Compost blankets for controlling erosion on
construction sites
Trials under Australian Conditions
Compost Australia Seminar Series
‘A New Standard in Erosion
Control’
Dr Mark Jackson
Department of Environment and
Conservation NSW
1
Outline

What are compost blankets?

Advantages

Applications

Compost production in Australia

Overseas developments

Barriers to compost blankets

R&D trials by Uni of Western
Sydney

Trial results

Siting and design considerations
Source: Rexius Inc.
2
What are compost blankets?
 Fine, surface applied compost
 Applied with plant/shrub/tree seed,
fertiliser and tackifier (optional)
 Surface applied via blower
(usually) for soil protection and as
plant germination layer
 Compost usually manufactured
from kerbside collected garden
organics
M7 Motorway, Blacktown, Sydney
3
What are compost blankets?
+ 5 cm deep
compost blanket
+ 1:1 rock slope
+ Pneumatic
blower used
+ Austin, Texas,
2002
Source: US EPA, (2006) and S. McCoy, Texas Commission on Environmental Quality (TECQ), 2005.
4
Compost blankets are a potentially better
alternative
 Conventional soil erosion control techniques
-
Hydroseeding (seed, water, dye, fertiliser, tackifier)
-
Geotextile blankets (US EPA, 2006)
Hydromulching (seed, water, dye, fertiliser, tackifier, straw or
fibre)
5
Advantages of compost blankets
 Provides immediate
protection of soil from wind
and rain
 Reduces sheet and rill
erosion by absorbing rainfall
 Prevents soil compaction
and crusting and facilitates
rainfall infiltration
Source: The Hills Bark Blower / Rexius Inc.
 Organic matter improves soil
fertility and structure
6
Advantages of compost blankets…
-
-
Compost can retain pollutants

Heavy metals

Nitrogen

Phosphorus

Oil and grease

Fuel

Herbicides & pesticides

Other potentially hazardous
substances from storm water
Improves downstream water quality
7
Advantages of compost blankets…
 Provides a nutrient and
organic matter rich soil layer
for rapid plant establishment
 Plant establishment provides
long term erosion control
 Highly effective two stage
integrated soil erosion
control solution
Road cutting stabilisation, Bella Vista, Sydney
8
Applications for compost blankets

Erosion control and vegetation
establishment:
-
-
Road construction
-
Roadside cuttings / slopes
-
Road shoulders, verges and
medians
-
Earth embankments
-
Soil stockpiles
Stream banks / riparian works
Land sub-divisions
General civil works
9
Applications for compost blankets
 US EPA (2006) recommends:
-
Most effective on slopes 1:1 to
4:1
-
Control of sheet flow
Not effective for concentrated
flow (e.g. channels / earth
drains)
 Excellent erosion and sediment
control on difficult terrain —
including steep, rocky slopes
M7 Motorway, Blacktown, Sydney
10
Compost production in Australia1

Over 3 M tonnes of organics
recycled in Australia in 2005

140 commercial composting facilities
around the country

Compost markets traditionally
domestic and commercial
landscaping, horticulture and some
agriculture

Council collected garden organics
largest feedstock

Industry sold ~ 3.7 M m3 of compost
nationally in 2005
1
Compost Australia National Processor Survey (2005).
Survey results for NSW, VIC, SA and WA.
11
Aerial view of a commercial composting facility
ANL, Wyong, NSW: 50,000 tpa capacity
Receival and
inspection
Raw material
processing
Product
blending
Windrow
composting
Leachate
collection /
treatment
Finished
compost
12
Drivers for developing markets for compost
 State Government policies driving
recovery of organics from landfill
 Major sustainability benefits from
organics recycling
 Improves sustainability of local
environment
-
e.g. reduced need for virgin materials in
landscaping and construction (e.g. sand,
gravel, soil, woodchip, pine bark)
 Organics recycling can deliver benefits
of ECO$114/tonne when recycled
13
Development of markets for compost blankets
overseas
 1993: First technical studies by Ettlin and Stewart, in
Oregon, USA
-
Compost applied to bare soil slopes up to 42%
Soil loss reduced by more than 96-97% with compost
blankets compared to bare soil; similar to hydromulch
 2001: Ros et al. reports compost blankets reduced runoff
by 54% compared to bare soil control
14
Development of markets for compost blankets
overseas…
 2003: Texas DOT adopts compost blankets as erosion control
BMP
 2003: AASHTO provisional standards adopts compost
blankets
 23 DOTs in USA adopt the spec
 2005: Faucette et al. reports total runoff after 1 year for
compost blankets was 50% of control; hydroseeding only
reduced it by 30%
 2006: US EPA adopts compost blankets as new best practice
for erosion control on construction sites
15
Barriers to developing the market for compost
blankets in Australia

