Environmental Flow in the Context of Small Reservoirs in

West Africa

Yongxuan Gao

21 March 2009

Session 3.2.4 2

Rainfall in West Africa

• Unevenly distributed spatially and temporally

• Often comes in the form of thunderstorm

• Droughts and flash floods are frequent

z

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Legend

z Navrongo Weather Station

Mean Annual Rainfall (mm)

High : 1716

Low : 399

0 200 400100

km

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Legend

z Navrongo Weather Station

Mean Annual Rainfall (mm)

High : 1716

Low : 399

0 200 400100

km

Session 3.2.4 3

Small Reservoirs

• Large inter-year variations in the agriculture production potential, leading to insecure livelihoods

• Many have been built in rural area for livestock watering, small-scale irrigation, fishing and construction

• There are 160 small reservoirs in the Upper East Region of Ghana, 1400 in Burkina Faso and 250 in Northern Cote d’Ivoire (www.smallreservoirs.org/)

Session 3.2.4 4

Small Reservoirs (2)

• Developments are spontaneous and many of them have deteriorated over time due to poor maintenance

• Construction and rehabilitation are funded by different agencies, at different times, with little coordinative effort among the agencies to facilitate a regional optimization of investments

Session 3.2.4 5

Small Reservoirs as a System

• Store a significant amount of water and influence downstream flows

• But have rarely been considered as a system

• Little consideration has been given to their collective impact on the watershed and livelihoods in the long term

• Impact is difficult to quantify given the diffuse nature of the small reservoirs

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#* Small Reservoir

River0 10 205

km Upper East Region

Ghana

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Upper East Region, Ghana

Session 3.2.4 6

Environmental Flow

• Study is needed to investigate the effect of the small reservoirs as a system on the river

• Appropriate planning strategies should be formulated if any negative finding is found

Session 3.2.4 7

Description of the Project

• A case study conducted in the Upper East Region of Ghana

• Hydrological, ecological and socio-economic implications of small reservoirs

• Interview with the farmers• Funded by IWMI

Session 3.2.4 8

Macroinvertebrate

• Ecological indicator• Preliminary result: little

difference between the sites upstream and downstream of the small reservoirs– No impact– Not enough samples to

reach a conclusion

• Need to do more analysis

Session 3.2.4 9

1. Can innovative engineering and water management techniques to restore environmental flows strike the right

balance between the human needs for which river systems were initially

developed and ecological needs?

Session 3.2.4 10

• Engineering can only take us a little further, but not too far

• In the long run– Holistic approach in reservoir operation– formulation and implementation of environmental flow

policy and regulation

• No such policy exists for many rivers or watersheds

• Even there is, very vague or hard to implement

Session 3.2.4 11

2. What has been recent experience in striking this balance and what new scientific, technological, and policy

approaches are on the horizon?

Session 3.2.4 12

• Ecological value should be the or part of the objective in reservoir operation or optimization model

• Need to develop effective hydrological indices• A dataset of streamflow, before and after

alteration, along with associated ecological impacts on selected fauna and flora– However, not much data exists pre- and post-dam

construction– Most studies focus on fish or insect collections made

immediately upstream and downstream from the dam, and even this kind of data is not abundant

Session 3.2.4 13

• Ecosurplus and ecodeficit

• High correlation with the IHA (Indicator of Hydrological Alteration)

0.1

1

10

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Exceedence Probability

Str

eam

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cfs)

Unregulated Median Flow Duration Curve

Regulated Median Flow Duration Curve

Ecosurplus

Ecodeficit

Session 3.2.4 14

3. How can the views and concerns of all stakeholders be considered and effectively

integrated into the design of such projects?

Session 3.2.4 15

• River is a legitimate stakeholder!• Involve stakeholders from the planning

stage of the project• Integration should begin on the village

(community) level• Information about the project should be

make readily available to the stakeholders, especially if the project is in rural area of a developing country

Session 3.2.4 16

• The role of traditional leadership is very important in water management

• Traditional practices, which have evolved with the biophysical and cultural settings in the society, are generally sustainable

• Water governance must take traditional values into account