Historical Origins Exhibition at the WODCON: the Beijing-Hangzhou Grand Canal

Last section of the Grand Canal in Beijing.

Another impressive dredging accomplishment in ancient China is the well-known Beijing-Hangzhou Grand Canal. Of course this was also featured in the Historical Origins of Dredging in China exhibition at the latest instalment of the WODCON in Shanghai. During our visits to Shanghai1 and Beijing2, we’ve seen the canal at both ends, although they are an impressive 1797km apart.

Grand Canal exhibit in the Historical Origins exhibition at the WODCON.

Triggered by the sign board at the exhibition, I wanted to know more about this immense project. 2500 Years ago, the designation of Beijing as capital of China, was followed by an increase of the population. Any further expansion of the city was limited to the resources available nearby for supporting all these new citizens. The great rulers of ancient China, wanted to access the supplies of the south, where food and crops were abundant. It was decided to dig a canal, all the way from Hangzhou to Beijing3. The importance of the canal for the ancient Chinese civilisation is equivalent to what nowadays the Intracoastal Waterway means for the New York area. Although the ICW is an even longer waterway, it consists mostly of natural water bodies. This makes the Beijing-Hangzhou Grand Canal the longest dredged canal in the world.

Map of the various sections of the Grand Canal (Credit: Wikipedia).

The sign falsely boasts, that the Grand Canal is the oldest canal in the world. Sorry, that honour belongs to our ancient Egyptian engineers4. But the Chinese can be proud their canal is still in use today, whereas the Canal of the Pharaohs is now only used for irrigation. The Beijing-Hangzhou Grand Canal in China is therefore actively maintained. Partly even the traditional way: by hand.

Maintenance of the Grand Canal in the last section in Beijing.

After establishing the age and the length of the Grand Canal, there is another property that might be interesting: the width. I’ve seen sections varying between 10 and 50 meters. Probably the range is even more. Initially the width was depending on the local circumstances, requirements for navigation and possibly the limitations of manual labour.

Explanation on parameters for channel width determination.

Today, the width of a canal can be carefully engineered and a customer may require that the contractor delivers the width exactly. Therefore, it is necessary to know exactly what the capabilities of your cutter suction dredge are. Both at the lowest depth and at shallower depths for the slope of the sides. Knowing the geometry and the dimensions of the cutter suction dredge, one can calculate the reach with complicated trigonometry. Or one can build a model in the 3D environment of the design of the project and see what is possible5. There is also another clever solution to this problem. For every cutter suction dredge we designed, we developed a geometric scale model. It takes into account ladder depth, spud carriage length and swing angle. The result is the canal width that is possible for that cutter suction dredge. A further simple multiplication of canal width, cut height and channel length reveals the production volume. Either onboard or at the office, it provides a nice little instrument for production estimation.

Geometric scale model of a CSD650 for canal width calculation.

References

  1. WODCON, Damen
  2. Historical Origins Exhibition at the WODCON: Yu the Great, Discover Dredging
  3. Grand Canal (China), Wikipedia
  4. The Ancient History of the Cutter Suction Dredge ‘10th of Ramadan’, Discover Dredging
  5. Positioning and Survey System, Damen

See also

 

 

HYDRO 2018 Gdansk: Selecting A Dredge For Your Reservoir Maintenance

Barrage du Ksob, M’Sila, Algeria with a DOP dredge 350

This week, I am here in Gdansk for a presentation on the HYDRO 2018 Conference1 and assist at the Damen booth at the corresponding exhibition. The paper and the presentation are already prepared and I am very excited to do the presentation, but I can’t wait till tomorrow and I like to share the story now, already. So, you, as my favourite audience, will have my personal spoiler after so many teasers have been floating around2,3,4.

General modes of siltation at the usual location in a reservoir

The thing is, dam maintenance and reservoir restoration is something already long on my attention list. Back already in 2008, I wrote a paper on this subject for the CEDA Dredging Days5. Over and over we’ve conveyed the message on various platforms, that dredging might be a viable solution for sedimentation problems in reservoirs. Usually, the solution by dam owners and operators is to flush, sluice or store the sediment. This looks horrible from a dredging perspective, but it is also to the environment. You either smother or starve the downstream river with sediment. As a right minded dredge enthusiast, you see many possibilities to dredge such a project. Immediately we can identify what dredge to use on which location for which purpose.

Selection of applicable dredges for reservoir dredging

If you are very close to the dam and the length of the discharge line allows it, you might even not need a dredge pump. (No wear parts!) It is a so called siphon dredge. But as soon as there is some further transport involved, either distance or uphill, you need a dredge like a cutter suction dredge or a DOP dredge. For even further discharge, you might employ a booster for increased discharge pressure. If the distance becomes very far, you might have to resort to grabs and barges.

