BATTER AND FENCING GUIDELINES FOR SQIDS AND DETENTION BASINS

Transcription

1 BATTER AND FENCING GUIDELINES FOR SQIDS AND DETENTION BASINS December 2013

2 TABLE OF CONTENTS 1. Intrductin Public Safety Cnsideratins Maintenance Cnsideratins Factrs fr Determining Batter Slpe and Fence Treatments Majr Strm Events Fencing and Gates Styles Pst and Cable Fence Style Exclusin Fence Style Gates References... 6 Appendix 1: Risk Assessment fr Batter and Fencing Treatments... 7 Step 1 Establish lcatin f water edge t be used fr risk assessment... 7 Step 2 Assess the risk factr as a result f the shape and lcatin f the facility... 7 Step 3 Sum the risk factr scres... 9 Step 4 Determine batter treatment and fencing requirement... 10

3 1. Intrductin Strmwater quality arising frm urbanised catchments is a majr prblem affecting Lake Macquarie. T address sme f the impacts Lake Macquarie City Cuncil is cnstructing a number f wetland prjects and requiring develpers t install cnstructed wetlands as part f the develpment prcess. There are great pprtunities fr wetlands, in particular, t be mre than water quality structures. Additinal values can include variety t areas f public pen space, increasing aesthetic appeal and creating aquatic habitat and places fr envirnmental educatin and awareness. This mixed use can raises the risk expsure f the wetlands in public areas. Levels f risks (especially fr cnstructed wetlands) can be determined by the: lcatin f the wetland, type f inflw, ease f access, wetland bjectives, nature f adjining land uses r activity and cntext f the site (DLWC 1998). Added t this list are the risks assciated with any maintenance activities and general management f the wetland. The bjective f these Guidelines is t prvide a cnsistent apprach t the treatment f batter slpes and the installatin f fencing near cnstructed wetlands and detentin basins. The Guidelines incrprate a risk management apprach t the decisin making prcess. Appendix 1 allws the designer t select the mst apprpriate batter r fence treatments fr a particular site. 1

4 2. Public Safety Cnsideratins Public safety is an imprtant cnsideratin near strmwater management devices. The fllwing pints may need t be cnsidered when designing a cnstructed wetland r detentin basin: T achieve greater cmmunity acceptance and integratin f the wetland n a site it may be desirable t allw peple t have access t specific areas arund the wetland. In such areas abve and belw water batter slpes need t be gentle (1V:6H t 1V:8H). Dense planting f vegetatin and/r fencing shuld be prvided where access is t be restricted. The incrpratin f features like bardwalks and viewing platfrms int the wetland can cntrl public access, allw the public t view wetland cmpnents (with pssible interpretive infrmatin), but nt access thse cmpnents. Densely planted vegetatin can be used in a number f situatins t discurage public access t parts f a site. Species with particularly spikey leaves (that culd cause serius eye damage), such as Elecharis acuta, shuld nt be used where there is easy access t the wetland area. Where dense vegetatin is t be used as part f the risk minimisatin strategy several factrs need t be cnsidered. Water levels in the wetland need t be manipulated t allw the establishment f macrphytes and t minimise water depths until terrestrial plant cntrls are well established. Advanced plants shuld be used adjacent t accidental entry fencing and alng the planting/ public interface t prvide a quick barrier whilst the remainder f the planting establishes. Temprary fencing in the frm f paraweb fencing (r similar) may be required until plantings are well established. Steeper underwater batter slpes (1V:3H r steeper) are ideal fr msquit cntrl. Slpes f 1V:4H (abve water) are usually cnsidered as a maximum especially where machinery is used fr maintenance. Apprpriate barriers such as fencing r dense vegetatin may be required t discurage public access n steeper batters. The Institutin f Engineers Australia (Rainfall & Runff 1998) utlines sme criteria fr detentin basins that includes : Rails r fences shuld be prvided at the mst dangerus sectins f drainage systems especially near schls, r upstream f culverts r clsed cnduits. Preferred slpes shuld nt be steeper than 1V:6H and areas steeper than 1V:4H may require fencing r rails. These requirements are mre imprtant where water areas are deeper than 1.2m. Fences shuld be 1.0 t 1.2m in height and shuld nt impede ptential rescuers. Where signs are used, signs shuld infrm the public f the functin f the facility as well as giving a warning. In sme situatins gauge bards culd 2

