erosion&sedimentcontrol

Transcription

1 Auckland Reginal Cuncil Wrks Within a Watercurse: 3 1 Wrks within watercurses have very high ptential fr ersin and discharge f sediment. This is because such wrk is undertaken in r near flwing water the majr cause f ersin. Flwing water causes nging scur and prvides the transprt mechanism t allw sediment t be dispersed dwnstream f the wrks and ultimately, int the marine envirnment. The fllwing ersin and sediment cntrl methds and techniques are specific t temprary watercurse wrks nly. Such wrks may als require a range f cntrl measures additinal t thse detailed belw. These ther measures are described in ther sectins f these Guidelines and include bth ersin cntrl and sediment cntrl techniques. Design and planning cnsideratin fr a permanent watercurse crssing need t take int accunt the permanent nature f the crssing in questin. Be sure that they are cnstructed in accrdance with all relevant requirements. 3.1 Temprary Watercurse Crssings Plate 3.1 Temprary Watercurse Crssing Definitin A bridge, frd r temprary structure installed acrss a watercurse fr shrt term use by cnstructin vehicles. Purpse T prvide a means fr cnstructin vehicles t crss watercurses withut mving sediment int the watercurse, damaging the bed r channel, r causing flding during the cnstructin, maintenance r remval f the structure. Applicatin Where heavy equipment is required t be mved frm ne side f a watercurse t the ther, r where traffic must crss the watercurse frequently fr a shrt perid f time.

2 Auckland Reginal Cuncil Wrks Within a Watercurse: 3 2 Design Careful planning can minimise the need fr watercurse crssings. Wherever pssible, avid crssing watercurses by cmpleting the develpment separately n each side f the channel, thus leaving the watercurse in its natural state. If n ther ptin exists and a watercurse crssing is required, select a lcatin where the ptential effects f the crssing (including cnstructin) are minimised. Plan watercurse crssings well befre yu need them and if pssible, cnstruct them during perids f dry weather. Cmplete cnstructin as rapidly as pssible and stabilise all disturbed areas immediately during and fllwing cnstructin. D nt build a watercurse crssing during the fish migratin perid fr the watercurse. The Auckland Reginal Cuncil can help identify these perids fr particular watercurses. There are three main types f crssing; bridges, culverts and frds. Bridges Where available materials and designs are adequate t bear the expected ladings, bridges are the preferred temprary watercurse crssing methd. They prvide the least bstructin t flw and fish migratin, cause little r n mdificatin f the bed r banks and generally require little maintenance. It shuld be nted, hwever, that bridges can be a safety hazard if nt designed, installed and maintained apprpriately. Culvert Crssings Culverts are the mst cmmnly used type f temprary watercurse crssing, and can be easily adapted t mst site cnditins. The installatin and remval f culverts, hwever, causes cnsiderable damage t watercurses and can als create the greatest bstructin t fld flws. Frds Made f stabilising material such as rck, frds are ften used in steep catchments subject t flding, but where nrmal flws are shallw. Only use frds where crssing requirements are infrequent. They can ffer little r n bstructin t flws, are relatively easy t install and maintain, and in mst cases can be left in place at the end f the cnstructin activity. As well as ersin and sediment cntrl measures, structural stability, utility and safety must als be taken int accunt when designing temprary watercurse crssings. These details must be supplied t the Auckland Reginal Cuncil fr apprval prir t cnstructin. In additin, a resurce cnsent may be required fr the cnstructin f the prpsed crssing. This can be determined by cnsultating with the Auckland Reginal Cuncil. Any temprary crssing shall cmply with the technical requirements f the varius agencies invlved and any specific requirements impsed by the Auckland Reginal Cuncil. If the structure is n lnger needed, remve the structure and all material frm the site. Immediately stabilise all areas disturbed during the remval prcess by revegetatin r artificial prtectin as a shrt term cntrl measure. Keep machinery clear f the watercurse while remving the structure. Maintenance Inspect temprary watercurse crssings after rain t check fr blckage in the channel, ersin f the banks, channel scur r signs f instability. Make all repairs immediately t prevent further damage t the installatin. Permanent crssings need t be inspected fllwing majr strm events, again with all repairs being made immediately.

