily leached from them and willform white deposits along the joints in the finishes. Eventually the finishes will lift.Joints can be filled with silicone or polysulphide jointing compounds. The surfaces

which are to be bonded should be abraded, degreased, and primed before the sealantis applied. Care should be taken to colour co-ordinate joint fillers with adjacentfinishes.

7 WATERFALLS AND WATERWALLS

Water can descend vertically in a number of ways. If flows are limited or splashingneeds to be controlled, then water can be run down a smooth surface such as glass orpolished granite. The maximum length of a sheet of glass is normally 6m. A top fixingwith a bottom restraint avoids distortion. The glass will need to be laminated or pre-ferably armoured. Perspex can be used but is flammable. However, there are othersimilar plastics which are fire resistant. Water can be jetted onto a vertical surface viasmall downward pointing nozzles mounted at 45 to and 15mm away from it. How-ever, a perfectly uniform film can only be formed if the water is fed gently onto the

surface. This means using a discharge trough with baffles (fig 9 & 10). It is importantto avoid irregularities in the surface of the wall as these may cause splashing. Nega-tive steps have little effect but even the smallest positive step will throw water forward(fig 9). Very fine square grooves, 6 x 6mm deep and 6mm apart, can be used to re-tard the flow down a wall and so create a slow wave effect without splashing. In thiscase a smooth initial flow is important and surface tension needs to be reduced. Tocreate a white water effect the surface needs to be rough. Granite or marble can beflame textured but this only makes a small difference. A coarse effect can be achievedby sawing the surface of a slab of stone into parallel ridges which are then broken off.Exposed aggregate concrete offers a cheap way to produce a rough surface. Atextured surface will need to be inclined at 3 to 5 from the vertical if water is toremain in close contact with it. No matter how rough the surface the water will not runwhite until it has accelerated over a distance of 200mm (8 in).

A large free-falling waterfall is always impressive. When water falls it drags air with it.A continuous curtain of falling water just in front of a wall creates a negative pressurebehind it, which in turn tries to draw it back to the wall. A large gap behind the curtainallows air to enter from the sides. Spillways need to be smooth to minimise frictionotherwise the upper and lower surfaces of the flow will move at different speeds. Thispredisposes the water to curl back on itself and to break up. If the last part of a spill-way is almost vertical then the water will be drawn backwards. Spillways can be made

Fig 9 Decorative finishes can befixed to a wall of engineering bricksto avoid penetrating the membrane

Fig 10 To establish a smooth flow ofwater it is necessary to have adischarge trough which is fitted withbaffles

Fig 11 A typical nozzle arrangementfor a linear droplet curtain

Table 2 Water flow rates overdifferent weirs for waterfalls,cascades and overflows. Note -depths measured at the spillway

sharp lightly smoothmetal textured metaledge wide edge wide edge

flow depth depth depthl/s/m mm mm mm

1 4.5 3.5 2.5

2 8.0 6.5 4.5

3 11 8.6 6.5

4 14 10 8.0

5 16 12 9.5

10 27 21 16

15 35 29 23

20 43 36 29

30 57 48 39

40 70 58 48

50 81 68 57

60 91 78 66

70 101 88 75


5/24

from concrete but the best effects are achieved with metal or polished stone. A sharpvertical or horizontal metal strip can produce a curtain but the effect tends to be unsta-ble, irregular and more water is required than is necessary. Ideally a spillway shouldhave a horizontal component to stabilise the flow, and then change to an inclinedsurface to accelerate the water. With a lightly textured material an acceleration slopeangle of 15 will just suffice (fig 12). However, the best solution is a metal or polishedstone spillway with a forward angle of between 30 and 45 to the horizontal, whichserves to throw the water forward (fig 13). The depth of water which is required topass over different spillways can be calculated from tables 3 and 4, and for other ac-tivities from table 2. For example, to determine the flow required for a 3m long

waterfall which is 2.5m high over a metal spillway use table 4. This shows that a dropof 2500mm needs 20mm of water to flow over the spillway. From tables 2 or 4 it canbe seen that this means a flow of approximately 13 l/s/m. The width of 3m is thenmultiplied by 13 l/s/m to give a flow rate of 39 l/s. To reduce the cost of a spillway itcan be limited to an inclined lip bolted to an upstand (fig 14). Such a lip is classified asa sharp edge when calculating flow rates (table 2).

As a curtain of water falls it accelerates and stretches until it finally breaks up. Thegreater the drop the greater the depth of water which needs to pass over the spillwayfor the curtain to maintain its integrity. Even so it is almost impossible to create aperfect unblemished sheet more than 2m high. On a windy site the chance ofproducing a pure curtain is reduced and so greater flows are required. When there isa series of pools linked by pure curtains of water the turbulence from one may disturbthe flow over the next. Baffles placed before each spillway will overcome this problem.

If the supply of water is limited or noise is a problem then the flow can be divided intofingers. A block of falling water droplets can also be striking, particularly if it is stronglylit from below (fig 11). The advantage of the latter system is that the water lands veryprecisely within a small area.

8 CASCADES

Stepped cascades offer an attractive way to handle water over a short verticaldistance. The patterns can range from a fine castelated chequer board to large steps.The larger the steps the greater the flow that is required (fig 15 & table 5). For thebest results the width of each step should be 1.0 to 1.25 times that of its height. Ingeneral the flow over the first step should be 10% of the height of the steps. A mini-mum water depth of 10mm is usually needed to accommodate possible errors in level.A slight back-fall on each horizontal step will even out the effect as it encourages

some lateral movement. In windy locations greater flows are required. There is littlevisual effect on the first step. Only by the third step is full turbulence achieved. Turbu-lence, which is generated by fountains splashing above a cascade, can overcome thisproblem. With angular features additional water must flow over external corners toensure a uniform effect because water does not readily move sideways.

9 ROCKWORK

There are many ways in which it is possible to create rockwork. The one way whichwill not create a good effect is to use natural stone as people s perception of what isnatural is very different to reality. A basic effect can be achieved by applying a sandcement render to a steel mesh which is fixed to a frame or armature. However, thequality of the final product is very workmanship dependent. The best effect is achievedby taking a silicone rubber mould from a natural rock surface and spraying glass

reinforced cement (GRC) onto it. The resultant panels are secured to a metal frame.The backs of the panels are then packed with mortar. Finally the joints arefilled with mortar which is worked insitu until it blends with the adjacent panels. Theeffect is brought to life by spraying with diluted UV stable emulsion paint. Individualpoints of interest, such as algae and lichen, are then added by hand.

Pebbles and cobbles are frequently used in conjunction with water. Below water theycan be very attractive but when dry they appear uniformly light and featureless. A per-manent wet look can be achieved by coating them with epoxy resin. Epoxy bonding isvital in areas where there is any chance of vandalism, such as in shopping malls.Although simple in theory the practice needs a scientific approach. The aggregates mustbe clean and dry, and the chemicals correctly handled if the end product is to endure.

10 METALWORK

Water is a corrosive material particularly if it contains chemicals such as halogens orsalts. As a result the only metal which should be used underwater for permanent fit-tings is medium grade stainless steel (BS 316 L or BS 304 L). Plastic pipework isideally suited for use with water features. However, it is potentially flammable and inpublic areas stainless steel pipework may have to be used. Stainless steel is not

Fig 12 The optimum stone spillwayprofile

Fig 13 The optimum metal spillwayprofile

Fig 14 A minimal sharp edge metalspillway

Table 3 Flow rates for waterfallswith a lightly textured stone spill-way

height width slope depth flowh w s d rate

mm mm mm mm l/s/m

500 100 - 150 30 10 04

1200 125 - 175 45 15 06

2000 150 - 200 55 20 09

2500 175 - 225 65 25 12

3000 200 250 75 30 15

3500 225 - 275 85 35 19

4000 250 - 300 100 40 23

4500 275 - 325 125 45 28

5000 300 - 350 150 50 32

Table 4 Flow rates for waterfallswith a smooth metal or polishedstone spillway

height width slope depth flowh w s d rate

mm mm mm mm l/s/m

500 100 - 150 30 05 02

1200 125 - 175 45 10 05

2000 150 - 200 55 15 10

2500 175 - 225 65 20 13

3000 200 250 75 25 16

3500 225 - 275 85 30 20

4000 250 - 300 100 35 25

4500 275 - 325 125 40 30

5000 300 - 350 150 45 36


6/24

indestructible and can become embrittled if used incorrectly. Condensation readilyforms on stainless steel pipework so lagging is necessary. Such lagging usuallyneeds to be fireproof. Stainless steel pipework, when filled with water, can donateelectrons to mild steel structures. For this reason stainless steel pipes should be elec-trically insulated from the structure which provides them with support.

