targeted retention of contaminated sediment in a green flood retention reservoir development of an...
TRANSCRIPT
Targeted Retention of Contaminated
Sediment
in a Green Flood Retention Reservoir
Development of an Integrated Management Strategy
for Green Flood Retention Reservoirs and PoldersSven Wurms
4th international Symposium on Flood Defence
Managing Flood Risk, Reliability and VulnerabilityToronto, Ontario, Canada, May 6–8, 2008
Motivation
Emission
conflict situation! Land use (environmental damage/
loss of values…)
Immission Integrated management strategy for green flood retention reservoirs, polders and floodplains
• Quantity/ quality of deposited sediments?
• Factors influencing deposition in retention
reservoirs as well as on floodplains?
Flood event
Erosionmobilisationof pollutants
Deposition floodplains &
retention reservoirs
Overview
1. Aim
2. Procedure
3. Numerical model “Flood retention reservoir Horchheim”
4. Boundary conditions and scenarios
5. Reservoir sedimentation
6. Conclusions
Aim
Integrated management strategy
1. Quantity and spatial distribution of reservoir sedimentation2. Can this be influenced by
• modified operation rules (outflow discharge)• modified reservoir design?
maximum retention
(enhance situation downstream)
minimum retention
(enhance situation
within reservoir)
Options concerning deposition of potentially contaminated sedimentsin green flood retention reservoirs
spatially targeted retention
(enhance situation within reservoir)
retain present situation
andadapt land use
1. Flow2D-numerical modelling (TELEMAC-2D) of filling and emptying phase
• present conditions
2. Transport2D-numerical modelling (SUBIEF-2D) of suspended sediment transport
• sediment is considered to be medium of conservative contaminant transport (grain diameter: 20 µm)
• only sedimentation, no erosion
Gre
en
flood
rete
nti
on
reserv
oir
H
orc
hh
eim
20-,
50-
an
d 100-
years
flood
even
ts
3. Mass balance/ deposition patternsLong term accumulation of reservoir sedimentation (100 years)
Procedure
• modified operation rules
• modified reservoirdesign
Numerical model “Flood retention reservoir Horchheim”
• ordinary flood retention volume 1.16*106 m³
• area 590000 m2
• HQ100 (inflow gauge) 43.7 m³/s
21849 elements
lmin = 1.25m/lmax = 23 m
• kst river bed 20 m1/3/s• kst agricultural land 25 m1/3/s• kst grassland 20 m1/3/s• kst developed area 10 m1/3/s
0,00
5,00
10,00
15,00
20,00
25,00
30,00
35,00
40,00
45,00
50,00
0 10 20 30 40 50 60 70 80t [h]
Q [
m³/
s]
HQ20 (5h rising time)HQ20 (35h rising time)HQ50 (5h rising time)HQ50 (35h rising time)HQ100 (5h rising time)HQ100 (35h rising time)
Boundary conditions and scenarios
Flow BC: Two sets of hydrographs (5 h and 35 h time of rise)
Transport BC:
Assumption: Linear relation between inflow discharge and suspended sediment concentration with a maximum of 1 g/l.
scenario operation rule reservoir design
• present conditionsconstant outflow (30
m³/s)present condition
• modified operation rules
reduced outflow to use entire ordinary retention volume and maximise
deposition
present condition
• modified reservoir design
constant outflow (30 m³/s)
modified design for spatially targeted
deposition
HQ time of
rise
present conditions/ modified design modified operation rules
outflow [m³/s]
volume [m³]
duration
[h]outflow [m³/s]
volume [m³]
duration
[h]
20 5 h
30
7980 4 8.3
1.16 * 106
98
50 5 h 110940 14 12 76
100 5 h 260580 21 15.4 65
Reservoir sedimentation – present conditions
5 h rise 35 h riseDeposition accumulated over 100 years
5107 sediment inflow [t] 13629
145 deposition [t] 535
2.8 deposition [%] 3.9
Reservoir sedimentation – modified operation rules
5 h rise 35 h rise
10489 sediment inflow [t] 21218
5107 deposition [t] 5737
48.7 deposition [%] 27.0
Deposition accumulated over 100 years
0
2000
4000
6000
8000
10000
12000
5*HQ20 2*HQ50 1*HQ100 total
sedi
men
t m
ass
[t]
deposition
sediment inflow
0
2000
4000
6000
8000
10000
12000
5*HQ20 2*HQ50 1*HQ100 total
sedi
men
t m
ass
[t]
deposition
sediment inflow
present conditions modified operation rules
5 h rise
Reservoir sedimentation – modified reservoir design
presentconditions5 h rise
modified design 5 h rise
5107 sediment inflow [t] 5107
145 deposition [t] 163
2.8 deposition [%] 3.2
Deposition accumulated over 100 years
Vmod = 12500 m³
20 µm 40 µm
80 µm 150 µm
Sediment deposition
Grain size
[µm]
inflow
[t]
deposition
[t]
20 2560115
(4,5%)
40 2560233
(9,1%)
80 2560535
(20,9%)
150 2560761
(29,7%)
Deposition height [m]
HQ 5035 h time of rise
Reservoir sedimentation – varying grain size
Conclusions
• Knowledge of deposited masses of potentially contaminated sediments provides a basis for an integrated management strategy for green flood retention reservoirs
• Possibilities of taking influence on sedimentation in green flood retention reservoirs could be shown
• Maximizing/ minimizing of reservoir sedimentation can be done efficiently by modifying operation rules
• Deposition pattern can be influenced up to a certain extent by modifying reservoir design
• Numerical transport simulations should be performed for every grain size of interest due to varying sedimentation pattern
Related works presented on ISFD 2008
• Christoffels, E. et al.
An Integrated Management Strategy for Green Flood Retention Reservoirs, Polders and Floodplains - Taking account of contaminants
(Poster)
• Schönau, S. et al.
Erosion and Sediment Yield Estimation for Flood Protection
(Presentation)
Thank you very much for your attention!