erosion&sedimentcontrol

Transcription

1 Auckland Reginal Cuncil Ersin Cntrl: 1 15 ersin&sedimentcntrl Guidelines fr Land Disturbing Activities in the Auckland Regin Turfing Plate Turfing Definitin The establishment and permanent stabilisatin f disturbed areas by laying a cntinuus cver f grass turf. Purpse T prvide immediate vegetative cver t stabilise sil n disturbed areas such as. Fr example: Critical ersin prne areas n the site. Critical areas n the site that cannt be stabilised by cnventinal swing methds. Runff Diversin Channels and ther areas f cncentrated flw where velcities will nt exceed the specificatins fr a grass lining. Applicatin Turfing is the preferred methd fr disturbed areas that must be immediately stabilised. It is particularly useful fr: Watercurses and channels carrying intermittent flw. Areas arund drp inlets. Residential r cmmercial lawns t allw prmpt use and fr aesthetic reasns. Steep areas. Design While there are n specific design criteria fr Turfing, Turf reinfrced with gesynthetic matting shuld be cnsidered fr areas f high ersin ptential; fr example, steep slpes r cncentrated verland flw paths. Cnstructin Specificatins Site Preparatin Befre Turfing, prperly prepare the site in rder t ensure the successful establishment f vegetatin. This includes applying fertiliser as in Table 1.6 f these Guidelines, unifrmly grading the area, clearing all debris, remving stnes and clds and scarifying hard packed surfaces.

2 Auckland Reginal Cuncil Ersin Cntrl: 1 16 ersin&sedimentcntrl Guidelines fr Land Disturbing Activities in the Auckland Regin Turf Installatin During perids f high temperatures, lightly irrigate sil immediately befre laying turf. Lay the first rw f turf in a straight line with subsequent rws placed parallel t and tightly wedged against each ther. Stagger lateral jints in a brick-like pattern. D nt stretch r verlap turf and make sure all jints are butted tight in rder t prevent vids, which can cause drying f the grass rts. On slping areas r channels where ersin may be a prblem, lay turf dwnslpe with the ends f the turf material verlapped such that the upslpe turf verlaps the dwnslpe turf by at least 100 mm. It may be necessary t secure the turf with pegs r staples. Ensure the turf at the tp f the slpe is apprpriately trenched in t prevent runff mving underneath it. As Turfing is cmpleted in ne area, rll r tamp the entire area t ensure slid cntact f the grass rts with the sil surface. After rlling, immediately water the Turf until the underside f the new turf and sil surface belw the turf are thrughly wet. Maintenance Water daily during the first week f laying unless there is adequate rainfall. D nt mw the area until the turf is firmly rted. Apply fertiliser regularly as in Table 1.6 f these Guidelines fr nging successful establishment.

3 Auckland Reginal Cuncil Ersin Cntrl: 1 17 ersin&sedimentcntrl Guidelines fr Land Disturbing Activities in the Auckland Regin 1.7 Gesynthetic Ersin Cntrl Systems (GECS) Definitin The artificial prtectin f channels and erdible slpes utilising artificial ersin cntrl material such as gesynthetic matting, getextiles r ersin matting. Purpse T immediately reduce the ersin ptential f disturbed areas and/r t reduce r eliminate ersin n critical sites during the perid necessary t establish prtective vegetatin. Sme frms f artificial prtectin may als help t establish prtective vegetatin. Applicatin On shrt steep slpes. On areas that have highly erdible sils. In situatins where tensile and shear strength characteristics f cnventinal mulches limit their effectiveness in high runff velcities. In channels (bth perennial and ephemeral) where the design flw prduces tractive shear frces greater than in-situ sil can withstand. In areas where there is nt enugh rm t install adequate sediment cntrls. In critical ersin-prne areas such as sediment retentin pnd utlet and inlet pints. In areas that may be slw t establish an adequate permanent vegetative cver. In areas where the dwnstream envirnment is f high value and rapid stabilisatin is needed. Design There are tw categries f GECS; temprary degradable and permanent nn-degradable. Temprary Degradable GECS These are used t prevent lss f seedbed and t prmte vegetatin establishment where vegetatin alne will be sufficient fr site prtectin nce established. Cmmn temprary GECS are ersin cntrl blankets, pen weave meshes/matting and rganic ersin cntrl netting (fibre mats factry-bnded t synthetic netting). Permanent Nn-Degradable GECS These are used t extend the ersin cntrl limits f vegetatin, sil, rck r ther materials. Cmmn permanent GECS are three-dimensinal ersin cntrl and revegetatin mats, gecellular cnfinement systems, ren mattresses and gabins. The selectin f an apprpriate GECS is a cmplex balancing f the relative imprtance f the fllwing requirements. Endurance: durability, degree f resistance t defrmatin ver time and ultravilet radiatin and t chemicals (natural r as pllutants). Physical: thickness, weight, specific gravity and degree f light penetratin. Generally a thicker heavier material will prvide better prtectin. Hydraulic: ability f the system t resist tractive shear strength and prtect against channel ersin, ersin f underlying sils r slpe ersin frm rainfall impact. Mechanical: defrmatin and strength behaviur. Tensile strength and elngatin, stiffness (hw well it will cnfrm t the subgrade) and hw well it will resist tractive shear frces. When a getextile is t be used fr temprary channel r spillway prtectin, cnsider cmbining a high strength, lw permeability clth ver a sft pliable needle punch clth pinned t ensure the clth is in cntact with the entire sil surface. Trench and pin all flw entry pints such that the upslpe getextile edge verlaps the dwnslpe getextile mat. Te in the upslpe end f the dwnslpe mat. In high risk areas such as spillways and diversins, pin getextiles dwn n a 0.5 grid r in accrdance with the manufacturers specificatins, whichever prvides the greatest number f cntact pints. There is a large number f prducts available fr all situatins and depending n the degree f prtectin needed, a prduct r cmbinatin f prducts will be available t suit the situatin. It is vital that the prduct utilised is designed fr the intended use and installed