Bronze and gun metal are easy to work and are widely used for luminaires andnozzles. They should not be used for components which might affect the integrity of awaterproof membrane. Plastic coated mild steel pipes can be used to carry water, butthey corrode rapidly if their surface layer is damaged. Mild steel and galvanised steel

pipes corrode very quickly and should never be used. For the same reason aluminiumis not appropriate for use in water features. Metals which are used underwater are hardto colour as most paints absorb water and eventually peel off. Powder coating is theonly reliable way to apply colour to underwater components. Stainless steel can besurface coloured using an electrolytic process, but the effect is very variable.

11 PIPEWORK AND VALVES

ABS (acrylonitrile butadiene styrene) and uPVC (un-plasticised polyvinyl chloride)pipes are widely used for water features. ABS has the advantage of being moreflexible at low temperatures than uPVC. If the ground is likely to settle then MDPE(medium density polyethylene) pipework, with fusion welded joints, is more appropri-ate. Pipes are available in several wall thicknesses but the abuse to which they aresubjected during installation means that only the heaviest grade should be used. There

are complex tables and calculations for designing plumbing systems, but forgeneral guidance figure 16 can be used for ABS and MDPE pipes, and figure 17 foruPVC pipes The theoretical output of a system should be increased by 20% to pro-vide flexibility and to accommodate unavoidable losses. The velocity of the water, as itpasses along a pipe, should not exceed 2m/s, or 2.5m/s at the most, otherwisecavitation, hammer and erosion may occur.

If pipes are to be buried then they should be laid on a sand bed, covered with sand andmarked with tape. Pipes need to be laid at least 750mm (2 ft 6 in) deep to protectthem against freezing conditions. Under roads or in localities which are prone tosevere frosts the depth of cover should be increased. Drain down points should beprovided in the lowest parts of a system. Above ground pipes need to be supported at

Fig 15 A typical section through astepped cascade

Table 5 Flow rates for steppedcascades

width height depth floww h d rate

mm mm mm l/s/m

100 - 200 100 15 6

150 - 250 150 20 9

200 - 300 200 25 12

250 - 400 200 - 250 30 15

300 - 450 225 - 300 40 23

300 - 450 300 - 450 50 32

Fig 16 Flow diagram for ABS & MDPE pipework Fig 17 Flow diagram for uPVC pipework

internal flow flow hydraulicdiameter rate velocity gradientin mm in l/s in m/s m/100m

internal flow flow hydraulicdiameter rate velocity gradientin mm in l/s in m/s m/100m


7/24

Plate 1 Flame textured granite slabs witha smooth bullnose overlap

Plate 2 Water on a finely slotted metal slabwill produce a slow wavelike effect

Plate 3 A slab of exposed aggregateconcrete will produce a white water effect

Plate 4 The best spillways are formed inmetal and in particular stainless steel

Plate 5 A good spillway consists of ahorizontal element and an inclined take-off

Plate 6 Water will splash forward from arough surface

Plate 7 Water can be thrown forward afterbeing accelerated

Plate 8 A vertical end to a spillway willcause the water to be drawn backwards

Plate 9 With a series of waterfalls theturbulence must be suppressed at each stage

Plate 10 Only by the third step of acascade does the water fully break up

Plate 11 The external corners of a cascadewill stay dry as water does not flow sideways

Plate 12 Fountain turbulence above acascade will animate the top two steps


8/24

Plate 13 As water falls it stretches until itbreaks

Plate 14 A curtain can be formed fromfingers of water

Plate 15 A block of falling water droplets willsparkle particularly if it is well lit

Plate 16 Artificial rock panels are formed byspraying GRC on to silicone rubber moulds

Plate 17 Moulded artificial rockwork canlook very natural

Plate 18 Emulsion paint can be used to addcolour to artificial rockwork

Plate 19 Black granite is ideal for pools as ithighlights any effects produced in the water

Plate 20 A thin film of water can be usedto enliven a decorative surface

Plate 21 A thin layer of water, running downa glass sheet, will produce a fast wave effect

Plate 22 Dappled colours can be used todisguise irregularities in the base of a pool

Plate 23 A lake, which is only 2.5 m deep,can be ecologically stable

Plate 24 A plant room needs to be large andwell planned


9/24

regular intervals. The distance between supports depends upon the type, size andgrade of pipe to be used, and the temperature of the fluid which is to be carried. ABSand uPVC pipes are usually supported at 1800mm intervals for a 110mm (4 in) pipedown to 1100mm for a 32mm (1 in) pipe. Before commissioning all pipework shouldbe tested to at least twice the theoretical maximum pressure to which it could besubjected. To facilitate testing all major sections of pipework must be capable of beingisolated. This usually means providing flanged connections that can receive blankingplates. It must be possible to drain down pipework in Winter and for maintenance.This may necessitate the provision of drain down points. If a pipe passes through afire barrier it must be fitted with an intumescent collar if it is more than 50mm (2 in) in

diameter.

Threaded connections should never be used to join pipes made from differentmaterials, eg. metal to plastic. Only flanges or composite connectors should be usedfor this purpose. Bolted flanges offer the best way of joining sections of pipework to-gether (fig 18 & tables 6 & 7). When a pipe passes through a slab it normally does sovia a puddle flange. This is usually taken to mean a short length of tube with a flangeat its centre through which a pipe can pass. However, if flanges and / or sockets arefitted to the ends of a puddle flange then it can form an active part of the plumbing sys-tem as well as providing a fixing point for nozzles, luminaires etc. The points at whichpipes pass through a membrane are where most leaks occur. Where possiblemembranes should be clamped, with a neoprene gasket and backing ring, to a flangewhich is fully welded to a puddle flange (fig 19). Threaded sealing rings should beused with caution as they can twist the membrane as they are tightened with the resultthat a seal is not achieved. Also water can track along a thread. Pipes which pass

through concrete or soil embankments should bear puddle flanges to preventseepage. A pipe, which is laid in soil, should be stabilised with a block of concrete atthe point where it passes through a flexible membrane.

There are a number of valves which are available for controlling the flow of waterthrough pipes. For manual control there are gate valves, which are usually formed inbrass or steel, and ball valves or butterfly valves which are usually formed in metaland plastic. Plastic diaphragm valves can be used for very precise control. Toautomate systems electric actuators can be bolted onto ball or butterfly valves. Theseare easy to install but prone to fail when subjected to a large number of cycles. Onlythe most rugged should be selected. Pneumatic actuators are far more durable butneed a compressor and a complex pneumatic control system. Hydraulically activateddiaphragm valves are useful but can be difficult to calibrate. These use the same ba-sic principle as a solenoid valve where a difference in pressure, either side of a rubberdiaphragm, is used to change its shape and so the rate of flow. No commonly availablemotorised or solenoid valves are suitable for extended use in a wet environment.

12 PLANT ROOMS

A plant room will usually contain most but not all of the following items of equipment:-

a. main pump(s)b. main pump strainer(s)c. manifold with valvesd. filter pump(s) with integral strainere. sand or cartridge filterf. ultra violet steriliser (usually for fish and / or plants)g. biological filter (for fish and / or plants only)h. acid or alkali dosing pump and tanki. sterilising compound diluter, or dosing pump and tank

j. water softener or deionising unitk. break tank and pressure setl. control panel

m. drain or drainage sump with pump(s)n. ventilation fano. frost protection heater and frost-statp. air compressor for special effects

Inside or immediately adjacent to a building it is advisable to treat the water withchemicals to prevent the growth of micro-organisms. It is also important to removefine debris from the water. This can be done by passing the water through a pleatedcartridge filter or preferably a sand filter. The water treatment system must operatecontinuously and should be independent to the display pump(s). In a multi-level systemthe filtered water can be used to replace that which leaks past non-return valves whenthe main pump(s) is inoperative. If the feature is at several levels or if there is a need

to have an uncluttered pool then it may be necessary to have a hidden fall back tank.Such a tank will need to accommodate several cubic metres of water (fig 21).

