Track design and management

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1 1 Track design and management Peter Fogarty, Certified Professional Soil Scientist NSW Soil Knowledge Network Cooma, June 18, 2018 Acknowledgements Antia Brademann, Cooma Waterwatch, Organiser Jo Powells, Cooma LLS, Organiser Ashley Bolton, Cooma Soil Conservation Service

2 2 Today we will cover Why it s worth putting thought into track design and construction Understanding soils and hydrology Planning track location Management practices; keeping soil erosion and runoff to acceptable levels Your situation New track or fixing and existing track Lots of space or tight site with few options

3 3 Why Protect your investment, cost of construction typically $2,500 to $20,000 Costs more to repair than to construct properly, get it right the first time Inconvenience, discomfort Emergency services access such as fire, household emergencies Off site impacts particularly water quality and stream condition

4 4 Help you avoid situations such as this Photos: Ashley Bolton, NSW Soil Conservation Service

5 5 Photos: Ashley Bolton, NSW Soil Conservation Service

6 6 And have something like this Photo: Ashley Bolton, NSW Soil Conservation Service

7 7 Resources Experience Soil Conservation Service and other agencies Publications and guides Research CRC for Catchment Hydrology major project

8 8 Published Information sources Key documents NSW RFS (2017) Fire Trail Design, Construction and Maintenance Manual NSW Dept of Environment and Climate Change (2008) Soils and Construction Volume 2C: Unsealed roads Useful background NSW Soil Conservation Service (1990) Earthmovers Training Course, Unit 17, Access Tracks Forests NSW (1999) Forest Practices Code, Part Four, Forest Roads And Fire Trails CRC for Catchment Hydrology (1999) Managing Sediment Sources and Movement in Forests

9 9 Understanding the processes Role of topsoil Runoff generation Soil erosion Transport of sediment and its delivery to drainage system Photo: Ashley Bolton, NSW Soil Conservation Service

10 10 Role of topsoil

11 11 Hillslope runoff process (a) with and (b) without topsoil (a) (b)

12 12 Soil erosion Erosion occurs when resistance to soil and plant cover is exceeded by energy in rainfall and runoff Conceptualised in Universal Soil Loss Equation Model (USLE) (Rainfall erosivity * Slope grade * Slope length) * (Soil erodibility * Vegetation cover) (Rfactor*LSfactor)*(Kfactor*Cfactor) Models allow scenarios (pre- and post-track) to be quantified and compared

13 Granite soil 13 USLE predicted soil erosion rate granite soil, gentle slope Site condition R L S K C Erosion rate (t/ha/yr) Natural % Bare surface % Bare 15cm % Bare 15cm % shale soil, gentle slope Site condition R L S K C Erosion rate (t/ha/yr) Natural % Bare surface % Bare 15cm % Bare 15cm %

14 14 Calculating track erosion (length * width * erosion rate) Pre track 1km X 4m X 0.02t/ha/yr = 0.008t/yr Track 1km X 4m X 24t/ha/yr = 9.6t/yr Hence, rough working guide is 10t/km/yr of track erosion

15 15 Soil erodibility classes Class A soils are stable, well aggregated with low potential to erode Class B soils are coarse grain / sandy, have weaker structure throughout, are erodible but, because they are coarse grained, sediment doesn t travel far Class C soils have medium to fine grain B horizon, are relatively stable but, because they have a high silt and/or clay content, their sediment will travel much further than Class B soil sediment. Class D soils are highly erosive and dispersive and because they also have a high silt and clay content pose the greatest hazard.

16 16 Soil erodibility classes cont d from RFS (2017)

17 17 Stable soil, coherent when wet Unstable soil, low coherence when wet Photos: Ashley Bolton, NSW Soil Conservation Service

18 18 Sediment export from tracks shale soil granite soil f forest track forest track From: CRC CH, 1999

19 19 Effect on streams Concept of connectivity; aim to minimise connectivity between tracks and streams Concentrated flow paths do not permit deposition and infiltration Dispersed flow paths allow infiltration and sediment deposition Track runoff tends to disperse and infiltrate within 20m on flat or divergent hillslope Track crossings most susceptible to sediment delivery to streams From: CRC CH, 1999

20 20 Track vocabulary and jargon From: RFS (2017)

21 21 What is it about tracks (summary to this point) Generate runoff even after few mm of rain Cut batters bring infiltrated rainfall to surface Bare surface so potential for high erosion rate Traffic breaks up surface into easily eroded particles Sediment enriched runoff connects directly to the drainage networks

22 22 Planning Purpose of track eg main access or fire egress; volume of traffic Site assessment Soil erosion hazards Drainage line crossings: depressions versus channelised; catchment size Landform issues; very rocky ground, poorly drained areas Steep slopes; affects amount of cut and fill Potential land slip areas Vegetation types Route identification

23 23 Site assessment tools 1:25000 scale topo maps: show contours for grade, drainage features Google imagery: good for vegetation Six Viewer ( imagery with overlay of lot boundary Soil landscape maps; 1:100,000 (see

24 24 Route identification getting to know your site Ridgelines rather than valleys; divergent rather than convergent contours; ie spreads rather than concentrates runoff Running up and down rather than across slope minimizes cut and fill Slope grade less than 10degrees or 18%; short sections may be steeper Maximum distance from a stream to allow sediment filtering Avoid highly erodible soils Avoid steep stream banks

25 25 Management practices Track surface drainage crowning Infall Outfall Table drains Relief drainage Cross (diversion) banks Mitre drains Culverts Drainage line crossings Track surfacing Natural Imported Batter stabilisation Cut Fill Topsoil management

26 26 Surface drainage: crowning From: RFS (2017)

27 27 Surface drainage: infall From: RFS (2017)

28 28 Surface drainage: outfall From: RFS (2017)