3 Auckland Reginal Cuncil Wrks Within a Watercurse: Temprary Watercurse Diversin Definitin A shrt term watercurse diversin t allw wrks t ccur within the main watercurse channel under dry cnditins. Purpse T enable watercurse wrks t be undertaken withut wrking in wet cnditins and withut mving sediment int the watercurse. Applicatin Temprary watercurse diversins are used as temprary measures t allw any wrks t be undertaken within permanent and ephemeral watercurses. Plate 3.2 Temprary Watercurse Diversin Design Divert all flw via a stabilised system arund the area f wrks and discharge it back int the channel belw the wrks t avid scur f the channel bed and banks. Figure shws the suggested steps t minimise sediment generatin and discharge frm wrks within a watercurse.

4 Auckland Reginal Cuncil Wrks Within a Watercurse: 3 4 Step 1 Excavate the diversin channel leaving a plug at each end s that the watercurse des nt breach the diversin. Size the diversin channel t allw fr a 5% AEP rain event. Stabilise the diversin channel apprpriately t ensure it des nt becme a surce f sediment. Anchr suitable getextile clth in place t the manufacturer s specificatins, which will include trenching int the tp f bth sides f the diversin channel t ensure that the fabric des nt rip ut. Open the dwnstream plug and allw water t flw up the channel, keeping sme water within the channel t reduce prblems when the upstream plug is excavated. Open the upstream plug and allw water t flw int the channel. Plug still t be pened Flw Prpsed watercurse diversin Existing watercurse Step 2 Immediately place a nn-erdible dam in the upstream end f the existing channel. Cnstruct the dam as specified in Figure 3.2.2,where a cmpacted earth bund has shtcrete/ cncrete placed, r apprpriate getextile pinned ver it, with rck rip-rap extending ver the upper face and adjacent t the lwer face fr scur prtectin. Dam New watercurse diversin Flw Existing watercurse Step 3 Immediately install a nn-erdible dwnstream dam t prevent backflw int the cnstructin area. Drain the existing watercurse by pumping t a Sediment Retentin Pnd where treatment f the pnded water can ccur prir t re-entering the live sectin f the watercurse. Cnstruct the structure and cmplete all channel wrk. Sediment retentin pnd Watercurse diversin Dam Flw Existing watercurse Prpsed structure Step 4 Remve the dwnstream dam first, allwing water t fld back int the riginal channel. Remve the upstream dam and fill in bth ends f the diversin channel with nn-erdible material. Pump any sedimentladen water t a Sediment Retentin Pnd. Fill in the remainder f the diversin and stabilise. New Flw structure Lcatin f watercurse diversin Existing watercurse New rad Figure Temprary Watercurse Diversin Wrks Sequence

5 Auckland Reginal Cuncil Wrks Within a Watercurse: 3 5 Figure Temprary Watercurse Diversin Dam Detail Maintenance Any wrks within a watercurse will require nging and vigilant maintenance t minimise sediment generatin. T achieve this, identify and crrect any signs that may indicate a ptential prblems. Take particular ntice f the fllwing signs. The getextile lining ripping. Scur ccurring where the flw re-enters the channel. Undercutting f the diversin lining. Make repairs immediately.

6 Auckland Reginal Cuncil Wrks Within a Watercurse: Rck Outlet Prtectin Plate 3.3 Rck Outlet Prtectin Definitin Rck placed at the utfall f channels r culverts. Purpse T break up cncentrated flws, t reduce the velcity f flws t nn ersive rates and t stabilise the utfall pint. Applicatin This practice applies where discharge velcities and energies at the utlets f pipes, culverts r flumes are sufficient t cause ersin. This will apply t mst cncentrated flw utfalls and utlets f all types such as sediment retentin pnds, strmwater management pnds and rad culverts. Design The fllwing design des nt apply t rck lining f watercurse channels. Detailed design f Rck Outlet Prtectin depends n the lcatin. D nt use ROP t prtect pipe utlets at the tp f cuts r n slpes steeper than 10 % because they recncentrate flws and generate high velcities after the flw leaves the aprn. Ensure the channel cntaining the Rck Outlet Prtectin is straight thrughut its entire length and is cnstructed using rck rip rap r gabin baskets/ren mattresses. Remve sft material dwn t a firm bed and smth and level the utfall area t eliminate vids.

