Rain Garden SuDS Planters

A Sustainable Way to Manage Rainwater Run-Off

Our rain garden Sustainable Drainage System (SuDS) planters are supplied fully assembled and ready to install into your drainage system.

They are supplied lined, with the complete internal drainage system fitted, including screened overflow and drainage pipe outlet ready to fit into your site drainage system.

The drainage support pipe system is supported by specialist, light-weight aerating leca granules. The whole SuDS system is then covered with geotextile membrane to keep it separate from the compost.

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Integrating Sustainble Drainage Systems (SuDS)

Rain garden planters are an appealing adaptation of Sustainable Drainage Systems (SuDS) feature which steadies surface water flows, and reduces surface water flood risk.

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

SuDS interventions, such as these planters, can of course have multiple Green Infrastructure benefits, in addition to their contribution to flood alleviation, when thoughtfully designed.

You could also opt for a planting palette that contribute towards boosting biodiversity.

Choose from our standard finishes or contact us to discuss custom colour options.

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Rain garden SuDS planters: Designed to help alleviate Flooding

As a result of climate change, we are seeing more and more flash floods occuring due to extreme rainfall. This is further amplified by the trend for covering gardens with impervious materials instead of rain absorbing lawns, including front gardens paved for driveways and the reduced sized of back gardens in favour of new buildings.

Rain garden planters, or stormwater planters, are a sustainable stormwater management solution with their clever internal drainage system.

They collect rooftop runoff and work like a rain garden in a planter allowing for sustainable stormwater management.

These planters are particularly useful if you have a significant amount of rain water traveling from the rooftop or other impervious surface directly into a drain causing flooding on your property.

All Rain Garden SuDS Planter sizes are bespoke to meet the requirements of each client, and made to order.

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How Do Rain Garden Planters work?

A rain garden planter utilises rain water that lands on the roof. Water from the drain pipe is directed into the planter. The soil absorbs and stores the rainwater for the plants to use, known as bioretention.

Excess rainwater filters into the gravel layer and drains out the perforated base drainage pipe.

Any water that pools on the surface, drains down the overflow upstand.

They work in the same way as rain gardens just on a smaller scale.

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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 by South 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 the overall site area being drained, to prevent rapid clogging of the bioretention surface. Based on this guidance, 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 standard planter sizes to use in

1000mm L x 650mm W x 900mm H - 2000mm L x 650mm W x 900mm H

These sizes are based on large, but manageable and movable sized units using a fork lift. This offers practical sized unit options 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 mentioned the storage value will depend on the dimensions of the planters.

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

With a minimum planting layer of 450 mm and further 50 mm gap 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 be achieved. Typically 250 mm depth of geocellular crates are used.

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

Table2*.Dimensions and storage volume – Gravel Sub-Base Planter.

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 –Geocellular Sub-Base Planter.

Features	Length (m)	Width (m)	Depth (m)	Void Space (%)	Storage Volume(m³)
Geocellular sub-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 200 slope.

Diameter of out flow mm)	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.

Rain Garden Planter Interior: All planters come fully lined

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

For an enhance 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: