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Rain Gardens and Rain Garden (SuDS) Planters


Our rain garden planter have been designed using the principles of rain gardens as outlined below. 

Rain gardens, or water runoff gardens, are a key component of eco-friendly and sustainable landscapes.
 

With the extensive loss of front gardens, and other planted areas, including lawns, urban flooding occurs.  This is because rain falls in towns and cities faster than it can be drained by the sewer network, absorbed into the soil or conveyed to streams, rivers, water bodies or reservoirs.

In recent years, with climate change, this is a major re-occurring problem in towns and cities throughout the UK.

 

Benefits of rain gardens, as recognised by the RHS

  • Low maintenance garden – no watering once plants have established
  • Can absorb up to 30% more water than a lawn
  • Offers opportunities to plant a wide range of perennials
  • Reduces erosion by slowing heavy rainfall
  • Increased planting attracts insects and birds
  • Avoids the need to sink a soakaway

Sustainable Drainage Systems (SuDS)

 

Rain gardens provide an inexpensive and instant way to create an attractive attenuating Sustainable Drainage System (SuDS)* that will:

  • slow surface water flows
  • significantly reduce surface water flood risk, particularly in urban areas with extensive sloping roof areas
  • filter pollution and improve water quality

*SuDS - Sustainable drainage systems include a range of techniques for holistically managing water run-off to reduce the quantity, of surface water that drains into sewers from a development. The SuDS increase the quality of the water release by a natural filtering purification processes. In general SuDS mimic natural systems, and manage rain close to where it falls. SuDS not only reduce the burden on our sewerage system, they can also help wildlife to thrive in urban areas, with many of the drainage systems being intrinsically wildlife friendly.   

rain garden
rain garden

Rain Garden Planters

 

Rain Garden Planters, or Gutter Planters, adopt the principles of SuDS,

 Designed to:

  • manage rainwater run-off from domestic and commercial roofs
  • reduce the risk of flooding in the sewer network
  • improve the quality of surface water entering streams and rivers

Rain garden planters make use of the water that lands on the roof and works in the following way:

1. Water from the downpipe is directed into the planter.

2. The soil / compost mix absorbs and stores the rainwater for the plants to use.

3. Excess rainwater filters into the gravel layer and drains out the base drainage pipe, as illustrated in the adjacent diagram. 

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Best Plants for Rain Gardens


Plants for rain planters have to be able to tolerate some wetness at the root zone as well as grow in more normal conditions.

Typical plants include Iris pseudocorus and a range of perennials such as:
  • Geraniums
  • Persicarias
  • Hemerocallis
  • Grasses such as Deschampsia or Miscanthus

Some shrubs such as Cornus sanguinea or even trees, such as Betula would be suitable for a large planter. 

See the table below for a comprehensive list of plants suitable for rain gardens:

 

Common name

Scientific name

Habit

Sunlight and Aspect

Origin

Guelder rose

Viburnum opulus

Perennial shrub

Any

Native. Flowers attract insects and berries are eaten by birds.

Dogwood

Cornus sanguinea

Perennial shrub

Any

Native. Leaves are larval food for vase bearer moth and berries eaten by birds. Often planted for attractive winter stems.

Culvers root

Veronicastrum virginicum

Herbaceous perennial

Full sun or partial shade

Non-native. Tall with long terminal blue flower spikes. On the RHS ‘plants for pollinators’ list.

Aster

Aster spp.

Herbaceous perennial

Full sun or partial shade

Non-native. Often late flowering. Clump forming. Several species on the RHS ‘plants for pollinators’ list.

 

Black eyed susan

Rudbeckia birta

Herbaceous annual or biennial

Full sun or partial shade

Non-native. Spectacular yellow and black flowers. On RHS ‘plants for pollinators’ list.

Stinking hellebore

Helleborus foetidus

Herbaceous perennial

Full sun or partial shade

Native. Winter flowers.

 

Montbretia

Crocosmia spp.

Deciduous rhizomatous perennial

 

Partial shade

 

Naturalised. Red flowers. Thrives in most conditions.

Bugle

Ajuga reptans

Rhizomatous perennial

Partial shade

Native. Low growing and will form a mat.

Columbine

Aquilegia spp.

Herbaceous perennial

Full sun or partial shade

Non-native. Clump forming with tall flower spikes. On RHS ‘plants for pollinators’ list.

