Effects of Forest Operations (HYDROFOR Project)

John Clarke

Forest Operations

Clearfelling

Windrowing

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.

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.

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.

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)

Windrowing- When?

When is a site windrowed?

• Before replanting- Typically 18 months after clearfelling.

Brash Mat Over Streams Removed New Drainage Channels Dug

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

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.

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.

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

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

Windrowing

3 sites with similar characteristics selected and located in Co. Wicklow.

• Site 1- Annalecka Brook

• Site 2- Kilcoagh

• Site 3- Oakwood

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.

Annalecka Brook Aerial Photographs

Peak TSS Recorded During Sampled Events (mg/l)

Peak TSS Recorded During Sampled Events (mg/l)

Peak TSS Recorded During Sampled Events (mg/l)

Peak TSS Recorded During Sampled Events (mg/l)

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

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

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

Flow and Sediment Relationship Event 6- 80% Windrowed

Flow and Sediment Relationship Event 7- 100% Windrowed

Peak Total Phosphorous Concentrations (mg/l)

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

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.

Clearfelling

2 sites with similar characteristics selected and located in Co. Wicklow.

• Site 1- Ow 1

• Site 2- Ow 2

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.

River Ow Site 1 Aerial Photograph

Peak TSS Recorded During Sampled Events (mg/l)

10 50 100 % Area Felled

Event Avg and Peak Flows (m3/s)

FWMC of TSS for Sampled Events (mg/l)

10 50 100 % Area Felled

566.7

5380.0

1600.0

260.0 54.0 17.0

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

Flo

w (

m3

/s)

SS (

mg

/l)

Time

DF6

SS (mg/l) Flow (m3/s)

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

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.

Site: Ow 1

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.

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.

Oakwood Aerial Photographs

Oakwood Map

Peak TSS Recorded During Sampled Events (mg/l)

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.

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.

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.

River Ow Site 2 Aerial Photograph

Peak TSS Recorded During Sampled Events (mg/l)

15 50 80 100 100 % Area Felled

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.

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.