A plant room will need to measure at least 2 x 2 x 1.8m high although 3 x 3 x 2m highis to be recommended. This will need to be increased to 7 x 4 x 4m high or more if thefeature is large and / or complex, or if there is a need for a large fall back tank.Prefabricated plant rooms can be assembled off-site in GRP (fibreglass) chambers.

Fig 18 The main features of a fullfaced drilled flange

Fig 19 A puddle flange detail whichallows a membrane to be fixed toa pipe which is already cast into aconcrete slab

Table 6 Flanges drilled to tableD (up to 100 lb/in2) and table E(up to 200 lb/in2)

size OD PCD holes drill

1/2 095 067 4 15

3/4 105 073 4 15

1 115 083 4 15

11/4 140 088 4 15

11/2 150 098 4 15

2 165 115 4 18

3 200 146 4 18

4 E 220 178 8 18

4 D 220 178 4 18

6 286 235 8 22

8 337 292 8 22

Table 7 Flanges drilled to NP10& NP16 (for a nominal pressureof 10 bar & 16 bar)

size OD PCD holes drill

1/2 095 065 4 14

3/4 105 075 4 14

1 115 085 4 14

11/4 140 100 4 18

11/2 150 110 4 18

2 165 125 4 18

3 200 160 8 18

4 220 180 8 18

6 285 240 8 22

8 340 295 12 22


10/24

These are quickly craned into place and buried. They offer a considerable saving intime on site but only a small reduction in cost. All plant rooms must be drained in casewater is lost from the equipment. Plant room drains must be connected to a foulsewer if chemicals are to be added to the water. If it is not possible toconnect to a gravity drainage system then a sump pump will have to be placed in adepression in the floor of the plant room. It is always wise to assume that a sumppump will fail when it is needed so, where possible, two pumps should be provided.To guarantee their operation they should be fed from different electrical sub-stations.A flood alarm, activated by a float switch or an electrode sensor, should be fitted asstandard. Despite the above all major items of equipment should be raised onconcrete plinths at least 300mm high.

Ideally the plant room should be located within 10m of the feature but distances of30m or more can be made to work. If the resistance in the suction pipework isexcessive the pump(s) will cavitate and its output pulsate. This problem can beovercome by increasing the size of the pipe which supplies water to the pump. Thelength of the delivery pipework is seldom of importance.

All plant rooms need to be ventilated to dispose of the heat which is released by theelectrical equipment and to avoid condensation. Plant rooms usually need at least sixair changes an hour. If fresh air is drawn in from outside then it is necessary to have afrost-stat to turn off the ventilation fan(s) when the air temperature falls below, say, 10C(50F). If the main pump(s) could be out of use for several hours at a time then aheater(s) may be needed to maintain the environment in the plant room. If the outsidetemperature is likely to remain below freezing for some time then it may be advisable torun the equipment continuously to prevent the formation of ice in nozzles. When very

low temperatures are anticipated there is no alternative but to drain down pipework,equipment and shallow pools.

13 WATER LEVEL CONTROL

Some nozzles draw additional water and / or air from their immediate surroundings toincrease their visual impact. Such nozzles are water level dependent. The maximumvariation in water level which they can tolerate is usually less than 25mm (1 in). Thisnecessitates very accurate water level control which in turn means an automatictopping up system and well sized overflows.

An overflow must be able to handle the maximum quantity of water which can enter thelowest part of a system (fig 20 & 37). In the case of a lake it is important that theoverflow can handle the worst flood which could occur in 100 years. This also means

that overflows should be able to accommodate run off from adjacent surfaces. Even alawn will discharge water during heavy rain. Overflows can be designed as floodcontrol weirs to provide a storm water balancing capability. The consequences ofperiodic flooding must be reflected in the design of the adjacent landscape. Mostplants will tolerate being inundated for one or two days at a time, as many as three orfour times a year, but only if the ground can drain freely afterwards.

In hot dry weather or inside buildings the evaporative loss from a flat water surface willbe 25mm per week. With agitation this rate can easily be doubled. It is important toavoid the accumulation of salts within a pool i.e. to control the level of suspendedsolids. When salt concentrations reach a critical level, crystals will precipitate onsurfaces within a pool. Such deposits are hard to remove. As a general rule 10% ofthe water, in a formal pool, should be replaced each week. This can usually beachieved by a long back-wash of the sand filter. In Summer even large lakes benefitfrom being flushed with clean water every few weeks.

Water can be obtained from natural sources such as streams, but it is oftencontaminated with silt and micro organisms. Boreholes are a good source of relativelyclean water. The land drains which are laid under a lake membrane can sometimes beused as a source of water. Water can be collected from roofs but it will contain nitrates,particularly after prolonged dry weather. The run-off from car parks may becontaminated with oil although, in theory, interceptors should minimise the risk. In mostlarge cities the municipal water supply is rich in nitrates and phosphates whichencourages the growth of algae.

Features in urban locations are normally supplied with mains water. It is important toensure that pool water cannot be drawn back into the supply pipework. Double actioncheck valves can be used but an air gap is the only certain way to avoid contaminatingthe local drinking water supply. Having an inlet 600mm higher than the surface of apool or a fall back tank is one option. A break tank with a pressure set to pump waterto the feature is the other. In hard water areas a softener may be used to converthard calcium salts into soft sodium salts to make cleaning easier. However, thesoftener must be of sufficient size to allow for rapid refilling of the pool after it has beencleaned. If the water needs to be very clean eg. for a glass wall, then it may benecessary to install a deionising unit. These units are expensive. It is also important toremember that deionised water is extremely aggressive and will corrode all but themost durable materials.

Fig 20 An up-stand overflow whichcan be removed to drain the feature

Table 8 The average full loadcurrent in amps for 3 phase 4pole squirrel cage motors, 50 or60hz, calibrated in kilowatts

240V 380V 415VkW HP

amp amp amp

0.37 0.5 1.8 1.03 -

0.55 0.75 2.75 1.6 -0.75 1.0 3.5 2.0 2.0

1.1 1.5 4.4 2.6 2.5

1.5 2.0 6.1 3.5 3.5

2.2 3.0 8.7 5.0 5.0

3.0 4.0 11.5 6.6 6.5

3.7 5.0 13.5 7.7 7.5

4.0 5.5 14.5 8.5 8.4

5.5 7.5 20 11.5 11

7.5 10 27 15.5 14

9.0 12 32 18.5 17

10 13.5 35 20 19

11 15 39 22 21

15 20 52 30 28

18.5 25 61 37 35

22 30 75 44 40

25 35 85 52 47

30 40 103 60 55

33 45 113 68 60

37 50 126 72 66

40 54 134 79 71

45 60 150 85 80

51 70 170 98 90

55 75 182 105 100

59 80 195 112 105

63 85 203 117 115

75 100 240 138 135

80 110 260 147 138

90 125 295 170 165

100 136 325 188 182


11/24

14 PLUMBING CONFIGURATION

There are a number of ways in which it is possible to plumb a water feature. However,the more common are illustrated below:-

Fig 21 A multi level feature with a fallback tank (IV = isolating valveRV = regulating valve NRV = non-return valve)

Fig 22 A single level feature with a large central nozzle (IV = isolatingvalve RV = regulating valve NRV = non-return valve)

Fig 23 A waterfall where the filtration system re-circulatesvia the main pool

Fig 24 A stepped cascade which uses the filtration systemto keep the upper pool filled and the pipework primed


12/24

15 PUMPS

Pumps can be divided into two main categories. They can be either submersible ordry mounted. These categories can be further sub-divided into single stage or multi-stage pumps. For urban water features single stage dry mounted pumps are the mostwidely used. These give the water one push and move relatively large quantities ofwater at low pressure. Multi-stage pumps contain a number of impellers and move asmall volume of water at high pressure. Dry mounted pumps should always belocated below the surface of the pool from which they have to draw water, otherwisethey may run dry and be damaged. If a pump is mounted above the surface of a pool

it is possible to use non-return valves to keep the pipework flooded, but eventuallydebris will prevent the gates from shutting fully and the pipework will drain. The filterpump can sometimes be used to keep the main system primed, but only if it runs con-tinuously.

