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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.
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