Hydrotechnology
CI/SfB 998
Technical Bulletin
DESIGNING A WATER FEATURE
1 INTRODUCTION
Few designers have the time that is necessary to master the intricacies of designing
water features and so they have to rely upon performance specifications to convey their
wishes. 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 requirements
with precision. This is a briefing document and should be treated as such. Each topic
covered in this bulletin is a complex subject in itself. All technical matters, particularly
those of an electrical nature, need to be resolved by a qualified person in a way that
reflects 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, to
use high quality materials, and not to be overly complex. If a feature is not well
designed and constructed it will become a burden rather than an asset. An adequate
budget is important as good quality materials are always expensive. Experimentation
is an important part of any creative design process. The feasibility of all key components should be demonstrated before construction commences.
Fig 1 In still conditions water will
spread outwards by half the distance
that it travels upwards
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
Fig 2 Water will splash forward by a
quarter to a half the height of a rough
wall depending upon its angle and
surface characteristics
When designing a water feature it is important to pay attention to all aspects of the
environment in which it is to be placed. For example, sun angles are particularly
important 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 lose
development space overrides the need to create a feature of adequate size. It is better not to have a feature than one which is too small. It is also important to anticipate
the activities that are to take place adjacent to any feature. For example, in a crowded
shopping 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 the
distance that it travels upwards (fig 1). This is a rule which can only be improved upon
by employing a very short burst effect in which the rising water does not collide with
the falling water. In external locations the radius of a pool should at least equal the
height 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 the
prevailing wind speed above 2.5m/s (5.5mph). An external feature should always
have 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 feature
as possible e.g. on top of an adjacent lamp post or flag pole.
Fig 3 Circular pools can surge up
and down if nozzles are used which
discharge below water
When water runs down a vertical surface the amount of spray which it creates
depends upon the physical characteristics of that surface. Water which passes down
a very rough surface can spread forward almost half the height of the wall (fig 2). This
contrasts with polished stone or glass, both of which will hold water in close contact
with their surface. The spread of water is surprisingly small when it is dropped as a
free falling curtain in a sheltered location. However, any curtain or wall of water is
susceptible to the effect of wind so an anemometer and / or a remote switch should
always be provided in external locations.
Around natural lakes the ground should slope gently to the water particularly if the
area is to be used for storm water balancing. Paving should fall away from formal
pools so that rain does not wash debris into the feature. The paving should fall to
drainage channels so that any water which is accidentally lost from the system can be
safely disposed of. During very cold weather some pools will need to be drained
down. Such features must be designed to be vandal proof and attractive when empty.
Fig 4 If the water is to be flush with
its surroundings then a tanked
recessed channel is needed to avoid
tracking under finishes
3 NOISE
Water will generate white noise when it is agitated. This can be useful if it masks
conversations or mechanical noise. In most retail locations the background noise level
is 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. In
such 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 to
reduce splashing. Alternatively, air can be mechanically entrained to reduce the
density of the water both in the effect and within the feature itself, which in turn serves
to reduce noise levels.
4 FREEBOARD
Fig 5
Complete circulation is
important if the water is to remain
clean (option 1)
High winds can produce waves over 300mm (1 ft) high on a lake only one hundred
metres (110 yds) across. Powerful fountain nozzles can also produce waves. Circular
pools may surge up and down if nozzles are used which initially discharge below the
surface (fig 3). If pools at different levels are linked together then the lowest pool will
receive any water which runs back when the feature is shut down. If the lowest pool is
not large enough to receive all the water then a hidden tank must be provided. When
calculating the size of a fall back tank, or the lowest pool in a series, it is prudent to
assume that any non-return valves in the pumping system will fail to close. Positioning
the 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 minimum
freeboard of 150mm (6 in) is to be recommended. With a ‘quiet’ feature this can be
reduced to 75mm (3 in). The risk of capillary action behind decorative finishes can be
avoided by close bonding. If water is to appear flush with an adjacent surface then a
drained channel needs to be recessed into the floor around the feature to avoid water
tracking back under the finishes (fig 4).
Fig 6
Complete circulation is
important if the water is to remain
clean (option 2)
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 overall
plumbing configuration. Water should be introduced and drawn off in a way that ensures full turnover (fig 5 & 6). Underwater jets pointing towards or away from the outer
walls 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 at
least 2° to a drainage point or sump to facilitate sweeping. Channel bottoms can also
be laid to falls to keep debris moving (table 1).
Fig 7 Water can be bled out below a
nozzle to keep the corners clean
Fig 8 A sump can be formed to
accommodate large nozzles
Table 1
Silt movement over a
flat concrete bed
flow rate
silt movement
0.075m/s
0.125m/s
no silt movement
slight movement when
disturbed but settling later
big conglomerations of
algae starting to move
silt moving well, large
inorganic material
stationary
usual speed required for
mass flow in sewers
0.150m/s
0.300m/s
1.000m/s
In urban locations it is advisable to minimise the depth of water so as to shorten maintenance periods and for reasons of safety. The industry standard water depth for a
decorative pool is 400mm (16 in). This depth is sufficient to cover most lights and
nozzles. With a freeboard of 150mm the base of a pool will still be less than 600mm
below its surroundings. It is not usual to provide safety rails for a drop of less than
600mm (2 ft) so this establishes the normal edge profile. If there is a requirement for
large nozzles then sumps can be formed in the base of a pool (fig 8). To avoid clutter
and 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 and
split pipework. Water trapped behind decorative finishes may force them away from
their backing as it freezes so full bonding is necessary. If water is to remain in a pool
during freezing conditions it may be necessary to have gently sloping sides which will
allow the ice to slide upwards. A feature must be designed so that it looks attractive
when it is switched off or drained down. A simple bed of cobbles can make an empty
pool look attractive in the middle of Winter. Alternatively a pool can be covered with
paving 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 a
pool consists of a single concrete structure it may not need lining but this is seldom the
case. Day work joints usually mean that a membrane is required. Liquid rubber or
bitumen 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 insitu with fibreglass, polypropylene or polyethylene mat to increase their resilience.
There are a range of sheet materials which are good for tanking but these cannot
support a decorative finish without a rigid internal structure. GRP (glass reinforced
plastic) or fibreglass is a useful material as it has structural properties of its own. It is
expensive but can carry decorative finishes particularly if the surface is textured with
crushed flint or silver sand. All membranes should be electronically and / or flood
tested before decorative finishes are applied. All penetrations need to be carefully detailed 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 external locations sunlight and freeze thaw cycles put an additional stress on finishes. At
the waterline they must be particularly durable as this is where environmental conditions are at their most extreme and where deposits accumulate. Pool walls should be
finished with smooth materials which are easy to clean. Horizontal surfaces may benefit from having some texture as it will improve traction, although rough surfaces will
present maintenance problems.
Historically marble was used for water features because it was widely available and
easy to work. Unfortunately, its surface dissolves quickly particularly when the water
has a low pH or is treated with aggressive chemicals such as chlorine. Sandstone and
limestone should be avoided as they absorb water. If natural stone is to be used then
the best material is granite. Terrazo should never be used as the pigments, which
provide much of its colour, are denatured by halogens and acids. High quality glazed
ceramic tiles are durable and much cheaper than stone.
Fig 9 Decorative finishes can be
fixed to a wall of engineering bricks
to avoid penetrating the membrane
It is important to select the right colour for a feature. Dark blues, dark greys and black
are 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 make
the water look dirty. Greens should be approached with caution as they often look
artificial and clash with adjacent vegetation. Uniform colours highlight imperfections
and 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 be
recommended. Thoughtful detailing often allows vertical stone panels to be fixed at
the top whilst the bottoms are retained by the floor. If large, complex or heavy panels
are to be used then an engineering brick wall can be built in front of the membrane to
receive mechanical fixings (fig 9). All mechanical fixings must be made from stainless
steel. Bedding layers under finishes should either be pure epoxy based (not epoxy cement) and preferably flexible ‘rubber’ compounds. Under no circumstances should
conventional cementatious mortars be used. Lime is easily leached from them and will
form 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 sealant
is applied. Care should be taken to colour co-ordinate joint fillers with adjacent
finishes.
