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Indeed, sedimentation and sediment transport morphodynamics constitute one of the major issues/concerns in the life of a hydraulic civil engineer. No wonder, they generate the necessity for billion dollar dredging industry to exist. The issues cover such aspects as: simultaneous erosion-deposition-scour in channel processes; and net depositional processes as in Coastal River Delta, harbors and reservoirs. Luckily, a hydraulic engineer has many tools at his or her disposal – from analytic investigation to numerical modeling – to understand the processes and propose/install engineering interventions. Further to refresh our understanding:
Perhaps the earliest treatise on the river sedimentation engineering started with the ASCE's Sedimentation Engineering 1974, VA Vanoni (Ed) that consolidated the works of many brilliant minds from all over the world. From that time forward, the Principles of River Engineering: The non-tidal alluvial river (PPh Jansen, Ed), and many other publications including the works of USACE (eg EM 1110-2-4000) fill our shopping list (further on Resistance to Flow). Because of the enormous importance of the management of sediment transport and sedimentation, literature on this topic is colossal.
Force-Response Fields of stream on alluvium are a showcase of continuous interactions – resulting in simultaneous sequences of erosion, sedimentation and scour of channel beds and unprotected banks – continuously shifting channels and sand bars – more in some than others. In contrast, Force-Response Fields of reservoirs are the showcase of a one-way sedimentation of river-borne sediments (if rivers feed the reservoir). The hydro-sediment physics of reservoir sedimentation, delta building processes and harbor sedimentation – are fundamentally same – except with different boundary forcing and conditions. For example, the destructive Metocean Force Field (further in Force Fields in a Coastal System) is very active in a delta and harbor, but absent or insignificant in a reservoir.
If one has numerical modeling tool at his or her disposal – the coupled water-wave-sediment-morphology modeling – is one of the best options to understand the processes, to experiment with different scenarios – and to investigate the efficacy and effects of engineering interventions (further in Water Modeling and Integrated Modeling and Sedimentation Management).
Dr. Dilip K Barua, Ph.D, P.Eng, M.ASCE
Original Message:Sent: 02-01-2022 03:10 PMFrom: Ebissa GadissaSubject: Reservoir and Channel SedimentationHello Konrad, thank you for your response and recommendations. we can see each separetly as ''Reservoir sedimentation and channel sedimentation'. As mentioned, siltation is a big problem. Because of this issue, some projects are failed and need cost for maintenance. To solve this problem different techniques may be used to minimize/reduce sedimentation as per your suggestions. However, it requires Energy and equipments. Yes, In Addis Ababa, Ethiopia, this year, flood problem was happend because of siltation (blocked channels). I hope channel/Reservoir conviyance/capacity should be considered during channel/Reservoir design. otherwise, it is difficult to minimize this issue at source or at the Dam.Thank you Konrad!Ebissa Gadissa S.M.ASCE------------------------------Ebissa Gadissa S.M.ASCEPhD ScholarAddis AbabaOriginal Message:Sent: 01-31-2022 11:51 AMFrom: Konrad MechSubject: Reservoir and Channel SedimentationHello Ebissa. I am not sure what you mean by 'controlling' sedimentation. If you mean reducing sedimentation at source before it enters a reservoir or a channel, that will be challenging since sedimentation is a result of solids carried into the waterways by precipitation run-off. In Canada one method that was used in a run-of-river hydro-electric power station (Forrest-Kerr) was to design de-sanding bays to reduce the velocity of water to allow precipitate to settle before entering the actual reservoir and turbine. The challenge at that point was to determine the rate of siltation since the de-sanding bays must be dredged to remove the precipitated solids. But in general all reservoirs and riverways are going to silt up. So the issue becomes one of monitoring the rate of siltation and then determining the optimum time to dredge to remove those solids. For monitoring, the classic method was to perform periodic bathymetric surveys using either single-beam or multi-beam echosounders mounted on a vessel and operated by skilled technicians. These instruments are increasingly being mounted on unmanned surface vessels which are quite small and can now be man-carried to reservoirs, even those that are normally inaccessible for a larger watercraft. However these surveys are periodic and do not account for sudden changes in condition occurring after storm events. There is also the cost of deploying the sensor, the watercraft, and the technicians to operate the equipment and analyze the data. Another method is to use permanently installed sensors at the dam face to monitor the rate of siltation over time. Siltation at the dam face is problematic not only due to reduction of reservoir capacity, but due to the added mechanical loading on the dam structure itself which could eventually lead to failure. One advantage of these sensors is they measure the rate of change of depth over time, making remediation planning easier. Also, the same system set-up can be used on the discharge side to monitor scour, or at the turbine inlet to monitor the increase in tramp debris where objects such as logs and other garbage can clog the inlet or even enter the system and cause damage.I would be happy to put you in contact with Ms. Aziah North and also refer you to Northwest Hydraulic Consultants. Aziah works for Kongsberg Maritime Canada (Ltd) out of our Port Coquitlam office (greater Vancouver, Canada) but is responsible for dam applications globally. The closest specialist for bathymetric applications in the Mediterranean basin is Mr. Simone di Giacomo of Kongsberg Maritime AS (office in Rome but lives in Norway). Northwest Hydraulic Consultants have over 200 engineers and are also based in greater Vancouver, but have offices in Asia and engage in projects globally. Their website is https://nhcweb.com/ and a good person to contact is Dr. Andre Zimmermann, who is also an Adjunct Professor at University of British Columbia Faculty of Engineering. Dr. Zimmermann has worked with Aziah on a few different applications. https://nhcweb.com/staff/andre-zimmermann/Finally, there is a White Paper written on Reservoir Sedimentation which may be informative - the list of authors and stakeholders is quite extensive. (File uploaded; URL is https://www.friendsofreservoirs.com/wp-content/uploads/2019/05/National-Res-Sed-White-Paper-2019-06-21.pdf)I hope this was of some assistance. Yours truly, Konrad MechP.S. I hope all is improving in Addis Ababa. One of my classmates Marian Miszkiel P.Eng. is managing the campus construction project for the UN in Addis.------------------------------Konrad Mech P.EngDirector, Sensors and Robotics Channel ManagementKongsberg Maritime ASPort Coquitlam BCOriginal Message:Sent: 01-28-2022 02:47 PMFrom: Ebissa GadissaSubject: Reservoir and Channel SedimentationHow can we control Reservoir and channel sedimentation? What are the most economical techniques to control sedimentation? Is there any new finding regarding to this issue?------------------------------Ebissa Gadissa S.M.ASCEPhD ScholarAddis Ababa------------------------------
Thank you Rollin for sharing the links of these two excellent treatise on sedimentation – the 2010 handbook (thanks to McGraw-Hill and the authors for making it open source) – and the 2019 multi-institutional collaborative white paper.
And thank you Ebissa, for floating this topic – it created lots of interest. Those of us who subscribe to ECOWI definitely benefit from many excellent posted discussions.