Re-optimization and

reoperation study of the

Akosombo and Kpong dams

- Scenario selection

Dr Marloes MulThor Windham-Wright

Scenario 1 current flow regime

• Optimising baseload hydropower generation

• Minimum flow fluctuations

• Average flow of 1,000 m3/s

Scenario 2&3 Environmental Management Classes A & B• Statistical approach using GEFC

• EMC A: Natural rivers with minor modification of in-stream and riparian habitat

• EMC B: Slightly modified and/or ecologically important rivers with largely intact biodiversity and habitats despite water resources development and/or basin modifications

Realistic scenarios?

What are the impacts of different sectors?

Scenario 4 Weeds control and fishery production• Weeds control through

• Reintroducing saltwater gradient• Increasing flow velocity

• Fishery production increment• Clams – increase saltwater intrusion• Freshwater fish – increase flooded area

during wet season

• Maximize saltwater intrusion during dry season

• Maximize flood peaks during Sep-Oct

• Gradual transition between seasons

• Total flow is less than natural flow because of Evap losses of the lake

Scenario 4 Weeds control and fishery productionflow targets/levels correct

dry season

wet season

Additional things to consider in cost-benefit analysis:

- Breaking sandbar

- Continual manual removing of weeds (necessary?)

- Moving of intakes

- Protect valuable infrastructure along the river

- Impact on irrigation

Scenario 5 Irrigation optimisation

• Provide sufficient water for irrigation activities during dry season

• Provide sufficient water during dry season so that saltwater intrusion is not affecting other water users (intakes)

• Compensated by increment of wet season flow to benefit fisheries and other sectors

Scenario 5 Irrigation optimisation

flow targets/levels correct

dry season

wet season

Things to consider in C/B analysis

• Protect valuable properties

• Manual removal of weeds

Scenario 6 Spilling levels 2010

• Wet season levels at 2010 spillway levels (confirm discharge from VRA)

• Drawing from knowledge of the spill and current low flows (confirm discharge from VRA)

Discussion

• For each scenario• Confirm/estimate flow targets

• Dry season

• Wet season

• Identify impact on (sub-)sectors• Compared to current or past

situation

• Identify issues/potential conflicts

• Additional measures required

Final discussion

• Summarize impact of all scenarios on different (sub-) sectors Qualitative• Quantitative Weed Fish Agric Health GW Sed Other

w1 w2

Sc1

Sc2

Sc3

Sc4

Sc5

Sc6

++ very good+ good+/- neutral- bad-- very bad

Voting on feasibility of scenarios and selection of scenarios for modelling