4 Auckland Reginal Cuncil Ersin Cntrl: 1 18 ersin&sedimentcntrl Guidelines fr Land Disturbing Activities in the Auckland Regin and maintained accrding t its specificatins. Decisin analysis techniques ranking the varius GECS available shuld be used based n the fllwing categries. Sediment yield (generally ranked highest) Stability under flw Vegetatin enhancement Durability Cst When installing GECS within a channel, it is imprtant that the design velcity f the prduct is cnsidered and again that the prduct chsen is apprpriate fr the use. Many prducts prvide fr the cmbinatin f a revegetatin technique and an artificial ersin cntrl measure. Again, design specificatins need t be clsely fllwed in all cases. Maintenance Inspect after every rainfall and undertake any maintenance immediately. Figure Getextile Laid n Slpe

5 Auckland Reginal Cuncil Ersin Cntrl: 1 19 ersin&sedimentcntrl Guidelines fr Land Disturbing Activities in the Auckland Regin Figure Getextile at Culvert Outlet

6 Auckland Reginal Cuncil Ersin Cntrl: 1 20 ersin&sedimentcntrl Guidelines fr Land Disturbing Activities in the Auckland Regin 1.8 Stabilised Cnstructin Entrance Plate 1.8 Stabilised Cnstructin Entrance Definitin A stabilised pad f aggregate n a filter clth base lcated at any pint where traffic will be entering r leaving a cnstructin site. Purpse T prevent site access pints frm becming sediment surces and t help minimise dust generatin and disturbance f areas adjacent t the rad frntage by giving a defined entry/exit pint. Applicatin Use a Stabilised Cnstructin Entrance at all pints f cnstructin site ingress and egress with a cnstructin plan limiting traffic t these entrances nly. They are particularly useful n small cnstructin sites but can be utilised fr all prjects. Design Clear the entrance and exit area f all vegetatin, rts and ther unsuitable material and prperly grade it. Prvide drainage t carry runff frm the Stabilised Cnstructin Entrance t a sediment cntrl measure. Place aggregate t the specificatins belw and smth it. Table 1.8 Aggregate Size Thickness Length Width Stabilised Cnstructin Entrance Aggregate Specificatins mm washed aggregate 150 mm minimum 10 minimum 4 minimum

7 Auckland Reginal Cuncil Ersin Cntrl: 1 21 ersin&sedimentcntrl Guidelines fr Land Disturbing Activities in the Auckland Regin Maintenance Maintain the Stabilised Cnstructin Entrance in a cnditin t prevent sediment frm leaving the cnstructin site. After each rainfall inspect any structure used t trap sediment frm the Stabilised Cnstructin Entrance and clean ut as necessary. When wheel washing is als required, ensure this is dne n an area stabilised with aggregate which drains t an apprved sediment retentin facility. Figure 1.8 Stabilised Cnstructin Entrance