Inula

Inula hookeri

Herbaceous perennial

Partial shade

Tall clump forming with yellow flowers. On RHS ‘plants for pol- linators’ list.

Hemp agrimony

Eupatorium cannabinum

Herbaceous perennial

Full sun or partial shade

Native. Sub-shrubs with pink flowers.

Bellflower

Campanula glomerata

Herbaceous perennial

Full sun or partial shade

Native. Clumps bearing violet-blue bell shaped flowers.

Sneezeweed

Helenium sp.

Herbaceous perennial

Full sun

Non-native. Clump forming with red flowers. On RHS ‘plants for pollinators’ list.

Lesser periwinkle

Vinca minor

Perennial sub-shrub

Any

Non-native. Ground cover with blue flowers.

Elephants ear

Bergenia sp.

Rhizomatous perennial

Full sun or partial shade

Non-native. Large leaves and pink flowers.

Plantain lilies

Hosta spp.

Herbaceous perennial

Part shade

Non-native. Attractive light coloured flowers.

Yellow flag

Iris pseudocorus

Rhizomatous perennial

Full sun or partial shade

Native. Likely to prefer wetter areas near inlet.

Siberian flag

Iris sibirica

Rhizomatous perennial

Full sun or partial shade

Non-native. Blue flowers. Prefers moist but well drained soil.

Garlic and onions

Allium spp.

Bulbous perennials

Full sun

Non-native. On RHS ‘plants for pollinators’ list.

Soft rush

Juncus effusus

Evergreen perennial

Full sun or partial shade

Native. Form tussocks – likely to prefer wetter areas.

Pendulous sedge

Carex pendula

Rhizomatous perennial

Full sun or partial shade

Native. Nodding flower spikes. Likely to prefer wetter areas near inlet.

 

Zebra grass

Miscanthis sinensis

Perennial, deciduous grass

 

Full sun

Non-native. Tussock forming ornamental grass with silky flowers.

 

Switch grass

Panicum virgatum

Deciduous perennial grass

 

Full sun

 

Non-native. Tussock forming ornamental grass.

Royal fern

Osmunda regalis

Deciduous fern

Any

Native. Large clump-forming plants.

 

Male fern

Dryopteris felix-mas

Deciduous or evergreen fern

Partial shade or full shade

 

Native. Large shuttlecock-like form.

 

Broad buckler fern

Dryopteris dilatata

Deciduous or evergreen fern

Partial shade or full shade

 

Native. Large shuttlecock-like form.

 

 

(From Thames Water UK Rain Garden-Guide)

Rain Garden Planters: An Attractive Adaptation of Sustainable Drainage Systems (SuDS)

 

 

Designed for Flooding


Even if you don’t have room for a rain garden you can still implement sustainable stormwater management. Rain garden planters, or gutter planters, handle rainwater runoff from rooftops and operate like a rain garden inside a planter.

Rain garden planters are perfectly suited to small spaces, as they can be built close to buildings in any configuration and don’t take up very much space.

These planters are an attractive adaptation of Sustainable Drainage Systems (SuDS) which slows surface water flows,
and reduces surface water flood risk.

With both bioretention and additional internal storage, these planters are an innovative solution to property level retro-fit SuDS, and can work out very much less expensive than most groundworks interventions.

The planter can be made from a number of materials, but we prefer commercial quality Larch Planters for the following reasons:

  • produced by UK craftsmen using Larch from sustainably grown larch woodlands.
  • Larch produces its own intrinsic preservative providing a very long planter life without the use of toxic preservatives.
  • Alternative materials are linked to non sustainable production issues from energy consumption to pollution or toxic issues.

A rain garden planter is a waterproof container filled with layers of:

  • mulch
  • soil
  • sand
These layers filter the water before it passes to the next stage of rainwater management.

Water may discharge from a planter into the normal drains or it could be diverted further into a Rain Garden.

For an enhanced biophilic and aesthetic effect, we like to encourage the construction of landscaped features that the water could travel along and slowly percolate into the soil, such as an attractively constructed rill, gulley or channel into a garden bed, as in the example below.
 
 

 


 

 

SuDS Planter Storage and Flow Rates

 

The storage volume and retention and subsequent outflow rates will vary with the dimension of the planter to be incorporated into the scheme. East of Eden SuDS planters are all based on the internal design features as recommended bySouth East Rivers Trust, which was founded on extensive trial studies (See tables 2-4* below).