Submersible pumps can be single stage eg. sump pumps, or multi-stage eg. boreholepumps. Sewage pumps, which are designed to handle solids, are ideal for themovement of large volumes of very low pressure water. As a rule mains voltagesubmersible pumps should only be used when the public cannot get within 20m ofthem. Even so the circuits must be protected by a residual current detector (RCD).

Once the flow rate has been calculated a pump supplier can determine the modelwhich is required. Table 8 gives an indication of the power supply, in amps, requiredfor a pump calibrated in kilowatts. This information is needed to determine the size ofthe supply cable and the method of starting. Method 1 and table 9 can be used to deter-

mine the size of the supply cable. Every country has its own electrical regulations whichshould always be followed.

16 STRAINERS

Debris will always accumulate in a water feature. As a result a strainer, with aremovable screen, should be placed before each pump to prevent it getting damaged.Valves must be placed before and after a strainer so that it can be opened, at leastonce a week, for cleaning. The screen in the strainer needs to have a large surfacearea, and to be heavily perforated. This means that only special water featurestrainers should be used. The holes in the screen should be half the diameter of thesmallest opening in the display. Some fountain nozzles have very small orifices inwhich case a second fine strainer(s) may be required. Fine screens block quickly andshould not be used in isolation.

17 FILTRATION

Dust and fine debris naturally accumulate in water and make it murky. Such debris canbe removed by the use of filters. Only a few passes a day are usually necessary fortreated water but filters are not ideally suited to removing algae and quickly becomeclogged in biologically active water. The most widely used filters are:-

pleated cartridge filters - these act in the same way as an oil filter on a car engine.They have a short life, are not particularly effective, and are time consuming tochange, but have the advantage of being cheap (fig 25).

sand filters - these consist of a stainless steel or GRP (fibre glass) drum filled withcoarse sand. Water normally passes down through the sand bed with the resultthat debris is deposited on its surface. Every few days the flow is reversed andany debris flushed to waste The sand must be changed once a year. Themaximum flow rate is usually 10 l/s for one square metre of sand area.

18 WATER TREATMENT

Water can be thought of as being either biologically active or treated. Micro-organismsthrive in the presence of light, carbon dioxide and water. Unicellular algae such asScenedesmus spp. colonise first, then a whole range of more complex organismsappear. If the water moves quickly (over 0.5 m/s) filamentous algae will develop. UVsterilisers can be used to kill micro organisms which are in circulation, but they will notaffect those which develop on surfaces within a feature. These can only be controlledby the use of chemicals. There are several algaecides which can be used in pools, butthey are not effective against diseases such as Legionella. Unfortunately even a smallerror in dosing with an algaecide can have a catastrophic effect on plants and fish.

The following processes are widely used for creating a sterile aquatic environment:-

chlorine and bromine ozone metal ions

Fig 25 A pleated cartridge filter

Fig 26 A typical water treatmentFig 26 system

Fig 27 A free standing float switch


13/24

Of these a mixture of chlorine and bromine is the simplest and most certain way ofcontrolling micro-organisms. The chemicals can be added as granules by hand or asa liquid via a pump. However, it is more usual for tablets of concentrated chemicalsto be placed in a diluter or brominator. If chlorine and bromine are used to sanitisewater there may be a smell, but this is usually due to chloroamines which are releasedwhen organic matter degrades. As a result reducing the level of chlorine can make theproblem worse. Dilute brine can be electrolysed to release free chloride radicals.Copper and silver ions can also be used to control the growth of micro organisms. Suchmetal ion systems still need an occasional dose of chlorine to maintain the clarity of thewater. For most treatment systems the pH of the water must be maintained between

7.2 and 7.5. Outside this range their efficacy is reduced and salts may precipitate.

Purifying chemicals can be added by hand. This approach has no capital cost but isunreliable. A time-clock can be used to open a solenoid valve before a diluter or toactivate a dosing pump, but this fails to reflect what is actually happening within thefeature. The best solution is to use an automatic electronic controller. With this asmall amount of water flows around sensor probes which generate signals which aremonitored by electronic circuitry (fig 26). Chemicals are then added automatically tomaintain the pH and redox (reduction / oxidation) potential or aggressiveness of thewater. A fully automatic system is expensive, but very reliable if correctly maintained.

19 FITTINGS

The following fittings are widely used in conjunction with water features:-

a) Skimmers are boxes which are set in the wall of a pool at the water level. Surfacewater flows through these units on its way back to the filter pump. They contain aremovable mesh basket to collect floating debris. They are best located in staticcorners. They are not widely used.

b) Eyeball Fittings are jets mounted in the wall of a pool just below the surface tokeep the water in motion particularly in still corners.

c) Overflows must be sized to accommodate the maximum flow which may resultfrom any eventuality. To prevent them from getting blocked they need to be fittedwith screens. Removable up-stand overflows can be pushed or screwed intodrainage points (fig 20).

d) Anti-vortex plates are placed over the open end of a suction pipe to prevent airgetting drawn into a pump. If this happens the output of the pump will pulsate. Toaccommodate high flow rates an abstraction point may need to be positioned in asump to prevent a vortex from forming. These plates should support coarse grillsto keep out large debris but they must not take the place of a strainer.

e) Supply baffles or diffusers are placed over the end of pipes where water isintroduced below the surface. Supply pipework is often used to drain a feature inwhich case grills must be fitted to hold back debris. When water is introducedclose to a spillway it must not disturb the surface so a large directional baffle maybe required.

f) Anemometers are necessary in most external locations. The electrical pulses

produced by the anemometer are monitored by a unit in the control panel. Thisunit can control the operation of or speed of a pump, or activate motorised valveswhich adjust the flow of water (fig 21 & 22).

g) Water level sensors are available in a number of forms and are used to regulatewater level. They can also be used to sound alarms if water runs to waste or toturn off pumps and lights if the level falls. The following types are widely used:-

Ball cocks or float valves are imprecise as they do not have a positive on-offposition and do not respond well to small changes in water level.

Reed switches contain two metal strips which normally hang apart inside a smalltube. They are forced together by a small magnet fixed to a float which slides upand down the outside of the tube. The signal from the switch is converted into auseable current by a relay which usually activates a solenoid or motorized valvewhich is mounted on the incoming water supply pipework (fig 27, 28 & 29).

Mercury tilt switches consist of a glass tube which contains a bead of mercury.They can be encased in a float or mounted in a cradle above the water where theyrock in response to a float which rests on the surface. They are robust and canswitch a modest current without the use of a relay (fig 30).

Fig 28 A hanging float switch

Fig 29 The reed mechanism whichis to be found in fig 27 & 28

Fig 30 A mercury tilt switch


14/24

Electrode sensors employ a minimum of three stainless steel rods which hang inthe water. The longest is a common return and its end is permanently in the water.As the level falls the middle rod comes out of the water and a relay closes causinga solenoid valve, on the incoming water supply, to open. When the upper rod isreached the relay breaks the electrical circuit and the valve closes. Additional rodsmay be fitted for ancillary functions such as flood alarms or to safeguard equipmentif the water level falls.

20 CONTROL PANELS

Single phase pumps are easy to start with simple switches and time clocks. Over 1kWa pump usually needs a three phase supply and as a result special starting equipment.A three phase power supply has a separate wire for each of the three phases. Theseare normally designated red, yellow and blue or U V W. Up to 5.5kW (7.5hp) a pumpis usually started direct on line (DOL). Over 5.5kW a pump should be started star-delta. In this case the pump starts in the star mode, and after a few seconds switchesto the delta. This allows the pump to build up its speed slowly, but it will still draw 3 to4 times its normal running current during start up. If the same pump was started DOLit would draw 6 to 7 times the normal running current which could affect the powersupply in the local area. A pump which is started DOL only requires 3 live wires andan earth, whereas a star-delta configuration requires six live wires and an earth.

Some large pumps can only be started DOL eg. bore hole pumps. To avoid a powerdrain with these motors a soft start unit is employed. In their more advanced formthese units are referred to as frequency inverters. These allow the speed of themotor and hence the output of the pump to be varied electrically. Such units are veryexpensive and usually cost more than the pump which they are controlling, althoughthey can save money in the long term.

Control cabinets are available in a range of standards. They are usually formed insteel with an anti-corrosion finish although in some countries plastic units are permit-ted. Doors are now fitted with splash proof rubber seals as a matter of course. Themost widely used panels are:-

IP 66 (UK) or Type 4X (USA) - for outdoor use to provide a degree of protectionagainst corrosion, windblown dust and rain, splashing water, hose-directed waterand damage from external ice formation.

