SuDS : Lets take a moment to soak up infiltration

http://ecogrid.co.uk/index.php/blog/lets-take-a-moment-to-soak-up-infiltration/Infiltration simply put is the ability of soil to absorb rainfall or overflows from rivers and streams. It is measured in inches per hour or millimetres per hour. Water being infiltrated soaks through the soil to the water table or becomes part of the sub-surface runoff process.Rates of infiltration reduce with levels of precipitation to a level where precipitation exceeds infiltration and run-off occurs.Various surface materials will either impede or improve the infiltration rates of an area, grassed surfaces will ensure that soil particles remain loose and will allow water to percolate through, forested areas are the best infiltrators of precipitation; however in the UK, we need to find a cost effective method of surfacing that allows a good level of infiltration.Infiltration trenchesTraditionally known as a soak-away, infiltration trenches used to be simple holes in the ground filled with gravel or stone, clay pipes formed a surface drainage system when connected to the soak-away. Modern methods now employ plastic crates or tunnels stacked on top of each other or laid in connected rows, these items are wrapped in permeable geotextile membrane. The theory being that the infiltration system ‘soaks up’ water and allows it to dissipate slowly in to the water table over an extended period of time, reducing the risk associated with storm surge situations that we have seen rather worryingly regularly in the UK lately.An interesting development in soak-away design is to use plastic grids such as Ecogrid in infiltrations, stacked on top of each other. Ecogrid comes in 30/40 and 50mm depths; thereby offering infiltration trenches that are both load bearing and modular to depths of 30/40/50/60/70/80/90/100mm and variations thereof. A Hydrocarbon filtration layer is placed on the top of the Ecogrid infiltration system to protect the water table from pollutants.Surfacing optionsGrassed pavinggrassGrassed plastic load bearing grids such as Ecogrid are laid on a ‘root friendly’ sub base and are filled with a 70/30 soil and sharp sand mix then either turfed or seeded. Grass parking is ideal when mixed with concrete or block paving for a highly aesthetic finish that combines both the traditional and the modern.Here is an example of an infiltration system with a grassed Ecogrid topgrass-infiltrationHere we have a grass filled, load bearing Ecogrid that can happily take the weight of anything from a person to an articulated lorry. This grid layer sits on a 50:50 soil/stone layer which sits on a membrane which covers the drainage layer which sits on another membrane, covering load bearing storm crates that are a trafficked version. Cost effective and invisible infiltration.Concrete blockgrass2Concrete interlocking block paving relies on larger than normal gaps between the blocks or cut-out sections of the block edge. Fine grit is brushed in-between the gaps and surface water is designed to soak through the surface and in to the sub-base. In these scenarios the infiltration rates of the top-surface are greatly improved if there is a definitive gap or infiltration trench underneath the surface. An ideal way of facilitating this is to use the Ecogrid permeable paving system in conjunction with concrete block; once again providing marriage between the new and the traditional methodology.Concrete block can easily be amalgamated with Ecogrid load bearing tilestyreHere we have an example where 1. is the layer of CBP, we then have a screed layer sat on a membrane, then a single, double or treble 30, 40 or 50mm layer each of Ecogrid load bearing grids which in turn sit on a drainage type 2 or 3 layer. Simple and cost effective amalgamation of two paving mediumsGravel Parking or surfacinggravelGravel filled grids are ideal methods to improve surface water infiltration, however a word of caution. These systems need to be fit for purpose. Thin plastic honeycomb sheets are too flimsy and will not stand up to the rigours of use, grids that do not have a sturdy clipping mechanism can easily come apart causing H&S problems. Ecogrid is a tried and tested gravel grid over a period of 20 years and over 2,000.000 metres sold every year means that confidence levels in this range are extremely high. Gravel parking systems such as Ecogrid can have loading capabilities of up to 800 tonnes per square metre, being capable of taking the loading from the largest of vehicles. Filtration levels are also very high with this method of surfacing. Surface gravel forms one, sub-screed another, geotextile hydrocarbon filtration layer next, sub-base type 3 level the last.Resin bound stoneegrd-rs-terThe newest ‘kid’ on the block, traditionally laid on the top of permeable concrete, permeable tarmac or asphalt; however these type of sub-bases are extremely expensive to lay, take time to cure and require a unique set of equipment and skill to install. Resin bound rubber crumb or shredded tyre mixes or stone mixes have been used as base systems; however again, these systems use up to 5 times the amount of resin as the surface material mix and are therefore very expensive to install. The Ecogrid resin bound system employs the use of the grids laid in the standard way on a permeable sub base and filtration membrane. The Ecogrid tiles are then filled with a lightweight material, compacted and then a resin bound permeable stone surface is installed over and slightly in the grids. The resin stone surface actually has voids in-between the stone pieces allowing water to flow freely through the surface and in to the water table below. The finished surface is very hard wearing and elastomeric, easily coping with a range of external temperatures.Here is an example of a resin bound surface with Ecogrid as a base and a crated infiltration trenchresin-stone-infiltrationa is the soil level, b is the woven membrane, c is the wrapped crates, d is the drainage layer, e is the secondary membrane, f is the screed layer, g is the Ecogrid course, filled with clean stone and h is the resin bound permeable stone layer at 20mm.Essentially, there are a great deal of surfaces available to create a stable and cost effective method of surface water infiltration and even more methods of creating cost effective infiltration trench designs.Lastly, when opting to use plastic grids in the built environment, one has to be sure that they meet standards, here are the certification that belong to Ecogrid.DIN 38412 - Neutral for the environmentDIN 4102 - Approval emergency access routes, fire resistanceDIN 1072 - Approval for 20 tonne axle load, driveways, road extensions, bridgesDIN IN ISO 124 and B125 - Approval for car parks, access roads & storage areasPoint axle loading up to 20 T/m², DIN 1072:1985UV-resistant, certified DIN EN 60068-2-5Heavy-duty, tried and tested DIN EN 124:2011Environmentally safe, tested OECD 202:2004Factory warranty: 20 years from purchase dateNATO certified E50 - MOD / 9330-99-858-1406TÜV CERT

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