7 Auckland Reginal Cuncil Wrks Within a Watercurse: 3 7 Ensure rip rap is cmpsed f a well graded mixture f washed rck and has an apprpriate getextile placed underneath it at all times t prevent sil mvement int and thrugh the rip-rap. Cnstruct gabin baskets f hexagnal twist mesh with heavy galvanised steel wire. Ensure fundatin cnditins fr the gabin baskets/ren mattresses are the same as fr rck rip rap and place filter clth beneath all gabin baskets. In sme circumstances a key may be needed t prevent undermining f the main gabin structure. Design the structure in accrdance with Auckland Reginal Cuncil apprval and use materials within the relevant manufacturer s and engineering specificatins. Remember that wrks within a watercurse such as the placement f rck rip rap r gabin baskets may require a resurce cnsent frm the Auckland Reginal Cuncil. Cntact the Cuncil well ahead f time s that any cnsents needed may be btained befre wrks are due t start. Maintenance Once installed, the maintenance requirements f the such structures is very lw. Inspect after high flws t check scur and disldgement and make repairs immediately.

8 Auckland Reginal Cuncil Quarries: 4 1 Quarries are ptentially a majr surce f sediment. They are ften expsed fr lng perids f time and the area f bare earth can be cnsiderable. Their cntinuus peratin means that site cnditins cntinually change. Careful planning is required t ensure that the peratins are carried ut with minimal envirnmental impact. It is the respnsibility f the quarry peratr t minimise the adverse envirnmental effects f the peratin. This sectin f these Guidelines is designed t help quarry peratrs address sil and water prblems which may arise as a result f quarry peratins. It shuld be read in cnjunctin with Part B, Sectins 1 and 2 f these Guidelines, which detail specific ersin and sediment cntrl practices. Quarries are required t prduce management plans cvering the varius aspects f their peratin. These Guidelines will help in the prductin f such plans. The fllwing specific issues assciated with quarry peratins are discussed belw. Rad access Strmwater Overburden dispsal Stckpile areas Rehabilitatin f wrked ut areas Riparian prtectin areas Maintenance schedule fr ersin and sediment cntrl treatment structures Rad Access Many quarries in the Auckland Regin are serviced by metal rads, used in all weather cnditins. Vehicle mvements during rain can generate a lt f sediment. These rads, hwever, are nt always within the designated quarry area and therefre, are nt cvered by the Quarry Management Plan. Careful cnsideratin needs t be given t managing rads and traffic. In cases such as these, ersin and sediment cntrl measures need t be installed alng rads as utlined in Part B, Sectins 1 and 2 f these Guidelines. Where pssible, incrprate rad access int the Quarry Management Plan, ensuring all measures necessary are put in place t prtect receiving envirnments. Strmwater Clean Runff As far as it is pssible, divert clean water flw away frm wrking and bare areas t prevent them frm becming cntaminated by sediment. This aids in reducing the vlume f cntaminated runff needing t be cntrlled and treated. Runff Diversin Channels arund the wrking site, as utlined in Part B, Sectin 1.1, are the simplest way t deal with the clean runff. Cntaminated Runff Any runff frm bare areas will cllect sediment and becme cntaminated. This cntaminated runff, which includes runff frm aggregate wash prcesses, must be cntained and treated in an apprpriate manner befre being discharged t natural watercurses. The Quarry Management Plan must detail the methds fr cntainment and treatment f all cntaminated runff. Particular attentin shuld be paid t sensitive areas such as permanent watercurses, watercurse crssings and steeply slping bare areas. Design all structures fr the 5% AEP rainfall event. Overburden Dispsal Methds f verburden dispsal vary fr each quarry peratin. Overburden remval and dispsal sites can be a majr surce f ersin and sediment discharges frm quarries, particularly if the dispsal site is nt prperly lcated and managed. The Quarry Management Plan fr the site shuld give a reasnable indicatin f the fllwing. The timing and extent f verburden stripping, which will be related t an expected vlume and area f extractin. The methds t be emplyed fr dispsing the verburden. Onging management f dispsal sites, including prvisin fr regular dispsal f material trapped in sediment retentin pnds. If verburden dispsal is dealt with in islatin frm the Quarry Management Plan, cnsideratin must be given t the fllwing pints.

