Transcript Methodology 1 Selection of a study area 2 Selection of

HOW INNOVATIVE HYDROLOGICAL MONITORING
AND MODELLING ARE NEEDED TO UNDERSTAND
WETLAND FUNCTIONING AND FUNCTIONS:
RECENT EXPERIENCES IN DIFFERENT TYPES OF
WETLANDS
Aljosja Hooijer
WL | Delft Hydraulics
nr. 1
BETTER TITLE:
THE VALUE OF WATER LEVEL INFORMATION IN
QUANTIFYING WETLAND HYDROLOGY FOR
WATER RESOURCES MANAGEMENT
Topics:
2 … type of data needed needed in order to
address the problems in wetlands
4 … advances in robust/accurate measurement
techniques
5 problems of data acquisition ...
nr. 2
Why is wetland hydrology
important?
• Conservation aim: it determines the ‘internal’ functioning
of the ecosystem, and
• Water Resources Management aim: it determines the
‘external’ functions that wetlands can have within the river
basin (flood peak reduction, storage of pollutants and
sediments, baseflow maintenance).
In many cases, conservation aims are not considered
important by decision makers, but WRM aims are…
 Claims on hydrological functions of wetlands only
valid in WRM if well-proven == quantified!
nr. 3
Some relevant studies
Presented:
• Sarawak peatswamps (Indonesia, 1995-1997)
• Sumatra peatswamps (Indonesia, 2003-2004)
• Danube Delta (Romania, 1997-2002)
Similar:
• Shannon floodplains (Ireland, 1990-1995)
• Madagascar coastal wetlands (1997-1998)
• Doňana National Park (Spain, 2003-2004)
(partly with WL | Delft Hydraulics)
nr. 4
What do these wetlands have
in common?
‘Disadvantages’
• Flat: (sub-)basins can not be delineated from topography.
• Wet, water tables near soil surface, often flooded: diffuse flow.
• Tidal/backwatered: no rating curves, discharges very hard to
measure.
• Inaccessible: only periodic visits possible, automatic monitoring
required.
 basin area and discharge can not be determined ‘as usually’;
(as in dryland).
 S = P - E - Q
nr. 5
What do these wetlands have
in common?
‘Advantages’
• High water tables (<40 cm) and soil types (organic, silt) keep
unsaturated zone at field capacity; any change in storage is
directly expressed in water level change.
• Water levels can be recorded permanently and cheaply, at many
points: with ‘diver’ dataloggers or by local inhabitants.
• Soils and topography highly uniform: point measurements of water
level representative for large areas.
• Little underground leakage across watershed boundary.
• Relatively low rainfall variability in these flat lands.
 changes in basin storage, actual evapotranspiration and rainfall
can be monitored well
 S = P - Eact - Q
nr. 6
0
Vietnam
Jemoreng
catchment
Philippines
South China Sea
Brunei
area
Singapore
h
ut
o
S
Sibu
h
Sarawak
w
ra
Study
a
in
h
C
Sa b a
ak
Malaysia
B orneo
an t a n
Ka l i m
an t a n
Ka l i m
km
0
a
Se
5
5m
D
Ba
t an
gM
a tu
B
Matu
4m
Augerhole with well
Instrument site:
A: rainfall, climate,
moderate flows.
B: low flows.
C: water levels,
throughfall.
D: rainfall.
5m
Transect 6
6m
Contour lines,
metres above
mean sea level.
7m
6
Peatswamp surface along transect 6
NNW
Sapric peat
Jemoreng
stream
Hemic peat
C Marine clay
S Sand & clay
C
2m
3m
A
S
0
nr. 7
100
km
Thailand
Indonesia
• Goal: Water Supply
Study (for Malaysian
Government)
• Question: how much
discharge during
1:25y droughts?
Worth conservation?
• Approach:
discharge, water
level, monitoring
studies in 10
catchments.
0
300
Sa
Sarawak
Peatswamp
Study
km
S
C
C
C
S
km
m
S
C
C
C
S
10 0
SE Asian
Peatswamps
(>25 Mha)
nr. 8
What do we want to study?