Hydromulching is an industry standard
-
e.g. NSW RTA QA Spec R178 – Vegetation – hydromulching for
erosion control on road projects
-
e.g. NSW Landcom blue book – Managing Urban Stormwater

Little experience with compost blankets under Aus climatic conditions

Key issues:
-
Performance and cost relative to hydromulching
Erosion control (sediment and nutrient loss)
Plant establishment success
Effect of local climate and rainfall frequency / intensity / duration
16
Program undertaken to overcome barriers
 DEC consulted industry on priorities
 Pioneering work being done, e.g. The Hills Bark Blower in
(Sydney), Groundworks (Brisbane) and We Blow Landscapes
(Melbourne)
 Need for independent assessments
 Little knowledge of opportunities in composting industry
 R&D project developed in consultation with industry
17
Key questions
 Performance of compost blankets compared to hydromulching
 Assess effects of the following factors on erosion control and
plant establishment:
-
Slope angle
Level of soil compaction
Rainfall intensity
Binder or tackifier
 Dr Charles Morris, University of Western Sydney contracted to
undertake project
18
R&D trials

Scientific trials undertaken to establish
performance of compost blankets

Trial under glasshouse conditions

Difficult to undertake work under field
conditions

Soil flats constructed to simulate road
verge construction process

50 mm sandy loam overlying 120 mm
Bringelly shale derived clay
19
R&D trials - overview

Four treatments were compared:
-
Compost blanket (25 mm) with binder
Compost blanket (25 mm) without binder
Hydromulch (RTA QA R178); and
Bare soil.

Compost blanket – AS 4454 (2003)
composted soil conditioner applied at US EPA
spec 25 mm deep

Other variables:
-
Two angles of slope (20 and 45)
Uncompacted and compacted
20
R&D trial – Set-up

Japanese millet applied via compost
blanket and hydromulch

Soil flats set at angle and watered for 5
weeks

Rainfall simulation at week 6 to test
erosion control performance

1 in 10 year design rainfall event (67
mm/hr for 30 mins)

Actual was 90 mm/hr for 30 mins:
-
1 in 75 yr event for Sydney
1 in 100 yr event for Melbourne
Hydromulch (LHS)
Compost blanket (RHS)
after 3 weeks
Rainfall simulation
1 in 10 yr event for Brisbane
21
Parameters measured
 Total and steady-state runoff
 Soil in runoff
 Total suspended solids in runoff
 Nutrients in run-off (total N and P)
 Plant establishment (density and biomass)
22
Mean run-off per 5 mins (mL)
Results – runoff
hydrograph
(low
angle)
(a) Run-off
vs. time at
low angle
900
poor
800
Control – compacted soil
Control – non-compacted soil
RO Comp
700
Hydromulch – non-compacted
soil
hydro comp
600
500
bare comp
400
RO non-comp
Hydromulch – compacted soil
300
hydro non-comp
Compost blanket – non-compacted soil
200
bare non-comp
Compost blanket – compacted soil
100
excellent
0
0
10
20
30
40
Time (mins)
23
Results - runoff
 Compost blankets reduced steady state runoff by 46 - 49%
compared to bare soil
 Compost blankets performed 2 times better than hydromulch
(23% reduction in steady state runoff) (P<0.05)
 More rainfall held and infiltrated into compost blankets
 Steeper slope significantly increased total run-off
24
Results – soil loss (or erosion)
80
70
a
60
Mean total soil
loss across
different
slopes and
levels of
compaction (g
DW per soil
flat)
50
40
30
20
10
b
b
b
Hydromulch
Compost
blanket - binder
Compost
blanket +
binder
0
Control
25
Results – soil loss (erosion)
 Both hydromulch and compost blankets highly effective in soil
erosion control
 Almost complete control of soil erosion
 At the steep slope, soil loss was reduced by 91% under
hydromulch, and even more under compost blankets (99.8 to
99.9%) compared to bare soil control
 Soil loss increased at the steeper slope
26
Results – total suspended solids
3000
a
2500
Mean total
suspended
solids in runoff
across
different
slopes and
levels of
compaction
(mg/L)
2000
1500
1000
500
b
c
c
Hydromulch
Compost
blanket binder
Compost
blanket +
binder
0
Control
27
Results – total suspended solids
 Both hydromulch and compost blankets highly effective in
reducing TSS in runoff
 Hydromulch slightly better in reducing TSS (TSS reduction of
98.5%) compared to compost blankets (95.9 - 97.3%)
 Compaction and slope angle had no effect on TSS
28
Nitrogen
Results – nitrogen Total
in run-off
2
1.6
1.4
1.2
compacted
1
non-compacted
0.8
0.6
0.4
0.2
low angle
+b
in
de
r
RO
-b
in
de
r
RO
ch
hy
dr
om
ul
so
il
ba
re
so
il
hy
dr
om
ul
ch
RO
-b
in
de
r
RO
+b
in
de
r
0
ba
re
Mean total N (mg/L
1.8
high angle
29
Results – nitrogen in run-off
 Total nitrogen (N) slightly higher in run-off from the compost
blankets (1.25 – 1.35 mg/L) (P<0.05) compared to control and
hydromulch
 Total N levels released still low
30
Results – phosphorus in run-off
Mean total Phosphorus (mg/L)
Total Phosphorus
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
re
ba
compacted
non-compacted
il
so
er
er
ch
l
d
d
u
n
n
m
bi
bi
o
+
dr
RO
hy
RO
low angle
re
ba
il
so
er
er
ch
l
d
d
u
n
n
m
bi
bi
o
+
dr
RO
hy
RO
high angle
31
Results – phosphorus in run-off
 No difference in total P on non-compacted slopes
 Small increase in total P in compost blankets on compacted
slopes
 Levels of total P released were low
32
Results – cover crop growth