Fig 10 To establish a smooth flow of
water it is necessary to have a
discharge trough which is fitted with
baffles
7 WATERFALLS AND WATERWALLS
Water can descend vertically in a number of ways. If flows are limited or splashing
needs to be controlled, then water can be run down a smooth surface such as glass or
polished granite. The maximum length of a sheet of glass is normally 6m. A top fixing
with a bottom restraint avoids distortion. The glass will need to be laminated or preferably armoured. Perspex can be used but is flammable. However, there are other
similar plastics which are fire resistant. Water can be jetted onto a vertical surface via
small downward pointing nozzles mounted at 45° to and 15mm away from it. However, 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 important
to avoid irregularities in the surface of the wall as these may cause splashing. Negative 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 retard the flow down a wall and so create a slow wave effect without splashing. In this
case a smooth initial flow is important and surface tension needs to be reduced. To
create a white water effect the surface needs to be rough. Granite or marble can be
flame textured but this only makes a small difference. A coarse effect can be achieved
by 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. A
textured surface will need to be inclined at 3° to 5° from the vertical if water is to
remain in close contact with it. No matter how rough the surface the water will not run
‘white’ 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 pressure
behind it, which in turn tries to draw it back to the wall. A large gap behind the curtain
allows air to enter from the sides. Spillways need to be smooth to minimise friction
otherwise the upper and lower surfaces of the flow will move at different speeds. This
predisposes the water to curl back on itself and to break up. If the last part of a spillway is almost vertical then the water will be drawn backwards. Spillways can be made
Fig 11 A typical nozzle arrangement
for a linear droplet curtain
Table 2 Water flow rates over
different weirs for waterfalls,
cascades and overflows. Note depths measured at the spillway
sharp
lightly
smooth
metal textured
metal
edge wide edge wide edge
flow
l/s/m
depth
mm
depth
mm
depth
mm
1
2
3
4
5
10
15
20
30
40
50
60
70
4.5
8.0
11
14
16
27
35
43
57
70
81
91
101
3.5
6.5
8.6
10
12
21
29
36
48
58
68
78
88
2.5
4.5
6.5
8.0
9.5
16
23
29
39
48
57
66
75
Fig 12 The optimum stone spillway
profile
Table 3 Flow rates for waterfalls
with a lightly textured stone spillway
height
h
mm
500
1200
2000
2500
3000
3500
4000
4500
5000
width
w
mm
100 - 150
125 - 175
150 - 200
175 - 225
200 250
225 - 275
250 - 300
275 - 325
300 - 350
slope depth flow
s
d
rate
mm
mm l/s/m
30
45
55
65
75
85
100
125
150
10
15
20
25
30
35
40
45
50
04
06
09
12
15
19
23
28
32
from concrete but the best effects are achieved with metal or polished stone. A sharp
vertical or horizontal metal strip can produce a curtain but the effect tends to be unstable, irregular and more water is required than is necessary. Ideally a spillway should
have a horizontal component to stabilise the flow, and then change to an inclined
surface to accelerate the water. With a lightly textured material an acceleration slope
angle of 15° will just suffice (fig 12). However, the best solution is a metal or polished
stone spillway with a forward angle of between 30° and 45° to the horizontal, which
serves to throw the water forward (fig 13). The depth of water which is required to
pass over different spillways can be calculated from tables 3 and 4, and for other activities 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 drop
of 2500mm needs 20mm of water to flow over the spillway. From tables 2 or 4 it can
be seen that this means a flow of approximately 13 l/s/m. The width of 3m is then
multiplied by 13 l/s/m to give a flow rate of 39 l/s. To reduce the cost of a spillway it
can be limited to an inclined lip bolted to an upstand (fig 14). Such a lip is classified as
a sharp edge when calculating flow rates (table 2).
As a curtain of water falls it accelerates and stretches until it finally breaks up. The
greater the drop the greater the depth of water which needs to pass over the spillway
for the curtain to maintain its integrity. Even so it is almost impossible to create a
perfect unblemished sheet more than 2m high. On a windy site the chance of
producing a pure curtain is reduced and so greater flows are required. When there is
a series of pools linked by pure curtains of water the turbulence from one may disturb
the 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 into
fingers. A block of falling water droplets can also be striking, particularly if it is strongly
lit from below (fig 11). The advantage of the latter system is that the water lands very
precisely within a small area.
8 CASCADES
Fig 13 The optimum metal spillway
profile
Table 4 Flow rates for waterfalls
with a smooth metal or polished
stone spillway
height
h
mm
500
1200
2000
2500
3000
3500
4000
4500
5000
width
w
mm
100 - 150
125 - 175
150 - 200
175 - 225
200 250
225 - 275
250 - 300
275 - 325
300 - 350
slope depth flow
s
d
rate
mm
mm l/s/m
30
45
55
65
75
85
100
125
150
05
10
15
20
25
30
35
40
45
02
05
10
13
16
20
25
30
36
Stepped cascades offer an attractive way to handle water over a short vertical
distance. 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 the
best results the width of each step should be 1.0 to 1.25 times that of its height. In
general the flow over the first step should be 10% of the height of the steps. A minimum 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 little
visual effect on the first step. Only by the third step is full turbulence achieved. Turbulence, which is generated by fountains splashing above a cascade, can overcome this
problem. With angular features additional water must flow over external corners to
ensure 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 which
will not create a good effect is to use natural stone as people’s perception of what is
natural is very different to reality. A basic effect can be achieved by applying a sand
cement render to a steel mesh which is fixed to a frame or armature. However, the
quality of the final product is very workmanship dependent. The best effect is achieved
by 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 are
filled with mortar which is worked insitu until it blends with the adjacent panels. The
effect is brought to life by spraying with diluted UV stable emulsion paint. Individual
points of interest, such as algae and lichen, are then added by hand.
Pebbles and cobbles are frequently used in conjunction with water. Below water they
can be very attractive but when dry they appear uniformly light and featureless. A permanent wet look can be achieved by coating them with epoxy resin. Epoxy bonding is
vital 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 must
be clean and dry, and the chemicals correctly handled if the end product is to endure.
10 METALWORK
Fig 14 A minimal sharp edge metal
spillway
Water is a ‘corrosive’ material particularly if it contains chemicals such as halogens or
salts. As a result the only metal which should be used underwater for permanent fittings is medium grade stainless steel (BS 316 L or BS 304 L). Plastic pipework is
ideally suited for use with water features. However, it is potentially flammable and in
public areas stainless steel pipework may have to be used. Stainless steel is not
indestructible and can become embrittled if used incorrectly. Condensation readily
forms on stainless steel pipework so lagging is necessary. Such lagging usually
needs to be fireproof. Stainless steel pipework, when filled with water, can donate
electrons to mild steel structures. For this reason stainless steel pipes should be electrically insulated from the structure which provides them with support.
Bronze and gun metal are easy to work and are widely used for luminaires and
nozzles. They should not be used for components which might affect the integrity of a
waterproof membrane. Plastic coated mild steel pipes can be used to carry water, but
they 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 aluminium
is not appropriate for use in water features. Metals which are used underwater are hard
to colour as most paints absorb water and eventually peel off. Powder coating is the
only reliable way to apply colour to underwater components. Stainless steel can be
surface coloured using an electrolytic process, but the effect is very variable.
Fig 15 A typical section through a
stepped cascade
Table 5 Flow rates for stepped
cascades
width
w
mm
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 more
flexible at low temperatures than uPVC. If the ground is likely to settle then MDPE
(medium density polyethylene) pipework, with fusion welded joints, is more appropriate. Pipes are available in several wall thicknesses but the abuse to which they are
subjected during installation means that only the heaviest grade should be used. There
are complex tables and calculations for designing plumbing systems, but for
general guidance figure 16 can be used for ABS and MDPE pipes, and figure 17 for
uPVC pipes The theoretical output of a system should be increased by 20% to provide flexibility and to accommodate unavoidable losses. The velocity of the water, as it
passes along a pipe, should not exceed 2m/s, or 2.5m/s at the most, otherwise
cavitation, hammer and erosion may occur.