IP 55 (UK) or Type 12 (USA) - for indoor use to provide a degree of protectionagainst circulating dust, falling dirt and dripping non-corrosive liquids.

Doors must be lockable with an integral isolator to prevent access whilst the panel islive. Immediately after the isolator there should be an RCD (residual current device),to detect any imbalance between the amount of electricity which is entering and exitingthe system, followed by a main relay. Emergency stop buttons should be positionedclose to the entrances to a plant room and connect into the control circuit whichholds in the main relay. A break in the control circuit will then result in the main relaydropping out and the equipment failing safe. If there is any chance of wateraccumulating within a plant room then a float switch should also be placed in thecontrol circuit. Some functions may need to continue even if the panel shuts itselfdown. For example, sump pumps which drain the plant room should always remainoperative. The supply to these should come from another source. However, this is of-ten impractical so some functions may need to connect directly to the incoming supply

after the main isolator, but before the main control circuit relay and RCD, and a noticeto this effect must be placed on the front of the panel. Any secondary items of equip-ment will then require their own RCD protection.

All panels require either an integral time clock or a Building Management Service(BMS) connection. Any relay which fails to engage should activate a warning light onthe front of the panel and a no volt contact to alert the BMS system which ismonitoring the equipment. Each major item of equipment will require a relay and aswitch on the front of the panel. It is advisable for all switches to be configured forhand-off-auto use. It is normal for the water level controls, the filter pump and thewater treatment equipment to run continuously, and so these items are usually left inthe hand position. However, the main pump(s) is usually switched on for limited peri-ods of time to conserve energy. Lights should not operate without the main pump(s),and need a secondary means of control such as a photo-electric cell. If the level risestoo high water will run to waste and an alarm should be activated. If the level falls

below a predetermined minimum then the lights and the pump(s) should be switchedoff and an alarm activated. This necessitates several water level monitoring devices.

It is common for micro-electronic circuits to malfunction at high or low temperatures.In locations where temperatures can be very low and / or humidities high a heater maybe required inside the panel. If the equipment within the panel is likely to generate a

Method 1 An abridged method forobtaining an indication of cable sizebased loosely on IEE Regulations16th Edition

It is necessary to check that the current rating ofthe selected cable is equal to or greater than thatwhich is required. Also the voltage drop betweenthe supply terminals and the equipment beingsupplied should not exceed 4% of the nominalvoltage of the supply, disregarding starting condi-tions.

max volt drop = approx volt drop x length x Ioad

1000or

approx voltage drop = max voltage drop x 1000

length x loadwhere;

approximate voltage drop is in mV / amp / m runcircuit length is in metrescircuit load is in amps

For example:

circuit load 100 amps per phasecircuit length 200 metresmax voltage drop 4% of 415V or 16.6 volts

therefore

approx volt drop = 16.6 x 1000 = 0.83mV200 x 100

From table 9 it can be seen that an approximatevoltage drop of 0.83mV falls below the figuregiven for a 50mm2 cable which is 0.87mV. As aresult a 70mm2 3 or 4 core armoured coppercable which has a value of 0.60mV is the one toselect.

It is also necessary to check that the currentrating of the selected cable is equal to orgreater than that which is required. In this ex-ample a 70mm2 cable has a rating of 251 ampswhich is greater than the 100 amps which isrequired and is therefore acceptable.

CAUTION - sizing cables is a complex taskwhich should be left to a specialist. Thereare many different types of cable and ways ofmounting them. The above is a quick way toget a feel for a cable size which ignores themore complex aspects of the subject. Alsoregulations differ between countries. Alwaysconsult a specialist.

Table 9 Copper conductor sizes formulti-core XLPE (as opposed to PVC)armoured cables with thermosettinginsulation attached to a perforated tray

2 core 3 or 4 core

con- single approx three approx

ductor phase volt phase voltcross AC or drop/ AC drop/

section DC amp/m amp/m

mm2 amps mV amps mV

1.5 29 31 25 27

2.5 39 19 33 16

4 52 12 44 10

6 66 7.9 56 6.8

10 90 4.7 78 4.0

16 115 2.9 99 2.50

25 152 1.90 131 1.65

35 188 1.35 162 1.15

50 228 1.00 197 0.87

70 291 0.69 251 0.60

95 354 0.52 304 0.45

120 410 0.42 353 0.37150 472 0.35 406 0.30

185 539 0.29 463 0.26

240 636 0.24 546 0.21

300 732 0.21 628 0.195

400 847 0.195 728 0.170


15/24

large amount of heat then a small ventilation fan may be required. Lightingtransformers should always be mounted in separate enclosures, away from the controlpanel, due to the heat which they generate. Every country has its own electrical regu-lations. These are always extensive and need to be reflected in the design of anypanel. All components which are used in a panel should be locally available so thatrepairs can be quickly effected.

21 LIGHTING

It is almost impossible to over illuminate a water feature. Luminaires should bedirected upwards if a fountain or waterfall is being lit. With individual nozzles thelighting should be symmetrical. With linear effects banding can be a problem if theluminaires are spaced too far apart. If underwater luminaires are mounted close to thehorizontal then total internal reflection will occur. This means that the bottom of thepool will be illuminated and no light will come through the surface. This may beacceptable if the base of the pool is clean and uncluttered. If not then attention will bedrawn to any shortcomings.

Luminaires need to be mounted as close to the surface as possible as even a smalldepth of agitated water significantly reduces light output. If possible they should bewashed by water from the display. Incandescent lamps are inefficient and generate agreat deal of heat. If a luminaire is switched on when it is uncovered its lens willoverheat and crack. As a result the water level needs to be automatically monitored

and the luminaires turned off if they become exposed. Also the lighting relay shouldbe linked to the main pump relay so that the lights will not operate in isolation. Aphoto-electric cell should be used to prevent the lights from operating during the day.

Most luminaires have interchangeable lenses although some seal round the front ofthe lamp. Coloured lenses are available but each chosen colour requires a separateset of luminaires or a multi lamped luminaire. Blue and red lenses dramatically reducelight output. Green and yellow lenses allow more light to pass through them. Amixture of luminaires with coloured and clear lenses can be used to create pasteleffects. Full spectrum LED luminaires will emit a wide range of coloured light, but theyare expensive and lack the power of more conventional units.

In several countries the normal mains power supply is 110/120 volt. Although not com-pletely safe such supplies carry far less risk than the 220/240 volt supply which is used

in many countries. If a number of luminaires are connected to different phases of thesame supply then the potential hazard increases to 415 volts. In theory 240 volt lampscan be used in underwater luminaires provided that there is adequate RCD protection.However, this is not to be recommended. Voltages can always be reduced by the useof a transformer. For sheer power 500 watt PAR 56 and 1000 watt PAR 64 110/120 voltlamps are the most popular. In swimming pools 12 volt luminaires are usuallymandatory. Water features are often used for recreation by children and so logicallyshould be engineered to the same standard. 50 or 75 watt 12 volt dichromic lamps arenow widely used but lack power. Powerful 6 volt and 12 volt lamps, up to 250 watts,are available but require very heavy cables. Transformers need to be located within10m of low voltage luminaires to avoid power loss in the cables. Greater distances canbe accommodated, but only if the transformers are customised to allow for the voltagedrop. Ideally all transformers should be toroidally wound so that the loss of one ortwo lamps does not affect the life of the remainder. Fibre optic systems have beendeveloped for use in swimming pools. They have the advantage that the light sourcecan be located away from the feature, but they lack power and are rarely appropriate.

Where possible the luminaires should be wired so that they can be li fted out of the waterfor relamping but this operation is still best done when the feature is drained down.Lamp life is usually much longer than anticipated because of the cooling effect of thewater. It is not uncommon to only change lamps once a year. Only vulcanised rubberor ethylene propylene cables should be used underwater. Cables with a PVC sheathshould not be used as they are slightly porous.

22 NOZZLES

There are many different types of nozzle manufactured by different companies. How-ever, to produce an outline design it is necessary to have some idea of how much

water is required for the display. The tables on the following pages are based on equip-ment from a number of sources. All that is necessary is to select the type ofnozzle and the height of the effect that is required. From the tables the flow ratesand hence the pipe sizes can be determined. Large pod effects are only a collection ofnozzles mounted together. It is possible to calculate their flow requirement by addingtogether the output of the individual jets (fig 32 & 33).