5 be used in channels r pnds t give tacit warnings as well as fr recrding fld infrmatin. Warning picturegram signs, nting it as a water treatment and/r fldway area, and swimming nt permitted, placed prminently upn the area. LMCC Nte: Standard signage shuld be used. Other infrmatin signage shuld prmte psitive public relatins and cnvey the message f prtecting the waterways f Lake Macquarie City. Fr example: This is a Water Quality Device Maintained by Lake Macquarie City Cuncil t Prtect ur Waterways. Exclusin fencing shuld be prvided where vertical drps ccur adjacent t permanent water. This shuld als apply where water is retained during the cnstructin phase. Cnsideratin shuld be given t prviding egress pints where there is danger f a persn, particularly children, nt being able t escape frm the water shuld they fall in. Lake Macquarie Cuncil has agreed t abide by the Crime Preventin Thrugh Envirnmental Design (CPTED) prtcls. Cuncils must (by legislatin) cnsider the CPTED principals when assessing all develpment applicatins and fencing and landscaping in public areas must address these issues. The guidelines, and checklist, are available n the Plice website. 3

6 3. Maintenance Cnsideratins Safe, practical and efficient maintenance is a primary cnsideratin in the selectin and layut f batters and fencing. Cnsideratins shuld include: Access and maneuvring areas fr vehicles and equipment. Gateways shuld preferably be lcated away frm high pedestrian use areas and gates shuld be 4.3m wide and lckable. Material handling and de-watering areas. Mwing peratins. Exclusin fencing shuld have a mwer strip 300mm wide laid at its base and the layut shuld facilitate tractr mwing. Use f standard prducts and mdule lengths. Limit the number f prducts used at any given site. 4. Factrs fr Determining Batter Slpe and Fence Treatments Appendix 1 shws each f the factrs; batter slpe angle, vertical drp height, water depth, and site cntext, that are t be used t determine the internal batter slpe treatments and fencing requirements arund cnstructed wetlands and detentin basins in the Lake Macquarie City Cuncil area. As a general principle, the designer shuld aim t minimise the use f exclusin fencing by selecting design elements with lwer risk factrs. Where a site requires special cnsideratins Cuncil may apprve alternative treatments based n their merits. 5. Majr Strm Events In the design f wetland layuts, particularly where dense planting, viewing platfrms and exclusin fencing is used, cnsideratin shuld be given t the majr event strmwater flws. Depth, velcity and debris lad can impart significant frces that can destry fencing. If resisted, flws can als be diverted frm their intended path and may have ptentially serius effects, fr example, causing the main wall t vertp rather than an verflw weir. 4

7 6. Fencing and Gates Styles Where the risk assessment suggests a fence treatment is required, there are tw that are used in Lake Macquarie. One is a pst and cable fence fr lwer risk situatins and the ther is an exclusin fence fr higher risk situatins. 6.1 Pst and Cable Fence Style The preferred style is the Cuncil s standard cable fencing design with 20mm diameter galvanised steel cable threaded thrugh 100mm ID galvanised steel psts spaced at 2.5m intervals. Refer t Drawing EGSD-601 fr details f the panel adjining a gate r pedestrian pening. A custm made fence, being a public art cmmissin t an apprved design and finish will als be cnsidered. 6.2 Exclusin Fence Style Cuncil s standard exclusin fence design is shwn in Drawing EGSD-602, hwever an apprved equivalent (t AS ) in a pwder cated clur (preferably black r dark green) is als permitted. Any apprved equivalent will include the LMCC badge shwn in Drawing EGSD-602. A custm made fence, being a public art cmmissin t an apprved design and finish, will be cnsidered fr high prfile r shwcase sites. 6.3 Gates Gate ways are ften required t prvide access fr machinery etc t maintain and clean ut the facility. This is particularly the case fr SQID treatments. The gate ways shuld preferably be lcated away frm high pedestrian use areas. They shuld be lckable and cnstructed t Drawing EGSD-603 fr a single gate and EGSD-604 fr a duble gate. 5

8 7. References Department f Land and Water Cnservatin, New Suth Wales, The Cnstructed Wetlands Manual. Vl 1. Lake Macquarie City Cuncil, Nutrient Pnds in Subdivisinal Wrks Design Guidelines. Subdivisin and develpment Sectin. Lake Macquarie City Cuncil, 20/2/1998. GPT s, Retentin Basins & Nutrient Pnds Design/Assessment Guidelines. Final Draft, (Nutrient.dc). The Institutin f Engineers Australia, Australian Rainfall and Runff Bk Eight, Urban strmwater management. Canberra. 6