9 Auckland Reginal Cuncil Quarries: 4 2 Selectin f dispsal site (why the site was chsen). Stability f the site and subsequent verburden fill (batter slpes, safety factrs, benching, underlying material, drainage). Ersin and sediment cntrl measures. Rehabilitatin f dispsal site (revegetatin, cnturing). Stckpile Areas Stckpile areas include thse used fr stckpiling bth raw r finished quarry prducts prir t further prcessing r final despatch. These areas can be a majr surce f cntaminated runff if nt prperly cntrlled. Psitin stckpiles well away frm any watercurses and runff flw paths. Rehabilitatin f Wrked Out Areas Planning fr rehabilitatin must be an integral part f all quarry peratins. A prperly planned and implemented rehabilitatin prgramme will reduce the need fr expensive nging ersin cntrl, and cntrl and treatment f cntaminated runff. The aim f site rehabilitatin, whether temprary r permanent, is t maintain the site in a cnditin such that ersin and cntaminated runff are limited t an acceptable level. The prime areas fr cnsideratin are: establishing suitable final grund cnturs; establishing a suitable envirnment fr vegetatin grwth; revegetating the site with suitable vegetatin cver. Riparian Prtectin Areas Riparian prtectin areas rely n vegetatin t prvide a buffer between the quarry peratins and a water bdy such as a watercurse r wetland. These margins act as a physical barrier t keep machines away frm sensitive areas as well as serving as a last resrt sediment trap fr diffuse runff and/r unfreseen discharges. D nt, hwever, rely n riparian prtectin areas as a primary sediment cntrl mechanism. Maintenance Schedule fr Ersin and Sediment Cntrl r Treatment Structures Because quarry peratins cntinue ver a very lng time frame, it is imprtant t develp a maintenance schedule fr any cntrl/treatment structures that are put in place. Mney spent n designing and cnstructing cntrl/ treatment structures will be wasted if these structures are nt adequately maintained. Prperly maintained structures will prvide ptimum perfrmance at all times, thereby minimising the adverse envirnmental effects f the quarry peratin. Cnversely, prly maintained structures are likely t result in unsatisfactry envirnmental prtectin despite being initially well designed and cnstructed. Develp a maintenance schedule fr the site that clearly indicates what is t be dne in terms f visual inspectins and maintenance wrks. Undertake rutine maintenance wrks when they will cause the least pssible detrimental envirnmental effects (either directly r indirectly). Fr example, d nt clean sediment retentin pnds during r immediately after rainfall events. T ensure that the peratin f the pnd is nt affected at these critical times, maintenance shuld be dne prir t events. It is als particularly imprtant that all cntrl/treatment structures are inspected after significant rainfall events, r during prlnged rainfall, in additin t any regular scheduled inspectins. In the maintenance schedule include a prcedure fr immediately repairing and remedying any damage caused t cntrl/treatment structures frm daily quarry activities. Within the verall quarry peratin, give the inspectin and maintenance f cntrl/treatment structures a high pririty. Ensure every persn invlved in the quarry peratin is familiar with all aspects f ersin and sediment cntrl n the site, including any special cnditins f cnsents that are relevant. Fr example, specific water quality sampling requirements. Fr all aspects f quarry peratins where ersin and sediment cntrls are required, install the ersin and sediment cntrl practices as specified in these Guidelines.