Fig 31 The relationship betweennozzles from a simple finger jetthrough all the major types


16/24

AERATOR JET (water level dependent)

These create a tall column of white water with a pulsating crown when mounted vertically. They are veryeconomical with water. The amount of air which enters the stream can be adjusted by raising or loweringthe outer collar. The column diameter at the base is very small. They are very useful when groupedtogether particularly as a pod. Their venturi design makes them very water level dependent. If there is anyfloating debris in the feature then a trash guard will need to be fitted around the base of each nozzle.

FOAM OR BUBBLER JET

These create a low pulsating mound of heavily aerated water which can be useful in windy locations. Alarge expanding spray can be created at higher flow rates. The column diameter at the base is about halfthe height. These nozzles should be covered before the water supply is turned on otherwise there will bea great deal of spray. The depth of water over the nozzles needs to be strictly maintained. These jets cancause surging in small features unless wave baffles are fitted. If surging is acceptable then the effect canbe exploited. These jets require a non-turbulent water supply. The breather pipe must be well clear of thesurface of the pool and may need extending if several nozzles are used close together.

CASCADE JET

These produce a tall conical block of highly aerated water. The column diameter at the base is onequarter of the height. They can be used on their own or as part of a group. Their venturi design makesthem very water level dependent. They can cause surging in small features unless wave baffles are fitted.They require a non-turbulent water supply.

optimumperformance

thread od ht height m 1.0 1.5 2.0 3.0 4.0 5.0 6.0 8.0 10.0 12.0 15.0

3/4 inch 25mm 185mm flow l/s 0.3 0.4 0.4 0.5 0.6

head m 6.0 8.0 10.5 14.5 17.0

1 inch 30mm 235mm flow l/s 0.4 0.5 0.6 0.7 0.8 0.9

head m 4.0 6.5 8.0 11.0 14.5 18.0

11/4 inch 40mm 255mm flow l/s 0.6 0.7 0.8 0.9 1.0 1.1 1.2

head m 3.5 5.0 6.0 8.5 10 13 18

11/2 inch 50mm 335mm flow l/s 0.6 0.7 0.9 1.2 1.4 1.6 1.8 2.0 2.2 2.4

head m 3.5 4.5 5.5 7.5 9.0 11 12 16 19 23

2 inch 65mm 385mm flow l/s 1.5 2.0 2.4 2.7 3.0 3.4 3.8 4.2 4.5 5.0

head m 3.0 4.0 5.5 7.0 8.5 10 13 16 18 22

3 inch 90mm 535mm flow l/s 5.3 6.2 7.0 7.8 8.6 9.5 10 11 13

head m 8.0 8.5 10 13 15 18 22 26 32


3/4 inch 185mm 235mm flow l/s 0.8 1.0 1.2 1.4 1.7

head m 3.1 4.8 5.9 8.3 9.6

1 inch 105mm 280mm flow l/s 1.2 1.5 1.7 1.9 2.1 2.2

head m 2.6 4.6 5.8 7.0 8.6 11.0

11/4 inch 115mm 345mm flow l/s 1.7 2.1 2.5 2.9 3.1 3.3 3.7

head m 2.5 4.5 6.7 8.0 8.9 10.7 14.7

11/2 inch 130mm 390mm flow l/s 2.2 2.8 3.4 3.9 4.3 4.7 5.6 6.3

head m 2.5 4.9 6.9 8.4 11.6 17.1 21.1 23.5

2 inch 175mm 450mm flow l/s 3.6 4.4 5.1 5.6 6.1 6.4 7.2 7.9 8.6 16.8

head m 2.2 3.9 5.2 6.3 7.4 8.2 9.9 11.6 13.2 21.0

3 inch 250mm 525mm flow l/s 6.0 7.1 7.8 8.5 8.9 10.8 12.8 14.2 18.2 19.2

head m 3.1 4.3 5.5 7.1 8.3 9.8 11.9 15.6 24.7 28.5


3/4 inch 150mm 135mm flow l/s 1.0 1.3 1.5 1.7 1.9 2.1

head m 7.1 11 15 20 24 27

11/4 inch 170mm 190mm flow l/s 1.4 1.7 2.0 2.2 2.4 2.6 2.9

head m 6.4 7.9 9.5 14 17 20 24

11/2 inch 180mm 230mm flow l/s 1.7 2.0 2.3 2.7 2.9 3.2 3.7

head m 2.9 6.6 9.9 13 15 16 24

2 inch 100mm 290mm flow l/s 4.9 5.3 5.9 6.3 7.0 7.8 8.2 9.5 12

head m 7.6 9.3 11 14 19 24 27 33 39

3 inch 160mm 365mm flow l/s 8.4 9.4 10 11 13 14 16 19 23

head m 6.1 8.1 9.3 11 15 18 20 35 47


17/24

Plate 25 A collection of aerating jets with500 watt PAR 56 luminaires

Plate 26 A block of water level independentaerating jets surrounded by a splash zone

Plate 27 A ring of water level dependentaerating jets set on a granite dome

Plate 28 Cascade jets produce thick densecolumns of water

Plate 29 A ring of cascade jets Plate 30 Five cascade jets with four 500watt PAR 56 luminaires

Plate 31 A foam or bubbler jet with itsbreather pipe projecting above the surface

Plate 32 A feature can be covered withpaving to create a piazza

Plate 33 Aerating jets discharging throughpaving slabs

Plate 34 A ring of aerating jets with a tallcentral column which is causing splashing

Plate 35 A large foam pod flanked by fourcascade jets (see fig 32)

Plate 36 A water level dependent aeratingjet castle pod (see fig 33)


18/24

Plate 37 A dandelion needs a very wellfiltered water supply

Plate 38 A bell nozzle display will form andcollapse repeatedly if perfectly adjusted

Plate 39 Calyx jets are very variable witheven a small amount of adjustment

Plate 40 Water can be blown out of a cylin-der below a jet with compressed air

Plate 41 Finger jets can be set in a ring Plate 42 Finger jets can be set on a linearmanifold

Plate 43 An aerator can be used tomechanically entrain air in water

Plate 44 Coloured lenses can be fitted toluminaires but they do reduce light output

Plate 45 White and coloured light can becombined to create pastel shades

Plate 46 A twin pump floating fountain,upside down, awaiting installation

Plate 47 A floating fountain with cascadejets

Plate 48 Small floating fountains can enli-ven and oxygenate static bodies of water


19/24

AERATOR JET (water level independent)

These create a tall column of white water when mounted vertically. Their totally enclosed design meansthat they are not water level dependent. They do not require a smooth water supply. They tend to be lessforceful than the water level dependent type of aerator nozzle described above. The column diameter atthe base is very small. As they discharge above water they can be used to introduce water to a multilevelsystem without the need for non-return valves.

CALYX, MORNING GLORY or TULIP JET

These create a clear circular mushroom of water from a low mounted nozzle (as opposed to a bell jet whichhas a tall pipe at its centre). The pattern can be adjusted from a full translucent sheet to a rough brokenhalf sheet with a droplet outer skirt. A constant water level is not required but windy locations should beavoided. The water supply needs to be non turbulent and very well filtered. As they discharge above waterthey can be used to introduce water to a multilevel system without the need for non-return valves. A num-

ber of different inserts and / or adjustable collars are available which can be used to change the initialsteepness of a curtain across a range of angles, which in turn affects its height and spread.