100
150
200
250
300
300
-
200
250
300
400
450
450
height
h
mm
depth
d
mm
flow
rate
l/s/m
100
150
200
200 - 250
225 - 300
300 - 450
15
20
25
30
40
50
6
9
12
15
23
32
If pipes are to be buried then they should be laid on a sand bed, covered with sand and
marked with tape. Pipes need to be laid at least 750mm (2 ft 6 in) deep to protect
them against freezing conditions. Under roads or in localities which are prone to
severe frosts the depth of cover should be increased. Drain down points should be
provided in the lowest parts of a system. Above ground pipes need to be supported at
internal
diameter
in mm
flow
rate
in l/s
flow
velocity
in m/s
hydraulic
gradient
m/100m
Fig 16 Flow diagram for ABS & MDPE pipework
internal
diameter
in mm
flow
rate
in l/s
flow
velocity
in m/s
Fig 17 Flow diagram for uPVC pipework
hydraulic
gradient
m/100m
Plate 1 Flame textured granite slabs with
a smooth bullnose overlap
Plate 2 Water on a finely slotted metal slab
will produce a slow wavelike effect
Plate 3 A slab of exposed aggregate
concrete will produce a white water effect
Plate 4 The best spillways are formed in
metal and in particular stainless steel
Plate 5 A good spillway consists of a
horizontal element and an inclined take-off
Plate 6 Water will splash forward from a
rough surface
Plate 7 Water can be thrown forward after
being accelerated
Plate 8 A vertical end to a spillway will
cause the water to be drawn backwards
Plate 9 With a series of waterfalls the
turbulence must be suppressed at each stage
Plate 10 Only by the third step of a
cascade does the water fully break up
Plate 11 The external corners of a cascade
will stay dry as water does not flow sideways
Plate 12 Fountain turbulence above a
cascade will animate the top two steps
Plate 13 As water falls it stretches until it
breaks
Plate 14 A curtain can be formed from
fingers of water
Plate 15 A block of falling water droplets will
sparkle particularly if it is well lit
Plate 16 Artificial rock panels are formed by
spraying GRC on to silicone rubber moulds
Plate 17 Moulded artificial rockwork can
look very natural
Plate 18 Emulsion paint can be used to add
colour to artificial rockwork
Plate 19 Black granite is ideal for pools as it
highlights any effects produced in the water
Plate 20 A thin film of water can be used
to enliven a decorative surface
Plate 21 A thin layer of water, running down
a glass sheet, will produce a fast wave effect
Plate 22 Dappled colours can be used to
disguise 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 and
well planned
regular intervals. The distance between supports depends upon the type, size and
grade of pipe to be used, and the temperature of the fluid which is to be carried. ABS
and uPVC pipes are usually supported at 1800mm intervals for a 110mm (4 in) pipe
down to 1100mm for a 32mm (1 in) pipe. Before commissioning all pipework should
be tested to at least twice the theoretical maximum pressure to which it could be
subjected. To facilitate testing all major sections of pipework must be capable of being
isolated. This usually means providing flanged connections that can receive blanking
plates. 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 a
fire barrier it must be fitted with an intumescent collar if it is more than 50mm (2 in) in
diameter.
Fig 18 The main features of a full
faced drilled flange
Table 6 Flanges drilled to table
D (up to 100 lb/in2) and table E
(up to 200 lb/in2)
size
OD
PCD
holes
drill
1/2
095
105
115
140
150
165
200
220
220
286
337
067
073
083
088
098
115
146
178
178
235
292
4
4
4
4
4
4
4
8
4
8
8
15
15
15
15
15
18
18
18
18
22
22
3/4
1
11/4
11/2
2
3
4E
4D
6
8
Table 7 Flanges drilled to NP10
& NP16 (for a nominal pressure
of 10 bar & 16 bar)
size
OD
PCD
holes
drill
1/2
095
105
115
140
150
165
200
220
285
340
065
075
085
100
110
125
160
180
240
295
4
4
4
4
4
4
8
8
8
12
14
14
14
18
18
18
18
18
22
22
3/4
1
11/4
11/2
2
3
4
6
8
Threaded connections should never be used to join pipes made from different
materials, eg. metal to plastic. Only flanges or composite connectors should be used
for this purpose. Bolted flanges offer the best way of joining sections of pipework together (fig 18 & tables 6 & 7). When a pipe passes through a slab it normally does so
via a puddle flange. This is usually taken to mean a short length of tube with a flange
at its centre through which a pipe can pass. However, if flanges and / or sockets are
fitted to the ends of a puddle flange then it can form an active part of the plumbing system as well as providing a fixing point for nozzles, luminaires etc. The points at which
pipes pass through a membrane are where most leaks occur. Where possible
membranes should be clamped, with a neoprene gasket and backing ring, to a flange
which is fully welded to a puddle flange (fig 19). Threaded sealing rings should be
used with caution as they can twist the membrane as they are tightened with the result
that 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 prevent
seepage. A pipe, which is laid in soil, should be stabilised with a block of concrete at
the point where it passes through a flexible membrane.
There are a number of valves which are available for controlling the flow of water
through pipes. For manual control there are gate valves, which are usually formed in
brass or steel, and ball valves or butterfly valves which are usually formed in metal
and plastic. Plastic diaphragm valves can be used for very precise control. To
automate systems electric actuators can be bolted onto ball or butterfly valves. These
are easy to install but prone to fail when subjected to a large number of cycles. Only
the most rugged should be selected. Pneumatic actuators are far more durable but
need a compressor and a complex pneumatic control system. Hydraulically activated
diaphragm valves are useful but can be difficult to calibrate. These use the same basic principle as a solenoid valve where a difference in pressure, either side of a rubber
diaphragm, is used to change its shape and so the rate of flow. No commonly available
motorised 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.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
l.
m.
n.
o.
p.
main pump(s)
main pump strainer(s)
manifold with valves
filter pump(s) with integral strainer
sand or cartridge filter
ultra violet steriliser (usually for fish and / or plants)
biological filter (for fish and / or plants only)
acid or alkali dosing pump and tank
sterilising compound diluter, or dosing pump and tank
water softener or deionising unit
break tank and pressure set
control panel
drain or drainage sump with pump(s)
ventilation fan
frost protection heater and frost-stat
air compressor for special effects
Inside or immediately adjacent to a building it is advisable to treat the water with
chemicals to prevent the growth of micro-organisms. It is also important to remove
fine debris from the water. This can be done by passing the water through a pleated
cartridge filter or preferably a sand filter. The water treatment system must operate
continuously and should be independent to the display pump(s). In a multi-level system
the filtered water can be used to replace that which leaks past non-return valves when
the 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).
Fig 19 A puddle flange detail which
allows a membrane to be fixed to
a pipe which is already cast into a
concrete slab
A plant room will need to measure at least 2 x 2 x 1.8m high although 3 x 3 x 2m high
is to be recommended. This will need to be increased to 7 x 4 x 4m high or more if the
feature 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.
These are quickly craned into place and buried. They offer a considerable saving in
time on site but only a small reduction in cost. All plant rooms must be drained in case
water is lost from the equipment. Plant room drains must be connected to a foul
sewer if chemicals are to be added to the water. If it is not possible to
connect to a gravity drainage system then a sump pump will have to be placed in a
depression in the floor of the plant room. It is always wise to assume that a sump
pump 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 as
standard. Despite the above all major items of equipment should be raised on
concrete plinths at least 300mm high.
Ideally the plant room should be located within 10m of the feature but distances of
30m or more can be made to work. If the resistance in the suction pipework is
excessive the pump(s) will cavitate and its output pulsate. This problem can be
overcome by increasing the size of the pipe which supplies water to the pump. The
length of the delivery pipework is seldom of importance.
Fig 20 An up-stand overflow which
can be removed to drain the feature
All plant rooms need to be ventilated to dispose of the heat which is released by the
electrical equipment and to avoid condensation. Plant rooms usually need at least six
air changes an hour. If fresh air is drawn in from outside then it is necessary to have a
frost-stat to turn off the ventilation fan(s) when the air temperature falls below, say, 10°C
(50°F). If the main pump(s) could be out of use for several hours at a time then a
heater(s) may be needed to maintain the environment in the plant room. If the outside
temperature is likely to remain below freezing for some time then it may be advisable to
run 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 to
increase their visual impact. Such nozzles are water level dependent. The maximum
variation in water level which they can tolerate is usually less than 25mm (1 in). This
necessitates very accurate water level control which in turn means an automatic
topping up system and well sized overflows.
An overflow must be able to handle the maximum quantity of water which can enter the
lowest part of a system (fig 20 & 37). In the case of a lake it is important that the
overflow 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 a
lawn will discharge water during heavy rain. Overflows can be designed as flood
control weirs to provide a storm water balancing capability. The consequences of
periodic flooding must be reflected in the design of the adjacent landscape. Most
plants will tolerate being inundated for one or two days at a time, as many as three or
four 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 will
be 25mm per week. With agitation this rate can easily be doubled. It is important to
avoid the accumulation of salts within a pool i.e. to control the level of suspended
solids. When salt concentrations reach a critical level, crystals will precipitate on
surfaces within a pool. Such deposits are hard to remove. As a general rule 10% of
the water, in a formal pool, should be replaced each week. This can usually be
achieved by a long back-wash of the sand filter. In Summer even large lakes benefit
from being flushed with clean water every few weeks.
Water can be obtained from natural sources such as streams, but it is often
contaminated with silt and micro organisms. Boreholes are a good source of relatively
clean water. The land drains which are laid under a lake membrane can sometimes be
used 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 be
contaminated with oil although, in theory, interceptors should minimise the risk. In most
large cities the municipal water supply is rich in nitrates and phosphates which
encourages the growth of algae.
Features in urban locations are normally supplied with mains water. It is important to
ensure that pool water cannot be drawn back into the supply pipework. Double action
check valves can be used but an air gap is the only certain way to avoid contaminating
the local drinking water supply. Having an inlet 600mm higher than the surface of a
pool or a fall back tank is one option. A break tank with a pressure set to pump water
to the feature is the other. In hard water areas a softener may be used to convert
‘hard’ calcium salts into ‘soft’ sodium salts to make cleaning easier. However, the
softener must be of sufficient size to allow for rapid refilling of the pool after it has been
cleaned. If the water needs to be very clean eg. for a glass wall, then it may be
necessary to install a deionising unit. These units are expensive. It is also important to
remember that deionised water is extremely ‘aggressive’ and will corrode all but the
most durable materials.