10 Auckland Reginal Cuncil Vegetatin Remval: 5 1 Vegetatin remval peratins can be a majr surce f sediment. They ften invlve earthwrks assciated with rading and landing (skid site) frmatin, as well as the direct disturbance and expsure f the sil surface. Careful planning is required t ensure that these peratins are carried ut with minimal envirnmental impact. This sectin f these Guidelines is designed t help peple invlved with vegetatin remval peratins t address sil and water prblems which may arise as a result f their peratin. This sectin shuld be read in cnjunctin with Part B, Sectins 1 and 2 f these Guidelines, which detail specific ersin and sediment cntrl practices. Vegetatin remval peratins are als required t prduce Harvesting Management Plans that cver the varius aspects f their peratin. These Guidelines can be used t assist in the prductin f these plans. Varius specific issues assciated with vegetatin remval peratins are discussed belw. Rading Firebreaks Landings and tracks Land preparatin Harvesting and management after harvesting Rading Rading activities undertaken as part f vegetatin remval peratins have a large ptential impact n sil and water values. Planning, Lcatin and Design Lcate rads n ridge tps, natural benches and flatter slpes, aviding steep side slpes where pssible. D nt lcate rads in gully bttms. Minimise gully crssings where pssible. Lcate rads a safe distance frm watercurses and gullies. D nt discharge runff directly t a watercurse, and where pssible, ensure runff is filtered thrugh vegetatin. Where steep side cuts cannt be avided, ensure adequate crss-frmatin drainage is installed and that these channels flw nt stable r ersin prf areas such as spurs. Ensure they d nt discharge nt areas f sft fill. Cnstructin Where cnstructin peratins are t be undertaken in ersin-prne areas r adjacent t a watercurse, use an excavatr t enable sil and ther lse material t be placed in a stable psitin. D nt bulldze lse material int watercurses r areas where it may wash int watercurses. Keep machines ut f watercurses and minimise the number f crssings. If peratins are suspended, put adequate drainage prvisins in place t avid cncentratin f runff and scur prblems until wrk resumes. Stabilise cut and fill slpes where required, using measures such as hydrseeding and straw mulching. Install cntur drains and flumes t prevent scuring. Flume r pipe runff t slid grund and then discharge nt lgging slash, gravel, rck rip-rap, r getextiles. Plan the peratinal sequence f installing culverts and bridges acrss watercurses. Ensure all materials, machinery and labur are n hand befre cmmencing cnstructin. Ensure that the supervisin f culvert and bridge installatins is carried ut by a suitably experienced persn. Cmplete the cnstructin f watercurse crssings, apprach rads and assciated ersin and sediment cntrl measures as a cntinuus peratin.

11 Auckland Reginal Cuncil Vegetatin Remval: 5 2 Firebreaks Lcate firebreaks t minimise the pssibility f debris entering watercurses. Keep earthwrks assciated with firebreaks clear f steep drp-ffs and watercurses. Cnsideratin must be given t the ersin ptential f tracks frmed alng gully bttms. These areas shuld be avided. Maintain firebreaks t a reasnable standard t cntrl runff, rilling and gully ersin. Cnstruct cntur drains as required. Avid pnding f water abve steep drp-ffs and, if pnding ccurs, implement an apprpriate drainage design t prevent gully ersin. At the cmpletin f peratins, check firebreaks fr any ptential ersin prblems. Landings and Tracks Landings and tracks are generally permanent features and therefre require careful lcatin preparatin, directin f fall and cntrl f runff. Skid tracks, while generally mre f a temprary feature, als require careful cnsideratin f the abve. Any tracking results in cncentratin f runff and cnsequently, an increase in ersin. Minimise ersin by tracking acrss cnturs and where pssible, lcating tracks n ridges rather than in gullies. Ensure that extractin tracks d nt lead directly dwn twards watercurses where runff may g directly int the channel. Where pssible try t keep skid tracks and landings at least 20 away frm watercurses. At the cmpletin f lgging peratins, cnstruct cntur drains acrss skid tracks wherever runff may be cncentrated. Ensure that cntur drains discharge t slid grund and nt t areas f fill. Keep landings well clear f permanent watercurses. Where n alternative exists, ensure that the watercurse is nt bstructed. Frm all landings s that surface runff des nt flw dwn twards r directly int a watercurse. Cnstruct earth bunds alng watercurse edge bundaries t prevent debris and sediment frm entering watercurses. Extra cautin must als be exercised in the planning and cnstructin measures which cntrl water flwing ff skid tracks nt landings, s as t minimise water runff nt the landing. Take extra cautin when frming landings within dry gullies. Where this is dne, ensure the fllwing. A slash is placed acrss the gully flr t act as a sediment barrier. Fill batters are swn with a suitable vegetatin cver. Land Preparatin Planning Plan and implement all land preparatin and frest establishment t match an apprpriate prpsed methd f harvesting. Prtectin Areas (Riparian Margins) Retain r establish prtectin areas alng all watercurses. Where prtectin areas d nt exist, they can be established in cnjunctin with the fllwing peratins. Land clearing r site preparatin n areas being cnverted t prductin frestry. Planting n farm land r similar sites. Replanting n extic clearfelled areas. Vegetatin remval n terrain which may be difficult, very steep r ersin prne. Re-evaluate all existing prtectin areas when harvesting r replanting adjacent t prductin stands. Generally, prtectin areas can be left t regenerate naturally. Hwever, in sme cases it may be apprpriate t accelerate revegetatin by actively planting prtectin species. Planting Bundaries When re-planting, establish planting bundaries adjacent t watercurses in rder t minimise ptential watercurse damage frm future harvesting peratins. Establish planting bundaries n a case by case basis with cnsideratin t bth tpgraphy and sil stability. V-Blading/Line Raking Where pssible perate acrss the cntur, t minimise runff cncentratin dwn the blade lines. Where dwnhill runs are unavidable, limit them t 50 maximum length. D nt attempt these runs n slpes t steep fr the tractr t reverse up. Blade r rake at