FINGER, PLUME OR CLEAR JET

These are the most basic jet and can be used individually or grouped in a pod where they can produce amassive column. They are ideally suited for use along a straight or circular manifold. They are availablewith a simple threaded socket connection or an adjustable swivel coupling. They require a very stable flowof water. If the supply is turbulent then flow straightening vanes will be required in the pipework before thejet. They should only be used a few degrees away from the direction of the supply flow.

spray height flowin m in l/s

spray diam headin m in m

thread ht spray 20o 25o 30o 35o 40o 45o

11/2 inch 200mm flow l/s 0.7 1.3 0.7 1.3 0.7 1.4 0.6 1.6 0.6 1.8 0.5 2.3

head m 0.4 0.9 0.4 0.6 0.5 0.6 0.6 0.6 0.7 0.6 0.8 0.6

2 inch 230mm flow l/s 0.8 2.6 0.7 2.2 0.7 2.5 0.6 2.8 0.6 3.2 0.5 3.8

head m 0.5 1.2 0.6 0.9 0.8 0.9 0.9 0.6 1.1 0.6 1.2 0.6

3 inch 300mm flow l/s 0.9 8.2 0.8 6.3 0.8 7.6 0.7 8.2 0.7 9.5 0.6 12

head m 0.9 1.5 1.5 1.2 1.7 1.2 1.9 1.2 2.0 0.9 2.5 0.9

4 inch 350mm flow l/s 1.1 13 1.0 11 0.9 12 0.8 12 0.7 15 0.7 21

head m 1.5 1.8 2.1 1.5 2.3 1.5 2.4 1.2 2.8 1.2 3.1 1.2

6 inch 400mm flow l/s 1.2 23 1.1 14 1.1 15 1.0 16 0.8 21 0.7 26

head m 1.8 2.1 2.4 1.8 2.5 1.8 2.8 1.5 3.1 1.5 3.4 1.5

thread od ht height m 1.0 1.5 2.0 3.0 4.0 5.0 6.0 8.0 10.0

1 inch 30mm 150mm flow l/s 0.7 0.8 0.9 1.1

11/4 inch 40mm 160mm flow l/s 1.0 1.2 1.3 1.5 1.7

11/2 inch 45mm 200mm flow l/s 1.5 1.7 1.9 2.2 2.4 2.7

2 inch 55mm 220mm flow l/s 1.8 2.2 2.6 3.3 3.9 4.5 5.0 6.0 7.0

3 inch 80mm 285mm flow l/s 4.0 4.5 5.0 6.0 7.0 8.0 9.0 10.5 12.0

head m 4.5 6.0 7.5 11 13 16 18 22 27

0.5 1.0 1.5 2.0 3.0 4.0 5.0 6.0 8.0 10 15 20 30 40 50 60 100

0.7 1.3 1.9 2.5 3.8 5.0 6.3 7.5 10 13 19 25 38 50 63 75 125

0.01 0.03 0.04 0.05 0.06

0.03 0.05 0.07 0.09 0.11 0.13

0.06 0.09 0.11 0.13 0.16 0.21

0.09 0.13 0.16 0.20 0.24 0.28

0.15 0.25 032. 0.40 0.45 0.50 0.55

0.25 0.35 0.45 0.55 0.65 0.75 0.85 0.95

0.40 0.55 0.65 0.75 0.95 1.15 1.25 1.40 1.60

0.70 0.90 1.20 1.50 1.85 2.25 2.70 3.10 3.50

1.75 2.20 2.65 3.20 3.80 4.40 4.75 5.58 6.33

2.40 3.20 3.85 4.60 5.80 7.00 7.81 9.06 10.2 12.5 14.3 16.2 17.1

4.50 5.50 6.65 7.80 9.00 11.3 13.4 15.0 16.8 20.4 23.4 27.0 30.0

7.10 9.00 10.8 12.5 14.9 17.8 20.3 24.0 26.8 32.7 38.0 42.5 47.7 58.2

9.60 12.0 15.0 18.5 23.4 28.2 31.8 37.2 42.0 52.8 61.2 68.9 76.1 90.0

17.3 21.6 27.0 31.3 38.8 46.0 52.0 60.6 68.8 84.3 97.9 111 122 143

24.6 31.8 37.8 42.0 52.2 63.6 72.7 82.1 93.5 116 141 155 171 200

A - a male threaded swivel connection secured by a lock nutB - a female threaded swivel connection secured by a bolted flange

thd thd ht orif height m

inch inch mm mm head m

1/4 60 3 flow l/s

1/4 60 4 flow l/s

3/8 70 5 flow l/s

3/8 70 6 flow l/s

1/2 B 85 8 flow l/s

1/2 3/4 84 10 flow l/s

3/4 11/4 105 12 flow l/s

A 11/2 140 16 flow l/s

11/2 155 20 flow l/s

2 190 25 flow l/s

3 310 30 flow l/s

4 390 40 flow l/s

4 or 5 475 50 flow l/s

6 550 65 flow l/s

6 600 75 flow l/s

optimumperformance


20/24

Water should not flow through pipework faster than 2.0m/s, or 2.5m/s at the most.When it reaches the nozzle the water has to be accelerated for it to create a visualeffect. As a result most nozzles taper so as to force the water into a jet. The remain-der usually squeeze the water through a narrow gap. The basic tapered nozzle willproduce a clear finger of water. These can be positioned around a circular or along alinear manifold. The flow entering the nozzle needs to be stable otherwise the jet willbreak up around the outside. For this reason there should always be a length ofstraight pipe immediately before a nozzle. Vanes in this pipework will significantlyimprove the stability of the flow. Even so, the stream will still break up if the force withwhich the water passes through the nozzle becomes excessive. This happens becausethe water which is adjacent to the wall of the nozzle and the supply pipe travels at adifferent speed to that which is at the centre of the flow. In some special applicationsthis problem is overcome by placing fine drinking straws, or metal mesh in the nozzle.This creates a jet of water which travels at a uniform speed or a lamina flow. Thisgives a very precise effect but needs very clean water otherwise the straws getblocked (see jumping jets below). To create more volume a simple tapered jet can beincorporated into a nozzle to draw in additional water and / or air (fig 31). Height is thensacrificed for volume. For a stronger effect a number of nozzles can be grouped into apod (fig 32 & 33). Nozzles are usually formed in brass or gun metal because thesematerials are easy to machine. Some small nozzles are formed in plastic but they arefragile and should be avoided.

Sudden changes in the flow rate to a jet cannot be achieved by valving as the water inthe pipework takes time to accelerate. A number of novelty effects are available whichemploy different techniques to overcome this problem. Probably the best known is thejumping jet where a smooth arching primary jet of water is periodically deflected by a

second unseen jet of water so that it fails to pass through an orifice in a plate. A pneu-matically or hydraulically operated guillotine can be used to achieve the same effect. Abrief intermittent effect can be achieved by blowing water out of a chamberimmediately below a nozzle with compressed air which is stored in an adjacent cylinder.This produces instant, powerful but short lived, jets of water.

Mists can be cooling in Summer but the water must be sterile if the threat of Legionellais to be avoided. Fogging nozzles use very high pressure water or water which isaccelerated with compressed air. The water needs to be free of particulate matter asthe opening in the nozzles are very small.

24 MAINTENANCE AND TESTING OF FORMAL POOLS

The maintenance cycle must be determined before a design is finalised. Formal poolsusually need to be drained down, cleaned and refilled in less than a day and sometimesovernight. The drainage system and the water supply need to be of sufficient size tomake this possible. In and around buildings the water usually needs to be treated toavoid a health risk. Adding chemicals to a system is pointless if their concentrations arenot regularly monitored. The pH and chemical content of the water should be testedtwice a week. The bacterial and fungal content should be monitored by exposing dipslides every two weeks. The presence of Legionella can only be detected by specialtests which should take place every two months.

25 FLOATING FOUNTAINS

On lakes where the water level fluctuates the only way to produce an effect is to havea fountain which floats. This is done by having a series of almost submerged floatswhich are bolted to a frame (fig 34). Below the frame hangs one or more sump pumpsor horizontally mounted bore hole pumps. The pump(s) feed into a chamber which lies

directly below the nozzle(s). Lights can be bolted to the frame. The great advantageof floating fountains is that they can be removed for routine maintenance and, ifnecessary, for the Winter. For safety, there must always be an earth leakage detector(RCD) in the supply and an isolator immediately next to the lake. No human activityshould be allowed within at least 20m of such equipment.

Standing bodies of water can become anaerobic particularly in hot weather. In suchcases aerators can be beneficial. In this case an electric motor hangs below a circularfloat and carries a propeller. The flow can be directed upwards to throw water into theair or mounted horizontally below the surface with a venturi system to entrain air.These units can be mounted several metres below the surface to direct warm waterupwards to keep boat moorings free of ice or to provide a better environment for fish.

