Filter Socks, FS-1 - Catchments and Creeks

1 Catchments & Creeks Pty LtdVersion 2 - April 2010 Page 1 Filter socks SEDIMENT CONTROL TECHNIQUEType 1 SystemSheet Flow Sandy Soils Type 2 SystemConcentrated FlowClayey Soils[1]Type 3 SystemSupplementary Trap Dispersive Soils[1]Can be used in clayey soils as a supplementary sediment trap to capture coarse-grained sediments;however, little control exists over the finer silt and clay-sized 1 Filter socks used to form a sag inlet sediment trapPhoto 2 Filter socks used to form a on-grade kerb sediment trapKey Principles1. Sediment trapping is achieved through gravity-induced settlement resulting from pondingup-slope of the socks , and some limited filtration of water passing through the Primarily used to collect the coarser sediment particles.

2 This technique typically has littleability to capture the finer silt and clay-sized particles as shown in Photo The key performance objective is to allow ponding to occur up-slope of the Filter sock (Photo2) such that coarse sediments are allowed to settle under Ideally, all sediment-laden water should be allowed to pass through the pond before beingreleased over a spill-through weir normally formed by a depression in the sock. The quantityof water bypassing around the pond should be minimised wherever InformationMinimum sock diameter of stake spacing of or six (6) times the sock diameter, whichever is the maximum stake spacing of applies when used in areas of potential high velocity. Thestability of Filter socks (un-staked) when used as check dam sediment traps varies depending onthe composition of the sock; however, most socks have been found to be stable when used inshallow drains with gradients less than 5%.

3 Though generally not suitable in broad areas of sheet flow, if used, the Filter socks must beplaced along the contour to maintain uniform flow conditions passing through the sock. The useof Sediment Fence, Compost Berms, Compost-filled Filter socks and possibly Fibre Rolls arepreferred in broad areas of sheet practical, adjoining socks should be overlapped at least 450mm. Catchments & Creeks Pty LtdVersion 2 - April 2010 Page 2 Photo 3 Sag inlet sediment trapPhoto 4 Field inlet sediment trapPhoto 5 check dam sediment trapsPhoto 6 Compost-filled Filter sockDescriptionFilter socks consist of a highly permeabilitysynthetic sock of varying lengths anddiameters, and filled with a variety ofmaterials including compost, straw, sandand socks are distinguished from FibreRolls through the use of non-woven orcomposite Filter fabric in the formation of thesock.

4 In a Filter sock, this outer tube aids inthe filtration of synthetic sock can be biodegradable ornon-biodegradable depending on desiredservice life; however, most commercial filtersocks are formed from in some circles as Filter tubes ;however, this can result in confusion withthe larger Filter Tubes used in de-wateringoperations and the formation of Filter TubeDams refer to separate fact as a supplementary sediment traparound or adjacent to minor also be used to form check DamSediment Traps in minor not suitable in broad areas ofsheet and easy to transport into can be installed without wash away if placed in areas of ProblemsLeakage around the socks (Photo 2).

5 Special RequirementsEnsure both ends of the Filter sock areadequately turned up the slope to preventflow bypassing prior to water passing overthe around or adjacent to minorstormwater inlets. Catchments & Creeks Pty LtdVersion 2 - April 2010 Page 3 Site InspectionCheck for displacement of the the Filter socks have been placedsuch that water will pond up-slope of that sediment is being removed fromthe sediment traps after each socks : minimum 200mm diametersynthetic or biodegradable tubesmanufactured from non-woven orcomposite fabric suitable for the filtration of coarse sediments. Fill material: Straw, cane mulch,composted material (Photo 6), coarsesand, or clean Refer to approved plans for locationand installation details.

6 If there arequestions or problems with the location,dimensions or method of installationcontact the engineer or responsible on-site officer for Ensure the socks are placedindividually or collectively (as a singlesediment trap) such that: (i) leakage around or under the socksis minimised; (ii) adjoining socks are tightly butted oroverlapped at least 450mm; (iii) the surface area of potential waterponding up-slope of each sedimenttrap is maximised; (iv) to the maximum degree practical, allsediment-laden water will passthrough the formed pond beforeflowing over the down-slope end ofthe sediment When placed across the invert of minordrains, ensure the socks are placedsuch that: (i) the crest of the downstream sock islevel with the channel invert at theimmediate upstream sock (if any); (ii) each sock extends up the channelbanks such that the crest of the sockat its lowest point is lower thanground level at either end of If stakes are required to anchor thesocks, their spacing does notexceeding or six times the sockdiameter (whichever is the lesser).

7 Maintenance1. Inspect all Filter socks prior to forecastrain, daily during extended periods ofrainfall, after significant runoffproducing storms or otherwise atweekly Repair or replace damaged Filter The bulk of the sediment collectedbehind the Filter socks should beremoved by shovel after each Remove collected sediment anddispose of in a suitable manner that willnot cause an erosion or All sand, soil, sediment or mud must bephysically removed from sealedsurfaces, first using a square-edgedshovel, and then a stiff-bristled broom,and then by a mechanical vacuum unit,if If necessary for safety reasons, thesealed surface shall only be washedclean after all reasonable efforts havebeen taken to shovel and sweep thematerial from the Dispose of collected sediment in asuitable manner that will not cause anerosion or pollution All synthetic (plastic) mesh or other nonreadily biodegradable material must beremoved from the site once the slope ordrain is stabilised, or the socks havedeteriorated to a point where they areno longer providing their intendeddrainage or sediment control function.