Balancing lake
Encyclopedia
A balancing lake is a term used in the U.K. describing an element of an urban drainage
system used to control flood
ing by temporarily storing flood water
s. The term balancing pond is also used, though typically for smaller storage facilities for stream
s and brook
s.
In open countryside, heavy rainfall soaks into the ground and is released relatively slowly into watercourses (ditches, streams, river
s). In an urban area, the extent of hard surfaces (roofs, roads) means that the rainfall is dumped immediately into the drainage system. If left unchecked, this will cause widespread flooding downstream. The function of a balancing lake is to contain this surge and release it slowly. Failure to do this, especially in older settlements without separate storm and foul sewers, can cause serious pollution as well as flooding.
More advanced systems are computer controlled such that the entire flow of a river can be diverted into a holding lake, perhaps to reduce the impact of a large scale rain storm in the catchment on communities down river.
For aesthetic and safety reasons, the system can be designed so that there is a permanent lake. A lake with an equivalent area of 1000 by 1000 metres rises by one metre will hold a million cubic metres of water. Typically such a lake would have an outer earth bank of 1 metre, then a leisure path, then a 10 cm inner bank to the steady state level.
Willen Lake
is one of the largest (400,000 m²) purpose-built stormwater balancing lakes in the UK. The lake is designed to take surface run-off from Milton Keynes
, the largest of a number designed to do so. The lake has capacity for an additional level increase of 1.3 metres, equivalent to a once in 200 years event. Unlike most of the rest of the UK, the city has separate storm and foul sewers, so sewage pollution is not a significant problem. Additionally, there are facilities to prevent accidental oil spills and the like from reaching the lake. As well as local storm drains, the lake's primary purpose is to intercept the river Ouzel
, a tributary of the river Great Ouse
. The catchment area is Oxford Clay
that tends to get saturated easily, so field run-off has always been a problem.
The South Basin is designed for recreational use, mainly dinghy sailing and wind surfing, with a circumference path and banks as described above. It is linked to the North (Wild-life) Basin and can be drawn on to manage the level of the latter more finely. The North Basin has a large, undisturbed, central island. The extensive shallows support a good crop of aquatic plants and invertebrates. Very quickly, it became a key wildfowl site. In winter, it attracts up to 2,500 wild birds, with a wide variety of migrating waders in spring and autumn. Common Tern
, Tufted Duck
, Ringed
and Little Ringed Plover
, Common Redshank
and Northern Lapwing
. Canada Geese have become naturalised and they are permanent residents. Both basins have deep ponds to maintain the fish population during droughts. The lake is managed as a public open space, receiving up to a million visits each year.
An Ordnance Survey
1:25000 map of the site is at and aerial photographs are available at: 52°03′25"N 0°43′10"W
Drainage
Drainage is the natural or artificial removal of surface and sub-surface water from an area. Many agricultural soils need drainage to improve production or to manage water supplies.-Early history:...
system used to control flood
Flood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...
ing by temporarily storing flood water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
s. The term balancing pond is also used, though typically for smaller storage facilities for stream
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
s and brook
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
s.
In open countryside, heavy rainfall soaks into the ground and is released relatively slowly into watercourses (ditches, streams, river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
s). In an urban area, the extent of hard surfaces (roofs, roads) means that the rainfall is dumped immediately into the drainage system. If left unchecked, this will cause widespread flooding downstream. The function of a balancing lake is to contain this surge and release it slowly. Failure to do this, especially in older settlements without separate storm and foul sewers, can cause serious pollution as well as flooding.
Engineering
At its simplest, a balancing lake can be constructed by creating a dam across a drain or stream at a convenient valley, with a restricted diameter outlet pipe through the dam. Normal flows are carried happily through the pipe, but heavy flows back up and the water behind the dam is choked back. Over the following few days, the level subsides. This is often enough for a small housing development.More advanced systems are computer controlled such that the entire flow of a river can be diverted into a holding lake, perhaps to reduce the impact of a large scale rain storm in the catchment on communities down river.
For aesthetic and safety reasons, the system can be designed so that there is a permanent lake. A lake with an equivalent area of 1000 by 1000 metres rises by one metre will hold a million cubic metres of water. Typically such a lake would have an outer earth bank of 1 metre, then a leisure path, then a 10 cm inner bank to the steady state level.
Other benefits
A permanent lake can provide useful recreation facilities such as sailing, windsurfing, or of wildlife. These uses do not mix well, though a scheme can have both in linked basins where the recreational basin fills first and the wildlife basin is only used in exceptional conditions.- A recreational use facility can have relatively steep banks (perhaps with a footpath inside the bank next to the permanent lake for aestheticsAestheticsAesthetics is a branch of philosophy dealing with the nature of beauty, art, and taste, and with the creation and appreciation of beauty. It is more scientifically defined as the study of sensory or sensori-emotional values, sometimes called judgments of sentiment and taste...
and safety). The water level can rise substantially without a significant increase in overall area. - A basin that is intended for use by wild life and for visual amenity needs to be relatively shallow for maximum plant life. It must be designed with the assumption that it will be invoked very rarely, especially during the nesting season.