12 Auckland Reginal Cuncil Vegetatin Remval: 5 3 least ne line n the cntur alng the lwer bundary f dwnhill peratins t prevent runff cncentratin at lw pints r gully systems. Finish dwnhill runs well befre any fill batter slpes such as landings and access rads. Near watercurses, ensure the peratin runs parallel t them at a minimum distance f 20. At the cmpletin f the peratin, inspect the site fr areas f ersin ptential and undertake apprpriate remedial actin. Establishing and Tending During establishing and tending stages, minimise sil lss and prevent cntaminatin f watercurses with chemicals, fertilisers, debris r detritus and. During thinning t waste peratins, fell trees away frm watercurses where pssible. Harvesting and Management After Harvesting Planning f Lgging Operatins Plan all lgging peratins, particularly the lcatin f skid tracks and rads, t prtect water and sil values. Off-site adverse effects must be avided r minimised when determining the ability and management f a catchment t be harvested. When harvesting near sensitive areas, extract twards landings lcated away frm them. Felling Operatins When trees are being felled within reach f a watercurse, ensure an experienced feller is in cntrl f the peratin. Where pssible, fell trees away frm watercurses. Extract any trees that have fallen int watercurses befre delimbing and crss cutting them. Back pull, r emply ther acceptable directinal felling techniques t fell prblem trees, particularly n steep r unstable watercurse faces and edges. Remve all large lgging debris frm watercurses at the cmpletin f the peratin, keeping machinery ut f the watercurse. Extractin Operatins Grund Based Systems - Keep tracking and stumping activities t a practical minimum. Use a few carefully chsen tracks and stay n these rather than taking shrtcuts which cause unnecessary grund disturbance. - Carry lgs ff the grund r n the machine where pssible. - Keep the machines blade up and d nt bulldze sil and stumps needlessly. - D nt crss watercurses (ther than at apprved crssing pints) and d nt haul alng them. - On sft and/r wet sils r steeper slpes, use lw-grund-pressure machines such as flexible-track r wide-tyre skidders. Cable Systems - Where cable systems are used in envirnmentally sensitive areas, keep the settings small, the haul distances shrt and the hauling directin uphill wherever practicable. Avid crss slpe haul lines that damage prtectin areas r sweep slash and sil int watercurses. - Whenever pssible when hauling acrss watercurses, use a system such as a skyline which allws full suspensin f lgs. Lift lgs clear f watercurse banks and prtectin areas. Cleanup Operatins On cmpletin f lgging peratins, carry ut the fllwing prcedures. Remve all temprary crssings. Cnstruct cntur drains n skid tracks t prevent runff cncentratin and sediment flw. Ensure landings are prperly drained and that sediment and debris are unable t directly enter any watercurse. Stabilise fill batters n landings and tracks by swing with suitable grass seed. Ensure runff is channelled safely ver batter slpes and nt stable areas. On all aspects f vegetatin remval peratins where ersin and sediment cntrls are required, install the ersin and sediment cntrl measures as specified in these Guidelines.