26 ORGANIC WATER

With natural water the rule is the deeper the better although at depths over 10mstratification, where the water separates into layers, can be a problem. Fountains canhelp to overcome this difficulty. To be ecologically stable a lake needs to be over 5m(16 ft) deep. However, it is seldom cost effective to construct lakes of this depth. If alarge part of a lake is over 2.5m (8 ft) deep and the water is circulated then there areseldom difficulties. The shade of trees can prevent overheating but their leaves can

Fig 32 A large foam pod consists ofnumerous aerating nozzles connectedto a lower manifold and an upper airsupply chamber (see plate 35).Indicative flow rates are as follows:-

4m high 30 l/s @ 30m head8m high 38 l/s @ 45m head

12m high 45 l/s @ 60m head

Fig 33 Aerating jet castle pod (seeplate 36). Many combinations arepossible but often 1 or 3 nozzles witha 2 inch bsp thread are surroundedby 8 to 16 nozzles with a 11/2 inchbsp thread. The total flow requirementcan be calculated from the waterlevel dependent aerating nozzle

table

Fig 34 A typical section through afloating fountain


21/24

cause problems. Soft leaves, from say Alder and Birch, can enrich a natural systemproviding that the quantity is not excessive. Algae will develop on all underwater sur-faces unless the depth of water is sufficient to prevent light from reaching the bottom.

The minimum depth of water which is required for fish is a balance between the cost ofconstruction, and the danger of over-heating in Summer and freezing in Winter. If thefeature is engineered so that it always remains cool, clean and well oxygenated, then300mm (1 ft) of water will often suffice. Unfortunately, the temperature of a shallowbody of water soon matches that of its surroundings, although careful environmentdesign can minimise this problem.

Water is at its most dense at 4C which is why ice floats. Toxic gases can accumulatewhen the surface is sealed with ice. It may be advisable to employ a heater, or to directwarm water from the bottom of a deep pool at the surface, to keep at least part of it freefrom ice, if the fish are of particular value (see section 25 above).

27 ORGANIC WATER QUALITY

Fish and plants add an interesting dimension to any water feature. Unfortunately, algaedevelop rapidly when water warms up. Water, which contains plants and fish, canbe treated with chemicals to reduce the growth of micro-organisms. They are notparticularly effective and can kill the plants and fish if the dosage is wrong. Salmonella,Listeria, E. coli and / or Legionella are usually present in natural water bodies. As aresult untreated water should never be agitated in the presence of people with a weakimmune system or in a confined space. In locations where the temperature of the water

is likely to exceed 20C on a regular basis the water may need to be chilled to controlthe development of Legionella.

When combined, bright sunlight and oxygen have a sanitising effect. Vigorousaeration in high light conditions is often sufficient to keep water clear. Air can beentrained below the surface by the use of venturi nozzles (fig 35). To keep water cleanfor fish it is necessary to provide a biological filter (fig 36). This is a large tank filledwith inert porous granular material, such as lytag, upon which bacteria can develop todigest plant and fish waste. Experience would indicate that 2m3 of filter medium areneeded to treat the waste from 100kg of fish. However, this is very variable anddepends upon the environment and the species. UV sterilisers will dramatically reducethe number of bacteria and algae in circulation. However, they will not prevent algaefrom developing on surfaces within a feature. Regular sweeping of the inside of a pool,even when it is full of water, will reduce this problem as it causes the algae to be drawninto the treatment system.

28 INFORMAL LAKES

When an embankment is built across a natural water course it is said to be onstream. With an on stream structure the riparian rights of users downstream must berespected. For example, in Summer the lake might evaporate the total flow of thestream which feeds it. In contrast an off stream lake is placed away from the bottomof a valley although it can be fed by a spur from a stream to keep it topped up withfresh water. Unless it is unavoidable no more than 25,000m3 (5,555,000 gallons) ofwater should be stored above ground level. Retaining structures which hold more thanthis quantity of water need routine inspections and certification which is costly. Theflow from a catchment area which is greater than 400ha (1000 acres) should not beintercepted due to the size of the overflow which is needed to accommodate the worststorm in 100 years (fig 37).

Fig 35 A simple aerating nozzlewhich draws air into the re-circulationsupply for an organic pool.

Fig 36 A biological filtration system


22/24

It is possible to produce an impervious water retaining structure from an homoge-nous subsoil which is comprised of 25% clay mixed with equal parts of sand andgravel (fig 38). If such material is in short supply then an impervious clay rich corecan be supported by less impervious material (fig 39). The top of an embankmentshould be 4 to 5m across and at least 1.2m higher than the normal water level. Thesides should have a slope which is no steeper than 1 in 3 or 33%. Pipes which passthrough earth structures should bear fully welded flanges which increase the lengthof any potential seepage by at least 50%. All open pipes should be fitted with hingedguards to prevent the entry of debris, animals and children.

Deep water can be a danger to people who do not anticipate its presence. At nopoint should the sides of a lake slope at more than 1 in 3 or 33%. A gently slopingledge 2 to 4m (6 ft to 12 ft) wide, covered by 450 to 600mm (1 ft 6 in to 2 ft) of water,should be formed around the perimeter of all decorative lakes to enable a person tocrawl out. Such a ledge can support emergent aquatic plants.

Unless the ground under an artificial lake has a very high clay content it will need tobe lined. A liner represents a considerable additional investment and will usuallydouble the cost of construction. Puddled clay was traditionally used but is seldompractical due to the problem of locating the correct grade of clay, spreading it andthen puddling it. Should puddled clay dry out it will crack and leak even when re-wetted. Bentonite (powdered clay) can be mixed with sub-soil to produce a fragilewaterproof layer. Several companies market a thin layer of bentonite sandwichedbetween two layers of geotextile. In this form it is easy to handle but must be placedcarefully and immediately covered with 300mm (1 ft) of soil. As the bentonite absorbs

water it swells. It cannot lift the weight of the overlying soil so it expands sideways toproduce a seal. The theory is simple but the practice often leaves much to be desireddue to difficulties which are encountered during installation.

Flexible non-elastic lake liners such as polyethylene and polyvinyl chloride (PVC) arecheap but are not particularly durable. PVC sheets are sometimes reinforced with asynthetic fibre mesh to increase their durability. The best membranes are producedfrom butyl rubber or the more modern EPDM (ethylene propylene diene monomer).

Fig 37 A section through a lakeoverflow which will accommodatestorm flows without backing up

Fig 38 A basic earth embankment with or without a liner softened by a downstream surcharge of soil to support small trees and shrubs

Fig 39 An embankment with a clay rich core for use where there is insufficient clay on site or where it is of the wrong grade

Fig 40 A part section through a typical lake with a membrane


23/24

Both materials will accept a great deal of stretching but are expensive. There are anumber of grades available but the most commonly used is 1.2mm thick. Large sheetsare fabricated from narrow rolls in factory conditions so as to keep on-site welding to aminimum. The maximum joint length is usually a multiple of 25m up to a maximum of100m. The largest area that can be handled with ease is 1000m2. The large concerti-na folded sheets are placed on the edge of the excavation and stretched out beforebeing welded together (fig 40). Sheet membranes have the advantage that the jointscan be vacuum tested. Flexible membranes are usually glued to any concrete struc-tures to support their weight. Stainless steel strips are then pressed against a thicklayer of flexible sealant, which is placed along the top edge of the membrane, before

being screwed in place.

Most lakes need to be emptied at some time during their life. To avoid the danger ofrising ground water lifting the membrane a land drain, with gravel back fill, shouldalways be positioned under a lake (fig 40). The drain should discharge to waste oropen into a chamber from which the water can be pumped when necessary. The edgeof a lake needs to be carefully detailed as the membrane has to be turned into a trenchand protected in a way that cannot be compromised by wave action. The excavationmust be cleared of all sharp objects to safeguard the well-being of the membrane. Instony areas a sand bed may be required. In all cases sheet membranes should beprotected both above and below by a thick geotextile fabric. The two geotextile layerswill usually cost 25% of the liner price. Placing a layer of sand or stone free sandy sub-soil 300mm (12 in) thick on top of the geotextile is the best way of completing theprotection. A strip of gravel, cobbles, timber and / or plants around the outside of thelake is necessary to prevent erosion.

29 PLANTS

Few aquatic plants prosper in water which is more than 1.5m deep (5ft). Even waterlilies prefer less than this depth. Marginal plants usually prefer water which is only 100to 3

Date post:	05-Apr-2018
Category:	Documents
Upload:	lee-brazier
View:	216 times
Download:	0 times

Designing a Water Feature_Tech Bulletin

Documents