Case study: Willen Lake, Milton Keynes
Willen
Willen is a district of Milton Keynes, England and is also one of the ancient villages of Buckinghamshire to have been included in the designated area of the New City in1967...
is one of the largest (400,000 m²) purpose-built stormwater balancing lakes in the UK. The lake is designed to take surface run-off from Milton Keynes
Milton Keynes
Milton Keynes , sometimes abbreviated MK, is a large town in Buckinghamshire, in the south east of England, about north-west of London. It is the administrative centre of the Borough of Milton Keynes...
, the largest of a number designed to do so. The lake has capacity for an additional level increase of 1.3 metres, equivalent to a once in 200 years event. Unlike most of the rest of the UK, the city has separate storm and foul sewers, so sewage pollution is not a significant problem. Additionally, there are facilities to prevent accidental oil spills and the like from reaching the lake. As well as local storm drains, the lake's primary purpose is to intercept the river Ouzel
River Ouzel
The River Ouzel , also known as the River Lovat, is a river in England, and a tributary of the River Great Ouse. It rises in the Chiltern Hills and flows 20 miles north to join the Ouse at Newport Pagnell....
, a tributary of the river Great Ouse
River Great Ouse
The Great Ouse is a river in the east of England. At long, it is the fourth-longest river in the United Kingdom. The river has been important for navigation, and for draining the low-lying region through which it flows. Its course has been modified several times, with the first recorded being in...
. The catchment area is Oxford Clay
Oxford Clay
The Oxford Clay Formation is a Jurassic marine sedimentary rock formation underlying much of southeast England, from as far west as Dorset and as far north as Yorkshire. The Oxford Clay is of middle Callovian to lower Oxfordian age and comprises 2 main facies. The lower facies comprises the...
that tends to get saturated easily, so field run-off has always been a problem.
The South Basin is designed for recreational use, mainly dinghy sailing and wind surfing, with a circumference path and banks as described above. It is linked to the North (Wild-life) Basin and can be drawn on to manage the level of the latter more finely. The North Basin has a large, undisturbed, central island. The extensive shallows support a good crop of aquatic plants and invertebrates. Very quickly, it became a key wildfowl site. In winter, it attracts up to 2,500 wild birds, with a wide variety of migrating waders in spring and autumn. Common Tern
Common Tern
The Common Tern is a seabird of the tern family Sternidae. This bird has a circumpolar distribution, breeding in temperate and sub-Arctic regions of Europe, Asia and east and central North America. It is strongly migratory, wintering in coastal tropical and subtropical regions. It is sometimes...
, Tufted Duck
Tufted Duck
The Tufted Duck, Aythya fuligula, is a medium-sized diving duck with a population of close to one million birds.- Description :The adult male is all black except for white flanks and a blue-grey bill. It has an obvious head tuft that gives the species its name.The adult female is brown with paler...
, Ringed
Ringed Plover
The Common Ringed Plover or Ringed Plover is a small plover.Adults are 17-19.5 cm in length with a 35–41 cm wingspan. They have a grey-brown back and wings, a white belly, and a white breast with one black neckband. They have a brown cap, a white forehead, a black mask around the eyes...
and Little Ringed Plover
Little Ringed Plover
The Little Ringed Plover is a small plover. Adults have a grey-brown back and wings, a white belly, and a white breast with one black neckband. They have a brown cap, a white forehead, a black mask around the eyes with white above and a short dark bill...
, Common Redshank
Common Redshank
The Common Redshank or simply Redshank is an Eurasian wader in the large family Scolopacidae.- Description and systematics :...
and Northern Lapwing
Northern Lapwing
The Northern Lapwing , also known as the Peewit, Green Plover or just Lapwing, is a bird in the plover family. It is common through temperate Eurasia....
. Canada Geese have become naturalised and they are permanent residents. Both basins have deep ponds to maintain the fish population during droughts. The lake is managed as a public open space, receiving up to a million visits each year.
An Ordnance Survey
Ordnance Survey
Ordnance Survey , an executive agency and non-ministerial government department of the Government of the United Kingdom, is the national mapping agency for Great Britain, producing maps of Great Britain , and one of the world's largest producers of maps.The name reflects its creation together with...
1:25000 map of the site is at and aerial photographs are available at: 52°03′25"N 0°43′10"W
See also
- StormwaterStormwaterStormwater is water that originates during precipitation events. It may also be used to apply to water that originates with snowmelt that enters the stormwater system...
- Surface runoffSurface runoffSurface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...
- Urban runoffUrban runoffUrban runoff is surface runoff of rainwater created by urbanization. This runoff is a major source of water pollution in many parts of the United States and other urban communities worldwide.-Overview:...
- Sustainable urban drainage systemsSustainable urban drainage systemsSustainable Drainage Systems , sometimes known as Sustainable Urban Drainage Systems , are designed to reduce the potential impact of new and existing developments with respect to surface water drainage discharges.-Background:...
Further reading
- Wetlands, Industry & Wildlife: A manual of principles and practices. (1994) ISBN 0-900806-18-4 (The Wildfowl & Wetlands Trust, UK). Chapter 15.