Mekong Forum on Water, Food and Energy. 2012. Presentation from Session 4: Food, Water and Energy in Catchments

1. Creating wetlands in
reservoirs for habitat
diversity, fisheries and
livelihoods
13 November 2012
Peter-John Meynell
Presentation at CPWF Mekong Forum on
Water, Energy and Food, Hanoi

2. The issue - What happens to the aquatic
ecosystem and fisheries when a dam is
built ?
 The free-flowing river is
converted to a lake
 There is an initial boom in
the fishery as the flooded
vegetation breaks down
 The fish productivity falls
back below that of the
original river
 The aquatic habitat and
fish diversity decreases
 There is often an ugly
scar of barren shoreline
exposed when the water
level is drawn down

3. Changes in fisheries in Lake Kariba
after impoundment – 1960s

4. The hypothesis
 The diversity of habitats and productivity in a
reservoir can be enhanced by introducing
constructed wetlands within the drawdown
area of the reservoir
 In designing a hydropower dam, attention is
also needed to design of the habitat in the
reservoir,
 Design objectives geared towards:
 increasing biodiversity,
 increasing productivity and contributing to the
livelihoods of the people living around the
reservoir.

5. The idea – creating wetlands in the
draw down to increase habitat diversity
• Build earth dykes with spillways across inlets
and seasonal streams coming into the
reservoir
• Water is trapped behind the dyke as the water
in the reservoir is drawn down, creating
permanent pools and wetlands
• Plant wetland plants

6. Has this been done before?
 Not quite like this
but note
experience of
Nam Theun 2
 Created about
30 wetlands for
conservation
around in the
forest above the
reservoir
 Compensated
for wetlands
inundated on the
Nakai plateau

7. Wetlands in NT2 catchment

8. Applying this idea in the Nam
Gnouang reservoir

9. Possible sites for wetlands within the
drawdown of Nam Gnouang reservoir
Nam Thong
Houay Mor
Keosaenkham
Areas for wetlands with conservation
objectives
Nam
Kabaa
Areas for wetlands with livelihood
objectives

10. The feasibility study – site selection
criteria
 Size and shape of inlets
 Don’t construct on a major tributary,
 Relatively small catchment area
 Look for areas where the slope below the full supply level is
low
 Look for inlets with a narrow point where dyke can be
constructed.
 Length and height of proposed dyke – about 2 – 3 m high and
not more than 50 m across.
 Location within drawdown – the FSL of the Nam Gnouang
reservoir is at 455 masl with the drawdown of 35 m to a Minimum
Operating Level of 420 masl. Best within the top 10 m.
 Opportunities for a cascade of wetlands
 Source of construction materials.

11. Identifying possible locations in the
Nam Gnouang reservoir

12. Site No 1 –
Dyke size = 30 m long x 2.7m high

13. Site No 3
Dyke size 10 m long x 2.2 m high

14. Existing fish ponds and Site no 5
Dyke size = 15 m long x 2.5 m
wide

15. Cost effectiveness
 Average cost per hectare of surface area about 1,000 $/ha
 Average cost per 1,000 cu.m is about 1,550 $/1,000 cu.m
Cost per
Water Cost per
Length Water Construction surface
Item Dyke Length Height Wide surface volume of
Reservoir Stock cost area of
Area water
wetland
m m m m (m2) (m3) USD $/m2 $/m3
1 Dy-01 30 2.70 2.00 250 10,110 5,713 7,760 0.77 1.36
2 Dy-02 10 2.00 2.00 970 7,618 4,775 2,696 0.35 0.56
3 Dy-03 10 2.20 2.00 500 9,275 8,609 3,652 0.39 0.42
4 Dy-04 7.5 2.20 2.00 190 1,500 1,034 3,444 2.30 3.33
5 Dy-05 15 2.50 2.00 200 2,542 1,922 4,056 1.60 2.11
 Compared to building a fish pond this is cheap.
 An equivalent sized fish pond for Site 4 at 1,500 m2 may cost
about 5,000 $ significantly more than the cost of a fish pond at site
4

16. How will it perform
hydrologically?
Period Hydrological functioning
Sept/Oct – • Water recharge from contact with
Feb/Mar reservoir
Feb/Mar – • Wetland isolated from main
May/Jun reservoir,
• Water loss from seepage and
evapo-transpiration
May/Jun – • Water recharge from direct rainfall
Sept/Oct and run-off from catchment.
• Discharge when wetland water
levels reach water flow level. E.g.

17. Simulating the water levels in the
reservoir and wetlands

18. Estimating when the wetlands and
reservoir will be connected
Wetland/ Location NGL WFL Number of days
Dyke No connected to main
reservoir
rainfall year
Masl Masl Average Low High
1 H. Gnang 441.00 443.00 124 0 206
2 H. Gnang 445.50 447.00 65 0 164
3 H. Kongko 441.98 443.50 124 0 206
4 H. Kaout 445.50 447.00 65 0 164
5 Upper fish pond 449.10 450.50 0 0 132
Existing Lower fish pond 444.50 448.00 49 0 152
dyke

19. Will these wetlands decrease the
potential for hydropower?
 Storage of water in wetlands will technically
remove water from its use for generating
electricity
 Total water stored in wetland is 22,000 cu.m with
a surface area of 3.1 ha
 Water stored in these wetlands is 0.001% of the
total active storage in reservoir
 Water in the Nam Gnouang can be used twice to
generate power at 3 cents/cu.m each time
 Theoretical loss of value = 1,320 $ per year
 If there were to be 50 such wetlands created, i.e.
10 times the proposed stored volume, theoretical
loss would be 13,200 $ per year

20. Trading off fish production for
hydropower
 Low input aquaculture has a fish production of 1-2
tonnes/ha/yr
 3.1 ha of fish ponds would yield 3.1- 6.2 tonnes
per year
 At a farm gate price 2 $/kg this would be worth
$6,200 – 12,400 per year
 Compared to theoretical loss of $1,320 per year in
hydropower potential
Conclusion: Increases in fish production more than
compensate for the theoretical loss in hydropower
potential

21. Next steps
 Theun Hinboun Power Company are interested to
build several of these dykes during the next dry
season
 IWMI are developing a monitoring project to:
 Follow the development of the wetland ecology over
several years
 Monitoring hydrology and water quality, development
of wetland flora and fauna
 Assess use of wetlands for fish breeding and refuges
 Assess use of wetlands as fish ponds for livelihoods
 Monitor fish populations in the reservoir and
production