Ei
P
Et
flooded
area
canopy
The ‘natural’
peatswamp
hydrology,
undisturbed
by drainage
QW
QBP
Pn
QD
SD
SS
QS
SW
peat
QG
SG
sand
clay
E
P
Ei
Canopy
QBP
SW
SD
Et
Surface
depression
storage
Open water
storage
QW
QD
SS
Subsurface
storage
QS
SG
Groundwater
storage
QG
Q
nr. 9
Sarawak peatswamp studies
- it started with Q …
nr. 10
Sarawak peatswamp studies
- and ended with P, L …
nr. 11
 2-weekly water
table monitoring
for changes in
basin storage (40
wells per basin)
5.5
N
S
4.5
-5
-2.5
0
2.5
5
7.5
Distance from Jemoreng stream (km)
0.1
0
-0.1
Average for Rentis 6 (13 wells)
Station levels, corrected
-0.2
25/04/96 9/05/96 23/05/96 25/05/96 6/06/96 20/06/96 22/6/96 29/6/96 4/07/96 8/01/96 15/08/96 29/8/96
Date
nr. 12
23-05-96
20-06-96
04-07-96
01-08-96
15-08-96
26-09-96
Stream
3.5
2.5
-7.5
Average water table depth (m)
• Peat dome and
water table ‘in
balance’
• Water level
fluctuations
uniform
Water level (m above datum)
Basin-wide water table studies
W a te r ta b le d e p th ( m a b o ve p e a t su r fa ce )
Diurnal water table studies
For:
• actual evapotranspiration rates
• recharge rates,
• (peat characteristics, for above)
0 .1 5
C Q D = (L (t)-L (t-1 ))/L (t)
0 .0 5
-0 .0 5
S f= d L (P )/P
-0 .1 5
Q G = d L (G )* S f
-0 .2 5
E t= d L (E t)* S f
0
6
-0 .3 5
1996 06 14 18
24 h
1996 07 05 14
1996 07 26 10
D a te
nr. 13
1996 08 16 06
1996 09 06 02
P e n m a n p o t e n t i a l e v a p o t ra n s p i ra t i o n (m m / d )
Data collection methods
Water table studies
• Diurnal
water table
studies for
actual
evapotran
spiration
rates
5
4
3
2
L = -0 .1 to -0 .2 m
L < -0 .2 m
1
0
0
1
2
3
4
A c t u a l e v a p o t r a n s p ir a t io n o n r a in le s s d a y s ( m m / d )
nr. 14
5
Data collection methods
Water table studies
10
Jemoreng (maximumdepth is 0.31 m)
8
Groundwater seepage rate (mm/d)
• Diurnal
water table
studies for
recharge
rates
Dalat (maximumdepth is 0.5 m)
6
Daro (maximumdepth is 0.38 m)
4
2
0
0
0.1
0.2
0.3
Depth belowpeat surface (m)
nr. 15
0.4
0.5
Data collection methods
Water table studies
0.2
nr. 16
0.1
Water level (m)
0
-0.1
-0.2
Lobserved
Lmodelled
-0.3
0
-05.4
40
Discharge(mm/d)
• Model
schematisation
with Sf, Qr and ET
from diurnal WT
record.
• Model calibration
with storage
changes from water
table record (and
with measured Q).
• Catchment area
optimimisation
through calibration.
Qobserved
Qmodelled
30
20
10
0
Jan-96
Mar-96
Jun-96
Sep-96
Dec-96
Mar-97
Sumatra: next step
Intact and impacted peatswamps
• Goal: Management
plan Air Hitam Laut
river basin.
• Question: Entire
peat dome needs
protection?
• Approach: water
table studies along
2*5 transects:
1 intact peatswamp
2 drained for agriculture
3 drained for plantation
4 logged
5 burnt
nr. 17
Batang Hari
Sumatra
 What do we want to study?
Effects of changes
Air
to the natural
Hitam
Dalan
hydrology, on:
• Water levels
• Peat Subsidence
• Watershed area 
• Lowest flows
• Peak flows
• Water quality
nr. 18
Basin
Boundary
Basin
Boundary
Air
Hitam
Laut
Peat dome
Drains
Air
?
Peat dome
Drains
Danube delta
lakes and reedlands
• Highly
complex
system of
lakes,
streams,
artificial
channels,
reedlands,
floating
reedlands
nr. 19
Danube delta
 What do we want to study?
• Goal: accurate
hydraulic/WQ model
for WQ management
(with DDNI)
• Question: connectivity
between lakes? how
much flow under
floating reedbeds, and
how much through
channels?