Table 8 The average full load
current in amps for 3 phase 4
pole squirrel cage motors, 50 or
60hz, calibrated in kilowatts
kW
HP
240V
amp
380V
amp
415V
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
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 valve
RV = regulating valve NRV = non-return valve)
Fig 22 A single level feature with a large central nozzle (IV = isolating
valve RV = regulating valve NRV = non-return valve)
Fig 23 A waterfall where the filtration system re-circulates
via the main pool
Fig 24 A stepped cascade which uses the filtration system
to keep the upper pool filled and the pipework primed
15 PUMPS
Pumps can be divided into two main categories. They can be either submersible or
dry mounted. These categories can be further sub-divided into single stage or multistage pumps. For urban water features single stage dry mounted pumps are the most
widely used. These give the water one ‘push’ and move relatively large quantities of
water at low pressure. Multi-stage pumps contain a number of impellers and move a
small volume of water at high pressure. Dry mounted pumps should always be
located below the surface of the pool from which they have to draw water, otherwise
they 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 eventually
debris will prevent the gates from shutting fully and the pipework will drain. The filter
pump can sometimes be used to keep the main system primed, but only if it runs continuously.
Submersible pumps can be single stage eg. sump pumps, or multi-stage eg. borehole
pumps. Sewage pumps, which are designed to handle solids, are ideal for the
movement of large volumes of very low pressure water. As a rule mains voltage
submersible pumps should only be used when the public cannot get within 20m of
them. Even so the circuits must be protected by a residual current detector (RCD).
Fig 25 A pleated cartridge filter
Once the flow rate has been calculated a pump supplier can determine the model
which is required. Table 8 gives an indication of the power supply, in amps, required
for a pump calibrated in kilowatts. This information is needed to determine the size of
the supply cable and the method of starting. Method 1 and table 9 can be used to determine the size of the supply cable. Every country has its own electrical regulations which
should always be followed.
16 STRAINERS
Debris will always accumulate in a water feature. As a result a strainer, with a
removable 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 least
once a week, for cleaning. The screen in the strainer needs to have a large surface
area, and to be heavily perforated. This means that only special water feature
strainers should be used. The holes in the screen should be half the diameter of the
smallest opening in the display. Some fountain nozzles have very small orifices in
which case a second fine strainer(s) may be required. Fine screens block quickly and
should not be used in isolation.
17 FILTRATION
Dust and fine debris naturally accumulate in water and make it murky. Such debris can
be removed by the use of filters. Only a few passes a day are usually necessary for
treated water but filters are not ideally suited to removing algae and quickly become
clogged 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 to
change, but have the advantage of being cheap (fig 25).
•
sand filters - these consist of a stainless steel or GRP (fibre glass) drum filled with
coarse sand. Water normally passes down through the sand bed with the result
that debris is deposited on its surface. Every few days the flow is reversed and
any debris flushed to waste The sand must be changed once a year. The
maximum flow rate is usually 10 l/s for one square metre of sand area.
Fig 26
Fig 26
A typical water treatment
system
18 WATER TREATMENT
Water can be thought of as being either biologically active or treated. Micro-organisms
thrive in the presence of light, carbon dioxide and water. Unicellular algae such as
Scenedesmus spp. colonise first, then a whole range of more complex organisms
appear. If the water moves quickly (over 0.5 m/s) filamentous algae will develop. UV
sterilisers can be used to kill micro organisms which are in circulation, but they will not
affect those which develop on surfaces within a feature. These can only be controlled
by the use of chemicals. There are several algaecides which can be used in pools, but
they are not effective against diseases such as Legionella. Unfortunately even a small
error 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 27 A free standing float switch
Of these a mixture of chlorine and bromine is the simplest and most certain way of
controlling micro-organisms. The chemicals can be added as granules by hand or as
a liquid via a pump. However, it is more usual for tablets of concentrated chemicals
to be placed in a diluter or ‘brominator’. If chlorine and bromine are used to sanitise
water there may be a smell, but this is usually due to chloroamines which are released
when organic matter degrades. As a result reducing the level of chlorine can make the
problem 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. Such
metal ion systems still need an occasional dose of chlorine to maintain the clarity of the
water. 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.
Fig 28 A hanging float switch
Purifying chemicals can be added by hand. This approach has no capital cost but is
unreliable. A time-clock can be used to open a solenoid valve before a diluter or to
activate a dosing pump, but this fails to reflect what is actually happening within the
feature. The best solution is to use an automatic electronic controller. With this a
small amount of water flows around sensor probes which generate signals which are
monitored by electronic circuitry (fig 26). Chemicals are then added automatically to
maintain the pH and redox (reduction / oxidation) potential or ‘aggressiveness’ of the
water. 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. Surface
water flows through these units on its way back to the filter pump. They contain a
removable mesh basket to collect floating debris. They are best located in static
corners. They are not widely used.
b) Eyeball Fittings are jets mounted in the wall of a pool just below the surface to
keep the water in motion particularly in still corners.
c) Overflows must be sized to accommodate the maximum flow which may result
from any eventuality. To prevent them from getting blocked they need to be fitted
with screens. Removable up-stand overflows can be pushed or screwed into
drainage points (fig 20).
d) Anti-vortex plates are placed over the open end of a suction pipe to prevent air
getting drawn into a pump. If this happens the output of the pump will pulsate. To
accommodate high flow rates an abstraction point may need to be positioned in a
sump to prevent a vortex from forming. These plates should support coarse grills
to keep out large debris but they must not take the place of a strainer.
Fig 29 The reed mechanism which
is to be found in fig 27 & 28
e) Supply baffles or diffusers are placed over the end of pipes where water is
introduced below the surface. Supply pipework is often used to drain a feature in
which case grills must be fitted to hold back debris. When water is introduced
close to a spillway it must not disturb the surface so a large directional baffle may
be 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. This
unit can control the operation of or speed of a pump, or activate motorised valves
which adjust the flow of water (fig 21 & 22).
g) Water level sensors are available in a number of forms and are used to regulate
water level. They can also be used to sound alarms if water runs to waste or to
turn off pumps and lights if the level falls. The following types are widely used:-
Fig 30 A mercury tilt switch
•
Ball cocks or float valves are imprecise as they do not have a positive on-off
position and do not respond well to small changes in water level.
•
Reed switches contain two metal strips which normally hang apart inside a small
tube. They are forced together by a small magnet fixed to a float which slides up
and down the outside of the tube. The signal from the switch is converted into a
useable current by a relay which usually activates a solenoid or motorized valve
which 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 they
rock in response to a float which rests on the surface. They are robust and can
switch a modest current without the use of a relay (fig 30).
•
Electrode sensors employ a minimum of three stainless steel rods which hang in
the 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 causing
a solenoid valve, on the incoming water supply, to open. When the upper rod is
reached the relay breaks the electrical circuit and the valve closes. Additional rods
may be fitted for ancillary functions such as flood alarms or to safeguard equipment
if the water level falls.
20 CONTROL PANELS
Single phase pumps are easy to start with simple switches and time clocks. Over 1kW
a 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. These
are normally designated red, yellow and blue or U V W. Up to 5.5kW (7.5hp) a pump
is usually started ‘direct on line’ (DOL). Over 5.5kW a pump should be started ‘stardelta’. In this case the pump starts in the star mode, and after a few seconds switches
to the delta. This allows the pump to build up its speed slowly, but it will still draw 3 to
4 times its normal running current during start up. If the same pump was started DOL
it would draw 6 to 7 times the normal running current which could affect the power
supply in the local area. A pump which is started DOL only requires 3 live wires and
an 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 ‘power
drain’ with these motors a ‘soft start’ unit is employed. In their more advanced form
these units are referred to as ‘frequency inverters’. These allow the speed of the
motor and hence the output of the pump to be varied electrically. Such units are very
expensive and usually cost more than the pump which they are controlling, although
they can save money in the long term.
Control cabinets are available in a range of standards. They are usually formed in
steel with an anti-corrosion finish although in some countries plastic units are permitted. Doors are now fitted with splash proof rubber seals as a matter of course. The
most widely used panels are:-
•
IP 66 (UK) or Type 4X (USA) - for outdoor use to provide a degree of protection
against corrosion, windblown dust and rain, splashing water, hose-directed water
and damage from external ice formation.
•
IP 55 (UK) or Type 12 (USA) - for indoor use to provide a degree of protection
against circulating dust, falling dirt and dripping non-corrosive liquids.
