The environmental flows study conducted at the Chara Chara weir at the outlet of Lake Tana is, to our knowledge, the first to have been carried out on the upper Abay River (i.e., the Blue Nile). This study found that:
- Some stakeholders (e.g. fishermen and farmers) have gained from the higher dry season river flows that result between Lake Tana and the power station off-take (located 35km downstream) as a consequence of the current operating regime of the Chara Chara weir. However, locals in the vicinity of the power station are unhappy because they do not benefit from electricity and are no longer able to sell arts and crafts to tourists who are unhappy with the low flows over the Tis Issat Falls, one of the major tourist attractions in Ethiopia.
- To maintain the basic ecological functioning of the river downstream of the weir requires an average annual allocation of 1,198 Mm3 (i.e. equivalent to 30% of the mean annual flow) and the absolute minimum mean monthly flow should not be less than approximately 5.7 m3s-1.
- Currently mean annual flows over the Tis Issat Falls total just 129 Mm3. They are below recommended ecological minimums in all months of the year and particularly critical from August to December. This analysis made no allowance for the aesthetic quality of the Falls.
The study of the implementation and follow-up of the Environmental Impact Assessment (EIA) of the Koga dam has found that:
- Although within Ethiopia there is recognition that follow-up of EIA is very important, the monitoring of impacts and the implementation of mitigation measures of the Koga dam project are currently poor. Of the twenty major plans recommended to be conducted in the EIA, only two are currently progressing satisfactorily.
- Public participation in the project is very limited with most farmers complaining that they are not provided with enough information. The project scored low in all aspects of participation: communication, fairness, timing, accessibility, information provision, influence on decision-making, competence, interaction, compromise, and trust.
- There are significant problems with the compensation being given to those farmers being re-located. The management project office has expressed concerns over the lack of pre-project planning of social concerns and feels that the issues that have now arisen are detracting from their ability to manage some aspects of the project adequately.
- The institutional arrangements for the ensuring that recommendations in the EIA are undertaken are weak, with no institution having overall responsibility for this.
The study of the Koka reservoir is one of the first attempts to quantify the impact of a large dam on malaria in Africa and to ascertain if the modification of dam operation might be a useful tool to mitigate some of the impact. We have found that:
- In the vicinity of the Koka dam, malaria case rates among people living within 3 km of the reservoir are about 1.5 times as great as for those living between 3 and 6 km from the reservoir and 2.3 times as great for those living 6–9 km from the reservoir.
- Proximity to the reservoir is associated with greater malaria case rates in periods of more intense transmission.
- In communities near the reservoir, shoreline puddles and seepage downstream of the dam were the most productive mosquito breeding habitats. About ten times as many adult anopheline mosquitoes (the malaria vector) occur in reservoir-adjacent communities as in communities located further from the reservoir.
- Water levels and water level changes resulting from reservoir management decisions produce conditions that influence vector abundance and malaria transmission. At high water levels, faster reservoir recession appears to desiccate mosquito breeding sites along the shoreline, reducing numbers of disease vectors and subsequent malaria case-rates. This indicates that there is at least the potential to use dam operation in integrated malaria control strategies.
The study being conducted on the Victoria White Nile is providing useful information on the current practices that are leading to the drawdown of Lake Victoria; arising from the rapid growth of electricity demand in Uganda. We have found that:
- Because of the importance of the hydropower dams at the outlet from lake Victoria, as well as the importance of the lake to the three riparian countries (Uganda, Tanzania and Kenya) politics plays a significant role in the decision-making
- To date the primary focus of dam operation has been on maximizing power production. If the complex web of ecological, economic, social and institutional issues is taken into account it will significantly complicate the operation of the existing dams as well as those dams planned for the future. However, there is the possibility of incorporating other concerns in the planning of dam operation by optimizing power production from the dams in conjunction with thermal power stations.