300

300

Place Bidim A24 geotextile or equal under concreteand down batter to minimum 500mm below the lowerof permanent water level or outlet spillway crest.Depending on soil properties, black plastic orconcrete may be required to minimise scour potential

500

100x25mm timber embedded into concrete beam.Timber to be at least 30mm proud of concrete withnails at 1.2m centres with at least 25mm exposed toprevent lifting.

Level Spreader Details - Typical Cross Section (NTS)

Mixing Zone Settling Basin

Outlet Spillway Details - Typical Cross Section (NTS)

Concrete plinth to seal spillway crest to preventwater seepage through rocksMaximum pond water prior to spillway discharge

Settling Basin

SpillwayChute Rock placement and

grading (refer toConstruction Notes)

Spillway Crest

Concrete to extend up side of level spreader

Refer to timber spillway section

Level Spreader Details - Typical Long Section (NTS)

Bidim A24 Geotextileor equal

Outlet Spillway Details - Typical Long Section (NTS)

Bidim A24 Geotextileor equal

Extend rock scour protection and concreteplinth (not shown) to embankment crest

1 in 2 Typical

Spillway to extend the full width of the basin.minimum embankment height 500mm overspillway concrete plinth level

Type B Sediment Basin Plan View (Typical NTS)

Rainfall activatedcoagulant dosing unit(refer detail)

Forebay Mixing Zone(10% of Settling Zone

Volume)

Settling Zone Length:Width (3:1)Refer to Table 1 for minimumSettling Zone Volume

Outlet Spillway(refer detail)

Inlet Drain/Culvert

Level Spreader(refer detail)

SupernatentRunoff

Settling Zone

Sediment Storage Zone

Level Spreader crest200mm (min) aboveOutlet Spillway Crest

Drain invert 200mm(min) above levelspreader crest RL

Forebay MixingZone

Outlet Spillway(refer detail)

Type B Sediment Basin Long Section (Typical NTS)

3

1

Notes:

Auto Doser1. Provided as either Floc Box or iFOD-Rainto manufacturers specification. Floc Boxunit sizing to be in accordance with thetable below if using Turbiclear Coagulant:.

Area Treated Floc Box Unit (Ha) (Litres)<0.3 75<0.75 200<2 400

2. Doser and supply of flocculant to beprovided on level pad 4mx4m within 10m ofdosing point.3. All-weather access track to be providedto doser.4. Flocculant provided as Turbiclear (ACH).If alternative flocculant used then thebasin size is to be increased according tojar settlement test (refer to table below.

Jar Settlementafter 15 mins

(mm)

5075100150

MultiplicationFactor to Settling

Zone Volume

x3x2x1.5x1

Basin construction:

Materials-

5. Earth Fill: clean soil with EmersonClass 2(1), 3, 4 or 5 and free of roots,woody vegetation, rocks and otherunsuitable material. Soil with EmersonClass 4 and 5 may not be suitabledepending on particle size distributionand degree of dispersion. Class 2(1)should only be used upon recommendation

from geotechnical specialist.

6. Spillway rock: hard, angular, durable,weather resistant and evenly graded rockwith 50% by weight larger than thespecified nominal (d50) rock size. Largerock should dominate, with sufficientsmall rock to fill the voids betweenlarger rock. the diameter of the largestrock should be no larger than 1.5 timesthe nominal rock size. The specific

gravity should be at least 2.5.

7. Geotextile fabric: heavy duty,needle-punched, non-woven cloth, minimum'bidim' A24 or equivalent.

Construction-8. Notwithstanding any description containedwith approved plans or specifications, theContractor shall be responsible forsatisfying themselves as to the nature andextent of the specified works and thephysical and legal conditions under whichthe works will be carried out. This shallinclude means of access, extent of clearing,nature of the materials to be excavated,type and size of mechanical plant required,location and suitability of water supply forconstruction and testing purposes, and anyother likely matters affecting theconstruction of the works.9. Refer to approved plans for location,dimensions, and construction details. Ifthere are questions or problems with thelocation, dimensions, or method ofinstallation, contact the engineer orresponsible on-site officer for assistance.10. Before starting any clearing orconstruction, ensure all the necessarymaterials and components are on the site toavoid delays in completing the sedimentbasin once works begin.11. Install requires short term sedimentcontrol measures downstream of the proposedearthworks to control sediment runoff duringconstruction of the basin.12. The area to be covered by theembankment, borrow pits and incidentalworks, together with an area extendingbeyond the limits of each for a distance notexceeding five (5) metres all around must becleared of all trees, scrub, stumps, roots,dead timber and rubbish and disposed of ina suitable manner. Delay clearing the mainbasin area until the embankment is complete.13. Ensure all holes made by grubbing withinthe embankment footprint are filled withsound material, adequately compacted, andfinished flush with the natural surface.

Cut-off Trench-14. Before construction of the cut-offtrench or any ancillary works within theembankment footprint, all grass growth andtopsoil must be removed from the area to beoccupied by the embankment and must bedeposited clear of this area and reservedfor topdressing the completed embankment.

