Denise Reed Pontchartrain Institute University of New
Mar 26, 2015
Denise ReedPontchartrain InstituteUniversity of New Orleans
Projected Coastal Louisiana Trends: 1956-2050
LandWater
Land Loss 1956-2000Projected Land Loss 2000-2050
Land Gain 1956-2000Projected Land Gain 2000-2050
1956 – 2000 1525 sq. mi. of coastal landscape lost average rate 35 sq.mi./yr. for 44 years
2000 – 2050 Projected loss - another 513 square miles
The Past
Land
Are
a
Time
Natural cycles
Rapid land loss
Limited land building
20th century
Delta building- River deposition
Delta loss- subsidence, storms
Existing marshes must build up to survive
NaturalSubsidence
Sea-Level Rise
+
= Higher relative water levels
Can marshes keep pace with subsidence and sea-level rise?
Marsh Building ProcessesPEAT PLUS TRAPPED SEDIMENT
MINERAL SUBSTRATE
SLNET ACCRETION
NA + S = AA
SEDIMENT
SUBSIDENCE
T1 TIME T2
ORGANICMATTER ACCUMULATION
CO2
CH4
PRIMARY PRODUCTION
SEALEVEL
ORGANICCARBON EXPORT
DE
CO
MP
OS
ITIO
NO
R
OX
IDA
TIO
N
AB
SO
LU
TE
EL
EV
AT
ION
DETRITUS
ROOTS
PEAT PLUS TRAPPED SEDIMENT
MINERAL SUBSTRATE
PEAT PLUS TRAPPED SEDIMENT
MINERAL SUBSTRATE
SLNET ACCRETION
NA + S = AA
SEDIMENT
SUBSIDENCE
T1 TIME T2
ORGANICMATTERORGANICMATTER ACCUMULATION
CO2
CH4
PRIMARY PRODUCTION
SEALEVELSEALEVEL
ORGANICCARBON EXPORT
ORGANICCARBON EXPORT
DE
CO
MP
OS
ITIO
NO
R
OX
IDA
TIO
N
DE
CO
MP
OS
ITIO
NO
R
OX
IDA
TIO
N
AB
SO
LU
TE
EL
EV
AT
ION
DETRITUS
ROOTS
DeLaune et al. 1990
How do marshes build withoutsediments from the river?
Storms!Increase water levels and mobilize sediment
BB JL CC OOB BC LL TB0.000
0.005
0.010
0.015
0.020
Hurricane Andrew
Sed
imen
t D
epo
siti
on
(g
/cm
2/d
ay)
Sites
Pre-Storm Storm Post-Storm
Cahoon et al., 1995
Fourchon
Date
5/7
/96
5/2
1/9
6
6/4
/96
6/1
8/9
6
7/2
/96
7/1
6/9
6
7/3
0/9
6
8/1
3/9
6
8/2
7/9
6
0
0.0002
0.0004
0.0006
Sed
imen
t D
epo
siti
on
(g/c
m2 /
day
)
0.2
0.4
0.6
0.8
Tid
e (m
ab
ove
loca
l dat
um
)
Hurricane Dolly 22 August 1996
10/3
0/01
11/1
3/01
11/2
7/01
12/1
3/01
1/9/
02
1/23
/02
2/7/
02
2/21
/02
3/6/
02
3/21
/02
4/2/
02
4/16
/02
4/30
/02
5/17
/02
6/3/
02
6/12
/02
6/28
/02
7/10
/02
7/30
/02
8/15
/02
9/3/
02
9/17
/02
10/1
/02
10/1
7/02
10/2
9/02
0.0000
0.0005
0.0010
0.0015
0.0020
0.020.030.04
S
edim
ent
Dep
osi
tio
n (
g/c
m2 /d
ay)
Collection Date
NaturalChannel Spoilbank Gaps
Reed et al., 2006
Hurricane Lilli 2002
How Much Sediment for Maintenance?
Katrina and Rita estimated to have delivered 130 million tonnes (Turner et al., 2006)
River levees stop restrict delta building to a few areas
Regular sediment supply from the river to existing marshes is eliminated. Storm reworking is their only source of sediment.
Houma Navigation Channel
“MRGO”
Navigation Channels
Pipeline Canals
Solutions?
Maintain what we haveRebuild what we’ve lost
Continuing Current Management
Achieving Sustainability
“Prevent loss of sediments into the deep Gulf”
Coast 2050 Coast 2050 Coast 2050 Coast 2050
“..large-scale concepts that could provide significant long-term ecosystem restoration benefits”
Photo taken by NASA April 29, 2008
Average annual loss to Gulf~120 million tons of sediment
21st Century• Sea level rise accelerates….• Storm impacts increase….• Using the River gives Coastal Louisiana a
fighting chance