9 Appendix 1: Risk Assessment fr Batter and Fencing Treatments The fencing treatment is determined thrugh a fur-step prcess invlving an assessment f the risk assciated with the shape and lcatin f the prpsed facility fllwed by an assessment f the type f fencing required based n the ttal assessed risk. Step 1 Establish lcatin f water edge t be used fr risk assessment In cnstructed wetlands and detentin basins the water level fluctuates which means that the lcatin f the water's edge als changes. T undertake the fllwing assessment, a civil designer must first establish the lcatin f the "water edge" t be used. In cnstructed wetlands and sediment basins the permanent water level is cnsidered t be the level established by the lw flw pipe/utlet structure and may be the design level. If the basin is designed t stre up t a higher temprary level during strm events (eg capture f first flush that then draws dwn f a subsequent 72 hur perid) then this higher temprary level will be the design level. If the facility is a stand alne detentin basin r a detentin basin with a wetland in its invert then the design level is the highest level at which the basin fills t, and then hlds water fr mre than ne hur during any strm event, up t and including the 100 year strm. (Nte that this will mean that lnger duratin strms 3-6 hurs will need t be mdelled). Where the facility is a cmbined basin / wetland facility the risk factr fr each shall be assessed with the higher risk prevailing. Once yu have established the design water level yu can then find the crrespnding lcatin fr the water edge. Step 2 Assess the risk factr as a result f the shape and lcatin f the facility The Risk factrs are determined fr each f the fur risks: Risk 1 Batter slpes leading dwn t the waters edge Risk 2 Vertical drp at the waters edge Risk 3 Maximum water depth between water edge and 4m frm the water edge Risk 4 Site cntext The ttal Risk Factr is then determined by summing the fur individual risk factrs. Where the terrain is nt unifrm, a Risk Factr needs t be established fr each terrain type. 7

10 Risk 1 Batter slpes leading dwn t the waters edge Risk Factr 1:6 r shallwer (1:8 ideal) 1 1:4 up t 1:6 2 Steeper than 1:4 6 Vertical Wall height adjacent t and/r abve water edge 0.1m < wall height 0.5m Vertical Wall height adjacent t and/r abve water edge Wall height > 500mm and 1000mm Vertical Wall height adjacent t and/r abve water edge > 1000mm Risk 2 Vertical drp at water edge Risk Factr i.e. Is there a vertical drp that is submerged at the waters edge (r within 4 m f the waters edge). Vertical Drp 0 t 150mm ie n drp r minr drp 0 Vertical Drp >150mm and 300mm 4 Vertical Drp >300mm and 500mm 8 Vertical Drp >500mm and 1000mm 16 Vertical Drp > 1000mm 21 Risk 3 Max water depth between water edge and 4m frm the water edge Risk Factr 500mm (1:8 underwater batters r flatter) 0 > 500mm and 670mm (1:6 t 1:8 underwater batter) 4 > 670mm and 1000mm (1:4 t 1:6 underwater batter) 8 > 1000mm (steeper than 1:4 batter) 16 8

11 Risk 4 Site cntext (Select the site cntext that best fits the site being assessed) Risk Factr Lw Risk Lcatin 4 Reserve designed t incrprate a cnstructed wetland as a landscape feature integral t the pen space. Adjacent areas may already cntain ther water bdies r watercurses. Residences within 100m f site and there is gd surveillance frm verlking huses. Infant/primary schls are >250m frm the site. Medium Risk Lcatin 6 Reserve, with ptential high use including likely high pedestrian and cyclist numbers, playgrund, picnic/bbq facilities and pssible larger public events. Infant/primary schl >250m frm the site. Residential areas 150m frm the site. Mderate/gd public surveillance. High Risk Lcatin 8 Reserve including parkland/natural areas, generally with lw use. Infant/primary schl 250m frm site and/r n a direct rute t/frm the schl. Residential areas >150m frm the site. Limited public surveillance. Step 3 Sum the risk factr scres Risk 1 - Batter slpes Risk 2 - Vertical drp Risk 3 - Max water depth Risk 4 - Site cntext Ttal Risk Factr Scre 9

12 Step 4 Determine batter treatment and fencing requirement Ttal Scre Treatment Required Mwn grass and/r planting fr aesthetic and shade purpses. Dense planting and pst and cable fencing. Planting is t have a minimum 2.5m (but ideally 4.0m) width. Plants are t be clumping preferably t apprximately 0.75m height and at 0.5m maximum spacing. Exclusin fencing which may be accmpanied by planting fr aesthetic and shade purpses. Ntes: 1. Any fencing is t be in accrdance with Cuncil s Engineering Guidelines Standard Drawings (Part 6 f the Engineering Guidelines). 2. The wetland r basin may have sme prtins that have steep batters r vertical walls and sme areas that have flat batters. If the facility is nt unifrm in its batter slpes, depth etc then a Risk Factr assessment shuld be applied t each different area t determine the batter treatment applicable t the area. Each treatment shall extend arund the whle f the area that generates the crrespnding Ttal Risk Factr Scre. 10