Doors must be lockable with an integral isolator to prevent access whilst the panel is
live. 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 exiting
the system, followed by a main relay. Emergency stop buttons should be positioned
close to the entrances to a plant room and connect into the control circuit which
holds in the main relay. A break in the control circuit will then result in the main relay
dropping out and the equipment failing safe. If there is any chance of water
accumulating within a plant room then a float switch should also be placed in the
control circuit. Some functions may need to continue even if the panel shuts itself
down. For example, sump pumps which drain the plant room should always remain
operative. The supply to these should come from another source. However, this is often 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 notice
to this effect must be placed on the front of the panel. Any secondary items of equipment 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 on
the front of the panel and a ‘no volt’ contact to alert the BMS system which is
monitoring the equipment. Each major item of equipment will require a relay and a
switch on the front of the panel. It is advisable for all switches to be configured for
‘hand-off-auto’ use. It is normal for the water level controls, the filter pump and the
water treatment equipment to run continuously, and so these items are usually left in
the ‘hand’ position. However, the main pump(s) is usually switched on for limited periods 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 rises
too 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 switched
off 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 may
be required inside the panel. If the equipment within the panel is likely to generate a
Method 1
An abridged method for
obtaining an indication of cable size
based loosely on IEE Regulations
16th Edition
It is necessary to check that the current rating of
the selected cable is equal to or greater than that
which is required. Also the voltage drop between
the supply terminals and the equipment being
supplied should not exceed 4% of the nominal
voltage of the supply, disregarding starting conditions.
max volt drop = approx volt drop x length x Ioad
1000
or
approx voltage drop = max voltage drop x 1000
length x load
where;
approximate voltage drop is in mV / amp / m run
circuit length is in metres
circuit load is in amps
For example:
circuit load
circuit length
max voltage drop
100 amps per phase
200 metres
4% of 415V or 16.6 volts
therefore
approx volt drop = 16.6 x 1000 = 0.83mV
200 x 100
From table 9 it can be seen that an approximate
voltage drop of 0.83mV falls below the figure
given for a 50mm2 cable which is 0.87mV. As a
result a 70mm2 3 or 4 core armoured copper
cable which has a value of 0.60mV is the one to
select.
It is also necessary to check that the current
rating of the selected cable is equal to or
greater than that which is required. In this example a 70mm2 cable has a rating of 251 amps
which is greater than the 100 amps which is
required and is therefore acceptable.
CAUTION - sizing cables is a complex task
which should be left to a specialist. There
are many different types of cable and ways of
mounting them. The above is a quick way to
get a ‘feel’ for a cable size which ignores the
more complex aspects of the subject. Also
regulations differ between countries. Always
consult a specialist.
Table 9 Copper conductor sizes for
multi-core XLPE (as opposed to PVC)
armoured cables with thermosetting
insulation attached to a perforated tray
2 core
3 or 4 core
single approx
phase
volt
AC or drop/
DC
amp/m
three approx
phase
volt
AC
drop/
amp/m
mm2
amps
mV
amps
mV
1.5
2.5
4
6
10
16
25
35
50
70
95
120
150
185
240
300
400
29
39
52
66
90
115
152
188
228
291
354
410
472
539
636
732
847
31
19
12
7.9
4.7
2.9
1.90
1.35
1.00
0.69
0.52
0.42
0.35
0.29
0.24
0.21
0.195
25
33
44
56
78
99
131
162
197
251
304
353
406
463
546
628
728
27
16
10
6.8
4.0
2.50
1.65
1.15
0.87
0.60
0.45
0.37
0.30
0.26
0.21
0.195
0.170
conductor
cross
section
large amount of heat then a small ventilation fan may be required. Lighting
transformers should always be mounted in separate enclosures, away from the control
panel, due to the heat which they generate. Every country has its own electrical regulations. These are always extensive and need to be reflected in the design of any
panel. All components which are used in a panel should be locally available so that
repairs can be quickly effected.
21 LIGHTING
It is almost impossible to over illuminate a water feature. Luminaires should be
directed upwards if a fountain or waterfall is being lit. With individual nozzles the
lighting should be symmetrical. With linear effects ‘banding’ can be a problem if the
luminaires are spaced too far apart. If underwater luminaires are mounted close to the
horizontal then total internal reflection will occur. This means that the bottom of the
pool will be illuminated and no light will come through the surface. This may be
acceptable if the base of the pool is clean and uncluttered. If not then attention will be
drawn to any shortcomings.
Luminaires need to be mounted as close to the surface as possible as even a small
depth of agitated water significantly reduces light output. If possible they should be
washed by water from the display. Incandescent lamps are inefficient and generate a
great deal of heat. If a luminaire is switched on when it is uncovered its lens will
overheat 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 should
be linked to the main pump relay so that the lights will not operate in isolation. A
photo-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 of
the lamp. Coloured lenses are available but each chosen colour requires a separate
set of luminaires or a multi lamped luminaire. Blue and red lenses dramatically reduce
light output. Green and yellow lenses allow more light to pass through them. A
mixture of luminaires with coloured and clear lenses can be used to create pastel
effects. Full spectrum LED luminaires will emit a wide range of coloured light, but they
are expensive and lack the ‘power’ of more conventional units.
In several countries the normal mains power supply is 110 / 120 volt. Although not completely 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 the
same supply then the potential hazard increases to 415 volts. In theory 240 volt lamps
can 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 use
of a transformer. For sheer power 500 watt PAR 56 and 1000 watt PAR 64 110/120 volt
lamps are the most popular. In swimming pools 12 volt luminaires are usually
mandatory. Water features are often used for recreation by children and so logically
should be engineered to the same standard. 50 or 75 watt 12 volt dichromic lamps are
now 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 within
10m of low voltage luminaires to avoid power loss in the cables. Greater distances can
be accommodated, but only if the transformers are customised to allow for the voltage
drop. Ideally all transformers should be toroidally wound so that the loss of one or
two lamps does not affect the life of the remainder. Fibre optic systems have been
developed for use in swimming pools. They have the advantage that the light source
can 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 lifted out of the water
for 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 the
water. It is not uncommon to only change lamps once a year. Only vulcanised rubber
or ethylene propylene cables should be used underwater. Cables with a PVC sheath
should not be used as they are slightly porous.
22 NOZZLES
Fig 31 The relationship between
nozzles from a simple finger jet
through all the major types
There are many different types of nozzle manufactured by different companies. However, 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 equipment from a number of sources. All that is necessary is to select the type of
nozzle and the height of the effect that is required. From the tables the flow rates
and hence the pipe sizes can be determined. Large pod effects are only a collection of
nozzles mounted together. It is possible to calculate their flow requirement by adding
together the output of the individual jets (fig 32 & 33).
AERATOR JET (water level dependent)
These create a tall column of white water with a pulsating crown when mounted vertically. They are very
economical with water. The amount of air which enters the stream can be adjusted by raising or lowering
the outer collar. The column diameter at the base is very small. They are very useful when grouped
together particularly as a pod. Their venturi design makes them very water level dependent. If there is any
floating debris in the feature then a trash guard will need to be fitted around the base of each nozzle.
thread
3/4
inch
1 inch
od
ht
25mm
185mm
30mm
235mm
11/4 inch
40mm
255mm
11/2 inch
50mm
335mm
2 inch
3 inch
65mm
90mm
385mm
535mm
height m
1.0
1.5
2.0
3.0
4.0
flow
0.3
0.4
0.4
0.5
0.6
17.0
l/s
5.0
6.0
8.0
10.0
12.0
2.4
15.0
head m
6.0
8.0
10.5
14.5
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
flow
l/s
0.6
0.7
0.8
0.9
1.0
1.1
head m
3.5
5.0
6.0
8.5
10
13
18
flow
l/s
0.6
0.7
0.9
1.2
1.4
1.6
1.8
2.0
2.2
head m
3.5
4.5
5.5
7.5
9.0
11
12
16
19
23
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
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
flow
flow
1.2
FOAM OR BUBBLER JET
These create a low pulsating mound of heavily aerated water which can be useful in windy locations. A
large expanding spray can be created at higher flow rates. The column diameter at the base is about half
the height. These nozzles should be covered before the water supply is turned on otherwise there will be
a great deal of spray. The depth of water over the nozzles needs to be strictly maintained. These jets can
cause surging in small features unless wave baffles are fitted. If surging is acceptable then the effect can
be exploited. These jets require a non-turbulent water supply. The breather pipe must be well clear of the
surface of the pool and may need extending if several nozzles are used close together.
thread
3/4
inch
1 inch
11/4 inch
od
ht
185mm
235mm
105mm
115mm
280mm
345mm
11/2 inch
130mm
390mm
2 inch
175mm
450mm
3 inch
250mm
525mm
height m
0.5
1.0
1.5
2.0
2.5
flow
3.0
l/s
0.8
1.0
1.2
1.4
1.7
head m
3.1
4.8
5.9
8.3
9.6
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
flow
4.0
5.0
6.0
8.0
10.0
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
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
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
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
flow
optimum
performance
CASCADE JET
These produce a tall conical block of highly aerated water. The column diameter at the base is one
quarter of the height. They can be used on their own or as part of a group. Their venturi design makes
them very water level dependent. They can cause surging in small features unless wave baffles are fitted.