Water injection dredging principle and example (this example would be too big for a common reservoir)

As an intermediate solution you might even consider using a water injection dredge. Usually the reservoir is in the mountains and a bottom gradient will be present, enabling the required gravity flow. The actual dredge should have created a silt trap where it can collect the inflowing material from the water injection dredge. Than it can handle the material as usual.

Alternative uses for the dredged sediment a) silt farming as fertile additive b) gravel extraction for concrete

Off course, the dredged sediment belongs to the river and the best thing would be to gradually release the sediment after the dam. But there might be conditions, where it is beneficial to extract the valuable fraction of the sediment and use it for agriculture or as aggregate in the construction industry.

Dredge selection diagram for reservoirs

We noticed, that it is often difficult to convey to dam owners and operators which dredge to select for which job. Sediment is seen as a liability and not as an asset and they rather neglect issues associated with the sediment. So, I made an attempt to have a plain and simple selection diagram. That is the core of my manuscript. But my objective is, that we will see many beautiful dredges contributing to a sustainable and viable operation of hydropower dams and reservoirs.

New DOP dredge family

References

  1. HYDRO 2018: Progress through partnerships, Hydropower and Dams
  2. LinkedIn Teaser, Saskia den Herder
  3. Damen: Spotlight on Hydro Power Dam Maintenance
  4. LinkedIn Teaser, Olivier Marcus
  5. Multi Functional Small Dredging Solution For Maintenance Of Deep Irrigation Reservoirs And Hydro Power Dams, CEDA

See also

A Simple Soil Sample Show

Demonstration at a workshop ‘Advise a dredging customer’

Recently I had to give a demonstration on one of the aspects of my work: investigate what type of soils the customer will be encountering, what type of dredging equipment is most suitable for that application and what will the production be under those conditions. At this demonstration, the purpose was, to show how I can make something simple very complicated in a short time. The challenge here will be to take you with me on this precipitous path to enlightenment.

Ingredients for a sand sieving demonstration

The example case was to examine two different soil samples. Each was artificially mixed, but representing a Particle Size Distribution of two different borrow areas. The samples are delivered in widely available standardised containers. Yeah, you recognised them: 1.5L soda pop bottles. As the samples were wet, they had to be dried. Normally, this can take two to three hours. Here we applied a magical temporal acceleration by employing a Calvin style cardboard box as an oven. The literal main ‘activity’ for the participants was to manually shake the sieve tower. Rest assured, in our own soil analysis lab we use an industrial automatic sieve tower. This antique specimen comes from our museum. The separated fractions from the sieves, then have to be weighed and finally plotted in a so called particle size diagram. Horizontally you can take a sieve diameter and vertically you can read what mass percentage will pass that mesh diameter.

Resulting Particle Size Distribution and key parameters

Although both samples have the same median diameter d50 (354µm), which is indicative of the general particle size, the distribution is very different. Sample A is almost totally the same diameter, where sample B has a broad distribution. A measure for the distribution is the Uniformity Index (d60/d10). Another important figure to be taken from this graph is the silt fraction. This is the percentage of particles that is smaller than 63µm. More parameters can be taken form this graph, but these are the most important for now.

Influence of particle size distribution on slurry transport

From the equation for the critical velocity, the uniformity index plays an active role. If the uniformity index increases, there is more fine material. Fines tend to increase the density and viscosity of the fluid. Consequently the resulting mixture behaves like a heavier fluid, carrying larger particles. Effectively, the resistance of a non-uniform sand is higher than for a more uniform sand mixture.

Influence of particle size distribution on cutter production

Another aspect of the dredging process is the ability of the CSD to excavate the material from the bottom. Here the uniformity index has the complete opposite influence. A uniform sand distribution will have a lot of voids between the grains. The particles will move easily over each other. When there are lot of smaller particles available, they tend to clog up the voids and bond the bigger particles in a gridlock. These sediments are very hard to excavate. If no geotechnical investigation is available, the PSD can help to estimate a SPT.
With the grains size and the SPT, the audience consulted our lovely looking assistant ‘Sandy’ for a first selection of the required CSD.

Short evaluation of a selected dredge at ‘www.dredgefinder.com’

References

Wilson, Addie & Clift, (1992), “Slurry Transport Using Centrifugal Pumps”, Chapter 5 “Heterogeneous Slurry Flow in Horizontal Pipes”

Youd, (1970), “Densification and Shear of Sand during Vibration”, Journal of the Soil Mechanics and Foundations Division, 1970, Vol. 96, Issue 3, Pg. 863-880

See also

Geotechnical investigation

Dredge Finder