TECHNICAL FEATURE
Understanding how Groundwater Dynamics ECO-90 Drainage System supports Tier 1 SuDS
Jon Maguire, Groundwater Dynamics fig.3
fig.1
through the trench and ECO-90s beneath, providing formore gradual increase in watercourse levels during heavy rainfall and slower reduction in levels once the rain has passed.
HowECO-90 reduces drought risk fig.2
Our first article looked atwhy SuDS has a hierarchy that is largely ignored in the construction sector. The second looked at the ecological imperative for SuDS to succeed, drawing it into the entire climate change movement. This third article looks at the ECO- 90 Tier 1 SuDS andwhy it is becoming a real head turner in the drainage industry.
Howthe ECO-90works
The ECO-90 is aworldwide patented technology that enhances and acceleratesmultiple soil stratas ability to holdwater. It is a cut length infiltrator,with a cross section of five open chambers (see fig.1). It is important to understand that the ECO-90 is NOT a pipe, the open chamber design is a key reasonwhy it works.
The ECO-90 come in lengths of 12metres and is installed vertically in a pre-drilled hole.Water held in the soil surrounding open chambers moves into themand then starts to descend, its natural propensity. Soil around the ECO-90 inevitably becomes saturated and this creates two key results:
■ A head ofwater creates significant vertical discharge pressure (a differential hydraulic
head), forcingwater out of the chambers into surrounding soils
■ Surrounding, less saturated soils start
suckingwater out of the chambers, creating lateral discharge that in laminated soils can be more significant than vertical.
These lateral and vertical discharges reduce saturation around the ECO-90, causingmore surface or trench stormwater to enter the chambers, creating a virtuous cycle ofwater being discharged to depth.
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www.draintraderltd.com Designing an ECO-90 system
For natural turfwhere it is impossible tomeasure stormwater volumes on a given area, the ECO-90 systemismost often installed directly into the ground. For construction,where stormwater volumes are known,we create an engineered drainage solution. This is based on a buffer trench (see fig.2) to take and store stormwater even in a major rainfall event,with ECO-90s installed below to discharge the trenchwater to depth.
HowECO-90 reduces flood risks
An ECO-90 systemthat incorporates a buffer trenchwillmitigate peakwater levels in local watercourses following stormevents, as shown by the hydrograph (see Illustration 3). This is because surfacewater takes time tomove
An ECO-90 systemwill dealwith stormwater at source, allowing catchment rainfall to infiltrate and percolate the soilmuch as it did prior to land being developed. This provides significant hydro- support to the local ecology.
ECO-90 unrivalled decarbonising credentials
(i) The ECO-90 systemuses no external energy source and is operationally carbon neutral
(ii) It is positive for plant growth suffering from saturated soils and increases drought resistance of the local ecology. Both of thesematters are carbon saving.
Taking (i) and (ii) together, the ECO-90 systemcan be carbon negative, the highest accolade available in the global drive for a carbon neutral world.
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