8 Auckland Reginal Cuncil Ersin Cntrl: 1 22 ersin&sedimentcntrl Guidelines fr Land Disturbing Activities in the Auckland Regin 1.9 Pipe Drp Structure/Flume Plate 1.9 Pipe Drp Structure Definitin A temprary pipe structure r cnstructed flume placed frm the tp f a slpe t the bttm. Purpse A Pipe Drp Structure r a Flume is installed t cnvey surface runff dwn the face f unstabilised slpes in rder t minimise ersin n the slpe face. Applicatin Pipe Drp Structures r Flumes are used in cnjunctin with Runff Diversin Channels. The Runff Diversin Channels direct surface runff t the Pipe Drp Structure r Flume which cnveys cncentrated flw dwn the face f a slpe. Limit the catchment area f each Pipe Drp Structure r Flume t 1.0 ha. If ther frms f Pipe Drp Structures r Flumes are being cnsidered, Auckland Reginal Cuncil apprval f thse structures will be necessary n a case by case basis. Design Cnstruct all Pipe Drp Structures r Flumes f watertight materials. Extend the Pipe Drp Structure r Flume beynd the te f the slpe and adequately prtect the utlet frm ersin using riprap ver a getextile aprn. Use f the fllwing Design Criteria fr Pipe Drp Structure, is shwn in Figure 1.9. Table 1.9 Pipe Diameter (mm) Design Criteria fr Pipe Drp Structure Maximum Catchment Area (ha)

9 Auckland Reginal Cuncil Ersin Cntrl: 1 23 ersin&sedimentcntrl Guidelines fr Land Disturbing Activities in the Auckland Regin Ensure that at the Pipe Drp Structure r Flume inlet, the height f the Runff Diversin Channel is at least twice the pipe diameter r height f Flume as measured frm the invert. Install a flared entrance sectin f cmpacted earth. T prevent ersin, place impermeable getextile fabric int the inlet extended a minimum f 1.0 in frnt f and t the side f the inlet and up the sides f the flared entrance. Ensure this getextile is keyed 150 mm int the grund alng all edges. When the catchment area is disturbed, ensure the Pipe Drp Structure r Flume discharges int a Sediment Retentin Pnd r a stable cnveyance system that leads t a pnd. When the catchment area is stabilised, ensure the Pipe Drp Structure r Flume utlets nt a stabilised area at a nn-ersive velcity. The pint f discharge may be prtected by rck rip rap. Ensure the Pipe Drp Structure r Flume has a minimum slpe f 3%. Cnstructin Specificatins fr Pipe Drp Structures A cmmn cause f failure f Pipe Drp Structures is water saturating the sil and seeping alng the pipe where it cnnects t the Runff Diversin Channel. Backfill prperly arund and under the pipe with stable material in rder t achieve firm cntact between the pipe and the sil at all pints t eliminate this type f failure. Pipe material used fr the Pipe Drp Structure can cnsist f rigid pipe material r flexible pipe as required. If flexible pipe material is utilised, it is vital that the material be pinned t the slpe in the required psitin. Place Pipe Drp Structures n undisturbed sil r well-cmpacted fill at lcatins as detailed within the Ersin and Sediment Cntrl Plan fr the site. Immediately stabilise all disturbed areas fllwing cnstructin. Secure the Pipe Drp Structure t the slpe at least every 4. Use n less than tw anchrs equally spaced alng the length f the pipe. Ensure all pipe cnnectins are watertight. Cnstructin Specificatins fr Flumes A cmmn failure f Flumes is utflanking f the Flume entrance r scuring f the invert t the Flume. This can be prevented by waterprfing the entrance t the Flume by trenching in an apprpriate impervius getextile r plastic liner s that all flws are channelled directly int the flume. Alternatively a piped entrance can be installed. Flumes can be cnstructed frm materials such as crrugated steel, cnstructin ply, sawn timber r halved plastic piping. Cnstruct the Flume t ensure there are n leaks. Fr wden r plywd Flumes r Flumes where leakage is likely, extend an impervius liner dwn the full length f the Flume structure. Fr slpes greater than 30%, a Flume can be cnstructed frm a standard 1.2 x 2.4 x 22mm plywd sheet. This will be adequate fr a catchment f up t ne ha. Specific design is required fr larger catchments. Fasten the Flume t the slpe using waratahs r wden stakes placed in pairs dwn the slpe at 1 t 4 spacings, depending n the Flume material used. Fasten the Flume t the waratahs r stakes using wire r steel strapping. Place Flumes n undisturbed sil r well cmpacted fill at lcatins as detailed in the site s Ersin and Sediment Cntrl Plan. Maintenance Inspect the Pipe Drp Structure/Flume peridically and after each rain event. Immediately carry ut any maintenance required. Keep the inlet pen at all times.

