Clearfelling and windrowing forest operations can significantly increase sediment and nutrient concentrations in runoff. Monitoring of three Irish forest sites found the largest increases in total suspended solids and phosphorus during windrowing. While one site with an intervening buffer saw lower increases. Proper management including silt fences, limiting streamside operations, and machine movement can help reduce water quality impacts.

1. Effects of Forest Operations
(HYDROFOR Project)
John Clarke

2. Forest Operations
Clearfelling Windrowing

3. Clearfelling
• Cutting of trees and the removal of the main tree bole.
• Different methods depending on site- cabling, skidding.
• Most common method practiced in Ireland uses -
Harvesters and Forwarders.

4. Water Quality Concerns During
Clearfelling
– An increase in soil disturbance caused by the harvester
moving on site.
– An increase in soil disturbance/rutting on extraction routes
caused by the forwarder hauling logs to the roadside.
– Increased risk of bank collapses if machinery is operating
close to streams.
– Increased risk of bank collapses if timber not stacked
properly on roadside or if stacked too close to
streams/drainage channels.
– Hydraulic oil spillages if pipes burst, diesel spillages during
refuelling.
– Removal of protective cover that the trees provided.

5. Windrowing- What?
What is windrowing?
• The gathering of brash and other materials leftover after clearfelling into
long narrow rows.
• In addition to this, site maintenance works may also be carried out at this
time such as clearing blockages from drainage channels and ditches and
the construction of new drainage channels in problematic wet locations.

6. Windrowing- What?
Some pine needles still attached to
branches and some have fallen off
What is windrowed?
• Decaying branches, leaves and needles stripped off trees during felling
• Brash mats and brash bridges left behind after clearfelling
• Tree stumps and roots (not practiced in sites during this study)

7. Windrowing- When?
When is a site windrowed?
• Before replanting- Typically 18 months after clearfelling.
Brash Mat Over Streams Removed New Drainage Channels Dug

8. Windrowing- Why?
Why are sites windrowed?
• To clear enough space to allow for the replanting of trees.
• To maintain the site- clear blocked drains, construct new drainage
channels in wet locations

9. Water Quality Concerns During
Windrowing
– An increased in soil disturbance caused by machinery
moving on site.
– An increased in soil disturbance caused by the
scraping and gathering of brash from the ground.
– Release and mobilisation of loose sediment and
nutrients from underneath the brash.
– Removal of protective cover that the brash provides
– Mobilisation of sediment during drain clearing, risk of
bank collapses, increased sediment loss if new
drainage channels are constructed.

10. Instrumentation
• Setup 1: Rectangular sharp
crested weirs with end
contractions constructed
instream to work with ISCO
automatic samplers with
bubbler module attached
for flow measurement.
• Setup 2: 15-20 inch
drainage pipes installed
instream to work with
automatic samplers and
flowmeters.

11. Type of Event Data Collected
• Rainfall events/storms sampled
– Sediment and nutrient runoff risk is highest.
• Automatic sampler triggered on rising water level. Trigger set manually based on
storm event data collected.
• Automatic sampler- can collect 24 samples (1L each).
• Once trigger level reached- time proportional sampling strategy used- First 8
samples collected in 15 mins intervals, next 6 every 30 mins, next 6 every 60 mins
and last 4 every 120 mins.
• Entire storm event sampled- more samples focused on the rising limb of the
hydrograph- period in which sediment and loading risk is highest

12. Analysis of Samples
 6 of the 24 samples picked out for full analysis
 Remaining samples analysed for pH, turbidity and
conductivity
Parameters included in Full
Analysis
• pH
•Alkalinity
•Total Hardness
•Ammonia
•Soluble Reactive Phosphorus
•Total Oxidised Nitrogen
•Nitrate
•Nitrite
•Total Phosphorus
•Dissolved Organic Carbon
•Aluminium
•Sodium
•Potassium
•Magnesium
•Calcium
•Chloride
•Sulphate
•Suspended Sediment
•Silicate
•Turbidity

13. Windrowing
3 sites with similar characteristics selected and
located in Co. Wicklow.
• Site 1- Annalecka Brook
• Site 2- Kilcoagh
• Site 3- Oakwood

14. Study Site 1- Annalecka
• Plantation Size- 10 Ha
• Catchment Size- 167.5 Ha
• Felled in Spring 2010- Sitka Spruce (Picea
sitchensis). Some needles still attached to
branches, more on ground.
• Windrowing began 3rd September 2011 and
lasted until 1st October 2011
• No new drainage channels constructed.

15. Annalecka Brook Aerial Photographs

16. Peak TSS Recorded During Sampled
Events (mg/l)

17. Peak TSS Recorded During Sampled
Events (mg/l)

18. Peak TSS Recorded During Sampled
Events (mg/l)

19. Peak TSS Recorded During Sampled
Events (mg/l)

20. Event Avg and Flow at the Time of
Peak TSS (m3/s)

21. Flow Weighted Mean Concentrations
(FWMC)
• Considers the effect of different flow
magnitudes when looking at sediment.
• Weighting concentrations by volume
• Total load for the time period/Total discharge
for the time period

22. Flow Weighted Mean Concentrations
for Sampled Events (mg/l)

23. Flow and Sediment Relationship
Event 6- 80% Windrowed

24. Flow and Sediment Relationship
Event 7- 100% Windrowed

25. Peak Total Phosphorous
Concentrations (mg/l)

26. SS and TP Relationship
0
100
200
300
400
500
600
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45
SS(mg/l)
TP (mg/l)
R2= 0.82

27. Windrowing Conclusions
• Peak and total sediment and nutrient
concentrations increased during windrowing
operations.
– Elevated concentrations, while declining, seem to
persist for up to 2 years after operations ceased
• Management
– No observed silt trapping structures used during
windrowing.
– Some rutting in places.
– No streams crossed by machinery.