Rapid plant establishment occurred on
hydromulch and compost blankets

No difference in amount of biomass
produced

Plant densities ranged from 2,000 –
5,000 /m2 - reduced by soil compaction,
and the compost blanket + binder
treatment.
33
Summary of key results

Performance results for hydromulch
and compost blankets very similar to
US field trials

Compost blankets performed at least
equally as well as hydromulch on
slopes up to 45

Compost blankets twice as effective
as hydromulch in terms of reducing
runoff after heavy rainfall events

Nutrient load in stormwater likely to be
lower due to reduced runoff

No observed benefits of using a binder
34
Siting and design considerations

Trials suggest US EPA specs likely to be
suitable for Australian application

Factors that need to be considered on the
job site:

-
Existing vegetation
-
Annual rainfall
Climate
Structural attributes of the site (steepness of
slope)
Source: The Hills Bark Blower
Rainfall erosivity
Critical for determining appropriate blanket
depth
35
Siting and design considerations…
 Compost quality
- Specs set out by US EPA (2006)
and AASHTO (2003)
-
Particle size, chemical properties
and maturity similar to a composted
soil conditioner in AS 4454 (2003)
-
CSC successfully used in trials
-
Moisture content of 30-50% as in
US EPA specs may need to be set
to enable easy blower application
CSC in AS 4454 has tighter specs
for most parameters
Source: The Hills Bark Blower
36
Siting and design considerations…
 Application rates at different rainfall rates: US EPA (2006)
Annual
Rainfall/
Flow Rate
Total Precipitation /
Rainfall Erosivity
Index
Compost Blanket
Depth (Vegetated
Surface)
Compost Blanket
Depth (Unvegetated
Surface)
Low
25 – 635 mm
20 – 90
12.5 – 19 mm
25 – 37 mm
Average
635 – 1270 mm
91 – 200
19 – 25 mm
37 – 50 mm
High
>1270 mm
>201
25 – 50 mm
50 – 100 mm
37
Installation
 US EPA (2006) recommends:
-
Compost should be applied to the soil surface in a uniform
thickness
-
Easiest applied with a pneumatic blower, especially on steep
slopes or difficult to access areas
-
The compost blanket should extend at least 1 m over the
shoulder of the slope to ensure that storm water runoff does
not flow under the blanket
-
Thicker compost blankets are recommended for areas with
higher annual rainfall or rainfall intensity and coarser
compost is recommended for areas subject to wind erosion
38
Further information and advice
 Contact your local compost blanket service provider
 Can provide advice regarding sediment and erosion control
planning
 Specific advice to maximise the success of your project
39
Acknowledgements
 Dr Charles Morris (Uni of Western Sydney)
 Compost NSW committee
 Jon Moon and Penny Smith (The Hills Bark Blower)
Further information
 Mark Jackson, (02) 8837 6010.
40