10 Auckland Reginal Cuncil Ersin Cntrl: 1 24 ersin&sedimentcntrl Guidelines fr Land Disturbing Activities in the Auckland Regin Figure 1.9 Pipe Drp Structure

11 Auckland Reginal Cuncil Ersin Cntrl: 1 25 ersin&sedimentcntrl Guidelines fr Land Disturbing Activities in the Auckland Regin 1.10 Level Spreader Definitin A nn-ersive utlet fr cncentrated runff cnstructed tdisperse flws unifrmly acrss a slpe. Purpse T cnvert cncentrated flw t sheet flw and release it unifrmly ver a stabilised area t prevent ersin. The Level Spreader prvides a relatively lw cst ptin which can release cncentrated flw where site cnditins are suitable. Particular care is needed t ensure the Level Spreader utlet lip is cmpletely level and is in stable, undisturbed sil r is well armured. Any depressins in the Level Spreader lip will recncentrate flws, resulting in further ersin. Applicatin Where sediment-free strm runff can be released in a sheet flw ver a stabilised slpe withut causing ersin. Where sediment-laden verland flw can be released in sheet flw acrss the inlet t a Sediment Retentin Pnd. Where the area belw the Level Spreader lip is unifrm with the slpe f 10% r less and/r is stable fr the anticipated flw cnditins. Where the runff water will nt re-cncentrate after release. Where there will be n traffic ver the Level Spreader. Design Determine the capacity f the Level Spreader by estimating peak flw frm the 20 year strm. Where pssible, chse a site fr the Level Spreader that has a natural cntur that will allw fr the rapid spreading f flws, fr example, at the end f a knll r ridge. Select the apprpriate length, width and depth f the spreader frm Table 1.10 belw. Table 1.10 Level Spreader Design Criteria Design Flw Inlet Depth End Width Length (m 3 /sec) Width () (mm) () () Cnstruct a 6 lng transitin sectin in the Runff Diversin Channel leading up t the Level Spreader s the width f the Runff Diversin Channel will smthly meet the width f the Level Spreader t ensure unifrm utflw. The Level Spreader trench tapers dwn t 1 at the end f the Level Spreader. Maintain a minimum inlet width f 3. Ensure that the grade f the Level Spreader is 0%. Cnstruct the Level Spreader lip n undisturbed sil, incrprating a 50 x 150 mm bard (Spreader Beam) levelled and psitined edge n as shwn belw. An alternative is t armur the Level Spreader t a unifrm height and zer grade ver the length f the Level Spreader. Use getextile and ensure the disturbed area is seeded and fertilised fr vegetatin establishment. Maintenance Inspect Level Spreaders after every rainfall until vegetatin is established and prmptly undertake any necessary repairs. Ensure vegetatin is kept in a healthy and vigrus cnditin. Figure 1.10 Level Spreader

12 Auckland Reginal Cuncil Ersin Cntrl: 1 26 ersin&sedimentcntrl Guidelines fr Land Disturbing Activities in the Auckland Regin 1.11 Surface Rughening

13 Auckland Reginal Cuncil Ersin Cntrl: 1 27 ersin&sedimentcntrl Guidelines fr Land Disturbing Activities in the Auckland Regin 1.11 Surface Rughening Definitin Rughening a bare earth surface with hrizntal grves running acrss the slpe, r tracking with cnstructin equipment. Purpse T aid in the establishment f vegetative cver frm seed, t reduce runff velcity, t increase infiltratin, t reduce ersin and assist in sediment trapping. Applicatin Apply Surface Rughening n all cnstructin sites requiring slpe stabilisatin with vegetatin, particularly n slpes steeper than 25%. Design Nt Applicable. Figure 1.11 Tracking Cnstructin Specificatins Surface Rughening is prmted by the Auckland Reginal Cuncil because it aids the establishment f vegetatin, imprves infiltratin and decreases runff velcity. Graded areas with smth, hard surfaces may be initially attractive but such surfaces increase the ptential fr ersin. A rugh, lse sil surface gives a mulching effect that prtects fertiliser and seed. Varius methds are available fr Surface Rughening such as stair step grading, discing and frming grves by machinery tracking. Factrs t be taken int accunt when chsing a methd are slpe steepness, mwing/ maintenance requirements and whether the slpe is frmed by cutting r filling. Machinery tracking up and dwn the slpe is the recmmended methd, with the cleats f the machine tracks prviding a series f mini cntur drains, slwing verland flw dwn the slpe and helping t keep the grass seed n the slpe. Maintenance Peridically check the slpes fr rills and washes. Reseed and/r rewrk the area as necessary.

14 Auckland Reginal Cuncil Ersin Cntrl: 1 28 ersin&sedimentcntrl Guidelines fr Land Disturbing Activities in the Auckland Regin Dzer cleats create grves perpendicular t the slpe Slpe