29 29 Surface drainage: table drains Run beside track surface Collect runoff from track and direct to safe disposal point From: RFS (2017)

30 30 Table drains: cont d Prone to washing out if: soil is erodible Inadequate relief ie water runs in drain too far Erodible soils (class 3 and 4) likely to need protection (rock, jute mesh)

31 31 Relief drainage: cross banks Simple and effective Pick up track runoff and direct onto undisturbed ground Easy to drive over if well constructed Maximum suitable grade 20% From: RFS (2017)

32 32 Cross banks cont d From: RFS (2017)

33 33 Cross banks: spacing From: RFS (2017)

34 34 Relief drainage: mitre drains From: RFS (2017)

35 35 Relief drainage: mitre drains cont d Sometimes called push outs Aim to take water from table drain out onto hillslope where it disperses Should slow water down before exit Should direct water onto undisturbed ground From: RFS (2017) From: DECC (2008)

36 Relief drainage: culverts Culverts convey water under the track Relieve flows in a table drain on the inside of the road surface; also for small drainage features Comprise pipes and headwalls,

36 36 Relief drainage: culverts Culverts convey water under the track Relieve flows in a table drain on the inside of the road surface; also for small drainage features Comprise pipes and headwalls, often with box inlet Without a headwall, fill around pipe will be prone to washing out Pipe size is crucial, too small and they will block up with debris Photo: Antia Brademann, Cooma Waterwatch From: RFS (2017)

37 37 Drainage line crossings Warning: approvals required for any disturbance to bed and banks of a stream Aim to cause as little disturbance as possible to bed and banks Do not obstruct or divert flow Likely to need engineering design on all but smallest drainage features Options include bed level crossing, culvert and bridge

38 38 Minor drainage features Depressions rather than streams, no banks so need to ensure flow remains diffuse Bed level crossing or ford Bed of watercourse reinforced From: RFS (2017)

non-perennial Best option is for bed level crossing Bed floor reinforced with

39 39 Major drainage features Discrete channel and banks, carry large flows during and after rain events Banks may be vertical or sloping May be perennial or non-perennial Best option is for bed level crossing Bed floor reinforced with rock if not natural Gullies and steep banks may require culvert or bridge From: RFS (2017)

40 40 Photos: Ashley Bolton, NSW Soil Conservation Service

41 41 Track surface Most suitable surface depends on Usage: heavy traffic will break up natural surface Soil type: erodible soils will need protection Slope grade: steep grades will be slippery when wet Natural surface Good for flatter (<10%) sites, low erodibility soils Well drained sites Steeper very gravely sites (self graveling) Imported material Gravel to protect surface Compactable fill for shaping surface Warning, know source of material (weeds, asbestos, other waste)

5m height plus substantial volume of fill Best practice to conserve topsoil from track construction then respread on batter Batter

42 42 Batter management Track construction across the slope creates a fill and a cut batter Risk of both erosion and slumping Likely to need geotechnical design on slope grades >30% as cut batter will exceed 1.5m height plus substantial volume of fill Best practice to conserve topsoil from track construction then respread on batter Batter grades need to be less than 2.5:1, steeper grades will not hold topsoil Drain outlets should be onto natural ground Photo: Ashley Bolton, NSW Soil Conservation Service From: RFS (2017)

43 43 Rock protection of fill batter at drain outlet From: RFS (2017)

44 44 Topsoil management Topsoil crucial for rehabilitation of track edges after construction Ensure it is retained separately in stockpiles Max depth 15cm Respread on batters, ensure even cover

45 45 Track maintenance Absolutely will be required, no track is maintenance free Assess after storms, at least every two years Preferable to import road base than keep cutting down surface Clean out culverts and mitre drains Cross banks fill with sediment and overtop Check during rain when runoff is occurring From: RFS (2017)

46 46 To recap How will track be used Rough out route on topo map or plan Identify hazards slopes >30%, poorly drained land erodible soil rocky ground vegetation to protect Identify drainage crossings Plan specific measures Surface drainage Relief drainage Road surface Batters Topsoil stockpiles Finalise route Approval

47 47 Specific examples Powerline maintenance track on red clay shale derived soils (class A) Soils not highly erodible, problem due to lack of surface drainage Also, track below adjacent land surface so water stays on track Repair entailed Drainage banks at 40m spacing, draining to left side so do not run back towards track Reform track surface Photo: Ashley Bolton, NSW Soil Conservation Service

48 Fire trail on yellow brown clay loam, shale derived soils (class A) Recent substandard contractor repairs to trail Lack of relief drainage due to windrow along

48 48 Fire trail on yellow brown clay loam, shale derived soils (class A) Recent substandard contractor repairs to trail Lack of relief drainage due to windrow along right side of trail, lack of surface drainage Repair entailed Removal of windrow Install cross banks at 60m spacing Photo: Ashley Bolton, NSW Soil Conservation Service

49 49 Fire trail on yellow brown sandy clay, granite derived soils (class C) Recent substandard contractor repairs to trail Lack of capacity in cross bank Repair entailed increase height and volume of cross bank to 0.5m freeboard on high side Photo: Ashley Bolton, NSW Soil Conservation Service

50 50 Fire trail on grey silty loam alluvial soils (class C) Recent substandard contractor repairs to trail Excessive disturbance along edge of trail Repair entailed reinstating topsoil cover on track verging to encourage natural regeneration Photo: Ashley Bolton, NSW Soil Conservation Service

51 51

Rock & Aggregate Drop Inlet Protection

Rock & Aggregate Drop Inlet Protection SEDIMENT CONTROL TECHNIQUE Type 1 System Sheet Flow Sandy Soils Type 2 System [1] Concentrated Flow Clayey Soils Type 3 System Supplementary Trap Dispersive Soils