They require a non-turbulent water supply.
thread
od
ht
150mm
135mm
11/4 inch 170mm
190mm
3/4
inch
11/2 inch 180mm
230mm
2 inch
290mm
3 inch
100mm
160mm
365mm
height m
0.5
1.0
1.5
2.0
2.5
3.0
flow
l/s
1.0
1.3
1.5
1.7
1.9
2.1
4.0
head m
7.1
11
15
20
24
27
flow
l/s
1.4
1.7
2.0
2.2
2.4
2.6
head m
6.4
7.9
9.5
14
17
20
24
flow
l/s
1.7
2.0
2.3
2.7
2.9
3.2
3.7
head m
2.9
6.6
5.0
6.0
8.0
10.0
2.9
9.9
13
15
16
24
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
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
flow
Plate 25 A collection of aerating jets with
500 watt PAR 56 luminaires
Plate 26 A block of water level independent
aerating jets surrounded by a splash zone
Plate 27 A ring of water level dependent
aerating jets set on a granite dome
Plate 28 Cascade jets produce thick dense
columns of water
Plate 29 A ring of cascade jets
Plate 30 Five cascade jets with four 500
watt PAR 56 luminaires
Plate 31 A foam or bubbler jet with its
breather pipe projecting above the surface
Plate 32 A feature can be covered with
paving to create a piazza
Plate 33 Aerating jets discharging through
paving slabs
Plate 34 A ring of aerating jets with a tall
central column which is causing splashing
Plate 35 A large foam pod flanked by four
cascade jets (see fig 32)
Plate 36 A water level dependent aerating
jet castle pod (see fig 33)
Plate 37 A dandelion needs a very well
filtered water supply
Plate 38 A bell nozzle display will form and
collapse repeatedly if perfectly adjusted
Plate 39 Calyx jets are very variable with
even a small amount of adjustment
Plate 40 Water can be blown out of a cylinder 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 linear
manifold
Plate 43 An aerator can be used to
mechanically entrain air in water
Plate 44 Coloured lenses can be fitted to
luminaires but they do reduce light output
Plate 45 White and coloured light can be
combined to create pastel shades
Plate 46 A twin pump floating fountain,
upside down, awaiting installation
Plate 47 A floating fountain with cascade
jets
Plate 48 Small floating fountains can enliven and oxygenate static bodies of water
AERATOR JET (water level independent)
These create a tall column of white water when mounted vertically. Their totally enclosed design means
that they are not water level dependent. They do not require a smooth water supply. They tend to be less
forceful than the water level dependent type of aerator nozzle described above. The column diameter at
the base is very small. As they discharge above water they can be used to introduce water to a multilevel
system without the need for non-return valves.
thread
od
ht
height m
1.0
1.5
2.0
3.0
1 inch
30mm
150mm
flow
l/s
0.7
0.8
0.9
1.1
4.0
5.0
6.0
8.0
10.0
11/4 inch
40mm
160mm
flow
l/s
1.0
1.2
1.3
1.5
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
1.7
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 which
has a tall pipe at its centre). The pattern can be adjusted from a full translucent sheet to a rough broken
half sheet with a droplet outer skirt. A constant water level is not required but windy locations should be
avoided. The water supply needs to be non turbulent and very well filtered. As they discharge above water
they can be used to introduce water to a multilevel system without the need for non-return valves. A number of different inserts and / or adjustable collars are available which can be used to change the initial
steepness of a curtain across a range of angles, which in turn affects its height and spread.
thread
ht
11/2 inch
200mm
2 inch
spray height
in m
flow
in l/s
spray diam
in m
head
in m
3 inch
4 inch
6 inch
20o
spray
230mm
300mm
350mm
400mm
25o
30o
35o
40o
45o
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
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
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
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
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
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 a
massive column. They are ideally suited for use along a straight or circular manifold. They are available
with a simple threaded socket connection or an adjustable swivel coupling. They require a very stable flow
of water. If the supply is turbulent then flow straightening vanes will be required in the pipework before the
jet. They should only be used a few degrees away from the direction of the supply flow.
th’d
th’d
ht
inch inch mm
orif height m 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
0.06
mm head m
1/4
60
3
flow l/s
0.01
0.03
0.04
0.05
1/4
60
4
flow l/s
0.03
0.05
0.07
0.09
0.11
0.13
3/8
70
5
flow l/s
0.06
0.09
0.11
0.13
0.16
0.21
3/8
70
6
flow l/s
0.09
0.13
0.16
0.20
0.24
0.28
optimum
performance
1/2
B
85
8
flow l/s
0.15
0.25
032.
0.40
0.45
0.50
0.55
1/2
3/4
84
10
flow l/s
0.25
0.35
0.45
0.55
0.65
0.75
0.85
0.95
3/4
11/4
105
12
flow l/s
0.40
0.55
0.65
0.75
0.95
1.15
1.25
1.40
1.60
A
11/2
140
16
flow l/s
0.70
0.90
1.20
1.50
1.85
2.25
2.70
3.10
3.50
11/2
155
20
flow l/s
1.75
2.20
2.65
3.20
3.80
4.40
4.75
2
190
25
flow l/s
2.40
3.20
3.85
4.60
5.80
7.00
3
310
30
flow l/s
4.50
5.50
6.65
7.80
9.00
11.3
7.10
9.00
10.8
12.5
14.9
17.8
20.3
5.58
6.33
7.81
9.06
10.2
12.5
14.3
16.2
17.1
13.4
15.0
16.8
20.4
23.4
27.0
30.0
24.0
26.8
32.7
38.0
42.5
47.7
58.2
4
390
40
flow l/s
4 or 5
475
50
flow l/s
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
6
550
65
flow l/s
17.3
21.6
27.0
31.3
38.8
46.0
52.0
60.º6
68.8
84.3
97.9
111
122
143
6
600
75
flow l/s
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 nut
B - a female threaded swivel connection secured by a bolted flange
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 visual
effect. As a result most nozzles taper so as to force the water into a jet. The remainder usually squeeze the water through a narrow gap. The basic tapered nozzle will
produce a clear finger of water. These can be positioned around a circular or along a
linear manifold. The flow entering the nozzle needs to be stable otherwise the jet will
break up around the outside. For this reason there should always be a length of
straight pipe immediately before a nozzle. Vanes in this pipework will significantly
improve the stability of the flow. Even so, the stream will still break up if the force with
which the water passes through the nozzle becomes excessive. This happens because
the water which is adjacent to the wall of the nozzle and the supply pipe travels at a
different speed to that which is at the centre of the flow. In some special applications
this 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. This
gives a very precise effect but needs very clean water otherwise the ‘straws’ get
blocked (see ‘jumping jets’ below). To create more volume a simple tapered jet can be
incorporated into a nozzle to draw in additional water and / or air (fig 31). Height is then
sacrificed for volume. For a stronger effect a number of nozzles can be grouped into a
‘pod’ (fig 32 & 33). Nozzles are usually formed in brass or gun metal because these
materials are easy to machine. Some small nozzles are formed in plastic but they are
fragile and should be avoided.
Sudden changes in the flow rate to a jet cannot be achieved by valving as the water in
the pipework takes time to accelerate. A number of novelty effects are available which
employ different techniques to overcome this problem. Probably the best known is the
‘jumping 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 pneumatically or hydraulically operated guillotine can be used to achieve the same effect. A
brief intermittent effect can be achieved by blowing water out of a chamber
immediately below a nozzle with compressed air which is stored in an adjacent cylinder.
This produces instant, powerful but short lived, jets of water.
Fig 32 A large foam pod consists of
numerous aerating nozzles connected
to a lower manifold and an upper air
supply chamber (see plate 35).
Indicative flow rates are as follows:4m high
8m high
12m high
30 l/s
38 l/s
45 l/s
@
@
@
30m head
45m head
60m head
Mists can be cooling in Summer but the water must be sterile if the threat of Legionella
is to be avoided. Fogging nozzles use very high pressure water or water which is
accelerated with compressed air. The water needs to be free of particulate matter as
the 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 pools
usually need to be drained down, cleaned and refilled in less than a day and sometimes
overnight. The drainage system and the water supply need to be of sufficient size to
make this possible. In and around buildings the water usually needs to be treated to
avoid a health risk. Adding chemicals to a system is pointless if their concentrations are
not regularly monitored. The pH and chemical content of the water should be tested
twice a week. The bacterial and fungal content should be monitored by exposing dip
slides every two weeks. The presence of Legionella can only be detected by special
tests 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 have
a fountain which floats. This is done by having a series of almost submerged floats
which are bolted to a frame (fig 34). Below the frame hangs one or more sump pumps
or 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 advantage
of floating fountains is that they can be removed for routine maintenance and, if
necessary, 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 activity
should be allowed within at least 20m of such equipment.