28. Clearfelling
2 sites with similar characteristics selected and
located in Co. Wicklow.
• Site 1- Ow 1
• Site 2- Ow 2

29. Study Site- Ow Site 1
• Study Plantation Size- 2.23 Ha.
• Drainage Catchment Size- 8.77 Ha.
• Tree Species- Sitka Spruce (Picea sitchensis)
• Felling began on the 10th April 2012 and forwarding
continued until the 26th April 2012.
• Felling Type- Harvester and forwarder used.

30. River Ow Site 1 Aerial Photograph

31. Peak TSS Recorded During Sampled
Events (mg/l)
10 50 100
% Area Felled

32. Event Avg and Peak Flows (m3/s)

33. FWMC of TSS for Sampled Events (mg/l)
10 50 100
% Area Felled

34. 566.7
5380.0
1600.0
260.0
54.017.0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0
1000
2000
3000
4000
5000
6000
00:00 12:00 00:00 12:00 00:00 12:00 00:00
Flow(m3/s)
SS(mg/l)
Time
DF6
SS (mg/l) Flow (m3/s)

35. 0.000
2.000
4.000
6.000
8.000
10.000
12.000
14.000
0.0 1000.0 2000.0 3000.0 4000.0 5000.0 6000.0
TP(mg/l)
SS (mg/l)
SS and TP Relationship
R2= 0.998

36. Felling Conclusions
• Controlling for the effect of flow and rainfall magnitude
indicates that increased sediment and nutrient
concentrations observed were as a result of felling
operations.
• Management
– No observed silt trapping structures, e.g. silt traps, straw
bales, geotextile silt fences used during felling. Roadside
ditch geotextile silt fences installed ~2/3 months after
forwarding finished- ineffective after large storm.
– Felling ceased during very heavy rainfall.
– Some use of brash mats.
– Streamside felling and forwarding.

37. Site: Ow 1

38. Overall Conclusions
• Large peaks in total suspended solids and total
phosphorous were recorded in all of the study
sites.
• Clearfelling and windrowing practices
increased total and peak concentrations
significantly.

40. Study Site- Oakwood
• Site Size- 1.17 Ha
• Catchment Size- 48 Ha
• Felled in 2010- Sitka Spruce (Picea sitchensis)
• Windrowing began 17th October 2011 and lasted
until 24th October 2011
• One new drainage channel dug
• Between the studied plantation and the study
stream there is a 2-3 year old strip (50-100m+
wide in places ) of planted pine trees.

41. Oakwood Aerial Photographs

42. Oakwood Map

43. Peak TSS Recorded During Sampled
Events (mg/l)

44. Oakwood Conclusions
• Sediment and nutrients increased during
windrowing but on a reduced scale.
• Concentrations recorded were lower due to the
presence of the 2-3 year old plantation of tree
saplings (acted like a 50-100m buffer strip).
• Management
– No observed silt trapping structures used during
windrowing.
– Some observable rutting in places.
– New drainage channel dug
– No streams crossed by machinery.

45. Windrowing Summary and
Conclusions
• Annalecka- large increases in sediment and nutrient
concentrations during windrowing.
• Oakwood- an increasing trend in sediment and
nutrients observed.
– Concentration increases not significant in terms of
biological impact due to the presence of the 2-3 year old
plantation and the size of the plantation windrowed.
• Kilcoagh- an increase in sediment and nutrient
concentrations recorded during windrowing.
– Some large peaks observed in sediment and phosphorous.

46. Study Site- Ow Site 2
• Plantation Size- 1.46 Ha
• Catchment Size- 21.81 Ha
• Felling began on the 16th
August 2011 and
forwarding continued
until the 7th September
2011.
• Sitka Spruce (Picea
sitchensis).
• Felling Type- Harvester
and forwarder used.

47. River Ow Site 2 Aerial Photograph

48. Peak TSS Recorded During Sampled
Events (mg/l)
15 50 80 100 100
% Area Felled

50. Ow2 Conclusions
• Removing the effect of flow indicates that
increased sediment and nutrient concentrations
observed were as a result of felling operations.
• Management
– No observed silt trapping structures, e.g. silt traps,
straw bales, geotextile silt fences used during felling.
– Felling ceased during very heavy rainfall.
– Some use of brash mats.
– Streamside felling and forwarding.
– Deep streamside rutting occurred.
– Timber stacked on stream banks.

51. Conclusions
• Felling operations increased sediment and
nutrient loading at both sites.
• Large increases were observed at Site Ow 1.
• At Site Ow 2 increases may not have been as
high due to deep rutting alongside the study
stream and some by-pass flows.