The SuDS Manual states that typically the surface area of a bioretention feature would be 2-4% of theoverall site area being drained, to prevent rapid clogging of the bioretention surface. Based on thisguidance, the surface area of any planter (or combination of planters) should not be less than 2-4%of the roof area it is draining. Where possible, the size of the planter should reflect this recommendation.
 

As such, we offer a range of standards planter sizes to use in

1000mm L x 650mmW x 900mm H to 2000mm L x 650mm W x 900mm H
 

These sizes are based on large, but manageable and movablesized units using a fork lift. This offers practical sized units option to be used in combination to achieve the recommendation catchment areas stated above.
 

If the site permits, we can also construct the SuDSplanter to bespoke requirements up to a maximum of:
 

       3000mm Lx 1000mm W x 950mm H
 

 

Storage Layer

 

As mentionedthe storage value will depend on the dimensions of the planters.
 

Based on a planter with the dimension of 3000 x 1000W x 750Htrials have provided the storage and outflow rates as in Tables 1 & 2

With a minimum planting layer of 450 mm and further 50 mmgap to the top of the planter, this would leave approximately 300 mm for a sub-base / storage layer.
 

Using geocellular crates in the planters a greater volume of storage can beachieved. Typically 250 mm depth of geocellular crates are used

 

Tables 1 and 2 compares the storage values ofthe standard Gravel sub-base SuDS planter with the Geocellular Sub-BaseSuDSplanter  -
 

Table2*.Dimensions and storage volume –GravelSub-BasePlanter.

 

Features

Length

(m)

Width

(m)

Depth

(m)

VoidSpace

(%)

Storage

Volume(m3)

Gravelsub-base

3

1

0.3

30 approx.

0.27

Planting Medium(soil)

3

1

0.35

20 approx.

0.21

Planter Surface to

OverflowPipe Level

3

1

0.05

100

0.15

Total Available

     Storage

 

 

 

 

0.63

(630 litres)

 

 

 

 

 

 



Table3*.Dimensions and storage volume –GeocellularSub-BasePlanter.
 

 

Features

Length

(m)

Width

(m)

Depth

(m)

VoidSpace

(%)

Storage

Volume(m3)

Geocellularsub-base

3

1

0.25

95

0.71

Planting Medium(soil)

3

1

0.4

20(highlevel

estimate)

0.24

Planter Surface to

Overflow Pipe Level

3

1

0.05

100

0.15

Total Available

Storage

 

 

 

 

1.10

 

 

 

 

 

(1110 litres)

 

Outflow rates

 

The standard SuDS planters are drained via a perforated drainage pipe running along the bottom of the planter. A number of factors influence the drainage rate including the drainage pipe diameter,soil mix and therefore infiltration rate,impact of plants and soil conditions prior to any particular rainfall event will be important.

Table 3 shows outflow rates from trials showing the effect of the outflow diameter on the outflow rate.

 

Table 4*. Estimated maximum flow rate for a 68 mm downpipe, with water distributed into planter via a pipe set at approximately 1 in 200slope.

 

 

Diameter of outflowmm)

Estimated maximum flowrate (litrespersecond)

Estimated maximum flowrate(cubicmetres

persecond)

Estimated maximum flowrate (litresperhour)

Estimated maximum flow rate (cubicmetres

perhour)

30

0.21

<0.001

752

0.75

40

0.46

<0.001

1648

1.65

50

0.84

<0.001

3020

3.00

 

 

 

 

 



* Based on data from South EastRivers Trust
 

Based on trial data, the narrower diameter is recommended to limit the flow out of the  planter to a reasonable level to maximise the potential for flood storage, especially where extra storage was provided by the geocellular storage. One hour after a rainfall event begins, up to 0.75m3of water can drain from the bottom of the planter.

Depending on the choice of storage layer,an additional 0.62-1.1m3of water can be stored in the planter before it over flows.This means that over an hour following the beginning of a rainfall event, between 1.37 m3 and 1.85 m3 can enter the planter before water drains via the over flowpipe.

 

In reality the infiltration rate of the soil will have a notable impact of the volume and rate of water which can drain out of the bottom of the planter. Hence the taller the planter  the slower the infiltration rate. Also, the larger the overall dimensions of the planter will allow for more storage before the water level reaches the overflow.

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