Fig 33 Aerating jet castle pod (see
plate 36). Many combinations are
possible but often 1 or 3 nozzles with
a 2 inch bsp thread are surrounded
by 8 to 16 nozzles with a 11/2 inch
bsp thread. The total flow requirement
can be calculated from the water
level dependent aerating nozzle
table
Standing bodies of water can become anaerobic particularly in hot weather. In such
cases aerators can be beneficial. In this case an electric motor hangs below a circular
float and carries a propeller. The flow can be directed upwards to throw water into the
air 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 water
upwards 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 10m
stratification, where the water separates into layers, can be a problem. Fountains can
help 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 a
large part of a lake is over 2.5m (8 ft) deep and the water is circulated then there are
seldom difficulties. The shade of trees can prevent overheating but their leaves can
Fig 34 A typical section through a
floating fountain
cause problems. Soft leaves, from say Alder and Birch, can enrich a natural system
providing that the quantity is not excessive. Algae will develop on all underwater surfaces 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 of
construction, and the danger of over-heating in Summer and freezing in Winter. If the
feature is engineered so that it always remains cool, clean and well oxygenated, then
300mm (1 ft) of water will often suffice. Unfortunately, the temperature of a shallow
body of water soon matches that of its surroundings, although careful environment
design can minimise this problem.
Water is at its most dense at 4°C which is why ice floats. Toxic gases can accumulate
when the surface is sealed with ice. It may be advisable to employ a heater, or to direct
warm water from the bottom of a deep pool at the surface, to keep at least part of it free
from ice, if the fish are of particular value (see section 25 above).
27 ORGANIC WATER QUALITY
Fig 35
A simple aerating nozzle
which draws air into the re-circulation
supply for an organic pool.
Fish and plants add an interesting dimension to any water feature. Unfortunately, algae
develop rapidly when water warms up. Water, which contains plants and fish, can
be treated with chemicals to reduce the growth of micro-organisms. They are not
particularly 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 a
result ‘untreated’ water should never be agitated in the presence of people with a weak
immune system or in a confined space. In locations where the temperature of the water
is likely to exceed 20°C on a regular basis the water may need to be chilled to control
the development of Legionella.
When combined, bright sunlight and oxygen have a sanitising effect. Vigorous
aeration in high light conditions is often sufficient to keep water clear. Air can be
entrained below the surface by the use of venturi nozzles (fig 35). To keep water clean
for fish it is necessary to provide a biological filter (fig 36). This is a large tank filled
with inert porous granular material, such as lytag, upon which bacteria can develop to
digest plant and fish waste. Experience would indicate that 2m3 of filter medium are
needed to treat the waste from 100kg of fish. However, this is very variable and
depends upon the environment and the species. UV sterilisers will dramatically reduce
the number of bacteria and algae in circulation. However, they will not prevent algae
from 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 drawn
into the treatment system.
Fig 36 A biological filtration system
28 INFORMAL LAKES
When an embankment is built across a natural water course it is said to be ‘on
stream’. With an ‘on stream’ structure the riparian rights of users downstream must be
respected. For example, in Summer the lake might evaporate the total flow of the
stream which feeds it. In contrast an ‘off stream’ lake is placed away from the bottom
of a valley although it can be fed by a spur from a stream to keep it topped up with
fresh water. Unless it is unavoidable no more than 25,000m3 (5,555,000 gallons) of
water should be stored above ground level. Retaining structures which hold more than
this quantity of water need routine inspections and certification which is costly. The
flow from a catchment area which is greater than 400ha (1000 acres) should not be
intercepted due to the size of the overflow which is needed to accommodate the worst
storm in 100 years (fig 37).
It is possible to produce an impervious water retaining structure from an homogenous subsoil which is comprised of 25% clay mixed with equal parts of sand and
gravel (fig 38). If such material is in short supply then an impervious clay rich core
can be supported by less impervious material (fig 39). The top of an embankment
should be 4 to 5m across and at least 1.2m higher than the normal water level. The
sides should have a slope which is no steeper than 1 in 3 or 33%. Pipes which pass
through earth structures should bear fully welded flanges which increase the length
of any potential seepage by at least 50%. All open pipes should be fitted with hinged
guards to prevent the entry of debris, animals and children.
Deep water can be a danger to people who do not anticipate its presence. At no
point should the sides of a lake slope at more than 1 in 3 or 33%. A gently sloping
ledge 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 to
crawl 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 to
be lined. A liner represents a considerable additional investment and will usually
double the cost of construction. Puddled clay was traditionally used but is seldom
practical due to the problem of locating the correct grade of clay, spreading it and
then puddling it. Should puddled clay dry out it will crack and leak even when rewetted. Bentonite (powdered clay) can be mixed with sub-soil to produce a fragile
waterproof layer. Several companies market a thin layer of bentonite sandwiched
between two layers of geotextile. In this form it is easy to handle but must be placed
carefully 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 to
produce a seal. The theory is simple but the practice often leaves much to be desired
due to difficulties which are encountered during installation.
Fig 37
A section through a lake
overflow which will accommodate
storm flows without backing up
Flexible non-elastic lake liners such as polyethylene and polyvinyl chloride (PVC) are
cheap but are not particularly durable. PVC sheets are sometimes reinforced with a
synthetic fibre mesh to increase their durability. The best membranes are produced
from butyl rubber or the more modern EPDM (ethylene propylene diene monomer).
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
Both materials will accept a great deal of stretching but are expensive. There are a
number of grades available but the most commonly used is 1.2mm thick. Large sheets
are fabricated from narrow rolls in factory conditions so as to keep on-site welding to a
minimum. The maximum joint length is usually a multiple of 25m up to a maximum of
100m. The largest area that can be handled with ease is 1000m2. The large concertina folded sheets are placed on the edge of the excavation and stretched out before
being welded together (fig 40). Sheet membranes have the advantage that the joints
can be vacuum tested. Flexible membranes are usually glued to any concrete structures to support their weight. Stainless steel strips are then pressed against a thick
layer 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 of
rising ground water lifting the membrane a land drain, with gravel back fill, should
always be positioned under a lake (fig 40). The drain should discharge to waste or
open into a chamber from which the water can be pumped when necessary. The edge
of a lake needs to be carefully detailed as the membrane has to be turned into a trench
and protected in a way that cannot be compromised by wave action. The excavation
must be cleared of all sharp objects to safeguard the well-being of the membrane. In
stony areas a sand bed may be required. In all cases sheet membranes should be
protected both above and below by a thick geotextile fabric. The two geotextile layers
will usually cost 25% of the liner price. Placing a layer of sand or stone free sandy subsoil 300mm (12 in) thick on top of the geotextile is the best way of completing the
protection. A strip of gravel, cobbles, timber and / or plants around the outside of the
lake is necessary to prevent erosion.
29 PLANTS
Few aquatic plants prosper in water which is more than 1.5m deep (5ft). Even water
lilies prefer less than this depth. Marginal plants usually prefer water which is only 100
to 300mm deep. Aquatic plants should only be planted when the water temperature is
rising in Spring. For this reason most planting takes place in May. The aquatic
environment can be very variable. With large projects a ‘shot gun’ approach, where a
large number of different species are planted in distinct blocks, is to be recommended.
Nature then eliminates the weak and within three years a stable planting pattern will
have evolved.
Plants which are used in water features are frequently divided into categories such as
‘bog plants’ and ‘marginals’. These terms are very flexible and many plants cross these
man-made boundaries. The table on the back cover of this bulletin describes the most
useful from a long list of species and cultivars. It is important to use only those species
which are indigenous or which pose no risk to established ecosystems.
30 BUDGETS
All water features need a realistic budget. The easiest way to apparently lower the cost
of a project is to omit the equipment which is needed to maintain the purity of the water
and to undersize the rest of the system. Using a membrane with a short life or poor
characteristics is another way to save money. All water features should be designed to
operate with a small amount of semi-skilled labour otherwise they will quickly fall into
disuse. This means having simple, well engineered systems, built with the very best
materials. Water features are expensive to construct and to maintain. If the budget is
inadequate then it is best to omit the feature.
31 SPECIFICATION
Few designers have the time which is needed to master the intricacies of designing
water features. As a result they have to rely on performance specifications and are
frequently dissapointed when the project is complete. With the aid of this publication
nozzles, spillways, flow rates, pipe sizes, membranes and engineering details can be
defined. This information can then be incorporated in a specification. To obtain a draft
specification telephone +44 (0) 1474 874 870 or facsimile +44 (0) 1474 874 873 or
Email technical@hydrotechnology.net. This draft specification needs to be carefully
reviewed and modified. It is always necessary to provide a description of the site and
to complete the schedule of components. Any unused, duplicated or mutually
exclusive clauses should be deleted. The final document must be checked by a
suitably qualified professional before it is issued.
