All rivers contain sediments: a river, in effect, can be considered a body of flowing sediments as much as one of flowing water. When a river is stilled behind a dam, the sediments it contains sink to the bottom of the reservoir. The proportion of a river’s total sediment load captured by a dam – known as its “trap efficiency” – approaches 100 per cent for many projects, especially those with large reservoirs. As the sediments accumulate in the reservoir, so the dam gradually loses its ability to store water for the purposes for which it was built. Every reservoir loses storage to sedimentation although the rate at which this happens varies widely. Despite more than six decades of research, sedimentation is still probably the most serious technical problem faced by the dam industry…
coming back to the topic of our seven fork dams, what’s the maximum efficiency are these dams running at ? i suspect the amount of sedimentation in these dams is massive, due to the fact that, they are located in the semi-arid regions,which has less vegetation cover, and the soil at the same time is sandy, hence soil erosion is high. these translates to higher overhead costs of running these power plants due turbine malfunction , and of course we are the people footing these.
Newer dams are built , with de-sedimentation features, which allows for sediments to be flushed out routinely . i highly doubt if the seven fork dams have these features. it’s a high time these dams get audited, and if they are found to be inefficient, G.o.K decommission, or dredge them.
@Soprano do you think dredging can address this problem? Ofcoz it can…now my question is, KenGen should invest in Dredging technologies since sedimentation is a serious threat. Or just build nuclear power plants.
Perhaps this is story is also suspect. How can we tell if we are not being made afraid of this other new demon called sedimentation, then iwe kwamba tenders must be floated to exorcise the demon, and then we go through an other round of shafting? Like Joseph talked about seven lean cows eating seven fat cows?!!!
there is serious sedimentation in the seven fork dams. the fact that, people harvest sand at the sagana bridge, on nairobi nyeri highway, which is miles away from the dams should ring a bell.
I won’t be surprised if it turns out that some of these dams aren’t commercially viable, just like the refinery we have at the coast.
I also saw a story about Tanzania where they had build a dam for power generation and today sedimenation has made the dam obsolete. It cant even generate a single kilowatt of power.
I agree and I admit that you have a point. I don’t really think that very many people have thought about, or whether they are even aware of this real problem.
what i’m interested in knowing is the capacity of water that these water reservoirs hold currently, vis a vis the capacity they held when they were newly constructed. also keep in mind, power plants have a lifespan to, they can’t run forever. our seven forks are located in sandy areas where soil erosion is very very high.
how i wish, if they are any persons who can get hold of the feasibility studies that were conducted.
And then, from a quick peep in the internet, i can see that dams are also a serious hazard to the environment. Dead vegetation at the bed of the dams produce green house gases, especially methane. And the silt we are talking about here, is restrained from reaching downstream where it’s meant to end up, denying the ecosystems down there the necessary natural replenishment as mother Nature prescribed since the genesis!
Perhaps we should not think that siltation is such a big problem for our Seven Forks Dams. Since we always have perennial draughts where a great deal of water is evaporated to an extent of forcing the generators to be shut, I think if the siltation was significant it would have been evident a long time ago during those intermittent exposures.
Great. But why are we speaking as if sedimentation started yesterday? Hasn’t it always been a part of the system maintenance ? Ama hawa Wachina wa tangu time ya Kibaki hufanyaje kwa hizo dams?
that something that accumulates with time. my main bone of contention was that these dams where built using the old technology, which i’m sure didn’t incorporate sediment removal, which left us with dredging only as a solution.
i would love to see a forensic audit on the well being of these dams. hiyo dam iko maryland, sedimentation is almost rendering it useless.