15. Excavate a cut-off trench along the centreline of the earth fill embankment. Cut thetrench to stable soil material, but in no casemake it less than 600mm deep. the cut-offtrench must extend into both abutments to atleast the elevation of the outlet spillwaycrest. Make the minimum bottom width wideenough to permit operation of the excavationand compaction equipment, but in no case lessthan 600mm. Make the side slopes of the trenchno steeper than 1:1 (H:V).16. Ensure all water, loose soil, and rock areremoved from the trench before backfillingcommences. The cut-off trench must bebackfilled with select earth-fill of the typespecified for the embankment, and this soilmust have a moisture content and degree ofcompaction the same as specified for the corezone.17. Material excavated from the cut-off trenchmay be used in the construction of theembankment provided it is suitable and it isplaced in the correct zone according to itsclassification.

Embankment-18. Scarify areas on which fill is to beplaced before placing the fill.19. Ensure al fill material used to form theembankment meets the specifications certifiedby a soil scientist of geotechnicalspecialist.20. The fill material must contain sufficientmoisture so it can be formed by hand into aball without crumbling. If water can besqueezed out of the ball, it is too wet forproper compaction. Place fill material in 150to 200mm continuous layers over the entirelength of the fill area and then compactbefore placement of further fill.21. Unless specified on the approved plans,compact the soil at about 1% to 2% wet optimumand to 95% modified or 100% standardcompaction.embankment to an elevation 10%higher than the design height to allow forsettling22. Where both dispersive and non-dispersiveclassified earth-fill materials are available,non-dispersive earth-fill must be used in thecore zone. the remaining classified earth-fillmaterials must only be used as directed by thesite superintendent.

23. Where specified, construct the embankmentto an elevation 10% higher than the designheight to allow for settling; otherwisefinished dimensions of the embankment afterspreading of topsoil must conform to thedrawing with a tolerance of 75mm fromspecified dimensions.24. Ensure debris and other unsuitablebuilding waste is not placed within the earthembankment.25. After completion of the embankment allloose uncompacted earth-fill material on theupstream and downstream batter must be removedprior to spreading topsoil.26. Topsoil and re-vegetate/stabilise allexposed earth as directed within the approvedplans.

Spillway construction-27. The spillway must be excavated as shown onthe plans, and the excavated material ifclassified as suitable, must be used in theembankment, and if not suitable it must bedisposed of into spoil heaps.28. Ensure excavated dimensions allow adequateboxing-out such that the specified elevations,grades, chute width, and entrance and exitslopes for the emergency spillway will beachieved after placement of the rock or otherscour protection measures as specified in theplans.29. Place specified scour protection measureson the emergency spillway. Ensure the finishedgrade blends with the surrounding area toallow a smooth flow transition from spillwayto downstream channel.30. If a synthetic filter fabric underlay isspecified, place the fabric directly on theprepared foundation. if more than 1 sheet offilter fabric is required, overlap the edgesby at least 300mm and place anchor pins atminimum 1m spacing along the overlap. bury theupstream end of the filter fabric a minimum300mm below ground and where necessary, burythe lower end of the fabric or overlap aminimum 300mm over the next downstream sectionas required. Ensure the filter fabric extendsat least 1000mm upstream of the spillwaycrest.31. Take care not to damage the fabric duringor after placement. If damage occurs, removethe rock and repair the sheet by addinganother layer of fabric with a minimum overlapof 300mm around the damaged area.3If extensivedamage is suspected, remove and replace theentire sheet.

32. where large rock is used, or machineplacement is difficult, a minimum 100mm layerof fine gravel, aggregate, or sand may beneeded to protect the fabric.33. Placement of rock should followimmediately after placement of the filterfabric. Place rock so that it forms a dense,well graded mass of rock with a minimum ofvoids. the desired distribution of rockthroughout the mass may be obtained byselective loading at the quarry and controlleddumping during final placement.34. The finished slope should be free ofpockets of small rock or clusters of largerocks. Hand placing may be necessary toachieve the proper distribution of rock sizesto produce a relatively smooth, uniformsurface. the finished grade of the rock shouldblend with the surrounding are. No overfall orprotrusion of rock should be apparent.35. Ensure that the final arrangement of thespillway crest will not promote excessive flowthrough the rock such that the water can beretained within the settling basin at theelevation no less than 50mm above of below thenominated spillway crest elevation.

Establishing the settling pond-36. The area to be covered by the stored wateroutside of the limits of the borrow pits mustbe cleared rubbish. Trees must be cut downstump high and removed from the immediatevicinity of the work.37. Establish all required inflow chutes andinlet baffles, if specified, to enable waterto discharge into the basin in a manner thatwill not cause soil erosion or there-suspension of settled sediment.38. Install a sediment storage level markerpost with a cross member set just below thetop of the sediment storage zone (as specifiedon the approved plans). Use at least a 75mmwide post firmly set into the basin floor.39. If specified, install internal settlingpond baffles. Ensure the crest of thesebaffles is set level with, or just below, theelevation of the emergency spillway.40. Install all appropriate measures tominimise safety risk to on-site personnel andthe public caused by the presence of thesettling pond. Avoid steep, smooth internalslopes. Appropriately fence the settling pondand post warning signs if unsupervised publicaccess is likely or there is considered to bean unacceptable risk to the public.

Basin Perspective (looking downstream) Basin Perspective (looking upstream)

Standard Type B High Efficiency SedimentBasin for Small Catchments (<2ha)

Table 1 - Settling Zone Volume