Disclaimer - this is a brief technical document intended only to guide and inform. No
warranty is offered or accepted for the contents of this document unless
Hydrotechnology are retained as design consultants or contractors.
Note - the illustrations used in this publication have been selected to explain
technical principals and represents the work of a number of organisations, and not
solely that of Hydrotechnology.
Table 10 A description of some of the more useful temperate aquatic plants
botanic name
common name
flower
colour
flowering
period
height
water
depth
sunlight
planting
density
type
Gunnera manicata
Prickly Rhubarb
brown
July - Sept
200cm
moist
shady
1 per 2m2
Hosta (many named cultivars)
bog
Plantain Lily
lilac
July - Aug
45cm
moist
shady
5 - 6 / m2
bog
Iris sibirica (many named cultivars)
Siberian Flag
blue & white
June - July
75cm
moist
sun
3 - 4 / m2
bog
Lobelia cardinalis
Cardinal Flower
scarlet
Aug - Sept
50cm
0 - 5cm
shady
5 - 6 / m2
bog
Lysichitum americanum
Yellow Skunk Cabbage
yellow
April - May
50cm
0 - 5cm
shady
4 - 5 / m2
bog
Lysichitum camtschatcense
White Skunk Cabbage
white
April - May
45cm
0 - 5cm
shady
4 - 5 / m2
bog
Lythrum salicaria
Purple Loosestrife
red & purple
July - Sept
100cm
0 - 5cm
sun
2 - 3 / m2
bog
Mimulus guttatus ‘Luteus’
Monkey Musk
yellow
May - Aug
30cm
0 - 5cm
sun
2 - 3 / m2
bog
Myosotis scorpioides
Water Forget-me-not
blue
Apri - Aug
15cm
0 - 5cm
sun
4 - 5 / m2
bog
Peltyphyllum peltatum
Umbrella Plant
pale pink
May - June
100cm
moist
shady
3 - 4 / m2
bog
Rheum palmatum
Ornamental Rhubarb
red
Aug - Sept
200cm
moist
sun
1 per 2m2
bog
Zantedeschia aethiopica
Arum Lily
white
June - Aug
75cm
moist
sun
4 - 5 / m2
bog
Acorus calamus
Sweet Scented Rush
green
June - July
100cm
0 - 15cm
sun
4 - 5 / m2
marginal
Alisma plantago-aquatica
Water Plantain
pink & white
June - Sept
75cm
0 - 15cm
sun
3 - 4 / m2
marginal
Butomus umbellatus
Flowering Rush
pink
July - Sept
75cm
0 - 10cm
sun
4 - 5 / m2
marginal
Calla palustris
Bog Arum
white
April - June
20cm
0 - 20cm
shady
4 - 5 / m2
marginal
Caltha palustris
Marsh Marigold
yellow
March - May
30cm
0 - 10cm
sun
5 - 6 / m2
marginal
Caltha polypetala
Giant Marsh Marigold
yellow
March - May
75cm
0 - 10cm
sun
2 - 3 / m2
marginal
Carex acutiformis
Lesser Pond Sedge
brown
June - Sept
75cm
0 - 20cm
shady
3 - 4 / m2
marginal
Carex riparia
Greater Pond Sedge
brown
May - June
120cm
0 - 25cm
shady
2 - 3 / m2
marginal
Cotula coronopifolia
Golden Buttons
yellow
May - Sept
15cm
0 - 10cm
sun
5 - 6 / m2
marginal
Cyperus longus
Sweet Galingale
red brown
July - Sept
100cm
0 - 20cm
sun
2 - 3 / m2
marginal
Eriophorum angustifolium
Common Cotton Grass
white
May - July
60cm
0 - 10cm
shady
3 - 4 / m2
marginal
Glyceria maxima ‘Variegata’
Striped Water Grass
light brown
June - July
60cm
0 - 10cm
shady
2 - 3 / m2
marginal
Iris laevigata
Japanese Iris
blue
May - June
75cm
0 - 10cm
sun
4 - 5 / m2
marginal
Iris laevigata ‘Alba’
Japanese Iris
white
May - June
75cm
0 - 10cm
sun
4 - 5 / m2
marginal
Iris laevigata ‘Rose Queen’
Japanese Iris
pink
May - June
75cm
0 - 10cm
sun
4 - 5 / m2
marginal
Iris laevigata ‘Snowdrift’
Japanese Iris
double white
May - June
75cm
0 - 15cm
sun
4 - 5 / m2
marginal
Iris pseudacorus
Yellow Flag
yellow
May - June
100cm
0 - 20cm
sun
3 - 4 / m2
marginal
Iris versicolor
Blue Flag Iris
blue
May - June
75cm
0 - 10cm
sun
3 - 4 / m2
marginal
Juncus effusus
Soft Rush
brown
June - July
75cm
0 - 10cm
shady
2 - 3 / m2
marginal
Mentha aquatica
Water Mint
pink
June - July
50cm
0 - 10cm
sun
4 - 5 / m2
marginal
Menyanthes trifoliata
Bog Bean
white
April - May
30cm
0 - 15cm
shady
3 - 4 / m2
marginal
Phalaris arundinacea ‘Picta’
Gardener’s Garters
white
June - Sept
100cm
0 - 10cm
sun
3 - 4 / m2
marginal
Phragmites communis
Common Reed
brown
Aug - Oct
150cm
0 - 30cm
any
4 - 5 / m2
marginal
Pontederia cordata
Pickerel Weed
blue
Aug - Sept
100cm
0 - 15cm
sun
2 - 3 / m2
marginal
Ranunculus lingua ‘Grandiflora’
Greater Spearwort
yellow
May - June
60cm
0 - 10cm
shady
2 - 3 / m2
marginal
Sagittaria japonica
Japanese Arrowhead
white
June - Sept
50cm
0 - 15cm
any
2 - 3 / m2
marginal
Sagittaria latifolia
American Arrowhead
white
June - Sept
100cm
0 - 30cm
any
2 - 3 / m2
marginal
Scirpus lacustris
Common Bulrush
brown
July - Aug
200cm
0 - 30cm
sun
2 - 3 / m2
marginal
Scirpus tabernaemontani ‘Zebrinus’
Zebra Rush
brown
July - Aug
120cm
0 - 15cm
sun
2 - 3 / m2
marginal
Typha latifolia
Greater Reedmace
brown
Aug - Sept
200cm
0 - 60cm
any
2 - 3 / m2
marginal
m2
Aponogeton disctachyus
Water Hawthorn
Hottonia palustris
Water Violet
white & black
May - Sept
15cm
10 - 75cm
sun
lilac
May - June
30cm
15 - 100cm
sun
1 bunch / m2
Hydrocharis morsus-ranae
floating
Frog Bit
white
June - Sept
20cm
10 - 150cm
sun
2 - 3 / m2
floating
Nuphar lutea
Brandy Bottle
yellow
June - Aug
15cm
50 - 200cm
shady
1 - 2 / m2
floating
Nymphaea ‘Alba’
Water Lily - medium
white
June - Sept
10cm
50 - 100cm
sun
1 per 5m2
floating
Nymphaea ‘Charles de Meurville’
Water Lily - medium
red
June - Sept
10cm
50 - 100cm
sun
1 per 5m2
floating
Nymphaea ‘Gold Medal’
Water Lily - large
yellow
June - Sept
10cm
50 - 100cm
sun
1 per 5m2
floating
Nymphaea ‘Gladstoniana’
Water Lily - large
white
June - Sept
10cm
50 - 150cm
sun
1 per 5m2
floating
Nymphaea ‘James Brydon’
Water Lily - medium
red
June - Sept
10cm
50 - 100cm
sun
1 per 5m2
floating
Nymphaea ‘Carnea’
Water Lily - medium
pink
June - Sept
10cm
50 - 100cm
sun
1 per 5m2
floating
Orontium aquaticum
Golden Club
gold & white
May - June
50cm
20 - 100cm
sun
1 - 2 / m2
floating
Stratiotes aloides
Water Soldier
white
June - Aug
15cm
10 - 150cm
any
1 per 5m2
floating
light green
May - Sept
-
15 - 100cm
any
1 bunch / m2
submerge
-
-
-
15 - 150cm
any
1 bunch / m2
submerge
brown
May - Sept
25cm
15 - 100cm
sun
1 bunch / m2
submerge
Callitriche stagnalis
Starwort
Elodea canadensis
Canadian Pond-weed
Potamogeton crispus
Curly Pond-weed
HYDROTECHNOLOGY
Fawkham Green
Longfield Kent
England DA3 8NL
2-3/
floating
Telephone
+44 (0) 1474 874 870
Facsimile
+44 (0) 1474 874 873
Email - technical@hydrotechnology.net