• Approach: collect
calibration data for
existing model.
nr. 20
Danube delta
monitoring & measurements
• Flows in
channels
measured
daily
(shown:
Lake Isac
system).
nr. 21
Danube delta
monitoring & measurements
nr. 22
2.5
2
1.5
1
Sf Gheorge Branch
Sulina Branch
Lake Isac
0.5
07
/0
9/
20
02
31
/0
8/
20
02
24
/0
8/
20
02
17
/0
8/
20
02
10
/0
8/
20
02
0
03
/0
8/
20
02
Water level (m)
• Water levels
monitored in
lakes
(‘divers’,
gauges).
• Ideal ‘Water
balance’
period: high
water, no
‘net’ water
level change
in lakes.
Danube delta
closed w. balance per lake system
• Using flowand water
level
measurements
 Flow under
reed very
limited, even
during high
water
4-sep
5-sep
6-sep
7-sep
8-sep
9-sep
10-sep
11-sep
Inputs
Average
Average
5-11 Sep
June
Inflows through channels (not Isac 3)*
Channel Isac 1 to Isac
3.64
3.3
2.93
3.3
3.7
4.01
4
4.02
3.61
4
Channel Isac 1 to Isacel
1.75
2
2.71
2.7
2.6
2.5
2.5
2.48
2.50
0.9****
Uzlina Channel
2.79
4.46
4.42
4
3.5
2.92
2.5
2.05
3.41
1.3
Total m3/s
8.18
9.76
10.06
10
9.8
9.43
9
8.55
9.51
6.2
822034
535680
Total m3/d 706752 843264 869184 864000 846720 814752 777600 738720
Rainfall (mm/d)
0
0
0
0
0
0
0
0
0
?*****
Outputs
Outflows through channels
3
3.75
4.12
5.25
5.5
5.87
5.02
6.18
5.10
2.5
Isac 3 (sometimes inflow)*
Isac 2
-2.21
0.37
-1.9
2.11
1.7
1.36
3
4.66
1.61
1.7
Total m3/s
0.79
4.12
2.22
7.36
7.2
7.23
8.02
10.84
Total m3/d 68256
355968 191808 635904 622080 624672 692928 936576
6.71
4.2
579991
362880
Loss to evapotranspiration
mm/d
3
3
3
3
3
3
3
3
m3/d** 126000 126000 126000 126000 126000 126000 126000 126000
equivalent m3/s
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
3
4
126000
168000
1.5
1.9
?*****
Change in storage, inferred from water level change2
Water level in Isac (m) 1.84
W. l. change in Isac (m)
**
Storage change, m3/d
0.022
1.861
1.878
1.88
1.87
1.864
1.855
1.84
0.02
0.017
0.002
-0.01
-0.006
-0.009
-0.015
84000
-4E+05
-3E+05
-4E+05
-6E+05
-6000
-7.3
-0.07
924000 840000 714000
Storage change m3/s 10.7
9.7
8.3
1.0
-4.9
-2.9
-4.4
Result: Outflow outside main channels (partly through reed) from Isac to Perivolovka channel to east
.
-4.8
-5.5
-1.9
0.2
6.0
3.7
3.9
3.5
1.4
17.4
1.3
0.0001
0.0024
0.0015
0.0016
0.0014
0.00057
0.00002
% of total outflow
nr. 23
flow velocity (m/s)*** -0.0019 -0.0022 -0.0008
0.1
Danube delta
hydrological system definition
• ‘Discharge
points’
outside of
channels
identified
el
Chann
v
o
c
t
Li
Gerasimova
Cha
nne
l
Isac
Closed system boundary
‘Open’ boundary
Channel flow
Flow through reedland
nr. 24
Uzlina
Per
?
ivol
ovk
a
Isacel
Definition of the Isac Lake System
(including Isacel and Gerasimova)
A. Hooijer, Delft Hydraulics / DDNI / RIZA
Danube delta
analysis  modelling  management
• Comparison of measured and modelled flows and
water levels, as basis for further calibration.
nr. 25
Summary conclusion…
In all cases, water level data and specific ‘wetland’
water level record analyses methods help(ed) improve
understanding and modelling of wetland hydrology:
• Actual evapotranspiration determined
• Soil characteristics determined (storage coefficient)
• Water balance ‘closed’ with storage information
• Hydrological models calibrated with water levels
• Catchment areas refined/determined
Water level monitoring & analysis will improve
hydrological studies in wetlands

nr. 26