Liwen XiaoCivil EngineeringNUI Galway

Michael Rodgers

Rodgers MorganEnvironmental Ltd.

* The SILTATION Project (2004-2006) (Srahrevagh) focused on theimpact of harvesting – using best management practice - on flowsand suspended sediments in receiving waters.( MR, LX, MarkusMueller)

* The SILTATION and PHOSPHORUS Project (2005-2008)(Srahrevagh) examined phosphorus and sediment changes in thereceiving waters after harvesting.( MR, LX, Mark O’Connor)

* The SANIFAC Project (2008-2012) ( Srahrevagh, Glennamong)examines mechanisms of nutrient releases after clearfelling,and mitigation measures, including the seeding clearfelled areaswith native grasses.(MR, LX, MOC, Connie O Driscoll, Zaki-ul-Zaman)

* The HYDROFOR Project (2008-2013)( Altaconey, Glennamong)evaluates the effects of clearfelling a riparian buffer zone, 3-4years ahead of harvesting the main forest.( MR, Mark Healy, JohnRegan, Joanne Finnegan)

Location of Burrishoole catchment

Location of study catchments withinBurrishoole catchment

Srahrevagh

Altaconey

Glennamong

Marine Institute

Lough Feagh

Lough Furnace

Srahrevagh River study site

US

DS

USC DSC

Srahrevagh River

Study stream

Clearfelled area 2005

Area clearfelled 2010

10.5 ha

10.8 ha

USDS

FlumesFlumes

Funded by EPA, COFORD, Coillte Teo., NPWSReadings every five minutes since April 2005

Average suspended sediment (SS) results for SrahrevaghRiver

Clearfelling

0

20

40

60

80

100

120

14/ 01

/ 2004

23/ 04

/ 2004

01/ 08

/ 2004

09/ 11

/ 2004

17/ 02

/ 2005

28/ 05

/ 2005

05/ 09

/ 2005

14/ 12

/ 2005

24/ 03

/ 2006

02/ 07

/ 2006

10/ 10

/ 2006

18/ 01

/ 2007

28/ 04

/ 2007

06/ 08

/ 2007

Ti me

Peak

SS

concentration

(mg/l)

Peak SS at US

Peak SS at DS

Peak suspended sediment (SS) results for Srahrevagh River

The impact of clearfelling on the SS only lastedfor about 6 months.

On August 1st, 2006, concentrations up to 500 μg TRP/l weremeasured in the samples leaving the study coupe; these were thehighest concentrations recorded during the study.

*Phosphorus results

0

100

200

300

400

500

17/07/05 15/09/05 14/11/05 13/01/06 14/03/06 13/05/06 12/07/06 10/09/06 09/11/06 08/01/07 09/03/07 08/05/07 07/07/07 05/09/07 04/11/07 03/01/08

Time

P( m

g/l

)

TP at DS

TRP at DS

TP at US

TRP at US

Clearfelling

TRP and TP are low and constant in US, giving the averageconcentrations of 6 g/l and 14 g/l, respectively.

Srahrevagh TRP(μg/l) Conc.

0

100

200

300

400

500

600

02/03/20

09 12:00

03/03/20

09 00:00

03/03/20

09 12:00

04/03/20

09 00:00

04/03/20

09 12:00

05/03/20

09 00:00

05/03/20

09 12:00

Time & Date

Flo

w(l

/se

c)

0

5

1015

20

25

30

35

40

45

50

Pc

on

c(u

g/l

)

Estimated Srah flow DS flow USC P conc DSC P conc DS P Conc

Main river flow

Stream flow

Harvesting didn’t significantly increase the average SSconcentrations in the receiving water when bestmanagement practices were strictly followed.

The forest clearfelling and harvesting in the SrahrevaghStudy area had very limited impact on flood riskdownstream.

Total reactive phosphorus (TRP) increased to about 200g/l in Nov. 2005, 1 month after clearfelling.

TRP reached a peak value of about 500 g/l in Aug.2006, one year after clearfelling. Important tocontrol P during the first 2 years.

In Oct. 2009, 4 years after clearfelling, thephosphorus concentration was back to the pre-clearfelling concentration of about 10 g/l.

Because of the dilution capacity, the P concentrationin the main river didn’t increase significantly duringthe study period.

Srahrevagh River Study Site

US

DS

USC DSC

10.8 ha.

10.5 ha.

Mobile station 1

Mobilestation 2

ExperimentalPlots

Possible treatments:

1. No brash no grass

2. Brash without grass

3. Brash with grass

4. Grass only

5. Brash taken away after 6months

Plot 1: Brash and Grass; Plot 2: Brash only; Plot 3 Brash mat;

Plot 4: no brash no grass; Plot 5: grass only

Brash mat

Brash

only

Grass onlyNo brashno grass

Grass and brash

Brash andGrass

Brash only Brash mat

No brashno grass

Grass only

Brash mat is the most significant nutrient release sourceafter clearfelling

Brash stockpiles are significant nutrient release sources.This can be reduced by whole-tree-harvesting or grassseeding

Immediate grassing of the clearfelled sites with nativegrasses has potential to take up soluble nutrients.

** GlennamongGlennamong River Study SiteRiver Study Site

Forest control site

Study site10ha (approx)

Bufferzone 0.1ha(approx)

S1

S2

S3

College of Engineering and Informatics

*Glennamong Buffer Area

StudyStream

Main Glennamong River

Station 2

Station 3

Buffer Areas

BA 3

BA 2

BA 1

BA1 100m2

BA2 360m2

BA3 660m2

3.6Kg ofseed /1000m2

30 ug/l

Buffer zone input

Buffer zone output

Clearfelling

BA1

BA2

BA3

Control

BA1

BA2 BA3

Control

Grass seeding of the buffer zones 1 year before mainclearfelling has the potential to reduce release ofsediment. However, reducing the release of solublenutrients is more problematic.

Engineered buffer strips to create uniform flowdistribution is very difficult on hilly ground.